Soil microbial and microfaunal communities and organic matter quality in reindeer winter and summer ranges in Finnish subarctic mountain birch forests

Reindeer husbandry has significant influences on the aboveground plant communities and the structure of the mountain birch forests in the Fennoscandian subarctic. We investigated how the reindeer-mediated aboveground changes affect soil microbial and microfaunal communities and enzymatic activities. We hypothesized that in areas with intensive summer browsing by reindeer, the carbon flow to belowground is reduced, but the carbon substances are more readily degradable. This is likely to influence both the abundance and the trophic structure of microbial and microfaunal communities. However, despite large differences in the vegetation, the reindeer ranges did not differ in the amount of microbial biomass or the abundance of nematodes. Furthermore, there was no difference in the microbial phospholipid fatty acid composition or in the trophic groups of soil nematodes. There were few effects on the organic fractions (non-polar extractives, water-soluble extractives, acid-soluble fraction, and acid-insoluble residue) of the soil organic matter. We suggest that the high stocks of organic matter in subarctic systems weaken the direct link between the aboveground and the belowground environments. Because soil carbon has a long turnover time in these systems, it takes at least several decades until the aboveground changes caused by large herbivores will influence the trophic structure in soils.