The soil nitrogen (N) cycle in cold terrestrial ecosystems is slow and organically bound N is an important source of N for plants in these ecosystems. Many plant species can take up free amino acids from these infertile soils, either directly or indirectly via their mycorrhizal fungi. We hypothesized that plant community changes and local plant community differences will alter the soil free amino acid pool and composition; and that long-term warming could enhance this effect. To test this, we studied the composition of extractable free amino acids at five separate heath, meadow, and bog locations in subarctic and alpine Scandinavia, with long-term (13 to 24 years) warming manipulations. The plant communities all included a mixture of ecto-, ericoid-, and arbuscular mycorrhizal plant species. Vegetation dominated by grasses and forbs with arbuscular and non-mycorrhizal associations showed highest soil free amino acid content, distinguishing them from the sites dominated by shrubs with ecto- and ericoid-mycorrhizal associations. Warming increased shrub and decreased moss cover at two sites, and by using redundancy analysis, we found that altered soil free amino acid composition was related to this plant cover change. From this, we conclude that the mycorrhizal type is important in controlling soil N cycling and that expansion of shrubs with ectomycorrhiza (and to some extent ericoid mycorrhiza) can help retain N within the ecosystems by tightening the N cycle.

This study explores mid-alpine ectomycorrhizal communities on Salix herbacea and Salix polaris in plant communities differing in nutrient status and snow conditions. Plant species were identified by tracking roots back to above ground structures while fungal species were identified using molecular methods. The fungi were identified to 34 molecular operational taxonomic units (MOTUs)/species but species accumulation curves indicated that the communities were only partially sampled. The estimated total species richness was 49 (±9 SD) MOTUs/species. No significant ectomycorrhizal community specificity was found between the two plant species and only weak specificity between different plant communities. Furthermore, no difference in proportion of colonized root tips could be demonstrated between plant communities. However, some fungal taxa showed tendencies to associate with specific environmental conditions. Sebacinaceae, Inocybe egenula, Russula cf. emetica, and a Tomentella sp. were found in meadow communities but not in the heath communities. Sistotrema cf. alboluteum and Tomentella cf. terrestris were only found in the dry and mesic heath communities. Classifications into exploration types showed that the contact type is more abundant in the dry heath community than the other communities. Cenococcum geophilum was the most common species but Cortinarius spp., Russula spp., Tomentella spp., and Lactarius spp. were also common. This study confirms that alpine communities are rich in ectomycorrhizal fungi including species from a wide variety of fungal lineages and also show that many dominant species have wide ecological amplitude.