Base cation nutrition for pine stands on lithic soils near Stockholm, Sweden

Abstract

This study reports on base cation nutrition for pine stands growing on lithic soils, i.e. areas of exposed bedrock where very little or no mineral soil cover exists. Since there is little soil, the exchangeable pool of base cations must be very small and the aim was to determine the source of nutrients for the trees— from atmospheric input or from mineral weathering. The method used Sr isotopes as analogues for Ca. Because the 87 Sr 86 Sr distribution is specific for the source, Sr found in the biomass can be treated as a binary mixture of Sr from deposition and weathered bedrock minerals. The bedrock comprised gneisses or gneissic granite, but with varying chemistry. In four out of five sites, atmospheric deposition was found to be the dominant Sr (Ca) source. In one area, though, mineral weathering seems to be effectively the only source. The reason is assumed to be a different weathering rate. Only 3–16% of the Ca, Mg and K released by weathering and received by atmospheric deposition is used for biomass accumulation in the pine stands.