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<p>Although tree stems act as conduits for greenhouse gases (GHGs) produced in the soil, the magnitudes of tree contributions to total (soil&thinsp;<span class="inline-formula">+</span>&thinsp;stem) nitrous oxide (N<span class="inline-formula">₂</span>O) emissions from tropical rainforests on heavily weathered soils remain unknown. Moreover, soil GHG fluxes are largely understudied in African rainforests, and the effects of land-use change on these gases are identified as an important research gap in the global GHG budget. In this study, we quantified the changes in stem and soil N<span class="inline-formula">₂</span>O fluxes with forest conversion to cacao agroforestry. Stem and soil N<span class="inline-formula">₂</span>O fluxes were measured monthly for a year (2017–2018) in four replicate plots per land use at three sites across central and southern Cameroon. Tree stems consistently emitted N<span class="inline-formula">₂</span>O throughout the measurement period and were positively correlated with soil N<span class="inline-formula">₂</span>O fluxes. <span class="inline-formula">¹⁵</span>N-isotope tracing from soil mineral N to stem-emitted <span class="inline-formula">¹⁵</span>N<span class="inline-formula">₂</span>O and correlations between temporal patterns of stem N<span class="inline-formula">₂</span>O emissions, soil–air N<span class="inline-formula">₂</span>O concentration, soil N<span class="inline-formula">₂</span>O emissions and vapour pressure deficit suggest that N<span class="inline-formula">₂</span>O emitted by the stems originated predominantly from N<span class="inline-formula">₂</span>O produced in the soil. Forest conversion to extensively managed, mature (<span class="inline-formula">&gt;20</span> years old) cacao agroforestry had no effect on stem and soil N<span class="inline-formula">₂</span>O fluxes. The annual total N<span class="inline-formula">₂</span>O emissions were 1.55&thinsp;<span class="inline-formula">±</span>&thinsp;0.20&thinsp;kg&thinsp;N&thinsp;ha<span class="inline-formula">⁻¹</span>&thinsp;yr<span class="inline-formula">⁻¹</span> from the forest and 1.15&thinsp;<span class="inline-formula">±</span>&thinsp;0.10&thinsp;kg&thinsp;N&thinsp;ha<span class="inline-formula">⁻¹</span>&thinsp;yr<span class="inline-formula">⁻¹</span> from cacao agroforestry, with tree N<span class="inline-formula">₂</span>O emissions contributing 11&thinsp;% to 38&thinsp;% for forests and 8&thinsp;% to 15&thinsp;% for cacao agroforestry. These substantial contributions of tree stems to total N<span class="inline-formula">₂</span>O emissions highlight the importance of including tree-mediated fluxes in ecosystem GHG budgets. Taking into account that our study sites' biophysical characteristics represented two-thirds of the humid rainforests in the Congo Basin, we estimated a total N<span class="inline-formula">₂</span>O source strength for this region of 0.18&thinsp;<span class="inline-formula">±</span>&thinsp;0.05&thinsp;Tg&thinsp;N<span class="inline-formula">₂</span>O-N&thinsp;yr<span class="inline-formula">⁻¹</span>.</p>