DIRT data for forest soil carbon, nutrients and microbes

Global changes can alter plant inputs from both above- and below-ground, which thus may differently affect soil carbon and microbial communities. However, the general patterns of how detritus input changes affect them in forests remain unclear. By conducting a meta-analysis of 3193 observations from 165 experiments worldwide, we found that alterations in aboveground litter and/or root inputs had profound effects on soil carbon and microbial communities in forest ecosystems. Litter addition stimulated soil organic carbon (SOC) pools and microbial biomass, while removal of litter, root or both (no inputs) decreased them. The increased SOC under litter addition suggested that aboveground litter inputs benefit SOC sequestration despite accelerated decomposition. Unlike root removal, litter alterations and no inputs altered particulate organic carbon, while all detrital treatments had minor effects on mineral-associated organic carbon. In addition, detrital treatments contrastingly altered soil microbial community, with litter addition or removal shifting it towards fungi, while root removal shifting it towards bacteria. Furthermore, the responses of soil C and microbial biomass to litter alterations positively correlated with litter input rate and total litter input, suggesting that litter input quantity is a critical controller of belowground processes. Taken together, these findings provide critical insights into understanding how altered plant productivity and allocation affects soil carbon cycling, microbial communities and functioning of forest ecosystems under global changes. Future studies can take full advantage of the existing plant detritus experiments, and should focus on the relative roles of litter and roots in forming SOC and its fractions.