The Dependence of Ecosystem Water Use Partitioning on Vegetation Productivity at the Inter-Annual Time Scale

摘要

The dependence of inter-annual ecosystem evapotranspiration (ET) partitioning on vegetation dynamics is crucial for understanding the long term coupling relationship between the water and carbon cycles. The objective of this study was to determine the spatial variation of ET partitioning (T/ET) and the inter-annual dependencies of T/ET on vegetation gross primary productivity (GPP). The investigation was conducted at the global scale based on seven global datasets and at the point scale at 37 flux sites. The spatial variations of T/ET were divided into three phases, that is, the rapidly increasing phase (P1), slowly increasing phase (P2), and decreasing phase (P3), which were located in arid and cold regions, temperate regions, and tropical rainforest regions, respectively. The three-phase spatial variations were primarily driven by the different spatial variations of the two water use pathways (i.e., transpiration, T and evaporation, E) in ecosystems with different productivity levels. In P1 and P2 ecosystems, the interannual dependencies of T/ET on GPP were mostly positive, and in P3 ecosystems, it was mostly negative. This revealed a significantly decreased dependence as GPP increased, which was attributed to the different dependencies of T and E on GPP. Based on the effects of GPP on ET under climate variations (represented by precipitation, P), ET had the smallest inter-annual variations in most of global vegetated grid cells due to the joint regulation of T and E by GPP and P. This study highlights the significant role of vegetation productivity in regulating inter-annual ET partitioning, and improves understandings on the coupled water-carbon cycles.