Insights into plant‐part‐specific N 2 O production in roots and shoots of chicory ( Cichorium intybus ) using stable isotope labelling

Summary Nitrous oxide (N 2 O) 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 N 2 O, but the mechanisms remain poorly constrained. For the first time, we resolved organ‐specific N 2 O formation in roots and shoots of aseptically cultivated chicory ( Cichorium intybus ) under light and dark conditions, combining 15 N‐labelling ( 15 NO 3 − / 15 NH 4 + ) with position‐specific isotope analysis to identify N 2 O formation pathways. All cultures produced N 2 O under dark conditions, whereas illuminated shoots showed reduced production or net uptake, indicating photosynthetically driven suppression or internal consumption. Roots supplied with 15 NO 3 − exhibited relatively symmetric 15 N enrichment at the α‐ and β‐positions of emitted N 2 O (compared to shoots), consistent with a reductive pathway that may involve nitric oxide as an intermediate. By contrast, shoots showed asymmetric intramolecular 15 N enrichment exclusively under dark conditions with 15 NO 3 − , indicating a NO 3 − ‐dependent pathway mechanistically distinct from that operating in roots. No significant 15 N incorporation was detected in any other shoot treatment. These organ‐specific, light‐dependent dynamics are absent from global N 2 O budgets and vegetation models. Our findings reveal unrecognized complexity in plant N 2 O exchange and provide a mechanistic framework for incorporating vegetation processes into future N 2 O budget assessments.