Plant electrical signals reveal the joint interactions of bicarbonate- selenium on cadmium transport in Cardamine violifolia

Cardamine violifolia (C. violifolia), a hyperaccumulator selenium plant species, is a common medicinal and edible species as the primary source of Se supplementation in karst areas. Bicarbonate (HCO3-), a byproduct of carbonate rock weathering, may interact with Se, but the synergistic effects of HCO3- and Se on Cd transport in selenium hyperaccumulators remain unclear. In this study, C. violifolia was used to examine the impact of different bicarbonate levels on its growth, photosynthesis, intracellular water dynamics, and nutrient transport. As one result, Se6+ improved the intracellular water-holding capacity (IWHC), the intracellular water/nutrient transfer rate (WTR/NTR), the nutrient translocation capacity (NTC), the nutrient active translocation capacity (NAC), while simultaneously reducing Cd2+ translocation. Bicarbonate and Se6+ together affected Cd2+ transport in C. violifolia. The BSC1 treatment (1 mm HCO3- addition, 0.46 mm Se6+ and 0.27 mm Cd2+) maximized biomass and photosynthesis, likely due to low HCO3- aiding Se6+ translocation and reducing Cd2+ movement. Conversely, BSC3 (15 mm HCO3- addition, 0.46 mm Se6+ and 0.27 mm Cd2+) resulted in the smallest biomass and photosynthesis in C. violifolia, as the high HCO3- level inhibited the translocation of Se6+, which decreased the IWHC, WTR(NTR), NTC and NAC. No significant correlation was found between Se-Cd translocation factors, suggesting that HCO3- may not directly affect Cd2+ transport but could increase root pH, hindering Cd2+ movement from roots to shoots. The 1 mm bicarbonate interacting with selenium can decrease translocation of cadmium and enhance the photosynthesis and growth, thereby enhancing the selenium enrichment capacity and biomass of C. violifolia in karst areas.