Microbial community succession in soil is mainly driven by carbon and nitrogen contents rather than phosphorus and sulphur contents

Abstract

Organic manure is widely applied in agricultural systems to improve soil nutrient cycling and other physicochemical properties. However, the biotic and abiotic mechanisms that drive C, N, P, and S cycling following manure application are not completely understood. In this study, soil samples were collected from long-term experimental plots that had been amended with farmyard manure or mineral fertilisers since 1964. Isotope labelling with 15N, 33P, and 35S; metagenomics; and high-throughput sequencing were used to reveal the relationships between C, N, P, and S dynamics and microbial community composition and functions depending on fertilisation. A clear niche differentiation was observed between bacteria and fungi under mineral and manure regimes. A network analysis showed that long-term manure application reduced the complexity and stability of soil microbial network. Furthermore, a variation partitioning analysis based on redundancy analysis indicated that microbial community variation was mainly driven by soil Cand N contents. Dissolved organic C was the most important factor regulating microbial community structure. Soil C and N contents explained 43.5% of bacterial and 37.9% of fungal community variations. In contrast, soil P and S contents explained 29.9% of bacterial and 20.3% of fungal community variations. Long-term manure application increased the abundance of most functional genes related to C, N, P, and S cycling. This led to increased C and N cycling rates under manure application, which provided sufficient substrates for microbial growth. Partial least squares path modelling indicated that soil physicochemical properties, especially dissolved organic carbon, directly influenced C and S cycling, whereas the N and P cycles were indirectly affected by the changes in microbial community composition. These results provide a new perspective on both direct and indirect effects of organic manure and inorganic fertilisers on the soil nutrient cycling processes mediated by soil microbial community.