In the last decades, average land surface temperatures in the Arctic have increased at rates up to six times higher than the global average increase. Similarly, precipitation in the Arctic also... Show moreIn the last decades, average land surface temperatures in the Arctic have increased at rates up to six times higher than the global average increase. Similarly, precipitation in the Arctic also increased, especially during the cold season when most precipitation falls as snow. In this thesis, the long-term effects of summer increased temperatures and increased winter snow depth in arctic soil fungal community composition in dry heath and moist tussock tundra were addressed using long-term ecological experiments at Toolik Lake, Alaska. Soil fungal composition was assessed through soil DNA extraction and massive parallel sequencing of rDNA ITS2. The fungal community composition responded strongly to summer warming in the moist tundra, but not in the dry tundra. Although total fungal richness was not significantly affected by warming, there were clear correlations among richness of various ecological and taxonomic groups and long-term warming. Regarding the effects of increased winter snow depth, the ectomycorrhizal fungal community composition of the dry tundra had a stronger response than the moist tundra community. The observed changes will likely affect ecosystem functions, such as C storage and N turnover, and have the potential to feedback to climate changes. Show less
Arctic regions are experiencing the greatest rates of climate warming on the planet and marked changes have already been observed in terrestrial arctic ecosystems. While most studies have focused... Show moreArctic regions are experiencing the greatest rates of climate warming on the planet and marked changes have already been observed in terrestrial arctic ecosystems. While most studies have focused on the effects of warming on arctic vegetation and nutrient cycling, little is known about how belowground communities, such as fungi root‐associated, respond to warming. Here, we investigate how long‐term summer warming affects ectomycorrhizal (ECM) fungal communities. We used Ion Torrent sequencing of the rDNA internal transcribed spacer 2 (ITS2) region to compare ECM fungal communities in plots with and without long‐term experimental warming in both dry and moist tussock tundra. Cortinarius was the most OTU‐rich genus in the moist tundra, while the most diverse genus in the dry tundra was Tomentella. On the diversity level, in the moist tundra we found significant differences in community composition, and a sharp decrease in the richness of ECM fungi due to warming. On the functional level, our results indicate that warming induces shifts in the extramatrical properties of the communities, where the species with medium‐distance exploration type seem to be favored with potential implications for the mobilization of different nutrient pools in the soil. In the dry tundra, neither community richness nor community composition was significantly altered by warming, similar to what had been observed in ECM host plants. There was, however, a marginally significant increase in OTUs identified as ECM fungi with the medium‐distance exploration type in the warmed plots. Linking our findings of decreasing richness with previous results of increasing ECM fungal biomass suggests that certain ECM species are favored by warming and may become more abundant, while many other species may go locally extinct due to direct or indirect effects of warming. Such compositional shifts in the community might affect nutrient cycling and soil organic C storage. Show less
Arctic tundra regions have been responding to global warming with visible changes in plant community composition, including expansion of shrubs and declines in lichens and bryophytes. Even though... Show moreArctic tundra regions have been responding to global warming with visible changes in plant community composition, including expansion of shrubs and declines in lichens and bryophytes. Even though it is well known that the majority of arctic plants are associated with their symbiotic fungi, how fungal community composition will be different with climate warming remains largely unknown. In this study, we addressed the effects of long‐term (18 years) experimental warming on the community composition and taxonomic richness of soil ascomycetes in dry and moist tundra types. Using deep Ion Torrent sequencing, we quantified how OTU assemblage and richness of different orders of Ascomycota changed in response to summer warming. Experimental warming significantly altered ascomycete communities with stronger responses observed in the moist tundra compared with dry tundra. The proportion of several lichenized and moss‐associated fungi decreased with warming, while the proportion of several plant and insect pathogens and saprotrophic species was higher in the warming treatment. The observed alterations in both taxonomic and ecological groups of ascomycetes are discussed in relation to previously reported warming‐induced shifts in arctic plant communities, including decline in lichens and bryophytes and increase in coverage and biomass of shrubs. Show less
