Poster, International Symposium Soil processes under extreme meteorological conditions, Bayreuth: 25.02.2007 - 28.02.2007
Abstract:
Soil frost may affect the structure, microbial biomass and fine root biomass of soils, but little is known about the long-term effects of such extreme events on nutrient turnover in forest soils. Here we present first results of a field experiment that was conducted in a mature Norway spruce stand on three replicated plots each of 400 m2 during the exceptionally cold winter of 2005/2006. Soil frost was induced down to 15 cm mineral soil depth by removing the snow cover from the soil surface. The frost effects on N mineralisation and element concentrations were related to the non-manipulated and unfrozen control plots (n=3). Soil solution was biweekly to monthly collected below the humus layer and at 20cm and 90cm soil depth and analysed for NH4+, NO3-, DOC, 14DOC and other main nutrients. Additionally, net N mineralisation was determined after thawing from April to June by in situ incubation of undisturbed soil columns. Our preliminary results did not indicate an enhanced mobilisation of DOC in soil solution from the top soil. Nitrate concentration increased in the humus layer and at 20 cm depth about 4 months after thawing of the soil whereas NH4+ concentration remained at the control level. The delayed increase in nitrate concentration suggests that N uptake by roots was reduced in the treatment plots because net N mineralisation was not affected by soil frost. Possibly, extreme soil frost may increase the risk of nitrate leaching in N saturated forest soils.