The depth distribution of carbon inputs to soil has been unquantified globally, hindering our understanding of belowground carbon dynamics. We synthesize global observational data to infer the allocation of carbon inputs to soil depths down to 2 m, and map depth-specific carbon inputs globally at 1 km resolution. Global average carbon input to the 0–20 cm soil layer is 1.1 Mg C ha–1 yr–1, accounting for >50% of total soil carbon inputs. Across the globe, the depth distribution of carbon inputs shows large variability, and there are relatively more carbon inputs to deeper layers in hotter and drier regions. Edaphic, climatic and topographic properties (in the order of importance) explain >80% of such variability in soil depths; and the direction and magnitude of the influence of individual properties are soil depth- and biome-dependent. Our results provide global benchmarks for prediction of whole-soil carbon profiles across global biomes.

The fate of soil carbon (C) under climatic warming predominantly depends on temperature sensitivity of soil microbial functioning, but it is poorly understood. Using temporal measurements of soil respiration in an incubation experiment with cross-inoculation of microbial communities to contrasting soils, we constrained a microbial-explicit C model to infer temperature responses of two general microbial functional groups: fast-growing r- vs slow-growing K-strategists. We found that the two groups exhibit distinct, non-monotonic temperature responses. Both historical environment, under which the microbial communities were originated, and current environment, under which the microbial communities are colonized/adapted, significantly shape the temperature responses of the two groups. Our findings highlight the importance of combined effects of historical and current environment on microbial decomposition for regulating soil C dynamics under warming. We suggest that distinct, non-monotonic temperature responses of microbial functional groups may cause pronounced feedbacks between soil C dynamics and warming depending on climate-soil-microbe interactions.