Impacts of wheat straw and sulfate application on soil cadmium availability and bacterial community composition in two waterlogged soils with contrasting cadmium levels

Straw incorporation and sulfur fertilizer are considered promising agronomic practices for remediating cadmium (Cd)-contaminated soil. However, their combined effects on Cd availability and soil bacterial communities in paddy soil remain unclear and may vary depending upon initial soil Cd levels. In this study, we conducted a 162-day incubation experiment under waterlogged conditions, applying wheat straw (0 and 1 % w /w) and sulfate (0 and 30 mg kg −1 ) individually or in combination to soils with high Cd (3.18 mg Cd kg −1 ) and low Cd (0.18 mg Cd kg −1 ) contamination. At the early stage, straw alone (W) or in combination with sulfate (W + S) reduced dissolved Cd concentration in both the low- and high-Cd soils. However, an increase in exchangeable Cd was observed only in the low-Cd soil during this period. Sulfate application (S) alone had no significant effect on either dissolved or exchangeable Cd. Both W and W + S treatments reduced bacterial community alpha diversity in the low- and high-Cd soil, primarily effecting the relative abundance of Firmicutes, Bacteroidota, Proteobacteria, and Acidobacteriota. Change in bacterial communities and soil properties, including an increase in dissolved organic carbon and decreases in Eh and pH, were associated with shifts in Cd availability. The effect of straw and sulfate application on Cd availability and bacterial community diversity varied with Cd contamination levels. Overall, straw incorporation, either alone or with sulfate, may help reduce Cd availability and modulate microbial communities in high-Cd paddy soil. • Effect of straw addition on Cd availability varied depending on Cd levels • Straw addition increased Cd availability in low Cd soil irrespective of sulfur levels • Straw addition decreased bacterial α-diversity in both low and high Cd soil • Sulfate supply showed minimal effect on Cd availability and bacterial community