Carbon–Water Flux Coupling Characteristics and Driving Factors at Multi-temporal Scales in an Alpine Meadow Ecosystem on the Tibetan Plateau

Abstract. Alpine meadow ecosystems play a crucial role in the global carbon and water cycles, with water use efficiency (WUE) serving as a key indicator of carbon-water coupling. Investigating the characteristics of carbon and water fluxes and WUE in alpine meadows on the Tibetan Plateau (TP) is essential for accurately assessing carbon budget, water cycling, and carbon–water interactions under climate change. This study utilized eddy covariance observations from 2012 to 2017 in an alpine meadow of the eastern TP to analyze the temporal dynamics of carbon fluxes (net ecosystem carbon exchange, NEE; ecosystem respiration, Re; gross primary productivity, GPP), water flux (evapotranspiration, ET), and WUE across daily, monthly to seasonal, and inter-annual timescales. Ridge regression was applied to identify the main drivers of carbon and water fluxes and WUE at different time-scale. The results indicate that: (1) the alpine meadow acted as a carbon sink, with a multi-year average NEE of 109.7 gC m^-2y^-1, and carbon and water fluxes as well as WUE exhibited pronounced temporal variations across daily, monthly to seasonal, and inter-annual timescales; (2) daily and monthly to seasonal variations of carbon fluxes were primarily driven by soil temperature (Ts), while ET was mainly controlled by radiation. At the inter-annual timescale, precipitation (PRE) and leaf area index (LAI) were the dominant factors influencing carbon and water fluxes; (3) Ts regulated WUE at daily, monthly to seasonal scales, whereas PRE was the key factor controlling carbon–water coupling at the inter-annual timescale. These findings enhance our understanding of the coupling characteristics and driving mechanisms of carbon and water fluxes in alpine meadows, providing a scientific basis for predicting the responses of grassland ecosystems on the TP to future climate change.