Relative importance of soil temperature and soil moisture on GHG fluxes is site specific: Results from three drying-rewetting experiments in Austrian forests

Climate change has increased the frequency and intensity of extreme weather events, including droughts and heavy rainfall, across large parts of Central Europe. Forest ecosystems in this region remain exposed to elevated nitrogen inputs from agricultural and industrial sources, despite declining atmospheric N deposition. The combined effects of altered precipitation regimes and N deposition are expected to modify key soil biogeochemical processes and greenhouse gas (GHG) fluxes, yet their interactive impacts remain poorly constrained.

We investigated soil GHG responses to combined drying–rewetting (DRW) cycles and N addition across three representative Austrian broadleaf forest sites. DRW treatments excluded natural rainfall during the growing season, thereby inducing soil drought, and redistributed long-term mean precipitation into three extreme rainfall events, thereby rewetting the dry soil. Nitrogen addition was applied at a rate of 40 kg N ha⁻¹ yr⁻¹. Soil CO₂, N₂O, and CH₄ fluxes were measured at high temporal resolution using automated chamber systems, alongside continuous soil moisture and temperature measurements, during the years 2021, 2022, and 2025. Ancillary soil chemical and biological data were collected to support field observations.

Soil GHG fluxes were analysed using empirical modelling and Bayesian inference. Drying–rewetting treatments led to reduced soil CO₂ emissions and strongly suppressed N₂O fluxes, as drought-induced reductions in these fluxes outweighed the rewetting pulses, while CH₄ uptake was enhanced compared to ambient conditions. During naturally dry periods, N₂O emissions converged between DRW and control plots. Nitrogen addition exerted only modest effects on GHG fluxes across sites. Modelling results revealed site-specific differences in the relative importance of soil moisture and temperature as drivers of GHG fluxes, linked to soil type and hydrological context.

Our findings highlight the importance of high-frequency automated chamber measurements combined with empirical modelling approaches for assessing the relative importance of extreme precipitation regimes and N deposition on forest soil GHG budgets, with implications for understanding ecosystem–climate feedbacks under future climate scenarios.