Spatiotemporal variations and environmental controls of carbon-water dynamics and coupling on the Tibetan Plateau

Carbon–water dynamics and coupling on the Tibetan Plateau (TP) exert critical control on ecosystem functions and climate feedback; however, their multiscale environmental controls remain poorly understood. This study is the first attempt to integrate 29 eddy covariance site observations on the TP to systematically examine spatiotemporal variations of gross primary productivity (GPP), evapotranspiration (ET), and water use efficiency (WUE) and quantitatively identify their environmental drivers across diverse climates and landscapes. Humid sites exhibit larger GPP, ET, WUE, while arid sites show weaker GPP dynamics and opposite seasonal WUE variation. Site-level spatial variations of GPP, ET, WUE exhibit significant climatic gradients, mainly associated with water and vegetation distribution rather than temperature. Regardless of climatic conditions, GPP is governed by LAI and air temperature (Tair), although their associations weaken during middle growing season, when net radiation (Rn) and soil moisture (SM) become dominant in humid and arid regions, respectively. ET is consistently dominated by Rn. WUE is negatively influenced by Rn during early and middle growing season, and positively driven by LAI and Tair during late growing season due to asynchronous responses of GPP and ET. Vapor pressure deficit in humid regions and SM in arid regions show secondary contributions to ET and WUE throughout growing season. Additionally, deeper soil moisture and temperature show stronger associations with GPP and WUE than shallow soil, highlighting its importance in sustaining plant activity. Overall, this study advances understanding of carbon–water processes, and provides insights for ecosystem management and improving process-based modeling on the TP.