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

Nitrous oxide (N ₂ O) 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 N ₂ O, though the underlying mechanisms and pathways remain poorly constrained.

To examine whether plants can form N ₂ O under sterile conditions and to assess the contribution of different plant parts, we applied a novel ¹⁵ N stable isotope labelling approach using sterile Cichorium intybus root and shoot cultures incubated separately under light and dark conditions.

All root/shoot cultures showed N ₂ O formation under dark conditions, whereas shoots under light showed reduced or even uptake of N ₂ O, indicating photosynthetically driven suppression of formation pathways or simultaneous internal degradation of N ₂ O.

Isotopic analyses revealed distinct formation pathways: roots supplemented with ¹⁵ NO ₃ ⁻ showed position-specific ¹⁵ N enrichment consistent with N ₂ O formation via nitric oxide as an intermediate, linking root-derived N ₂ O to NO ₃ ⁻ reduction. In contrast, root/shoot incubations with ¹⁵ N-NH ₄ ⁺ supplementation and shoots in darkness emitted N O without clear ¹⁵ N enrichment suggesting alternative formation pathways independent of these compounds. Our isotopic labelling approach powerfully disentangled N ₂ O formation mechanisms yet highlights necessary further exploration of plant N ₂ O cycling to improve global budgets and enable potential mitigation strategies.