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

Abstract

Prolonged 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.

Nitrogen turnover in fresh Douglas fir litter directly after additions of moisture and inorganic nitrogen

“…Almost immediate increase in respiration after rewetting has been recorded by others (e.g., Borken et al 2003), though recovery of CO 2 respiration to optimal levels may also take a few days (Muhr et al 2008). Secondary peaks or oscillation periods of CO 2 respiration, as observed for the MO incubations, have also been reported by Clein and Schimel (1994) for birch litter that was kept moist after an initial drying.…”

N2O fluxes from the native and grazed semi-arid steppes and their driving factors in Inner Mongolia, China

“…The rapid decreases in oxygen availability caused larger emissions of N 2 O by denitrification (Kester et al 1997). In addition, drying-rewetting alternation could restrict reduction of N 2 O to N 2 through further denitrification, and led to more N 2 O production, so the post precipitation N 2 O fluxes were usually high (Muhr et al 2008).…”

CO<sub>2</sub> efflux from soils with seasonal water repellency

“…It is, however, very common in climates with distinct dry seasons or more prolonged dry periods (Doerr et al, 2003;Doerr and Moody, 2004;Leighton-Boyce et al, 2005;Stoof et al, 2011) and may become more common in the UK in the future climate predictions (IPCC, 2013). It is also an important scenario to be considered during the rewetting of extremely waterrepellent soils after drought, as reported by Muhr et al (2008Muhr et al ( , 2010, who observed a slower regeneration of CO 2 fluxes following wetting that could have been caused by SWR.…”