Poster, Eprecot, Elsinore, Dänemark: 22.05.2006 - 25.05.2006
Abstract:
Many field and laboratory studies suggest that wetting of dry soil may cause an exceptional strong increase in the mineralization of soil organic matter resulting from accumulation or exposition of labile organic compounds during dry periods. Here we report the results of a laboratory study on the effects of wetting intensity on carbon and nitrogen mineralization rates of a Norway spruce soil. After mild drying undisturbed soil columns were exhibited to (i) 8 mm, (ii) 20 mm and (iii) 50 mm of artificial throughfall per day and subsequently to 4 mm throughfall per day at a temperature of 15°C. The control columns (not dried) received 4 mm throughfall per day during the wetting periods. The same amount of throughfall (156 mm) was added to all treatments throughout the three repeated drying/wetting cycles. In all three cycles, CO2 production recovered within 2-4 days close to the level of the control columns following wetting of dry soil and remained afterwards below the level of the control columns (Fig. 1a). CO2 production decreased in all treatments during the three cycles. Inorganic N fluxes were higher in the control than in the treatments and increased gradually from the first to the third cycles (Fig. b). The intensity of wetting had no effect on both CO2 production and inorganic N fluxes. We conclude that no significant amounts of labile soil organic compounds were accumulated during the drying periods. The microbial community could have been affected by drying because the C and N mineralization rates of the control columns were higher than those of the treatments. Overall, our results suggest that (1) soil organic matter including litter may accumulate during extended drying periods and that (2) wetting of dry soil cause no surplus release of CO2 and inorganic N due to mineralization of ‘accumulated’ soil organic matter. The sink strength of spruce forest soils might increase with increasing intensity and length of summer droughts.