Impacts of fire on soil respiration and its components: A global meta-analysis

As a general disturbance in terrestrial ecosystems, fire can have far-reaching consequences on the carbon (C) cycle. Although soil respiration (SR) is important in regulating atmospheric CO2 concentrations, a general pattern of the response of SR to fire in terrestrial ecosystems remains unclear. In this study, a meta-analysis of 91 studies on fires across 116 global sites was conducted to investigate the effects of fire on SR and its components. The results revealed that the responses of SR and heterotrophic respiration (HR) to fire were dependent on fire severity (low-, moderate-, and high-severity) and types (wildfire and prescribed fire). Specifically, the high- and low-severity fires reduced SR and HR, whereas moderate-severity fires had negligible effects on these parameters. On average, wildfires significantly decreased SR and HR by 13.9% and 18.6%, respectively, across all ecosystems, while prescribed fire reduced SR by 8.4% but did not change HR. In addition, the responses of SR and HR varied with the ecosystem types. Fire decreased SR in all three types of forests (boreal forests: -14.8%, temperate forests: -13.8%, and tropical forests: -28.9%), whereas decreased HR only in boreal and temperate forests (-23.8% and 20.7%, respectively) but not in tropical forests. Moreover, SR decreased directly followed by an increase, whereas HR declined with time after low- and high-severity fires. At a global scale, the responses of SR and HR to fire largely resulted from the changes in soil organic C, dissolved C, microbial biomass C, and belowground biomass, as indicated by the correlation analysis. In addition, the response of SR to fire was negatively affected by the mean annual precipitation in the forests. Overall, our study revealed the mechanisms driving the effects of fire and provided a framework for understanding soil C emissions under intensified fire regimes.