Periphytic biofilm (PB) in paddy field: A natural cadmium barrier for rice (Oryza sativa L.) safe production through physiological detoxification and gene regulation

Periphytic biofilm (PB) is ubiquitous in paddy fields and has significant impacts on the behavior of cadmium at the soil-water interface. However, its effects on rice growth and Cd accumulation remain largely unknown. Here, we conducted pot and field experiments to explore how PB affects rice growth and Cd migration pathways. Results showed that PB promoted rice growth and alleviated the toxic effects to rice in Cd-polluted soil, reducing Cd accumulation in rice shoot, root, and grain under both pot and field trials. PB treatment reduced the activities of antioxidant enzymes, particularly superoxide dismutase in rice leaves, which indicated less Cd-induced damage in rice leaves. Furthermore, PB enhanced the formation of iron/ manganese plaque around rice roots by 21–34 % under Cd-polluted soil, and increased the nitrogen and phosphorus uptake of rice root significantly. These were further verified by transcriptomic analyses that the expression of Cd-uptake associated genes such as OsCDT9, LCT, and HMA5 of rice plants in PB treatment was down-regulated, while nutrient uptake-related genes including OsISC12, OsGLU, and OsHAK7 were up-regulated. This study not only expands our understanding of Cd biogeochemistry in paddy ecosystem, but also provides a promising in situ approach to reducing Cd migration from soil to rice grain.