Base cation dynamics in rainfall, throughfall, litterflow and soil solution under Oriental beech ( Fagus orientalis Lipsky) trees in northern Iran

Key message Fluxes of base cations were studied in an Oriental beech forest and an adjacent forest gap. The fluxes of base cations in throughfall, litterflow, topsoil and subsoil solution were higher in a mixed Oriental beech forest compared to the fluxes in rainfall and topsoil and subsoil solution in the forest gap. A large proportion of cations were adsorbed or biologically immobilised by passing through the litter layer in the forest. In the mineral topsoil, a new equilibrium between the solid phase and soil solution was established where desorption/leaching surpassed adsorption/immobilisation for Ca 2+ and Mg 2+ while the opposite was true for K + . The contribution of throughfall is considerable in biogeochemical cycling. Context Although it is important to measure nutrient fluxes to establish forest soil chemical fertility, little data is available for Oriental beech forests, one of the most important commercial hardwood forests in Iran. The quantification of nutrient fluxes above and below ground is essential because nutrients in the soil solution are most easily available for tree uptake. A thorough understanding of biogeochemical nutrient cycling requires an investigation of nutrient fluxes between different compartments. Aims We evaluated the effect of Oriental beech forests on biogeochemical cycling of Ca 2+ , Mg 2+ , K + and Na + by analysing their fluxes in rainfall, throughfall, litterflow and soil solution. Methods Throughfall, litterflow and soil solution were sampled during one whole year under five Oriental beech trees in a mixed Hyrcanian beech forest. The amounts of Ca 2+ , Mg 2+ , K + and Na + in these fluxes were calculated based on their concentrations and the sampled volumes and subsequently compared with the respective fluxes in the rainfall and soil solution of an adjacent forest gap. Results We found significantly higher fluxes in all the measured base cations in throughfall compared to rainfall. Entering the litter layer in the forest, nearly 50% of the dissolved base cations adsorb to the solid phase or are biologically immobilised prohibiting their leaching to deeper soil horizons. In the mineral soil, the interactions between the solid phase and soil solution were comparable between the forest and the forest gap. Conclusion This study highlights the role of interactions of rainwater with tree crowns and the litter layer in biogeochemical cycling and emphasises its importance for the maintenance of soil chemical fertility in Oriental beech forests.