Increasing moisture limitation predominates recent decline trend in ecosystem respiration

Abstract

Abstract Due to the temperature sensitivity of many plant and microbial processes, climate warming generally stimulates terrestrial ecosystem respiration (ER), the largest land-to-air CO2 flux annually. However, climate change is also steadily enhancing drought risk in most regions on the Earth, and given sensitivity of plant and microbial metabolism to soil moisture, this consequently makes uncertain the degree to which and dynamics of how, where, and whether climate change will stimulate ER at the global scale. Here, we provide a data-driven estimate of global ER product from 1989 to 2018 using a modified CO2 flux partitioning model based on eddy covariance, a Random Forest model, meteorological and remote-sensing observations. Our results showed that global ER increased at a rate of 0.110 ± 0.097 Pg C yr− 2 in 1989–1998 but then decreased at a rate of -0.090 ± 0.018 Pg C yr− 2 in 1998–2018. This declining trend in the global terrestrial ER was primarily driven by increasing moisture limitation, especially in a majority of tropical and temperate regions. However, current global land models do not adequately capture this apparent decreased trend in ER over the past two decades, likely because they overestimate impacts of rising temperature on global ER while underestimating the associated soil moisture effect. Our findings pose new scientific challenges and opportunities for model benchmarking, hypothesis generation and testing, and ecological forecasting.