Varying microbial utilization of straw-derived carbon with different long-term fertilization regimes explored by DNA stable-isotope probing

Abstract

The decomposition processes of crop residues, which represent the largest organic carbon input in agricultural ecosystems, are determined by soil microbes. However, the impact of different long-term fertilization practices on residue decomposition has not been clearly established. In this study, a microcosm experiment using 13C-labeled maize residues and high-throughput sequencing was performed to investigate bacterial and fungal microbes utilizing straw-derived carbon in soils under separate regimes of long-term fertilization (CK: no fertilizer; NPK: mineral fertilizers; NPKS: mineral fertilizers plus straw). During the 60-day incubation period, a total of 524 bacterial OTUs and 72 fungal OTUs, which utilized straw-derived carbon, were identified and were found to be primarily distributed in the bacterial phyla of Proteobacteria, Actinobacteria and Bacteroidetes, and the fungal class of Sordariomycetes within Ascomycota. The three fertilized soils exhibited distinct straw-utilizing microbial communities along the decomposition process, in which key bacterial taxa (Flavobacterium, Nocardioides, Pseudomonas, Pseudoxanthomonas, Agromyces and Herpetosiphon) and key fungal taxa (Pleosporaceae, Lasiosphaeriaceae and Chaetomiaceae) exhibited significantly positive relationships with extracellular enzymes activities, thereby accelerating the straw decomposition process. Furthermore, due to higher nutrient availability, microbes can rapidly respond to straw addition, therefore, more bacteria and fungi, which are referred to as rapid responders, were identified in NPK and NPKS soils, relative to CK soils. Hierarchical and variation Partitioning (HP) analysis revealed a strong potential impact of multiple edaphic factors in shaping the microbial community to utilize the straw-derived carbon. N resources (NO3−-N and TN) and β-glucosidase were found to be significantly positively correlated with microbial utilizers’ community. In conclusion, our findings elucidate the processes of establishment of microbial community and straw decomposition, as well as the association between microbial communities and edaphic factors under different long-term fertilization regimes.