The impact of reduced atmospheric depositions on soil microbial parameters in a strongly acidified Norway spruce forest at Solling,Germany

To simulate a future ion input reduction scenario in forests, a large scale field experiment was set up in a (1999) 66‒year‒old Norway spruce plantation at Solling, central Germany. Throughfall input of H⁺, SO₄^2—, and N‒compounds is artificially reduced by means of a permanent roof construction below the canopy and a de‒ionizing equipment since 1991. Here we present long term soil solution records for SO₄^2—, NO₃^—, Al³⁺ and the pH of the 10 cm mineral soil sampling depth. A significant decrease in ion concentrations since the start of the treatment is observed, but no change of the soil solution pH. Even in the fourth year pH values remained well within the aluminium buffer range (pH < 4.2). Three years after the start of the experiment (July 1994) it was examined whether microbial biomass (C_mic), specific activity (heat production per unit biomass), and the percentage of C_mic in organic C material indicated any changes. Furthermore chemical standard parameters (CEC, base saturation, pH) were analyzed for all soil samples. Results indicate that despite of drastic decreases of soil solution ion concentrations in the upper soil horizons microbial parameters were not affected and that the soil solid phase is not deacidified by the treatment until now.