Arsenate exposure shifts microbial functions in the drilosphere: Enhanced C fixation, denitrification and P mobilization

Earthworms serve as vital ecosystem engineers, yet their functional responses to arsenic pollution remain incompletely understood. This study investigated how the native earthworm, Metaphire guillelmi , regulated drilosphere soil physicochemical properties, greenhouse gas emission and microbial communities under arsenate exposure (EA, 30 mg kg −1 ) compared with unpolluted condition (E). Corresponding treatments without earthworms (As, CK) served as controls. The results showed no significant differences in most soil properties between As and CK treatments. Earthworms significantly increased CO 2 and N 2 O emissions and available phosphorus (AP). However, in arsenate-polluted soils (EA vs As), the stimulatory effect of earthworms on CO 2 and N 2 O emissions was 53 % and 24 % lower, respectively, compared to that in unpolluted soils (E vs CK). In contrast, the earthworm-induced enhancement of AP was 92 % greater under arsenate pollution. Meanwhile, the earthworm-induced promotions of C fixation ( frdA ), denitrification ( napA , nirK , nosZ ) and P mobilization ( phoD , phnK , gcd, pqqC ) gene abundance were more pronounced under arsenate exposure, whereas the promotion of C degradation gene ( sga ) was weakened. Bacterial ASVs (n = 22) exhibited more associations with the abundance of C, N, P transformation genes than fungal ASVs (n = 4). Specifically, Flavobacteriaceae, Chitinophagaceae, and Shewanellaceae were keystone bacteria in mediating the abundance of C, N, P transformation genes, and their abundances were higher under EA vs As than E vs CK. Therefore, arsenate exposure can alter the ecological functions of M. guillelmi , improving carbon sequestration and phosphorus mobilization, while increasing the risk of nitrogen loss. These can provide a reference for correctly evaluating the ecological functions, as well as practical applications of earthworms in arsenic-polluted environments. • As did not significantly change C, N, P transformation in soils without earthworms. • Earthworm increased CO 2 , N 2 O emission and AP in the drilosphere without As. • As reduced CO 2 , N 2 O emissions but further enhanced AP in the drilosphere. • As increased frdA , nosZ , phnK abundance in the drilosphere. • As enriched Pseudomonadota, Bacteroidota to regulate C, N, P in the drilosphere.