Soil Carbon and Nitrogen Responses to Root and Litter Removal Depend on Experimental and Environmental Context: A Meta-Analysis

Environmental change can alter aboveground and belowground plant inputs, with consequences for soil carbon (C) and nitrogen (N) cycling and their coupling. However, how soil C and N respond differently to root and litter removal, and which factors regulate these responses, remain unclear. Here, we conducted a meta-analysis to quantify changes in soil C and N following root and aboveground litter (hereafter, litter) removal and to identify the factors associated with these changes. We found that (1) litter removal significantly decreased soil organic C (SOC), dissolved organic C, total N, microbial biomass N, ammonium N concentrations and nitrous oxide emissions by 11%–30%, whereas root removal increased nitrate N concentration by 88%; (2) the response ratios of microbial biomass C and N were not correlated under either root or litter removal, whereas those of total C and N concentrations were positively correlated; (3) the effects of root and litter removal on soil C and N varied with season and soil depth, with the strongest responses occurring in autumn and winter and in the surface soil layer (0–10 cm); and (4) these responses were moderated primarily by leaf type and, to a lesser extent, by ecosystem type, elevation, mean annual precipitation, soil properties and experimental duration. Overall, our results clarify how altered plant inputs affect soil C and N pools and identify the conditions under which these effects are strongest, thereby informing predictions of C and N cycling under global change.