Abstract. We analysed nitrogen oxides (N2O, NO and NO2) and carbon dioxide (CO2) emissions from two beech forest soils close to Vienna, Austria, which were exposed to different nitrogen input from the atmosphere. The site Schottenwald (SW) received 22.6 kg N y-1 and Klausenleopoldsdorf (KL) 13.5 kg N y-1 through wet and dry deposition. Nitrogen oxide emissions from soil were measured hourly with an automatic dynamic chamber system. Daily N2O measurements were carried out by an automatic gas sampling system. Measurements of nitrous oxide (N2O) and CO2 emissions were conducted over larger areas on a biweekly (SW) or monthly (KL) basis by manually operated chambers. We used an autoregression procedure (time-series analysis) for establishing time-lagged relationships between N-oxide emissions and different climate, soil chemistry and N-deposition data. It was found that changes in soil moisture and soil temperature significantly effected CO2 and N-oxide emissions with a time lag of up to two weeks and could explain up to 95% of the temporal variations of gas emissions. Event emissions after rain or during freezing and thawing cycles contributed significantly (for NO 50%) to overall N-oxides emissions. In the two-year period of analysis the annual gaseous N2O losses at SW ranged from 0.65 to 0.77 kg N ha-1 y-1 and NO losses were 0.18 to 0.67 kg N ha-1 per vegetation period. In KL significantly lower annual N2O emissions (0.52 kg N2O-N kg ha-1 y-1) as well as considerably lower NO-losses were observed. During a three-month measurement campaign NO losses at KL were 0.02 kg, whereas in the same time period significantly more NO was emitted in SW (0.32 kg NO-N ha-1). Higher N-oxide emissions, especially NO emissions from the high N-input site (SW) indicate that atmospheric deposition had a strong impact on losses of gaseous N from our forest soils. At KL there was a strong correlation between N-deposition and N-emission over time, which shows that low N-input sites are especially responsive to increasing N-inputs.

Abstract. We measured nitrogen oxides (N2O and NOx), dinitrogen (N2) and carbon dioxide (CO2) emissions from a spruce-fir-beech forest soil in the North Tyrolean limestone Alps in Austria. The site received 12.1 kg nitrogen via wet and dry deposition. Fluxes of nitric oxide (NO) were measured by an automatic dynamic chamber system on an hourly basis over a two year period. Daily N2O emissions were obtained by a semi-automatic gas measuring system. In order to cover spatial variability biweekly manual measurements of N2O and CO2 emissions were carried out, additionally. For acquiring information on the effects of soil and meteorological conditions and of N-deposition on N-emissions we chose the autoregression procedure (time-series analysis) as our means of investigation. Hence, we could exclude the data's autocorrelation in the course of the time. We found that soil temperature, soil moisture and wet N-deposition followed by air temperature and precipitation were the most powerful influencing parameters effecting N-emissions. With these variables up to 89% of observed temporal variations of N-emissions could be explained. During the two-year investigation period between 2.5 and 3.5% of deposited N was reemitted in form of N2O whereas only 0.2% were emitted as NO. At our mountain forest site the main end-product of microbial activity processes was N2 and trace gases (N2O and NO) were only of minor importance.