The Effect of Climate Change and Nitrogen Deposition on the Water Use Efficiency of Grassland in Xinjiang

ABSTRACT

Water use efficiency (WUE) is a key link in the quantitative study of carbon (C) and the water cycles. Although numerous studies have investigated ecosystem water and carbon cycles, it remains uncertain how grassland ecosystems in Xinjiang respond to climate change and nitrogen (N) deposition and which processes govern these responses. To answer these questions, the WUE value was estimated using the Denitrification–Decomposition (DNDC) model and use a sensitivity formula and scenario simulations to assess the role of N deposition, precipitation and temperature on WUE. The analysis revealed that the WUE in Xinjiang was approximately 1.13 g C kg ⁻¹ H ₂ O and the overall WUE increased by 0.37 g C kg ⁻¹ H ₂ O from 1979 to 2018. In our study, the sensitivity analysis results revealed that the highest WUE was found at temperatures between 0°C and 6°C. For precipitation, the lowest WUE was found with precipitation between 350 and 500 mm. Under the current N deposition level, the increasing N deposition led to the continuous increase of WUE. Precipitation was responsible for 47.47% of the increase in WUE, whereas temperature contributed 5.76% to the WUE variation. In addition, the background N deposition enhanced the overall magnitude of WUE by 4.34% compared to a zero‐N scenario. This study offers empirical evidence on grassland WUE responses to N deposition and climate change and further illuminated differences in carbon‐water coupling among different regions in Xinjiang.