An innovative soil mesocosm system for studying the effect of soil moisture and background NO contribution on soil surface trace gas fluxes

This research investigates the complex dynamics of how soil NO concentrations and soil moisture affect the exchange of greenhouse gases between soils and the atmosphere. To this end, we have developed and tested an automated soil mesocosm system (AU-MES), which allows for dynamically change of headspace and soil NO concentrations, measures trace and greenhouse gas fluxes based on a dynamic chamber approach, and observes and manipulates key soil and environmental metrics such as temperature, light conditions, or moisture. Initial a brief phase of soil-only incubation experiments demonstrated the influence of soil moisture and soil and headspace NO concentrations of 400 ppbv on gas emissions. We observed that under low soil moisture conditions (30% water-filled pore space), nitrification was favored, as indicated by increased emissions of NO (at zero NO concentration 0.191 kg N ha-1 and at high NO concentration 0.180 kg N ha-1) and NO2 (at zero NO concentration 0.002 kg N ha-1 and at high NO concentration 0.001 kg N ha-1). In contrast, under higher soil moisture conditions (50% water-filled pore space), we observed increased N2O (at zero NO concentration 0.149 kg N ha-1and at high NO concentration 0.147 kg N ha-1) and CO2 (at zero NO concentration 0.122 t C ha-1 and at high NO concentration 0.110 t C ha-1) fluxes, suggesting that denitrification may become more important. These results, particularly under soil rewetting and fertilizer application, illustrate the complex interplay between soil nitric oxide concentrations, moisture levels, microbial activities, and gas emissions. In summary, the AU-MES system is a valuable tool for investigating soil-atmosphere gas interactions and the effects of various environmental elements on these processes. Our research provides important insights into how nitric oxide may affect soil processes and trace gas exchange at the soil-atmosphere interface. Keywords Automated soil mesocosm system, nitric oxide, gas concentrations, headspace purging, soil purging