Deciphering the translocation of cadmium in indica rice under high-cadmium soil conditions

The migration and translocation dynamics of cadmium (Cd) across the growth spectrum of indica rice, including two conventional (C1, C2) and two hybrid (H1, H2) cultivars, were deciphered through a field experiment at a high Cd-contaminated site for the first time. It was determined that the phloem was the most important transport route for Cd in the grains for both conventional and hybrid cultivars under high Cd conditions. This is supported by the evidence that the translocation factor TF_{leaves-brown rice} exhibited highly significant positive correlations with the Cd concentration in brown rice for C1, C2 and H2 (p < 0.01), with correlation coefficients being 0.59 for C1, 0.87 for C2, and 0.50 for H2 respectively. A highly significant correlation between TF_{stem-brown rice} and the Cd concentration in brown rice was revealed for H1 and H2 only (p < 0.01). Soil microbial diversity was generally higher after rice cultivation, and a negative correlation between Cd content and microbial richness was determined. At phylum level, it was verified that Firmicutes were more abundant in soils with medium or severe Cd pollution, and MBNT15 were typically enriched in conventional rice types, including both japonica and indica. The abundance of Bacteroidota were enhanced under high Cd conditions, and Gemmatimonadetes may be dominant only under low to medium Cd pollution conditions. At the other levels, it was inferred that both hybrid and conventional rice can enrich Bacillus, and SBR1031 played a more important role, contributing to higher Cd content in the brown rice of H2.