N2O flux from plant-soil systems in polar deserts switch between sources and sinks under different light conditions

Abstract

Production and consumption of greenhouse gases such as CO2, CH4 and N2O are key factors driving climate change. While CO2 sinks are commonly reported and the mechanisms relatively well understood, N2O sinks have often been overlooked and the driving factors for these sinks are poorly understood. We examined CO2, CH4 and N2O flux in three High Arctic polar deserts under both light (measured in transparent chambers) and dark (measured in opaque chambers) conditions. We further examined if differences in soil moisture, evapotranspiration, Photosynthetically Active Radiation (PAR), and/or plant communities were driving gas fluxes measured in transparent and opaque chambers at each of our sites. Nitrous oxide sinks were found at all of our sites suggesting that N2O uptake can occur under extreme polar desert conditions, with relatively low soil moisture, soil temperature and limited soil N. Fluxes of CO2 and N2O switched from sources under dark conditions to sinks under light conditions, while CH4 fluxes at our sites were not affected by light conditions. Neither evapotranspiration nor PAR were significantly correlated with CO2 or N2O flux, however, soil moisture was significantly correlated with both gas fluxes. The relationship between soil moisture and N2O flux was different under light and dark conditions, suggesting that there are other factors, in addition to moisture, driving N2O sinks. We found significant differences in N2O and CO2 flux between plant communities under both light and dark conditions and observed individual communities that shifted between sources and sinks depending on light conditions. Failure of many studies to include plant-mediated N2O flux, as well as, N2O soil sinks may account for the currently unbalanced global N2O budget.