| Summary: | Rice is the main staple food worldwide, yet paddy fields are a primary source of artificial methane (CH<sub>4</sub>) emissions. Phosphorus (P) is a key element in the growth of plants and microbes, and P fertilizer input is a conventional agricultural practice adopted to improve rice yield. However, the impact of long-term P fertilizer addition on CH<sub>4</sub> emissions in rice paddies is still unclear. To test this impact, a 36-yr field experiment with and without P fertilizer application treatments under a double-rice cropping system was used in this study to explore how continuous P application affects CH<sub>4</sub> emissions and related plant and soil properties. The cumulative CH<sub>4</sub> emissions were 21.2% and 28.6% higher without P fertilizer application treatment than with P fertilizer application treatment during the early and late season, respectively. Long-term P fertilizer application increased the rice aboveground biomass by 14.7–85.1% and increased grain yield by 24.5–138.7%. However, it reduced the ratio of root biomass to aboveground biomass. Long-term P fertilizer input reduced the soil NH<sub>4</sub><sup>+</sup> concentrations in both rice seasons but increased the soil DOC concentrations in the late season. The soil methanogenic abundance and CH<sub>4</sub> production potential were similar without and with P fertilizer application treatments; however, the methanotrophic abundance and soil CH<sub>4</sub> oxidation potential with P fertilizer application treatment were significantly higher than without P fertilizer application treatment. Our findings indicate that long-term P fertilizer input reduces CH<sub>4</sub> emissions in rice fields, mainly by improving CH<sub>4</sub> oxidation, which highlights the need for judicious P management to increase rice yield while reducing CH<sub>4</sub> emissions.
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