Vegetation restoration increased the diversity and network complexity of carbon-fixing functional bacteria in heavily eroded areas of southern China.

• Vegetation restoration has improved the soil multifunctionality in eroded areas. • Vegetation restoration has increased the abundance and diversity of carbon-fixing functional bacteria. • Vegetation restoration has enhanced the network complexity of carbon-fixing functional bacteria. • The changes in carbon-fixing functional bacteria are closely related to the changes in soil multifunctionality. Carbon-fixing bacteria are a key functional group in soil carbon fixation processes, but their relationship with soil multifunctionality during vegetation restoration in eroded areas remains unclear. This hinders our ability to assess the true impact of vegetation restoration on soil ecosystem services. Therefore, we studied the impacts of three vegetation communities (tree-shrub, tree-grass, and tree-shrub-grass) in the same small watershed in a severely eroded area in southern China on the community of carbon-fixing bacteria in the soil. Compared to eroded areas, vegetation restoration sites had more complex networks of carbon-fixing bacteria, more carbon-fixing bacterial taxa, and more associations among these bacteria. Particularly, in the tree-shrub communities, the Chao1 index, Shannon index, node number, and edge number increased significantly by 291.29%, 49.65%, 364.58%, and 530.89%, respectively. The vegetation community pattern shifted the dominant carbon-fixing bacteria in the eroded areas from Rhodovastum to Nocardia. In the tree-shrub, tree-grass, and tree-shrub-grass patterns, the relative abundance of Rhodovastum decreased by 90.11%, 96.76%, and 95.37%, respectively, compared to that in the control group (CK). This indicates that vegetation community patterns have the potential to shift the dominant carbon-fixing bacteria from strict autotrophs to facultative autotrophs. The changes in the characteristics of the carbon-fixing bacterial community are closely related to the changes in soil multifunctionality caused by vegetation restoration. These results demonstrate that vegetation communities have a significant positive impact on the soil carbon fixation capacity. [ABSTRACT FROM AUTHOR]