Evapotranspiration components and water use efficiency from desert to alpine ecosystems in drylands

Abstract

Water use efficiency (WUE), the ratio of carbon gain to water loss, is an important physiological indicator in assessing the interactions between the carbon and water cycles. Quantifying the spatiotemporal patterns of WUE at both canopy and ecosystem levels across main dryland ecosystems along climate gradients is vital for water resource management in water-limited regions. However, the patterns of WUE among natural and managed ecosystems in drylands are not well understood. We partitioned the evapotranspiration (ET) components and calculated WUE at both canopy and ecosystem levels across dryland ecosystems in an arid region in Northwest China using observations from a regional flux observation network. Our results showed divergent variations of canopy and ecosystem WUE across the main ecosystems along climate gradients in arid regions. The ecosystem WUE and canopy WUE ranged from 0.7 to 1.8 gC Kg−1 H2O and from 0.8 to 2.4 gC Kg−1 H2O, respectively. Climatic gradients were the dominant factors controlling the spatial patterns of WUE across dryland ecosystems. Divergences were also observed between oasis and natural ecosystems because of different environmental conditions and management practices. Climatic regulation of the spatial WUE patterns was dominated by water variability rather than temperature. The higher canopy WUE for desert ecosystems indicated that these ecosystems were adapted to the water-limited environment. The discrepancies of both canopy and ecosystem WUE between croplands in arid and hyper-arid climate zones were caused by the differences in agricultural management techniques for these crops. Human activities (e.g., irrigation and agriculture management) altered the distribution of water resource and water use strategies, which further affected the magnitude and patterns of WUE in drylands. This study provides insights into the spatiotemporal patterns of ET components and both canopy and ecosystem WUE over dryland ecosystems and can inform regional water resources management in water-limited regions.