Land inclination controls CO₂ and N₂O fluxes, but not CH₄ uptake, in a temperate upland forest soil

Inclination and spatial variability in soil and litter properties influence soil greenhouse gas (GHG) fluxes and thus ongoing climate change, but their relationship in forest ecosystems is poorly understood. To elucidate this, we explored the effect of inclination, distance from a stream, soil moisture, soil temperature, and other soil and litter properties on soil–atmosphere fluxes of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) with automated static chambers in a temperate upland forest in eastern Austria. We hypothesised that soil CO₂ emissions and CH₄ uptake are higher in sloped locations with lower soil moisture content, whereas soil N₂O emissions are higher in flat, wetter locations. During the measurement period, soil CO₂ emissions were significantly higher on flat locations (p < 0.05), and increased with increasing soil temperature (p < 0.001) and decreasing soil moisture (p < 0.001). The soil acted as a CH₄ sink, and CH₄ uptake was not significantly related to inclination. However, CH₄ uptake was significantly higher at locations furthest away from the stream as compared to at the stream (p < 0.001) and positively related to litter weight and soil C content (p < 0.01). N₂O fluxes were significantly higher on flat locations and further away from the stream (p < 0.05) and increased with increasing soil moisture (p < 0.001), soil temperature (p < 0.001), and litter depth (p < 0.05). Overall, this study underlines the importance of inclination and the resulting soil and litter properties in predicting GHG fluxes from forest soils and therefore their potential source-sink balance.