Effects of vegetation control on ecosystem water use efficiency within and among four grassland ecosystems in China
Effects of vegetation control on ecosystem water use efficiency within and among four grassland ecosystems in China
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DOI：
10.1111/j.1365-2486.2008.01582.x
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发表时间：
2008-07-01
影响因子：
11.6
通讯作者：
Zheng, Zemei
中科院分区：
文献类型：
--
作者：
Hu, Zhongmin;Yu, Guirui;Zheng, Zemei
通过连续2-3年(2003年-2005年)的二氧化碳和水汽通量的涡动协方差测量，研究了青藏高原和中国北部4个草地生态系统水分利用效率的季节、年际和生态系统间的变化。这四个生态系统代表了中国最普遍的草地类型，分别是高寒沼泽草甸生态系统、高寒灌丛草甸生态系统、高寒草甸草原生态系统和温带草原生态系统，这说明了水分可利用性的梯度，从而为我们在不同的时空尺度上量化环境和生物控制生态系统WUE提供了机会。从季节上看，WUE在四个生态系统中与GPP密切相关，在生长季节开始和结束时较低，在植物生长活跃期较高。WUE和GPP之间的一致性表明，光合作用过程是WUE季节变化的主要调节因素。进一步研究表明，叶面积指数(LAI)对碳同化和蒸腾/蒸腾速率(T/ET)的影响主要是由于叶面积指数(LAI)对碳同化作用的影响。此外，除沼泽草甸外，LAI还以同样的方式控制WUE的年际变化和站点间变化，导致高生产力的年份或地点伴随着高WUE。叶面积指数与生态系统WUE之间具有较好的相关性，表明仅用叶面积指数预测草地生态系统WUE是可能的。我们的结果还表明，气候变化导致植被结构的变化，从而可能对草原生态系统碳和水循环之间的关系产生重大影响。
Through 2-3-year (2003-2005) continuous eddy covariance measurements of carbon dioxide and water vapor fluxes, we examined the seasonal, inter-annual, and inter-ecosystem variations in the ecosystem-level water use efficiency (WUE, defined as the ratio of gross primary production, GPP, to evapotranspiration, ET) at four Chinese grassland ecosystems in the Qinghai-Tibet Plateau and North China. Representing the most prevalent grassland types in China, the four ecosystems are an alpine swamp meadow ecosystem, an alpine shrub-meadow ecosystem, an alpine meadow-steppe ecosystem, and a temperate steppe ecosystem, which illustrate a water availability gradient and thus provide us an opportunity to quantify environmental and biological controls on ecosystem WUE at different spatiotemporal scales. Seasonally, WUE tracked closely with GPP at the four ecosystems, being low at the beginning and the end of the growing seasons and high during the active periods of plant growth. Such consistent correspondence between WUE and GPP suggested that photosynthetic processes were the dominant regulator of the seasonal variations in WUE. Further investigation indicated that the regulations were mainly due to the effect of leaf area index (LAI) on carbon assimilation and on the ratio of transpiration to ET (T/ET). Besides, except for the swamp meadow, LAI also controlled the year-to-year and site-to-site variations in WUE in the same way, resulting in the years or sites with high productivity being accompanied by high WUE. The general good correlation between LAI and ecosystem WUE indicates that it may be possible to predict grassland ecosystem WUE simply with LAI. Our results also imply that climate change-induced shifts in vegetation structure, and consequently LAI may have a significant impact on the relationship between ecosystem carbon and water cycles in grasslands.