Sap flow characteristics and their response to environmental variables in a desert riparian forest along lower Heihe River Basin, Northwest China

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• 作者：Wei Li ; TengFei Yu ; XiaoYan Li ; ChunYan Zhao
• 关键词：Sap flow ; Hysteresis ; Principal component analysis ; Canopy conductance ; Populus euphratica
• 刊名：Environmental Monitoring and Assessment
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：188
• 期：10
• 全文大小：1,546 KB
• 刊物类别：Earth and Environmental Science
• 刊物主题：Environment
  Monitoring, Environmental Analysis and Environmental Ecotoxicology
  Ecology
  Atmospheric Protection, Air Quality Control and Air Pollution
  Environmental Management
  
• 出版者：Springer Netherlands
• ISSN：1573-2959
• 卷排序：188

文摘

Hysteresis, related to tree sap flow and associated environmental variables, plays a critical ecological role in the comprehensive understanding of forest water use dynamics. Nevertheless, only limited researches related to this unique ecological phenomenon have been conducted to date in desert riparian forests under extreme arid regions. Populus euphratica Oliv sap flow velocity (V_S) was measured during the 2012 growing season using the heat ratio method, at the same time as environmental variables, such as photosynthetically active radiation (PAR), vapor pressure deficit (VPD), and leaf water potential. We found clockwise patterns of hysteresis between V_S and VPD but anticlockwise patterns between V_S and PAR. Pronounced hysteretic V_S lag time, a function of PAR and VPD, was approximately 1.0~1.5 and −0.5 h, respectively. Hysteresis was primarily caused by the biophysical declining in canopy conductance. Sigmoid response of V_S to synthetic meteorological variables was enhanced by approximately 56 % after hysteresis calibration to sunny days. Consequently, hysteresis can be seen as a protection mechanism for plants to avoid the overlapping of peak V_S and environmental variables. Furthermore, the consistent presence of hysteresis suggested that estimating of plant water use in large temporal and spatial models may require certain provisions to different V_S responses to variables between morning and afternoon and between seasons.