Abstract
Understanding the effect of soil erosion on soil carbon (C) fixation is of great significance for evaluating the complicated connection between land degradation and C cycle. To investigate erosion-induced changes in autotrophic bacterial community and microbial carbon dioxide (CO2) fixation, three typical eroding sites and three depositional sites were selected in the hilly red soil region of southern China with severe erosion. Positive responses of autotrophic microbial abundance to soil deposition were observed, whereas no obvious changes in microbial diversity were observed between eroding and depositional sites. The relative abundances of obligate autotrophic bacteria, such as Rhodopseudomonas and Pseudonocardia, were enhanced in the eroding sites. Deposition of organic matter-rich soil was not conducive to the growth of obligate autotrophic bacteria. The average rate and amount of microbial CO2 fixation at the depositional sites (30.86 mg C km-2 year-1 and 0.05 g kg-1) were higher than those at the eroding sites (18.04 mg C km-2 year-1 and 0.025 g kg-1), which indicated that soil deposition significantly enhanced autotrophic microbial CO2 fixation. In addition, multiple stepwise linear regression showed that compared with microbial properties (abundance and diversity), dissolved organic carbon is a more important explanation factor for the change of microbial CO2 fixation rate (68.8%, P = 0.001).