Zheng Han, Wang Qiufeng, Zhu Xianjin, Li Yingnian, Yu Guirui
Synthesis Research Center of Chinese Ecosystem Research Network, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China; University of Chinese Academy of Sciences, Beijing, China.
Synthesis Research Center of Chinese Ecosystem Research Network, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China.
PLoS One. 2014 Jun 4;9(6):e98857. doi: 10.1371/journal.pone.0098857. eCollection 2014.
Evapotranspiration (ET) is an important component of the water cycle in terrestrial ecosystems. Understanding the ways in which ET changes with meteorological factors is central to a better understanding of ecological and hydrological processes. In this study, we used eddy covariance measurements of ET from a typical alpine shrubland meadow ecosystem in China to investigate the hysteresis response of ET to environmental variables including air temperature (Ta), vapor pressure deficit (VPD) and net radiation (Rn) at a diel timescale. Meanwhile, the simulated ET by Priestly-Taylor equation was used to interpret the measured ET under well-watered conditions. Pronounced hysteresis was observed in both Ta and VPD response curves of ET. At a similar Ta and VPD, ET was always significantly depressed in the afternoon compared with the morning. But the hysteresis response of ET to Rn was not evident. Similar hysteresis patterns were also observed in the Ta/VPD response curves of simulated ET. The magnitudes of the measured and simulated hysteresis loops showed similar seasonal variation, with relatively smaller values occurring from May to September, which agreed well with the lifetime of plants and the period of rainy season at this site. About 62% and 23% of changes in the strength of measured ET-Ta and ET-VPD loops could be explained by the changes in the strength of simulated loops, respectively. Thus, the time lag between Rn and Ta/VPD is the most important factor generating and modulating the ET-Ta/VPD hysteresis, but plants and water status also contribute to the hysteresis response of ET. Our research confirmed the different hysteresis in the responses of ET to meteorological factors and proved the vital role of Rn in driving the diel course of ET.
蒸散（ET）是陆地生态系统水循环的重要组成部分。了解ET随气象因素变化的方式是更好地理解生态和水文过程的核心。在本研究中，我们利用中国典型高寒灌丛草甸生态系统的ET涡度相关测量数据，在日尺度上研究ET对包括气温（Ta）、水汽压差（VPD）和净辐射（Rn）在内的环境变量的滞后响应。同时，利用普里斯特利 - 泰勒方程模拟的ET来解释充分供水条件下实测的ET。在ET的Ta和VPD响应曲线中均观察到明显的滞后现象。在相似的Ta和VPD条件下，与上午相比，ET在下午总是显著降低。但ET对Rn的滞后响应不明显。在模拟ET的Ta/VPD响应曲线中也观察到类似的滞后模式。实测和模拟滞后环的幅度呈现相似的季节变化，5月至9月的值相对较小，这与该地点植物的生长周期和雨季时间相吻合。实测ET - Ta和ET - VPD环强度变化的约62%和23%可分别由模拟环强度的变化来解释。因此，Rn与Ta/VPD之间的时间滞后是产生和调节ET - Ta/VPD滞后的最重要因素，但植物和水分状况也对ET的滞后响应有贡献。我们的研究证实了ET对气象因素响应的不同滞后现象，并证明了Rn在驱动ET日变化过程中的重要作用。
