Repeated drying–rewetting cycles and their effects on the emission of CO2, N2O, NO, and CH4 in a forest soil

Abstract

AbstractProlonged summer droughts due to climate change are expected for this century, but little is known about the effects of drying and wetting on biogenic trace‐gas fluxes of forest soils. Here, the response of CO2, N2O, NO, and CH4 fluxes from temperate forest soils towards drying–wetting events has been investigated, using undisturbed soil columns from a Norway spruce forest in the “Fichtelgebirge”, Germany. Two different types of soil columns have been used for this study to quantify the contribution of organic and mineral horizons to the total fluxes: (1) organic horizons (O) and (2) organic and mineral soil horizons (O+M). Three drying–wetting treatments with different rewetting intensities (8, 20, and 50 mm of irrigation d–1) have been compared to a constantly moist control to estimate the influence of rainfall intensity under identical drying conditions and constant temperature (+15°C). Drought significantly reduced CO2, N2O, and NO fluxes in most cycles. Following rewetting, CO2 fluxes quickly recovered back to control level in the O columns but remained significantly reduced in the O+M columns with total CO2 fluxes from the drying–wetting treatment ranging approx. 80% of control fluxes. Fluxes of N2O and NO remained significantly reduced in both O and O+M columns even after rewetting, with cumulative fluxes from drying–wetting treatments ranging between 20% and 90% of the control fluxes, depending on gas and cycle. Fluxes of CH4 were small in all treatments and seem to play no significant role in this soil. No evidence for the release of additional gas fluxes due to drying–wetting was found. The intensity of rewetting had no significant effect on the CO2, N2O, NO, and CH4 fluxes, suggesting that the length of the drought period is more important for the emission of these gases. We can therefore not confirm earlier findings that fluxes of CO2, N2O, and NO during wetting of dry soil exceed the fluxes of constantly moist soil.