Nitrogen-shaped microbiotas with nutrient competition accelerate early-stage residue decomposition in agricultural soils

Plant residue decomposition is critical for carbon cycling in terrestrial ecosystems. Nitrogen (N) availability alters this process through orchestrating the microbial community, yet the mechanisms remain elusive. By investigating the wheat residue decomposition process and the microbial succession under different N input levels in agricultural fields, we find that higher N availability accelerates residue breakdown mainly at the early stage by promoting the rapid colonization of a soil-derived microbial consortium with key interactions. Metabolic potential evaluations show that the Bacillus decomposers harbor diverse carbohydrate-active enzymes that degrade cellulose and hemicellulose, whereas the non-decomposer Staphylococcus sciuri efficiently transports and consumes downstream sugar products. Synthetic communities combined with omics techniques confirm that the N-enriched non-decomposer S. sciuri restricts the growth of weak decomposers through sugar depletion, thereby restructuring the community dominated by strong decomposers. This shift increases the residue decomposition rate by 16.77% under N fertilization. Our results highlight the important role of usually overlooked fast-growing non-decomposers in agricultural soil carbon cycling. The mechanisms by which N inputs alter residue decay remain elusive. Here, the authors find that the usually overlooked fast-growing non-decomposers reshape a community dominated by strong decomposers through sugar depletion, facilitating residue decay.