Effect of manure application on diazotrophs in an acidic Ultisol

Biological nitrogen (N) fixation by diazotrophs contributes substantially to N input and is a viable solution to sustainable agriculture via reducing inorganic N fertilization. However, how manure application influences the abundance, community structure and assembly process of diazotrophs in soil aggregates is not fully understood. Here, we investigated the effect of manure amendment on diazotrophic communities in soil aggregates of an arable soil.Manure application increased soil aggregation, crop yield and the abundance of nifH genes. The abundance of nifH genes increased with the increase of aggregate sizes, indicating that diazotrophs prefer to live in larger sizes of aggregates. The abundance of nifH genes in large macroaggregates, rather than in microaggregates and silt and clay, was positively associated with plant biomass and crop yield. Taken together, our findings demonstrated that long-term manure application increased the abundance of nifH genes and altered the community structure and assembly process of diazotrophs in soil aggregates, which advanced our understanding of the ecophysiology of diazotrophs in an acidic Ultisol.