Plant-mediated nitrous oxide emissions

Plants are increasingly recognized as active contributors to nitrous oxide (N 2 O) fluxes. However, the physiological and biochemical processes underlying these plant-mediated N 2 O emissions remain poorly defined. This review synthesizes current understanding of direct N 2 O production pathways within plants, including chloroplast- and mitochondrial-associated processes involving nitrate and nitrite reductases, as well as cytochrome-mediated reactions under specific conditions. Plant-microbe interactions in the rhizosphere and phyllosphere further influence N 2 O dynamics. Symbiotic nitrogen-fixing bacteria and ammonia-oxidizing organisms modulate nitrogen availability and transformation, altering net fluxes. Evidence is also growing for conduit-mediated N 2 O transport from roots to aerial tissues, as well as for foliar N 2 O uptake, suggesting plants may function as both sources and sinks depending on context. Methodological limitations in separating plant- from microbe-derived N 2 O are critically evaluated, with a focus on challenges in isotopic tracing and sterile growth conditions. Key plant traits and environmental drivers influencing emissions are identified, including leaf area, root length, stomatal density, and hypoxic stress. This review provides an integrated physiological and ecological perspective on plant-associated N 2 O fluxes and proposes a framework linking plant traits, microbial partnerships, and environmental conditions to N 2 O outcomes. Clarifying these mechanisms is essential for incorporating plant processes into global N 2 O budgets and mitigation strategies.