Microbial mediation of carbon-cycle feedbacks to climate warming

Understanding the mechanisms of biospheric feedbacks to climate change is critical to project future climate warming1–3. Although microorganisms catalyse most biosphere processes related to fluxes of greenhouse gases, little is known about the microbial role in regulating future climate change4. Integrated metagenomic and functional analyses of a long-term warming experiment in a grassland ecosystem showed that microorganisms play crucial roles in regulating soil carbon dynamics through three primary feedback mechanisms: shifting microbial community composition, which most likely led to the reduced temperature sensitivity of heterotrophic soil respiration; differentially stimulating genes for degrading labile but not recalcitrant carbon so as to maintain long-term soil carbon stability and storage; and enhancing nutrient-cycling processes to promote plant nutrient-use efficiency and hence plant growth. Elucidating microbially mediated feedbacks is fundamental to understanding ecosystem responses to climate warming and provides a mechanistic basis for carbon–climate modelling. Feedback between terrestrial carbon (C) and climate warming is one of the major uncertainties in projecting future climate warming5,6. Most carbon–climate modelling studies predict a positive feedback in that warming leads to a decrease in ecosystem C storage due to a warming-induced increase in soil C release through respiration1,7,8. Results from various experimental studies on the effects of climate warming on ecosystem C storage, however, are controversial and contradictory9. Such controversy is partially due to the lack of a mechanistic understanding of the feedback responses of below-ground microbial communities to climate warming1–4,10 because most of those experiments have primarily focused on plant communities. Although microorganisms mediate biogeochemical cycles of C, nitrogen (N), phosphorus (P), sulphur (S) and various metals, and play critical roles in ecosystem C dynamics, their responses and feedback mechanisms to climate warming are poorly understood4,11. The lack of a mechanistic understanding of microbial responses is mostly because of technological limitations for analysing microbial communities. The recently emerged metagenomic technologies, such as high-throughput sequencing12 and GeoChip13–16, have revolutionized microbial research, allowing us to address research questions previously unapproachable. Here, we used integrated metagenomics technologies to determine the feedback responses of microbial community structure and functions to climate warming in a tall-grass prairie ecosystem in