Water-use efficiency of an old-growth forest in lower subtropical China

Xiaodong Liu,Ronghua Li,Lu Zhang,Xiuzhi Chen,Qianmei Zhang,Fengling Long,Jiyue Li

doi:10.1038/srep42761

Xiaodong Liu, Ronghua Li + Show 5 more

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https://doi.org/10.1038/srep42761

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Abstract

Carbon and water fluxes are key properties of ecosystem processes and functions. A better understanding of their temporal dynamics and coupling mechanism between these fluxes will help us improve ecosystem management for mitigation as well as adaption to future climatic change. From 2003 to 2009, carbon and water flux data were obtained by the eddy covariance method over an old-growth forest in the lower subtropical China. The 7 years of observational data indicated that the water-use efficiency (WUE) of the old-growth forest exhibited weak inter-annual variability. The mean annual WUE ranged from 1.70 to 1.98 g C kg−1 H2O. An analysis of the effects of environmental variables on the monthly gross primary productivity (GPP) and evapotranspiration (ET) indicated that solar radiation, air temperature, precipitation and vapor pressure deficit (VPD) produced similar effects on the monthly GPP and ET, which suggests that photosynthesis and ET were similarly driven by the climatic variables. At the monthly scale, the WUE decreased significantly as the precipitation and soil moisture content increased. However, a significant correlation was not detected between the WUE and the VPD at the monthly scale. Moisture conditions tend to be major drivers of the ecosystem WUE.

Highlights

Monsoon evergreen broad-leaved forests (MEBFs) in southern China is the climax vegetation of the subtropics with a monsoon climate characteristics
We found that the ecosystem Water-use efficiency (WUE) decreased with monthly precipitation, with strong decreases in WUE observed at precipitation levels of up to 200 mm and declining slowly thereafter
Our study indicates that the ecosystem WUE exhibited a “saddle pattern” as the monthly mean air temperature increased

Summary

Introduction

Monsoon evergreen broad-leaved forests (MEBFs) in southern China is the climax vegetation of the subtropics with a monsoon climate characteristics. Previous studies have shown that WUE at the ecosystem level is typically controlled by climatic and soil variables, including precipitation, air temperature, vapor pressure deficit (VPD) and soil water content, because of their effects on energy partitioning and canopy conductance[8,9], the magnitude and direction of the response might be different or even opposite[10]. Grünzweig et al.[15] reported the same opposite effect on WUE in an Aleppo pine forest These mixed results deeply reflected the complexity between carbon and water coupling at the ecosystem scale, which varies under different environments and vegetation characteristics. Limited by the number of flux towers in the subtropical area and the length of observation period[23], previously related studies mainly focus on relatively short time-scales (e.g., diurnal, daily and seasonal), which inhibits our ability to accurately predict ecosystem carbon and water response to environmental change[24]. Long-term studies investigating the inter-annual variability in WUE and its environmental controls are needed, especially for lower subtropical forests

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