Vegetation Productivity Slowdown on the Tibetan Plateau Around the Late 1990s

Tibetan Plateau (TP) has experienced a slowdown of the vegetation greening since the late 1990s. This structural change (i.e., greening) along with canopy physiology (i.e., potential photosynthetic productivity) regulates vegetation gross primary productivity (GPP). However, it remains unclear how the joint regulation influences the trend of alpine GPP under climate change. Here, we validate a universal productivity model against flux‐based and satellite‐derived observations at TP and diagnose the long‐term climatic impacts on GPP via canopy physiology and structure. We found an increasing but weakening trend of GPP after 1998. About 3/4 of this slowdown was attributed to the slowing greening after 1998, which was caused by the fact that the stress of atmospheric aridity and reduced benefits of warming overwhelmed the positive effects of CO2 fertilization and radiation enhancement. This study highlights the coupling between canopy structure and productivity for the long‐term period. Plain Language Summary Plants absorb CO2 from the atmosphere through their leaves via process of photosynthesis. The green surface area of leaves and portions exposed to sunlight harvest the energy from the sun, while the plant's physiology determines how much and how well light radiation is used. The Tibetan Plateau is one of the most sensitive regions to climate change and has experienced a slowdown since 1998 of its hitherto increasing total vegetation greenness. An important point that remains unclear is whether, and to what proportion this slowdown in the capacity to absorb CO2 is attributed to the green canopy vegetation and/or its physiology. To gain insight into this question, we input data from 1982 to 2015 into a simulation model to separate the contributions of different environmental factors that brought about variation in CO2 capture. In this way we can understand what factors related to the canopy structure and/or plant physiology. We found that increased atmospheric aridity and reduced warming together led to a marked slowdown of canopy greening after 1998, leading to a continuous decline in efficiency to capture atmospheric CO2. Our research continues to highlight the important role of canopy structure on carbon capture trends for the alpine ecosystem and provides insights for the vegetation‐climate response. Key Points The increasing trend of gross primary productivity on the Tibetan Plateau has slowed down from +3.15 ± 0.41 to +0.77 ± 0.03 g C m−2 yr−2 around