Herbivores regulate the sensitivity of soil organic carbon decomposition to warming

Abstract

There is considerable interest in how the sensitivity of soil organic carbon (SOC) decomposition to warming is determined by the degree of recalcitrance (i.e., quality) of SOC. Although herbivores have widespread effects on the quality of plant litter, from which SOC is derived, herbivores are seldom considered in studies that examine the response of SOC degradation and greenhouse gas emissions to warming. In this study, we addressed the question: do herds of wild ungulates affect the temperature sensitivity of SOC decomposition in grasslands of Yellowstone National Park (YNP)? We examined the effects of ungulates on temperature sensitivity by comparing microbial respiration at different temperatures in incubated soils collected inside and outside long-term ungulate exclosures. Exclosure sites included grasslands on hilltops, slopes, and at the base of slopes that varied considerably in soil properties. Herbivores reduced the temperature sensitivity of SOC decomposition uniformly among sites by 20% (P = 0.002). The herbivore—induced decline in temperature sensitivity was probably governed by YNP grazers increasing the quality of grassland SOC. Results from this study suggest that herbivores regulate how global warming modifies grassland SOC decomposition, stability, and CO2 emissions.