Quantifying the variation in water use efficiency across climates and biomes on the Qinghai-Tibetan Plateau

Water use efficiency (WUE) is an important indicator in linking the carbon and water cycles of ecosystems. Previous studies performed in alpine and cold regions have contributed greatly to understanding the WUE response of single ecosystem or specific species in small-scale regions to climatic factors; however, studies focusing on differences in the WUE response among ecosystems or species are insufficient, which has limited the understanding of the climatic adaptation of WUE in alpine and cold regions. Here, based on the 134 leaf delta 13C records measured for the 46 dominant species in two main ecosystems on the Qinghai-Tibetan Plateau, variation in the response of WUE among biomes was analyzed by grouped linear regression, redundancy analysis (RDA), and structural equation models (SEMs). The results showed that (1) photosynthetically active radiation (PAR0), moisture index (MI) and vapor pressure deficit (VPD) were significantly correlated with the variation in WUE; (2) compared with the WUE of alpine grasslands, alpine desert grasslands was more sensitive to climatic factors, which presenting a steeper slope that varied with modified growing degree days (MGDD0), PAR0, MI, VPD and CO2; (3) composition of genera distributions explained 32.22% of the variation in WUE, while the WUE of Stipa was more sensitive compared to other species to most climatic factors; (4) climate (composition of genera) and their joint effects explained 58.98% (63.53%) of the variation in WUE of alpine desert grasslands (alpine grasslands), while altitude indirectly controlled the WUE variation in alpine grasslands and MI directly controlled the WUE variation in alpine desert grasslands. This study quantified the driving effects of climates and biomes on the variation in WUE and contributed to the understanding of vegetation adaptation in alpine and cold regions.