Vegetation Restoration Reduces the Capacity of Autotrophic Microbes to Fix <scp> CO ₂ </scp> in Eroded Areas

ABSTRACT Autotrophic microorganisms directly increase the soil organic carbon pool through CO 2 fixation. However, their carbon fixation capacities during the restoration of vegetation in degraded soils are not well characterized. To address this issue, we selected three vegetation restoration approaches (small hole seeding grass management, contour grass and shrub belt management, and mixed grass–shrub–tree management) in a severely eroded region of China and compared them with an untreated control site. We conducted 13 C‐labeling experiments to assess how vegetation restoration influences autotrophic microbial communities and how their CO 2 fixation contributes to soil carbon sequestration. Compared with the soil erosion area, the vegetation‐restored sites presented greater soil nutrients and greater diversity of autotrophic microorganisms. The average Chao1 and Shannon indices of the three vegetation restoration plots increased by 2.81 times and 38.10%, respectively, compared with those of the control plots. Vegetation restoration shifted the autotrophic microbial community from being dominated by obligate autotrophs to being dominated by facultative autotrophs. An increase in autotrophic microbial diversity and a decrease in Rhodovastum diversity led to a reduction in the microbial carbon fixation rate. Compared with that in the CK plots, the average carbon fixation rate in the vegetation restoration plots decreased by 77.43%. However, readily oxidizable organic carbon (82.60%, p = 0.000), rather than biological characteristics, was identified as the dominant factor controlling the microbial carbon fixation rate.