Effects of drying/rewetting and irrigation on gross ammonification and nitrification in an acid coniferous forest soil
2 Soil Physics, Helmholtz Centre for Environmental Research, UFZ, D-06120 Halle/Saale, Germany
O 1.2 in Ecosystem Function
15.04.2010, 09:00-09:15, H13
The frequency and intensity of soil drought are likely to increase in many areas as a result of global climate change which might influence the N turnover and fluxes in soils. Throughfall exclusion shelters and irrigation system were used to simulate precipitation patterns of dry and wet years in a Norway spruce forest (Picea abies L.). We tested the hypotheses that enhanced drought leads to a decrease and the rewetting causes a temporary pulse of gross N turnover rate. Intact soil cores of 100 cm3 from Oi+Oe and Oa+EA horizons were taken at 5 dates during the period of manipulation in 2009. Gross N turnover rates were determined using the 15N pool dilution technique.
With the help of roof construction, 142 mm throughfall was excluded during 57 days. The soil water potential at throughfall exclusion plots decreased from -0.2 MPa to -1.9 MPa in the Oi+Oe horizon and from -0.2 MPa to -0.8 MPa in the Oa+EA horizon. The soil water potentials of the control and irrigation plots were not different and ranged from -0.1 MPa to -0.4 MPa in both horizons. Gross ammonification rates at the throughfall exclusion plots decreased by 40% in the Oi+Oe horizon and by 30% in the Oa+EA horizon in August. Gross nitrification rates were always much less than gross ammonification rates. Although gross nitrification rates at throughfall exclusion plots decreased by 45% in the Oi+Oe horizon and by 32% in the Oa+EA horizon in August, rates were not significantly different from those at control and irrigation plots due to the huge spatial variation. No effect of rewetting and irrigation was found on gross ammonification and nitrification rates in both horizons.
Our results suggested that lower ammonification rate is likely in forest soil if the duration and frequency of drought periods increase in the future. Such changes of N cycling might lead to an accumulation of organic N and reduce inorganic N availability for plants and microorganisms in periods of soil drying.
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