Calcium carbonate enhanced As uptake in Pteris vittata by increasing pH and As bioavailability and mediating rhizosphere As-transformation bacterial community

Pteris vittata is the first reported arsenic (As) hyperaccumulator, which is also a calcium (Ca) indicator and adapts to calcareous environment. Therefore, it is hypothesized that Ca plays a role in As accumulation but detail effects and mechanisms are unclear. Typical Ca-compounds (CaCO₃, Ca₃(PO₄)₂ and CaSO₄) were added to hydroponics. CaCO₃ and Ca₃(PO₄)₂ increased pH by 0.75 and 0.31, while CaSO₄ decreased it by 0.26. Besides, CaCO₃ increased As concentration in P. vittata frond by 25.8 % from 65.4 to 82.3 mg kg^–1, while Ca₃(PO₄)₂ and CaSO₄ decreased it by 15.1–38.2 % to 40.4–55.5 mg kg^–1. So the effect of CaCO₃ on soil pH, As bioavailability and As-transformation bacterial community was further examined. In pots, CaCO₃ increased soil pH by 0.57 and increased bioavailable As concentration by 6.2 μg kg^–1, thereby induced 27.3–28.5 % promotion in As plant accumulation. Rhizosphere bacterial community variance can be explained by soil pH and bioavailable As changes at 49–66 %. P. vittata frond As concentration was negatively correlated with rhizosphere As-transformation bacterial diversity (arrA and arsM) (R=-0.57 and -0.66), and positively correlated with the relative abundance of Geobacter (R=0.66) and Pseudomanas (R=0.48), which mediating As mobilization and transformation. This indicated that CaCO₃ can enhance As uptake by P. vittata via increasing soil pH, As bioavailability and mediating As-transformation bacterial community in the rhizosphere. The information helps to better understand how calcareous environment-adaptation benefits P. vittata to uptake and accumulate As. This helps to strategize more efficient processes for As-contaminated soils remediation using the hyperaccumulating plants.