Purpose <p>Phosphorus (P) release via reductive dissolution of Fe(III)(hydr)oxides is an important strategy to increase P availability in soil, and previous studies have reported that labile organic matter intensifies P mobilization in paddy soils by microbial Fe(III) reduction. This study aimed to demonstrate the involved microbial mechanism and the benefit of stimulated microbial Fe(III) reduction to the growth of rice plant.</p> Methods <p>This study stimulated microbial Fe(III) reduction via the input of labile carbon substrates (acetate, propionate, and lactate) and identified the key Fe(III)-reducing bacteria responsible for Fe(III) reduction and P availability. The effect of stimulated microbial Fe(III) reduction on the growth of rice plant was explored.</p> Results <p>Results showed that the labile carbon substrate significantly stimulated microbial Fe(III) reduction and concurrently increased the available P content. Specifically, 5 mM acetate increased Fe(III) reduction by 156% and available P release by 67.6% at the end of 7-d incubation. Key Fe(III)-reducing bacteria including <i>Anaeromyxobacter</i>, <i>Citrifermentans</i> and <i>Geobacter</i> were enriched by the labile carbon supplementation, and their abundances positively correlated with Fe(II) and available P contents. The addition of <i>Geobacter</i> and acetate to soil improved the rice plant height by 17.2% and the aboveground biomass by 16.3% after 35 days of cultivation compared to the control soil without supplementation, and the partial least squares path models analysis suggested that the available P increment caused by <i>Geobacter</i> and acetate supplementation was the main driver for the rice plant enhancement.</p> Conclusion <p>Our study demonstrated the potential of using specific carbon substrates to modulate soil microbial community for improving P fertility and crop growth, and provided a scientific basis for the regulation of Fe(III)-reducing microbial communities to relieve P deficiency in soils.</p>