Reducing methane emission by promoting its oxidation in rhizosphere through nitrogen-induced root growth in paddy fields

Purpose Nitrogen (N) fertilizer could promote rice root growth and alter methane (CH 4 ) emissions in paddy fields. This study investigated the mechanism of different N application rates and timing affecting CH 4 emissions, focusing on the interactions between rice root growth, soil properties, and CH 4 -related microbes in the rhizosphere. Methods N fertilizer was applied only as basal and tillering fertilizer (BF) in 2016–2017 and applied as panicle fertilizer (PF) as top-dressing in 2018–2019. A validation experiment was conducted in 2020 to compare the soil chemical properties and CH 4 production and oxidation in rhizosphere soil with those in soil with root effects eliminated by removing rice aboveground parts. Results Based on the local high-yielding BF rate, applying PF had a more significant effect on CH 4 mitigation than increasing BF application rate. PF notably increased the rice root biomass, carbon substrates in root exudate (including organic acids) during rice reproductive growth phase (RGP), and the dissolved organic carbon and dissolved oxygen concentration in rhizosphere soil, simultaneously promoting the abundance and potential activities of methanogens and methanotrophs. A mantel test and the validation experiment confirmed that the increase of CH 4 oxidation activity and a high ratio of methanotrophs to methanogens in rhizosphere soil driven by rice root was the main reason for CH 4 mitigation after N application. Conclusion An appropriate PF rate can stimulate rice root growth, root exudation, and oxygen secretion, increasing the CH 4 oxidation in rhizosphere soil that contributes significantly to the CH 4 mitigation in paddy fields.