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 Astransformation bacterial community was further examined. In pots, CaCO3 increased soil pH by 0.57 and increased bioavailable As concentration by 6.2 mu g 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 Astransformation 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.