Nutrient fluxes and soil microbial processes under tree species after conversion from Norway spruce

The biogeochemical cycling in forest ecosystems is highly dependent on the interactions between plants and soil. Tree species affect element cycling through deposition in throughfall, litter composition, microbial activities in soil and rhizosphere processes. Species diversification has been suggested for maintaining forest ecosystem services and uniting provisioning and supporting services within multifunctional and sustainable forestry. However, most information on species impacts has been derived from studies performed at different sites, where the influence of cofactors cannot be accounted for. Here we synthesize results from a study performed 11 years after conversion of a Norway spruce stand (Picea abies (L.) KARST.) to a mixed stand composed of Norway spruce, common alder (Alnus glutinosa (L.) GAERTN.), european beech (Fagus sylvatica L.), pedunculate oak (Quercus robur L.), silver birch (Betula pendula ROTH.), goat willow (Salix caprea L.) and rowan (Sorbus aucuparia L.). As stand closure was not achieved yet, the impact of individual species could be evaluated. We measured fresh leaf element composition, element return to the soil via throughfall and litterfall (leaves, twigs, reproductive parts), forest floor chemical characteristics, microbial biomass and microbial activities (N mineralization, potential nitrification, respiration) in the forest floor under the different tree species.
Our results suggested that (1) foliar element concentrations differed between species and were highest for rowan, (2) high base cation litterfall and throughfall fluxes under rowan lead to better soil quality, (3) input of acidifying cations was reduced under broadleaves, (4) potential nitrification increased under the N2 fixing alder.