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

Nitrous oxide (N2O) contributes substantially to climate change and stratospheric ozone degradation, yet large uncertainties in its global budget point to overlooked sources. Growing evidence suggests plants produce N2O, but the mechanisms remain poorly constrained. For the first time, we resolved organ-specific N2O formation in roots and shoots of aseptically cultivated chicory (Cichorium intybus) under light and dark conditions, combining 15N-labelling (15NO3 -/15NH4 +) with position-specific isotope analysis to identify N2O formation pathways. All cultures produced N2O under dark conditions, whereas illuminated shoots showed reduced production or net uptake, indicating photosynthetically driven suppression or internal consumption. Roots supplied with 15NO3 - exhibited relatively symmetric 15N enrichment at the α- and β-positions of emitted N2O (compared to shoots), consistent with a reductive pathway that may involve nitric oxide as an intermediate. By contrast, shoots showed asymmetric intramolecular 15N enrichment exclusively under dark conditions with 15NO3 -, indicating a NO3 --dependent pathway mechanistically distinct from that operating in roots. No significant 15N incorporation was detected in any other shoot treatment. These organ-specific, light-dependent dynamics are absent from global N2O budgets and vegetation models. Our findings reveal unrecognized complexity in plant N2O exchange and provide a mechanistic framework for incorporating vegetation processes into future N2O budget assessments.