Stefan Olin

Nitrogen (N) transformation processes by soil microbes account for significant nitrous oxide (N₂O) emissions from natural ecosystems and cropland. However, understanding and quantifying global soil N₂O emissions and their responses to changing environmental conditions remain challenging. Here, we implemented a soil nitrification–denitrification module into the dynamic vegetation model LPJ-GUESS to estimate N₂O emissions from global lands. The performance of this new development is examined using observed N₂O fluxes from natural-soil and cropland field trials and independent global-scale estimates. LPJ-GUESS broadly reproduces the cumulative N₂O emissions under different climate conditions and N fertilizer applications that are observed in the field experiments, with some deviations in emission seasonality. Globally, simulated soil N₂O emissions from terrestrial ecosystems increase from 5.6±0.2 Tg N yr⁻¹ in the 1960s to 9.9±0.3 Tg N yr⁻¹ in the 2010s, with croplands contributing about two-thirds of the total increase. East Asia and South Asia show the fastest growth rates in N2O emissions over the study period due to the expansion of fertilized croplands. On a global scale, N fertilization (including synthetic fertilizer and manure use), atmospheric N deposition, and climate change contribute 58 %, 46 %, and 24 %, respectively, to the simulated soil N₂O emissions in the 2010s. Rising CO₂ levels in the atmosphere reduce the simulated emissions by 32 % through increased plant N uptake, whereas land use changes have varied spatial effects on emissions depending on N management intensity after land cover conversion. Our estimates only account for the direct soil N₂O emissions, excluding those from fertilized pastures. This study highlights the importance of environmental factors in influencing global soil N₂O emissions, particularly for assessing greenhouse gas mitigation potential in agricultural ecosystems.