Phosphate rock drives greater arsenic accumulation in Pteris vittata than calcium carbonate by enhancing arsenic metabolism and reshaping rhizosphere microbiome.

Poorly-soluble phosphate rock (PR) and CaCO3 can enhance arsenic accumulation in calcicolous As-hyperaccumulator Pteris vittata, but their mechanisms under soil conditions remain unclear. P. vittata was grown for two months in As-contaminated soil (100 mg kg-1) receiving 2.0 g kg-1 Ca as PR, CaCO3, or soluble CaCl2. Plant nutrients, rhizosphere chemistry and bacterial communities, and As-metabolism genes were examined. Compared with CaCO3, PR increased frond As and P by 35% and 28% to 3128 and 3158 mg kg-1, while CaCO3 produced slightly greater biomass and 10-15% higher rhizosphere available As and P. PR upregulated P-transporter PvPht1;3, arsenate reductase PvHAC2, and arsenite antiporters PvACR3 and PvACR3;3 by 2.0-2.3 fold, whereas CaCO3 induced PvPht1;3, PvPTB1;2, and PvACR3;1/3;2 by 1.7-3.3 fold relative to the soil control. PR retained a more diverse bacterial community (Shannon: 4.20) containing taxa associated with P cycling and As tolerance, whereas CaCO3 showed lower diversity (3.76) under elevated pH. These findings link superior As accumulation under PR to P acquisition, distinct As-metabolism transcriptional responses, and rhizosphere restructuring, providing a mechanistic basis for selecting PR to enhance As accumulation during phytoremediation of As-contaminated soils.