Unfolding the Potential of Soil Microbial Community Diversity for Accumulation of Necromass Carbon at Large Scale

Microorganisms are the main drivers of soil organic carbon (SOC) formation, especially through the accumulation of microbial necromass C. It is unclear, however, how microorganisms mediate the accumulation of necromass in soil because microbial communities are prohibitively diverse. To bridge this knowledge gap, biomarkers of microbial cell walls (amino sugars) were combined with high-throughput sequencing, spanning a 900 km climatic gradient through the Loess Plateau. The cropland and three restoration types (grassland, shrubland, and forestland) were included, and 291 samples were collected. Necromass C, microbial diversity, and enzyme activities showed the same trend after vegetation restoration (from cropland to forestland). Soil pH, clay, microbial biomass C, and α-1,4-glucosidase were the strong predictors for both bacterial and fungal necromass C. There was a strong positive linear relationship that existed between bacterial necromass C and diversity and also between fungal necromass C and diversity (p < 0.01), pointing to the strong links between microbial diversities and residues. Specifically, necromass C was strongly correlated with dominant microbial taxa, suggesting that these taxa might control the variation of necromass and other metabolic residues. The relative abundances of Actinobacteria, Proteobacteria, and Bacteroidetes gradually increased after vegetation restoration, and changed from oligotrophic to copiotrophic groups. It means that vegetation restoration promoted opportunistic and resilient microbial taxa that may have copiotrophic or fast-response characteristics to increase the accumulation of necromass C and potentially contribute to soil C sequestration in these systems. In this regard, vegetation restoration governs SOC storage by shaping the unique dominant microbial communities, facilitating the accumulation of necromass C. This research enhances our understanding of the survival strategies of microbial life and suggests greater contribution to necromass than previously recognized for soil microbiomes.