Cadmium bioavailability and accumulation in rice grains: A comprehensive assessment of soil properties and rhizobacterial influences using in vitro-in vivo assays and multivariate modeling

Identifying key soil parameters and rhizobacterial communities that control cadmium (Cd) transfer throughout the soil-microorganism-rice-human continuum is crucial to guarantee rice consumption safety and safeguarding human health. Here, a pot experiment investigated that how edaphic properties of four different soils and their associated microbial communities influence Cd buildup and bioavailability in two different rice cultivars. Results demonstrated that Cd-low accumulating rice cultivar exhibited significantly lower grain Cd concentration than Cd-high accumulating rice cultivar. Grain Cd concentrations (total and bioavailable) showed strongest correlations with soil total Cd (T-Cd), phytoavailable Cd (A-Cd), and available potassium (AK) contents. Notably, in vitro-in vivo assays revealed lesser Cd bioavailability in rice despite elevated Cd levels in soils, with significant interactions observed between grains T-Cd and bioaccessible and bioavailable Cd concentration. Additionally, high-throughput sequencing revealed that rhizobacterial community composition, diversity and network were influenced with soil type. Specific taxa involved in organic matter decomposition (Blastocatellales and Anaerolineae) were associated with reduced grains Cd absorption and accumulation by changing the rhizosphere Cd availability. Moreover, Partial least squares path modeling (PLS-PM) confirmed that Cd accumulation and bioavailability in rice grains was affected not only by edaphic properties and Cd exposure level, but also by soil rhizobacterial community composition. This study advances understanding of how soil properties and rhizobacterial communities jointly regulate Cd transfer across the soil-microorganism-rice-human continuum in diverse soil environments.