Reductive soil disinfestation with biochar amendment modified microbial community composition in soils under plastic greenhouse vegetable production

Reductive soil disinfestation (RSD) and biochar amendment are considered sustainable management practices to improve degraded vegetable soil. However, the combined effects of these two remediation methods on soil microbial communities and vegetable yields remain unclear. In the present field study, the interactive impacts of conventional RSD treatment and biochar were tested in plastic greenhouse soils under a continuous vegetable cultivation system. Six treatments consisted of different management practices: soil untreated (CK), soil amended with biochar (BC), soil flooded (SF), soil flooded and mulched with plastic film (SFM), soil amended with alfalfa residue, flooded and mulched with plastic film (RSD), and soil amended with alfalfa residue plus biochar, flooded and mulched with plastic film (RSD+BC). Analysis of the soil samples collected at 0–20 cm for a range of physicochemical and microbial properties revealed that both RSD and RSD+BC treatments decreased soil nitrate (NO3-) concentrations while increasing soil pH, ammonium (NH4+), dissolved organic carbon (DOC), and the low-valent ion (Fe2+, Mn2+) concentrations (P < 0.05). Unlike the BC, SF and SFM treatments, the RSD and RSD+BC treatments decreased the bacterial and fungal diversity (P < 0.05) compared to the CK, and altered microbial community composition. The RSD treatment significantly reduced the relative abundance of genus Fusarium while increasing the relative abundances of genera Bacillus and Clostridium, and the increase was more evident in the RSD+BC treatment, suggesting the potential of the latter to suppress pathogenic fungi while increasing beneficial bacteria. The structural equation model revealed the key role of soil redox potential (Eh) and NH4+ concentration in the regulation of microbial community composition. Furthermore, BC, RSD, and RSD+BC treatments increased pepper yield by 27.4%, 55.3% and 44.4%, respectively, compared to CK. The yield of pepper was positively correlated with the contents of DOC, NH4+, and the relative abundance of Bacillus and Clostridium in soil (P < 0.01), and negatively correlated with NO3- and relative abundance of Fusarium (P < 0.05). This study provides evidence for the efficiency of the combined application of RSD and biochar to amend the quality of degraded soils in plastic sheds under continuous cultivation.