The responses of soil Cd fractions to disinfestation regimes associated with microbial communities

While reductive soil disinfestation (RSD)-related practices have been shown to mediate soil cadmium (Cd) fraction to a certain extent, the underlying mechanisms remain unclear. Here, a pot experiment was conducted to investigate the effects of various reductive soil disinfestation regimes on Cd fraction and its driving mechanisms underlying them. Five Cd fractions, soil physicochemical properties as well as microbial communities were simultaneously measured. Results revealed that, relative to the control treatment, all RSD-related regimes contributed to decrease exchangeable Cd fraction (EX-Cd) by transforming it to unexchangeable Cd fractions (RES-Cd CB/OX-Cd fractions) (P < 0.05). RSD with Hermetia illucens L. feces treatment (abbr.: HI treatment) had the greatest reduction rate (9.7 %), which higher than that of other treatment (3.5 % and 2.6 %), this largely attributed to more functional genera in association with Cd fixation and Fe (III) reduction enriched. In addition, soil disinfestation regimes altered soil microbial community composition and structure, which was a critical factor responsible for the changes of soil Cd fraction. Correlation analysis showed that the changes of Cd fraction were closely related to biotic and abiotic factors. Both pH and soil organic material were main abiotic factors, while microbial groups, including Bacteroidetes, Hydrogenedentes (Hydrogenispora), Ascomycota, Acidobacteria and Verrucucomicrobia were key biotic factors for Cd conversion and immobilization. The validation experiment in four vegetables further confirmed that RSD-related regimes were indeed favorable for decreasing soil availability and plant uptake of Cd by improving soil pH, and HI treatment showed optimal remediation and utilization potential to Cd-contaminated soils. Together, the results provide a theoretical basis and reference for the RSD-related disinfestation regimes in remediation of Cd-contaminated soils, and highlighted the significant potential of Hermetia illucens L. feces as a novel addition in RSD technology for reducing available Cd from soils.