Cultivar-dependent rhizobacteria community and cadmium accumulation in rice: Effects on cadmium availability in soils and iron-plaque formation

The association between the rhizospheric microbial community and Cd accumulation in rice is poorly understood. A field trial was conducted to investigate the different rhizobacterial communities of two rice cultivars with high Cd accumulation (HA) and low Cd accumulation (LA) at four growth stages. Results showed that the Cd content in the roots of the HA cultivar was 1.23 - 27.53 higher than that of the LA cultivar (0.08 - 10.5 mu g/plant) at four stages. The LA cultivar had a significantly lower Cd availability in rhizosphere and a higher quantity of iron plaque (IP) on the root surface than the HA cultivar at four stages. This resulted in the reduction of Cd concentration in IPs and Cd translocation from IP-to-root. Mi-crobial analysis indicated that the LA cultivar formed a distinct rhizobacterial community from the HA cultivar and had less a-diversity. The rhizosphere of the LA cultivar was enriched in specific bacterial taxa (e.g., Massilia and Bacillus) involved in Cd immobilization by phosphate precipitation and IP formation by iron oxidization. However, the rhizosphere in the HA cultivar assembled abundant sulfur-oxidizing bacteria (e.g., Sulfuricurvum) and iron reduction bacteria (Geobacter). They promoted Cd mobilization and reduced IP formation via the metal redox process. This study reveals a potential approach in which specific rhizobacteria decrease or increase Cd accumulation in rice on contaminated soil and provides a new perspective for secure rice production. (C) 2022 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

Automated summary

This study investigates the rhizobacterial communities of two rice cultivars with different levels of Cd accumulation and their relationship with Cd accumulation at different growth stages. The results show that the HA cultivar has higher Cd content in the roots compared to the LA cultivar, and the LA cultivar has lower Cd availability in the rhizosphere and more iron plaque formation on the root surface. Microbial analysis reveals that the LA cultivar has specific bacterial taxa involved in Cd immobilization and iron plaque formation, while the HA cultivar has sulfur-oxidizing bacteria and iron reduction bacteria that promote Cd mobilization.