Shifts in the Bacterial Population and Ecosystem Functions in Response to Vegetation in the Yellow River Delta Wetlands

Vegetation represents probably the most crucial step for the ecosystem functions of wetlands, but it is unclear how microbial populations and functions shift along with vegetation. In this study, we found that the richness and diversity of soil bacteria increased with vegetation levels and that the community composition was distinctly shifted from bare to vegetative places. The bare land displayed an extremely high abundance of Cyanobacteria as a monospecies genus, while a Gemmatimonadetes genus was predominant as multiple species in all the vegetative wetlands, suggesting their important ecosystem functions and potential mechanisms. Expression of the genes related to photosynthesis was enriched exclusively in bare land. Genes involved in biological organic carbon metabolism and the cycling of main elements (C, N, S, and P) were highly expressed in vegetative wetlands and were mostly included in the metagenome-assembled genome (MAG) of Gemmatimonadetes. Some compounds identified from soil metabolomic results also corresponded to pathways involving these key active genes. Cyanobacteria is thus responsible for the carbon sink in early infertile wetlands, and Gemmatimonadetes plays a crucial role in ecosystem functions in vegetative wetlands. Our results highlight that the soil microbial populations execute ecosystem functions for wetlands and that vegetation is the determinant for the population and functional shifts in the coastal estuarine wetland of the Yellow River Delta. IMPORTANCE Vegetation probably represents the most crucial step for the ecosystem functions of wetlands, but it is unclear how microbial populations and functions shift in pace with the colonization and succession of vegetation. In this study, we found that a Cyanobacteria monospecies genus and a Gemmatimonadetes multispecies genus are fastidiously predominant in the bare and vegetative wetlands of the Yellow River Delta, respectively. Consistently, photosynthesis genes were enriched exclusively in bare land, while genes involved in biological organic carbon metabolism and the cycling of main elements were highly expressed in vegetative wetlands, were mostly included in the MAG of Gemmatimonadetes, and were consistent with soil metabolomic results. Our results provide insight into the adaptive succession of predominant bacterial species and their ecosystem functions in response to the presence of vegetation.