Arctic grazers are known to prevent the establishment of deciduous shrubs and, under certain conditions, promote the dominance of evergreen shrubs. As these shrubs associate with contrasting soil fungal communities, a grazer-induced shift in shrub abundance could alter the processes sustained by soil fungi – such as soil carbon sequestration. This role of grazers is of particular interest today now that both deciduous and evergreen shrubs are expanding their ranges, and arctic grazer could determine their relative success.
We assessed soil fungal community composition and its links to soil carbon storage in two contrasting long-term reindeer grazing regimes in the subarctic treeline ecotone at the border between Finland and Norway. We found that root-associated basidiomycetes and free-living moulds and yeasts were characteristic to the regime with only wintertime grazing, whereas few taxa of root-associated ascomycota dominated fungal communities on the open heaths in the year-round grazing regime. These patterns in fungal functional guild abundance were linked to organic soil carbon storage: root-associated ascomycetes were more abundant in plots with high soil carbon storage, whereas saprotrophic guilds were typical to plots with low soil carbon storage.
Overall, these findings suggest that when grazers promote the dominance of evergreen dwarf shrubs, they may induce shifts in soil fungal communities that, in the long term, increase soil carbon sequestration. This implies an overlooked role of grazers and grazing regimes in controlling soil carbon storage at the treeline ecotone.
Reference: Ylänne, H., Madsen, R.L., Castaño, C., Metcalfe, D.B. and Clemmensen, K.E. (2021) Reindeer control over subarctic treeline alters soil fungal communities with potential consequences for soil carbon storage. Global Change Biology, pp. 1– 15. https://doi.org/10.1111/gcb.15722
Text by Henni Ylänne, Lund University
Pictures from the two grazing regimes by Henni Ylänne