Straw Removal Reduces Cd Availability and Rice Cd Accumulation in Cd-Contaminated Paddy Soil: Cd Fraction, Soil Microorganism Structure, and Soil Porewater's Doc and Cd

Abstract

Experiments were conducted in paddy fields over two consecutive seasons to investigate the impact of continuous straw removal on Cd absorption by rice plants and the composition of microbial communities in soil. The results of two fields revealed that the treatments reduced the content of soil available Cd, accompanied by the reduction of dissolved organic carbon and Cd in soil porewater, thereby reducing Cd contents in rice. For soil Cd, the proportion of exchangeable and oxidizable fraction decreased, while the proportion of residual fraction increased. The Cd content in brown rice cultivated in both slightly and heavily Cd-contaminated soils showed significant reductions ranging from 10.72% to 47.26% and 18.33% to 41.50%, respectively. Specifically, the Cd content in brown rice was below 0.2 mg·kg-1 when all rice straw and roots were removed in slight-Cd-contaminated soils. The soil microbial α–diversity was a less influenced by continuous straw treatments, while the β-diversity was altered. Redundancy analysis exhibited that pH was predominated to influence the microbial community. Structural equation modeling revealed that the primary influencers on brown rice Cd were DTPA-Cd and porewater’s Cd. Straw removal will be an economical and effective technique to reduce the risk of Cd in rice.

Keywords: Cd-contaminated soil, Rice straw removal, Accumulation, Soil porewater, Microbial community