Soil microbial activity and community structure along a primary succession transect on the land-uplift coast in western Finland

We investigated the changes in basal respiration (BASAL), microbial biomass as substrate-induced respiration (SIR) and their ratio (qCO2) in the organic layer along a primary successional transect (alder/rowan, birch, birch/spruce, spruce I and spruce II) typical of the land-uplift coast in western Finland. PLFA analysis was used to detect concurrent successional changes in microbial community structure. Along the transect the soil C/N ratio increased (from 16 to 37) and pH (H2O) decreased (from 5.11 to 3.98) substantially. Concurrently, BASAL and SIR remained mainly stable although, during the most favorable temperature and moisture conditions in the field, they tended to increase along the transect from the alder/rowan site to spruce I, and decreased again in spruce II. qCO2 showed no consistent trend along the transect. The soil of the birch site had the highest total PLFA and bacterial PLFA concentrations, while the soils of both spruce sites had the lowest. The ordination configuration of the PLFA data in non-metric multidimensional scaling was clearly related to the C/N ratio and pH, and separated the forest sites relatively well. It was possible, on the basis of the similarities in the variation pattern along the transect, to divide the PLFAs into six groups.