,
,1,3,*, 何永涛1,3, 张宪洲1,31 2
3
4
CO2 flux dynamics and its limiting factors in the alpine shrub-meadow and steppe-meadow on the Qinghai-Xizang Plateau
CHAI Xi1,3, LI Ying-Nian2, DUAN Cheng1,3, ZHANG Tao4, ZONG Ning1, SHI Pei-Li,,1,3,*, HE Yong-Tao1,3, ZHANG Xian-Zhou1,31 2
3
and 4
通讯作者:
| 基金资助: |
Online:2018-01-20
| Fund supported: |
摘要
关键词：
Abstract
Keywords：
PDF (2476KB)元数据多维度评价相关文章导出EndNote|Ris|Bibtex收藏本文
本文引用格式
柴曦, 李英年, 段呈, 张涛, 宗宁, 石培礼, 何永涛, 张宪洲. 青藏高原高寒灌丛草甸和草原化草甸CO2通量动态及其限制因子. 植物生态学报[J], 2018, 42(1): 6-19 doi:10.17521/cjpe.2017.0266
CHAI Xi.
草地是全球分布面积最广的陆地生态系统(Adams et al., 1990), 环境变化对草地碳通量及全球碳循环具有重要的影响(Knapp et al., 2002; Piao et al., 2012)。草地CO2通量特征在不同时空尺度上存在较大的差异, 并且容易受到气候变化的影响。任何影响植被生长发育的环境因子(例如水分、温度、光照等)都有可能影响草地生态系统CO2通量 (Suyker, 2003; Xu & Baldocchi, 2004; Yuan et al., 2009)。有控制试验表明, 温度和水分的季节动态是影响生态系统CO2动态的最重要因子(Wan et al., 2009; Jongen et al., 2014; Ryan et al., 2015)。此外, 植被变化也是碳通量变化的主要驱动力(Street et al., 2007; Deyn et al., 2008), 对生态系统碳通量响应气候变化具有调节作用(Xu et al., 2015)。尽管草地生态系统受到越来越多的关注, 但是大部分研究都集中于低海拔地区, 高海拔高寒生态系统碳通量的研究还比较缺乏。
高海拔草地生态系统因较高的太阳辐射和较低的气温常被预期为“碳汇”, 但草地生态系统的源/汇动态存在较大的变异。高光合有效辐射是促进高海拔植物光合作用的能量基础, 较大的温度日较差有利于光合产物的积累, 较低的温度(特别是夜间和冬季)又可以抑制植物和土壤呼吸, 减少碳损失, 通常被认为有利于生态系统碳固定(Saito et al., 2009)。一些研究揭示, 青藏高原的高寒草甸具有“碳汇”功能(Gu, 2003; Kato, 2004; Zhao et al., 2005)。但也有研究发现, 高原上的草原化草甸随水热等环境因子的季节分配和年际变异而发生“汇-源”或者“源-汇”的转变(Chai et al., 2017)。这说明, 虽然高寒草地具有利于碳固定的环境条件, 但其碳源/汇动态仍因生物环境因子的变化存在较大的变异, 这会给未来气候变化影响下高寒草地的碳通量动态预测带来更多的不确定性。
青藏高原气候温凉, 温度是植物生长的重要限制因子, 温度升高会促进湿润地区植物光合作用和碳固定(Kato et al., 2005), 但在干旱地区, 温度升高会导致土壤水分蒸发的增加, 加剧植被受干旱胁迫的程度, 导致植被生产力降低(Guo et al., 2015), 因此气候变化对青藏高原不同植被类型生态系统源/汇动态的影响目前还不十分明确, 尤其水热因子组合的变化对草地生态系统CO2通量的季节和年际变异的影响更具有不确定性, 需要深入研究。因此, 研究青藏高原不同植被类型高寒草甸生态系统的CO2通量特征及其影响因子对评价青藏高原生物地球化学循环对全球变化的响应和反馈就具有重要的科学意义(李东, 2005)。本研究选择青藏高原东西部两个水热条件有差异的高寒灌丛草甸和草原化草甸作为研究对象, 对其CO2通量的季节、年际动态及其影响因子进行对比研究, 研究目标是: 1)对比青藏高原高海拔地区的两高寒草地生态系统CO2通量的季节和年际动态; 2)确定两高寒生态系统CO2通量变异的主要限制因子; 3)探讨碳源/汇动态差异的原因。
1 资料和方法
1.1 研究区概况
供比较的两个通量站分别位于青藏高原东部的中国科学院海北高寒草甸生态系统定位站(海北站)和腹地的中国科学院当雄高寒草甸研究站(当雄站)。海北站(101.3° E, 37.6° N)地处祁连山北支冷龙岭东段南麓坡地的大通河谷西段, 站区地形开阔, 海拔3 200 m左右, 属于高原大陆性气候, 气温极低, 无明显四季之分, 仅有冷暖二季之别, 干湿季分明。年平均气温-1.7 ℃, 最冷月平均气温为-14.8 ℃, 最暖月平均气温为9.8 ℃; 多年平均降水量570 mm, 80%集中在5-9月。植被为高寒灌丛草甸(以下简称灌丛), 植被上层结构为灌木层, 以金露梅(Potentilla fruticosa)为优势种, 该层植被盖度为60%-70%; 下层是草本层, 以小嵩草(Korbresia humilis)等草甸植物为主, 植被盖度为60%-70%。土壤为高山草甸土(草毡土)(高以信, 1980)。生长季节通常是4月下旬至10月中旬(李英年, 2006; Li et al., 2016)。当雄站(91.0° E, 30.9° N)地处念青唐古拉山南缘, 地形属于高原丘间盆地, 地势平坦, 海拔4 300 m左右, 属于高原亚寒带季风气候, 太阳辐射强, 气温低, 雨热同期, 干湿分明, 年蒸散量大, 属于半湿润与半干旱地区。年平均气温1.3 ℃, 最冷月平均气温为-10.4 ℃, 最暖月平均气温为10.7 ℃;多年平均降水量477 mm, 85%集中在6-8月。植被为高寒草原化草甸(以下简称草甸), 以丝颖针茅(Stipa capillacea)、窄叶薹草(Carex montis-everestii)和高山嵩草(Kobresia pygmaea)为优势种, 盖度50%左右。土壤为高山草原土(卢耀曾, 1982)。生长季节通常是5月至10月(Chai et al., 2017)。1.2 通量和相关观测
利用涡度相关技术对两个研究区CO2通量进行长期连续的观测(2004-2008年)。海北站和当雄站的涡度相关系统分别始建于2002年和2003年, 通量塔高均为2.2 m。2个站点通量观测的主要仪器均为开路式涡度相关观测系统和常规气象观测系统, 其中涡度相关系统包括三维超声风速仪(CSAT3, Campbell Scientific, Logan, USA)、红外气体分析仪(LI-7500, LI-COR Lincoln, USA)和数据采集器(CR5000, Campbell Scientific, Logan, USA), 主要用于观测植被与大气界面的CO2通量, 数据采集频率均为10 Hz。常规气象观测系统主要用于连续气象要素采集, 数据采集(Model CR23X, Campbell Scientific, Logan, USA)时段与通量数据相同, 观测项目主要包括温度、湿度、辐射、风向、风速等。光合有效辐射(PAR)传感器(L1190SB, LI-COR, Lincoln, USA)安装在高1.2 m的支架上。空气温度/湿度传感器(Model HMP45C, Vaisala, Helsinki, Finland)安装在防辐射罩内(Model 41002, RM Young Company, Michigan, USA), 分别观测1.2 m和2.2 m高处的空气温度(Ta)和相对湿度(RH), 并计算得出水汽压。风速传感器(A100R, Vector, Somerset, UK)与Ta和RH传感器安装在同一高度上。风向(Model W200P, Vector, Somerset, UK)测定高度为2.2 m。雨量传感器(Model 52203, RM Young Company, Michigan, USA)置于样地内0.5 m高处记录站区的降水量(PPT)。土壤环境要素观测项包括土壤温湿度和土壤热通量。土壤温度(Ts)主要是利用热电偶温度传感器(107-L, Campbell Scientific, Logan, USA)分别测定5、10、20、40和80 cm处的Ts。5、20和50 cm处的土壤含水量(SWC)利用时域反射计(Model CS615-L, Campbell Scientific, Logan, USA)测定。2个土壤热通量板(HFP01, Hukseflux, Delft, The Netherlands)测定5 cm处土壤热通量。
我们选择2004-2008年连续5年的数据进行对比, 因为首先这5年除极端降水年份(2006年)之外, 两站之间年降水量和生长季降水量差异较小, 其次两站都有完备和高质量的通量和生物环境因子数据用来比较灌丛和草甸的CO2通量的季节、年际变异特征及其关键影响因子。
1.3 数据处理和插补
由于各种天气、电力及仪器故障等原因, 涡度相关观测系统采集到的原始数据会出现丢失或异常的现象, 因此对原始数据进行预处理是必不可少的, 这是控制数据质量、保证数据可靠性的重要前提。预处理包括野点去除(±3σ)、坐标旋转(三维风旋转)、Webb-Pearman-Leuning校正等。数据处理过程中去掉雨时和夜晚(PAR < 1 μmol·m-2·s-1)摩擦风速u*< 0.15 m·s-1时的数据。缺失数据通过CO2通量值(Fc)与环境因子之间的非线性经验公式进行插补(Shi et al., 2006)。灌丛研究期内(2003-2008年)每一年原始数据缺失值不超过1%, 草甸研究期内(2004-2011年)每一年原始数据缺失值不超过15%。非生长季节全天和生长季节夜间数据根据与 5 cm土壤温度(Ts)的指数方程进行拟合得到拟合系数, 然后根据拟合系数和Ts对缺失数据进行插补, 本文应用的插补公式为公式(1)和(2)。
Fc, nighttime = R10Q10((Ts - Tref)/10) (1)
Q10 = exp(b1Ts) (2)
式中Fc, nighttime为夜间u* > 0.15 m·s-1 生态系统CO2净交换量(NEE), 即夜间生态系统总呼吸量(Re), 单位为mg CO2·m-2·s-1, Tref是参数温度, 通常为10 ℃, R10表示10 ℃时的标准呼吸系数, 单位为mg CO2·m-2·s-1, Q10是生态系统呼吸的温度敏感系数, b1为系数(Hoff, 1898)。
生长季节白天CO2通量采用Michaelis-Menten 模型(Flanagan, 2002; Xu & Baldocchi, 2004)对NEE与PAR的关系式(3)进行拟合, 然后根据拟合系数和PAR值对缺失的通量值(Fc)进行插补。
${{F}_{\text{c,daytime}}}=\frac{{{P}_{\max }}\times a\times PAR}{(a+{{P}_{\max }})+{{R}_{e}}}$ (3)
式中, Fc, daytime为日间u* > 0.15 m·s-1 NEE值, 单位为mg CO2·m-2·s-1, α为表观量子效率, 单位为mg CO2·μmol photons-1, Pmax为最大光合强度, 单位为mg CO2·m-2·s-1, PAR为光合有效辐射, 单位为μmol·m-2·s-1, Re为白天生态系统呼吸量, 单位为mg CO2·m-2·s-1 (Ruimy et al., 1995; Shi et al., 2006)。
1.4 生态系统净初级生态系统生产力(NEP)组分的拆分
NEP = - NEE, 表征了生态系统净CO2固定和净释放量, 为生态系统总初级生产力(GPP)与Re的差值。当NEP > 0时, 生态系统是大气CO2的汇; 当NEP < 0时, 生态系统是大气CO2的源; 当NEP = 0时, 生态系统CO2固定与排放处于平衡状态。涡度相关系统无法直接测定生态系统GPP和Re, 需利用公式外推得到。利用夜间数据建立Re与温度的回归关系并外推到白天的Re。日间NEP与日间Re的差值为GPP, 至此NEE可被拆分为GPP和Re (Gitta et al., 2010)。1.5 能量闭合分析
涡度相关技术所观测数据质量常用能量平衡方程进行检验, 即:H+LE=Rn-G-S-Q (4)
式中, Rn为净辐射, G为土壤热通量, S为冠层热储量(由于植被低矮, 群落稀疏, 热储量可以忽略不计), Q为附加能量源、汇的总和(因Q值很小, 常忽略不计), H为感热通量, LE为潜热通量。能量闭合方程的理想状况为斜率为1, 截距为0, 但能量不闭合现象已是草地和森林等通量观测中普遍存在的问题, 其不闭合程度通常在10%-30%。对两样地研究期内所有日数据进行能量闭合分析(图1), 灌丛和草地闭合方程斜率分别为0.90和0.86, 表明两站点的能量闭合较好。造成能量不完全闭合的原因可能有: 1)空间取样误差, 2)忽略了相关能量项的误差, 3)仪器系统误差, 4)平流效应的误差等。
图1
新窗口打开|下载原图ZIP|生成PPT图12004-2008年高寒灌丛草甸(A)和草原化草甸(B)能量闭合分析。图中数据分别是每日潜热通量(LE)与感热通量(H)的和以及净辐射(Rn)与土壤热通量(G)的差。黑色线为线性拟合线。
Fig. 1Energy balance during 2004-2008 at the alpine shrub-meadow (A) and steppe-meadow (B). Data are the daily sums of latent (LE) and sensible (H) heat flux and net radiation (Rn) minus soil heat storage (G), respectively. Black lines are linear fitting lines.
1.6 归一化植被指数(NDVI)数据的提取
本文利用NDVI来反映植被生产力的季节变化, MODIS NDVI数据来源于美国国家航空和航天局(NASA)开发的MODIS植被指数产品, 本文所应用的主要是MOD13Q1, 即250 m分辨率16天合成的植被指数产品。该数据集已经过了大气校正、几何校正等预处理, 消除了太阳高度角、传感器时间灵敏度等影响。时间跨度从2004年到2008年。数据来源网址:1.7 数据分析
本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响。SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(蔡甲冰等, 2008), 路径系数表示自变量与因变量之间带有方向性的相关系数(谢仲伦, 1996)。本文使用R软件(3.2.4版本, 2016-03-10)中的“lavaan”软件包来完成SEM分析, 最终建立两组(生长季和非生长季)最优路径图, 自变量和因变量因子均为16天的平均值。生长季因变量包括NEP、GPP和Re, 自变量包括NDVI、Ta、Ts、饱和水汽压差(VPD)、SWC、PAR及PPT。由于所研究的两类生态系统的植被在非生长季凋萎, 不能进行光合作用, GPP为0, 因此非生长季只分析Re (即NEP)。在建立“最优”路径图的过程中, 一些自变量会因与χ2检验相关的p > 0.05 (王酉石和储诚 进, 2011)而被剔除, 当相对拟合指数(CFI) > 0.9时, 说明所拟合模型是一个“好”模型(曹小曙, 2011)。在SEM分析中, 除NEP和生物环境因子进行单独分析外, 将GPP和Re放在一组与影响因子进行分析, 因为这两个变量的变化是相辅相成的(Peichl et al., 2010; 刘冉等, 2011; Du & Liu, 2013)。所有统计分析均在SPSS 15.0 (SPSS, Chicago, USA)环境下进行, 作图采用Origin Pro 2016 (OriginLab Corporation, Massachusetts, USA)。
2 结果
2.1 环境因子对比
根据两站点多年年均水热情况的初步判定, 当雄站年平均气温和生长季平均气温高于海北站, 相对干暖, 而海北相对冷湿。研究时段(2004-2008年)内两地区年平均气温与多年平均气温相比较为相似, 虽然当地气象站数据显示海北站多年平均年降水量高于当雄站, 但研究期内除了2006年外, 两站年降水量没有多大差异(图2F)。从两站点主要的气象因子和生物因子5年季节变化趋势(图3)可以看出, 灌丛与草甸的PAR (图3A)、Ta (图3B)以及5 cm Ts (图3C)的季节动态总体呈单峰曲线, 变化不明显, 但逐年的方差分析都是草甸显著高于灌丛(p < 0.05)。两个站点的月PPT (图3E)存在较大差异, 每一年都有波动。海北站PPT波动要小于当雄站, 各月份降水量分布相对均匀。此外, 海北站Ta和PPT的年际变异系数都较小, 尤其生长季节变异系数更小(图2H), 当雄Ta变异系数也较小且与海北基本持平, 但当雄的PPT年际变异系数较大, 是海北的2倍, 生长季差异更大, 达6倍左右。这说明即使这5年间两站点降水总量相差不多, 但当雄站的降水变异显著高于海北, 降水年际分布不均匀。月平均VPD (图3D)和月平均SWC (图3E)都是随PPT的变化而呈现显著的季节差异, VPD和SWC随着降雨的变化呈现相反的变化趋势, 前者几乎全年都是草甸显著大于灌丛(p < 0.05), 后者全年灌丛高于草甸, 生长季节更为显著(p < 0.05)。显著不同的是, 灌丛在4月进入生长季后SWC就基本达到生长季高值区, 受降水量影响不大, 而草甸SWC要在最大降水月(7-8月)才能达到高值期, 而且与降水量有约1个月的迟滞期。从平均值来看, 海北的生长季SWC是当雄的2.6倍。综上所述, 海北站低温、湿润, 受湿润季风气候影响, 而当雄站相对温暖、干旱、降水变异性强且分布不均、辐射更强, 属于半干旱高原大陆性季风气候。图2
新窗口打开|下载原图ZIP|生成PPT图2高寒灌丛草甸和草原化草甸生长季节(GS)和年际(Ann) CO2通量(包括生态系统净初级生产力(NEP)、总初级生产力(GPP)和生态系统呼吸(Re))的总值、环境因子(平均气温(Ta)和降水总量(PPT))以及年际碳利用效率(CUE)、Re/GPP、归一化植被指数(NDVI)以及各因子年际变异系数(CV)对比。
Fig. 2Comparison of annual (Ann) and growing season (GS) accumulative values of CO2 fluxes (including net ecosystem productivity (NEP ), gross primary productivity (GPP) and ecosystem respiration (Re)) and environmental factors (including mean air temperature (Ta) and total precipitation (PPT )) as well as annual carbon use efficiency (CUE), Re/GPP, normalized difference vegetation index (NDVI) and coefficients of variation (CV) of these factors in the alpine shrub-meadow and steppe-meadow.
图3
新窗口打开|下载原图ZIP|生成PPT图32004-2008年高寒灌丛草甸和草原化草甸月平均光合有效辐射(A, PAR, μmol·m-2·s-1)、月平均空气温度(B, Ta, ℃)、月平均 5 cm土壤温度(C, Ts, ℃)、月平均饱和水汽压差(D, VPD, kPa)、 月平均5 cm土壤含水量(E, SWC, m3·m-3)、 月降水量(E, PPT, mm)和归一化植被指数(F, NDVI)16天平均值的季节动态。黑色点线和黑色柱形图代表灌丛草甸, 灰色点线和灰色柱形图代表草原化草甸。
Fig. 3Seasonal dynamic of monthly average photosynthetically active radiation (A, PAR, μmol·m-2·s-1), monthly average air temperature (B, Ta, ℃), monthly average soil temperature at a depth of 5 cm (C, Ts, ℃), monthly average vapor press deficit (D, VPD, kPa), monthly average soil water content at a depth of 5 cm (E, SWC, m3·m-3), and monthly total precipitation (E, PPT, mm), 16-day mean normalized difference vegetation index (F, NDVI) in the alpine shrub-meadow and steppe-meadow form 2004 to 2008. The black squares and histograms represent the shrub-meadow and the grey circles and histograms denote the steppe-meadow.
NDVI在一定程度上可以表示植被冠层的变化趋势(Nagler et al., 2005), 图3F是灌丛和草甸每一年的月平均NDVI, 两站点NDVI的变化趋势基本保持一致, 在生长季均呈现单峰曲线变化, 但在数值上草甸要显著低于灌丛(p < 0.001)。灌丛的NDVI最大值 (图2G)显著大于草甸(p < 0.01), 且年际变异系数较小。
2.2 CO2通量对比
2.2.1 CO2通量季节动态图4A-4C显示了两个生态系统的NEP、GPP和Re的季节动态。NEP在非生长季都是处于净碳释放的状态, 而在生长季的大部分时间处于净碳吸收的状态。在生长季前期两个生态系统的净碳释放量是逐渐增加的, 表明在返青前Re占主导作用, 灌丛的Re高于草甸。随着植被冠层的发育和盖度增加, 碳吸收加速, 两生态系统均是6月上旬左右突破零线后进入“碳汇”状态, 但草甸具有较大的变异, 如在2007和2008年。在生长季中期(7-8月)吸收值达到最大值, 这与NDVI的动态变化是一致的(图3F), 进入生长季末期(9-10月)碳吸收量逐渐降低, 直至突破零线进入“碳源”状态, 随后生态系统进入休眠期, 即非生长季(图4A)。灌丛进入休眠期的时间要早于草甸。灌丛和草甸年均碳吸收天数(CUP)分别为108和115天, 虽然草甸具有稍长的碳吸收天数但更具有较大的变异系数, 其大小是灌丛的5倍。在研究期所有年份的生长季, 灌丛生态系统碳吸收值要高于草甸, 两个生态系统CO2最大吸收日值分别在2004年7月(灌丛)和2008年7月(草甸), 其值分别为5.05和2.0 g C·m-2·d-1。
图4
新窗口打开|下载原图ZIP|生成PPT图42004-2008年高寒灌丛草甸和草原化草甸生态系统净初级生产力(NEP, A), 总初级生产力(GPP, B)和生态系统呼吸(Re, C)日值(g C·m-2·d-1)的季节变化动态。灰色点代表草原化草甸, 黑色点代表灌丛草甸。
Fig. 4Seasonal patterns of daily (g C·m-2·d-1) values of net ecosystem productivity (NEP, A), gross primary productivity (GPP, B) and ecosystem respiration (Re, C) for the alpine shrub-meadow and the steppe-meadow from 2004 to 2008. The black solid circles represent shrub-meadow and the grey hollow circles denote steppe-meadow.
GPP的季节动态与NDVI基本保持一致(图3F, 图4B), 高峰时期分别出现在7月中旬(灌丛)和8月中旬(草甸), 最大值分别出现在2004年7月(8.43 g C·m-2·d-1, 灌丛)和2007年8月(3.30 g C·m-2·d-1, 草甸), 并且灌丛各年份最大值均要高于草甸。生长季节灌丛生态系统的GPP日值也要明显高于草甸生态系统, 草甸的GPP启动增长的时间要晚于灌丛(图4B), 但呈现快速增加的时间(2007年除外)基本相同。图4C是Re的季节动态, 两个生态系统各年份Re均是生长季高于非生长季, 并且灌丛明显高于草甸。
2.2.2 CO2通量年际动态
草甸的NEP累计值比灌丛要小得多, 且两者之间存在较大的季节和年际间差异(图2A; 图4A)。灌丛都是在7、8月份开始大于0, 直到12月份NEP累计值仍然大于0, 说明灌丛在下半年一直处于“碳汇”状态, 但是草甸2006和2007年的NEP累计值全年 都处于持续低于0的“碳源”状态。灌丛连续5年都 持续为“碳汇”, 其中2004年累计值最高, 为 103.28 g C·m-2·d-1, 5年平均值为69.59 g C·m-2·d-1, 变异系数为0.35 (图2H)。而草甸生态系统5年内有3年“碳汇”, 2年“碳源”, 最大“碳汇”年份是2008年, NEP累计值为53.67 g C·m-2·d-1, 最大“碳源”年是2006年, NEP累计值为-87.70 g C·m-2·d-1, 5年NEP年际平均值为-4.55 g C·m-2·d-1, 变异系数是13.18 (图2H), 基本处于微小“碳源”状态。虽然两生态系统年际源/汇动态存在较大差异, 但在整个生长季尺度上两生态系统都是“碳汇”, 只是灌丛CO2净吸收量要高于草甸(图2A)。
草甸的GPP和Re累计值都明显低于灌丛(图2B、 2C), 其中2006年最低。即使是在水分最好, GPP和Re达到了极大值的2008年, 草甸仍低于灌丛。草甸的GPP和Re还具有较高的年际变异系数。灌丛的碳利用效率(CUE = NEP/GPP)稍高于草甸, 如果遇到雨水较多的年份, 草甸CUE会大于灌丛, 但若是遇到干旱就会出现CUE为负值的情况。除此之外, 两生态系统都是Re/GPP值高于CUE值, 说明光合作用所固定的CO2主要被生态系统呼吸所释放(图2D)。
2.3 环境因子对CO2通量季节变异的影响
2.3.1 生长季节生物环境因子对CO2通量的影响可用SEM来确定NEP及其组分(GPP和Re)的主要环境限制因子及其相对贡献量。草甸CO2通量的影响因子路径要比灌丛复杂。在生长季, 灌丛NEP有2个显著直接影响因子Ta和NDVI, 以及不显著影响因子SWC, 相对贡献量分别为0.60、0.25和-0.13, Ta的贡献量最大(图5A), 草甸NEP有3个显著的直接影响因子SWC、NDVI和Ta, 其中SWC和NDVI是主要控制因子(图5B)。灌丛GPP主要受Ta、NDVI和SWC影响, 其中Ta是最主要的限制因子(图5C), 草甸GPP同样显著受这3个因子的直接影响, 但贡献量的大小正好相反, 其中SWC是主要限制因子(图5D)。Re的影响因子要比GPP简单些, 两生态系统的Re都只受GPP和Ts的显著直接影响, 并且最大贡献者都是GPP (图5C、5D)。其他因子如PPT、Ts等都是通过间接作用显著影响两生态系统NEP及其组分。在SEM中, 环境因子对灌丛和草甸NEP的解释量(R2)分别为75%和83%, 对GPP的解释力分别为88%和77%, 对Re的解释力分别为95%和74%。
图5
新窗口打开|下载原图ZIP|生成PPT图5高寒灌丛草甸和草原化草甸2004-2008年16天平均生物和环境影响因子(气温, Ta, ℃; 5 cm土壤温度, Ts, ℃; 5 cm土壤含水量, SWC, m3·m-3; 降水量PPT, mm; 光合有效辐射, PAR, μmol·m-2·s-1; 归一化植被指数, NDVI)对CO2通量(净初级生产力, NEP, g C·m-2·d-1; 总初级生产力, GPP, g C·m-2·d-1; 生态系统呼吸, Re, g C·m-2·d-1)的结构方程模型图。A, C, E, 海北高寒灌丛草甸。B, D, F, 当雄高寒草原化草甸。A, B, C, D, 生长季节。E, F, 非生长季。黑色箭头是正相关, 灰色箭头是负相关, 实线箭头表示p ≤ 0.05, 虚线箭头表示p > 0.05, 箭头上的数字代表通径系数, 箭头的宽窄代表通径系数的大小。
Fig. 5Path diagrams illustrating the effects of 16-day mean biotic and abiotic factors (air temperature, Ta, ℃; soil temperature at the depth of 5 cm, Ts, ℃; soil water content at the depth of 5 cm, SWC, m3·m-3; precipitation, PPT, mm; photosynthetically active radiation, PAR, μmol·m-2·s-1; normalized difference vegetation index, NDVI) on 16-day mean CO2 fluxes (net ecosystem productivity, NEP, g C·m-2·d-1, gross primary productivity, GPP, g C·m-2·d-1 and ecosystem respiration, Re, g C·m-2·d-1) during the growing season (A-D) and non-growing season (E, F) from 2004-2008 in the alpine shrub-meadow (A, C, E) and steppe-meadow (B, D, F). The grey solid arrows represent significantly negative correlation and the black solid arrows denote significantly positive correlation (p ≤ 0.05). The dashed arrows represent non-significantly correlation (p > 0.05). Data on the arrows are the standardized SEM coefficients. The thickness of the arrows reflects the magnitude of the standardized SEM coefficient.
NDVI是两个生态系统CO2通量主要的生物影响因子, 在草甸直接受SWC、Ta和PAR的显著影响,但是在灌丛只受Ta的显著直接影响。PPT、Ts等因子虽然没有直接影响CO2通量和NDVI, 但能通过影响Ta、SWC和NDVI等因子间接显著影响CO2通量的变化。
2.3.2 非生长季节环境因子对CO2通量的控制
在非生长季节, 两生态系统没有光合作用, 只有呼吸作用, NEP只是生态系统呼吸作用释放的CO2量。两生态系统NEP都是受Ts显著的直接影响, 并受Ta和PAR的间接影响(图5E、5F), 唯一不同的就是在草甸中PAR也直接显著影响NEP。主要影响因子对灌丛和草甸非生长季NEP的解释力分别为77%和30%。
2.4 年际NEP的影响因子
两生态系统年际NEP与年CUE和NDVI具有显著线性相关性, NEP随着CUE和NDVI的增大而增加, 而且CUE的相关性高于NDVI (图6)。从图5中还可以看出两生态系统中年CUE和NDVI量级具有明显差异, 即灌丛大于草甸, 这也间接说明为什么灌丛年际CO2吸收能力强于草甸。利用逐步回归方程来分析两生态系统CUE的影响因子, 得到的逐步回归方程式如下:CUE = 0.002PPT + 0.984NDVI - 1.248
(p = 0.002, Adj. R2 = 0.79) (5)
年际PPT和NDVI共同解释CUE 79%的年际变化, 这也就是说两生态系统CUE和NEP的差异是由PPT和NDVI共同导致的。并且草甸受年PPT的影响更加明显, 图2A和2F数据可看出年际NEP随着年PPT的增加而增大, 2006年最为干旱, 因此是最大的“碳源”年, 相反, 2008年最湿润, 是最大的“碳汇”年。
图6
新窗口打开|下载原图ZIP|生成PPT图62004-2008年两生态系统年累积净初级生产力NEP (g C·m-2·a-1)与年碳利用效率CUE (A)、年归一化植被指数NDVI (B)的相关关系。△海北高寒灌丛草甸。〇当雄高寒草原化草甸。Adj.R2, 调整过的决定系数。
Fig. 6The correlative relationships of annual accumulative net ecosystem productivity (NEP, g C·m-2·a-1) with annual carbon use efficiency (CUE, A) and normalized difference vegetation index (NDVI, B) from 2004 to 2008. Hollow triangles represent the alpine shrub- meadow in Haibei (△) and hollow circles denote the alpine steppe-meadow in Damxung (〇). Adj.R2, adjusted coefficient of determination.
3 讨论
对青藏高原东部湿润的灌丛草甸和腹地半干旱气候条件下的草原化草甸CO2通量的季节变化进行比较, 前者主要受温度限制, 而后者主要受土壤水分和温度共同限制。尽管研究期内两地生态系统的年降水量和生长季降水量没有明显差异, 草原化草甸的生长季平均温度还较高, 但土壤水分明显低于灌丛草甸, 水分和温度耦合的协调度不高, 导致了草原化草甸的GPP和NEP都比灌丛草甸低得多, 灌丛草甸是“碳汇”, 而草原化草甸是碳中性生态系统。本研究结果很好地验证了限制因子定律。3.1 CO2通量的比较
尽管草甸比灌丛具有较高的温度和辐射条件, 研究期的年降水总量差异不大, 但土壤水分条件较差, 植被指数NDVI也较低, 这造成高原腹地半干旱气候条件下的草甸草原的NEP及其分量都低于高原东部湿润的灌丛。虽然草甸生长季节5年平均值是碳汇(62.64 g C·m-2·a-1), 但其年际总量平均值基本维持碳平衡状态(-4.55 g C·m-2·a-1), 远低于生长季平均(141.22 g C·m-2·a-1)和年际平均(69.59 g C·m-2·a-1)均是“碳汇”作用的灌丛。因为降水变异较大, 植被稀疏(Ma et al., 2010), 草原土的持水性较差, 温度较高和风速较大等多重因子的影响导致蒸发较为强烈, 土壤水分有效性较低, 导致半干旱高寒草甸年际NEP在“碳源”和“碳汇”之间转换, 而这种情况在其他草地生态系统, 例如内蒙古(Liu et al., 2012)、加拿大(Flanagan, 2002)和欧洲(Gilmanov et al., 2007)也是常见的。这种现象的发生是由水分的可利用性 (有效性)和初级生产力的大小所决定的(Liu et al., 2012)。高寒灌丛连续5年生长季节和年际NEP都高, 主要归因于该生态系统具有较高的植被指数以及充足水分条件下较低温度和较高的太阳辐射, 这种条件有利于生态系统光合作用固定较多的CO2以及低温下较小的碳消耗(Saito et al., 2009)。另外, 海北站的高寒草甸生态系统CO2净吸收量也较高(赵亮, 2006), 说明水分条件对于高寒草甸生态系统的碳收支是非常重要的。而当雄的草原化草甸年降水量年际变异大, 土壤水分含量较低, 导致了NEP的巨大波动。虽然本研究中两生态系统年固碳能力差异较大, 但与欧洲20多个草地生态系统(Gilmanov et al., 2007)以及美国南部大草原(Meyers, 2001) NEP年际值变异范围相当。3.2 CO2通量季节变异控制因子的比较
3.2.1 气候因子的控制两站点虽然都地处高海拔青藏地区, 但环境条件有一定差异, 为对比两类生态系统CO2通量及其限制因子提供了良好的平台。在众多的环境因子中, Ta和SWC直接影响着NEP和GPP生长季节的变异, 但对两生态系统的影响效果却不同。东部灌丛草毡土的水分含量达到30%以上, 远高于高原腹地的草原土, 而且生长季开始就处于比较稳定的高值, 受降水量的影响没有草原土那么大, 因此, NEP和GPP主要受温度限制, 而受水分影响较小, 反之, 草甸的NEP和GPP主要受土壤水分限制, 其次受温度限制。这种差异的原因一方面源于海北年降水量在生长季分布相对较均匀, 而温度和光强低于当雄, 这在一定程度上减少了较高温度和高辐射所带来的水分损失, 降低了该地区的干旱程度; 另一方面, 灌丛植被根系要深于草甸植被根系, 降低了植被根系对表层土壤干旱的敏感性, 缓解表层土壤水分的缺失对根系的影响(Wolf et al., 2011)。而这种环境条件的差异也造就了当雄草甸CO2通量具有较大的变异性, 同时也源于该站的SWC和PPT都具有较大的年际和季节变异(Zhao et al., 2017)。低温是高寒生态系统最为普遍的环境影响因子(Kato et al., 2004; Saito et al., 2009), 它通过影响生态系统的生态过程, 例如冠层发育(Wan et al., 2009)、蒸散速率(Polley et al., 2006)和土壤水分(Zhou et al., 2007)等来影响CO2通量及其对气候变化的响应(Wang et al., 2011)。但如果辐射加强、温度持续升高以及干旱频繁发生, 那么水分胁迫就会成为植被生长的限制因子, 这是因为干旱的土壤会减少组织和细胞中水分的供应(Fu et al., 2006)。而东部灌丛生态系统温度和水分的季节和年际变异都较小, 这也是为什么其CO2通量季节和年际变异性较小的原因。
两生态系统Re生长季节变异都与GPP和Ts显著正相关, 且GPP的相关性要强于Ts, 揭示了GPP和Ts是高寒草地生态系统Re季节变异的主要决定因素。这一结果与CUE和Re/GPP的比例也是相一致的, 两生
态系统光合作用所固定的CO2平均80%以上甚至更多都因为呼吸而被排放, 只有10%左右被固定。GPP和Re季节动态的相关性在很多研究中都有发现(Lasslop et al., 2010; Yu et al., 2013), GPP是呼吸的主要供应基质, 必然会影响Re季节和年际变化, 这表明GPP和Re的环境控制因子在季节和年际动态过程上具有一定的相似性。两生态系统非生长季节由于温度过低和地上光合器官枯萎而停止光合作用, 因此NEP就只有微弱的呼吸作用且都直接受Ts的影响, 而Ta和PAR显著影响Ts的变化。当雄高寒草甸生态系统较高的太阳辐射也会对Re造成直接的影响, 这是因为较高的PAR可以缓解低温对Re的限制, 促进生态系统呼吸。
3.2.2 NDVI的影响
NDVI代表植被冠层的发育程度, 是重要的控制CO2通量的生物因子(Polley et al., 2010), 常用作叶面积指数(LAI)的代用指标表征植物叶片吸收光能和植被固定CO2的能力, 在一定程度上可以确定GPP (Ge et al., 2011)。本研究中无论从季节动态还是年际动态的影响因子分析中都显示NDVI与NEP是显著正相关的, 这说明两生态系统碳吸收量是受植被冠层变化影响的。Jia等(2014)也发现LAI可以解释NEE 45%以及GPP 65%的变化。而且相似的GPP-LAI和NEP-LAI关系的报道在其他草地生态系统也有发现(Flanagan, 2002; Yang et al., 2011), 进一步说明了植被发育和冠层对碳平衡的重要控制作用。
3.3 年际NEP差异的影响因子
不同草地生态系统年际NEP差异的原因是比较复杂的, 这主要是因为它受到草地植被类型、生物环境因子以及草地管理策略(施肥、刈割和放牧等)等多方面因素的影响(Jensen et al., 2017), 水热因子的配合尤为关键。我们的数据表明, 两生态系统年际CO2吸收能力主要取决于NDVI和碳利用效率。NDVI的大小差异决定了两生态系统在年际和季节光合固碳量上的差异, 因为有灌丛存在的草甸要比只有草本植物的草原化草甸具有更高的冠层盖度和层次分化, 从而表现出更高的生产力和碳固定能力(Yashiro, 2010)。但是从另一方面来讲, 高NDVI在促进GPP的同时也会导致较高的Re, 很难确定是否有高的NEP, 其大小主要取决于其组分GPP和Re所占的比例(Lu et al., 2017)。有研究表明, NEP的大小不取决于GPP或者Re, 而是由CUE决定的(Adrianv & Michaell, 2009; Peichl et al., 2010)。在我们所研究的两个生态系统中, CUE的大小对NEP也起到了决定性作用, 而所有影响CUE的因子也成了决定NEP大小的因子。逐步回归结果显示年降水量和年际NDVI对两生态系统CUE起着决定性作用, CUE随着年降水量和NDVI的增加而增加。无论从降水量还是降水的季节分布均匀性来看, 灌丛草甸都优于草甸化草甸, 加之又具有高的NDVI, 这在一定程度上解释了为什么高寒灌丛的NEP会高于高寒草原化草甸。此外, 水热因子的匹配程度也是影响生态系统GPP和NEP的关键因子, 高原东部湿润区灌丛草甸的土壤水分从4月开始就保持高的水平, 与降水高峰期的土壤水分基本持平, 在生长季盛期能保持水热同步, 而半干旱区的草原化草甸土壤水分受降水量影响较大且出现时间上的迟滞性, 植被生产力受到水分和温度的共同限制, 水热匹配程度较低, 这也是该生态系统NEP低于东部灌丛草甸的重要原因。4 结论
受高原季风气候影响, 由于湿润程度和水热匹配性的差异, 青藏高原东部高寒灌丛草甸和腹地高寒草原化草甸两生态系统的生产力和固碳能力呈现显著差异。东部湿润区高寒灌丛草甸是生产力较高的“碳汇”, 而高原腹地半干旱区的草原化草甸生产力低下, 处于碳平衡状态, 但其源/汇动态极不稳定, 具有较大的年际变异性。两种生态系统NEP差异主要取决于NDVI和碳利用效率, 而NDVI和年降水量是决定两生态系统碳利用效率的关键因子。两地区CO2通量除了量级上的差异外, 其主要限制因子也有明显差异。NDVI是直接显著影响两生态系统NEP和GPP变化的主要生物因子, 水、热季节变化及其协调程度是影响其大小和季节变异的主要环境因子。灌丛草甸主要受温度限制, NEP和GPP主要受Ta的直接影响, 生长季水热协调程度高, 生产力高, 草原化草甸则是以水分限制为主, 受SWC和Ta的共同影响, 但水热匹配程度较低, 由于干旱的影响, 生产力常较低。两生态系统生长季节Re主要受GPP和Ts的直接影响, GPP的影响要大于Ts, 非生长季节Re主要受Ts影响。上述结果表明, 高寒生态系统CO2通量都是受温度限制, 但在水分梯度上, 水分的限制及其与温度的协调程度也是影响生态系统生产力和碳固定的决定因素。
参考文献 原文顺序
文献年度倒序
文中引用次数倒序
被引期刊影响因子
DOI:10.1038/348711a0URL [本文引用: 1]
EVIDENCE from ice cores 1 indicates that concentrations of atmospheric carbon dioxide were lower by about 75 p.p.m. during the Last Glacial Maximum (LGM; 6518,000 years ago) than during the present interglacial (10,000 years ago to the present). The causes of such large changes in atmospheric CO 2 remain uncertain. Using a climate model, Prentice and Fung 2 have estimated that there was approximately the same amount of carbon in vegetation and soils during the LGM as there was during the present (pre-industrial) interglacial. In contrast, we present here results based on palynological, pedological and sedimentological evidence which indicate that in fact the amount of carbon in vegetation, soils and peatlands may have been smaller during the LGM by 651.3x 10 12 tonnes. Thus, organic carbon in vegetation and soils has more than doubled (from 0.96 to 2.3 x 10 12 tonnes) since the LGM. Oceanic CO 2 reservoirs seem to be the only possible source of this large quantity of carbon that has entered the terrestrial biosphere since the LGM (in addition to that which has entered the atmosphere to give the higher interglacial CO 2 levels).
DOI:10.1016/j.agrformet.2008.07.010URL [本文引用: 1]
Researchers have a poor understanding of the mechanisms that allow freshwater marshes to achieve rates of net primary production (NPP) that are higher than those reported for most other types of ecosystems. We used an 8-year record of the gross primary production (GPP) and NPP at the San Joaquin Freshwater Marsh (SJFM) in Southern California to determine the relative importance of GPP and carbon use efficiency (CUE; the ratio of total NPP to GPP calculated as NPP GPP 1) in determining marsh NPP. GPP was calculated from continuous eddy covariance measurements and NPP was calculated from annual harvests. The NPP at the SJFM was typical of highly productive freshwater marshes, while the GPP was similar to that reported for other ecosystem types, including some with comparatively low NPPs. NPP was weakly related to GPP in the same year, and was better correlated with the GPP summed from late in the previous year's growing season to early in the current growing season. This lag was attributed to carbohydrate reserves, which supplement carbon for new leaf growth in the early growing season of the current year. The CUE at the SJFM for the 8-year period was 0.61 卤 0.05. This CUE is larger than that reported for tropical, temperate, and boreal ecosystems, and indicates that high marsh NPP is attributable to a high CUE and not a high GPP. This study underscores the importance of autotrophic respiration and carbon allocation in determining marsh NPP.
DOI:10.3321/j.issn:0559-9350.2008.01.014URL [本文引用: 1]
根据冬小麦田间试验结果,用通径分析的方法,把不同灌溉决策指标对干物质和叶片水分利用效率(WUE)的影响进行了分析。通过土壤水分含量、叶面蒸腾、光合有效辐射、光合作用速率、气孔导度和叶温对作物干物质产量的通径分析发现,影响干物质产量最大的是叶面蒸腾,其次是光合有效辐射和叶温。通过充分灌溉和干旱水分处理相应时刻太阳辐射、光合有效辐射、空气水汽压差、气孔导度和叶温对作物叶片WUE的通径分析发现,对于适宜水分处理来说,主要影响WUE因子不是上述5个指标,而是土壤水分状况起到决定因素;对于干旱处理来说,主要影响因子是光合有效辐射和叶面温度。通过对干物质通径分析自变量指标的增减对结果的影响分析,发现,在考虑干物质生产和作物水分利用效率最优的目标时,灌溉决策指标要注意叶面蒸腾、光合有效辐射、叶面温度和土壤水分的变化。
DOI:10.3321/j.issn:0559-9350.2008.01.014URL [本文引用: 1]
根据冬小麦田间试验结果,用通径分析的方法,把不同灌溉决策指标对干物质和叶片水分利用效率(WUE)的影响进行了分析。通过土壤水分含量、叶面蒸腾、光合有效辐射、光合作用速率、气孔导度和叶温对作物干物质产量的通径分析发现,影响干物质产量最大的是叶面蒸腾,其次是光合有效辐射和叶温。通过充分灌溉和干旱水分处理相应时刻太阳辐射、光合有效辐射、空气水汽压差、气孔导度和叶温对作物叶片WUE的通径分析发现,对于适宜水分处理来说,主要影响WUE因子不是上述5个指标,而是土壤水分状况起到决定因素;对于干旱处理来说,主要影响因子是光合有效辐射和叶面温度。通过对干物质通径分析自变量指标的增减对结果的影响分析,发现,在考虑干物质生产和作物水分利用效率最优的目标时,灌溉决策指标要注意叶面蒸腾、光合有效辐射、叶面温度和土壤水分的变化。
[本文引用: 1]
[本文引用: 1]
DOI:10.5814/j.issn.1674-764x.2017.01.005URL [本文引用: 2]
Inter-annual variability in total precipitation can lead to significant changes in carbon flux.In this study,we used the eddy covariance(EC) technique to measure the net CO_2 ecosystem exchange(NEE) of an alpine meadow in the northern Tibetan Plateau.In 2005 the meadow had precipitation of 489.9 mm and in 2006 precipitation of 241.1 mm,which,respectively,represent normal and dry years as compared to the mean annual precipitation of 476 mm.The EC measured NEE was 87.70 g C m~(-2) yr~(-1) in 2006 and-2.35 g C m~(-2) yr~(-1) in 2005.Therefore,the grassland was carbon neutral to the atmosphere in the normal year,while it was a carbon source in the dry year,indicating this ecosystem will become a CO_2 source if climate warming results in more drought conditions.The drought conditions in the dry year limited gross ecosystem CO_2 exchange(GEE),leaf area index(LAI) and the duration of ecosystem carbon uptake.During the peak of growing season the maximum daily rate of NEE and Pmax and a were approximately 30%-50% of those of the normal year.GEE and NEE were strongly related to photosynthetically active radiation(PAR) on half-hourly scale,but this relationship was confounded by air temperature(Ta),soil water content(SWC) and vapor pressure deficit(VPD).The absolute values of NEE declined with higher Ta,higher VPD and lower SWC conditions.Beyond the appropriate range of PAR,high solar radiation exacerbated soil water conditions and thus reduced daytime NEE.Optimal T_a and VPD for maximum daytime NEE were 12.7鈩 and 0.42 KPa respectively,and the absolute values of NEE increased with SWC.Variation in LAI explained around 77% of the change in GEE and NEE.Variations in R_e were mainly controlled by soil temperature(T_s),whereas soil water content regulated the responses of R_e to T_s.
DOI:10.1111/j.1461-0248.2008.01164.xURLPMID:18279352 [本文引用: 1]
Abstract Plant functional traits control a variety of terrestrial ecosystem processes, including soil carbon storage which is a key component of the global carbon cycle. Plant traits regulate net soil carbon storage by controlling carbon assimilation, its transfer and storage in belowground biomass, and its release from soil through respiration, fire and leaching. However, our mechanistic understanding of these processes is incomplete. Here, we present a mechanistic framework, based on the plant traits that drive soil carbon inputs and outputs, for understanding how alteration of vegetation composition will affect soil carbon sequestration under global changes. First, we show direct and indirect plant trait effects on soil carbon input and output through autotrophs and heterotrophs, and through modification of abiotic conditions, which need to be considered to determine the local carbon sequestration potential. Second, we explore how the composition of key plant traits and soil biota related to carbon input, release and storage prevail in different biomes across the globe, and address the biome-specific mechanisms by which plant trait composition may impact on soil carbon sequestration. We propose that a trait-based approach will help to develop strategies to preserve and promote carbon sequestration.
DOI:10.1016/j.agee.2013.04.009URL [本文引用: 1]
Based on eddy covariance measurement over a degraded grassland and a cropland with maize (Zea mays) ecosystems from 2003 to 2009, carbon exchange processes and their responses to environmental factors in different temporal scales were analyzed in semiarid of China. Accounting for carbon export and import, NBP (net biome production) of cropland with maize ranged from 54.3 to 100.6g Cm612yr611. NBP remained positive indicating a carbon net loss from this ecosystem although NEE (net ecosystem exchange) was negative in most of years. Due to negligible carbon import and export, NBP of degraded grassland ecosystem was equal to NEE, with an average value of 138.4g Cm612yr611. The grassland ecosystem behaved as carbon source during the whole period. PPFD (incident photosynthetic active radiation) was the main driver for diurnal variation of NEE during growing season in most years. NDVI (normal difference vegetation index) was in accordance with seasonal patterns of NEE especially for cropland with maize ecosystem. Soil temperature at a depth of 5cm was also a main driver for seasonal variation of NEE at the degraded grassland ecosystem in normal precipitation years (2003 and 2005). Annual peak NDVI (NDVImax) was significantly correlated with annual NEE and GPP (gross primary productivity). The amount of growing season precipitation was more responsible for annual variation of NEE. The increasing number of precipitation event (>1mmday611) was associated with increasing annual carbon uptake. Drought in the early growing period is more critical to carbon dynamics of degraded grassland ecosystem while drought in the middle of growing season was more critical for cropland with maize ecosystem.
DOI:10.1051/0004-6361:200810276URL [本文引用: 3]
Net ecosystem carbon dioxide (CO2 ) exchange (NEE) was measured in a northern temperate grassland near Lethbridge, Alberta, Canada for three growing seasons using the eddy covariance technique . The study objectives were to document how NEE and its major component processes-gross photosynthesis (GPP) and total ecosystem respiration (TER)-vary seasonally and interannually, and to examine how environmental and physiological factors influence the annual C budget. The greatest difference among the three study years was the amount of precipitation received. The annual precipitation for 1998 (481.7 mm) was significantly above the 1971-2000 mean (+/- SD, 377.9 +/- 97.0 mm) for Lethbridge, whereas 1999 (341.3 mm) was close to average, and 2000 (275.5 mm) was significantly below average. The high precipitation and soil moisture in 1998 allowed a much higher GPP and an extended period of net carbon gain relative to 1999 and 2000. In 1998, the peak NEE was a gain of 5 g C m(-2) d(-1) (day 173). Peak NEE was lower and also occurred earlier in the year on days 161 (3.2 g C m(-2) d(-1) ) and 141 (2.4 g C m(-2) d(-1) ) in 1999 and 2000, respectively. Change in soil moisture was the most important ecological factor controlling C gain in this grassland ecosystem. Soil moisture content was positively correlated with leaf area index (LAI). Gross photosynthesis was strongly correlated with changes in both LAI and canopy nitrogen (N) content. Maximum GPP (A (max) : value calculated from a rectangular hyperbola fitted to the relationship between GPP and incident photosynthetic photon flux density (PPFD)) was 27.5, 12.9 and 8.6 mumol m(-2) s(-1) during 1998, 1999 and 2000, respectively. The apparent quantum yield also differed among years at the time of peak photosynthetic activity, with calculated values of 0.0254, 0.018 and 0.018 during 1998, 1999 and 2000, respectively. The ecosystem accumulated a total of 111.9 g
[本文引用: 1]
[本文引用: 1]
[本文引用: 1]
DOI:10.1016/j.agrformet.2010.10.003URL [本文引用: 1]
In order to assess the capacity of the boreal forest ecosystem to intercept atmospheric carbon over a period of years, a climate-driven growth model (FinnFor, process-based) was applied to calculate the seasonal and inter-annual variability of net ecosystem CO 2 exchange (NEE) and component carbon fluxes (gross primary production – GPP and total ecosystem respiration – TER) against a 10-year (1999–2008) period of eddy covariance (EC) measurements in a Scots pine ( Pinus sylvestris L.) stand in Eastern Finland. Furthermore, the role of climatic factors, leaf area index ( LAI) and physiological responses of trees regarding the ecosystem carbon fixation processes were evaluated. An hourly time-step was used to simulate the carbon exchange based on measured tree/stand characteristics and meteorological input for the experimental site, and the dynamic LAI was used throughout the 10-year simulations. The model predicted well the annual course of NEE compared to the measured values for most of the years, with the development of LAI (2.4–3.3 m 2 m 612, as simulated). The simulated NEE over the study period shows that, on average, 62% of the variation refers to daily and 88% to monthly measured NEE. Both modeled and measured daily NEE showed similar responses to the temperature, photosynthetically active radiation and vapor pressure deficit during the growing seasons. In the simulation, the annual amount of GPP varied from 720.8 to 910.4 g C m 612 with a mean value of 825.3 g C m 612, and the annual mean TER/GPP ratio was 0.79, close to the measured value. Carbon efflux from the forest floor was the dominant contributor to the forest ecosystem respiration. The inter-annual variation of GPP mostly corresponded to the development of LAI, temperature sum and total incoming radiation over the 10-year simulation period. It was suggested that the process-based model could be applied to study the carbon processes for natural and management-induced dynamics of Scots pine forest ecosystem over longer periods across a wider climate gradient in the boreal zone.
DOI:10.1016/j.agee.2006.12.008URL [本文引用: 2]
Tower CO 2 flux measurements from 20 European grasslands in the EUROGRASSFLUX data set covering a wide range of environmental and management conditions were analyzed with respect to their ecophysiological characteristics and CO 2 exchange (gross primary production, P g , and ecosystem respiration, R e ) using light-response function analysis. Photosynthetically active radiation ( Q ) and top-soil temperature ( T s ) were identified as key factors controlling CO 2 exchange between grasslands and the atmosphere at the 30-min scale. A nonrectangular hyperbolic light-response model P ( Q ) and modified nonrectangular hyperbolic light–temperature-response model P ( Q , T s ) proved to be flexible tools for modeling CO 2 exchange in the light. At night, it was not possible to establish robust instantaneous relationships between CO 2 evolution rate r n and environmental drivers, though under certain conditions, a significant relationship r n =r 0 65ek T T s r n = r 0 65 e k T T s mathContainer Loading Mathjax was found using observation windows 7–14 days wide. Principal light-response parameters—apparent quantum yield, saturated gross photosynthesis, daytime ecosystem respiration, and gross ecological light-use efficiency, 07 02=02 P g / Q , display patterns of seasonal dynamics which can be formalized and used for modeling. Maximums of these parameters were found in intensively managed grasslands of Atlantic climate. Extensively used semi-natural grasslands of southern and central Europe have much lower production, respiration, and light-use efficiency, while temperate and mountain grasslands of central Europe ranged between these two extremes. Parameters from light–temperature-response analysis of tower data are in agreement with values obtained using closed chambers and free-air CO 2 enrichment. Correlations between light-response and productivity parameters provides the possibility to use the easier to measure parameters to estimate the parameters that are more difficult to measure. Gross primary production ( P g ) of European grasslands ranges from 170002g02CO 2 02m 612 02year 611 in dry semi-natural pastures to 690002g02CO 2 02m 612 02year 611 in intensively managed Atlantic grasslands. Ecosystem respiration ( R e ) is in the range 180002240002g02CO 2 02m 612 02year 611 ) to significant release (<6160002g02CO 2 02m 612 02year 611 ), though in 15 out of 19 cases grasslands performed as net CO 2 sinks. The carbon source was associated with organic rich soils, grazing, and heat stress. Comparison of P g , R e , and NEE for tower sites with the same characteristics from previously published papers obtained with other methods did not reveal significant discrepancies. Preliminary results indicate relationships of grassland P g and R e to macroclimatic factors (precipitation and temperature), but these relationships cannot be reduced to simple monofactorial models.
DOI:10.1111/j.1365-2486.2009.02041.xURL [本文引用: 1]
Abstract The measured net ecosystem exchange (NEE) of CO 2 between the ecosystem and the atmosphere reflects the balance between gross CO 2 assimilation [gross primary production (GPP)] and ecosystem respiration (R eco ). For understanding the mechanistic responses of ecosystem processes to environmental change it is important to separate these two flux components. Two approaches are conventionally used: (1) respiration measurements made at night are extrapolated to the daytime or (2) light–response curves are fit to daytime NEE measurements and respiration is estimated from the intercept of the ordinate, which avoids the use of potentially problematic nighttime data. We demonstrate that this approach is subject to biases if the effect of vapor pressure deficit (VPD) modifying the light response is not included. We introduce an algorithm for NEE partitioning that uses a hyperbolic light response curve fit to daytime NEE, modified to account for the temperature sensitivity of respiration and the VPD limitation of photosynthesis. Including the VPD dependency strongly improved the model's ability to reproduce the asymmetric diurnal cycle during periods with high VPD, and enhances the reliability of R eco estimates given that the reduction of GPP by VPD may be otherwise incorrectly attributed to higher R eco . Results from this improved algorithm are compared against estimates based on the conventional nighttime approach. The comparison demonstrates that the uncertainty arising from systematic errors dominates the overall uncertainty of annual sums (median absolute deviation of GPP: 47gCm 612 yr 611 ), while errors arising from the random error (median absolute deviation: 652gCm 612 yr 611 ) are negligible. Despite site-specific differences between the methods, overall patterns remain robust, adding confidence to statistical studies based on the FLUXNET database. In particular, we show that the strong correlation between GPP and R eco is not spurious but holds true when quasi-independent, i.e. daytime and nighttime based estimates are compared.
DOI:10.1029/2003JD003584URL [本文引用: 1]
[1] The alpine meadow ecosystem on the Qinghai-Tibetan Plateau may play a significant role in the regional carbon cycle. To assess the CO2 flux and its relationship to environmental controls in the ecosystem, eddy covariance of CO2, H2O, and energy fluxes was measured with an open-path system in an alpine meadow on the plateau at an elevation of 3,250 m. Net ecosystem CO2 influx (Fc) averaged 8.8 g m0908082 day0908081 during the period from August 9 to 31, 2001, with a maximum of 15.9 g m0908082 day0908081 and a minimum of 2.3 g m0908082 day0908081. Daytime Fc averaged 16.7 g m0908082 day0908081 and ranged from 10.4 g m0908082 day0908081 to 21.7 g m0908082 day0908081 during the study period. For the same photosynthetic photon flux density (PPFD), gross CO2 uptake (Gc) was significantly higher on cloudy days than on clear days. However, mean daily Gc was higher on clear days than on cloudy days. With high PPFD, Fc decreased as air temperature increased from 1000°C to 2300°C. The greater the difference between daytime and nighttime air temperatures, the more the sink was strengthened. Daytime average water use efficiency of the ecosystem (WUEe) was 8.7 mg (CO2)(g H2O)0908081; WUEe values ranged from 5.8 to 15.3 mg (CO2)(g H2O)0908081. WUEe increased with the decrease in vapor pressure deficit. Daily albedo averaged 0.20, ranging from 0.19 to 0.22 during the study period, and was negatively correlated with daily Fc. Our measurements provided some of the first evidence on CO2 exchange for a temperate alpine meadow ecosystem on the Qinghai-Tibetan Plateau, which is necessary for assessing the carbon budget and carbon cycle processes for temperate grassland ecosystems.
DOI:10.5254/1.3539616URL [本文引用: 1]
Sulfur group analyses of reinforced MBTS accelerated vulcanizates reveal chemical differences which can be related to the surface chemistry of the carbon blacks. The analytical procedure is based on the treatment of the vulcanizate with lithium aluminum hydride followed by potentiometric titration of sulfide and mercaptan sulfur. The polysulfide crosslink density and the values of x in the RSSxSR polysulfides are dependent upon the quinone content of the carbon black. Both the quinone content and the surface area of a carbon black appear to determine its influence on the disappearance of free sulfur and the apparent crosslinking of the vulcanizate.
DOI:10.1002/zaac.18980180102URL [本文引用: 1]
First page of article
DOI:10.1016/j.agrformet.2016.10.023URL [本文引用: 1]
The understanding of the controlling factors determining interannual variability (IAV) of carbon dioxide (CO 2 ) exchange between different ecosystems is crucial when assessing present and future responses to climate variability and climate change. Six years of eddy covariance (EC) data from three neighboring sites (agriculture, forest, and meadow) subjected to management in variable degree were evaluated to determine typical CO 2 budgets and controlling factors of IAV. In terms of average annual net ecosystem exchange (NEE) the agricultural and wet meadow site showed identical rates of 61156 (±110 and ±116, respectively) g C m 612 02y 611 , with large IAV and individual years even showing near zero net uptake. In contrast, the forest was a substantial and persistent sink of CO 2 (avg.02±02s.d. 6169102±0214302g02C02m 612 02y 611 ), but had a higher absolute IAV. A homogeneity-of-slopes (HOS) model was utilized to partition sources of IAV of CO 2 fluxes between direct climatic effects and indirect effects (functional changes). This analysis showed that NEE at the forest (through both GPP and RE) was most prone to interannual functional changes. The wet meadow showed moderate functional changes with respect to RE and thus NEE, whereas the cropland did not show any statistically significant functional changes. We argue that the delicate interplay between climate forcing, land use specific traits, management practices and intensities, and functional changes has to be taken into account when predicting the atmospheric CO 2 sink/source strengths of land ecosystems for longer timescales.
DOI:10.5194/bg-11-4679-2014URL
DOI:10.1007/s00442-014-3090-8URLPMID:25241297 [本文引用: 1]
To date the implications of greater intra-annual variability and extremes in precipitation on ecosystem functioning have received little attention. This study presents results on soil and vegetation carbon and water fluxes in the understorey of a Mediterranean oak woodland in response to increasing precipitation variability, with an extension of the dry period between precipitation events from 3 to 602weeks, without altering total annual precipitation inputs. With prolonged dry periods soil moisture did breach the stress thresholds for ecosystem processes, which led to short-term treatment differences in photosynthesis, but not in system carbon losses, with subsequent short-term decreases in net ecosystem exchange. Independent of treatment, irrigation events rapidly increased carbon and water fluxes. However, contradicting the predictions drawn from the ‘bucket model’, over the course of the growing season no all-over treatment differences were found in system assimilation and respiration, nor in evapotranspiration and ecosystem water use efficiency. This lack of responsiveness is attributed to the ecosystem’s resilience to low soil moisture during the growing season of the herbaceous understorey, with temperature rather than soil moisture controlling key ecosystem processes. Moreover, severe nitrogen limitation of the studied ecosystem may explain the lack of moisture effects on net system carbon dynamics. Thus, although the bucket model predicts changes in soil water dynamics with increasing precipitation variability, ecosystem responses to more extreme precipitation regimes may be influenced by additional factors, such as inter-annual variability in nutrient availability.
DOI:10.1029/2003JD003951URL [本文引用: 2]
[1] We measured the net ecosystem CO2 exchange (NEE) in an alpine meadow ecosystem (latitude 3700°2909000509000945090005N, longitude 10100°1209000509000923090005E, 3250 m above sea level) on the Qinghai-Tibetan Plateau throughout 2002 by the eddy covariance method to examine the carbon dynamics and budget on this unique plateau. Diurnal changes in gross primary production (GPP) and ecosystem respiration (Re) showed that an afternoon increase of NEE was highly associated with an increase of Re. Seasonal changes in GPP corresponded well to changes in the leaf area index and daily photosynthetic photon flux density. The ratio of GPP/Re was high and reached about 2.0 during the peak growing season, which indicates that mainly autotrophic respiration controlled the carbon dynamics of the ecosystem. Seasonal changes in mean GPP and Re showed compensatory behavior as reported for temperate and Mediterranean ecosystems, but those of GPPmax and Remax were poorly synchronized. The alpine ecosystem exhibited lower GPP (575 g C m0908082 y0908081) than, but net ecosystem production (78.5 g C m0908082 y0908081) similar to, that of subalpine forest ecosystems. The results suggest that the alpine meadow behaved as a CO2 sink during the 1-year measurement period but apparently sequestered a rather small amount of C in comparison with similar alpine ecosystems.
DOI:10.1016/j.soilbio.2005.02.018URL [本文引用: 1]
We examined the CO 2 exchange of a Kobresia meadow ecosystem on the Qinghai–Tibetan plateau using a chamber system. CO 2 efflux from the ecosystem was strongly dependence on soil surface temperature. The CO 2 efflux–temperature relationship was identical under both light and dark conditions, indicating that no photosynthesis could be detected under light conditions during the measurement period. The temperature sensitivity ( Q 10) of the CO 2 efflux showed a marked transition around 611.0 °C; Q 10 was 2.14 at soil surface temperatures above and equal to 611.0 °C but was 15.3 at temperatures below 611.0 °C. Our findings suggest that soil surface temperature was the major factor controlling winter CO 2 flux for the alpine meadow ecosystem and that freeze–thaw cycles at the soil surface layer play an important role in the temperature dependence of winter CO 2 flux.
DOI:10.1016/j.agrformet.2003.12.008URL
We used the eddy covariance method to measure the CO 2 exchange between the atmosphere and an alpine meadow ecosystem (37°29–45′N, 101°12–23′E, 3250 m a.s.l.) on the Qinghai–Tibetan Plateau, China in the 2001 and 2002 growing seasons. The maximum rates of CO 2 uptake and release derived from the diurnal course of CO 2 flux ( F CO 2) were 6110.8 and 4.4 μmol m 612 s 611, respectively, indicating a relatively high net carbon sequestration potential as compared to subalpine coniferous forest at similar elevation and latitude. The largest daily CO 2 uptake was 3.9 g C m 612 per day on 7 July 2002, which is less than half of those reported for lowland grassland and forest at similar latitudes. The daily CO 2 uptake during the measurement period indicated that the alpine ecosystem might behave as a sink of atmospheric CO 2 during the growing season if the carbon lost due to grazing is not significant. The daytime CO 2 uptake was linearly correlated with the daily photosynthetic photon flux density each month. The nighttime averaged F CO 2 showed a positive exponential correlation with the soil temperature, but apparently negative correlation with the soil water content.
DOI:10.1126/science.1076347URLPMID:12481139 [本文引用: 1]
Abstract Ecosystem responses to increased variability in rainfall, a prediction of general circulation models, were assessed in native grassland by reducing storm frequency and increasing rainfall quantity per storm during a 4-year experiment. More extreme rainfall patterns, without concurrent changes in total rainfall quantity, increased temporal variability in soil moisture and plant species diversity. However, carbon cycling processes such as soil CO2 flux, CO2 uptake by the dominant grasses, and aboveground net primary productivity (ANPP) were reduced, and ANPP was more responsive to soil moisture variability than to mean soil water content. Our results show that projected increases in rainfall variability can rapidly alter key carbon cycling processes and plant community composition, independent of changes in total precipitation.
DOI:10.1111/j.1365-2486.2009.02041.xURL [本文引用: 1]
Abstract The measured net ecosystem exchange (NEE) of CO 2 between the ecosystem and the atmosphere reflects the balance between gross CO 2 assimilation [gross primary production (GPP)] and ecosystem respiration (R eco ). For understanding the mechanistic responses of ecosystem processes to environmental change it is important to separate these two flux components. Two approaches are conventionally used: (1) respiration measurements made at night are extrapolated to the daytime or (2) light–response curves are fit to daytime NEE measurements and respiration is estimated from the intercept of the ordinate, which avoids the use of potentially problematic nighttime data. We demonstrate that this approach is subject to biases if the effect of vapor pressure deficit (VPD) modifying the light response is not included. We introduce an algorithm for NEE partitioning that uses a hyperbolic light response curve fit to daytime NEE, modified to account for the temperature sensitivity of respiration and the VPD limitation of photosynthesis. Including the VPD dependency strongly improved the model's ability to reproduce the asymmetric diurnal cycle during periods with high VPD, and enhances the reliability of R eco estimates given that the reduction of GPP by VPD may be otherwise incorrectly attributed to higher R eco . Results from this improved algorithm are compared against estimates based on the conventional nighttime approach. The comparison demonstrates that the uncertainty arising from systematic errors dominates the overall uncertainty of annual sums (median absolute deviation of GPP: 47gCm 612 yr 611 ), while errors arising from the random error (median absolute deviation: 652gCm 612 yr 611 ) are negligible. Despite site-specific differences between the methods, overall patterns remain robust, adding confidence to statistical studies based on the FLUXNET database. In particular, we show that the strong correlation between GPP and R eco is not spurious but holds true when quasi-independent, i.e. daytime and nighttime based estimates are compared.
DOI:10.3969/j.issn.1007-0435.2005.02.013URL [本文引用: 1]
以金露梅(Potentillafruticosa)灌丛草甸生态系统为对象,应用静态密闭箱-气相色谱法对高寒灌丛(GG)、丛内草甸(GC)和裸地(GL)的CO2释放进行了初步研究。结果表明:GG、GC和GLCO2的释放速率均呈明显的单峰型日变化进程,最大释放速率出现在15∶00～17∶00之间,最小值在7∶00前后出现,白天释放速率大于夜晚;CO2释放速率具有明显的季节性变化特征,生长期CO2释放速率明显高于枯黄期,且均表现为正排放,8月为CO2释放高峰期,释放速率GGGCGL(P0.01);2003年6月30日至2004年2月28日,高寒灌丛植被-土壤系统CO2释放量为3088.458±287.02g/m2,丛内草甸植被-土壤系统CO2释放量为2239.685±183.68g/m2,其中基础土壤呼吸CO2的释放量约为1346.748±176.24g/m2,分别占GG和GC释放量的43.61%和60.13%;CO2释放速率的日变化主要受地表和5cm地温制约,而季节动态与5cm地温呈显著正相关关系(P0.01)。
DOI:10.3969/j.issn.1007-0435.2005.02.013URL [本文引用: 1]
以金露梅(Potentillafruticosa)灌丛草甸生态系统为对象,应用静态密闭箱-气相色谱法对高寒灌丛(GG)、丛内草甸(GC)和裸地(GL)的CO2释放进行了初步研究。结果表明:GG、GC和GLCO2的释放速率均呈明显的单峰型日变化进程,最大释放速率出现在15∶00～17∶00之间,最小值在7∶00前后出现,白天释放速率大于夜晚;CO2释放速率具有明显的季节性变化特征,生长期CO2释放速率明显高于枯黄期,且均表现为正排放,8月为CO2释放高峰期,释放速率GGGCGL(P0.01);2003年6月30日至2004年2月28日,高寒灌丛植被-土壤系统CO2释放量为3088.458±287.02g/m2,丛内草甸植被-土壤系统CO2释放量为2239.685±183.68g/m2,其中基础土壤呼吸CO2的释放量约为1346.748±176.24g/m2,分别占GG和GC释放量的43.61%和60.13%;CO2释放速率的日变化主要受地表和5cm地温制约,而季节动态与5cm地温呈显著正相关关系(P0.01)。
DOI:10.1016/j.agrformet.2016.06.020URL [本文引用: 1]
Alpine ecosystems play an important role in the global carbon cycle, yet the long-term response ofin situground-based observations of carbon fluxes to climate change remains not fully understood. Here, we analyzed the continuous net ecosystem CO2exchange (NEE) measured with the eddy covariance technique over an alpinePotentilla fruticosashrubland on the northeastern Qinghai-Tibetan Plateau from 2003 to 2012. The shrubland acted as a net CO2sink with a negative NEE (6174.4±12.7gCm612year611, Mean±S.E.). The mean annual gross primary productivity (GPP) and annual ecosystem respiration (RES) were 511.8±11.3 and 437.4±17.8gCm612year611, respectively. The classification and regression trees (CART) analysis showed that aggregated growing season degree days (GDD) was the predominant determinant on variations in monthly NEE and monthly GPP, including its effect on leaf area index (LAI, satellite-retrieved data). However, variations in monthly RES were determined much more strongly by LAI. Non-growing season soil temperature (Ts) and growing season length (GSL) accounted for 59% and 42% of variations in annual GPP and annual NEE, respectively. Growing season soil water content (SWC) exerted a positive linear influence on variations in annual RES (r2=0.40,p=0.03). The thermal conditions and soil water status during the onset of the growing season are crucial for inter-annual variations of carbon fluxes. Our results suggested that an extended growing season and warmer non-growing season would enhance carbon assimilation capacity in the alpine shrubland.
URL [本文引用: 1]
URL [本文引用: 1]
URLMagsci [本文引用: 1]
<FONT face=Verdana>采用涡度相关法,并结合小气候观测,对荒漠生态系统净二氧化碳通量进行了连续3个生长季的观测（2004—2006年）,并据此分析了荒漠生态系统净二氧化碳通量及其主要成分GPP和Reco的季节和年际间变化特征。结果表明,在生长季尺度上,各个阶段二氧化碳吸收量的大小分别为:生长旺盛期>生长初期>生长末期,这可能与植物叶面积的大小以及光合有效辐射,大气温度等环境要素有关系。在年际尺度上,3个生长季同阶段的二氧化碳吸收量存在明显差异,生长季初期5月,2004年碳吸收最强,2006年次之,2005年最小。对于生长旺盛期,降水量最大的2004年碳吸收能力最强,正午最大值可以达到-0.12 mg·m-2·s-1,2005年次之,最大值达-0.06 mg·m-2·s-1,仅仅是2004年最大值的1/2,2006年最小,正午吸收的最大值为-0.02 mg·m-2·s-1,生长季末期,3个生长季的月均日变化非常相似,其在正午的最大吸收值也没有显著差异,正午最大吸收量为-0.01 mg·m-2·s-1左右,其他时段均在0值附近。即使在降水量相近的两个年份里（2005—2006年）,其NEE的最大值出现时间也不一致,2005年NEE的最大月累计量出现在8月和9月,而2006年则出现在6月和7月,这可能与年内降水量分布格局有关。3个生长季荒漠生态系统均表现为净二氧化碳吸收,其吸收量分别为:-236.18 g·m-2,-63.07 g·m-2和-91.97 g·m-2。年际差异的形成原因是降水差异造成的一年生草本植物数量变化,不利用降水的建群种应该对此没有贡献。</FONT>
URLMagsci [本文引用: 1]
<FONT face=Verdana>采用涡度相关法,并结合小气候观测,对荒漠生态系统净二氧化碳通量进行了连续3个生长季的观测（2004—2006年）,并据此分析了荒漠生态系统净二氧化碳通量及其主要成分GPP和Reco的季节和年际间变化特征。结果表明,在生长季尺度上,各个阶段二氧化碳吸收量的大小分别为:生长旺盛期>生长初期>生长末期,这可能与植物叶面积的大小以及光合有效辐射,大气温度等环境要素有关系。在年际尺度上,3个生长季同阶段的二氧化碳吸收量存在明显差异,生长季初期5月,2004年碳吸收最强,2006年次之,2005年最小。对于生长旺盛期,降水量最大的2004年碳吸收能力最强,正午最大值可以达到-0.12 mg·m-2·s-1,2005年次之,最大值达-0.06 mg·m-2·s-1,仅仅是2004年最大值的1/2,2006年最小,正午吸收的最大值为-0.02 mg·m-2·s-1,生长季末期,3个生长季的月均日变化非常相似,其在正午的最大吸收值也没有显著差异,正午最大吸收量为-0.01 mg·m-2·s-1左右,其他时段均在0值附近。即使在降水量相近的两个年份里（2005—2006年）,其NEE的最大值出现时间也不一致,2005年NEE的最大月累计量出现在8月和9月,而2006年则出现在6月和7月,这可能与年内降水量分布格局有关。3个生长季荒漠生态系统均表现为净二氧化碳吸收,其吸收量分别为:-236.18 g·m-2,-63.07 g·m-2和-91.97 g·m-2。年际差异的形成原因是降水差异造成的一年生草本植物数量变化,不利用降水的建群种应该对此没有贡献。</FONT>
DOI:10.1016/j.agrformet.2012.04.015URL [本文引用: 2]
Eddy covariance measurements of water and carbon (C) fluxes were carried out in a desert halophyte community in western China, during two years differing greatly in precipitation (2006 and 2007). The first year was dry, with annual precipitation 22% below the long-term mean (163mm) and the second year was wet (42% above the long-term mean). The main goal of this study was to develop an understanding of how ecological and hydrological processes and vegetation composition respond to precipitation variability in halophyte desert ecosystems. On an annual basis, the desert halophyte community was a weak sink or source in the dry year (615±12gCm612year611), but a strong sink in the wet year (6140±12gCm612year611). Groundwater was a stable water source for evaporation and transpiration, supplying average of 14mm in both the dry and the wet years for each part. However, water supply for plant transpiration from precipitation differed remarkably between the two years: 17 and 48mm for the dry and wet years, respectively. Connecting water use and C gain, ecosystem water use efficiency was markedly different for the dry and wet years, with values of 0.03 and 0.15gC per kg H2O, respectively; however, plant water use efficiency was differed only slightly (3.58 and 3.51gC per kg H2O). Vegetation community surveys and root investigations revealed that more shallow-rooted herbaceous plants occurred in the wet year compared to the dry year. Thus the inter-annual variation of water and C fluxes may have resulted from adjustment of community structure to precipitation with more annuals or ephemeral plants in the wet year. These shallow-rooted plants use the extra water input in the wet year, and consequently the community productivity increases. Water use efficiency at the ecosystem level increased in the wet year at this desert, contrary to findings in more humid environments where water use efficiency increases in dry years.
DOI:10.1111/gcb.13424URLPMID:27400026 [本文引用: 1]
Abstract Wetlands play an important role in regulating the atmospheric carbon dioxide (CO 2 ) concentrations and thus affecting the climate. However, there is still lack of quantitative evaluation of such a role across different wetland types, especially at the global scale. Here, we conducted a meta-analysis to compare ecosystem CO 2 fluxes among various types of wetlands using a global database compiled from the literature. This database consists of 143 site-years of eddy covariance data from 22 inland wetland and 21 coastal wetland sites across the globe. Coastal wetlands had higher annual gross primary productivity (GPP), ecosystem respiration (R e ), and net ecosystem productivity (NEP) than inland wetlands. On a per unit area basis, coastal wetlands provided large CO 2 sinks, while inland wetlands provided small CO 2 sinks or were nearly CO 2 neutral. The annual CO 2 sink strength was 93.15 and 208.370002g0002C0002m -2 for inland and coastal wetlands, respectively. Annual CO 2 fluxes were mainly regulated by mean annual temperature (MAT) and mean annual precipitation (MAP). For coastal and inland wetlands combined, MAT and MAP explained 71%, 54%, and 57% of the variations in GPP, R e , and NEP, respectively. The CO 2 fluxes of wetlands were also related to leaf area index (LAI). The CO 2 fluxes also varied with water table depth (WTD), although the effects of WTD were not statistically significant. NEP was jointly determined by GPP and R e for both inland and coastal wetlands. However, the NEP/R e and NEP/GPP ratios exhibited little variability for inland wetlands and decreased for coastal wetlands with increasing latitude. The contrasting of CO 2 fluxes between inland and coastal wetlands globally can improve our understanding of the roles of wetlands in the global C cycle. Our results also have implications for informing wetland management and climate change policymaking, for example, the efforts being made by international organizations and enterprises to restore coastal wetlands for enhancing blue carbon sinks. 0008 2016 John Wiley & Sons Ltd.
[本文引用: 1]
[本文引用: 1]
DOI:10.1007/s11427-010-4054-9URL [本文引用: 1]
DOI:10.1016/S0168-1923(00)00213-6URL [本文引用: 1]
During the summer period (day 150–240), total evapotranspiration for non-drought years ranged from 224 to 27302mm with a mean and standard error of ja:math . The mean and standard error of the net ecosystem exchange (NEE) rate of carbon dioxide for the same summer period was ja:math . In a year with severe drought (1998) total evapotranspiration for the summertime period was 14502mm. The lack of precipitation during this time resulted in total losses to the atmosphere of 15502g C/m 2 from soil respiration.
DOI:10.1016/j.rse.2004.08.009URL [本文引用: 1]
A vegetation index (VI) model for predicting evapotranspiration (ET) from data from the Moderate Resolution Imaging Spectrometer (MODIS) on the EOS-1 Terra satellite and ground meteorological data was developed for riparian vegetation along the Middle Rio Grande River in New Mexico. Ground ET measurements obtained from eddy covariance towers at four riparian sites were correlated with MODIS VIs, MODIS land surface temperatures (LSTs), and ground micrometeorological data over four years. Sites included two saltcedar ( Tamarix ramosissima ) and two Rio Grande cottonwood ( Populus deltoides ssp. Wislizennii) dominated stands. The Enhanced Vegetation Index (EVI) was more closely correlated ( r =0.76) with ET than the Normalized Difference Vegetation Index (NDVI; r =0.68) for ET data combined over sites and species. Air temperature ( T a ) measured over the canopy from towers was the meteorological variable that was most closely correlated with ET ( r =0.82). MODIS LST data at 1- and 5-km resolutions were too coarse to accurately measure the radiant surface temperature within the narrow riparian corridor; hence, energy balance methods for estimating ET using MODIS LSTs were not successful. On the other hand, a multivariate regression equation for predicting ET from EVI and T a had an r 2 =0.82 across sites, species, and years. The equation was similar to VI T models developed for crop species. The finding that ET predictions did not require species-specific equations is significant, inasmuch as these are mixed vegetation zones that cannot be easily mapped at the species level.
DOI:10.1007/s10021-010-9398-2URL [本文引用: 2]
Variability and future alterations in regional and global climate patterns may exert a strong control on the carbon dioxide (CO 2 ) exchange of grassland ecosystems. We used 6years of eddy-covariance measurements to evaluate the impacts of seasonal and inter-annual variations in environmental conditions on the net ecosystem CO 2 exchange (NEE), gross ecosystem production (GEP), and ecosystem respiration (ER) of an intensively managed grassland in the humid temperate climate of southern Ireland. In all the years of the study period, considerable uptake of atmospheric CO 2 occurred in this grassland with a narrow range in the annual NEE from 61245 to 61284gCm 612 y 611 , with the exception of 2008 in which the NEE reached 61352gCm 612 y 611 . None of the measured environmental variables (air temperature (Ta), soil moisture, photosynthetically active radiation, vapor pressure deficit (VPD), precipitation (PPT), and so on) correlated with NEE on a seasonal or annual scale because of the equal responses from the component fluxes GEP and ER to variances in these variables. Pronounced reduction of summer PPT in two out of the six studied years correlated with decreases in both GEP and ER, but not with NEE. Thus, the stable annual NEE was primarily achieved through a strong coupling of ER and GEP on seasonal and annual scales. Limited inter-annual variations in Ta (±0.5°C) and generally sufficient soil moisture availability may have further favored a stable annual NEE. Monthly ecosystem carbon use efficiency (CUE; as the ratio of NEE:GEP) during the main growing season (April 1–September 30) was negatively correlated with temperature and VPD, but positively correlated with soil moisture, whereas the annual CUE correlated negatively with annual NEE. Thus, although drier and warmer summers may mildly reduce the uptake potential, the annual uptake of atmospheric CO 2 , in this intensively managed grassland, may be expected to continue even under predicted future climatic changes in the humid temperate climate region.
DOI:10.1016/j.gloplacha.2012.08.009URL [本文引用: 1]
78 We investigated changes in NPP and NEP of Qinghai–Tibetan grasslands from 1961 to 2009. 78 A systematically calibrated process-based ecosystem model called ORCHIDEE was applied. 78 Qinghai–Tibetan grassland NPP significantly increased with a rate of 1.9Tg Cyr612 since 1961. 78 NEP increased from a net carbon source of 610.5Tg Cyr611 in the 1960s to a net carbon sink of 21.8Tg Cyr611 in the 2000s.
DOI:10.1111/j.1365-2486.2009.01966.xURL [本文引用: 1]
For most ecosystems, net ecosystem exchange of CO2 (NEE) varies within and among years in response to environmental change. We analyzed measurements of CO2 exchange from eight native rangeland ecosystems in the western United States (58 site-years of data) in order to determine the contributions of photosynthetic and respiratory (physiological) components of CO2 exchange to environmentally caused variation in NEE. Rangelands included Great Plains grasslands, desert shrubland, desert grasslands, and sagebrush steppe. We predicted that (1) week-to-week change in NEE and among-year variation in the response of NEE to temperature, net radiation, and other environmental drivers would be better explained by change in maximum rates of ecosystem photosynthesis (Amax) than by change in apparent light-use efficiency ( ) or ecosystem respiration at 10 C (R10) and (2) among-year variation in the responses of NEE, Amax, and to environmental drivers would be explained by changes in leaf area index (LAI). As predicted, NEE was better correlated with Amax than or R10 for six of the eight rangelands. Week-to-week variation in NEE and physiological parameters correlated mainly with time-lagged indices of precipitation and water-related environmental variables, like potential evapotranspiration, for desert sites and with net radiation and temperature for Great Plains grasslands. For most rangelands, the response of NEE to a given change in temperature, net radiation, or evaporative demand differed among years because the response of photosynthetic parameters (Amax, ) to environmental drivers differed among years. Differences in photosynthetic responses were not explained by variation in LAI alone. A better understanding of controls on canopy photosynthesis will be required to predict variation in NEE of rangeland ecosystems.
DOI:10.1111/j.1365-2486.2006.01187.xURL [本文引用: 1]
Abstract Respiration (carbon efflux) by terrestrial ecosystems is a major component of the global carbon (C) cycle, but the response of C efflux to atmospheric CO 2 enrichment remains uncertain. Respiration may respond directly to an increase in the availability of C substrates at high CO 2 , but also may be affected indirectly by a CO 2 -mediated alteration in the amount by which respiration changes per unit of change in temperature or C uptake (sensitivity of respiration to temperature or C uptake). We measured CO 2 fluxes continuously during the final 2 years of a 4-year experiment on C 3 /C 4 grassland that was exposed to a 200 560 molmol 1 CO 2 gradient. Flux measurements were used to determine whether CO 2 treatment affected nighttime respiration rates and the response of ecosystem respiration to seasonal changes in net C uptake and air temperature. Increasing CO 2 from subambient to elevated concentrations stimulated grassland respiration at night by increasing the net amount of C fixed during daylight and by increasing either the sensitivity of C efflux to daily changes in C fixation or the respiration rate in the absence of C uptake (basal ecosystem respiration rate). These latter two changes contributed to a 30鈥47% increase in the ratio of nighttime respiration to daytime net C influx as CO 2 increased from subamient to elevated concentrations. Daily changes in net C uptake were highly correlated with variation in temperature, meaning that the shared contribution of C uptake and temperature in explaining variance in respiration rates was large. Statistically controlling for collinearity between temperature and C uptake reduced the effect of a given change in C influx on respiration. Conversely, CO 2 treatment did not affect the response of grassland respiration to seasonal variation in temperature. Elevating CO 2 concentration increased grassland respiration rates by increasing both net C input and respiration per unit of C input. A better understanding of how C efflux varies with substrate supply thus may be required to accurately assess the C balance of terrestrial ecosystems.
DOI:10.1016/S0065-2504(08)60063-XURL [本文引用: 1]
DOI:10.1111/gcb.12910URLPMID:25711935 [本文引用: 1]
Abstract Terrestrial plant and soil respiration, or ecosystem respiration (Reco), represents a major CO2 flux in the global carbon cycle. However, there is disagreement in how Reco will respond to future global changes, such as elevated atmosphere CO2 and warming. To address this, we synthesized six years (2007–2012) of Reco data from the Prairie Heating And CO2 Enrichment (PHACE) experiment. We applied a semi-mechanistic temperature–response model to simultaneously evaluate the response of Reco to three treatment factors (elevated CO2, warming, and soil water manipulation) and their interactions with antecedent soil conditions [e.g., past soil water content (SWC) and temperature (SoilT)] and aboveground factors (e.g., vapor pressure deficit, photosynthetically active radiation, vegetation greenness). The model fits the observed Reco well ( R 202=020.77). We applied the model to estimate annual (March–October) Reco, which was stimulated under elevated CO2 in most years, likely due to the indirect effect of elevated CO2 on SWC. When aggregated from 2007 to 2012, total six-year Reco was stimulated by elevated CO2 singly (24%) or in combination with warming (28%). Warming had little effect on annual Reco under ambient CO2, but stimulated it under elevated CO2 (32% across all years) when precipitation was high (e.g., 44% in 2009, a ‘wet’ year). Treatment-level differences in Reco can be partly attributed to the effects of antecedent SoilT and vegetation greenness on the apparent temperature sensitivity of Reco and to the effects of antecedent and current SWC and vegetation activity (greenness modulated by VPD) on Reco base rates. Thus, this study indicates that the incorporation of both antecedent environmental conditions and aboveground vegetation activity are critical to predicting Reco at multiple timescales (subdaily to annual) and under a future climate of elevated CO2 and warming.
DOI:10.1111/j.1365-2486.2008.01713.xURL [本文引用: 3]
Abstract Alpine ecosystems are extremely vulnerable to climate change. To address the potential variability of the responses of alpine ecosystems to climate change, we examined daily CO 2 exchange in relation to major environmental variables. A dataset was obtained from an alpine meadow on the Qinghai-Tibetan Plateau from eddy covariance measurements taken over 3 years (2002–2004). Path analysis showed that soil temperature at 5cm depth ( T s5 ) had the greatest effect on daily variation in ecosystem CO 2 exchange all year around, whereas photosynthetic photon flux density (PPFD) had a high direct effect on daily variation in CO 2 flux during the growing season. The combined effects of temperature and light regimes on net ecosystem CO 2 exchange (NEE) could be clearly categorized into three areas depending on the change in T s5 : (1) almost no NEE change irrespective of variations in light and temperature when T s5 was below 0°C; (2) an NEE increase (i.e. CO 2 released from the ecosystem) with increasing T s5 , but little response to variation in light regime when 0°C≤ T s5 ≤8°C; and (3) an NEE decrease with increase in T s5 and PPFD when T s5 was approximately >8°C. The highest daily net ecosystem CO 2 uptake was observed under the conditions of daily mean T s5 of about 15°C and daily mean PPFD of about 50molm 612 day 611 . The results suggested that temperature is the most critical determinant of CO 2 exchange in this alpine meadow ecosystem and may play an important role in the ecosystem carbon budget under future global warming conditions.
[本文引用: 2]
DOI:10.1111/j.1365-2745.2006.01187.xURL [本文引用: 1]
Summary 1 The arctic environment is highly heterogeneous in terms of plant distribution and productivity. If we are to make regional scale predictions of carbon exchange it is necessary to find robust relationships that can simplify this variability. One such potential relationship is that of leaf area to photosynthetic CO 2 flux at the canopy scale. 2 In this paper we assess the effectiveness of canopy leaf area in explaining variation in gross primary productivity (GPP): (i) across different vegetation types; (ii) at various stages of leaf development; and (iii) under enhanced nutrient availability. To do this we measure net CO 2 flux light response curves with a 1×1m chamber, and calculate GPP at a photosynthetic photon flux density (PPFD) of 60008molm 612 s 611 . 3 At a subarctic site in Sweden, we report 10-fold variation in GPP among natural vegetation types with leaf area index (LAI) values of 0.05–2.31m 2 m 612 . At a site of similar latitude in Alaska we document substantially elevated rates of GPP in fertilized vegetation. 4 We can explain 80% of the observed variation in GPP in natural vegetation (including vegetation measured before deciduous leaf bud burst) by leaf area alone, when leaf area is predicted from measurements of normalized difference vegetation index (NDVI). 5 In fertilized vegetation the relative increase in leaf area between control and fertilized treatments exceeds the relative increase in GPP. This suggests that higher leaf area causes increased self-shading, or that lower leaf nitrogen per unit leaf area causes a reduction in the rate of photosynthesis. 6 The results of this study indicate that canopy leaf area is an excellent predictor of GPP in diverse low arctic tundra, across a wide range of plant functional types.
[本文引用: 1]
DOI:10.1890/08-2026.1URLPMID:19886480 [本文引用: 2]
A mechanistic understanding of the carbon (C) cycle-climate change feedback is essential for projecting future states of climate and ecosystems. Here we report a novel field mechanism and evidence supporting the hypothesis that nocturnal warming in a temperate steppe ecosystem in northern China can result in a minor C sink instead of a C source as models have predicted. Nocturnal warming increased leaf respiration of two dominant grass species by 36.3%, enhanced consumption of carbohydrates in the leaves (72.2% and 60.5% for sugar and starch, respectively), and consequently stimulated plant photosynthesis by 19.8% in the subsequent days. Our experimental findings confirm previous observations of nocturnal warming stimulating plant photosynthesis through increased draw-down of leaf carbohydrates at night. The enhancement of plant photosynthesis overcompensated the increased C loss via plant respiration under nocturnal warming and shifted the steppe ecosystem from a minor C source (1.87 g C·m6305·yr6301) to a C sink (21.72 g C·m6305·yr6301) across the three growing seasons from 2006 to 2008. Given greater increases in daily minimum than maximum temperature in many regions, plant photosynthetic overcompensation may partially serve as a negative feedback mechanism for terrestrial biosphere to climate warming.
DOI:10.1016/j.scitotenv.2011.09.067URLPMID:22024234 [本文引用: 1]
The CO 2 flux was measured by the eddy covariance method on a temperate Leymus chinensis steppe over a period of 1702months spanning two consecutive growing seasons. The amount of precipitation was nearly normal, but it was low in the early and high in the late growing period in 2006. In the 2007 growing season, the amount of precipitation was about 45% less than the multi-year average and more evenly distributed. Comparisons were made between a moderately grazed site and a 28-year-old fenced site. The maximum instantaneous CO 2 release and uptake rates were 0.12 (May) and 61020.1102mg CO 2 02m 612 02s 611 (July) at the fenced site, and 0.11 and 61020.1602mg CO 2 02m 612 02s 611 (both in July) at the grazed site. In both growing seasons, the grazed site always had a higher daily uptake rate or lower release rate than the fenced site. The grazed site was a CO 2 sink during the growing season of 2007 and a CO 2 source in the growing season of 2006, whereas the fenced site was a CO 2 source in both seasons. Lower precipitation decreased CO 2 loss during the growing season more in the grazed site than in the fenced site, mainly because of depression of total ecosystem respiration ( R e ) in the former and stimulation in the latter. During the dormant season (from October to April), the fenced and grazed sites released 60.0 and 32.402g of C per m 2 , respectively. Path analysis showed that temperature had the greatest effect on daily variation of ecosystem CO 2 exchange during the growing seasons at the two study sites. The results suggest that decrease of precipitation and/or increase of temperature will likely promote C loss from L. chinensis steppes, whether fenced or grazed, and that a grazed site is more sensitive.
DOI:10.3724/SP.J.1258.2011.00337URL [本文引用: 1]
基于多变量统计方法同时研究自然系统内多个因子之间的相互关系,是阐释复杂的自然系统的一个重要手段.相比传统的多变量统计法,结构方程模型基于研究者的先验知识预先设定系统内因子间的依赖关系,不仅能够判别各因子之间的关系强度(路径系数),还能对整体模型进行拟合和判断,从而能更全面地了解自然系统.由于结构方程模型只在近年才被应用到生态学的数据分析中,因此该文试图对其作一简略介绍,包括结构方程模型的定义和变量类型,结合事例研究展现结构方程模型分析的一般步骤、在生态学中的应用以及相关软件的介绍等.望能为相关研究人员提供直观的认识,加强结构方程模型在生态学数据分析中的应用.
DOI:10.3724/SP.J.1258.2011.00337URL [本文引用: 1]
基于多变量统计方法同时研究自然系统内多个因子之间的相互关系,是阐释复杂的自然系统的一个重要手段.相比传统的多变量统计法,结构方程模型基于研究者的先验知识预先设定系统内因子间的依赖关系,不仅能够判别各因子之间的关系强度(路径系数),还能对整体模型进行拟合和判断,从而能更全面地了解自然系统.由于结构方程模型只在近年才被应用到生态学的数据分析中,因此该文试图对其作一简略介绍,包括结构方程模型的定义和变量类型,结合事例研究展现结构方程模型分析的一般步骤、在生态学中的应用以及相关软件的介绍等.望能为相关研究人员提供直观的认识,加强结构方程模型在生态学数据分析中的应用.
DOI:10.1016/j.agrformet.2011.04.002URL [本文引用: 1]
Pasture and afforestation are land-use types of major importance in the tropics, yet, most flux tower studies have been conducted in mature tropical forests. As deforestation in the tropics is expected to continue, it is critical to improve our understanding of alternative land-use types, and the impact of interactions between land use and climate on ecosystem carbon dynamics. Thus, we measured net ecosystem CO 2 fluxes of a pasture and an adjacent tropical afforestation (native tree species plantation) in Sardinilla, Panama from 2007 to 2009. The objectives of our paired site study were: (1) to assess seasonal and inter-annual variations in net ecosystem CO 2 exchange (NEE) of pasture and afforestation, (2) to identify the environmental controls of net ecosystem CO 2 fluxes, and (3) to constrain eddy covariance derived total ecosystem respiration (TER) with chamber-based soil respiration ( R Soil ) measurements. We observed distinct seasonal variations in NEE that were more pronounced in the pasture compared to the afforestation, reflecting changes in plant and microbial activities. The land conversion from pasture to afforestation increased the potential for carbon uptake by trees vs. grasses throughout most of the year. R Soil contributed about 50% to TER, with only small differences between ecosystems or seasons. Radiation and soil moisture were the main environmental controls of CO 2 fluxes while temperature had no effect on NEE. The pasture ecosystem was more strongly affected by soil water limitations during the dry season, probably due to the shallower root system of grasses compared to trees. Thus, it seems likely that predicted increases in precipitation variability will impact seasonal variations of CO 2 fluxes in Central Panama, in particular of pasture ecosystems.
[本文引用: 1]
[本文引用: 1]
DOI:10.1016/j.agrformet.2003.10.004URL [本文引用: 2]
Integrated values of GPP, R eco , and net ecosystem exchange (NEE) were 867, 735, and 6113202g02C02m 612 , respectively, for the 2000–2001 season, and 729, 758, and 2902g02C02m 612 for the 2001–2002 season. Thus, the grassland was a moderate carbon sink during the first season and a weak carbon source during the second season. In contrast to a well-accepted view that annual production of grass is linearly correlated to precipitation, the large difference in GPP between the two seasons were not caused by the annual precipitation. Instead, a shorter growing season, due to late start of the rainy season, was mainly responsible for the lower GPP in the second season. Furthermore, relatively higher R eco during the non-growing season occurred after a late spring rain. Thus, for this Mediterranean grassland, the timing of rain events had more impact than the total amount of precipitation on ecosystem GPP and NEE. This is because its growing season is in the cool and wet season when carbon uptake and respiration are usually limited by low temperature and sometimes frost, not by soil moisture.
DOI:10.1111/gcb.12940URLPMID:25846478 [本文引用: 1]
Abstract Soil respiration is recognized to be influenced by temperature, moisture, and ecosystem production. However, little is known about how plant community structure regulates responses of soil respiration to climate change. Here, we used a 13-year field warming experiment to explore the mechanisms underlying plant community regulation on feedbacks of soil respiration to climate change in a tallgrass prairie in Oklahoma, USA. Infrared heaters were used to elevate temperature about 202°C since November 1999. Annual clipping was used to mimic hay harvest. Our results showed that experimental warming significantly increased soil respiration approximately from 10% in the first 702years (2000–2006) to 30% in the next 602years (2007–2012). The two-stage warming stimulation of soil respiration was closely related to warming-induced increases in ecosystem production over the years. Moreover, we found that across the 1302years, warming-induced increases in soil respiration were positively affected by the proportion of aboveground net primary production (ANPP) contributed by C3 forbs. Functional composition of the plant community regulated warming-induced increases in soil respiration through the quantity and quality of organic matter inputs to soil and the amount of photosynthetic carbon (C) allocated belowground. Clipping, the interaction of clipping with warming, and warming-induced changes in soil temperature and moisture all had little effect on soil respiration over the years (all P > 0.05). Our results suggest that climate warming may drive an increase in soil respiration through altering composition of plant communities in grassland ecosystems.
DOI:10.1016/j.agee.2011.05.032URL [本文引用: 1]
Measurements of net ecosystem carbon dioxide (CO 2) exchange (NEE) were made, using eddy covariance, to investigate the biophysical regulation of a temperate desert steppe characterized drought in Inner Mongolia, China during 2008. The half-hourly maximum and minimum NEE were 613.07 and 0.85 μmol CO 2 m 612 s 611 (negative values denoting net carbon uptake). The maximum daily NEE was 616.0 g CO 2 m 612 day 611. On an annual basis, integrated NEE was 617.2 g C m 612 y 611, indicating a weak carbon sink. The light response curves of NEE showed a rather low apparent quantum yield ( α) and saturation value of NEE (NEE sat). Moreover, α and NEE sat varied with canopy development, soil water content (SWC), air temperature ( T a), and vapor pressure deficit (VPD). Piecewise regression results suggested that the optimal SWC, T a, and VPD for half-hourly daytime NEE were 12.6%, 24.3 °C, and 1.7 kPa, respectively. The apparent temperature sensitivity of ecosystem respiration was 1.6 for the entire growing season, and it was significantly controlled by soil moisture. During the growing season, leaf area index explained about 26% of the variation in daily NEE. Overall, NEE was strongly suppressed by water stress and this was the dominant biophysical regulator in the desert steppe.
[本文引用: 1]
DOI:10.1111/gcb.12079URLPMID:23504837 [本文引用: 1]
Understanding the dynamics and underlying mechanism of carbon exchange between terrestrial ecosystems and the atmosphere is one of the key issues in global change research. In this study, we quantified the carbon fluxes in different terrestrial ecosystems in China, and analyzed their spatial variation and environmental drivers based on the long-term observation data of ChinaFLUX sites and the published data from other flux sites in China. The results indicate that gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem productivity (NEP) of terrestrial ecosystems in China showed a significantly latitudinal pattern, declining linearly with the increase of latitude. However, GEP, ER, and NEP did not present a clear longitudinal pattern. The carbon sink functional areas of terrestrial ecosystems in China were mainly located in the subtropical and temperate forests, coastal wetlands in eastern China, the temperate meadow steppe in the northeast China, and the alpine meadow in eastern edge of Qinghai-Tibetan Plateau. The forest ecosystems had stronger carbon sink than grassland ecosystems. The spatial patterns of GEP and ER in China were mainly determined by mean annual precipitation (MAP) and mean annual temperature (MAT), whereas the spatial variation in NEP was largely explained by MAT. The combined effects of MAT and MAP explained 79%, 62%, and 66% of the spatial variations in GEP, ER, and NEP, respectively. The GEP, ER, and NEP in different ecosystems in China exhibited ositive coupling correlation in their spatial patterns. Both ER and NEP were significantly correlated with GEP, with 68% of the per-unit GEP contributed to ER and 29% to NEP. MAT and MAP affected the spatial patterns of ER and NEP mainly by their direct effects on the spatial pattern of GEP.
DOI:10.1111/j.1365-2486.2009.01870.xURL [本文引用: 1]
Over the last two and half decades, strong evidence showed that the terrestrial ecosystems are acting as a net sink for atmospheric carbon. However the spatial and temporal patterns of variation in the sink are not well known. In this study, we examined latitudinal patterns of interannual variability (IAV) in net ecosystem exchange (NEE) of CO2 based on 163 site-years of eddy covariance data, from 39 northern-hemisphere research sites located at latitudes ranging from 29 N to 64 N. We computed the standard deviation of annual NEE integrals at individual sites to represent absolute interannual variability (AIAV), and the corresponding coefficient of variation as a measure of relative interannual variability (RIAV). Our results showed decreased trends of annual NEE with increasing latitude for both deciduous broadleaf forests and evergreen needleleaf forests. Gross primary production (GPP) explained a significant proportion of the spatial variation of NEE across evergreen needleleaf forests, whereas, across deciduous broadleaf forests, it is ecosystem respiration (Re). In addition, AIAV in GPP and Re increased significantly with latitude in deciduous broadleaf forests, but AIAV in GPP decreased significantly with latitude in evergreen needleleaf forests. Furthermore, RIAV in NEE, GPP, and Re appeared to increase significantly with latitude in deciduous broadleaf forests, but not in evergreen needleleaf forests. Correlation analyses showed air temperature was the primary environmental factor that determined RIAV of NEE in deciduous broadleaf forest across the North American sites, and none of the chosen climatic factors could explain RIAV of NEE in evergreen needleleaf forests. Mean annual NEE significantly increased with latitude in grasslands. Precipitation was dominant environmental factor for the spatial variation of magnitude and IAV in GPP and Re in grasslands.
DOI:10.5814/j.issn.1674-764x.2017.01.007URL [本文引用: 1]
Vegetation phenology is a sensitive indicator of global warming,especially on the Tibetan Plateau.However,whether climate warming has enhanced the advance of grassland phenology since 2000 remains debated and little is known about the warming effect on semiarid grassland phenology and interactions with early growing season precipitation.In this study,we extracted phenological changes from average NDVI in the growing season(GNDVI) to analyze the relationship between changes in NDVI,phenology and climate in the Northern Tibetan Damxung grassland from 2000 to 2014.The GNDVI of the grassland declined.Interannual variation of GNDVI was mainly affected by mean temperature from late May to July and precipitation from April to August.The length of the growing season was significantly shortened due to a delay in the beginning of the growing season and no advancement of the end of the growing season,largely caused by climate warming and enhanced by decreasing precipitation in spring.Water availability was the major determinant of grass growth in the study area.Warming increased demand for water when the growth limitation of temperature to grass was exceeded in the growing season.Decreased precipitation likely further exacerbated the effect of warming on vegetation phenology in recent decades due to increasing evapotranspiration and water limitations.The comprehensive effects of global warming and decreasing precipitation may delay the phenological responses of semiarid alpine grasslands.
DOI:10.3321/j.issn:1000-4025.2006.01.024URL [本文引用: 1]
利用涡度相关技术观测了青藏高原两个典型的生态系统即矮嵩草(K obresia hum ilis)草甸和金露梅(P oten-tilla f ruticosa)灌丛草甸的CO2通量,并就2003年8月份的数据,分析了生态系统通量变化与环境因子的关系.8月份是这两个生态系统的叶面积指数达到最高也是相对稳定的时期,在此期间矮嵩草草甸和金露梅灌丛草甸净碳吸收量分别达56.2和32.6 g C.m-2,日CO2吸收量最大值分别为12.7μm o l.m-2.-s 1和9.3μm o l.m-2.-s 1,排放量最大值分别为5.1μm o l.m-2.-s 1和5.7μm o l.m-2.-s 1.在相同光合有效光量子通量密度(PPFD)条件下,矮嵩草草甸CO2吸收速度大于金露梅灌丛草甸;在PPFD高于1 200μm o l.m-2.s-1的条件下,随气温增加,两生态系统的CO2吸收速度都下降,但矮嵩草草甸的下降速度(-0.086)比金露梅灌丛草甸(-0.016)快.土壤水分影响土壤呼吸,并且影响差异因植被类型不同而不同.生态系统日CO2吸收量随昼夜温差增加而增大;较大的昼夜温差导致较高的净CO2交换量;植物反射率与CO2通量之间存在负相关关系.
DOI:10.3321/j.issn:1000-4025.2006.01.024URL [本文引用: 1]
利用涡度相关技术观测了青藏高原两个典型的生态系统即矮嵩草(K obresia hum ilis)草甸和金露梅(P oten-tilla f ruticosa)灌丛草甸的CO2通量,并就2003年8月份的数据,分析了生态系统通量变化与环境因子的关系.8月份是这两个生态系统的叶面积指数达到最高也是相对稳定的时期,在此期间矮嵩草草甸和金露梅灌丛草甸净碳吸收量分别达56.2和32.6 g C.m-2,日CO2吸收量最大值分别为12.7μm o l.m-2.-s 1和9.3μm o l.m-2.-s 1,排放量最大值分别为5.1μm o l.m-2.-s 1和5.7μm o l.m-2.-s 1.在相同光合有效光量子通量密度(PPFD)条件下,矮嵩草草甸CO2吸收速度大于金露梅灌丛草甸;在PPFD高于1 200μm o l.m-2.s-1的条件下,随气温增加,两生态系统的CO2吸收速度都下降,但矮嵩草草甸的下降速度(-0.086)比金露梅灌丛草甸(-0.016)快.土壤水分影响土壤呼吸,并且影响差异因植被类型不同而不同.生态系统日CO2吸收量随昼夜温差增加而增大;较大的昼夜温差导致较高的净CO2交换量;植物反射率与CO2通量之间存在负相关关系.
DOI:10.1111/j.1744-7909.2005.00066.xURL [本文引用: 1]
Abstract Abstract: In the present study, we used the eddy covariance method to measure CO 2 exchange between the atmosphere and an alpine shrubland meadow ecosystem (37°36’N, 101°18’E; 3 250 m a.s.l.) on the Qinghai-Tibetan Plateau, China, during the growing season in 2003, from 20 April to 30 September. This meadow is dominated by formations of Potentilla fruticosa L. The soil is Mol-Cryic Cambisols. During the study period, the meadow was not grazed. The maximum rates of CO 2 uptake and release derived from the diurnal course of CO 2 flux were -9.38 and 5.02 μmol·m -2 ·s -1 , respectively. The largest daily CO 2 uptake was 1.7 g C·m -2 ·d -1 on 14 July, which is less than half that of an alpine Kobresia meadow ecosystem at similar latitudes. Daily CO 2 uptake during the measurement period indicated that the alpine shrubland meadow ecosystem may behave as a sink of atmospheric CO 2 during the growing season. The daytime CO 2 uptake was correlated exponentially or linearly with the daily photo synthetic photon flux density each month. The daytime average water use efficiency of the ecosystem was 6.47 mg CO 2 /g H 2 O. The efficiency of the ecosystem increased with a decrease in vapor pressure deficit. (Managing editor: Ya-Qin HAN)
DOI:10.1111/j.1365-2486.2007.01333.xURL [本文引用: 1]
Partitioning soil CO 2 efflux into autotrophic ( R A ) and heterotrophic ( R H ) components is crucial for understanding their differential responses to climate change. We conducted a long-term experiment (2000–2005) to investigate effects of warming 2°C and yearly clipping on soil CO 2 efflux and its components (i.e. R A and R H ) in a tallgrass prairie ecosystem. Interannual variability of these fluxes was also examined. Deep collars (70 cm) were inserted into soil to measure R H . R A was quantified as the difference between soil CO 2 efflux and R H . Warming treatment significantly stimulated soil CO 2 efflux and its components (i.e. R A and R H ) in most years. In contrast, yearly clipping significantly reduced soil CO 2 efflux only in the last 2 years, although it decreased R H in every year of the study. Temperature sensitivity (i.e. apparent Q 10 values) of soil CO 2 efflux was slightly lower under warming ( P >0.05) and reduced considerably by clipping ( P <0.05) compared with that in the control. On average over the 4 years, R H accounted for approximately 65% of soil CO 2 efflux with a range from 58% to 73% in the four treatments. Over seasons, the contribution of R H to soil CO 2 efflux reached a maximum in winter (6590%) and a minimum in summer (6535%). Annual soil CO 2 efflux did not vary substantially among years as precipitation did. The interannual variability of soil CO 2 efflux may be mainly caused by precipitation distribution and summer severe drought. Our results suggest that the effects of warming and yearly clipping on soil CO 2 efflux and its components did not result in significant changes in R H or R A contribution, and rainfall timing may be more important in determining interannual variability of soil CO 2 efflux than the amount of annual precipitation.
Increases in terrestrial carbon storage from the Last Glacial Maximum to the present
1
1990
... id="C4">草地是全球分布面积最广的陆地生态系统(
Why is marsh productivity so high? New insights from eddy covariance and biomass measurements in a Typha marsh
1
2009
... id="C49">不同草地生态系统年际NEP差异的原因是比较复杂的, 这主要是因为它受到草地植被类型、生物环境因子以及草地管理策略(施肥、刈割和放牧等)等多方面因素的影响(
基于通径分析原理的冬小麦缺水诊断指标敏感性分析
1
2008
... id="C22">本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响.SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(
基于通径分析原理的冬小麦缺水诊断指标敏感性分析
1
2008
... id="C22">本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响.SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(
基于结构方程模型的广州城市社区居民出行行为
1
2011
... id="C22">本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响.SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(
基于结构方程模型的广州城市社区居民出行行为
1
2011
... id="C22">本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响.SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(
Biophysical regulation of carbon flux in different rainfall regime in a northern Tibetan alpine meadow
2
2017
... id="C5">高海拔草地生态系统因较高的太阳辐射和较低的气温常被预期为“碳汇”, 但草地生态系统的源/汇动态存在较大的变异.高光合有效辐射是促进高海拔植物光合作用的能量基础, 较大的温度日较差有利于光合产物的积累, 较低的温度(特别是夜间和冬季)又可以抑制植物和土壤呼吸, 减少碳损失, 通常被认为有利于生态系统碳固定(
... id="C7">供比较的两个通量站分别位于青藏高原东部的中国科学院海北高寒草甸生态系统定位站(海北站)和腹地的中国科学院当雄高寒草甸研究站(当雄站).海北站(101.3° E, 37.6° N)地处祁连山北支冷龙岭东段南麓坡地的大通河谷西段, 站区地形开阔, 海拔3 200 m左右, 属于高原大陆性气候, 气温极低, 无明显四季之分, 仅有冷暖二季之别, 干湿季分明.年平均气温-1.7 ℃, 最冷月平均气温为-14.8 ℃, 最暖月平均气温为9.8 ℃; 多年平均降水量570 mm, 80%集中在5-9月.植被为高寒灌丛草甸(以下简称灌丛), 植被上层结构为灌木层, 以金露梅(Potentilla fruticosa)为优势种, 该层植被盖度为60%-70%; 下层是草本层, 以小嵩草(Korbresia humilis)等草甸植物为主, 植被盖度为60%-70%.土壤为高山草甸土(草毡土)(
Plant functional traits and soil carbon sequestration in contrasting biomes
1
2008
... id="C4">草地是全球分布面积最广的陆地生态系统(
Seven years of carbon dioxide exchange over a degraded grassland and a cropland with maize ecosystems in a semiarid area of China
1
2013
... id="C22">本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响.SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(
Seasonal and interannual variation in carbon dioxide exchange and carbon balance in a northern temperate grassland
3
2002
... id="C16">生长季节白天CO2通量采用Michaelis-Menten 模型(
... id="C42">尽管草甸比灌丛具有较高的温度和辐射条件, 研究期的年降水总量差异不大, 但土壤水分条件较差, 植被指数NDVI也较低, 这造成高原腹地半干旱气候条件下的草甸草原的NEP及其分量都低于高原东部湿润的灌丛.虽然草甸生长季节5年平均值是碳汇(62.64 g C·m-2·a-1), 但其年际总量平均值基本维持碳平衡状态(-4.55 g C·m-2·a-1), 远低于生长季平均(141.22 g C·m-2·a-1)和年际平均(69.59 g C·m-2·a-1)均是“碳汇”作用的灌丛.因为降水变异较大, 植被稀疏(
... id="C48">NDVI代表植被冠层的发育程度, 是重要的控制CO2通量的生物因子(
Depression of net ecosystem CO2 exchange in semi-arid Leymus chinensis steppe and alpine shrub
1
2006
... id="C44">两站点虽然都地处高海拔青藏地区, 但环境条件有一定差异, 为对比两类生态系统CO2通量及其限制因子提供了良好的平台.在众多的环境因子中, Ta和SWC直接影响着NEP和GPP生长季节的变异, 但对两生态系统的影响效果却不同.东部灌丛草毡土的水分含量达到30%以上, 远高于高原腹地的草原土, 而且生长季开始就处于比较稳定的高值, 受降水量的影响没有草原土那么大, 因此, NEP和GPP主要受温度限制, 而受水分影响较小, 反之, 草甸的NEP和GPP主要受土壤水分限制, 其次受温度限制.这种差异的原因一方面源于海北年降水量在生长季分布相对较均匀, 而温度和光强低于当雄, 这在一定程度上减少了较高温度和高辐射所带来的水分损失, 降低了该地区的干旱程度; 另一方面, 灌丛植被根系要深于草甸植被根系, 降低了植被根系对表层土壤干旱的敏感性, 缓解表层土壤水分的缺失对根系的影响(
西藏土壤分类的原则和依据
1
1980
... id="C7">供比较的两个通量站分别位于青藏高原东部的中国科学院海北高寒草甸生态系统定位站(海北站)和腹地的中国科学院当雄高寒草甸研究站(当雄站).海北站(101.3° E, 37.6° N)地处祁连山北支冷龙岭东段南麓坡地的大通河谷西段, 站区地形开阔, 海拔3 200 m左右, 属于高原大陆性气候, 气温极低, 无明显四季之分, 仅有冷暖二季之别, 干湿季分明.年平均气温-1.7 ℃, 最冷月平均气温为-14.8 ℃, 最暖月平均气温为9.8 ℃; 多年平均降水量570 mm, 80%集中在5-9月.植被为高寒灌丛草甸(以下简称灌丛), 植被上层结构为灌木层, 以金露梅(Potentilla fruticosa)为优势种, 该层植被盖度为60%-70%; 下层是草本层, 以小嵩草(Korbresia humilis)等草甸植物为主, 植被盖度为60%-70%.土壤为高山草甸土(草毡土)(
西藏土壤分类的原则和依据
1
1980
... id="C7">供比较的两个通量站分别位于青藏高原东部的中国科学院海北高寒草甸生态系统定位站(海北站)和腹地的中国科学院当雄高寒草甸研究站(当雄站).海北站(101.3° E, 37.6° N)地处祁连山北支冷龙岭东段南麓坡地的大通河谷西段, 站区地形开阔, 海拔3 200 m左右, 属于高原大陆性气候, 气温极低, 无明显四季之分, 仅有冷暖二季之别, 干湿季分明.年平均气温-1.7 ℃, 最冷月平均气温为-14.8 ℃, 最暖月平均气温为9.8 ℃; 多年平均降水量570 mm, 80%集中在5-9月.植被为高寒灌丛草甸(以下简称灌丛), 植被上层结构为灌木层, 以金露梅(Potentilla fruticosa)为优势种, 该层植被盖度为60%-70%; 下层是草本层, 以小嵩草(Korbresia humilis)等草甸植物为主, 植被盖度为60%-70%.土壤为高山草甸土(草毡土)(
Evaluation of carbon exchange in a boreal coniferous stand over a 10-year period: An integrated analysis based on ecosystem model simulations and eddy covariance measurements
1
2011
... id="C48">NDVI代表植被冠层的发育程度, 是重要的控制CO2通量的生物因子(
Partitioning European grassland net ecosystem CO2 exchange into gross primary productivity and ecosystem respiration using light response function analysis
2
2007
... id="C42">尽管草甸比灌丛具有较高的温度和辐射条件, 研究期的年降水总量差异不大, 但土壤水分条件较差, 植被指数NDVI也较低, 这造成高原腹地半干旱气候条件下的草甸草原的NEP及其分量都低于高原东部湿润的灌丛.虽然草甸生长季节5年平均值是碳汇(62.64 g C·m-2·a-1), 但其年际总量平均值基本维持碳平衡状态(-4.55 g C·m-2·a-1), 远低于生长季平均(141.22 g C·m-2·a-1)和年际平均(69.59 g C·m-2·a-1)均是“碳汇”作用的灌丛.因为降水变异较大, 植被稀疏(
... 的巨大波动.虽然本研究中两生态系统年固碳能力差异较大, 但与欧洲20多个草地生态系统(
Separation of net ecosystem exchange into assimilation and respiration using a light response curve approach: Critical issues and global evaluation
1
2010
... id="C18">NEP = - NEE, 表征了生态系统净CO2固定和净释放量, 为生态系统总初级生产力(GPP)与Re的差值.当NEP > 0时, 生态系统是大气CO2的汇; 当NEP < 0时, 生态系统是大气CO2的源; 当NEP = 0时, 生态系统CO2固定与排放处于平衡状态.涡度相关系统无法直接测定生态系统GPP和Re, 需利用公式外推得到.利用夜间数据建立Re与温度的回归关系并外推到白天的Re.日间NEP与日间Re的差值为GPP, 至此NEE可被拆分为GPP和Re (
Short-term variation of CO2 flux in relation to environmental controls in an alpine meadow on the Qinghai-Tibetan Plateau
1
2003
... id="C5">高海拔草地生态系统因较高的太阳辐射和较低的气温常被预期为“碳汇”, 但草地生态系统的源/汇动态存在较大的变异.高光合有效辐射是促进高海拔植物光合作用的能量基础, 较大的温度日较差有利于光合产物的积累, 较低的温度(特别是夜间和冬季)又可以抑制植物和土壤呼吸, 减少碳损失, 通常被认为有利于生态系统碳固定(
Response of gross primary productivity to water availability at different temporal scales in a typical steppe in Inner Mongolia temperate steppe
1
2015
... id="C6">青藏高原气候温凉, 温度是植物生长的重要限制因子, 温度升高会促进湿润地区植物光合作用和碳固定(
über die zunehmende bedeutung der anorganischen chemie. Vortrag, gehalten auf der 70. Versammlung der gesellschaft deutscher naturforscher und rzte zu düsseldorf
1
1898
... id="C15">式中Fc, nighttime为夜间u* > 0.15 m·s-1 生态系统CO2净交换量(NEE), 即夜间生态系统总呼吸量(Re), 单位为mg CO2·m-2·s-1, Tref是参数温度, 通常为10 ℃, R10表示10 ℃时的标准呼吸系数, 单位为mg CO2·m-2·s-1, Q10是生态系统呼吸的温度敏感系数, b1为系数(
Direct and indirect controls of the interannual variability in atmospheric CO2 exchange of three contrasting ecosystems in Denmark
1
2017
... id="C49">不同草地生态系统年际NEP差异的原因是比较复杂的, 这主要是因为它受到草地植被类型、生物环境因子以及草地管理策略(施肥、刈割和放牧等)等多方面因素的影响(
Biophysical controls on net ecosystem CO2 exchange over a semiarid shrubland in northwest China
2014
Effects of precipitation variability on carbon and water fluxes in the understorey of a nitrogen-limited montado ecosystem
1
2014
... id="C4">草地是全球分布面积最广的陆地生态系统(
Seasonal patterns of gross primary production and ecosystem respiration in an alpine meadow ecosystem on the Qinghai-Tibetan Plateau
2
2004
... id="C5">高海拔草地生态系统因较高的太阳辐射和较低的气温常被预期为“碳汇”, 但草地生态系统的源/汇动态存在较大的变异.高光合有效辐射是促进高海拔植物光合作用的能量基础, 较大的温度日较差有利于光合产物的积累, 较低的温度(特别是夜间和冬季)又可以抑制植物和土壤呼吸, 减少碳损失, 通常被认为有利于生态系统碳固定(
... id="C44">两站点虽然都地处高海拔青藏地区, 但环境条件有一定差异, 为对比两类生态系统CO2通量及其限制因子提供了良好的平台.在众多的环境因子中, Ta和SWC直接影响着NEP和GPP生长季节的变异, 但对两生态系统的影响效果却不同.东部灌丛草毡土的水分含量达到30%以上, 远高于高原腹地的草原土, 而且生长季开始就处于比较稳定的高值, 受降水量的影响没有草原土那么大, 因此, NEP和GPP主要受温度限制, 而受水分影响较小, 反之, 草甸的NEP和GPP主要受土壤水分限制, 其次受温度限制.这种差异的原因一方面源于海北年降水量在生长季分布相对较均匀, 而温度和光强低于当雄, 这在一定程度上减少了较高温度和高辐射所带来的水分损失, 降低了该地区的干旱程度; 另一方面, 灌丛植被根系要深于草甸植被根系, 降低了植被根系对表层土壤干旱的敏感性, 缓解表层土壤水分的缺失对根系的影响(
Strong temperature dependence and no moss photosynthesis in winter CO2 flux for a Kobresia meadow on the Qinghai-Tibetan Plateau
1
2005
... id="C6">青藏高原气候温凉, 温度是植物生长的重要限制因子, 温度升高会促进湿润地区植物光合作用和碳固定(
Carbon dioxide exchange between the atmosphere and an alpine meadow ecosystem on the Qinghai-Tibetan Plateau, China
2004
Rainfall variability, carbon cycling, and plant species diversity in a mesic grassland
1
2002
... id="C4">草地是全球分布面积最广的陆地生态系统(
Separation of net ecosystem exchange into assimilation and respiration using a light response curve approach: Critical issues and global evaluation
1
2010
... id="C46">态系统光合作用所固定的CO2平均80%以上甚至更多都因为呼吸而被排放, 只有10%左右被固定.GPP和Re季节动态的相关性在很多研究中都有发现(
海北高寒灌丛草甸生态系统CO2释放的初步研究
1
2005
... id="C6">青藏高原气候温凉, 温度是植物生长的重要限制因子, 温度升高会促进湿润地区植物光合作用和碳固定(
海北高寒灌丛草甸生态系统CO2释放的初步研究
1
2005
... id="C6">青藏高原气候温凉, 温度是植物生长的重要限制因子, 温度升高会促进湿润地区植物光合作用和碳固定(
Seasonal and inter-annual variations in CO2 fluxes over 10 years in an alpine shrubland on the Qinghai-Tibetan Plateau, China
1
2016
... id="C7">供比较的两个通量站分别位于青藏高原东部的中国科学院海北高寒草甸生态系统定位站(海北站)和腹地的中国科学院当雄高寒草甸研究站(当雄站).海北站(101.3° E, 37.6° N)地处祁连山北支冷龙岭东段南麓坡地的大通河谷西段, 站区地形开阔, 海拔3 200 m左右, 属于高原大陆性气候, 气温极低, 无明显四季之分, 仅有冷暖二季之别, 干湿季分明.年平均气温-1.7 ℃, 最冷月平均气温为-14.8 ℃, 最暖月平均气温为9.8 ℃; 多年平均降水量570 mm, 80%集中在5-9月.植被为高寒灌丛草甸(以下简称灌丛), 植被上层结构为灌木层, 以金露梅(Potentilla fruticosa)为优势种, 该层植被盖度为60%-70%; 下层是草本层, 以小嵩草(Korbresia humilis)等草甸植物为主, 植被盖度为60%-70%.土壤为高山草甸土(草毡土)(
青藏高原金露梅灌丛草甸净生态系统CO2交换量的季节变异及其环境控制机制
1
2006
... id="C7">供比较的两个通量站分别位于青藏高原东部的中国科学院海北高寒草甸生态系统定位站(海北站)和腹地的中国科学院当雄高寒草甸研究站(当雄站).海北站(101.3° E, 37.6° N)地处祁连山北支冷龙岭东段南麓坡地的大通河谷西段, 站区地形开阔, 海拔3 200 m左右, 属于高原大陆性气候, 气温极低, 无明显四季之分, 仅有冷暖二季之别, 干湿季分明.年平均气温-1.7 ℃, 最冷月平均气温为-14.8 ℃, 最暖月平均气温为9.8 ℃; 多年平均降水量570 mm, 80%集中在5-9月.植被为高寒灌丛草甸(以下简称灌丛), 植被上层结构为灌木层, 以金露梅(Potentilla fruticosa)为优势种, 该层植被盖度为60%-70%; 下层是草本层, 以小嵩草(Korbresia humilis)等草甸植物为主, 植被盖度为60%-70%.土壤为高山草甸土(草毡土)(
青藏高原金露梅灌丛草甸净生态系统CO2交换量的季节变异及其环境控制机制
1
2006
... id="C7">供比较的两个通量站分别位于青藏高原东部的中国科学院海北高寒草甸生态系统定位站(海北站)和腹地的中国科学院当雄高寒草甸研究站(当雄站).海北站(101.3° E, 37.6° N)地处祁连山北支冷龙岭东段南麓坡地的大通河谷西段, 站区地形开阔, 海拔3 200 m左右, 属于高原大陆性气候, 气温极低, 无明显四季之分, 仅有冷暖二季之别, 干湿季分明.年平均气温-1.7 ℃, 最冷月平均气温为-14.8 ℃, 最暖月平均气温为9.8 ℃; 多年平均降水量570 mm, 80%集中在5-9月.植被为高寒灌丛草甸(以下简称灌丛), 植被上层结构为灌木层, 以金露梅(Potentilla fruticosa)为优势种, 该层植被盖度为60%-70%; 下层是草本层, 以小嵩草(Korbresia humilis)等草甸植物为主, 植被盖度为60%-70%.土壤为高山草甸土(草毡土)(
盐生荒漠生态系统二氧化碳通量的年内、年际变异特征
1
2011
... id="C22">本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响.SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(
盐生荒漠生态系统二氧化碳通量的年内、年际变异特征
1
2011
... id="C22">本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响.SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(
High efficiency in water use and carbon gain in a wet year for a desert halophyte community
2
2012
... id="C42">尽管草甸比灌丛具有较高的温度和辐射条件, 研究期的年降水总量差异不大, 但土壤水分条件较差, 植被指数NDVI也较低, 这造成高原腹地半干旱气候条件下的草甸草原的NEP及其分量都低于高原东部湿润的灌丛.虽然草甸生长季节5年平均值是碳汇(62.64 g C·m-2·a-1), 但其年际总量平均值基本维持碳平衡状态(-4.55 g C·m-2·a-1), 远低于生长季平均(141.22 g C·m-2·a-1)和年际平均(69.59 g C·m-2·a-1)均是“碳汇”作用的灌丛.因为降水变异较大, 植被稀疏(
... )也是常见的.这种现象的发生是由水分的可利用性 (有效性)和初级生产力的大小所决定的(
Contrasting ecosystem CO2 fluxes of inland and coastal wetlands: A meta-analysis of eddy covariance data
1
2017
... id="C49">不同草地生态系统年际NEP差异的原因是比较复杂的, 这主要是因为它受到草地植被类型、生物环境因子以及草地管理策略(施肥、刈割和放牧等)等多方面因素的影响(
《西藏土壤分类》草案
1
1982
... id="C7">供比较的两个通量站分别位于青藏高原东部的中国科学院海北高寒草甸生态系统定位站(海北站)和腹地的中国科学院当雄高寒草甸研究站(当雄站).海北站(101.3° E, 37.6° N)地处祁连山北支冷龙岭东段南麓坡地的大通河谷西段, 站区地形开阔, 海拔3 200 m左右, 属于高原大陆性气候, 气温极低, 无明显四季之分, 仅有冷暖二季之别, 干湿季分明.年平均气温-1.7 ℃, 最冷月平均气温为-14.8 ℃, 最暖月平均气温为9.8 ℃; 多年平均降水量570 mm, 80%集中在5-9月.植被为高寒灌丛草甸(以下简称灌丛), 植被上层结构为灌木层, 以金露梅(Potentilla fruticosa)为优势种, 该层植被盖度为60%-70%; 下层是草本层, 以小嵩草(Korbresia humilis)等草甸植物为主, 植被盖度为60%-70%.土壤为高山草甸土(草毡土)(
《西藏土壤分类》草案
1
1982
... id="C7">供比较的两个通量站分别位于青藏高原东部的中国科学院海北高寒草甸生态系统定位站(海北站)和腹地的中国科学院当雄高寒草甸研究站(当雄站).海北站(101.3° E, 37.6° N)地处祁连山北支冷龙岭东段南麓坡地的大通河谷西段, 站区地形开阔, 海拔3 200 m左右, 属于高原大陆性气候, 气温极低, 无明显四季之分, 仅有冷暖二季之别, 干湿季分明.年平均气温-1.7 ℃, 最冷月平均气温为-14.8 ℃, 最暖月平均气温为9.8 ℃; 多年平均降水量570 mm, 80%集中在5-9月.植被为高寒灌丛草甸(以下简称灌丛), 植被上层结构为灌木层, 以金露梅(Potentilla fruticosa)为优势种, 该层植被盖度为60%-70%; 下层是草本层, 以小嵩草(Korbresia humilis)等草甸植物为主, 植被盖度为60%-70%.土壤为高山草甸土(草毡土)(
Changes in individual plant traits and biomass allocation in alpine meadow with elevation variation on the Qinghai-Tibetan Plateau
1
2010
... id="C42">尽管草甸比灌丛具有较高的温度和辐射条件, 研究期的年降水总量差异不大, 但土壤水分条件较差, 植被指数NDVI也较低, 这造成高原腹地半干旱气候条件下的草甸草原的NEP及其分量都低于高原东部湿润的灌丛.虽然草甸生长季节5年平均值是碳汇(62.64 g C·m-2·a-1), 但其年际总量平均值基本维持碳平衡状态(-4.55 g C·m-2·a-1), 远低于生长季平均(141.22 g C·m-2·a-1)和年际平均(69.59 g C·m-2·a-1)均是“碳汇”作用的灌丛.因为降水变异较大, 植被稀疏(
A comparison of summertime water and CO2 fluxes over rangeland for well-watered and drought conditions
1
2001
... id="C42">尽管草甸比灌丛具有较高的温度和辐射条件, 研究期的年降水总量差异不大, 但土壤水分条件较差, 植被指数NDVI也较低, 这造成高原腹地半干旱气候条件下的草甸草原的NEP及其分量都低于高原东部湿润的灌丛.虽然草甸生长季节5年平均值是碳汇(62.64 g C·m-2·a-1), 但其年际总量平均值基本维持碳平衡状态(-4.55 g C·m-2·a-1), 远低于生长季平均(141.22 g C·m-2·a-1)和年际平均(69.59 g C·m-2·a-1)均是“碳汇”作用的灌丛.因为降水变异较大, 植被稀疏(
Predicting riparian evapotranspiration from MODIS vegetation indices and meteorological data
1
2005
... id="C25">NDVI在一定程度上可以表示植被冠层的变化趋势(
Six-year stable annual uptake of carbon dioxide in intensively managed humid temperate grassland
2
2010
... id="C22">本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响.SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(
... id="C49">不同草地生态系统年际NEP差异的原因是比较复杂的, 这主要是因为它受到草地植被类型、生物环境因子以及草地管理策略(施肥、刈割和放牧等)等多方面因素的影响(
Impacts of climate and CO2 changes on the vegetation growth and carbon balance of Qinghai- Xizang grasslands over the past five decades
1
2012
... id="C4">草地是全球分布面积最广的陆地生态系统(
Physiological and environmental regulation of interannual variability in CO2 exchange on rangelands in the western United States
1
2010
... id="C48">NDVI代表植被冠层的发育程度, 是重要的控制CO2通量的生物因子(
Increasing CO2 from subambient to elevated concentrations increases grassland respiration per unit of net carbon fixation
1
2006
... id="C44">两站点虽然都地处高海拔青藏地区, 但环境条件有一定差异, 为对比两类生态系统CO2通量及其限制因子提供了良好的平台.在众多的环境因子中, Ta和SWC直接影响着NEP和GPP生长季节的变异, 但对两生态系统的影响效果却不同.东部灌丛草毡土的水分含量达到30%以上, 远高于高原腹地的草原土, 而且生长季开始就处于比较稳定的高值, 受降水量的影响没有草原土那么大, 因此, NEP和GPP主要受温度限制, 而受水分影响较小, 反之, 草甸的NEP和GPP主要受土壤水分限制, 其次受温度限制.这种差异的原因一方面源于海北年降水量在生长季分布相对较均匀, 而温度和光强低于当雄, 这在一定程度上减少了较高温度和高辐射所带来的水分损失, 降低了该地区的干旱程度; 另一方面, 灌丛植被根系要深于草甸植被根系, 降低了植被根系对表层土壤干旱的敏感性, 缓解表层土壤水分的缺失对根系的影响(
CO2 fluxes over plant canopies and solar radiation: A review
1
1995
... id="C17">式中, Fc, daytime为日间u* > 0.15 m·s-1 NEE值, 单位为mg CO2·m-2·s-1, α为表观量子效率, 单位为mg CO2·μmol photons-1, Pmax为最大光合强度, 单位为mg CO2·m-2·s-1, PAR为光合有效辐射, 单位为μmol·m-2·s-1, Re为白天生态系统呼吸量, 单位为mg CO2·m-2·s-1 (
Antecedent moisture and temperature conditions modulate the response of ecosystem respiration to elevated CO2 and warming
1
2015
... id="C4">草地是全球分布面积最广的陆地生态系统(
Temperature controls ecosystem CO2 exchange of an alpine meadow on the northeastern Tibetan Plateau
3
2009
... id="C5">高海拔草地生态系统因较高的太阳辐射和较低的气温常被预期为“碳汇”, 但草地生态系统的源/汇动态存在较大的变异.高光合有效辐射是促进高海拔植物光合作用的能量基础, 较大的温度日较差有利于光合产物的积累, 较低的温度(特别是夜间和冬季)又可以抑制植物和土壤呼吸, 减少碳损失, 通常被认为有利于生态系统碳固定(
... id="C42">尽管草甸比灌丛具有较高的温度和辐射条件, 研究期的年降水总量差异不大, 但土壤水分条件较差, 植被指数NDVI也较低, 这造成高原腹地半干旱气候条件下的草甸草原的NEP及其分量都低于高原东部湿润的灌丛.虽然草甸生长季节5年平均值是碳汇(62.64 g C·m-2·a-1), 但其年际总量平均值基本维持碳平衡状态(-4.55 g C·m-2·a-1), 远低于生长季平均(141.22 g C·m-2·a-1)和年际平均(69.59 g C·m-2·a-1)均是“碳汇”作用的灌丛.因为降水变异较大, 植被稀疏(
... id="C44">两站点虽然都地处高海拔青藏地区, 但环境条件有一定差异, 为对比两类生态系统CO2通量及其限制因子提供了良好的平台.在众多的环境因子中, Ta和SWC直接影响着NEP和GPP生长季节的变异, 但对两生态系统的影响效果却不同.东部灌丛草毡土的水分含量达到30%以上, 远高于高原腹地的草原土, 而且生长季开始就处于比较稳定的高值, 受降水量的影响没有草原土那么大, 因此, NEP和GPP主要受温度限制, 而受水分影响较小, 反之, 草甸的NEP和GPP主要受土壤水分限制, 其次受温度限制.这种差异的原因一方面源于海北年降水量在生长季分布相对较均匀, 而温度和光强低于当雄, 这在一定程度上减少了较高温度和高辐射所带来的水分损失, 降低了该地区的干旱程度; 另一方面, 灌丛植被根系要深于草甸植被根系, 降低了植被根系对表层土壤干旱的敏感性, 缓解表层土壤水分的缺失对根系的影响(
Net ecosystem CO2 exchange and controlling factors in a steppe— Kobresia meadow on the Tibetan Plateau
2
2006
... id="C11">由于各种天气、电力及仪器故障等原因, 涡度相关观测系统采集到的原始数据会出现丢失或异常的现象, 因此对原始数据进行预处理是必不可少的, 这是控制数据质量、保证数据可靠性的重要前提.预处理包括野点去除(±3σ)、坐标旋转(三维风旋转)、Webb-Pearman-Leuning校正等.数据处理过程中去掉雨时和夜晚(PAR < 1 μmol·m-2·s-1)摩擦风速u*< 0.15 m·s-1时的数据.缺失数据通过CO2通量值(Fc)与环境因子之间的非线性经验公式进行插补(
... id="C17">式中, Fc, daytime为日间u* > 0.15 m·s-1 NEE值, 单位为mg CO2·m-2·s-1, α为表观量子效率, 单位为mg CO2·μmol photons-1, Pmax为最大光合强度, 单位为mg CO2·m-2·s-1, PAR为光合有效辐射, 单位为μmol·m-2·s-1, Re为白天生态系统呼吸量, 单位为mg CO2·m-2·s-1 (
What is the relationship between changes in canopy leaf area and changes in photosynthetic CO2 flux in arctic ecosystems?
1
2007
... id="C4">草地是全球分布面积最广的陆地生态系统(
Interannual variability in NEE of a native tallgrass prairie
1
2003
... id="C4">草地是全球分布面积最广的陆地生态系统(
Photosynthetic overcompensation under nocturnal warming enhances grassland carbon sequestration
2
2009
... id="C4">草地是全球分布面积最广的陆地生态系统(
... id="C44">两站点虽然都地处高海拔青藏地区, 但环境条件有一定差异, 为对比两类生态系统CO2通量及其限制因子提供了良好的平台.在众多的环境因子中, Ta和SWC直接影响着NEP和GPP生长季节的变异, 但对两生态系统的影响效果却不同.东部灌丛草毡土的水分含量达到30%以上, 远高于高原腹地的草原土, 而且生长季开始就处于比较稳定的高值, 受降水量的影响没有草原土那么大, 因此, NEP和GPP主要受温度限制, 而受水分影响较小, 反之, 草甸的NEP和GPP主要受土壤水分限制, 其次受温度限制.这种差异的原因一方面源于海北年降水量在生长季分布相对较均匀, 而温度和光强低于当雄, 这在一定程度上减少了较高温度和高辐射所带来的水分损失, 降低了该地区的干旱程度; 另一方面, 灌丛植被根系要深于草甸植被根系, 降低了植被根系对表层土壤干旱的敏感性, 缓解表层土壤水分的缺失对根系的影响(
The fluxes of CO2 from grazed and fenced temperate steppe during two drought years on the Inner Mongolia Plateau, China
1
2011
... id="C44">两站点虽然都地处高海拔青藏地区, 但环境条件有一定差异, 为对比两类生态系统CO2通量及其限制因子提供了良好的平台.在众多的环境因子中, Ta和SWC直接影响着NEP和GPP生长季节的变异, 但对两生态系统的影响效果却不同.东部灌丛草毡土的水分含量达到30%以上, 远高于高原腹地的草原土, 而且生长季开始就处于比较稳定的高值, 受降水量的影响没有草原土那么大, 因此, NEP和GPP主要受温度限制, 而受水分影响较小, 反之, 草甸的NEP和GPP主要受土壤水分限制, 其次受温度限制.这种差异的原因一方面源于海北年降水量在生长季分布相对较均匀, 而温度和光强低于当雄, 这在一定程度上减少了较高温度和高辐射所带来的水分损失, 降低了该地区的干旱程度; 另一方面, 灌丛植被根系要深于草甸植被根系, 降低了植被根系对表层土壤干旱的敏感性, 缓解表层土壤水分的缺失对根系的影响(
结构方程模型及其在生态学中的应用
1
2011
... id="C22">本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响.SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(
结构方程模型及其在生态学中的应用
1
2011
... id="C22">本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响.SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(
Strong seasonal variations in net ecosystem CO2 exchange of a tropical pasture and afforestation in Panama
1
2011
... id="C44">两站点虽然都地处高海拔青藏地区, 但环境条件有一定差异, 为对比两类生态系统CO2通量及其限制因子提供了良好的平台.在众多的环境因子中, Ta和SWC直接影响着NEP和GPP生长季节的变异, 但对两生态系统的影响效果却不同.东部灌丛草毡土的水分含量达到30%以上, 远高于高原腹地的草原土, 而且生长季开始就处于比较稳定的高值, 受降水量的影响没有草原土那么大, 因此, NEP和GPP主要受温度限制, 而受水分影响较小, 反之, 草甸的NEP和GPP主要受土壤水分限制, 其次受温度限制.这种差异的原因一方面源于海北年降水量在生长季分布相对较均匀, 而温度和光强低于当雄, 这在一定程度上减少了较高温度和高辐射所带来的水分损失, 降低了该地区的干旱程度; 另一方面, 灌丛植被根系要深于草甸植被根系, 降低了植被根系对表层土壤干旱的敏感性, 缓解表层土壤水分的缺失对根系的影响(
相关性通径分析问题剖析
1
1996
... id="C22">本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响.SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(
相关性通径分析问题剖析
1
1996
... id="C22">本研究中使用结构方程模型(SEM), 通过路径图和路径系数来确定环境和生物因子对CO2通量直接和间接的影响.SEM是研究变量间相互关系、自变量对因变量作用方式和相对贡献率的多元统计分析技术, 它可以帮助我们找出自变量对因变量的直接影响因子和间接影响因子, 并剔除没有关系的自变量, 建立“最优”的路径图(
Seasonal variation in carbon dioxide exchange over a Mediterranean annual grassland in California
2
2004
... id="C4">草地是全球分布面积最广的陆地生态系统(
... id="C16">生长季节白天CO2通量采用Michaelis-Menten 模型(
Plant community structure regulates responses of prairie soil respiration to decadal experimental warming
1
2015
... id="C4">草地是全球分布面积最广的陆地生态系统(
Biophysical regulation of net ecosystem carbon dioxide exchange over a temperate desert steppe in Inner Mongolia, China
1
2011
... id="C48">NDVI代表植被冠层的发育程度, 是重要的控制CO2通量的生物因子(
The role of shrub ( Potentilla fruticosa) on ecosystem CO2 fluxes in an alpine shrub meadow
1
2010
... id="C49">不同草地生态系统年际NEP差异的原因是比较复杂的, 这主要是因为它受到草地植被类型、生物环境因子以及草地管理策略(施肥、刈割和放牧等)等多方面因素的影响(
Spatial patterns and climate drivers of carbon fluxes in terrestrial ecosystems of China
1
2013
... id="C46">态系统光合作用所固定的CO2平均80%以上甚至更多都因为呼吸而被排放, 只有10%左右被固定.GPP和Re季节动态的相关性在很多研究中都有发现(
Latitudinal patterns of magnitude and interannual variability in net ecosystem exchange regulated by biological and environmental variables
1
2009
... id="C4">草地是全球分布面积最广的陆地生态系统(
Declining precipitation enhances the effect of warming on phenological variation in a semiarid Tibetan meadow steppe
1
2017
... id="C44">两站点虽然都地处高海拔青藏地区, 但环境条件有一定差异, 为对比两类生态系统CO2通量及其限制因子提供了良好的平台.在众多的环境因子中, Ta和SWC直接影响着NEP和GPP生长季节的变异, 但对两生态系统的影响效果却不同.东部灌丛草毡土的水分含量达到30%以上, 远高于高原腹地的草原土, 而且生长季开始就处于比较稳定的高值, 受降水量的影响没有草原土那么大, 因此, NEP和GPP主要受温度限制, 而受水分影响较小, 反之, 草甸的NEP和GPP主要受土壤水分限制, 其次受温度限制.这种差异的原因一方面源于海北年降水量在生长季分布相对较均匀, 而温度和光强低于当雄, 这在一定程度上减少了较高温度和高辐射所带来的水分损失, 降低了该地区的干旱程度; 另一方面, 灌丛植被根系要深于草甸植被根系, 降低了植被根系对表层土壤干旱的敏感性, 缓解表层土壤水分的缺失对根系的影响(
青藏高原矮嵩草草甸和金露梅灌丛草甸CO2通量变化与环境因子的关系
1
2006
... id="C42">尽管草甸比灌丛具有较高的温度和辐射条件, 研究期的年降水总量差异不大, 但土壤水分条件较差, 植被指数NDVI也较低, 这造成高原腹地半干旱气候条件下的草甸草原的NEP及其分量都低于高原东部湿润的灌丛.虽然草甸生长季节5年平均值是碳汇(62.64 g C·m-2·a-1), 但其年际总量平均值基本维持碳平衡状态(-4.55 g C·m-2·a-1), 远低于生长季平均(141.22 g C·m-2·a-1)和年际平均(69.59 g C·m-2·a-1)均是“碳汇”作用的灌丛.因为降水变异较大, 植被稀疏(
青藏高原矮嵩草草甸和金露梅灌丛草甸CO2通量变化与环境因子的关系
1
2006
... id="C42">尽管草甸比灌丛具有较高的温度和辐射条件, 研究期的年降水总量差异不大, 但土壤水分条件较差, 植被指数NDVI也较低, 这造成高原腹地半干旱气候条件下的草甸草原的NEP及其分量都低于高原东部湿润的灌丛.虽然草甸生长季节5年平均值是碳汇(62.64 g C·m-2·a-1), 但其年际总量平均值基本维持碳平衡状态(-4.55 g C·m-2·a-1), 远低于生长季平均(141.22 g C·m-2·a-1)和年际平均(69.59 g C·m-2·a-1)均是“碳汇”作用的灌丛.因为降水变异较大, 植被稀疏(
Carbon dioxide exchange between the atmosphere and an alpine shrubland meadow during the growing season on the Qinghai-Tibetan Plateau
1
2005
... id="C5">高海拔草地生态系统因较高的太阳辐射和较低的气温常被预期为“碳汇”, 但草地生态系统的源/汇动态存在较大的变异.高光合有效辐射是促进高海拔植物光合作用的能量基础, 较大的温度日较差有利于光合产物的积累, 较低的温度(特别是夜间和冬季)又可以抑制植物和土壤呼吸, 减少碳损失, 通常被认为有利于生态系统碳固定(
Source components and interannual variability of soil CO2 efflux under experimental warming and clipping in a grassland ecosystem
1
2007
... id="C44">两站点虽然都地处高海拔青藏地区, 但环境条件有一定差异, 为对比两类生态系统CO2通量及其限制因子提供了良好的平台.在众多的环境因子中, Ta和SWC直接影响着NEP和GPP生长季节的变异, 但对两生态系统的影响效果却不同.东部灌丛草毡土的水分含量达到30%以上, 远高于高原腹地的草原土, 而且生长季开始就处于比较稳定的高值, 受降水量的影响没有草原土那么大, 因此, NEP和GPP主要受温度限制, 而受水分影响较小, 反之, 草甸的NEP和GPP主要受土壤水分限制, 其次受温度限制.这种差异的原因一方面源于海北年降水量在生长季分布相对较均匀, 而温度和光强低于当雄, 这在一定程度上减少了较高温度和高辐射所带来的水分损失, 降低了该地区的干旱程度; 另一方面, 灌丛植被根系要深于草甸植被根系, 降低了植被根系对表层土壤干旱的敏感性, 缓解表层土壤水分的缺失对根系的影响(
