Observed decoupling of vegetation greenness and productivity despite regional coupling patterns across the Tibetan Plateau

Global vegetation greenness has increased since the 1980s, boosting productivity, facilitating CO2 absorption, and contributing to climate mitigation. The Tibetan Plateau plays a crucial role in maintaining carbon balance and climate stability. However, the dynamics in the coupling relationship between vegetation greenness and productivity remain poorly understood. In this study, we delved into the coupling relationship between vegetation greenness and productivity across the Tibetan Plateau, utilizing a long time series of MODIS Leaf Area Index (LAI) and Gross Primary Productivity (GPP) data, and further examined how these coupling relationships varied along environmental gradients. The results revealed that 77.9% of the pixels, primarily in northeastern and northern regions, exhibited concurrent increasing trends in both annual mean LAI and GPP during 2000–2021. Conversely, 19.8% of the pixels demonstrated inconsistent trends. Notably, annual mean LAI and GPP displayed a strong coupling strength of 0.73, which weakened during the late growing season. A critical transition threshold was observed, when LAI exceeded 6 m² m−2. Additionally, we identified decoupling in the southern and northwestern regions, attributed to pronounced leaf-shading effects and drought adaptation strategies. This study highlights the importance of understanding the coupling relationships of vegetation greenness and productivity in the carbon cycle.