Microbial autotrophy explains large-scale soil CO 2 fixation.

Microbial communities play critical roles in fixing carbon from the atmosphere and fixing it in the soils. However, the large-scale variations and drivers of these microbial communities remain poorly understood. Here, we conducted a large-scale survey across China and found that soil autotrophic organisms are critical for explaining CO 2 fluxes from the atmosphere to soils. In particular, we showed that large-scale variations in CO 2 fixation rates are highly correlated to those in autotrophic bacteria and phototrophic protists. Paddy soils, supporting a larger proportion of obligate bacterial and protist autotrophs, display four-fold of CO 2 fixation rates over upland and forest soils. Precipitation and pH, together with key ecological clusters of autotrophic microbes, also played important roles in controlling CO 2 fixation. Our work provides a novel quantification on the contribution of terrestrial autotrophic microbes to soil CO 2 fixation processes at a large scale, with implications for global carbon regulation under climate change.