Drought-Induced Weakening of Temperature Control on Ecosystem Carbon Uptake Across Northern Lands.

Rapid warming in northern lands has led to increased ecosystem carbon uptake. It remains unclear, however, whether and how the beneficial effects of warming on carbon uptake will continue with climate change. Moreover, the role played by water stress in temperature control on ecosystem carbon uptake remains highly uncertain. Here, we systematically explored the trend in the temperature control on gross primary production (measured by "S") across northern lands (> 15°N) using a standardized multiple regression approach by controlling other covarying factors. We estimated S using three types of GPP datasets: four satellite-derived GPP datasets, FLUXNET tower observed GPP datasets, and GPP outputs from nine CMIP6 models. Our analysis revealed a significant positive-to-negative transition around the year 2000 in the trend of S. This transition was primarily driven by synchronized changes in soil water content over time and space. The S trend transition covered about 32% of northern lands, especially in grasslands and coniferous forests where leaf water mediation and structural overshoot accelerated the drought-induced transition, respectively. In the future, widespread negative S trends are projected in northern lands corresponding with decreasing soil water availability. These findings highlight the shrinking temperature control on northern land carbon uptake in a warmer and drier climate.