|Goldberg, S; Gebauer, G: N2O and NO fluxes between a Norway spruce forest soil and atmosphere as affected by prolonged summer drought, Soil Biology & Biochemistry, 41, 1986-1995 (2009), doi:10.1016/j.soilbio.2009.07.001|
Global change scenarios predict an increasing frequency and duration of summer drought periods in Central Europe especially for higher elevation areas. Our current knowledge about the effects of soil drought on nitrogen trace gas fluxes from temperate forest soils is scarce. In this study, the effects of experimentally induced drought on soil N2O and NO emissions were investigated in a mature Norway spruce forest in the Fichtelgebirge (northeastern Bavaria, Germany) in two consecutive years. Drought was induced by roof constructions over a period of 46 days. The experiment was run in three replicates and three non-manipulated plots served as controls. Additionally to the N2O and NO flux measurements in weekly to monthly intervals, soil gas samples from six different soil depths were analysed in time series for N2O concentration as well as isotope abundances to investigate N2O dynamics within the soil. N2O fluxes from soil to the atmosphere at the experimental plots decreased gradually during the drought period from 0.2 to -0.0 mmol m-2 h-1, respectively, and mean cumulative N2O emissions from the manipulated plots were reduced by 43% during experimental drought compared to the controls in 2007. N2O concentration as well as isotope abundance analysis along the soil profiles revealed that a major part of the soil acted as a net sink for N2O, even during drought. This N2O sink, together with diminished N2O production in the organic layers, resulted in successively decreased N2O fluxes during drought, and may even turn this forest soil into a net sink of atmospheric N2O as observed in the first year of the experiment. Enhanced N2O fluxes observed after rewetting up to 0.1 mmol m-2 h-1 were not able to compensate for the preceding drought effect. During the experiment in 2006, with soil matric potentials in 20 cm depth down to -630 hPa, cumulative NO emissions from the throughfall exclusion plots were reduced by 69% compared to the controls, whereas cumulative NO emissions from the experimental plots in 2007, with minimum soil matric potentials of -210 hPa, were 180% of those of the controls. Following wetting, the soil of the throughfall exclusion plots showed significantly larger NO fluxes compared to the controls (up to 9 mmol m-2 h-1 versus 2 mmol m-2 h-1). These fluxes were responsible for 44% of the total emission of NO throughout the whole course of the experiment. NO emissions from this forest soil usually exceeded N2O emissions by one order of magnitude or more except during wintertime.
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