Effects of polymer modifiers on the bacterial communities in cadmium-contaminated alkaline soil

Abstract

Polymer modifiers are widely used in the remediation of cadmium-contaminated soil. However, little is known about how polymer modifiers affect soil bacterial communities. The purpose of this study was to measure the effects of polymer modifiers (polyacrylate polymer and organic polymer) on the composition and network structure of bacterial communities in cadmium-contaminated soils combined with phloem girdling of cotton. The results showed that polyacrylate polymer increased soil urease, sucrase, and alkaline phosphatase activities (P < 0.05), while organic polymer increased soil catalase and urease activities (P < 0.05). Polymer modifiers decreased soil Ex-Cd (exchangeable Cd) concentration (P < 0.05) but increased Carb-Cd (carbonate-bound Cd), Ox-Cd (FeMn oxides-bound Cd), Org-Cd (organic Cd), and Res-Cd (residuals Cd) concentrations. Polyacrylate polymer increased the relative abundances of Proteobacteria, Gemmatimonadetes, and Chloroflexi (P < 0.05), while organic polymer only increased the relative abundance of Chloroflexi (P < 0.05). Co-occurrence network analysis showed that polymer modifiers decreased the relative abundances of rhizosphere bacteria, negatively affected the symbiosis, and triggered the competition among the key bacterial species. Polymer modifiers has good effects on reducing the bioavailability of soil cadmium and increasing soil pH, enzyme activities, and relative abundances of dominant bacteria, which changes the relationships of rhizosphere bacteria and may be help for the remediation of cadmium-contaminated alkaline soil.