Soil nitrous oxide emissions from global land ecosystems and their drivers within the LPJ-GUESS model (v4.1)

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.: