Excessive input of phosphorus significantly affects microbial Fe(III) reduction in flooded paddy soils by changing the abundances and community structures of Clostridium and Geobacteraceae

- Phosphorus addition significantly inhibited the early Fe(III) reduction.
- Suppression of microbial Fe(III) reduction by phosphorus addition was eliminated during the late stage of incubation.
- The growth of Clostridium and Geobacteraceae was greatly inhibited by phosphorus addition.
- The community structures of Clostridium and Geobacteraceae dynamically responded to phosphorus addition.

Microbial Fe(III) reduction can make an excellent contribution to the bioremediation of contaminated environments and potentially reduce methanogenesis. Excessive input of phosphorus (P) by P fertilizer application and eutrophied irrigation water might have a substantial influence on the process of microbial Fe(III) reduction in flooded paddy soils. To evaluate the effect of P application on microbial Fe(III) reduction, the responses of Clostridium and Geobacteraceae communities to different concentrations of P addition (CK: 0 mmol P kg− 1 soil; P1: 3.3 mmol P kg− 1 soil; P2: 20 mmol P kg− 1 soil) were investigated in anaerobically incubated paddy slurries. P addition significantly inhibited Fe(III) reduction during the early stage of incubation (from days 0 to 20). Compared with the CK treatment, the maximum Fe(III) reduction rate (Vmax) in treatments P1 and P2 remarkably decreased by 0.281 and 0.439 mg·g− 1·d− 1, respectively. However, the addition of P had no significant effect on Fe(III) reduction during the later stage of incubation (after 20 days). The abundances of Clostridium and Geobacteraceae were suppressed by P addition, and the suppression effect was more obvious with higher P concentration. P addition significantly changed the community structures of Clostridium and Geobacteraceae during the entire incubation. The communities of Clostridium and Geobacteraceae were closely correlated with the process of Fe(III) reduction. In conclusion, P addition could inhibit the microbial reduction of Fe(III) during the early stage of incubation by reducing the abundances and altering the community structures of Clostridium and Geobacteraceae, however, the inhibition could be eliminated with increased incubation time. This study demonstrates that soil microbial communities are sensitive to excessive P application, which can jointly impact relevant biogeochemical processes in flooded paddy soils.

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