Change in straw decomposition rate and soil microbial community composition after straw addition in different long-term fertilization soils

Fertilization practices can change soil fertility and biological properties, and influence its ecological functions. We studied the change in the straw decomposition rate and microbial community composition in soils with different long-term fertilization regimes (no-fertilizer control (CK); nitrogen, phosphorus, and potassium fertilizers (NPK); and NPK plus straw (NPKS)) with addition of straw in a 75-day incubation experiment. Carbon dioxide (CO2) emission rates from the straw material were 13.9, 15.8, and 17.9 mu g C g(-1) soil day(-1) in the CK + S, NPK + S, and NPKS + S treatments, respectively. After straw addition, the biomass of fungi and bacteria increase following the order of CK + S <= NPK + S < NPKS + S; while the bacterial richness decreased and did not change with incubation time, the fungal richness decreased and presented different responses among treatments with incubation time. Their diversities presented a decreasing-increasing trend with incubation time in all treatments. The richness and diversity of bacteria and fungi were positively correlated with soil NO3--N. Bacterial community structure on days 1 and 3 were significantly separated from that on day 75; however, fungal community structure did not differ significantly as that of bacteria across different stages in the same treatment. A redundancy analysis showed that straw addition changed the community structure of bacteria and fungi by decreasing soil NO3--N, and their community structures were regulated by soil organic C in the early stage and by NH4+-N in the later incubation stage. The relative abundance of the bacterial phyla Proteobacteria, Firmicutes, and fungal phyla Ascomycota showed synchronized changes with straw CO2 emissions rate. Our findings suggested that long-term fertilization and the return of straw to soils increased straw decomposition relative to the unfertilized soil, the latter difference in decomposition attributed to greater biomass of bacteria and fungi resulting from the improvement in soil fertility.