Microclimatological consequences for plant and microbial composition in Sphagnum-­dominated peatlands

In three Scandinavian peatlands we studied to what extent plant and microbial community composition are governed by local scale microhabitat, with a special interest in the effect of aspect (i.e. exposition of slopes). Despite differences in solar irradiance between south-facing and north-facing slopes, maximum temperature was elevated in the south-facing slopes at the most northern site only. Porewater nutrient concentrations were not affected by aspect, yet dissolved organic carbon concentrations were higher in south-facing microhabitats. This is likely caused by higher vascular plant biomass. Plant and microbial community composition clearly differed between sites. In all three sites, microhabitat (i.e. prevailing water table depth) exerted a large control on the plant and microbial community composition. Aspect, however, did not affect community composition, even though microclimate significantly differed between the south- and the north‐facing aspect in the northernmost site. Our results highlight the complex link between plant community composition, microbial community and environmental conditions, which deserves much more attention than it currently does in order to fully understand the effects of climate change on peatland ecosystem function.