Soil pore architecture as a regulator of nitrous oxide dynamics in tropical agroecosystems

Soil structure is a dynamic property strongly influenced by soil management, directly affecting biogeochemical cycling of nitrous oxide (N₂O). Here, we evaluated how long-term land use systems influence soil pore architecture and N₂O production pathways under controlled conditions in a tropical Amazonian soil. The study was conducted in a 12-year field experiment comparing three systems: (i) crop-succession, (ii) integrated crop-livestock, and (iii) well-managed pasture. Synchrotron-based X-ray computed microtomography (SRXCT) was used to characterize micro-scale pore architecture, while laboratory incubation experiments conducted on undisturbed soil cores measured N₂O production. Soil aggregates (6 mm) were scanned using a SRXCT at the MOGNO beamline of Sirius, operating at 22 keV, indirect photon detection, and 2x objective lens, achieving an effective pixel size of 3.35 µm. 3D image analysis quantified pore size distribution, connectivity, and average pore distance. Results show that the fraction of pores between 10-30 µm (in diameter) and global average pore distance were key drivers in N₂O production by promoting anaerobic microsites favorable to denitrification. The integrated crop-livestock system showed the highest N₂O production, attributed to elevated nitrate availability, a greater fraction of 10-30 µm pores, higher global average pore distances, and more connected pore networks. Overall, our findings showed that soil pore architecture influenced oxygen availability, microbial activity, and the spatial distribution of N substrates. These results underscore the impact of soil pore heterogeneity in mediating N₂O dynamics and reinforce the importance of land use strategies that consider the micro-scale to support climate-resilient agriculture in tropical systems.