Chitin degradation and the temporary response of bacterial chitinolytic communities to chitin amendment in soil under different fertilization regimes

Chitin amendment is a promising agricultural management strategy to control fungal and nematodal plant diseases and to improve crop yield. Chitin degradation in the soil contributes significantly to carbon and nitrogen cycling in terrestrial ecosystems. However, little is known about chitin degradation and bacterial chitinolytic communities in agricultural soil under different fertilization regimes. Thus, in the present study, a 42-day soil incubation experiment was conducted, in which soil under four fertilization regimes (i.e., no fertilization (CK), chemical fertilizer (CF), pig manure plus 50% chemical fertilizer (PMCF), and rice straw plus 100% chemical fertilizer (SRCF)) were amended or not with chitin or its monomer, N-acetylglucosamine (NAG). Different nitrogen forms and CO2 and N2O emission were measured to evaluate chitin degradation and its environmental implications. SRCF soil had the highest CO2 emission, chitin N mineralization, and fungal abundance. NAG and chitin were enriched to exploit the chitin degraders. High-throughput sequencing analyses reveled that Streptomycetaceae, Oxalobacteraceae, Gemmatimonadaceae, and Acidobacteria were generally increased upon chitin amendment in CK, CF, and PMCF soil, whereas Streptomycetaceae dominated chitin-amended SRCF soil. Herpetosiphonaceae was enriched only in chitin-amended CK soil. LEfSe and network analysis were used to predict chitinolytic and opportunistic species, and revealed that most previously reported chitinolytic bacteria were detected in the present study and new potential chitin degraders, including unidentified_Solibacterales, Gemmatimonadaceae, and Herpetosiphonaceae, were identified. Some members of Firmicutes, Actinobacteria, and Proteobacteria, including Bacillus, and Kitasatospora, were speculated to be opportunistic species. The findings improve our understanding of the effects of chitin degradation on carbon and nitrogen cycling in agricultural soil under different fertilization regimes and help to identify chitinolytic bacteria. (C) 2019 Published by Elsevier B.V.