,*, 孙建新北京林业大学林学院, 北京 100083Temporal changes of vegetation water use efficiency and its influencing factors in Northern China
FENG Chao-Yang, WANG He-Song,*, SUN Jian-xinCollege of Forestry, Beijing Forestry University, Beijing 100083, China通讯作者: (wanghs119@126.com)
编委: 陈世苹
责任编辑: 王葳
| 基金资助: |
Online:2018-04-20
| Fund supported: |
摘要
水分利用效率(WUE)既是衡量植被生长适应性的重要指标, 也是连接生态系统水碳循环的纽带。认识不同类型植被WUE的时间变化特征及驱动机制有助于增进对生态系统水碳循环过程的理解。已有研究表明, 在不同时间尺度下, WUE呈现不同的时间变化特征, 但现有研究多是集中在单一的时间尺度下开展的, 对不同植被类型在不同时间尺度下的动态变化及影响因子分析开展得较少。该研究选用中国北方地区9个定位观测台站的通量与气象数据, 分析了WUE的日内变化和季节变化特征, 并在0.5 h、1 d、8 d以及月尺度下, 分别分析了气温(Ta)、相对湿度(RH)、饱和水汽压差(VPD)以及光合有效辐射(PAR)等非生物因子对WUE的影响。同时, 该研究也分析了植被叶面积指数(LAI)和降水(P)对WUE的影响。研究发现: (1) WUE的日变化呈现不对称的“U”型特征, 日出时的WUE普遍高于日落时。荒漠地区WUE的季节变化呈“U”型, 而其他站点呈现单峰型。不同站点WUE的季节变化可以分为总初级生产力(GPP)主导型和蒸发散(ET)主导型, 并随着时间尺度的扩大, GPP或ET的主导作用逐渐增强。(2)在较短的时间尺度(0.5 h、1 d)上, Ta、RH、VPD和PAR是影响WUE变化的主要因子, 但随着时间尺度的扩大, Ta和RH成为影响WUE变化的主要因子, 并且与WUE的相关关系受GPP或ET对WUE主导作用的影响, 随着时间尺度增大, Ta和RH与WUE的线性关系更加显著。(3) WUE大体上随LAI的增加而增加, 但当LAI超过一定值时, 在长白山、海北和张掖站, WUE对LAI的敏感性降低。降水与WUE的关系在研究区域内并不显著。(4)不同植被类型的WUE由大到小依次为森林、农田、草地、湿地和荒漠。
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本文引用格式
冯朝阳, 王鹤松, 孙建新. 中国北方植被水分利用效率的时间变化特征及其影响因子. 植物生态学报[J], 2018, 42(4): 453-465 DOI:10.17521/cjpe.2017.0214
FENG Chao-Yang, WANG He-Song, SUN Jian-xin.
植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(Bohn & Kershner, 2002), 它也在一定程度上反映了植物的耗水性和干旱适应性(Munns, 2005)。植物的光合作用和蒸腾作用是生态系统能量流动和物质循环的两个基本生理生态学过程, WUE是二者联系的重要纽带(于贵瑞等, 2006)。高的WUE既是植物应对水分亏缺的一种调控机制(孙学凯等, 2008), 也是植物适应干旱环境的一种重要生理指标(Jaleel et al., 2008)。研究WUE的时间变化特征及其与外界驱动因子之间的关系不仅有助于增进对生态系统水碳循环过程与驱动机制的理解(Wang et al., 2016), 而且对模拟和评估生态系统对未来气候变化的响应具有重要意义(Guo et al., 2010)。中国北方大部分地区属干旱半干旱气候, 随着经济发展、粮食需求增加以及城市化的加剧, 该地区水分供需间的矛盾日益突出, 使水资源问题成为制约区域发展的主要因素(李新周等, 2004; 黄荣辉等, 2013)。为使区域发展更好地应对气候变化的挑战, 政府部门在制定水资源管理政策时需要相应的科学依据。
目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法。腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(Farquhar & Sharkey, 1982)。这种方法操作简单、方便快捷, 但由于其测得的叶片尺度瞬时值与长期植株总体值的关系尚不确定, 不能很好地进行尺度扩展与分析(王庆伟等, 2010)。同位素法利用稳定同位素(如δ13C)分析植被在一定时间内总体WUE, 不适用于短时间尺度下的动态研究与相关性分析(陈世苹等, 2002)。涡度相关法可在高时间分辨率下观测生态系统冠层尺度的CO2和H2O交换量, 进而可实现WUE的连续观测, 这为研究WUE的时间动态过程及其在不同时间尺度下对环境变化的响应提供了一个有效的观测手段(Law et al., 2002)。目前基于涡动相关法, 已经开展了大量关于WUE的研究工作, 如Hu等(2008)在中国北方和青藏高原对比分析了4个草地生态系统的WUE; Yu等(2008)对中国东部3个不同气候带森林生态系统的WUE进行了比较和影响因子分析; 此外也有在更大区域范围内对不同生态类型WUE的时间动态和影响因子进行对比分析的工作(Beer et al., 2009; Zhang et al., 2014; 李辉东等, 2015; Wang et al., 2016; Liu et al., 2017)。但上述研究大多是集中在单一时间尺度下开展的分析。已有研究发现, 在不同时间尺度下WUE呈现不同的时间变化特征(Song et al., 2017), 控制生态系统WUE的主导因子也会随着时间尺度的变化而变化。比如多数研究发现饱和水汽压差(VPD)与WUE呈负相关关系, 但这种关系多局限于短时间尺度的研究(Ponton et al., 2006; 胡中民等, 2009), 也有研究发现随着时间尺度的扩大, VPD与WUE并无明显关系(Liu et al., 2017; Song et al., 2017)。那么, 在不同时间尺度下的不同植被类型中, 影响WUE的主要因子是保持同步性变化, 还是因植被类型的不同而表现出差异性?
综上所述, 本研究选择了代表中国北方地区不同植被类型的9个通量台站数据, 分析了WUE在不同时间尺度下的时间变化特征, 并结合气象与遥感资料分别研究了温度(Ta)、相对湿度(RH)、水汽压亏缺(VPD), 光合有效辐射(PAR)和降水量(P)等非生物因素以及生物因素叶面积指数(LAI)在不同时间尺度上对WUE的影响。研究主要开展了以下几方面工作: 1)分析WUE的日内变化动态与季节变化动态; 2)分析不同时间尺度下, 影响WUE的生物与非生物因子; 3)比较不同植被类型WUE的大小。
1 材料和方法
1.1 研究站点
本研究选取的数据来自中国通量观测研究联盟(ChinaFLUX,图1
新窗口打开|下载原图ZIP|生成PPT图1各通量站点的空间分布图。
Fig. 1Geographical location of the flux sites.
Table 1
表1
表1各站点基础地理与植被信息
Table 1
| 站点 Site | 纬度 Latitude (° N) | 经度 Longitude (°E ) | 数据时期 Data period | 年降水量 Mean annual precipitation (mm) | 年平均气温 Mean annual Temperature (℃) | 海拔 Altitude (m) | 仪器高度 Height of Instrument (m) | 植被类型 Vegetation type |
|---|---|---|---|---|---|---|---|---|
| 长白山 Changbaishan | 42.40 | 128.09 | 2003-2005 | 695 | 3.6 | 738 | 40.0 | 针阔混交林 Evergreen broad-leaved forest |
| 密云 Miyun | 40.63 | 117.32 | 2008-2009 | 615 | 10.9 | 350 | 26.6 | 玉米、果树 Maize, fruit tree |
| 内蒙古 Nei Mongol | 43.54 | 116.67 | 2004-2005 | 350 | -0.4 | 1 252 | 4.0 | 温带草原 Temperate steppe |
| 大兴 Daxing | 39.62 | 116.43 | 2009-2010 | 590 | 11.6 | 20 | 3.0 | 玉米/小麦 Maize/wheat |
| 海北 Haibei | 37.67 | 101.33 | 2003-2005 | 560 | -1.6 | 3 358 | 2.2 | 灌丛 Shrubland |
| 大满 Daman | 38.86 | 100.37 | 2013-2014 | 122 | 7.3 | 1 556 | 4.5 | 玉米 Maize |
| 花寨子 Huazhaizi | 38.77 | 100.32 | 2013-2014 | 130 | 7.3 | 1 731 | 2.9 | 荒漠 Desert |
| 张掖 Zhangye | 38.98 | 100.30 | 2013-2014 | 130 | 6.0 | 1 460 | 5.2 | 湿地 Wetland |
| 巴吉滩 Bajitan | 38.92 | 100.30 | 2013-2014 | 130 | 7.3 | 1 562 | 4.6 | 荒漠 Desert |
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1.2 数据处理与分析方法
通量数据通过涡动相关系统和自动气象站进行同步观测与采集, 其中涡动相关观测的采集频率为10 Hz, 气象数据为每10 min一次。各站点对涡动原始数据的处理主要包括: 野点剔除、延迟时间校正、坐标旋转、频率响应修正、超声虚温修正以及密度(WPL订正)修正。同时, 我们对各通量值进行了质量评价, 包括大气平稳性和湍流相似性特征的检验。并对输出的30 min通量数据进行了筛选: (1)剔除仪器故障时的观测数据; (2)剔除降水前后1 h的观测数据; (3)剔除原始10 Hz数据中, 每30 min内缺失率大于3%的数据; (4)剔除夜间弱湍流观测数据; (5)对缺失时间较短的数据进行非线性拟合, 对缺失时间较长的数据则直接舍弃。观测数据经上述处理后, 通量数据与气象数据统一输出为30 min时间间隔, 详细的数据处理步骤见Xu等(2013)和Liu等(2016)。叶面积指数(LAI)的空间分辨率为500 m, 时间分辨率为8 d, 来源于MODIS陆地产品的第6版数据集(MOD15A2H,本文中WUE (g C·kg-1 H2O)的计算采用以下公式(Liu et al., 2017):
WUE = GPP/ET (1)
式中蒸发散(ET)是由涡度观测中的潜热通量LE
(W·m-2)换算得到的(Tang et al., 2015):
ET = LE/λ (2)
其中λ为蒸发潜热, 单位是J·kg-1, 表示为:
λ = (2500 - 2.4Ta) × 103 (3)
式中Ta是空气温度, 单位是℃。而式中的总初级生产力(GPP)是由公式
GPP = NEP + Re = -NEE + Re (4)
得到的(Yu et al., 2008), Re表示白天生态系统的呼吸, NEE表示白天生态系统CO2净交换量, 可以经观测直接得到。根据夜间生态系统呼吸与土壤温度的关系可以推算得到生态系统白天的呼吸值(Reichstein et al., 2007)。
从国家气象科学数据共享服务平台(
降水对生态系统WUE的影响有一定的延迟性, 同时LAI也不会在短时间内剧烈变化, 故单独进行降水量(P)和LAI与WUE关系的分析。在各因子对WUE的影响的分析中, 我们采用了Pearson系数来分析各因子与WUE的相关性, 公式(Zhang et al., 2015)为:
R表示皮尔逊相关系数; x表示自变量, 这里指代影响WUE的各因子; y表示因变量, 这里指代WUE。数据的作图在Origin 8.0中完成。
基于SPSS 19.0软件, 分别在0.5 h、1 d、8 d和1月的时间尺度对Ta、RH、VPD、PAR与WUE进行了逐步回归分析(杜家菊和陈志伟, 2010)。
2 结果
2.1 各个站点WUE的日内变化与季节变化特征
WUE的日内变化大致呈现不对称的“U”型曲线(图2), 表现为先下降后缓慢回升的趋势, 2个峰值分别出现在早晨和傍晚, 最高值大多出现在早晨。同时, 通过对比发现每个站点WUE的最低值及其出现的时间都有所不同, 各个站点WUE的最低值、最低值及出现的时间分别为: 巴吉滩0.74 g C·kg-1 H2O, 12:00; 大满1.95 g C·kg-1 H2O, 15:30; 大兴2.05 g C·kg-1 H2O, 14:30; 花寨子0.64 g C·kg-1 H2O, 10:30; 密云1.56 g C·kg-1 H2O, 13:00; 张掖0.89 g C·kg-1 H2O, 15:00。其中花寨子与巴吉滩较为干旱的站点WUE达到最小值的时间较早。图2
新窗口打开|下载原图ZIP|生成PPT图2本研究台站水分利用效率(WUE)的日变化, 虚线标注了WUE达到最小值的时间。
Fig. 2Diurnal changes of water use efficiency (WUE) for the study sites. The dash line indicates the time of WUE reached the minimum.
各个站点WUE的季节变化特征为: 在巴吉滩与花寨子荒漠站WUE总体呈现“U”型变化趋势, 在生长季开始和结束的时候较高, 而在生长季中期, WUE值较低。在其他站点, WUE呈现单峰型的变化趋势在生长季早期和末期较低, 而在生长季中期较高(图3)。在大兴站, WUE在一年内呈现2个峰, 这是由于大兴站为农田站, 一年两熟种植制度(种植小麦(Triticum aestivum)和玉米(Zea mays)), 所以WUE会在小麦收割后, 玉米成长前急速下降。内蒙古站由于2005年遭逢大旱(Hu et al., 2008), 故相比于2004年, 无论GPP最大值还是年GPP总量, 都有显著的降低, 因此造成2005年WUE的显著降低。
图3
新窗口打开|下载原图ZIP|生成PPT图3本研究台站水分利用效率(WUE)的季节变化。海北和长白山是3年的数据, 其他站点是2年的数据。
Fig. 3Seasonal changes of water use efficiency (WUE) for the study sites. Data of three years from Haibei and Changbaishan, and two years form others.
2.2 WUE对环境因子的响应
为了探究在不同时间尺度下WUE的驱动因子, 我们将各因子与WUE进行单因素相关性分析并将通过显著性检验的因子显示出来(图4)。在0.5 h尺度上, 影响WUE的主要气象因子为Ta、RH、VPD和PAR, 通过对比发现在0.5 h尺度上RH的相关性最高, 在水分条件较好的站(大满、大兴、密云和张掖)呈现正相关关系, 而在花寨子和巴吉滩两个荒漠站中则呈负相关关系, VPD和PAR在0.5 h尺度上与WUE主要呈负相关关系。在日尺度上, 影响WUE的气象因子主要为Ta、RH、VPD和PAR, 其中VPD和PAR主要与WUE呈现负相关关系, Ta、RH与WUE主要呈正相关关系。在8 d以及月尺度上, 影响WUE的主要气象因子为Ta和RH。总体看来, 随着时间尺度的扩大, 与Ta、RH相关性显著的站点会减少, 但线性关系更加显著。VPD和PAR则是在对WUE的影响降低的同时, 相关站点数也减少。图4
新窗口打开|下载原图ZIP|生成PPT图4本研究台站不同因子与水分利用效率(WUE)的相关性(p < 0.05)。GPP (g C·m-2), 总初级生产力; ET (kg H2O·m-2), 蒸发散; PAR (W·m-2), 光合有效辐射; RH (%), 相对湿度; Ta (℃), 温度; VPD (kPa), 大气水汽压亏缺。
Fig. 4Pearson’s correlations of different factors with water use efficiency (WUE). GPP (g C·m-2), gross primary production; ET (kg H2O·m-2), evapotranspiration; PAR (W·m-2), photosynthetically active radiation; RH (%), relative humidity; Ta (°C), temperature; VPD (kPa), vapor pressure deficit.
逐步回归分析的结果与单因素分析结果大体一致(表2)。总体表现为随着时间尺度的增大, 各站点回归方程的决定系数(R2)增大。同时, 显著影响WUE的因子减少, 从0.5 h尺度的Ta、RH、VPD和PAR逐步减少为月尺度的Ta和RH。逐步回归分析与单因素相关性分析的结果比较再次说明, Ta、RH、VPD和PAR在0.5 h尺度上与1 d尺度上都是影响WUE的主要气象因子, 而对于8 d以及逐月相对较长的时间尺度而言, 主要影响因子是Ta和RH, 即在短期时间尺度上, 影响WUE的主要气象因子为Ta、RH、VPD和PAR, 而在长期时间尺度上, 影响WUE的主要气象因子为Ta、RH, 并且它们与WUE的相关性也逐渐增加。随着时间尺度的扩大, 在巴吉滩与花寨子荒漠站, WUE与ET的相关性逐渐增加, 而GPP与WUE的相关性逐渐减小, 在其他站, 随着时间尺度的扩大, WUE与GPP的相关性逐渐增强, 而ET与WUE的相关性由负相关变为正相关或者不相关。
Table 2
表2
表2不同时间尺度下逐步回归方程中各气象因子标准回归系数及总体决定系数(R2) (p < 0.05)
Table 2
| 台站名 Site | 0.5 h | R2 | 1 d | R2 | 8 d | R2 | 逐月 Monthly | R2 | |
|---|---|---|---|---|---|---|---|---|---|
| 长白山 Changbaishan | Ta (0.97), RH (-0.54), VPD (-0.91), PAR (-0.17) | 0.49 | Ta (0.83), VPD (-0.27) | 0.68 | Ta (0.82) | 0.67 | |||
| 内蒙古 Nei Mongol | Ta (0.29), RH (0.14), PAR (-0.19) | 0.14 | RH (0.45) | 0.20 | (无显著因子) (No significant factor) | ||||
| 海北 Haibei | Ta (0.90), VPD (-0.42), PAR (-0.27) | 0.71 | Ta (1.05), VPD (-0.36), PAR (-0.12) | 0.93 | Ta (0.89), PAR (-0.33) | 0.94 | |||
| 大兴 Daxing | Ta (0.51), VPD (-0.57), PAR (-0.34) | 0.36 | Ta (0.80), RH (-0.27), VPD (-0.80), PAR (-0.37) | 0.46 | RH (0.61) | 0.40 | PAR (-0.85) | 0.73 | |
| 密云 Miyun | Ta (0.18), RH (0.26), VPD (-0.13), PAR (-0.18) | 0.20 | Ta (0.71), VPD (-0.57), PAR (-0.33) | 0.49 | RH (0.51), Ta (0.57) | 0.69 | RH (0.80) | 0.65 | |
| 张掖 Zhangye | Ta (0.30), RH (0.50), PAR (-0.39) | 0.45 | Ta (0.32), RH (0.70), PAR (-0.14) | 0.61 | Ta (0.36), RH (0.58), PAR (-0.44) | 0.69 | (无显著因子) (No significant factor) | ||
| 大满 Daman | Ta (0.68), RH (0.37), VPD (-0.52), PAR (-0.21) | 0.57 | Ta (0.54), RH (0.53), PAR (-0.31) | 0.63 | Ta (0.94), VPD (-0.46) | 0.70 | Ta (0.84) | 0.71 | |
| 巴吉滩 Bajitan | Ta (-0.36), RH (-0.48), PAR (-0.24) | 0.20 | Ta (-0.33), RH (-0.58), PAR (-0.12) | 0.30 | RH (-0.77), VPD (-0.46) | 0.70 | RH (-0.87) | 0.70 | |
| 花寨子 Huazhaizi | RH (-0.27), PAR (-0.27) | 0.12 | RH (-0.65), PAR (-0.50) | 0.31 | RH (-0.66) | 0.40 | (无显著因子) (No significant factor) | ||
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2.3 LAI和降水对WUE的影响
由于巴吉滩与花寨子站植被稀疏, LAI信息弱, MODIS数据没有很好地捕捉到LAI, 故没有使用这2个站点的LAI数据。从图5可看出, 总体来看, WUE随着LAI的增加而增加, 尤其是在LAI较小时, WUE随LAI增加而增加得较快, 随着LAI的进一步增大, 表现出2种不同的趋势: 张掖、长白山和海北3站, WUE与LAI并非呈现线性关系, 当LAI增大到某一值时, 随LAI的增大, WUE的增加速率变小; 而在其他站点, WUE与LAI呈线性变化趋势, 在海北站LAI与WUE的相关性最高, R2达到了0.82。从图6年生长季平均LAI与年平均WUE的关系图来看, 在研究区域内, WUE随着LAI的增加而增大, R2达到了0.52, 说明在我国北方, LAI是决定WUE大小的一个重要因子。图5
新窗口打开|下载原图ZIP|生成PPT图5不同站点叶面积指数(LAI)与水分利用效率(WUE)的关系(p < 0.05)。
Fig. 5Relationships between leaf area index (LAI) and water use efficiency (WUE) for different sites (p < 0.05).
图6
新窗口打开|下载原图ZIP|生成PPT图6年生长季平均叶面积指数(LAI)与年平均水分利用效率(WUE)的关系(p < 0.05)。
Fig. 6Relationship between annual average leaf area index (LAI) and water use efficiency (WUE) in growing season (p < 0.05).
由于大兴与密云站缺少降水量数据, 因此只分析其余7个站点的降水与WUE关系。在8 d尺度上, 除海北站WUE随降水量有明显的相关关系外, 在其他站点降水量与WUE并没有明显的相关性(图7), 由图8可以看出, 在年尺度上, 在降水量较大的地区, WUE年际波动较小, 如长白山、海北站; 而在降水量较小的地区, 如巴吉滩、花寨子、张掖站, 其WUE年际波动较大。通过内蒙古站干旱年的数据可以看出, 当年降水量较低时, WUE也会下降很多, 即遭遇大旱时, 会严重影响该生态系统的WUE。
图7
新窗口打开|下载原图ZIP|生成PPT图7不同站点8 d平均降水量(P)与8 d平均水分利用效率(WUE)的关系。
Fig. 7Relationships between precipitation (P) and water use efficiency (WUE) at 8-days scale.
图8
新窗口打开|下载原图ZIP|生成PPT图8年降水量(AP)与年平均水分利用效率(WUE)的关系。
Fig. 8Relationship between annual precipitation (AP) and water use efficiency (WUE) in growing season.
2.4 台站间WUE的比较
WUE由大到小依次为: 长白山>大兴>大满>密云>内蒙古>海北>张掖>巴吉滩>花寨子, 按照植被类型依次为: 森林>农田>草地>湿地>荒漠(图9)。Lu和Zhuang (2010)在对美国通量网的28个通量站研究中发现在生态系统水平, 生长季平均WUE为森林>灌丛>农田>草地, 而在Beer等(2009)选择的美国通量网的43个通量站研究中同样发现就生态系统平均WUE而言, 森林>农田>草地>湿地。戈壁与荒漠地区由于植被较少, 生产力较弱, GPP因此较低, 同时在这些地区土壤裸露, 植被蒸腾较低, 使得土壤蒸发在ET中占主导作用, 从而导致这些地区的WUE较低(Zhang et al., 2014)。值得注意的是, 生态系统WUE是由生态系统的GPP与ET共同决定的, 高的GPP并不代表其生态系统的WUE也较高, 比如张掖湿地的GPP是高于草原站的, 但是由于其平均每天ET值较大, 从而导致其WUE低于草原站WUE。图9
新窗口打开|下载原图ZIP|生成PPT图9各站点平均每天总初级生产力(GPP)、蒸发散(ET)和水分利用效率(WUE)的值。横坐标根据WUE的由小到大的顺序排列的。
Fig. 9The average daily gross primary production (GPP), evapotranspiration (ET) and water use efficiency (WUE) for the study sites. The sites were arranged in the order of increasing WUE.
3 讨论
3.1 GPP和ET与WUE的关系(8 d尺度)
由图10可以看出在生长季内, 除巴吉滩与花寨子荒漠站外, 其余站点的WUE与GPP的季节性变化具有高度的一致性, 且根据图10, 在8 d尺度上, 这些站点的GPP可以解释WUE季节变化的60%以上。根据图11同样可以发现在这些站点WUE与ET呈现正相关或不相关关系。这种变化可能是因为GPP对WUE的影响远大于ET所产生的影响所致, 即WUE与GPP之间变化的同步性表明光合作用可能是主导WUE季节差异的主要原因(Hu et al., 2008)。在张良侠等(2014)与胡中民等(2009)的研究中同样发现, 在干旱地区的生态系统内, WUE的变化与GPP具有同步性, 即在生长季内, WUE在生长季初期与末期较低, 而在生长旺盛期较高。同时, Tang等(2015)对美国3个农田站的研究也发现WUE与GPP的变化具有同步性。图10
新窗口打开|下载原图ZIP|生成PPT图10不同站点水分利用效率(WUE)与总初级生产力(GPP)的相关关系(p < 0.05)。
Fig. 10Relationships between water use efficiency (WUE) and gross primary production (GPP) for the study sites (p < 0.05).
根据图11可以看出在巴吉滩与花寨子荒漠站WUE与ET呈反比关系, R2超过0.7。同时, 这两个站点WUE与GPP相关性很低, 由此可以看出在荒漠中ET是主导WUE生长季变化的主要原因。这可能是由于荒漠地区植被稀疏, LAI较小, 土壤蒸发在整个生态系统蒸发散中占较高比例。在Hu等(2008)以及赵丽雯等(2015)的研究中都发现, 当LAI较小时, 土壤蒸发会在生态系统ET中占较高的比例。随着夏季的到来, 在LAI较小的地区可能由于温度的升高、降水的增多而导致ET明显升高, 但GPP在此时增加有限, 从而使得ET成为该地区WUE变化的主导因子。
图11
新窗口打开|下载原图ZIP|生成PPT图11不同站点水分利用效率(WUE)与蒸发散(ET)的相关关系(p < 0.05)。
Fig. 11Relationships between water use efficiency (WUE) and evapotranspiration (ET) for the study sites (p < 0.05).
3.2 不同时间尺度下影响WUE的因子
WUE的影响因子随地区和尺度的不同而变化(Tan et al., 2015)。在0.5 h、1 d的时间尺度上, PAR和VPD与WUE的相关关系显著, 呈现负相关关系, 尤其是在0.5 h时间尺度上, 它们与WUE的相关关系更加显著, 这表明在短时间尺度上, 环境因子是影响WUE变化的主要因素。在叶片水平上, 较高的VPD会降低气孔导度, 而气孔导度的降低, 相比于对碳吸收速率的限制, 对蒸腾速率的影响更大, 从而会增加叶片的WUE, 但在生态系统尺度, 尽管气孔关闭, ET也是增加的, 故WUE与VPD呈负相关关系(Farquhar & Sharkey, 1982; Ponton et al., 2006)。虽然植物的固碳能力以及植物对水分的消耗都随着PAR的增大而增加, 但是GPP与ET对PAR的响应程度及其响应方式存在差异, 即当GPP在强光条件下逐渐达到饱和状态时, ET仍随着PAR的增大而增加, 因此WUE会随着PAR的增大而减小。而在8 d、逐月尺度上, PAR和VPD对WUE变化的影响并不显著。很多研究也发现在1 d、0.5 h或者更小的时间尺度上, WUE与VPD有很强的相关性(Zhou et al., 2015)。Song (2017)在对亚热带常绿林5年WUE的研究中发现仅在较短的时间尺度上, VPD显著影响WUE。Hu等(2008)认为在较短的时间内, VPD可以显著影响WUE变化的主要原因是在较短的时间内LAI变化较小, 蒸腾(T)与ET的比值相对稳定, 在这种情况下环境因子就会起主导作用, 故VPD在较短的时间内可以显著影响WUE的变化。有研究发现WUE随温度的升高而降低(Law et al., 2002; Ponton et al., 2006), 这是因为在较高的温度下, ET增加的速率大于GPP增加的速率(Yu et al., 2008), 但在本研究中, 在逐日以及更长的时间尺度上, 除巴吉滩与花寨子外, 其他站点, WUE与Ta为正相关, 与他人的研究结果相同。通过对亚洲区域水分利用效率的研究, Zhang等(2014)发现在25°-40° N范围内WUE随温度的增加而增加, 认为可能的原因是温度对光合作用的影响大于ET的影响。随着时间尺度的扩大, WUE与Ta的相关性逐渐增强, 同时在这些站点出现ET与WUE不相关或者正相关的情况, 也说明随着温度的升高, GPP的上升速率大于ET。另外, 由于我国雨热同季的季风气候, 在温度升高的时候, LAI也增大, 也促进了GPP更快增长。
随时间尺度的扩大, Ta、RH、VPD和PAR与WUE的相关关系是负相关还是正相关, 这可能是由该站点的WUE是由GPP主导还是由ET主导所决定的。比如在1 d以及1 d以上的时间尺度上, Ta和RH与WUE呈现负相关关系的站点是ET主导型的巴吉滩和花寨子站, 而在GPP主导型的其余站点中, 并没有出现Ta和RH与WUE呈现负相关的现象, 这间接说明了在不同地区GPP、ET对相同气象因子的响应是不同步的, 而对WUE显著影响的因子在不同的时间尺度下是不同的, 也说明了时间尺度对于WUE研究的重要性, 在不同的时间尺度下开展的研究可能得出不同的结论。
3.3 LAI和降水与WUE的关系
LAI不仅能有效地增强植物的光能利用率, 也能有效地抑制土壤蒸发, 是研究WUE变化的一个重要影响因子(Tong et al., 2009)。由图5可见WUE总体上随LAI的增加而增加, 当LAI较小时, WUE随其增加而增加, 当LAI大于某一值时, 长白山、张掖、海北站WUE随LAI的增加而缓慢增加。这可能是因为当LAI较小时, 随着LAI的增大, 冠层能够拦截光能的有效面积迅速增大, 同时也减少了下垫面土壤的蒸发(Hu et al., 2008), 因此WUE能迅速增加。而当LAI达到某一值时, 即使LAI继续增加, 能够有效拦截光能的表面积也变化不明显, 故而后期WUE增加缓慢(Muraoka et al., 2010)。而对于农田和果园这样的人为干预较大的生态系统(如大兴、大满和密云站), WUE随LAI的增加而持续增加, 这可能是由于人为的灌溉活动维持了GPP的增长强度, 使得WUE与LAI保持了同步的增长。至于内蒙古站, 由于LAI较小, 并未达到饱和, 故LAI与WUE保持了线性增加的关系。年降水量是驱动年际间生态系统WUE和NEP差异的主要因子(Dong et al., 2011), 但在本研究中, 降水并未能很好地解释WUE的变化, 说明降水并不是主导研究区域内WUE变化的主要因素。在Jia等(2016)对半干旱地区灌木的研究中发现, 年际间降水量的差异并不能解释年际间GPP、ET和WUE变化的差异, 因为在较高的降水年份, 灌木林表现出了较低的GPP与WUE, 这可能是因为小的降水事件并不能有效地补充植物可利用的水分, 反而可能引起浅层土壤微生物的呼吸。还有研究发现, 即使年降水总量是一定的, 但降水的频次和每次降水量的不同也可能会对植物生长产生不同的影响(Thomey et al., 2011)。同时WUE与降水量(P)关系的弱相关也可能是因为: 生态水文过程主要取决于物候期可利用水的多少, 而P与植物需求量并不一定同步(Dong et al., 2011); ET中的水分并不完全来自P, 也可能来自径流或地下水的补给; 降水具有延迟效应, 即上一年的降水可能会对今年的生态系统产生影响(Sala et al., 2012), 可见降水对WUE影响的复杂性, 这也告诉我们应该从多角度来看待降水对陆地生态系统的影响。
4 结论
在中国北方地区, WUE的日变化大致呈“U”型变化趋势, 即早晨与傍晚的值相对较大, 中午前后较小。整个生长季的WUE可以分为GPP主导型和ET主导型, 并且随着时间尺度的扩大, 其主导作用会逐渐增强。在GPP主导型地区, WUE季节变化趋势与GPP大致相同, 呈现单峰变化趋势。而在ET主导型地区, WUE的变化趋势大致呈现“U”型。VPD和PAR仅在短时间尺度内对WUE的影响效果显著, 而Ta和RH无论时间尺度长短都是影响WUE的重要气象因子。随着时间尺度的增大, Ta和RH与WUE的线性关系会更加显著。LAI不仅是影响WUE季节变化的重要因子, 而且在一定程度上决定了不同生态系统间WUE的差异。由于降水对生态系统影响的过程较为复杂, 本文并未发现降水与WUE关系的显著性。通过比较不同植被类型发现, WUE由大到小依次为: 森林、农田、草地、湿地和荒漠。需要注意的是, 受台站数量限制, 本研究仅就WUE的时间变化与影响因子开展了初步的分析与讨论, 今后应进一步增加研究选取的台站数量, 来深入分析GPP主导型和ET主导型的WUE的变化差异及其影响因素。
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DOIURL [本文引用: 1]
Half-hourly measurements of the net exchanges of carbon dioxide and water vapor between terrestrial ecosystems and the atmosphere provide estimates of gross primary production (GPP) and evapotranspiration (ET) at the ecosystem level and on daily to annual timescales. The ratio of these quantities represents ecosystem water use efficiency. Its multiplication with mean daylight vapor pressure def...
DOIURLPMID [本文引用: 1]
Since the passage of the Clean Water Act in 1972, the United States has made great strides to reduce the threats to its rivers, lakes, and wetlands from pollution. However, despite our obvious successes, nearly half of the nation surface water resources remain incapable of supporting basic aquatic values or maintaining water quality adequate for recreational swimming. The Clean Water Act established a significant federal presence in water quality regulation by controlling point and non-point sources of pollution. Point-sources of pollution were the major emphasis of the Act, but Section 208 specifically addressed non-point sources of pollution and designated silviculture and livestock grazing as sources of non-point pollution. Non-point source pollutants include runoff from agriculture, municipalities, timber harvesting, mining, and livestock grazing. Non-point source pollution now accounts for more than half of the United States water quality impairments. To successfully improve water quality, restoration practitioners must start with an understanding of what ecosystem processes are operating in the watershed and how they have been affected by outside variables. A watershed-based analysis template developed in the Pacific Northwest can be a valuable aid in developing that level of understanding. The watershed analysis technique identifies four ecosystem scales useful to identify stream restoration priorities: region, basin, watershed, and site. The watershed analysis technique is based on a set of technically rigorous and defensible procedures designed to provide information on what processes are active at the watershed scale, how those processes are distributed in time and space. They help describe what the current upland and riparian conditions of the watershed are and how these conditions in turn influence aquatic habitat and other beneficial uses. The analysis is organized as a set of six steps that direct an interdisciplinary team of specialists to examine the biotic and abiotic processes influencing aquatic habitat and species abundance. This process helps develop an understanding of the watershed within the context of the larger ecosystem. The understanding gained can then be used to identify and prioritize aquatic restoration activities at the appropriate temporal and spatial scale. The watershed approach prevents relying solely on site-level information, a common problem with historic restoration efforts. When the watershed analysis process was used in the Whitefish Mountains of northwest Montana, natural resource professionals were able to determine the dominant habitat forming processes important for native fishes and use that information to prioritize, plan, and implement the appropriate restoration activities at the watershed scale. Despite considerable investments of time and resources needed to complete an analysis at the watershed scale, the results can prevent the misdiagnosis of aquatic problems and help ensure that the objectives of aquatic restoration will be met.
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植物光合作用是自然界产生碳同位素分馏的最重要过程 ,也是碳同位素技术在生态学研究中应用的基础。最初 ,碳同位素主要应用于光合途径的鉴别。随着技术的不断完善和研究的不断深入 ,目前此项技术在生态学研究的许多领域都得到了广泛的应用。作者从植物叶片、功能群、群落冠层、生态系统以及全球等几个不同的尺度上 ,对碳同位素技术在生态学研究中的主要应用进行了简要的总结
DOIURL [本文引用: 1]
植物光合作用是自然界产生碳同位素分馏的最重要过程 ,也是碳同位素技术在生态学研究中应用的基础。最初 ,碳同位素主要应用于光合途径的鉴别。随着技术的不断完善和研究的不断深入 ,目前此项技术在生态学研究的许多领域都得到了广泛的应用。作者从植物叶片、功能群、群落冠层、生态系统以及全球等几个不同的尺度上 ,对碳同位素技术在生态学研究中的主要应用进行了简要的总结
DOIURL [本文引用: 1]
由于通径分析可以将因变量与自变量的相互影响（相关系数）分解为直接影响（通径系数）和间接影响（间接通径系数），因此在遗传学等领域受到广泛的重视。目前在软件实现方法上，一方面缺乏必要的正态性检验，另一方面通径系数及间接相关系数计算步骤过于繁琐，限制通径分析的教学和使用。在应用中，我们注意到通过SPSS的线性回归“Linear”程序可以一次性获得计算通径系数的全部数据，从而简化通径分析的步骤。
DOIURL [本文引用: 1]
由于通径分析可以将因变量与自变量的相互影响（相关系数）分解为直接影响（通径系数）和间接影响（间接通径系数），因此在遗传学等领域受到广泛的重视。目前在软件实现方法上，一方面缺乏必要的正态性检验，另一方面通径系数及间接相关系数计算步骤过于繁琐，限制通径分析的教学和使用。在应用中，我们注意到通过SPSS的线性回归“Linear”程序可以一次性获得计算通径系数的全部数据，从而简化通径分析的步骤。
DOIURL [本文引用: 2]
Global climate change projections suggest an increasing frequency of droughts and extreme rain events in the steppes of the Eurasian region. Using the eddy covariance method, we measured carbon and water balances of a meadow steppe ecosystem in Northeast China during 2 years which had contrasting precipitation patterns in spring seasons in 2007 and 2008. The meadow steppe sequestrated only 6400·2 gC m0908082 year0908081 in 2007 compared to 16000·5 gC m0908082 year0908081 in 2008, due to a severe spring drought in 2007. The 2007 spring drought resulted in a dramatic reduction of leaf area index (LAI) and aboveground net primary productivity (ANPP). However, the meadow steppe still acted as a carbon sink in 2007. The strength of the sink was much greater than that in the typical steppes in Central Mongolia and Inner Mongolia. Spring drought also caused a reduction of plant transpiration (Tr) and total ecosystem evapotranspiration (ET). However, the suppression of ET in 2007 was relatively small in comparison to gross ecosystem productivity (GEP) reduction. Thus, ecosystem water use efficiency (WEU) (GEP/ET) in 2007 was reduced to 500·0 gCO2 kg0908081 H2O or 75% of that of 2008. We concluded that spring drought detrimentally impacted meadow steppe ecosystem by reducing leaf areas, biomass, GEP, WUE and associated increases in soil evaporation (Es) that might aggravate soil salinization of the Songnen Plain. Copyright 0008 2011 John Wiley & Sons, Ltd.
DOIURL [本文引用: 2]
DOIURL [本文引用: 1]
Based on future climate change projections offered by IPCC, the responses of yields and water use efficiencies of wheat and maize to climate change scenarios are explored over the North China Plain. The climate change projections of 21st century under A2A, B2A and A1B are from HadCM3 global climate model. A climate generator (CLIGEN) is applied to generate daily weather data of selected stations and then the data is used to drive CERES-Wheat and Maize models. The impacts of increased temperature and CO 2 on wheat and maize yields are inconsistent. Under the same scenario, wheat yield ascended due to climatic warming, but the maize yield descended. As a more probable scenario, climate change under B2A is moderate relative to A2A and A1B. Under B2A in 2090s, average wheat yield and maize yield will respectively increase 9.8% and 3.2% without CO 2 fertilization in this region. High temperature not only affects crop yields, but also has positive effect on water use efficiencies, mainly ascribing to the evapotranspiration intensification. There is a positive effect of CO 2 enrichment on yield and water use efficiency. If atmospheric CO 2 concentration reaches nearly 600 ppm, wheat and maize yields will increase 38% and 12% and water use efficiencies will improve 40% and 25% respectively, in comparison to those without CO 2 fertilization. However, the uncertainty of crop yield is considerable under future climate change scenarios and whether the CO 2 fertilization may be realized is still needed further research.
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Through 2-3-year (2003-2005) continuous eddy covariance measurements of carbon dioxide and water vapor fluxes, we examined the seasonal, inter-annual, and inter-ecosystem variations in the ecosystem-level water use efficiency (WUE, defined as the ratio of gross primary production, GPP, to evapotranspiration, ET) at four Chinese grassland ecosystems in the Qinghai-Tibet Plateau and North China. Representing the most prevalent grassland types in China, the four ecosystems are an alpine swamp meadow ecosystem, an alpine shrub-meadow ecosystem, an alpine meadow-steppe ecosystem, and a temperate steppe ecosystem, which illustrate a water availability gradient and thus provide us an opportunity to quantify environmental and biological controls on ecosystem WUE at different spatiotemporal scales. Seasonally, WUE tracked closely with GPP at the four ecosystems, being low at the beginning and the end of the growing seasons and high during the active periods of plant growth. Such consistent correspondence between WUE and GPP suggested that photosynthetic processes were the dominant regulator of the seasonal variations in WUE. Further investigation indicated that the regulations were mainly due to the effect of leaf area index (LAI) on carbon assimilation and on the ratio of transpiration to ET ( T /ET). Besides, except for the swamp meadow, LAI also controlled the year-to-year and site-to-site variations in WUE in the same way, resulting in the years or sites with high productivity being accompanied by high WUE. The general good correlation between LAI and ecosystem WUE indicates that it may be possible to predict grassland ecosystem WUE simply with LAI. Our results also imply that climate change-induced shifts in vegetation structure, and consequently LAI may have a significant impact on the relationship between ecosystem carbon and water cycles in grasslands.
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Two varieties, rosea and alba, of Catharanthus roseus (L.) G. Don. were screened for their water use efficiency under two watering regimes, viz. 60 and 100% filed capacity in the present study. Drought stress was imposed at 60% filed capacity from 30 to 70 days after sowing, while the control pots were maintained at 100% filed capacity throughout the entire growth period. Leaf area duration, cumulative water transpired, water use efficiency, net assimilation rate, mean transpiration rate, harvest index, biomass and yield under the water deficit level were measured from both stressed and well-watered control plants. Water use efficiency significantly increased in both varieties under water stress. Drought stress decreased leaf area duration, cumulative water transpired, net assimilation rate, mean transpiration rate, harvest index, and biomass yield in both varieties studied. Among the varieties, rosea variety showed the best results. To cite this article: C.A. Jaleel et al., C. R. Biologies 331 (2008).
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Water is considered a key factor affecting ecosystem carbon exchange in dryland regions. However, the relationship between inter-annual variations in precipitation and ecosystem productivity remains to be clarified for arid and semi-arid areas. Based on eddy-covariance measurements, we examined how ecosystem production in a shrubland of northern China varied over three years (2012–2014) with contrasting precipitation and soil moisture patterns. Net ecosystem production (NEP) was 77±10 (±standard deviation), 614±10 and 6122±5gCm612in 2012–2014, respectively, indicating a rapid shift from an annual sink to a source of carbon. Gross ecosystem production (GEP), total ecosystem respiration (TER) and evapotranspiration (ET) also declined over the three years. Annual carbon and water fluxes appeared to be suppressed in years with low spring soil moisture, which declined dramatically from 2012 to 2014.GEPdeclined more thanTERandET, leading to reduced carbon sequestration capacity and water use efficiency (WUE=GEP/ET). Neither annual nor growing-season precipitation could explain the year-to-year variations in carbon fluxes, whereas at our siteETwas a better proxy for water available to ecosystem carbon exchange on an annual basis. Autumn soil moisture levels were carried over winter to the following spring, and, thus, may affect the rates of leafout, plant growth and carbon uptake in the early- to mid-growing season. Our conclusions were drawn from only three years of measurements and are therefore preliminary. Longer timeseries encompassing a wider range of precipitation and soil moisture conditions are needed to confirm or refine these conclusions. Our findings highlight the importance of precipitation timing and soil moisture carry-over in controlling ecosystem productivity. Winter warming and decreases in autumn and winter precipitation may induce spring drought and thus impair the carbon sequestration potential of shrubland and steppe ecosystems in semi-arid and arid Eurasia.
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The objective of this research was to compare seasonal and annual estimates of CO 2 and water vapor exchange across sites in forests, grasslands, crops, and tundra that are part of an international network called FLUXNET, and to investigating the responses of vegetation to environmental variables. FLUXNETs goals are to understand the mechanisms controlling the exchanges of CO 2, water vapor and energy across a spectrum of time and space scales, and to provide information for modeling of carbon and water cycling across regions and the globe. At a subset of sites, net carbon uptake (net ecosystem exchange, the net of photosynthesis and respiration) was greater under diffuse than under direct radiation conditions, perhaps because of a more efficient distribution of non-saturating light conditions for photosynthesis, lower vapor pressure deficit limitation to photosynthesis, and lower respiration associated with reduced temperature. The slope of the relation between monthly gross ecosystem production and evapotranspiration was similar between biomes, except for tundra vegetation, showing a strong linkage between carbon gain and water loss integrated over the year (slopes=3.4 g CO 2/kg H 2O for grasslands, 3.2 for deciduous broadleaf forests, 3.1 for crops, 2.4 for evergreen conifers, and 1.5 for tundra vegetation). The ratio of annual ecosystem respiration to gross photosynthesis averaged 0.83, with lower values for grasslands, presumably because of less investment in respiring plant tissue compared with forests. Ecosystem respiration was weakly correlated with mean annual temperature across biomes, in spite of within site sensitivity over shorter temporal scales. Mean annual temperature and site water balance explained much of the variation in gross photosynthesis. Water availability limits leaf area index over the long-term, and inter-annual climate variability can limit carbon uptake below the potential of the leaf area present.
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生态系统水分利用效率(WUE)是衡量碳水循环耦合程度的重要指 标.利用科尔沁温带草甸草地碳水通量观测数据,对该生态系统总初级生产力水分利用效率(WUEGPP)的日季变化规律及对环境和生理因子的响应进行分析. 结果表明:(1)WUEGPP日变化呈下降-稳定-上升的变化趋势,最大值出现在日出后1-2 h,阴天条件下WUEGPP高于晴天,生长中期WUEGPP高于生长初期和末期;(2)总初级生产力、总蒸散和WUEGPP季节变化均呈夏季高、春秋低的 形式,生长季平均值分别为0.57 mgm-2 s-1、0.08 g m-2 s-1和5.97 mg/g,最大值分别为1.49 mg m-2 s-1、0.16 g m-2 s1和13.62 mg/g; (3)总初级生产力与饱和差、气温和叶面积指数均呈二次曲线关系,与冠层导度呈对数曲线关系;总蒸散与气温呈二次曲线关系,与饱和差、叶面积指数和冠层导 度相关性均不显著;(4)WUEGPP与饱和差、气温和叶面积指数均呈二次曲线关系,与冠层导度呈对数曲线关系,饱和差、冠层导度和叶面积指数分别为 2.0 kPa、0.0015 m/s和4.2是控制WUEGPP增加的阈值;(5)净生态系统生产力水分利用效率(WUENEP)和净初级生产力水分利用效率(WUENPP)季节变化 规律与WUEGPP一致,均值分别为3.47和5.47 mg/g.
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生态系统水分利用效率(WUE)是衡量碳水循环耦合程度的重要指 标.利用科尔沁温带草甸草地碳水通量观测数据,对该生态系统总初级生产力水分利用效率(WUEGPP)的日季变化规律及对环境和生理因子的响应进行分析. 结果表明:(1)WUEGPP日变化呈下降-稳定-上升的变化趋势,最大值出现在日出后1-2 h,阴天条件下WUEGPP高于晴天,生长中期WUEGPP高于生长初期和末期;(2)总初级生产力、总蒸散和WUEGPP季节变化均呈夏季高、春秋低的 形式,生长季平均值分别为0.57 mgm-2 s-1、0.08 g m-2 s-1和5.97 mg/g,最大值分别为1.49 mg m-2 s-1、0.16 g m-2 s1和13.62 mg/g; (3)总初级生产力与饱和差、气温和叶面积指数均呈二次曲线关系,与冠层导度呈对数曲线关系;总蒸散与气温呈二次曲线关系,与饱和差、叶面积指数和冠层导 度相关性均不显著;(4)WUEGPP与饱和差、气温和叶面积指数均呈二次曲线关系,与冠层导度呈对数曲线关系,饱和差、冠层导度和叶面积指数分别为 2.0 kPa、0.0015 m/s和4.2是控制WUEGPP增加的阈值;(5)净生态系统生产力水分利用效率(WUENEP)和净初级生产力水分利用效率(WUENPP)季节变化 规律与WUEGPP一致,均值分别为3.47和5.47 mg/g.
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The acquisition of “ground-truth” land surface evapotranspiration (ET) data at the satellite pixel scale over heterogeneous land surfaces is crucial to develop ET estimation models and improve the accuracy of remotely sensed ET values. However, few studies have focused on methods of acquiring ET data at the satellite pixel scale. Based on multi-site eddy covariance (EC) system measurements from the “Multi-Scale Observation Experiment on Evapotranspiration over heterogeneous land surfaces” in the middle reaches of the Heihe River Basin, five upscaling methods were compared and a combined method was developed to acquire “ground-truth” ET data at the satellite pixel scale. First, this study evaluated the performances of three simple upscaling methods (the arithmetic average, area-weighted and footprint-weighted methods). The results showed that the three simple upscaling methods perform well in the relatively homogeneous pixels. For the area-weighted method, the mean absolute percentage error (MAPE) for these pixels was 6.1%. However, the accuracy was worse in the relatively heterogeneous pixels, with a MAPE of 10.8% due to the surface heterogeneity significantly affecting the accuracy of the upscaled results. Second, the upscaling of ET results from heterogeneous land surfaces at the satellite pixel scale can be significantly improved by using two upscaling methods introducing auxiliary variables (the integrated Priestley-Taylor equation method and the area-to-area regression kriging method), that can characterize the heterogeneity of the surface water and heat conditions. Finally, a combined method (applied the area-weighted method for relative homogeneous surfaces, otherwise used the method introducing auxiliary variables) was proposed to acquire both instantaneous and daily “ground-truth” ET data at the satellite pixel scale at the time of a MODIS overpass. The uncertainties of the “ground-truth” ET data were evaluated, taking the large aperture scintillometer (LAS) measurements as the satellite pixel reference. The results show that the proposed upscaling method is reasonable and feasible, and therefore could bridge the gap between in situ ET measurements and remote-sensing estimates of ET.
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Abstract Carbon and water fluxes are key properties of ecosystem processes and functions. A better understanding of their temporal dynamics and coupling mechanism between these fluxes will help us improve ecosystem management for mitigation as well as adaption to future climatic change. From 2003 to 2009, carbon and water flux data were obtained by the eddy covariance method over an old-growth forest in the lower subtropical China. The 7 years of observational data indicated that the water-use efficiency (WUE) of the old-growth forest exhibited weak inter-annual variability. The mean annual WUE ranged from 1.70 to 1.98090009g090009C kg -1 H 2 O. An analysis of the effects of environmental variables on the monthly gross primary productivity (GPP) and evapotranspiration (ET) indicated that solar radiation, air temperature, precipitation and vapor pressure deficit (VPD) produced similar effects on the monthly GPP and ET, which suggests that photosynthesis and ET were similarly driven by the climatic variables. At the monthly scale, the WUE decreased significantly as the precipitation and soil moisture content increased. However, a significant correlation was not detected between the WUE and the VPD at the monthly scale. Moisture conditions tend to be major drivers of the ecosystem WUE.
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In this study, we used the remotely-sensed data from the Moderate Resolution Imaging Spectrometer (MODIS), meteorological and eddy flux data and an artificial neural networks (ANNs) technique to develop a daily evapotranspiration (ET) product for the period of 2004-2005 for the conterminous U.S. We then estimated and analyzed the regional water-use efficiency (WUE) based on the developed ET and MODIS gross primary production (GPP) for the region. We first trained the ANNs to predict evapotranspiration fraction (EF) based on the data at 28 AmeriFlux sites between 2003 and 2005. Five remotely-sensed variables including land surface temperature (LST), normalized difference vegetation index (NDVI), normalized difference water index (NDWI), leaf area index (LAI) and photosynthetically active radiation (PAR) and ground-measured air temperature and wind velocity were used. The daily ET was calculated by multiplying net radiation flux derived from remote sensing products with EF. We then evaluated the model performance by comparing modeled ET with the data at 24 AmeriFlux sites in 2006. We found that the ANNs predicted daily ET well ( R 2 = 0.52-0.86). The ANNs were applied to predict the spatial and temporal distributions of daily ET for the conterminous U.S. in 2004 and 2005. The ecosystem WUE for the conterminous U.S. from 2004 to 2005 was calculated using MODIS GPP products (MOD17) and the estimated ET. We found that all ecosystems' WUE-drought relationships showed a two-stage pattern. Specifically, WUE increased when the intensity of drought was moderate; WUE tended to decrease under severe drought. These findings are consistent with the observations that WUE does not monotonously increase in response to water stress. Our study suggests a new water-use efficiency mechanism should be considered in ecosystem modeling. In addition, this study provides a high spatial and temporal resolution ET dataset, an important product for climate change and hydrological cycling studies for the MODIS era.
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Abstract Salinity tolerance comes from genes that limit the rate of salt uptake from the soil and the transport of salt throughout the plant, adjust the ionic and osmotic balance of cells in roots and shoots, and regulate leaf development and the onset of senescence. This review lists some candidate genes for salinity tolerance, and draws together hypotheses about the functions of these genes and the specific tissues in which they might operate. Little has been revealed by gene expression studies so far, perhaps because the studies are not tissue-specific, and because the treatments are often traumatic and unnatural. Suggestions are made to increase the value of molecular studies in identifying genes that are important for salinity tolerance.
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The European CARBOEUROPE/FLUXNET monitoring sites, spatial remote sensing observations via the EOS-MODIS sensor and ecosystem modelling provide independent and complementary views on the effect of the 2003 heatwave on the European biosphere's productivity and carbon balance. In our analysis, these data streams consistently demonstrate a strong negative anomaly of the primary productivity during the summer of 2003. FLUXNET eddy-covariance data indicate that the drop in productivity was not primarily caused by high temperatures ('heat stress') but rather by limitation of water (drought stress) and that, contrary to the classical expectation about a heat wave, not only gross primary productivity but also ecosystem respiration declined by up to more than to 80 gC m 612 month 611 . Anomalies of carbon and water fluxes were strongly correlated. While there are large between-site differences in water-use efficiency (WUE, 1–6 kg C kg 611 H 2 O) here defined as gross carbon uptake divided by evapotranspiration (WUE=GPP/ET), the year-to-year changes in WUE were small (<1 g kg 611 ) and quite similar for most sites (i.e. WUE decreased during the year of the heatwave). Remote sensing data from MODIS and AVHRR both indicate a strong negative anomaly of the fraction of absorbed photosynthetically active radiation in summer 2003, at more than five standard deviations of the previous years. The spatial differentiation of this anomaly follows climatic and land-use patterns: Largest anomalies occur in the centre of the meteorological anomaly (central Western Europe) and in areas dominated by crops or grassland. A preliminary model intercomparison along a gradient from data-oriented models to process-oriented models indicates that all approaches are similarly describing the spatial pattern of ecosystem sensitivity to the climatic 2003 event with major exceptions in the Alps and parts of Eastern Europe, but differed with respect to their interannual variability.
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Variability of above-ground net primary production (ANPP) of arid to sub-humid ecosystems displays a closer association with precipitation when considered across space (based on multiyear averages for different locations) than through time (based on year-to-year change at single locations). Here, we propose a theory of controls of ANPP based on four hypotheses about legacies of wet and dry years that explains space versus time differences in ANPP-precipitation relationships. We tested the hypotheses using 16 long-term series of ANPP. We found that legacies revealed by the association of current- versus previous-year conditions through the temporal series occur across all ecosystem types from deserts to mesic grasslands. Therefore, previous-year precipitation and ANPP control a significant fraction of current-year production. We developed unified models for the controls of ANPP through space and time. The relative importance of current-versus previous-year precipitation changes along a gradient of mean annual precipitation with the importance of current-year PPT decreasing, whereas the importance of previous-year PPT remains constant as mean annual precipitation increases. Finally, our results suggest that ANPP will respond to climate-change-driven alterations in water availability and, more importantly, that the magnitude of the response will increase with time.
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We calculated water use efficiency (WUE) using measures of gross primary production (GPP) and evapotranspiration (ET) from five years of continuous eddy covariance measurements (2009-2013) obtained over a primary subtropical evergreen broadleaved forest in southwestern China. Annual mean WUE exhibited a decreasing trend from 2009 to 2013, varying from similar to 2.28 to 2.68 g C kg H2O-1. The multiyear average WUE was 2.48 +/- 0.17 (mean +/- standard deviation) g C kg H2O-1. WUE increased greatly in the driest year (2009), due to a larger decline in ET than in GPP. At the diurnal scale, WUE in the wet season reached 5.1 g C kg H2O-1 in the early morning and 4.6 g C kg H2O-1 in the evening. WUE in the dry season reached 3.1 g C kg H2O-1 in the early morning and 2.7 g C kg H2O-1 in the evening. During the leaf emergence stage, the variation of WUE could be suitably explained by water-related variables (relative humidity (RH), soil water content at 100 cm (SWC_100)), solar radiation and the green index (Sgreen). These results revealed large variation in WUE at different time scales, highlighting the importance of individual site characteristics.
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Abstract We used a continuous 9 year (2003–2011) eddy flux time series with 3065min resolution to examine water use efficiency in a tropical rainforest and determine its environmental controls. The multiyear mean water use efficiency ( W ue) of this rainforest was 3.1665±650.33 gC per kg H2O, which is close to that of boreal forests, but higher than subtropical forests, and lower than temperate forests. The water vapor deficit ( V PD) had a strong impact on instantaneous W ue, in the manner predicted by stomatal optimization theory. At the seasonal scale, temperature was the dominant controller of W ue. The negative correlation between temperature and W ue was probably caused by high continuous photosynthesis during low-temperature periods. The V PD did not correlate with W ue at the interannual scale. No interannual trend was detected in W ue or inherent water use efficiency ( W ei), either annually or seasonally. The fact that no increasing trend of W ei was found in the studied tropical rainforest, along with other evidence of CO2 stimulation in tropical rainforests, requires special attention and data validation. There was no significant difference between W ue during a drought and the 9 year mean values in the forest we studied, but we found that dry season transpiration ( Tr ) was consistently lower during the drought compared to the mean values. Finally, whether W ue increases or decreases during a drought is determined by the drought sensitivity of gross primary production ( G PP).
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One of the most important linkages that couple terrestrial carbon and water cycles is ecosystem water use efficiency (WUE), which is relevant to the reasonable utilization of water resources and farming practices. Eddy covariance techniques provide an opportunity to monitor the variability in WUE and can be integrated with Moderate Resolution Imaging Spectroradiometer (MODIS) observations. Scaling up in situ observations from flux tower sites to large areas remains challenging and few studies have been reported on direct estimation of WUE from remotely-sensed data. This study examined the main environmental factors driving the variability in WUE of corn/soybean croplands, and revealed the prominent role of solar radiation and temperature. Time-series of MODIS-derived enhanced vegetation indices (EVI), which are proxies for the plant responses to environmental controls, were also strongly correlated with ecosystem WUE, thereby implying great potential for remote quantification. Further, both performance of the indirect MODIS-derived WUE from gross primary productivity (GPP) and evapotranspiration (ET), and the direct estimates by exclusive use of MODIS EVI data were evaluated using tower-based measurements. The results showed that ecosystem WUE were overpredicted at the beginning and ending of crop-growth periods and severely underestimated during the peak periods by the indirect estimates from MODIS products, which was mainly attributed to the error source from MODIS GPP. However, a simple empirical model that is solely based on MODIS EVI data performed rather well to capture the seasonal variations in WUE, especially for the growing periods of croplands. Independent validation at different sites indicates the method has potential for broad application.
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Abstract Precipitation regimes are predicted to become more variable with more extreme rainfall events punctuated by longer intervening dry periods. Water-limited ecosystems are likely to be highly responsive to altered precipitation regimes. The bucket model predicts that increased precipitation variability will reduce soil moisture stress and increase primary productivity and soil respiration in aridland ecosystems. To test this hypothesis, we experimentally altered the size and frequency of precipitation events during the summer monsoon (July through September) in 2007 and 2008 in a northern Chihuahuan Desert grassland in central New Mexico, USA. Treatments included (1) ambient rain, (2) ambient rain plus one 20/mm rain event each month, and (3) ambient rain plus four 5/mm rain events each month. Throughout two monsoon seasons, we measured soil temperature, soil moisture content, soil respiration ( R s), along with leaf-level photosynthesis ( A net), predawn leaf water potential (pd), and seasonal aboveground net primary productivity (ANPP) of the dominant C4 grass, Bouteloua eriopoda . Treatment plots receiving a single large rainfall event each month maintained significantly higher seasonal soil which corresponded with a significant increase in R s and ANPP of B. eriopoda when compared with plots receiving multiple small events. Because the strength of these patterns differed between years, we propose a modification of the bucket model in which both the mean and variance of soil water change as a consequence of interannual variability from 1 year to the next. Our results demonstrate that aridland ecosystems are highly sensitive to increased precipitation variability, and that more extreme precipitation events will likely have a positive impact on some aridland ecosystem processes important for the carbon cycle.
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The eddy covariance technique and the cuvette method were used to investigate water use efficiency in an irrigated winter wheat ( Triticum asetivum L.)/summer maize ( Zea mays L.) rotation system in the North China Plain. The results show that ecosystem water use efficiency (WUE e) changed diurnally and seasonally. Daily maximal WUE e appeared in the morning. WUE e generally peaked in late April in wheat field and in late July/early August in maize field. From 2003 to 2006, seasonal mean WUE e was 6.7–7.4 mg CO 2 g 611 H 2O for wheat and 8.4–12.1 mg CO 2 g 611 H 2O for maize. WUE e was much lower than canopy water use efficiency (WUE c) under small leaf area index (LAI) but very close to WUE c under large LAI. With the increase in LAI, WUE e enlarged rapidly under low LAI but slowly when LAI was higher than one. WUE e was greater on the cloudy days than on the sunny days. Under the same solar radiation, WUE e was higher in the morning than in the afternoon. The ratio of internal to ambient CO 2 partial pressure ( C i/ C a) decreased significantly with the increase in photosynthetically active radiation (PAR) when PAR was lower than the critical values (around 500 and 1000 μmol m 612 s 611 for wheat and maize, respectively). Beyond critical PAR, C i/ C a was approximately constant at 0.69 for wheat and 0.42 for maize. Therefore, when LAI and solar radiation was large enough, WUE e has negative correlation with vapor pressure deficit in both of irrigated wheat and maize fields.
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[1] Agreement among instruments is very important for the Multi-Scale Observation Experiment on Evapotranspiration over heterogeneous land surfaces of The Heihe Watershed Allied Telemetry Experimental Research (HiWATER-MUSOEXE), particularly in regard to radiation and turbulent flux measurements. Before HiWATER-MUSOEXE was conducted, 20 eddy covariance (EC) system sets, 18 radiometer sets, and seven large aperture scintillometers (LASs) sets were intercompared over the Gobi desert between 14 and 24 May 2012. For radiometers, the four-component radiation measurements exhibited good agreement090000the average root-mean-square error (RMSE) and mean relative error (MRE) for the net radiation were 10.38090009W090009m0908082 and 1.24%, respectively. With regard to the EC systems, the best consistency for sensible heat fluxes was found among CSAT3 sonic anemometers and Li7500A/Li7500/EC150 combinations (average RMSE, 12.30090009W090009m0908082 and MRE, 0908081.36%), followed by Gill sonic anemometers and Li7500A/Li7500 combinations when a proper angle of attack correction method was applied (average RMSE, 16.75090009W m0908082 and MRE, 0908085.52%). The sensible heat flux measured using different LASs agreed well with high correlation coefficients090000the average RMSE and MRE values were 10.26090009W090009m0908082 and 5.48% for boundary layer scintillometer (BLS) 900, 16.32090009W090009m0908082 and 10.47% for BLS450, and 14.38090009W090009m0908082 and 0908083.72% for ZZLAS, respectively. The EC and LAS measurements were compared and agreed well over homogeneous underlying surfaces, which also indicated that the EC and LAS measurements would be comparable in the follow-up experiment. The intercomparison results can be used to determine instrument placement and are very helpful for subsequent data analysis.
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090004 Carbon (C) and water cycles of terrestrial ecosystems are two coupled ecological processes controlled partly by stomatal behavior. Water-use efficiency (WUE) reflects the coupling relationship to some extent. At stand and ecosystem levels, the variability of WUE results from the trade-off between water loss and C gain in the process of plant photosynthetic C assimilation. 090004 Continuous observations of C, water, and energy fluxes were made at three selected forest sites of ChinaFLUX with eddy covariance systems from 2003 to 2005. WUE at different temporal scales were defined and calculated with different C and water flux components. 090004 Variations in WUE were found among three sites. Average annual WUE was 9.43 mg CO 2 g 0908081 H 2 O at Changbaishan temperate broad-leaved Korean pine mixed forest, 9.27 mg CO 2 g 0908081 H 2 O at Qianyanzhou subtropical coniferous plantation, and 6.90 mg CO 2 g 0908081 H 2 O at Dinghushan subtropical evergreen broad-leaved forest. It was also found that temperate and subtropical forest ecosystems had different relationships between gross primary productivity (GPP) and evapotranspiration (ET). 090004 Variations in WUE indicated the difference in the coupling between C and water cycles. The asynchronous response of GPP and ET to climatic variables determined the coupling and decoupling between C and water cycles for the two regional forest ecosystems.
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Water use efficiency (WUE), defined as the ratio of gross primary productivity to evapotranspiration, is an important indicator of the trade-off between water loss and carbon gain. We used a biophysical process-based model to examine the relative importance of climate-induced changes in meteorological factors and leaf area index (LAI) on the changes in WUE in East Asia. Validation showed that our simulation could capture the magnitudes and variations of WUE at 18 flux sites in Asia. Regional results indicated that the highest WUE occurred in boreal forests at high latitudes and the lowest WUE in desert areas of China. Changes in meteorological factors negatively affected WUE in the northwestern, northern, and eastern study regions. Changes in LAI had determinant impacts on changes in WUE in most areas except for those with sparse or low-density vegetation (e.g., western interior China, southeast island countries) where meteorological factors dominated. We conclude that, aside from the impact of meteorological factors on WUE, climate-induced changes in LAI may play a prominent role in regulating WUE changes.
DOIURL [本文引用: 1]
Water use efficiency (WUE) is a useful indicator to illustrate the interaction of carbon and water cycles in terrestrial ecosystems. MODIS gross primary production (GPP) and evapotranspiration (ET) products have been used to analyze the spatial and temporal patterns of WUE and their relationships with environmental factors at regional and global scales. Although MODIS GPP and ET products have been evaluated using eddy covariance flux measurements, the accuracy of WUE estimated from MODIS products has not been well quantified. In this paper, we evaluated WUE estimated from MODIS GPP and ET products against eddy covariance measurements of GPP and ET during 2003-2008 at eight sites of the Chinese flux observation and research network (ChinaFLUX) and conducted sensitivity analysis to investigate the possible key contributors to the bias of MODIS products. Results show that MODIS products underestimate eight-day water use efficiency in four forest ecosystems and one cropland ecosystem with the bias from 0.36--2.28 g.C.kg-1 H20, while overestimating it in three grassland ecosystems with the bias from 0.26-1.11 g. C . kg-1 H20. Mean annual WUE was underestimated by 14%-54% at four forest sites, 45% at one cropland site and 7% at an alpine grassland site, but overestimated by 66% and 9% at a temperate grassland site and an alpine meadow site, respectively. The underestimation of WUE by MODIS data results from underestimated GPP and overestimated ET at four forest sites, while MODIS WUE values are significantly overvalued mainly due to underestimated ET in the three grassland ecosystems. The maximum light use efficiency and fraction of photosynthetically-active radiation (FPAR) were the two most sensitive factors to the estimation of WUE derived from the MODIS GPP and ET algorithms. The error in meteorological data partly caused the overestimation of ET and accordingly underestimation in WUE in subtropical and tropical forests. The bias of MODIS-produced WUE was also derived from the uncertainties in eddy flux data due to gap-filling processes and unbalanced surface energy issue. Their contributions to the uncertainty in estimated WUE at both eight-day and annual scales still need to be further quantified.
DOIURL
利用中国生态系统研究网络临泽内陆河流域研究站绿洲农田2009 年小气候、湍流交换、土壤蒸发和叶片气孔导度等综合观测试验数据,应用Shuttleworth-Wallace (S-W)双源模型以半小时为步长估算了绿洲农田玉米生长季实际蒸散量,并利用涡动相关与微型蒸渗仪实测数据对田间蒸散发量和棵间土壤蒸发量计算结果进行 了检验.结果表明:S-W模型较好地估算研究区的蒸散量,并能有效区分农田作物蒸腾和土壤蒸发;全生育期玉米共耗水640 mm,其中作物蒸腾累积量为467 mm,土壤蒸发累积量为173 mm,分别占总量的72.9％和27.1％;日时间尺度上,作物蒸腾和土壤蒸发分别在0-6.3 mm/d和0-4.3 mm/d之间变化,其日平均分别为2.9和1.0 mm/d;田间供水充足,作物蒸腾与土壤蒸发比值明显受作物生长过程影响,播种—出苗期、出苗—拔节期、拔节—抽雄期、抽雄—灌浆期、灌浆—成熟期,其比 值分别为0.04、0.8、7.0、5.2和1.4,不同阶段的比值差异主要受叶面积指数影响.
DOIURL
利用中国生态系统研究网络临泽内陆河流域研究站绿洲农田2009 年小气候、湍流交换、土壤蒸发和叶片气孔导度等综合观测试验数据,应用Shuttleworth-Wallace (S-W)双源模型以半小时为步长估算了绿洲农田玉米生长季实际蒸散量,并利用涡动相关与微型蒸渗仪实测数据对田间蒸散发量和棵间土壤蒸发量计算结果进行 了检验.结果表明:S-W模型较好地估算研究区的蒸散量,并能有效区分农田作物蒸腾和土壤蒸发;全生育期玉米共耗水640 mm,其中作物蒸腾累积量为467 mm,土壤蒸发累积量为173 mm,分别占总量的72.9％和27.1％;日时间尺度上,作物蒸腾和土壤蒸发分别在0-6.3 mm/d和0-4.3 mm/d之间变化,其日平均分别为2.9和1.0 mm/d;田间供水充足,作物蒸腾与土壤蒸发比值明显受作物生长过程影响,播种—出苗期、出苗—拔节期、拔节—抽雄期、抽雄—灌浆期、灌浆—成熟期,其比 值分别为0.04、0.8、7.0、5.2和1.4,不同阶段的比值差异主要受叶面积指数影响.
DOIURL [本文引用: 1]
Water use efficiency (WUE) is a crucial parameter to describe the interrelationship between gross primary production (GPP) and evapotranspiration (ET). Incorporating the nonlinear effect of vapor pressure deficit (VPD), underlying WUE (uWUE = GPP VPD/ET) is better than inherent WUE (IWUE = GPP VPD/ET) at the half-hourly time scale. However, appropriateness of uWUE has not yet been evaluated at the daily time scale. To determine whether uWUE is better than IWUE, daily data for seven vegetation types from 34 AmeriFlux sites were used to validate uWUE at the daily time scale. First, daily mean VPD was shown to be a good substitute for the effective VPD that was required to preserve daily GPP totals. Second, an optimal exponent, k*, corresponding to the best linear relationship between GPP VPDand ET, was about 0.55 both at half-hourly and daily time scales. Third, correlation coefficient between GPP VPDand ET showed that uWUE (k = 0.5 and r = 0.85) was a better approximation of the optimal WUE (k = k* and r = 0.86) than IWUE (k = 1 and r = 0.81) at the daily scale. Finally, when yearly uWUE was used to predict daily GPP from daily ET and mean VPD, uWUE worked considerably better than IWUE. Comparing observed and predicted daily GPP, the average correlation coefficient and Nash-Sutcliffe coefficient of efficiency were 0.81 and 0.59, respectively, using yearly uWUE, and only 0.59 and -0.83 using yearly IWUE. As a nearly optimal WUE, uWUE consistently outperformed IWUE and could be used to evaluate the effects of global warming and elevated atmosphere COon carbon assimilation and evapotranspiration.
Temporal and among site variability of inherent water use efficiency at the ecosystem level.
1
2009
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
Establishing aquatic restoration priorities using a watershed approach.
1
2002
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
稳定性碳同位素技术在生态学研究中的应用
1
2002
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
稳定性碳同位素技术在生态学研究中的应用
1
2002
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
使用SPSS线性回归实现通径分析的方法
1
2010
... 基于SPSS 19.0软件, 分别在0.5 h、1 d、8 d和1月的时间尺度对Ta、RH、VPD、PAR与WUE进行了逐步回归分析(
使用SPSS线性回归实现通径分析的方法
1
2010
... 基于SPSS 19.0软件, 分别在0.5 h、1 d、8 d和1月的时间尺度对Ta、RH、VPD、PAR与WUE进行了逐步回归分析(
Effects of spring drought on carbon sequestration, evapotranspiration and water use efficiency in the Songnen meadow steppe in northeast China.
2
2011
... 年降水量是驱动年际间生态系统WUE和NEP差异的主要因子(
... 与植物需求量并不一定同步(
Stomatal conductance and photosynthesis.
2
1982
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
... WUE的影响因子随地区和尺度的不同而变化(
Responses of crop yield and water use efficiency to climate change in the North China Plain.
1
2010
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
Effects of vegetation control on ecosystem water use efficiency within and among four grassland ecosystems in China.
3
2008
... 各个站点WUE的季节变化特征为: 在巴吉滩与花寨子荒漠站WUE总体呈现“U”型变化趋势, 在生长季开始和结束的时候较高, 而在生长季中期, WUE值较低.在其他站点, WUE呈现单峰型的变化趋势在生长季早期和末期较低, 而在生长季中期较高(
... 由
... LAI不仅能有效地增强植物的光能利用率, 也能有效地抑制土壤蒸发, 是研究WUE变化的一个重要影响因子(
生态系统水分利用效率研究进展
1
2009
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
生态系统水分利用效率研究进展
1
2009
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
关于中国西北干旱区陆—气相互作用及其对气候影响研究的最近进展
1
2013
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
关于中国西北干旱区陆—气相互作用及其对气候影响研究的最近进展
1
2013
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
Differential responses in water use efficiency in two varieties of Catharanthus roseus under drought stress.
1
2008
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
Carbon and water exchange over a temperate semi-arid shrubland during three years of contrasting precipitation and soil moisture patterns.
2016
Environmental controls over carbon dioxide and water vapor exchange of terrestrial vegetation.
2
2002
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
... 有研究发现WUE随温度的升高而降低(
科尔沁草甸生态系统水分利用效率及影响因素
1
2015
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
科尔沁草甸生态系统水分利用效率及影响因素
1
2015
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
近百年来全球主要干旱区的干旱化特征分析
1
2004
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
近百年来全球主要干旱区的干旱化特征分析
1
2004
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
Upscaling evapotranspiration measurements from multi-site to the satellite pixel scale over heterogeneous land surfaces.
1
2016
... 本研究选取的数据来自中国通量观测研究联盟(ChinaFLUX,
Water-use efficiency of an old-growth forest in lower subtropical China.
3
2017
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
... 并无明显关系(
... 本文中WUE (g C·kg-1 H2O)的计算采用以下公式(
Evaluating evapotranspiration and water-use efficiency of terrestrial ecosystems in the conterminous United States using MODIS and AmeriFlux data.
2010
Effects of seasonal and interannual variations in leaf photosynthesis and canopy leaf area index on gross primary production of a cool-temperate deciduous broadleaf forest in Takayama, Japan.
1
2010
... LAI不仅能有效地增强植物的光能利用率, 也能有效地抑制土壤蒸发, 是研究WUE变化的一个重要影响因子(
Genes and salt tolerance: Bringing them together.
1
2005
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
Comparison of ecosystem water-use efficiency among Douglas-fir forest, aspen forest and grassland using eddy covariance and carbon isotope techniques.
3
2006
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
... WUE的影响因子随地区和尺度的不同而变化(
... 有研究发现WUE随温度的升高而降低(
Reduction of ecosystem productivity and respiration during the European summer 2003 climate anomaly: A joint flux tower, remote sensing and modelling analysis.
1
2007
... 得到的(
Legacies of precipitation fluctuations on primary production: Theory and data synthesis.
1
2012
... 年降水量是驱动年际间生态系统WUE和NEP差异的主要因子(
Water use efficiency in a primary subtropical evergreen forest in Southwest China.
2
2017
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
... ;
科尔沁沙地复叶槭等3个阔叶树种的光合特性及其水分利用效率
1
2008
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
科尔沁沙地复叶槭等3个阔叶树种的光合特性及其水分利用效率
1
2008
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
Interannual and seasonal variability of water use efficiency in a tropical rainforest: Results from a 9 year eddy flux time series.
1
2015
... WUE的影响因子随地区和尺度的不同而变化(
Tracking ecosystem water use efficiency of cropland by exclusive use of MODIS EVI data.
1
2015
... (W·m-2)换算得到的(
Effect of precipitation variability on net primary production and soil respiration in a Chihuahuan Desert grassland.
1
2011
... 年降水量是驱动年际间生态系统WUE和NEP差异的主要因子(
Ecosystem water use efficiency in an irrigated cropland in the North China Plain.
1
2009
... LAI不仅能有效地增强植物的光能利用率, 也能有效地抑制土壤蒸发, 是研究WUE变化的一个重要影响因子(
Bamboo forest water use efficiency in the Yangtze River Delta Region, China. Terrestrial,
2
2016
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
全球气候变化下植物水分利用效率研究进展
1
2010
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
全球气候变化下植物水分利用效率研究进展
1
2010
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
Intercomparison of surface energy flux measurement systems used during the HiWATER-MUSOEXE.
1
2013
... 本研究选取的数据来自中国通量观测研究联盟(ChinaFLUX,
Water-use efficiency of forest ecosystems in eastern China and its relations to climatic variables.
1
2008
... 得到的(
中国陆地生态系统通量观测研究网络(ChinaFLUX)的研究进展及其发展思路
1
2006
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
中国陆地生态系统通量观测研究网络(ChinaFLUX)的研究进展及其发展思路
1
2006
... 植物的水分利用效率(WUE)是其生理活动过程中消耗水形成有机物质的基本效率, 是确定植物体生长发育所需最优水分供应的重要指标(
How recent climate change influences water use efficiency in East Asia.
2
2014
... 目前常用的WUE观测方法主要有腔室气体交换法、同位素法以及涡度相关法.腔室气体交换法通过测定密闭空间内单叶CO2和H2O的瞬时交换量来计算, 主要用于叶片尺度研究(
... WUE由大到小依次为: 长白山>大兴>大满>密云>内蒙古>海北>张掖>巴吉滩>花寨子, 按照植被类型依次为: 森林>农田>草地>湿地>荒漠(
Evaluation of water use efficiency derived from MODIS products against eddy variance measurements in China.
1
2015
... 降水对生态系统WUE的影响有一定的延迟性, 同时LAI也不会在短时间内剧烈变化, 故单独进行降水量(P)和LAI与WUE关系的分析.在各因子对WUE的影响的分析中, 我们采用了Pearson系数来分析各因子与WUE的相关性, 公式(
区域尺度生态系统水分利用效率的时空变异特征研究进展
2014
区域尺度生态系统水分利用效率的时空变异特征研究进展
2014
西北黑河中游荒漠绿洲农田作物蒸腾与土壤蒸发区分及作物耗水规律
2015
西北黑河中游荒漠绿洲农田作物蒸腾与土壤蒸发区分及作物耗水规律
2015
Daily underlying water use efficiency for AmeriFlux sites.
1
2015
... WUE的影响因子随地区和尺度的不同而变化(
