Effects of modifiers on soil enzyme activity and microbial community diversity in cadmium-contaminated farmland soil

Abstract

Cadmium (Cd) contamination, with great toxicity, seriously threatens soil environment. In this study, the effects of biochar and biofertilizer used as modifiers on the biochemical properties, enzyme activity, and microbial diversity in Cd-contaminated soils (1, 2, and 4 mg·kg− 1) were investigated. The results showed that the soil C/N ratio and electrical conductance could be increased by biochar and biofertilizer (P < 0.05). The soil pH in the biochar and biofertilizer treatments increased by 0.99 and 0.95, respectively, and the soil available Cd concentration decreased by 60.24% and 74.34% (P < 0.05), respectively, compared with those in the control group. The increase of soil alkaline phosphatase activity was observed in the biochar treatment (P < 0.05), and the increases of the activities of soil invertase, alkaline phosphatase, catalase, and urease were observed in the biofertilizer treatment (P < 0.05). The relative abundances of Acidobacteria, Gemmatimonadetes, and Proteobacteria were increased and the soil microbial community structure was improved in the biochar and biofertilizer treatments. Redundancy analysis (RDA) and structural equation model (SEM) showed that soil available Cd concentration had negative effects on soil pH, C/N ratio, urease and alkaline phosphatase activity, and relative abundances of Acidobacteria and Proteobacteria. The increase of soil urease activity was the main reason for the increase of soil microbial diversity. In summary, the applications of biochar and biofertilizer could decrease soil available Cd concentration, increase soil microbial community diversity, and reduce the damage of Cd stress.