Control of Nitrous Oxide Emissions in European Beech, Norway Spruce and Scots Pine Forests

Abstract

Elevated nitrogen deposition has increased tree growth, the storage of soil organic matter, and nitrate leaching in many European forests, but little is known about the effect of tree species and nitrogen deposition on nitrous oxide emission. Here we report soil N2O emission from European beech, Scots pine and Norway spruce forests in two study areas of Germany with distinct climate, N deposition and soils. N2O emissions and throughfall input of nitrate and ammonium were measured biweekly during growing season and monthly during dormant season over a 28 months period. Annual N2O emission rates ranged between 0.4 and 1.3 kg N ha−1 year−1 among the stands and were higher in 1998 than in 1999 due to higher precipitation during the growing season of 1998. A 2-way-ANOVA revealed that N2O fluxes were significantly higher (p<0.001) at Solling than at Unterlus while tree species had no effect on N2O emissions. Soil texture and the amount of throughfall explained together 94% of the variance among the stands, indicating that increasing portions of silt and clay may promote the formation of N2O in wet forest soils. Moreover, cumulative N2O fluxes were significantly correlated (r2 = 0.60, p<0.001) with cumulative NO 3 − fluxes at 10 cm depth as an indicator of N saturation, however, the slope of the regression curve indicates a rather weak effect of NO 3 − fluxes on N2O emissions. N input by throughfall was not correlated with N2O emissions and only 1.6–3.2% of N input was released as N2O to the atmosphere. Our results suggest that elevated N inputs have little effect on N2O emissions in beech, spruce and pine forests.