Evaluation of soil microbial communities and enzyme activities in cucumber continuous cropping soil treated with spent mushroom (Flammulina velutipes) substrate

Purpose This study aimed to assess the effects of spent Flammulina velutipes substrate (SFS) amendment on microbial properties of cucumber continuous cropping soil. Materials and methods A laboratory microcosm experiment was designed with four treatments: fresh SFS (F-SFS), sterilized SFS (S-SFS), mineral NPK fertilizer (NPK) and control (CK). Soil chemical properties, microbial biomass carbon (MBC) and nitrogen (MBN) and enzyme activity were determined on days 2, 7, 14, 28 and 56 after amendment. Soil microbial community structures and abundances were measured by denaturing gradient gel electrophoresis (DGGE) and real-time quantitative PCR, respectively. Results The results show that soil pH, total organic carbon, dissolved organic carbon, MBC, MBN, abundances of bacteria and fungi and enzyme activity were significantly enhanced under the F-SFS and S-SFS treatments relative to the NPK and CK treatments. The DGGE profiles show that the soil bacterial and fungal community structures of both SFS treatments were significantly different from those of the NPK and CK treatments, and the highest levels of bacterial and fungal diversity were found in soil amended with fresh SFS (Shannon-Wiener diversity index showed highest bacterial diversity (3.78) at day 14 and highest fungal diversity (2.69) at day 28). The lowest values for the indices (Shannon for bacteria 2.48 at day 7 and Shannon for fungi 1.65 at Day 2) were observed in CK treatment. Conclusion These findings suggest that the addition of SFS and of fresh SFS in particular can diversify microbial communities and enhance microbial biomass and enzyme activities in long-term cropped vegetable greenhouse soil.