Effects and mechanisms of different organic manure on minimizing cadmium concentrations in rice grains

Cadmium (Cd) contamination in agricultural soils represents a global issue for soil health and food safety. This study aimed to investigate the effects of organic fertilizers from different sources on Cd uptake and accumulation in rice plants, as well as the biochemical properties of Cd-contaminated soil. We performed high-throughput sequencing of 16S ribosomal RNA (16S rRNA) gene amplicons to characterize soil bacterial communities. The zeta potential of the soil colloids became more negative following the application of GM and EM. In terms of Cd fractionation, chicken manure (CM) amendment reduced the residual fraction of soil Cd, while GM and EM exerted an opposing effect. FT-IR spectroscopy demonstrated that organic fertilizers derived from different sources possessed distinct chemical structural features. At the phylum level, the relative abundance of soil bacteria was largely comparable among treatments receiving different manure application rates. Taxonomic analysis further revealed that Proteobacteria, Actinobacteria, Gemmatimonadetes, Bacteroidetes, and Acidobacteria were the five dominant bacterial phyla in the Cd-contaminated soil. Furthermore, GM and EM applications mitigated Cd uptake by rice plants at all growth stages and across all examined Cd concentration gradients. By contrast, excessive CM amendment amplified the risk of heavy metal bioaccumulation in rice tissues.