Vegetation restoration dominates increase in water use efficiency in drylands of China.

[Display omitted] • Water use efficiency (WUE) in China's drylands is on an upward trend for 2003–2018. • WUE increased rapidly in semiarid regions due to vegetation restoration projects. • WUE can decrease if vapour pressure deficit and plantation saturation increases. Dryland ecosystems are crucial components within the Earth and atmospheric systems, and a number of projects have been implemented to restore vegetation in drylands in the recent years. However, these regions are experiencing extreme climatic changes, and the impact of these projects are unclear. To gain a better understanding of the effectiveness of these projects, we employed water use efficiency (WUE), the ratio of gross primary production (GPP) to terrestrial evapotranspiration (ET), to predict future dryland ecosystem dynamics, and detected the underlying causes of WUE changes. We analysed the WUE trends and the decomposed components of WUE, namely the GPP to plant transportation ratio (GPP/T) and the plant transportation to terrestrial evapotranspiration (T/ET) ratio, between 2003 and 2018 in China's drylands. The results indicated that 70.3 % of the study area had an upward WUE trend, and T/ET was the dominant factor of the WUE trend in 74.9 % of the areas investigated. Furthermore, the increase in T/ET was associated with growth in leaf area index (LAI). The rising WUE rate in the vegetation restoration project areas was significantly higher than that in other areas along with the drought gradient (P < 0.05), which indicated WUE increasing was strongly influenced by the increase in LAI resulting from vegetation restoration. Thus, our research affirms that vegetation restoration greatly influences WUE increase. However, over time, WUE in these restored drylands is likely to decrease due to increased VPD and plantation saturation, so future strategies for vegetation restoration in drylands are therefore required. [ABSTRACT FROM AUTHOR]