Responses of soil microbial communities to manure and biochar in wheat cultivation of a rice-wheat rotation agroecosystem in East China

Abstract

Soil contamination in agroecosystems remains an environmental problem of global concern. Biochar has been suggested as an organic amendment to alleviate soil pollution, sequester carbon, and improve fertility. Yet, information is still lacking on how bacterial and fungal communities in acidic bulk and rhizosphere soils respond to swine manure and its biochar. In this study, biochar and swine manure were applied at two rates of 1.5 and 3 t ha-1 in a rice-wheat rotation field study to assess how soil characteristics, especially pH and the availability of chemical elements, correlate to compositional variations of bacteria and fungi in bulk and rhizosphere soils. Our results showed that biochar and manure amendments at higher rates promoted bacterial richness index in bulk and rhizosphere soils through increasing soil pH and reducing As and Cu availability. For beta diversity, compared with As and Cu availability, soil pH had opposite effects on both bacterial and fungal communities. Specifically, biochar and swine manure application stimulated bacterial class of Gemmatimonadetes, Deltaproteobacteria, and Gammaproteobacteria via increasing pH and decreasing available chemical elements. Opposite trends of fungal community responding to biochar and manure was found. For example, biochar restrained the fungal class of Eurotiomycetes via decreasing As and Cu, but manure inhibited Leotiomycetes mainly due to an increase in soil pH and a decrease in soil dissolved organic C (DOC). These evidences suggest that both bacterial and fungal communities respond significantly to biochar and manure amendments in both bulk and rhizosphere soils, possibly due to their sensitive adaptation to soil environmental variations, such as pH levels and availability of chemical elements.