Soil microsites controls N2O production and emission in undisturbed soils

Soil structures regulate the production and emission of N2O from soils mainly through influencing substrate availability and gas diffusion. However, the respective impacts of substrate availability and gas diffusion and their response to moisture changes remain elusive. This study conducted laboratory incubation experiments with disturbed (sieved) and undisturbed (intact) soil cores under different soil moisture levels (i.e., 40, 60, 80 and 100% water filled pore space (WPFS)). Soil N2O fluxes were continuously monitored over a 21-day incubation period, during which O2 concentration profile was occasionally measured and relative soil gas diffusivity was measured at the end of experiments. The results show that the N2O fluxes from the disturbed soil cores were 2~25 times higher, respectively, than those from undisturbed cores, which are similar to field observations. Nevertheless, the difference in the relative soil gas diffusivity between them was not obvious, especially under high moisture conditions. Therefore, the overestimated soil N2O emission from sieved soil experiments was attributed to increased C availability caused by disturbance rather than changes in gas diffusivity. Additional incubation experiments with 15N tracing further demonstrated the key impacts of soil microsites on N2O production and emission. Overall, this study highlighted the physical protection of soil microsites on carbon sequestration and N2O mitigation.