Impact of changes in temperature and precipitation on N₂O and NO emissions from forest soils

Abstract

Processes involved in production, consumption and diffusion of trace gases in soils are sensitive to changes in environmental/climatic conditions. Most likely future climate changes will feed back on trace gas fluxes. In order to study possible effects of future climate change on N₂O and NO emissions from forest soils, we used PnET-N-DNDC, a process oriented model which simulates biogeochemical cycling of C and N in forest ecosystems and predicts N-trace gas emissions. The sensitivity of PnET-N-DNDC to changes in N-trace gas fluxes was tested by varying various environmental parameters. Validation against the measured data sets from several field sites revealed the capability of PnET-N-DNDC in predicting trace gas fluxes from forest soils. The effect of future climate change on N-trace gas emission from temperate forest soils was tested for the Höglwald Forest in Germany. Based on the predicted results from the global climate model ECHAM, two different climate scenarios were selected, which represent conditions of today’s climate and of the climate at doubled atmospheric CO₂ concentration. Coupling of ECHAM to the regional climate model MCCM allowed us to predict possible changes in climate for the Höglwald Forest. Climatic conditions for doubled atmospheric CO₂ concentrations increased N-trace gas emissions from a beech and a spruce site at the Höglwald Forest by 5–9% (N₂O) and 27–29% (NO), respectively. The predicted results indicate that the increases in N₂O and NO were due to the increase in decomposition and nitrification. The lower soil moisture in summer limited the microbial turnover of C and N in the soil although the higher temperature was in favor for microbial activity. Therefore, we conclude that changes of precipitation regimes in future may superimpose the effect of temperature on N-trace gas emissions.