Impact of Drought and Rewetting Cycles on Soil Greenhouse Gas Fluxes across an N Deposition Gradient in Austrian Forests

Stockholm

2024

1404

Bandaufführung

40005286

Climate change has increased the frequency and intensity of extreme weather events such as drought periods and heavy rainfall in large areas of the world, including Central Europe. Despite decreasing nitrogen deposition rates in this region, forests are still subjected to high N deposition rates from agricultural and industrial sources. These disturbances affect fundamental biogeochemical processes and likely alter greenhouse gas fluxes in forest soils. However, the full impact of N deposition on the response of forest soils to increasing extreme weather events is still unknown. In this project, our approach combines the use of active manipulation simulating drying-rewetting (DRW) cycles on a natural gradient over three representative Austrian broadleaf-forest sites with detailed field GHG observations, microbial laboratory analyses and process-based modelling. The DRW plots received the long-term averaged rainfall concentrated in three single extreme precipitation events and were excluded from rain the rest of the vegetation period. N-addition plots received extra N at a rate of 50 kg N ha-1 y-1. Soil GHG fluxes were measured with automated chambers at a high temporal resolution on all plots. Soil samples were taken before and after each irrigation event to measure microbial responses to drying and rewetting and the abundance of methanotrophic bacteria. Measurements were conducted in 2021 and 2022. Results show reduced soil CO2 fluxes, extremely reduced N2O fluxes, and increased CH4 uptake under DRW treatments compared to natural environmental conditions. Natural drought conditions led to a convergence of N2O emission levels in the DRW and control plots. N addition only had modest effects on GHG fluxes The significance of the interplay between a higher frequency and intensity of DRW cycles and N deposition rates for the soil GHG budget and the feedback between
forests and climate change will be presented and discussed.