Impact of stem water storage on diurnal estimates of whole‐tree transpiration and canopy conductance from sap flow measurements in Japanese cedar and Japanese cypress trees
Impact of stem water storage on diurnal estimates of whole‐tree transpiration and canopy conductance from sap flow measurements in Japanese cedar and Japanese cypress trees
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DOI：
10.1002/hyp.7338
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发表时间：
2009-07
影响因子：
3.2
通讯作者：
T. Kumagai;Sayaka Aoki;K. Otsuki;Yasuhiro Utsumi
中科院分区：
文献类型：
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作者：
T. Kumagai;Sayaka Aoki;K. Otsuki;Yasuhiro Utsumi
当使用在茎基部测量的液流（Q）估计昼夜全树蒸腾（ET）和冠层气孔导度（GC）时，茎中储存的水量引入了不确定性。因此，为了研究如何从Q计算ET，我们使用树干液流和茎含水量测量以及全树水分平衡方程获得ET，并将其与Q进行比较。在这项研究中，我们测量了33年生的柳杉单木的液流。唐和钝叶山海棠Chamaparis obtusa Endl.使用恒温液流探针在茎基部的几个深度处测量了液流，并在上部树干处作为ET的替代物。茎含水量在树干上的三个垂直位置使用振幅域反射计（ADR）传感器测量。我们还测量了边材体积的研究树木。通过同时测定树干液流和树干沿着含水量，证实了树干储水量对蒸腾流的影响。这些包括液流滞后沿着树高和茎液流的蒸腾作用增强的高峰。这些结果使我们能够通过将Q乘以1·18并将其时间序列向前移动30分钟来计算正确的ET。然后使用ET值计算两个树种的GC。因子1·18是基于中午ET值高于Q值的事实，这是由于晚上Q的延长。建立时间滞后相对简单，并且通过比较Q和蒸汽压差来确定。由于难以正确获得ET，因此确定乘数更具挑战性。版权所有© 2009约翰威利父子有限公司。
The amount of water stored in the stem introduces uncertainty when estimating diurnal whole‐tree transpiration (ET) and canopy stomatal conductance (GC) using sap flow measured at the base of the stem (Q). Thus, to examine how ET can be calculated from Q, we obtained ET using sap flow and stem water content measurements and a whole‐tree water balance equation, and compared it with Q. In this study, we measured sap flows in 33‐year‐old individual trees of Cryptomeria japonica D. Don and Chamaecyparis obtusa Endl. using constant‐heat sap flow probes. Sap flows were measured at several depths at the base of the stem, and at the upper trunk as a surrogate of ET. Stem water contents were measured at three vertical positions on the trunk using amplitude‐domain reflectometry (ADR) sensors. We also measured sapwood volumes of the study trees. Using simultaneous sap flow and stem water content measurements along the tree stem, we confirmed that stem water storage has impacts on the transpiration stream. These include sap flow lags along the tree heights and an enhanced peak of transpiration from stem sap flow. These results enabled us to calculate the correct ET by multiplying Q by 1·18 and shifting its time series forward by 30 min. The ET value was then used to calculate GC for both tree species. The factor of 1·18 is based on the fact that at noon, the value of ET was higher than that of Q, due to the prolonged Q during the evening. Establishing the time lag was relatively simple and was determined by comparing Q and vapor pressure deficit. The multiplier is more challenging to ascertain due to the difficulty in obtaining ET correctly. Copyright © 2009 John Wiley & Sons, Ltd.