,2,3,*Sap flow of Robinia pseudoacacia in response to rainfall exclusion treatment and environment factors in a sub-humid area in Loess Plateau
HE Qiu-Yue1,2, YAN Mei-Jie2,3, ZHANG Jian-Guo4, DU Sheng,2,3,*通讯作者: (shengdu@ms.iswc.ac.cn)
编委: 赵平
责任编辑: 李敏
| 基金资助: |
Online:2018-04-20
| Fund supported: |
摘要
随着全球气候变化加剧, 局部地区温度上升和降水量改变将对区域植被的分布与生长产生重要影响。在黄土高原半湿润及半干旱地区植被恢复中, 刺槐(Robinia pseudoacacia)是大面积种植的人工林树种。为探究该树种蒸腾耗水特征对降水量改变及水分条件差异的响应, 于2015年4月起, 在地处黄土高原半湿润区的陕西省永寿县槐平林场, 于35年生刺槐人工林样地中布设了人工截留降雨试验, 减少了47.5%的降雨输入。处理当年生长季内, 截留降雨处理区0-100 cm土层的平均土壤含水量相对于对照区(23.76%)有明显降低(22.59%)。采用Granier热扩散探针对截留降雨处理区和对照区的样树树干液流动态进行连续监测, 并同步监测主要气象环境因子(太阳辐射、空气温度和湿度)和林地土壤含水量, 分析了截留降雨处理区与对照区树干液流通量密度动态特征及其对环境因子的响应。结果表明: 截留降雨输入处理降低了刺槐树干液流通量密度, 截留降雨处理期间典型天气的平均液流通量密度(1.64 mL·m -2·s -1)不仅低于同组样树在处理前一年同期的水平(2.42 mL·m -2·s -1), 而且远低于试验期间对照区样树的平均水平(3.38 mL·m -2·s -1); 同时, 截留降雨处理还降低了刺槐液流通量密度对气象因子变化的敏感性, 截留降雨处理区样树液流通量密度响应空气水汽压亏缺的拟合方程参数值与对照区样树差异显著。分析可知, 降水量水平不仅影响土壤水分状况, 而且影响刺槐对气象环境因子响应的敏感性, 降水量减少导致的土壤含水量整体降低会使得该区域刺槐蒸腾耗水量下降, 显示其对环境因子的适应性, 但最终会导致生产力的大幅度降低。
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本文引用格式
何秋月, 闫美杰, 张建国, 杜盛. 黄土高原半湿润区刺槐树干液流对人工截留降雨输入及环境因子的响应. 植物生态学报[J], 2018, 42(4): 466-474 DOI:10.17521/cjpe.2017.0249
HE Qiu-Yue, YAN Mei-Jie, ZHANG Jian-Guo, DU Sheng.
蒸腾不仅是植物吸收和运输水分、无机离子的主要驱动力, 而且是森林水文循环的重要组分。植物蒸腾除受物种本身特性调控外, 也受气象和土壤等环境因素的影响。
降雨改变引起的干旱会对森林蒸腾耗水产生重要影响, 而降雨的随机性会造成旱期强度和持续时间的变化, 从而影响林分蒸腾(Wullschleger & Hanson, 2006; Knapp et al., 2008)。国内外多数研究表明, 区域范围降雨格局的变化, 会引起土壤含水量的变化, 从而影响蒸腾。降雨增加引起的土壤含水量升高通常会促进树木蒸腾; 降雨减少则会导致蒸腾的降低。Cermak等(1995)在瑞典中部的研究表明, 欧洲赤松(Pinus silvestris)和挪威云杉(Picea abies)林分蒸腾在降雨后分别增加了3.5和4.5倍。Llorens等(2010)对伊比利亚半岛欧洲赤松林研究发现, 在贫水年的夏季, 林分日蒸腾量比平常年份减少约40%。Wullschleger和Hanson (2006)通过人工控雨试验证明, 增加降雨的林分季节蒸腾增加了9%, 而减少降雨的样地降低了26%-30%。在长期人工截留降雨试验的栎林, 降水量减少29%导致年蒸腾量下降23% (Limousin et al., 2009)。不过, 也有一些研究未发现减少降雨对蒸腾有显著的影响, Wightman等(2016)在美国佛罗里达州北部的人工截留降雨试验并未说明降低降雨量对蒸腾耗水的影响, 可能的原因是该区域存在可利用的地下水, 人工截留降雨试验尚未对林分水分供应产生影响。Otieno等(2005)在肯尼亚对当地两个树种的对比研究发现, 当土壤含水量下降到一定阈值时, 树干液流开始下降, 其土壤含水量阈值的大小和液流下降的速率与树木根系深度有关。因此, 降雨改变对土壤水分条件的影响因环境条件不同而异, 而降水量改变对树木及林分蒸腾的影响不仅与土壤水分变化幅度有关, 而且与植物本身的生理状况关系密切, 对其影响程度及作用机理还需进一步的研究与分析。
人工造林是黄土高原地区植被恢复的主要措施。刺槐(Robinia pseudoacacia)是一种典型的中生树种, 既喜湿润肥沃, 又耐旱耐瘠薄, 生长迅速, 是优良造林树种(中国树木志编委会, 1978)。广泛人工造林促进了刺槐生态适应性, 使其具有向更暖、更冷以及更干旱区迁移的趋势(Li et al., 2018)。在黄土高原, 刺槐的栽种面积居该区域人工林面积之首(杜盛和刘国彬, 2015)。由于刺槐具有高耗水特性, 对土壤水分吸收较快, 消耗较大(韩蕊莲等, 1994; 茹桃勤等, 2005), 对水分条件的变化也表现得较为敏感, 因而适生区存在很大局限性, 加之全球气候变化引起降雨波动, 使得人们对黄土高原人工刺槐林的长期可持续发展仍有质疑, 亟待考证。
测定树干液流是实时监测蒸腾耗水动态的重要手段, 便于分析植物生理作用对环境因子的适应性和响应特征。本研究人工设置野外截留降雨输入实验, 研究刺槐树干液流对土壤水分变化的响应, 以及不同土壤水分条件下树干液流与气象环境因子的响应关系, 为探究刺槐人工林的适生范围和降水量阈值提供数据支撑。
1 材料和方法
1.1 研究地概况及截留降雨处理
试验样地(34.80° N, 107.97° E, 海拔1 430 m)位于陕西省永寿县槐平林场, 属于黄土高原沟壑区的温带半湿润森林区(Tsunekawa et al., 2014; 杜盛和刘国彬, 2015)。据永寿县气象局资料, 当地年平均气温10.8 ℃, 年降水量601.6 mm, 其中70%发生在7-9月, 年潜在蒸散约807.4 mm (Wang et al., 2015)。刺槐人工林固定样地(20 m × 20 m)布设于东北向坡面, 坡度25°, 林龄35年(2015年测), 林分密度 1β700株·hm-2, 林分平均胸径14.0 cm, 平均树高 14.7 m。2014年和2015年生长季林分叶面积指数分别为2.54和2.14。降雨截留板于2015年4月开始设置, 在树木行间搭建的塑料材质截留板占截留降雨处理区样地面积的57.8%, 高度1-2 m, 可将截留的穿透雨导流至样地外。
通过设置穿透雨收集筒, 测量林分多次降雨事件的穿透雨比例, 依据截雨板面积比例, 计算得到截留降雨处理区截留降雨约为总降雨量的47.5%。
1.2 环境因子监测
通过安装于样地外开阔地的自动气象站对主要气象因素连续自动监测。测定指标包括太阳辐射、空气温度、空气湿度和降雨量等。太阳辐射监测采用LI-200型传感器(LI-COR, Lincoln, USA), 水平安装于距地面2 m高的观测塔顶端; HMP110型温湿度传感器(Vaisala, Helsinki, Finland)安装于距地面 1.8 m高的防辐射罩内。太阳辐射和温湿度数据每 30 s读取一次, 用CR1000数据采集器(Campbell Scientific, Logan, USA)记录每30 min的平均值; 降雨量由7852型翻斗式自记雨量桶(Davis Instruments, Hayward, USA)测定, 水平安装于地面50 cm高处。为反映大气温湿度的协同效应, 本文采用Campbell和Norman (1998)公式依据空气温度(T, ℃)和相对湿度(RH, %)计算空气水汽压亏缺(VPD, kPa), 其计算公式为:$VPD=0.611{{\text{e}}^{\left( \frac{17.502T}{T+240.97} \right)}}\left( 1-RH \right)$
同时, 在截留降雨处理区和对照区内, 均安装土壤水分自动监测系统, 在100 cm深度内土壤剖面上设置6个S-SMC-M005土壤水分探头(Onset, Bourne, USA), 对不同深度土壤水分实时连续监测, 每60 s读取一次数据, 每隔1 h记录一个平均值, 存储于HOBO的H21-002型数据采集器中(Onset, Bourne, USA)。按照各探头所代表的土层深度加权平均计算获得0-100 cm土层的平均土壤含水量。
1.3 树干木质部边材液流测定
本研究测定6株生长正常、具代表性的刺槐样树的树干液流。其中1-3号样树位于截留降雨处理区, 4-6号样树位于对照区。6株样树基本信息见表1。Table 1
表1
表1供试样树基本信息
Table 1
| 年份 Year | 样树号 Sample tree No. | 树高 Tree height (m) | 胸径 Diameter at breast height (cm) | 边材厚度 Sap wood thinkness (cm) |
|---|---|---|---|---|
| 2014 | 1 | 14.1 | 13.8 | 3.6 |
| 2 | 17.7 | 19.5 | 4.6 | |
| 3 | 10.7 | 10.3 | 2.9 | |
| 4 | 10.4 | 10.4 | 2.9 | |
| 5 | 10.6 | 10.4 | 2.9 | |
| 6 | 18.7 | 20.0 | 4.7 | |
| 2015 | 1 | 16.5 | 14.1 | 3.6 |
| 2 | 19.9 | 20.0 | 4.7 | |
| 3 | 10.7 | 10.3 | 2.9 | |
| 4 | 11.3 | 10.8 | 3.0 | |
| 5 | 11.3 | 10.5 | 2.9 | |
| 6 | 18.8 | 20.3 | 4.7 |
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采用长10 mm的Granier型热扩散探针对样树边材进行液流监测, 在样树南北两侧各安装一组探针, 包括参考和加热探针, 两探针间距约15 cm, 采用专用电流调节装置为加热探针提供稳定电流以保持0.15 W功率的持续加热(James et al., 2002; Wang et al., 2010)。为防止太阳辐射对树干造成自然温度梯度差, 将所有探针覆盖铝箔。采用CR1000数据采集器每30 s读取一次加热和参考探针的温差, 并记录每30 min的平均值。根据Granier经验公式(Granier, 1987)计算液流通量密度, 计算公式如下:
${{F}_{\text{d}}}=119\times {{\left( \frac{\Delta {{T}_{\text{MAX}}}-\Delta T}{\Delta T} \right)}^{1.231}}$
式中, Fd为液流通量密度(mL·m-2·s-1), ?T为两探针之间的温度差, ?TMAX为液流通量密度为0时两探针间的温度差值, 通常为温度差的最大值。
1.4 数据分析与处理
本文涉及液流数据为截留降雨试验布设前的2014年7月以及截留降雨试验布设后的2015年7月期间典型天气(非阴天和雨天)监测值。使用Baseliner 软件将探针温度差数据转换为树干液流通量密度数 据, 通过SigmaPlot 12.5软件建立截留降雨处理区和对照区样树液流通量密度与空气水汽压亏缺的回归方程。选取两个试验时段内从早晨(7:00)液流启动到液流通量密度达到最大值(14:00)之间液流迅速增长期的数据, 采用线性回归方程拟合分析该时段平均液流通量密度与空气水汽压亏缺的响应关系。使用SPSS 23.0统计分析软件对试验数据分析和处理, 并对不同处理的样本拟合方程系数进行差异性检验。作图工具为SigmaPlot 12.5。2 结果
2.1 截留降雨处理前与截留降雨处理中降雨量及林地土壤含水量变化特征
选取截留降雨处理实施前后的生长盛期各一个月(2014和2015年7月), 两个时段内研究区的降雨量和平均土壤含水量变化动态如图1所示。从图中可以看出, 土壤含水量的变化动态与降雨密切相关, 降雨事件使得土壤含水量得到明显的补充, 但截留降雨处理区和对照区对降雨的响应不尽相同。实施截留降雨处理期间(2015年7月), 处理区土壤含水量(22.59%)显著低于(p < 0.001, n = 31)对照区土壤含水量(23.76%), 且对照区土壤含水量在降雨事件后补充迅速, 变化幅度较为明显, 而截留降雨处理区的土壤含水量变化幅度总体较小, 在雨量较小的降雨事件后, 截留降雨处理区土壤含水量没有明显变化。例如, 在2015年7月19日出现40.64 mm的短时间强降雨事件后, 对照区的平均土壤含水量升高了1.60%, 而截留降雨处理区的土壤含水量只升高了1.08%; 在2015年7月23日38.35 mm的降雨事件后, 对照区的土壤含水量升高了0.92%, 截留降雨处理区的土壤含水量仅升高了0.09%。但是, 在降雨过后, 对照区土壤含水量的下降幅度明显大于截留降雨处理区, 说明对照区的蒸散水平总体上高于处理区。图1
新窗口打开|下载原图ZIP|生成PPT图1两个试验时段土壤含水量(SWC)及降雨量动态。
Fig. 1Soil water content (SWC) and precipitation during the two study periods.
尽管两个试验时段属于两年内对应的同期, 但是降雨量和土壤水分动态也都有所不同。2014年对照区7月初的土壤含水量为23.79%, 而2015年7月初的土壤含水量为25.62%, 比2014年高1.83%; 两个试验时段内的降雨量差异也极为明显, 2014年该月内降雨8次, 总降水量43.18 mm, 而2015年该月内降雨13次, 总降水量达127.76 mm。由于2015年的降雨事件多为强降雨, 雨量大但降雨时间短, 在一定程度上影响了对土壤水分的补充作用, 因此2014和2015年同期该月末的土壤含水量分别为20.42%和22.54%, 差值较月初略有扩大。
2.2 截留降雨处理前与截留降雨处理中刺槐边材液流日变化特征
为了阐明截留降雨处理对树干边材液流的影响, 在截留降雨处理前(2014年)和截留降雨处理中(2015年)各选择了6个较为典型的天气(晴天或多云), 对6株样树的液流日变化动态进行对比分析(图2)。从图中可以看出, 虽然处理区和对照区样树间存在个体差异, 相同样树在不同年份、不同日期的表现也有所不同, 但日变化的总体趋势都大致相同, 基本反映了对当日太阳辐射和空气水汽压亏缺的响应。刺槐液流通常于7:00启动, 在12:00左右到达峰值, 稍早于太阳辐射和空气水汽压亏缺的峰值时间。12:00-15:00为液流通量密度较为稳定的高峰段, 15:00后开始下降, 于次日凌晨日出前达到最低点。该区域刺槐液流日变化曲线通常为单峰型, 偶尔受气象因子影响呈现不规则的变化, 但总体上与太阳辐射和空气水汽压亏缺变化趋势相同, 说明在日尺度上蒸腾作用的主要驱动因子是太阳辐射及空气水汽压亏缺。图2
新窗口打开|下载原图ZIP|生成PPT图2两试验时段刺槐样树液流通量密度及气象因子日变化曲线(2015年7月14日为阴天, 未包括)。
Fig. 2Diurnal courses of sap flux density of sample trees and meteorology factors during two study periods (14 July 2015 was excluded from analyses due to overcast).
虽然两组样树因个体差异在截留降雨处理前的2014年也存在液流通量密度的差异, 但实施截留降
雨处理后, 2015年截留降雨处理区和对照区样树之间液流通量密度的差异比2014年有明显的增大, 表明截留降雨处理明显降低了液流日变化的峰值。
为了联系气象环境因子比较处理之间及两个试验时段的液流通量密度, 将两个时段的观测值进行汇总分析(表2)。结果表明, 两个时段的平均日总太阳辐射和空气水汽压亏缺比值分别为1.07和0.81, 即差值在20%之内; 样树1-3 (对照区)平均液流通量密度对应的比值为0.96, 处理区样树4-6平均液流通量密度对应的比值却仅为0.68。说明截留降雨处理中的样树液流通量密度不仅远低于同一时期的对照区样树, 而且远低于处理实施前的水平。
Table 2
表2
表2两个试验时段太阳辐射、空气水汽压亏缺、液流通量密度及比值(平均值±标准误差, n = 6)
Table 2
| 测定时段 Study period | 平均日总太阳辐射 Mean daily solar radiation (MJ·m-2·d-1) | 平均空气水汽压亏缺 Mean vapor pressure deficit (kPa) | 样树1-3平均液流通量密度 Mean sap flux density of sample tree 1-3 (mL·m-2·s-1) | 样树4-6平均液流通量密度 Mean sap flux density of sample tree 4-6 (mL·m-2·s-1) |
|---|---|---|---|---|
| 处理前 Before treatment (2014) | 20.62 ± 1.69 | 0.65 ± 0.03 | 3.53 ± 2.67 | 2.42 ± 1.84 |
| 处理期 Treatment (2015) | 21.96 ± 1.51 | 0.53 ± 0.0201 | 3.38 ± 2.93 | 1.64 ± 1.39 |
| 处理期/处理前Treatment/Before treatment | 1.07 | 0.81 | 0.96 | 0.68 |
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2.3 截留降雨处理前与截留降雨处理中刺槐液流通量密度对主要环境因子的响应特征
一般认为, 在短时间尺度上植物的蒸腾作用主要受到气象因子的影响, 空气水汽压亏缺和光照是植物气孔蒸腾的主要驱动因子(Green, 1993; Zhang et al., 1997)。目前, 对于树干液流通量密度对气象环境因子的响应规律多采用指数饱和曲线函数进行拟合分析, 例如Du等(2011)以及张建国等(2011)。由于空气水汽压亏缺和太阳辐射较低蒸腾作用未出现气孔调节时, 液流通量密度与气象环境因子的关系近似线性, 为了避免空气水汽压亏缺和液流通量密度时滞效应对二者的回归关系分析产生影响, 采用线性回归方程y = ax分别对样树1-3和样树4-6的平均液流通量密度在迅速上升时段对空气水汽压亏缺的响应进行拟合。结果(图3)表明, 两年试验期间的线性回归关系均达到极显著水平。截留降雨处理前, 样树1-3与样树4-6的回归方程斜率分别为8.41和6.78, 斜率值相近; 截留降雨处理中, 样树1-3和样树4-6的斜率值差异加大, 分别为12.33和5.34。进一步对拟合直线的斜率进行差异显著性检验, 结果(表3)显示, 在2014年试验期间, 样树1-3与样树4-6的拟合方程斜率差异未达到显著水平(p > 0.05); 在2015年截留降雨处理中, 两组样树的拟合方程斜率差异呈现极显著水平(p < 0.001), 进一步说明了截留降雨处理中的样树液流通量密度随着空气水汽压亏缺上升速率明显低于对照区样树, 且相同气象条件下, 截留降雨处理下的样树液流通量密度也明显低于对照区样树。可以推测, 截留降雨处理导致的土壤供水不足使蒸腾作用明显受到吸水阻力的抑制。
图3
新窗口打开|下载原图ZIP|生成PPT图3两试验时段液流通量密度在上升阶段对空气水汽压亏缺的响应特征。
Fig. 3Response patterns of sap flux density to vapor pressure deficit for the arising stage in the morning.
Table 3
表3
表3两试验时段平均液流通量密度与空气水汽压亏缺拟合直线斜率的差异性检验
Table 3
| 年份 Year | 样树1-3 Sample tree 1-3 | 样树4-6 Sample tree 4-6 | 斜率差异检验 Difference between slopes |
|---|---|---|---|
| 2014 | a = 8.41 | a = 6.78 | NS |
| R2 = 0.64 | R2 = 0.63 | ||
| p < 0.000 1 | p < 0.000 1 | ||
| 2015 | a = 12.33 | a = 5.34 | p < 0.001 |
| R2 = 0.59 | R2 = 0.69 | ||
| p < 0.000 1 | p < 0.000 1 |
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3 讨论
截留降雨处理明显降低了该区域土壤含水量, 对比对照区的土壤含水量, 截留降雨处理区土壤含水量波动也较小。通常情况下, 两区土壤含水量的差异在降雨事件后增大, 随着时间逐渐减小, 直到下一次降雨的发生。说明截留降雨处理不仅降低了降雨对土壤含水量的补充作用, 而且降低了总的蒸散作用。由于该地区地下水位较深, 降雨是土壤水分补充的唯一来源, 减少降水量必然会引起土壤含水量的降低, 最终导致林分蒸腾耗水大幅度降低。关于黄土高原其他地区刺槐人工林的研究有相似的报道, Du等(2011)对黄土高原半干旱区的辽东栎(Quercus liaotungensis)、刺槐和山杏(Armeniaca sibirica)树干液流在降雨前后的对比研究发现, 刺槐为干旱敏感型树种, 其液流对降雨事件的响应较强烈, 林地的土壤含水量变化对其蒸腾耗水影响大, 而乡土树种对土壤水分的敏感度较低, 对降雨事件的响应不明显。王进鑫等(2005)通过旱棚人工控水对侧柏(Platycladus orientalis)、刺槐幼树的生理需水规律、蒸腾耗水与土壤含水量关系的研究表明, 刺槐的蒸腾耗水量随土壤供水能力的增加而增大, 年均生理需水量是侧柏的5.13倍。
部分其他阔叶类树种蒸腾耗水对降水量变化响应的研究结论也基本相似。Limousin等(2009)通过对地中海地区Quercus ilex林的研究发现, 减少该林分29%的降雨会导致林分年蒸腾耗水减少23%, 截留降雨处理对蒸腾作用的影响持续了整个处理期, 即使在雨季, 截留降雨处理样树的蒸腾耗水也明显低于对照的样树。Besson等(2014)通过在葡萄牙南部对Quercus suber林进行了截留降雨和灌溉的试验得出了同样的结论: 在干旱的夏季, 减少20%降雨处理的Q. suber冠层蒸腾耗水降低了20%-27%, 林分年蒸腾耗水量降低了8%-13%, 而同一时期增加降水量的Q. suber冠层蒸腾增加了14%-63%, 林分年蒸腾耗水量增加了11%, 但样树蒸腾耗水存在季节差异, 由于Q. suber在生长高峰时期主要依赖降雨补充水分, 而干旱的夏季则主要依赖地下水, 所以春天生长季节截留降雨和对照样地之间蒸腾耗水的差异明显加大, 而夏季差异明显减小。Fisher等(2007)在亚马孙地区的人工截留降雨试验发现, 两个干旱时期中自然条件的林分蒸腾量没有显著变化, 而截去50%降雨的林分年蒸腾量降低了41%-44%, 在极度干旱时期, 林分蒸腾量甚至减少了80%, 说明林分对土壤干旱的抵御能力存在阈值。同时, Pataki和Oren (2003)对河谷地落叶林6个树种的冠层气孔导度研究发现, 在干旱时期, 除北美鹅掌楸(Liriodendron tulipifera)的液流受影响下降外, 其余的北美枫香(Liquidambar styraciflua)、美国白蜡(Fraxinus Americana)、白橡(Quercus alba)、山核桃(Carya tomentosa)和红栎(Quercus rubra)液流都没有下降, 仅表现为生长季后期叶片衰老和提前凋落。可以看出, 不同树种对降雨改变引起土壤干旱的适应策略和能力存在差异。
Oren等(1996)认为, 植物从土壤到大气的水力导度的大小可以从液流通量密度对空气水汽压亏缺变化响应的相关关系的斜率反映出, 斜率越大说明该植物水力导度越大, 即相同水势梯度下, 土壤水分从植物根系传输到冠层的效率越高, 同时, 土壤含水量下降可能会导致水力导度减小。Du等(2011)发现延安地区的刺槐在降雨事件前后液流的变化远大于乡土树种辽东栎, 显示刺槐对土壤水分的变化有比较显著的反应。本试验中, 对两年间截留降雨处理区和对照区样树液流通量密度与空气水汽压亏缺回归关系的差异性检验发现, 截留降雨处理区样树拟合关系斜率值有明显减小的趋势, 说明刺槐的水力导度随着土壤含水量降低发生了显著变化, 不能迅速响应空气水汽压亏缺的变化, 气孔导度和光合作用必然受到影响。
不少研究人员认为, 减少蒸腾耗水会导致林分生产力的降低。Alberti等(2007)在意大利对Arbutus cenedo林地的研究发现, 减少降雨使得该区域生态系统蒸散降低了35%, 最终导致该生态系统初级生产力减少了35%。Fisher等(2007)的模型模拟研究有相似的结论, 在两年截留降雨处理下, 其试验区域的初级生产力降低了13%-14%。袁瀛等(1996)在黄土丘陵区的研究表明, 年降雨量对刺槐胸径生长的影响最为突出, 远大于林龄、坡度、林分密度、地形部位等其他指标, 是该地区刺槐生长的限制因子。结合本试验研究内容, 可以推断截留降雨处理减少了穿透雨量, 降低了土壤含水量, 从而引起刺槐人工林蒸腾耗水大幅度降低, 响应环境因子变化能力也大幅度降低, 这种影响将会进一步降低该林地的生产力。随着全球气候变化, 如果该地区降水量出现减少, 人工林的生产力和稳定性将面临严峻挑战。
4 结论
本研究基于对布设人工截留降雨处理前后2个生长季内典型天气刺槐树干液流通量密度特征的分析, 重点对比了处理区和对照区样树对气象环境因子的响应差异, 可以得出如下结论:(1)截留降雨处理减少降水量输入导致土壤含水量显著降低。在降雨事件后, 截留降雨处理区的土壤含水量变化幅度总体较小, 在雨量较小的降雨事件后, 截留降雨处理区土壤含水量甚至没有明显变化。
(2)截留降雨处理中的样树液流通量密度不仅远低于同一时期的对照区样树, 而且远低于处理实施前的水平。其中, 处理前的2014年与处理期的2015年平均液流通量密度比值, 对照区样树的比值为0.96, 而处理区对应的比值仅为0.68。
(3)截留降雨处理导致的土壤水分下降, 进一步使蒸腾作用受到吸水阻力的限制。截留降雨处理中的样树液流通量密度随空气水汽压亏缺上升的速率明显低于对照区样树, 且相同气象条件下, 截留降雨处理下的样树液流通量密度也明显低于对照区 样树。
(4)降雨减少在短期内会表现为土壤含水量减少, 导致林分蒸腾耗水下降和响应环境因子变化能力的降低, 在长时间尺度上还具有林分生产力降低的必然性。
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URL [本文引用: 1]
Will Mediterranean terrestrial ecosystems be affected by the expected changes in precipitation regimes? If so, by how much and in which direction? These questions are at the basis of the research performed in context of the EU MIND project, whose key objectives were: i) to investigate the potential effects of increasing drought on Mediterranean terrestrial ecosystems at the process, ecosystem and regional scales and ii) to assess ecosystem vulnerability to changes in rainfall patterns. A network of experimental study sites has been created in Portugal, Spain, France and Italy, where field manipulations alter the amount of water available to the ecosystem. The most up-to-date methods of ecophysiology, micrometeorology, soil ecology and remote sensing have been used to elucidate the mechanisms that regulate the response of vegetation and soil to changes in water availability. This information is providing the basis for the implementation and validation of simulation models capable of predicting the drought response of Mediterranean terrestrial ecosystems, and their vulnerability to future climate change, on a larger scale. The out-coming results are elucidating how water availability affects plant ecophysiological processes, the dynamics of soil carbon and the overall exchange of mass and energy between the land and the atmosphere. This paper focuses on some of the important, yet preliminary, results on C and energy fluxes that have been obtained at the large scale troughfall manipulation experiment (Tolfa, Italy), in a forest dominated by Arbutus unedo L.
DOIURL [本文引用: 1]
This study details the physiological responses of cork oak (Quercus suber L.) to manipulated water inputs. Treatments named as dry, ambient and wet, which received 80, 100 and 120% of the annual precipitation, respectively, were applied to a Mediterranean woodland in southern Portugal. Tree ecophysiology and growth were monitored from 2003 to 2005. The impacts of the water manipulation were primarily observed in tree transpiration, especially during summer drought. Rainfall exclusion reduced the annual stand canopy transpiration by 10% over the 2-year study period, while irrigation increased it by 11%. The accumulated tree transpiration matched precipitation in spring 2004 and 2005 at the stand level, suggesting that cork oak trees rely on precipitation water sources during the peak of the growing season. However, during the summer droughts, groundwater was the main water source for trees. Despite the significant differences in soil water content and tree transpiration, no treatment effects could be detected in leaf water potential and leaf gas exchange, except for a single event after spring irrigations in the very dry year 2005. These irrigations were intentionally delayed to reduce dry spell duration during the peak of tree growing season. They resulted in an acute positive physiological response of trees from the wet treatment one week after the last irrigation event leading to a 32% raise of stem diameter increment the following months. Our results suggest that in a semi-arid environment precipitation changes in spring (amount and timing) have a stronger impact on cork oak physiology and growth than an overall change in the total annual precipitation. The extreme drought of 2005 had a negative impact on tree growth. The annual increment of tree trunk diameter in the ambient and dry treatments was reduced, while it increased for trees from the wet treatment. Water shortage also significantly reduced leaf area. The latter dropped by 10.4% in response to the extreme drought of 2005 in trees from the ambient treatment. The reduction was less pronounced in trees of the wet treatment (7.6%), and more pronounced in trees of the dry treatment (14.7%). Cork oak showed high resiliency to inter-annual precipitation variability. The annual accumulated tree transpiration, the minimum midday leaf water potential and the absolute amount of groundwater used by trees appeared unaffected by the extreme drought of 2005. Our study shows that cork oak rapidly and completely recovered from the extreme dry year of 2005 or from rainfall exclusion. Our results support the eco-hydrological equilibrium theory by which plant acquire complementary protective mechanisms to buffer the large variability in water availability experienced in semi-arid ecosystems. In optimizing their structural biomass increase in response to increasing drought stress, cork oak trees succeeded in restricting water losses to maintain the minimum leaf water potential above the critical threshold of xylem embolism, though with narrower hydraulic safety margins in 2005. Our findings highlight cork oak's sensitivity to the amount and timing of late spring precipitation. This could be critical as future climate scenarios predict a reduction of spring precipitation as well as enhanced severity of droughts in the Iberian Peninsula by the end of the 21st century. In inducing water stress before the onset of summer droughts, the predicted spring precipitation decline could drive the species closer to the threshold of catastrophic xylem embolism at the peak of the drought period.
[本文引用: 1]
DOIURL [本文引用: 2]
Transpiration in a mixed old stand of sub-boreal forest in the Norunda region (central Sweden) was estimated on the basis of direct measurement of sap flow rate in 24 large Scots pine and Norway spruce trees in July and August 1993. Sap flow rate was measured using the trunk tissue heat balance method based on internal (electric) heating and sensing of temperature. Transpiration was only 0.7 mm day in a relatively dry period in July (i.e. about 20% of potential evaporation) and substantially higher after a rainy period in August. The error of the estimates of transpiration was higher during a dry period (about 13% and 22% in pine and spruce, respectively) and significantly lower (about 9% in both species) during a period of sufficient water supply. Shallow-rooted spruce trees responded much faster to precipitation than deeply rooted pines.
[本文引用: 2]
[本文引用: 2]
DOIURL [本文引用: 3]
In the semiarid Loess Plateau region of China, ecosystems are frequently affected by water shortages. Late spring and early summer are periods when forest communities tend to suffer from soil drought. To clarify the water-use strategies of the main species in this area, the xylem sap flow of trees from three species in the field was monitored for three successive periods in summer using Granier-type thermal dissipation probes. Vapor pressure deficit (VPD), solar radiation ( R s) and soil moisture had varying influences on sap flux density ( F d) in the species. Normalized F d values could be fitted to VPD using an exponential saturation function, but the fit was better with a derived variable of transpiration (VT), an integrated index calculated from VPD and R s. From differences in model coefficients, the species were roughly divided into two types with contrasting drought sensitivity. The exotic Robinia pseudoacacia was defined as drought-sensitive type. It showed higher sapflow increases in response to rainfall, suggesting a high water demand and high influence of soil water conditions on transpiration. This species showed relatively late stomatal response to increasing VPD. The wide-peak pattern of diurnal sapflow course also suggests relatively low stomatal regulation in this species. The drought-insensitive type consisted of the naturally dominant Quercus liaotungensis and an indigenous concomitant species, Armeniaca sibirica, in the forest. The sap flow of these species was not very sensitive to changes in soil water conditions. The results suggest that typical indigenous species can manage the water consumption conservatively under both drought and wet conditions. Variations in water use strategies within indigenous species are also detected.
DOIURL [本文引用: 2]
Warmer and drier climates over Eastern Amazonia have been predicted as a component of climate change during the next 50–100 years. It remains unclear what effect such changes will have on forest–atmosphere exchange of carbon dioxide (CO 2 ) and water, but the cumulative effect is anticipated to produce climatic feedback at both regional and global scales. To allow more detailed study of forest responses to soil drying, a simulated soil drought or 'throughfall exclusion' (TFE) experiment was established at a rain forest site in Eastern Amazonia, Brazil, for which time-series sap flow and soil moisture data were obtained. The experiment excluded 50% of the throughfall from the soil. Sap flow data from the forest plot experiencing normal rainfall showed no limitation of transpiration throughout the two monitored dry seasons. Conversely, data from the TFE showed large dry season declines in transpiration, with tree water use restricted to 20% of that in the control plot at the peak of both dry seasons. The results were examined to evaluate the paradigm that the restriction on transpiration in the dry season was caused by limitation of soil-to-root water transport, driven by low soil water potential and high soil-to-root hydraulic resistance. This paradigm, embedded in the soil–plant–atmosphere (SPA) model and driven using on-site measurements, provided a good explanation ( R 2 > 0.69) of the magnitude and timing of changes in sap flow and soil moisture. This model-data correspondence represents a substantial improvement compared with other ecosystem models of drought stress tested in Amazonia. Inclusion of deeper rooting should lead to lower sensitivity to drought than the majority of existing models. Modelled annual GPP declined by 13–14% in response to the treatment, compared with estimated declines in transpiration of 30–40%.
DOIURLPMID [本文引用: 1]
Abstract Transpiration of a Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stand was evaluated by sap flow measurements during a 4-month period. Between-tree variation in sap flow depended on crown class. On a sunny day, total transpiration was 1.6, 8.0 and 22.0 liters day(-1) for suppressed, codominant and dominant trees, respectively. Transpiration estimated by sap flow fell below potential evapotranspiration when available soil water decreased below 30% of its maximum value. Sap flow measurements gave transpiration values similar to those obtained by the water balance method.
DOIURL [本文引用: 1]
The radiation balance of an isolated walnut tree was measured using an experimental Whirligig device. The total amount of all-wave radiation absorbed by the tree canopy was used to estimate transpiration rates using a Penman-Monteith model. The results compared favourably with tree water use, measured by the heat-pulse technique. The total amount of photosynthetically active radiation (PAR) absorbed by the tree canopy was combined with a photosynthetic light response curve to estimate net photosynthesis rates. The results compare favourably with published data from other tree canopies. Daily energy balance calculations showed that on average, about two-thirds of the total radiant energy absorbed by the tree canopy was dissipated as latent heat in the form of transpiration. The dominant environmental variable influencing transpiration was the vapour pressure deficit of the air. Almost two-thirds of the net latent heat flux was attributable to the vapour pressure deficit component, with the remainder owing to the radiation component. Daily transpiration-assimilation ratios varied from day to day in response to changing environmental conditions, but generally decreased with increasing net photosynthesis and with increasing transpiration. This appears to be the first time that such a direct measurement of the energy balance and photosynthesis of a single tree has been made. (author)
[本文引用: 1]
[本文引用: 1]
DOIURLPMID [本文引用: 1]
Abstract Robust thermal dissipation sensors of variable length (3 to 30 cm) were developed to overcome limitations to the measurement of radial profiles of sap flow in large-diamet..
DOIURL [本文引用: 1]
Shrub encroachment into grass-dominated biomes is occurring globally due to a variety of anthropogenic activities, but the consequences for carbon (C) inputs, storage and cycling remain unclear. We studied eight North American graminoid-dominated ecosystems invaded by shrubs, from arctic tundra to Atlantic coastal dunes, to quantify patterns and controls of C inputs via aboveground net primary production (ANPP). Across a fourfold range in mean annual precipitation (MAP), a key regulator of ecosystem C input at the continental scale, shrub invasion decreased ANPP in xeric sites, but dramatically increased ANPP (>1000 g m 2 ) at high MAP, where shrub patches maintained extraordinarily high leaf area. Concurrently, the relationship between MAP and ANPP shifted from being nonlinear in grasslands to linear in shrublands. Thus, relatively abrupt (<50 years) shifts in growth form dominance, without changes in resource quantity, can fundamentally alter continental-scale pattern of C inputs and their control by MAP in ways that exceed the direct effects of climate change alone.
DOIURL [本文引用: 1]
Black locust (Robinia pseudoacacia L.) is a tree species of high economic and ecological value, but is also considered to be highly invasive. Understanding the global potential distribution and ecological characteristics of this species is a prerequisite for its practical exploitation as a resource. Here, a maximum entropy modeling (MaxEnt) was used to simulate the potential distribution of... [Show full abstract]
DOIURL [本文引用: 2]
In the Mediterranean basin, precipitation is expected to decline as a consequence of climate change. The response of a Quercus ilex forest in southern France to such a decline in water availability was studied using a 4-year throughfall exclusion experiment. Seasonal courses of sap flow and leaf water potential were obtained from 2004 to 2007 and used to characterize tree water relations in a control and a dry treatment. The experiment reduced the average precipitation input to the soil by 29%, and resulted in a 23% reduction in annual transpiration. Soil water potential was significantly lower in the dry treatment only during summer drought, but transpiration was reduced all year round even during well-watered periods. Despite a tight stomatal control over transpiration, whole-tree hydraulic conductance was found to be lower in the trees growing in the driest conditions. This reduction in water transport capacity was observed jointly with a reduction in leaf transpiring area. Canopy leaf area decreased by 18% in the dry treatment as a consequence of the throughfall exclusion, which was found to validate the ecohydrological equilibrium theory.
DOIURL [本文引用: 1]
This study is focused on the analysis of the relationship between sap-flow-derived transpiration measured in a Scots pine stand in the Vallcebre research catchments (NE Iberian Peninsula) and meteorological and rainfall data. The first part of the study is focused on the analysis of temperature and rainfall anomalies. Then, the Scots pine transpiration response to inter-annual rainfall variability, soil water stress and water table depth variations during the period 1997-2000 is analysed. This period includes the extremely dry year of 1998, which allows us to infer the response of Scots pine transpiration to severe droughts. Scots pine transpiration during the summer presented a high inter-annual variability, largely related to rainfall amounts. Daily transpiration during dry summers was 40% of the transpiration of a summer day with average rainfall. Moreover, during dry summers, transpiration rates were not fully recovered even after significant rainfall events. The analysis of the dependence of Scots pine transpiration on available water indicated the strong limitation on transpiration induced by water content in the whole soil profile as well as by water table position. Under these drought conditions, a reduction of runoff and deep water stores was observed at the catchment scale, suggesting that the predicted increase in the frequency of severe summer droughts may threaten the current role of Mediterranean mountain catchments as suppliers of water resources for lowland areas. Copyright 2010 John Wiley & Sons, Ltd.
DOIURL [本文引用: 1]
The fecundity of clonal animals and plants is determined by the number of gravid modules (polyps, zooids, shoots, ramets) and their reproductive output. We examined the fecundity of modules (polyps) and colonies of six reef-building corals (Acropora hyacinthus, A. nana, A. gemmifera, A. millepora, Goninstrea retiformis, and Stylophora pistillata) to explore how modularity influences reproductive strategies and the evolution of life histories in clonal animals. In unitary, aclonal organisms, fecundity often reaches a plateau or declines in old age. In contrast, we found that fecundity of colonies was indeterminate because vegetative growth can lead to an indefinite number of repeated, reproductive modules. However, colony fecundity was not a simple linear function of the number of modules. The species ranking of polyp fecundities (G. retiformis > the Acropora species > S. pistillata) was very different from the ranks of size-specific colony fecundities (A. hyacinthus, A. millepora, A. gemmifera > A. nana and G. retiformis). Colony fecundity for small S. pistillata was the lowest of all, but large colonies were more fecund than any of the other species at a comparable colony size (despite Stylophora having the lowest polyp fecundity). This contrast highlights clearly the effects of modularity on the reproductive biology and life histories of clonal organisms. The volume of eggs and testes, and the number of eggs and testes per polyp varied greatly among species (20-, 13-, 17-, and 3-fold, respectively). Egg volume was smallest for S. pistillata (the only brooder in the study) and for G. retiformis (which also had the most eggs per polyp, indicating a trade-off between egg size and number). The total reproductive volume per polyp (egg and testes combined) varied three-fold among the six species, and was correlated with a similar range of polyp diameters. In some cases, components of polyp fecundity depended on colony size; egg size in A. hyacinthus and A. nana and the number of planulae per polyp in S. pistillata increased by two- to fourfold with a one to two order of magnitude change in colony size. However, egg size was constant for the other species. Similarly, colony size had no effect on egg or testes number per polyp or testes volume per polyp for any species. We also found striking differences in sex allocation, which may relate to the fertilization biology of these hermaphroditic species. The ratio of total egg volume to testes volume per polyp varied fivefold, and was lowest for S. pistillata (a brooder) and G. retiformis (which produced the most and smallest eggs). The ratio increased with colony size for all species, especially A. hyacinthus. An early investment predominantly in testes allows sex to commence without the initial expense of egg production, perhaps so that colony growth can continue to a larger, safer size. All species had a characteristic colony size at maturation, which varied ninefold among taxa, corresponding to a minimum puberty age of 1-3 yr. This is the first comparative study to simultaneously measure male and female function in a range of clonal animals.
DOIURL [本文引用: 1]
Comparative field studies were conducted on Acacia tortilis (Forsk.) Hyne and Acacia xanthophloea Benth. trees growing in a semi-arid environment in Kibwezi, Kenya, to assess root access to soil water at varying soil depths and how this may affect the expression of morphological and physiological traits developed during drought. Measurements of soil water content, leaf growth, shoot elongation, sap flow in the xylem of stems and branches, leaf water potential, leaf transpiration and stomatal conductance were carried out. Further, water use efficiency (WUE) over long-term periods was examined via carbon isotope discrimination (δ 13C) on leaves. Whole tree and leaf specific hydraulic conductance were determined from sap flux or leaf transpiration and the water potential gradient between soil (as predawn potential) and canopy, respectively. Leaf growth and shoot elongation depended on soil water availability (SWC) and plant tissue water status. A. xanthophloea showed greater (40 kg d 611) water use compared to A. tortilis trees of comparable sizes (20 kg d 611) during favorable conditions of SWC. Decline in SWC reduced water use and the onset and rate of decline in sap flux was determined by the rooting depth. A. xanthophloea showed earlier response (onset at SWC=0.24 m 3 m 613) to water stress than A. tortilis (onset at SWC=0.14 m 3 m 613). Midday depression in stomatal conductance and subsequent decline in transpiration during favorable SWC as observed in A. xanthophloea was attributed to increased hydraulic resistance and stomatal closure. Rooting patterns and root characteristics could account for the observed morphological and physiological differences between A. tortilis and A. xanthophloea as well as between small and large A. tortilis trees. However, seasonal responses were modified by species-inherent characteristics, which are expressed during drought. Access to deeper soil water resources and the abilities of trees to extract and efficiently transport water may explain differences in drought resistance among species and tree distribution in the arid savanna.
DOIURL [本文引用: 2]
In order to evaluate factors controlling transpiration of six common eastern deciduous species in North America, a model describing responses of canopy stomatal conductance ( G S) to net radiation ( R N), vapor pressure deficit ( D) and relative extractable soil water (REW) was parameterized from sap flux data. Sap flux was measured in 24 mature trees consisting of the species Carya tomentosa, Quercus alba, Q. rubra, Fraxinus americana, Liriodendron tulipifera, and Liquidambar styraciflua in a bottomland oak-hickory forest in the Duke Forest, NC. Species differences in model coefficients were found during the 1997 growing season. All species showed a reduction in G S with increasing D. R N influenced G S in the overstory shade intolerant L. styraciflua to a larger extent than the other species measured. In addition, despite a severe drought during the study period, only L. tulipifera showed a decline in G S with decreasing REW. The primary effect of the drought for the other species appeared to be early autumn leaf senescence and abscission. As a result, despite the drought in this bottomland forest accustomed to ample water supply, maximum daily transpiration (1.6 mm) and growing season transpiration (264 mm) were similar to a nearby upland forest measured during a year of above average precipitation. These results may aid in assessing differences in water use and the ability of bottomland deciduous species to tolerate alterations in the frequency or amount of precipitation. Results also suggest little variation in water use among forests of similar composition and structure growing in different positions in the landscape and subjected to large interannual variation in water supply.
DOIURL [本文引用: 1]
刺槐是干旱半干旱地区的多用途造林树种，水分生理研究是抗旱造林和林分管理的基础，从苗木、单木和林分三个层面论述了刺槐耗水特性及其研究进展。苗木耗水是林木水分生理研究的基础，刺槐苗木耗水量和耗水速率的日变化均呈单峰型，峰值出现在中午12：00左右。苗木耗水速率除与自身遗传特性有关外，还与土壤水分条件密切相关，随着土壤水分亏缺的加重，耗水速率呈下降趋势。单木耗水除表现与苗木相似的日动态外，其耗水量和蒸腾强度还表现季节动态，生长季节初期和末期耗水量和蒸腾强度较低，生长盛期较强，此外蒸腾耗水还与光照、气温和风速等环境因子呈显著相关关系。林分蒸腾耗水占林分总耗水量的57．7％～60．2％，季节变化与单木相同，一般阴坡耗水大于阳坡，高密度林分耗水量大于低密度林分。
DOIURL [本文引用: 1]
刺槐是干旱半干旱地区的多用途造林树种，水分生理研究是抗旱造林和林分管理的基础，从苗木、单木和林分三个层面论述了刺槐耗水特性及其研究进展。苗木耗水是林木水分生理研究的基础，刺槐苗木耗水量和耗水速率的日变化均呈单峰型，峰值出现在中午12：00左右。苗木耗水速率除与自身遗传特性有关外，还与土壤水分条件密切相关，随着土壤水分亏缺的加重，耗水速率呈下降趋势。单木耗水除表现与苗木相似的日动态外，其耗水量和蒸腾强度还表现季节动态，生长季节初期和末期耗水量和蒸腾强度较低，生长盛期较强，此外蒸腾耗水还与光照、气温和风速等环境因子呈显著相关关系。林分蒸腾耗水占林分总耗水量的57．7％～60．2％，季节变化与单木相同，一般阴坡耗水大于阳坡，高密度林分耗水量大于低密度林分。
DOIURL [本文引用: 1]
Bonnabeau RC Jr.
[本文引用: 1]
[本文引用: 1]
DOIURL [本文引用: 1]
Black locust (Robinia pseudoacacia) is a major reforestation species in the semiarid region in the Loess Plateau of China. There has been increasing concern about the sustainability of the plantations because of their possible high water-use. This study was, accordingly, undertaken to quantify the stand-scale water use of a middle-aged black locust plantation in the region. The thermal dissipation probe method was applied to 27 trees to measure sap flux densities in an experimental plot during the growing season of 2008. The monoculture stand has a basal area of 23.3 m2 ha0908081 and a maximum plant area index (PAI) of 2.89. Sapwood areas were estimated by use of a regressive relationship with the diameter at breast height (DBH) for scaling up of stand transpiration. The results showed that DBH could be a good predictor of sapwood area of individual trees. The diurnal cycles of average sap flux densities differed among DBH classes. Daily transpiration can be predicted from mean daily daytime vapor pressure deficit (VPDm) using a fitted exponential saturation model. Model variables were different among seasons, probably owing to different soil water conditions and leaf phenology. By using the derived model for each month, stand canopy transpiration over the growing season was estimated to be 73.8 mm, with an average daily value of 0.41 mm day0908081 and a maximum of 0.89 mm day0908081. The relatively small estimates of stand transpiration might be attributed to low PAI and sap wood area of the middle-aged stand.
DOIURL [本文引用: 1]
Eleven field experiments were conducted in Yongshou County, Shanxi Province and seven in Luoyang, Henan Province, and five layers of soil were sampled in 20-cm increments to 100cm depth for each experimental field to study the difference of wheat (Triticum aestivum) responses to nitrate and ammonium nitrogen (N) and the relation of its responses to nitrate N cumulative amount in different soil layers. In Yongshou, each experimental site included seven treatments (control, two varieties of nitrate N, two varieties of ammonium N, and two combinations of ammonium to nitrate N in a ratio of 1:2) while in Luoyang, six treatments (only one variety of nitrate N). Total 150kgha1N was added as basal for N fertilization treatments at wheat seeding time. Results showed that differences in two varieties of each N form or combinations were much less than those of N forms. As a whole, wheat responses to nitrate N were better in most cases and in few cases, there was no significant difference between nitrate N and ammonium N on wheat yield. Using averages of yield, yield increase amount (kgha1) and percentage (%) of different N forms for comparison, nitrate N was highest in yield and yield increase, followed by the combination, while the ammonium N was lowest. The lower the amount of accumulated nitrate N in the soil profile, the better the nitrate N superiority. Our finding was that the superiority of nitrate N over ammonium N on wheat yield depended on the accumulative nitrate amounts in soil, and only in soil having low cumulative nitrate N amount at the rooting depth, did the nitrate N show its superiority over the ammonium N. In contrast, if the accumulative nitrate N amount was high, the two N forms had no significant difference on wheat yield.
DOIURL [本文引用: 1]
Loblolly pine (Pinus taeda L.) forests are of great ecological and economic value in the southeastern United States, where nutrient availability frequently limits productivity. The impact of fertilizer application on the growth and water relations of loblolly pine has been investigated by numerous studies; however, few field experiments have examined the effects of drought. Drought is of particular interest due to the potential for climate change to alter soil water availability. In this study, we investigated the impact of fertilizer application and a 30% reduction in throughfall on loblolly pine productivity, transpiration, hydraulic conductance, and stomatal conductance. The study was installed in a ten-year-old loblolly pine plantation on a somewhat poorly drained site in northern Florida. Throughfall reduction did not impact tree productivity or water relations of the trees. This lack of response was attributed to abundant rainfall and the ability of trees to access the shallow water table at this site. Fertilizer application increased basal area production by 20% and maximum leaf area index by 0.5 m22, but it did not affect whole-tree hydraulic conductance or the sensitivity of stomatal conductance to vapor pressure deficit. During the spring, when leaf area and vapor pressure deficit were high, the fertilizer-only treatment increased monthly transpiration by 17% when compared to the control. This relationship, however, was not significant during the rest of the year.
DOIURL [本文引用: 2]
Climate-induced changes in regional precipitation could have important implications for the carbon, water, and nutrient cycles of forest ecosystems. However, few studies have examined the response of deciduous forests to increases or decreases in precipitation. Therefore, the throughfall displacement experiment (TDE) was established in 1993 near Oak Ridge, Tennessee to examine the sensitivity of an upland oak ( Quercus spp.) forest to ambient, wet (+33%), and dry (6133%) precipitation regimes. Sap flux measurements on co-occurring tree species were scaled using species-specific estimates of stand sapwood area to derive daily and seasonal rates of canopy transpiration ( E C ) from 2000 to 2003. With the exception of 2003, which was an extremely wet year, daily E C in the dry plot, and occasionally during extended droughts in the ambient and wet plots, declined as water potential in the upper 0.35 m soil profile approached -3.0 MPa. Seasonal patterns of soil water potential and treatment-specific differences in E C were dependent on precipitation frequency and intensity. Supplemental precipitation added to the wet plot increased seasonal E C on average by 9% (range 611% to 19%), whereas extended periods of drought on the dry plot in 2000, 2001, and 2002 were sufficient to reduce seasonal E C by 26–30% compared with the ambient plot. There was a strong correlation between seasonal E C and the water stress integral, a cumulative index of drought severity and duration. A polynomial fitted to these data indicated that reductions in seasonal E C on the order of 40% were possible given TDE-imposed reductions in soil water potential. Application of this equation to all years of the TDE (1994–2003) revealed considerable interannual and treatment-specific variation in canopy transpiration. In general, a 33% removal of throughfall on the dry plot during 1995, 1998, and 2002 resulted in a 23–32% reduction in seasonal E C compared with the ambient plot. While droughts in deciduous forests are often limited in duration and tend to occur late in the growing season, soil water deficits of the magnitude observed in this study have the potential to impact local and regional forest water budgets.
DOIURL [本文引用: 1]
Sap flow estimates for whole trees (scaled from measurements on selected branches using the heat balance method) were compared with estimates of transpiration based on porometry in a study of poplar trees in an agroforestry system in the south of the UK. Sap flow showed good agreement with the transpiration rate estimated using the Penman-Monteith equation with measured stomatal conductance ( R 2 = 0.886) on six selected days during the season. The dominant environmental variable influencing transpiration was the vapour pressure deficit, as the “aerodynamic term” in the Penman-Monteith equation accounted for more than 70% of daily total transpiration, with the rest due to the “radiation component”. Stomatal conductance, estimated by inverting the Penman-Monteith equation from continuous measurements of sap flow over 55 days, was used to determine the parameters for a multiplicative stomatal conductance model. For an independent data set there was better agreement between measured sap flow and transpiration predicted from the stomatal conductance ( R 2 = 0.90) than for calculated and predicted stomatal conductance ( R 2 = 0.51).
URL [本文引用: 1]
利用Granier树干液流测定系统,长期监测黄土高原半干旱区延安市南郊天然辽东栎林优势木的树干液流,并同步监测环境因子（空气温度、湿度、太阳辐射、土壤含水量）。分析3株优势木边材液流在生长季内各月份的日变化特征以及液流通量密度与环境因子的关系。结果显示：辽东栎液流日变化总体上与太阳辐射和空气水气压亏缺呈相同趋势,但液流峰值出现时间较早,通常为10：00左右。随着生长季内物候变化,液流通量密度总体表现为前期（4—6月）较低、中后期（7—9月）较高、末期（10月）迅速下降的变化趋势。采用指数饱和曲线函数对液流通量密度和空气水气压亏缺进行拟合,有效地反映了各月份液流通量密度对空气水气压亏缺的响应特征。各月份的曲线特征和拟合参数的差异表明,蒸腾耗水过程也受到土壤水分状况等其他因素的影响。
URL [本文引用: 1]
利用Granier树干液流测定系统,长期监测黄土高原半干旱区延安市南郊天然辽东栎林优势木的树干液流,并同步监测环境因子（空气温度、湿度、太阳辐射、土壤含水量）。分析3株优势木边材液流在生长季内各月份的日变化特征以及液流通量密度与环境因子的关系。结果显示：辽东栎液流日变化总体上与太阳辐射和空气水气压亏缺呈相同趋势,但液流峰值出现时间较早,通常为10：00左右。随着生长季内物候变化,液流通量密度总体表现为前期（4—6月）较低、中后期（7—9月）较高、末期（10月）迅速下降的变化趋势。采用指数饱和曲线函数对液流通量密度和空气水气压亏缺进行拟合,有效地反映了各月份液流通量密度对空气水气压亏缺的响应特征。各月份的曲线特征和拟合参数的差异表明,蒸腾耗水过程也受到土壤水分状况等其他因素的影响。
Cambiamenti nel regime pluviometrico in ecosistemi mediterranei: II progetto MIND
1
2007
... 不少研究人员认为, 减少蒸腾耗水会导致林分生产力的降低.
Cork oak physiological responses to manipulated water availability in a Mediterranean woodland
1
2014
... 部分其他阔叶类树种蒸腾耗水对降水量变化响应的研究结论也基本相似.
An Introduction to Environmental Biophysics. Springer-Verlag
1
1998
... 通过安装于样地外开阔地的自动气象站对主要气象因素连续自动监测.测定指标包括太阳辐射、空气温度、空气湿度和降雨量等.太阳辐射监测采用LI-200型传感器(LI-COR, Lincoln, USA), 水平安装于距地面2 m高的观测塔顶端; HMP110型温湿度传感器(Vaisala, Helsinki, Finland)安装于距地面 1.8 m高的防辐射罩内.太阳辐射和温湿度数据每 30 s读取一次, 用CR1000数据采集器(Campbell Scientific, Logan, USA)记录每30 min的平均值; 降雨量由7852型翻斗式自记雨量桶(Davis Instruments, Hayward, USA)测定, 水平安装于地面50 cm高处.为反映大气温湿度的协同效应, 本文采用
Individual variation of sap-flow rate in large pine and spruce trees and stand transpiration: A pilot-study at the central NOPEX site
2
1995
... 降雨改变引起的干旱会对森林蒸腾耗水产生重要影响, 而降雨的随机性会造成旱期强度和持续时间的变化, 从而影响林分蒸腾(
... 人工造林是黄土高原地区植被恢复的主要措施.刺槐(Robinia pseudoacacia)是一种典型的中生树种, 既喜湿润肥沃, 又耐旱耐瘠薄, 生长迅速, 是优良造林树种(
2
... 人工造林是黄土高原地区植被恢复的主要措施.刺槐(Robinia pseudoacacia)是一种典型的中生树种, 既喜湿润肥沃, 又耐旱耐瘠薄, 生长迅速, 是优良造林树种(
... 试验样地(34.80° N, 107.97° E, 海拔1 430 m)位于陕西省永寿县槐平林场, 属于黄土高原沟壑区的温带半湿润森林区(
2
... 人工造林是黄土高原地区植被恢复的主要措施.刺槐(Robinia pseudoacacia)是一种典型的中生树种, 既喜湿润肥沃, 又耐旱耐瘠薄, 生长迅速, 是优良造林树种(
... 试验样地(34.80° N, 107.97° E, 海拔1 430 m)位于陕西省永寿县槐平林场, 属于黄土高原沟壑区的温带半湿润森林区(
2015
2015
Sapflow characteristics and climatic responses in three forest species in the semiarid Loess Plateau region of China
3
2011
... 环境因子的响应规律多采用指数饱和曲线函数进行拟合分析, 例如
... 由于该地区地下水位较深, 降雨是土壤水分补充的唯一来源, 减少降水量必然会引起土壤含水量的降低, 最终导致林分蒸腾耗水大幅度降低.关于黄土高原其他地区刺槐人工林的研究有相似的报道,
...
The response of an Eastern Amazonian rain forest to drought stress: Results and modelling analyses from a throughfall exclusion experiment
2
2007
... 部分其他阔叶类树种蒸腾耗水对降水量变化响应的研究结论也基本相似.
... 不少研究人员认为, 减少蒸腾耗水会导致林分生产力的降低.
Evaluation of transpiration in a Douglas-fir stand by means of sap flow measurements
1
1987
... 采用长10 mm的Granier型热扩散探针对样树边材进行液流监测, 在样树南北两侧各安装一组探针, 包括参考和加热探针, 两探针间距约15 cm, 采用专用电流调节装置为加热探针提供稳定电流以保持0.15 W功率的持续加热(
Radiation balance, transpiration and photosynthesis of an isolated tree
1
1993
... 一般认为, 在短时间尺度上植物的蒸腾作用主要受到气象因子的影响, 空气水汽压亏缺和光照是植物气孔蒸腾的主要驱动因子(
黄土高原适生树种苗木的耗水特性
1
1994
... 人工造林是黄土高原地区植被恢复的主要措施.刺槐(Robinia pseudoacacia)是一种典型的中生树种, 既喜湿润肥沃, 又耐旱耐瘠薄, 生长迅速, 是优良造林树种(
黄土高原适生树种苗木的耗水特性
1
1994
... 人工造林是黄土高原地区植被恢复的主要措施.刺槐(Robinia pseudoacacia)是一种典型的中生树种, 既喜湿润肥沃, 又耐旱耐瘠薄, 生长迅速, 是优良造林树种(
Heat dissipation sensors of variable length for the measurement of sap flow in trees with deep sapwood
1
2002
... 采用长10 mm的Granier型热扩散探针对样树边材进行液流监测, 在样树南北两侧各安装一组探针, 包括参考和加热探针, 两探针间距约15 cm, 采用专用电流调节装置为加热探针提供稳定电流以保持0.15 W功率的持续加热(
Shrub encroachment in North American grasslands: Shifts in growth form dominance rapidly alters control of ecosystem carbon inputs
1
2008
... 降雨改变引起的干旱会对森林蒸腾耗水产生重要影响, 而降雨的随机性会造成旱期强度和持续时间的变化, 从而影响林分蒸腾(
Afforestation and climate niche dynamics of black locust (Robinia pseudoacacia)
1
2018
... 人工造林是黄土高原地区植被恢复的主要措施.刺槐(Robinia pseudoacacia)是一种典型的中生树种, 既喜湿润肥沃, 又耐旱耐瘠薄, 生长迅速, 是优良造林树种(
Long-term transpiration change with rainfall decline in a Mediterranean Quercus ilex forest
2
2009
... 降雨改变引起的干旱会对森林蒸腾耗水产生重要影响, 而降雨的随机性会造成旱期强度和持续时间的变化, 从而影响林分蒸腾(
... 部分其他阔叶类树种蒸腾耗水对降水量变化响应的研究结论也基本相似.
A multi-year study of rainfall and soil water controls on Scots pine transpiration under Mediterranean mountain conditions
1
2010
... 降雨改变引起的干旱会对森林蒸腾耗水产生重要影响, 而降雨的随机性会造成旱期强度和持续时间的变化, 从而影响林分蒸腾(
Transpiration in upper Amazonia floodplain and upland forests in response to drought-breaking rains
1
1996
...
Responses of Acacia tortilis and Acacia xanthophloea to seasonal change in soil water availability in the savanna region of Kenya
1
2005
... 降雨改变引起的干旱会对森林蒸腾耗水产生重要影响, 而降雨的随机性会造成旱期强度和持续时间的变化, 从而影响林分蒸腾(
Species differences in stomatal control of water loss at the canopy scale in a mature bottomland deciduous forest
2
2003
... 部分其他阔叶类树种蒸腾耗水对降水量变化响应的研究结论也基本相似.
... 不少研究人员认为, 减少蒸腾耗水会导致林分生产力的降低.
刺槐耗水研究进展
1
2005
... 人工造林是黄土高原地区植被恢复的主要措施.刺槐(Robinia pseudoacacia)是一种典型的中生树种, 既喜湿润肥沃, 又耐旱耐瘠薄, 生长迅速, 是优良造林树种(
刺槐耗水研究进展
1
2005
... 人工造林是黄土高原地区植被恢复的主要措施.刺槐(Robinia pseudoacacia)是一种典型的中生树种, 既喜湿润肥沃, 又耐旱耐瘠薄, 生长迅速, 是优良造林树种(
Restoration and Development of the Degraded Loess Plateau, China. Springer Japan
1
2014
... 试验样地(34.80° N, 107.97° E, 海拔1 430 m)位于陕西省永寿县槐平林场, 属于黄土高原沟壑区的温带半湿润森林区(
不同供水条件下侧柏和刺槐幼树的蒸腾耗水与土壤水分应力订正
1
2005
... 由于该地区地下水位较深, 降雨是土壤水分补充的唯一来源, 减少降水量必然会引起土壤含水量的降低, 最终导致林分蒸腾耗水大幅度降低.关于黄土高原其他地区刺槐人工林的研究有相似的报道,
不同供水条件下侧柏和刺槐幼树的蒸腾耗水与土壤水分应力订正
1
2005
... 由于该地区地下水位较深, 降雨是土壤水分补充的唯一来源, 减少降水量必然会引起土壤含水量的降低, 最终导致林分蒸腾耗水大幅度降低.关于黄土高原其他地区刺槐人工林的研究有相似的报道,
Estimating water use of a black locust plantation by the thermal dissipation probe method in the semiarid region of Loess Plateau, China
1
2010
... 采用长10 mm的Granier型热扩散探针对样树边材进行液流监测, 在样树南北两侧各安装一组探针, 包括参考和加热探针, 两探针间距约15 cm, 采用专用电流调节装置为加热探针提供稳定电流以保持0.15 W功率的持续加热(
Effect of ammonium and nitrate nitrogen fertilizers on wheat yield in relation to accumulated nitrate at different depths of soil in drylands of China
1
2015
... 试验样地(34.80° N, 107.97° E, 海拔1 430 m)位于陕西省永寿县槐平林场, 属于黄土高原沟壑区的温带半湿润森林区(
Loblolly pine productivity and water relations in response to throughfall reduction and fertilizer application on a poorly drained site in northern Florida
1
2016
... 降雨改变引起的干旱会对森林蒸腾耗水产生重要影响, 而降雨的随机性会造成旱期强度和持续时间的变化, 从而影响林分蒸腾(
Sensitivity of canopy transpiration to altered precipitation in an upland oak forest: Evidence from a long-term field manipulation study
2
2006
... 降雨改变引起的干旱会对森林蒸腾耗水产生重要影响, 而降雨的随机性会造成旱期强度和持续时间的变化, 从而影响林分蒸腾(
... 对伊比利亚半岛欧洲赤松林研究发现, 在贫水年的夏季, 林分日蒸腾量比平常年份减少约40%.
黄土丘陵区刺槐生长的影响因子研究
1996
黄土丘陵区刺槐生长的影响因子研究
1996
Estimation of transpiration by single trees: Comparison of sap flow measurements with a combination equation
1
1997
... 一般认为, 在短时间尺度上植物的蒸腾作用主要受到气象因子的影响, 空气水汽压亏缺和光照是植物气孔蒸腾的主要驱动因子(
黄土高原半干旱区辽东栎的树干液流动态
1
2011
... 环境因子的响应规律多采用指数饱和曲线函数进行拟合分析, 例如
黄土高原半干旱区辽东栎的树干液流动态
1
2011
... 环境因子的响应规律多采用指数饱和曲线函数进行拟合分析, 例如
