Assistant effects of spent mushroom substrate and its derived biochar on soil phytoremediation

Purpose The massive applications of fertilizers and unreasonable management have resulted in serious soil degradation. Spent mushroom substrate (SMS) could be used as the raw material to produce biochar, and the SMS and SMS-derived biochar applications might affect the phytoremediation performances of contaminated soils. This study aimed to reveal the differences in functional mechanisms of SMS and SMS-derived biochar affecting the phytoremediation of soil heavy metal contamination. Materials and methods Alfalfa ( Medicago sativa L.) was used to remediate the agricultural soil contaminated with cadmium (Cd), arsenic (As), and copper (Cu), and the effects of SMS and SMS-derived biochar applications on alfalfa phytoremediation, contaminant phytoextractions, microbial activities, and antibiotic and heavy metal resistance genes and were quantified. Results and discussion Relative to the alfalfa alone, extra biochar application reduced soil available Cd contents by 44% and enhance the phytoremediation performances via enhancements in plant biomass. The combined applications of SMS and biochar significantly enhanced soil urease, β-glucosidase, and phosphatase activities increased As resistance gene abundance by 264% but had negligible impact on antibiotic resistance gene abundance, relative to the alfalfa alone. The alfalfa phytoremediation with the SMS applications significantly enhanced the relative abundances of Proteobacteria and Bacteroidetes and significantly changed the community structures of microorganisms containing heavy metal resistance genes. Conclusions Our study suggested that the SMS-derived biochar reduced the soil’s available Cd content and enhanced the phytoremediation performance, and the SMS application could enhance microbial resistances to heavy metals and stimulate microbial activities in contaminated soil.