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, litterfall, microbial activities in soil and rhizosphere processes. Tree species diversification has been suggested for maintaining forest ecosystem services and combining provisioning and supporting services with multifunctional and sustainable forestry. However, the understanding of the role of biodiversity in forests is unclear, in particular concerning the microbial diversity and activity in soils. This file contains data of bacterial metabolic diversity, microbial biomass, pH, labile carbon and nitrogen, and potential nitrification (upper layers only) in organic and upper mineral soil horizons sampled in 2012 in the 209 plots of the Exploratory Platform of the FunDivEUROPE project (http://www.fundiveurope.eu/). This Exploratory Platform is a network of comparative plots of 1-5 tree species established in existing mature forest in 6 countries. These six focal regions represent important European forest types along the gradient from boreal forest to Mediterranean forest.

Samples were taken in two regions (Germany-Biotree-Kaltenborn and FInland-Satakunta) of the Experimental Platform of FunDivEUROPE. Satakunta: A soil sample was taken in all of the 9 10x10m subplots (in the 30*30 m plots) and mixed to obtain one representative composite sample from each plot. All 20 plots of area 1 were sampled (1, 2, 3, 5 species mixtures). Organic (if present; only Satakunta) and mineral (5 cm) soil horizons were samples separately. Kaltenborn: all 16 plots (M: mangament; U: unmanaged. 9 crossing points of the mineral horizon per plot, over subplots M and U, are selected. Whereby respectively 4 and 5 crossing points are randomly selected in those subplots. In which plot (M or U) the 4, either 5 samples are taken, is randomly decided. The nine subsamples are put together in a composite sample.In case of 1 species plots, we randomly select 9 points per plot over the M and U subplot. Whereby respectively 4 and 5 crossing points are randomly selected in those subplots. In which plot (M or U) the 4, either 5 samples are taken, is randomly decided. Soils were sieved fresh (4mm), stored at 4°C and analysed within 2 weeks. There was no upper organic horizon in Germany.

Experimental FunDivEurope: Finland (Satakunta), Germany (Kaltenborn-BIOTREE)

Soil sampling dates: Finland: 20-21/9/2011; Germany: 10/12/2011;

Response variables: Microbial biomass carbon (Cmic) and Nitrogen (Nmic) Ctot . Water-content ot. qmicot. pHH2O pHKCl ot. NitPot ot. NtotCW NtotHW CCW ClabileCtot. Planned data analyses: mixed models, strucutural equation modelling