Rainfall and vegetation primary productivity control the stochastic behavior of soil heterotrophic respiration across ecosystems

Soil heterotrophic (microbial) respiration (Rh) is an important ecosystem flux that plays a crucial role in the global carbon budget. However, it remains one of the least-documented carbon fluxes likely due to the difficulty in partitioning soil respiration into its autotrophic and heterotrophic components and to the intertwined biotic and abiotic processes influencing Rh. Although some efforts have been made to explore the effects of environmental factors such as soil temperature and moisture on Rh, the integrated effects of climate, soil, and vegetation properties on Rh dynamics remain poorly understood, which limits our ability to project future climate trajectories. Here we develop a probabilistic model based on microbial growth dynamics to describe the ecosystem-scale dynamics of Rh. The model is tested using the global FLUXNET 2015 database. The theoretical mean, variance, and full probability distribution of Rh are well supported by empirical observations across different ecosystems. Despite the complexity of soil microbial dynamics, the variability in Rh is dependent on rainfall characteristics only regardless of ecosystem type after the effect of vegetation primary productivity (NPP) is accounted for. In addition, the shape of the Rh distribution is mainly driven by rainfall dynamics while NPP, which is linked to soil properties and substrate availability, only affects the amplitude of Rh fluctuations. Our model therefore provides insights into how changes in rainfall regime and NPP influence the dynamical behavior of Rh, with important implications for global carbon budget. Future investigations will explore how the stochastic dynamics of Rh respond to climate change projected by the Coupled Model Intercomparison Project Phase 6 (CMIP6).