The effect of warming on grassland evapotranspiration partitioning using laser-based isotope monitoring techniques
The effect of warming on grassland evapotranspiration partitioning using laser-based isotope monitoring techniques
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DOI：
10.1016/j.gca.2012.12.047
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发表时间：
2011-12
影响因子：
5
通讯作者：
Lixin Wang;S. Niu;S. Good;K. Soderberg;M. Mccabe;R. Sherry;Yiqi Luo;Xuhui Zhou;J. Xia
中科院分区：
文献类型：
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作者：
Lixin Wang;S. Niu;S. Good;K. Soderberg;M. Mccabe;R. Sherry;Yiqi Luo;Xuhui Zhou;J. Xia
蒸散量（T）占总蒸散量（ET）的比例是反映生物对水文循环影响程度的重要参数。解决气候变暖对生态系统总水量平衡的影响的研究很少，在野外实验中测得的变暖对T/ET比值的影响在文献中还没有看到。在这项研究中，我们量化的T/ET比值在环境和变暖的处理在草地生态系统中使用稳定同位素的方法。这些测量是在2011年5月至6月的生长高峰期在俄克拉荷马州的一个长期草原变暖地点进行的。采用室内法估算了蒸发量（δE）、蒸腾量（δT）和累积蒸散量（δET）的δ 2 H同位素组成。采用改良的商用针叶树叶室测定δT，采用改良的商用土壤室测定δ E，采用定制室测定δET。用Keeling作图法和质量平衡法对δE、δ ET和δ T进行了定量计算，并用Craig-Gordon模型法计算了δE。多种方法表明，控制和变暖的地块之间的δ ET和δT没有显着差异。尽管基于电离室的估算值与Craig-Gordon的结果相差约12‰，但所有方法都表明，在变暖的地块中，δ E更趋于亏损。δ E的减小表明，为使δ ET保持不变，蒸发通量占总水分通量的百分比必然减小，这一点得到了野外观测的证实。基于箱法和Craig-Gordon方法，对照处理中的T/ET比率为0.65或0.77，在加温处理中发现的比率为0.83或0.86。对Craig-Gordon模型的敏感性分析表明，变暖引起的土壤液态水同位素组成的减少是导致δ E亏损的主要因素，温度相关的平衡效应较小。多条证据表明，变暖时T/ET比值的增加主要是由蒸发量减少引起的。
The proportion of transpiration (T) in total evapotranspiration (ET) is an important parameter that provides insight into the degree of biological influence on the hydrological cycles. Studies addressing the effects of climatic warming on the ecosystem total water balance are scarce, and measured warming effects on the T/ET ratio in field experiments have not been seen in the literature. In this study, we quantified T/ET ratios under ambient and warming treatments in a grassland ecosystem using a stable isotope approach. The measurements were made at a long-term grassland warming site in Oklahoma during the May–June peak growing season of 2011. Chamber-based methods were used to estimate the δ2H isotopic composition of evaporation (δE), transpiration (δT) and the aggregated evapotranspiration (δET). A modified commercial conifer leaf chamber was used for δT, a modified commercial soil chamber was used for δEand a custom built chamber was used for δET. The δE, δETand δTwere quantified using both the Keeling plot approach and a mass balance method, with the Craig–Gordon model approach also used to calculate δE. Multiple methods demonstrated no significant difference between control and warming plots for both δETand δT. Though the chamber-based estimates and the Craig–Gordon results diverged by about 12‰, all methods showed that δEwas more depleted in the warming plots. This decrease in δEindicates that the evaporation flux as a percentage of total water flux necessarily decreased for δETto remain constant, which was confirmed by field observations. The T/ET ratio in the control treatment was 0.65 or 0.77 and the ratio found in the warming treatment was 0.83 or 0.86, based on the chamber method and the Craig–Gordon approach. Sensitivity analysis of the Craig–Gordon model demonstrates that the warming-induced decrease in soil liquid water isotopic composition is the major factor responsible for the observed δEdepletion and the temperature dependent equilibrium effects are minor. Multiple lines of evidence indicate that the increased T/ET ratio under warming is caused mainly by reduced evaporation.