Composition, predicted functions, and co-occurrence networks of fungal and bacterial communities_ Links to soil organic carbon under long-term fertilization in a rice-wheat cropping system

Soil microbial community compositions and soil labile organic carbon (LOC) fractions change rapidly in response to fertilizers and crop rotation, but our understanding of the associations between specific microbial taxa and C fractions is still limited. The objective of this study was to compare the composition and function of soil bacterial and fungal communities in response to fertilization and crop rotation and their correlations with LOC fractions. Communities were analyzed by PCR-amplification of bacterial 16S rRNA gene and fungal ITS sequences from soil DNA. Functions were predicted by in-silico tools. A long-term experimental rice-wheat cropping system was studied, and the soil collected from plots treated with different fertilizers, including a control without fertilizer (CK), inorganic nitrogen, phosphorous, and potassium (NPK), manure (M), and NPKM, was analyzed. Fertilizations, non-crop types, significantly modified the soil bacterial community composition and suspected functions, while both fertilization and crop types significantly affected the fungal community composition. Compared with CK, NPKM treatment significantly increased the relative bacterial abundances of Candidatus Solibacter, Nitrosporia, Geobacter and Bryobacter, but decreased the relative fungal abundances of Paraphaeosphaeria sporulosa, Emericellopsis, Cladosporium tennuissimum, Curvularia lunata, Stachybotrys chlorolonate and Moleospora. All responding OTUs correlated significantly with soil LOC fractions, especially particulate organic C. The suspected functions suggest that organic amendment provided larger quantities of organic C, then promoting the growth of microorganism involved in C degradation, which in turn contributing to C sequestration. Our results indicate that fertilizers and crop rotation alter the diversity and function of soil bacterial and fungal communities, thereby causing an impact on agroecosystems.