Soil CO2, CH4 and N2O fluxes, soil parameters and meteorological data from two temperate upland forest sites

Extreme weather events such as drought periods and heavy rainfalls are increasing in frequency and intensity in Central Europe, however we have a limited understanding of how these changes, in combination with other stress factors such as nitrogen (N) deposition, affect soil greenhouse gas (GHG) fluxes in different forest ecosystems. Here, we explored the combination of drying-rewetting cycles with N-addition treatments on soil fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in two Austrian beech forests with differing background N-deposition levels and different soil types: Klausen-Leopoldsdorf (KL) and Zöbelboden (ZB). We hypothesised that drought periods combined with episodic rainfall events would induce a decrease in soil GHG emissions compared to natural conditions. Furthermore, we expected that N-addition would increase CO2 and N2O emissions while reducing CH4 uptake, and that soil moisture and temperature will modulate GHG fluxes differently at each site. We measured soil GHG fluxes and soil temperature and moisture at high temporal resolution using an automated chamber system over the course of one vegetation period at each site. Soil CO2 and N2O emissions were reduced by drying-rewetting at both sites, while CH4 uptake was periodically enhanced by altered rainfall patterns only at ZB. Short-term N addition had no effect on fluxes. Soil CO2 emissions were more influenced by soil temperature at ZB and by soil moisture at KL, respectively. At KL, CO2 fluxes were modulated to a greater extent by soil moisture dynamics below 10 cm than those from the uppermost 10 cm. Overall, this study suggests that altered precipitation patterns influence consumption and production patterns of GHG in the soil, and that soil temperature and moisture dynamics below 10 cm depth should be examined when assessing the effects of drought and rewetting events on forest soils.