背景:了解不同生态系统的时间趋势和水分利用效率(WUE)对环境变化的变化响应是预测植被生长的关键。主要生态系统类型的WUE动态(例如,森林,草地和农田)已经使用各种WUE定义/指标进行了研究,但是缺乏使用多种WUE指标对不同生态系统类型之间的WUE动态及其驱动力的比较研究。我们使用了1997年至2014年42个FLUXNET2015站点(396个站点年)的涡流协方差测量,以及三个常用的WUE指标(即,生态系统,固有的,和潜在的WUE),以调查落叶阔叶林(DBF)之间WUE趋势和驱动因素的共性和差异,常绿针林(ENFs),草原,和农田。
结果:我们的结果表明,WUE的时间趋势在73.8%的森林中没有统计学意义,草地和农田,在量化WUE方面,这三个WUE指标都没有表现出比其他指标更好的表现。同时,三个WUE指标观察到的趋势在森林之间没有显着差异,草地和农田生态系统。此外,WUE主要由具有显著WUE趋势的地点的大气二氧化碳浓度驱动,以及没有明显趋势的站点(农田除外)的蒸气压赤字(VPD)。
结论:我们的发现揭示了三种WUE指标在不同生态系统中应用的共性和差异,并进一步强调了VPD对WUE变化的重要影响。
BACKGROUND: Understanding temporal trends and varying responses of water use efficiency (WUE) to environmental changes of diverse ecosystems is key to predicting vegetation growth. WUE dynamics of major ecosystem types (e.g., forest, grassland and cropland) have been studied using various WUE definitions/metrics, but a comparative study on WUE dynamics and their driving forces among different ecosystem types using multiple WUE metrics is lacking. We used eddy covariance measurements for 42 FLUXNET2015 sites (396 site years) from 1997 to 2014, as well as three commonly used WUE metrics (i.e., ecosystem, inherent, and underlying WUE) to investigate the commonalities and differences in WUE trends and driving factors among deciduous broadleaf forests (DBFs), evergreen needleleaf forests (ENFs), grasslands, and croplands.
RESULTS: Our results showed that the temporal trends of WUE were not statistically significant at 73.8% of the forest, grassland and cropland sites, and none of the three WUE metrics exhibited better performance than the others in quantifying WUE. Meanwhile, the trends observed for the three WUE metrics were not significantly different among forest, grassland and cropland ecosystems. In addition, WUE was mainly driven by atmospheric carbon dioxide concentration at sites with significant WUE trends, and by vapor pressure deficit (VPD) at sites without significant trends (except cropland).
CONCLUSIONS: Our findings revealed the commonalities and differences in the application of three WUE metrics in disparate ecosystems, and further highlighted the important effect of VPD on WUE change.