Continuous straw return for 8 years mitigates the negative effects of inorganic fertilisers on C-cycling soil bacteria

To elucidate the identity and mechanisms by which specific bacterial members drive efficient decomposition and utilisation of straw, the succession and co-occurrence patterns of C-13-labelled bacteria were analysed using DNA-stable isotope probing (SIP) techniques. Microcosms with C-13-labelled maize straw incorporated into soils subjected to no nitrogen (N) fertiliser (CK), chemical fertiliser (NPK) and chemical fertiliser with straw return (NPKS) treatments for 8 years were incubated for 360 days. The results showed that fertilisation regimes changed the C-13-labelled bacterial groups by abundance but not taxonomic composition, where N fertiliser application (NPK and NPKS treatments) reduced the relative abundance of maize straw carbon assimilators affiliated with Arthrobacter, Sphingomonas, Streptomyces, Burkholderia-Caballeronia-Paraburkholderia and Kribbella, but increased the relative abundance of Nocardioides, Rhodanobacter, Granulicella and Chujaibacter. Compared with CK and NPKS-treated soils, continuous inorganic fertilisation reduced the alpha-diversity of the C-13-labelled bacterial community and resulted in a loose and less competitive co-occurrence network of straw C-assimilators with more hubs needed to sustain its structural stability. Interestingly, straw return mitigated the negative effects of inorganic fertilisation by forming a tight and complex co-occurrence network of maize straw utilizers associated with NPKS-treated soils. Taken together, we emphasise the vital function of long-term straw return for sustaining soil biodiversity under intensive fertilised agricultural conditions and provide reference bacterial members for efficient straw utilisation.