Jarl, Ingrid2025-08-052025-08-052025-08-05https://hdl.handle.net/2077/89120Climate warming is driving increased vegetation growth and shifts in species composition in tundra regions, which may also lead to changes in mycorrhizal communities. An increase in deciduous shrubs has been observed, however, several studies suggest that herbivores can limit this expansion. This study investigates how reindeer grazing affects mycelial biomass using an exclosure experiment at two Oroarctic sites: Kilpisjärvi (Finland) and Ritsem (Sweden). Ingrowth mesh bags filled with sand have been incubated into the soil at the sites with various incubation times, spanning from one growing season length to two years plus growing season length. The dominant vegetation at these sites includes deciduous shrubs, evergreen ericaceous shrubs, and graminoids. And the main mycorrhizal types, analysed from soil samples, are ectomycorrhiza (ECM), arbuscular mycorrhiza AM and a small proportion of ericoid mycorrhiza (ERM). Mycelial biomass was estimated using two methods: ergosterol extraction (a fungal-specific biomarker) and loss on ignition (LOI). Results show higher mycelial biomass in exclosure plots compared to grazed (ambient) plots at both Kilpisjärvi and Ritsem, with a statistically significant treatment effect at Ritsem. These findings suggest that reindeer grazing can suppress mycorrhizal growth. Changes in mycorrhizal composition may also affect soil carbon dynamics. While the expansion of deciduous shrubs could increase above ground carbon storage due to enhanced plant productivity, their associated ectomycorrhizal (ECM) fungi are suggested to have a faster turnover rate than the ericoid mycorrhizal (ERM) fungi that dominate evergreen shrub systems. A shift from evergreen to deciduous vegetation may lead to increased soil carbon respiration and decreasing soil C storage.engMyceliaHerbivoresReindeerOroarcticMycorrhizal fungi