Luteolin inhibits nitrogen-induced methane emissions from rice fields

Nitrogen (N) fertilization is essential for sustaining stable rice production; however, it also contributes substantially to anthropogenic methane (CH 4 ) emissions. Previous studies have primarily attributed N-induced increases in CH 4 emissions to enhanced availability of labile carbon from root exudates while neglecting the roles of specific metabolites. Here, we conducted a comprehensive analysis combining a meta-analysis of 62 fertilization studies, field experiments at three sites, and an anaerobic incubation experiment to elucidate how different N application rates modulate CH 4 emissions through rhizosphere metabolite enrichment. Both the meta-analysis and field experiments consistently showed that N fertilization generally increased CH 4 emissions compared with the N-free control, but the magnitude of this effect varied significantly with application rate. Compared with other N application rates, moderate N input (180–210 kg N ha –1 ) showed only a minor effect (11.1–29.7 % higher than zero-N treatment). This variation was associated with luteolin concentration, as demonstrated by both field and anaerobic incubation experiments. Moderate N input stimulated luteolin secretion in rice roots, which subsequently suppressed the growth of Anaerolineaceae, Lachnospiraceae, Syntrophaceticus , Methanosarcina , Methanothrix , and Methanocellaceae. This suppression reduced the thermodynamic feasibility of syntrophic acetate oxidation, acetoclastic methanogenesis, and hydrogenotrophic methanogenesis. Consequently, under moderate N input, both mcrA abundance and cumulative CH 4 emissions were lower than under low N input. Our findings provide novel mechanistic insights into N-driven CH 4 emissions in rice fields and suggest that optimizing N application rates could promote luteolin accumulation in the rhizosphere, thereby effectively mitigating CH 4 production. • Moderate N (180–210 kg ha −1 ) minimizes CH 4 rise (+11–30 %) vs. low/high N. • Luteolin, induced by moderate N, inhibits methanogens and syntrophic bacteria. • Luteolin disrupts acetate/H 2 pathways, lowering mcrA and CH 4 production. • First link between N rate, root metabolites, and methanogen thermodynamics.