Microbial activity response and immobilization of cadmium in saturated-unsaturated soils with the combined application of sepiolite and goat fertilizer

This study investigated cadmium (Cd) transport and immobilization in two passivators-sepiolite (SP) and goat manure (GM)-and in soils under saturated and unsaturated moisture conditions. Illumina high-throughput sequencing explored rhizosphere bacterial community responses. Results showed SP increased soil pH and decreased dissolved organic matter (DOM) under both conditions, while GM elevated both pH and DOM. Both reduced Cd accumulation in pak choi shoots, with reductions of 37.3%-75.3% for SP and 57.7%-60.7% for GM. GM enhanced microbial abundance; notably, Proteobacteria peaked in SP-amended soils under saturated conditions with GM co-application. Redundancy analysis (RDA) revealed Bacteroidetes, Patescibacteria, and Proteobacteria were positively correlated with soil pH, DOM, and DTPA-extractable Cd, whereas Acidobacteria were positively correlated with DTPA-Cd but negatively with pH and DOM. These correlations indicate that combined GM and SP application may indirectly regulate soil microbial communities by altering soil physicochemical properties and bioavailable Cd content.