5. Conclusions
Long-term mineral and organic fertilization were demonstrated to have a positive effect on microbial biomass enhancement. Our data clearly showed that the soil microbial biomass and PLFAs decreased with soil depth owing to decreasing available nutrients along soil profiles. The microbial sensitivity of nutrients declined with soil depth in the following order: fungi > G− bacteria > G+ bacteria > actinomycetes; this order cannot be changed by fertilization type. Moreover, mineral fertilizers induced G+ bacteria more than G− bacteria and actinomycetes, which suggested a close link between G+ bacteria and mineral fertilizers. With equal fertilizer input, straw addition especially promoted fungi at 10−20cm soil depth, while chicken manure further stimulated G+ bacteria. In broader perspective, understanding the mechanisms of microbial group shift due to fertilization in paddy systems may help improving soil quality through better fertilization management. Further studies should include isotope analyses (13C, 14C,15N) and microbial molecular analyses (16S rRNA sequencing, PLFA, SIP, etc) to fully reveal the fertilizer nutrient turnover in situ in paddy soil systems.
Conflict of interest statement: The authors declare no conflict of interest.
Data Availability Statement: The data that support the findings of this study are available from the corresponding author upon reasonable request.