Environment selected microbial function rather than taxonomic species in a plateau saline-alkaline wetland.

Comprehending the microbial community in plateau saline-alkaline wetlands, an understudied and vulnerable ecosystem, is vital for predicting ecosystem functions within the context of global climate change. Despite the rapid shrinkage and potential drying up of some of these wetlands, our knowledge of the microbial community in this ecosystem remains fragmented. Here, we utilized metagenomic sequencing to investigate the distribution of methane, nitrogen, and sulfur cycling genes/pathways and formation mechanism of microbial communities across sediment, surface rhizosphere soils (R_surface), subsurface rhizosphere soils (R_subsurface), surface bulk soils (B_surface), and subsurface bulk soils (B_subsurface) in Cuochuolong Wetland, a typical saline-alkaline wetland located in the Tibetan Plateau. The results showed that sediment exhibited relatively higher functional potentials for methanogenesis but lower potentials for methane oxidation. Denitrification and dissimilatory sulfate reduction potentials increased with decreasing salinity across the five habitats, following the trend: sediment surface < R_subsurface surface < B_subsurface. The taxonomic compositions of microbial communities varied more dramatically, yet functional genes distributed relatively evenly, indicating functional redundancy. Greater determinacy was observed in functional compositions, whereas taxonomic compositions exhibited more stochasticity. Similar patterns were observed within individual habitats, with the relative importance of deterministic processes increasing as salinity levels increased across the five habitats. Additionally, 188 non-redundant medium- and high-quality metagenome-assembled genomes (MAGs) were reconstructed, with 18 MAGs containing the nod gene, a marker gene of disproportionation of nitric oxide. This study provided a novel perspective on the formation mechanism of microbial community by emphasizing the deterministic selection of extreme environments on microbial function.

Importance: Understanding the formation mechanism of microbial communities is a central goal in ecology. However, our understanding of microbial community remains fragmented in plateau saline-alkaline wetlands, despite their unique status as a vulnerable ecosystem characterized by high altitude, low disturbance, high salinity, sensitivity to global climate change, and localized shrinkage in some areas. Furthermore, previous studies on community formation mechanism have predominantly focused on microbial taxonomic structure, neglecting their functional compositions. Beyond providing a comprehensive understanding of the distribution patterns of methane, nitrogen, and sulfur cycling microbial communities within plateau saline-alkaline wetland, this study offers a novel perspective on formation mechanism of microbial community by emphasizing the deterministic selection of extreme environment on microbial function. This study also expands our comprehension of the diversity of microbes containing the nod gene, which may substantially contribute to global methane and nitrogen budgets.