Insights into plant-part specific N2O production in roots and shoots of chicory (C. intybus) using stable isotope labelling

O_LINitrous oxide (N2O) substantially contributes to climate change and stratospheric ozone degradation, yet large uncertainties in its global budget indicate unknown or overlooked sources. Increasing evidence suggests that plants may also produce N2O, though the underlying mechanisms and pathways remain poorly constrained. C_LIO_LITo examine whether plants can form N2O under sterile conditions and to assess the contribution of different plant parts, we applied a novel 15N stable isotope labelling approach using sterile Cichorium intybus root and shoot cultures incubated separately under light and dark conditions. C_LIO_LIAll root/shoot cultures showed N2O formation under dark conditions, whereas shoots under light showed reduced or even uptake of N2O, indicating photosynthetically driven suppression of formation pathways or simultaneous internal degradation of N2O. C_LIO_LIIsotopic analyses revealed distinct formation pathways: roots supplemented with 15NO3- showed position-specific 15N enrichment consistent with N2O formation via nitric oxide as an intermediate, linking root-derived N2O to NO3- reduction. In contrast, root/shoot incubations with 15N-NH4+ supplementation and shoots in darkness emitted N O without clear 15N enrichment suggesting alternative formation pathways independent of these compounds. Our isotopic labelling approach powerfully disentangled N2O formation mechanisms yet highlights necessary further exploration of plant N2O cycling to improve global budgets and enable potential mitigation strategies. C_LI