Exopolysaccharides from Enterococcus faecium alleviate cadmium damage in rice seedlings via regulating soil-root...

This study investigated the effects of exogenous exopolysaccharides (EPS) on nitrogen cycling and its influencing factors in rice seedlings and soil under cadmium (Cd) stress. The results demonstrated that Cd stress severely inhibited rice seedlings growth, reduced total nitrogen (N), nitrite (NO₂⁻) and nitrate (NO₃⁻) content in both soil and rice roots while increasing ammonium (NH₄⁺) levels, and markedly decreased the synthesis efficiency of N-containing antioxidants in rice seedlings. EPS application not only enhanced total N, NO₂⁻ and NO₃⁻ content in soil and rice roots while reducing NH₄⁺ accumulation, but also significantly improved the production of N-containing antioxidants, which may represent a key mechanism for EPS-mediated heavy metal resistance. Furthermore, EPS modulated soil bacterial community structure under Cd stress by influencing key factors in nitrogen cycling, and Mantel-test analysis revealed that NH₄⁺ content in soil was the most significant factor affecting dominant microbial communities and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional profiles (P < 0.05), with soil nitrite reductase (NiR) also showing significant influence on microbial communities and functions (P < 0.1). These findings collectively demonstrate that regulation of nitrogen cycling systems likely serves as a crucial factor in EPS-mediated alleviation of Cd toxicity in rice.