Herbivores stimulate respiration from labile and recalcitrant soil carbon pools in grasslands of Yellowstone National Park

Quantifying the effects of grazing on soil organic carbon (SOC) decomposition is of crucial importance for understanding soil C dynamics. However, less attention has been paid to the pool-specific SOC decomposition and the underlying factors associated with each C pool, representing critical knowledge gaps on soil C dynamics. In this study, we applied a state-of-the-art Bayesian data assimilation technique to re-analyze previous soil incubation data to examine how herbivores influenced the fraction and cumulative respiration of labile and recalcitrant soil C pools from seven edaphically diverse sites in Yellowstone National Park, whereas those variables were not explored in the earlier study. Our results showed that grazing significantly increased cumulative respiration from both labile and recalcitrant C pools. Greater cumulative respiration from the labile C pool was related to grazers increasing labile C pool fractions, while higher cumulative respiration from the recalcitrant C pool was associated with grazers accelerating the decomposition rate of the recalcitrant C pool. Cumulative respiration from both labile and recalcitrant C pools was positively correlated with shoot biomass, soil gravimetric moisture, and soil C and nitrogen content. Our results underscore how knowledge of pool-specific SOC decomposition can provide a better mechanistic understanding of soil C dynamics along topo-edaphic gradients in grazed grassland.