Anders Bjørnsgard Aas

• Aas, Anders Bjørnsgard; Andrew, Carrie Joy; Blaalid, Rakel; Vik, Unni; Kauserud, Håvard & Davey, Marie Louise (2019). Fine-scale diversity patterns in belowground microbial communities are consistent across kingdoms. FEMS Microbiology Ecology.  ISSN 0168-6496.  95(6), s 1- 11 . doi: 10.1093/femsec/fiz058 Show summary

  The belowground environment is heterogeneous and complex at fine spatial scales. Physical structures, biotic components and abiotic conditions create a patchwork mosaic of potential niches for microbes. Questions remain about mechanisms and patterns of community assembly belowground, including: Do fungal and bacterial communities assemble differently? How do microbes reach the roots of host plants? Within a 4 m2 plot in alpine vegetation, high throughput sequencing of the 16S (bacteria) and ITS1 (fungal) ribosomal RNA genes was used to characterise microbial community composition in roots and adjacent soil of a viviparous host plant (Bistorta vivipara). At fine spatial scales, beta-diversity patterns in belowground bacterial and fungal communities were consistent, although compositional change was greater in bacteria than fungi. Spatial structure and distance-decay relationships were also similar for bacteria and fungi, with significant spatial structure detected at <50 cm among root- but not soil-associated microbes. Recruitment of root microbes from the soil community appeared limited at this sampling and sequencing depth. Possible explanations for this include recruitment from low-abundance populations of soil microbes, active recruitment from neighbouring plants and/or vertical transmission of symbionts to new clones, suggesting varied methods of microbial community assembly for viviparous plants. Our results suggest that even at relatively small spatial scales, deterministic processes play a significant role in belowground microbial community structure and assembly.

• Botnen, Synnøve Smebye; Davey, Marie Louise; Aas, Anders Bjørnsgard; Carlsen, Tor; Thoen, Ella; Heegaard, Einar; Vik, Unni; Dresch, Philipp; Mundra, Sunil; Peintner, Ursula; Taylor, Andy F. S. & Kauserud, Håvard (2019). Biogeography of plant root-associated fungal communities in the North Atlantic region mirrors climatic variability. Journal of Biogeography.  ISSN 0305-0270.  46(7), s 1532- 1546 . doi: 10.1111/jbi.13613 Show summary

  Aim Polar and alpine ecosystems appear to be particularly sensitive to increasing temperatures and the altered precipitation patterns linked to climate change. However, little is currently known about how these environmental drivers may affect edaphic organisms within these ecosystems. In this study, we examined communities of plant root‐associated fungi (RAF) over large biogeographical scales and along climatic gradients in the North Atlantic region in order to gain insights into the potential effects of climate variability on these communities. We also investigated whether selected fungal traits were associated with particular climates. Locations Austria, Scotland, Mainland Norway, Iceland, Jan Mayen and Svalbard. Taxa Root fungi associated with the ectomycorrhizal and herbaceous plant Bistorta vivipara. Methods DNA metabarcoding of the ITS1 region was used to characterize the RAF of 302 whole plant root systems, which were analysed by means of ordination methods and linear modelling. Fungal spore length, width, volume and shape, as well as mycelial exploration type (ET) of ectomycorrhizal (ECM) basidiomycetes were summarized at a community level. Results The RAF communities exhibited strong biogeographical structuring, and both compositional variation as well as fungal species richness correlated with annual temperature and precipitation. In accordance with general island biogeography theory, the least species‐rich RAF communities were found on Jan Mayen, a remote and small island in the North Atlantic Ocean. Fungal spores tended to be more elongated with increasing latitude. We also observed a climate effect on which mycelial ET was dominating among the ectomycorrhizal fungi. Main conclusions Both geographical and environmental variables were important for shaping root‐associated fungal communities at a North Atlantic scale, including the High Arctic. Fungal OTU richness followed general biogeographical patterns and decreased with decreasing size and/or increasing isolation of the host plant population. The probability of possessing more elongated spores increases with latitude, which may be explained by a selection for greater dispersal capacity among more isolated host plant populations in the Arctic.

• Thoen, Ella; Aas, Anders Bjørnsgard; Vik, Unni; Brysting, Anne Krag; Skrede, Inger; Carlsen, Tor & Kauserud, Håvard (2019). A single ectomycorrhizal plant root system includes a diverse and spatially structured fungal community. Mycorrhiza.  ISSN 0940-6360.  29(3), s 167- 180 . doi: 10.1007/s00572-019-00889-z
• Aas, Anders Bjørnsgard; Davey, Marie Louise & Kauserud, Håvard (2017). ITS all right mama: investigating the formation of chimeric sequences in the ITS2 region by DNA metabarcoding analyses of fungal mock communities of different complexities. Molecular Ecology Resources.  ISSN 1755-098X.  17(4), s 730- 741 . doi: 10.1111/1755-0998.12622
• Lorberau, Kelsey; Botnen, Synnøve Smebye; Mundra, Sunil; Aas, Anders Bjørnsgard; Rozema, Jelte; Eidesen, Pernille Bronken & Kauserud, Håvard (2017). Does warming by open-top chambers induce change in the root-associated fungal community of the arctic dwarf shrub Cassiope tetragona (Ericaceae)?. Mycorrhiza.  ISSN 0940-6360.  27(5), s 513- 524 . doi: 10.1007/s00572-017-0767-y
• Mysterud, Atle; Easterday, William Ryan; Stigum, Vetle Malmer; Aas, Anders Bjørnsgard; Meisingset, Erling L. & Viljugrein, Hildegunn (2016). Contrasting emergence of Lyme disease across ecosystems. Nature Communications.  ISSN 2041-1723.  7 . doi: 10.1038/ncomms11882 Full text in Research Archive. Show summary

  Global environmental changes are causing Lyme disease to emerge in Europe. The life cycle of Ixodes ricinus, the tick vector of Lyme disease, involves an ontogenetic niche shift, from the larval and nymphal stages utilizing a wide range of hosts, picking up the pathogens causing Lyme disease from small vertebrates, to the adult stage depending on larger (non-transmission) hosts, typically deer. Because of this complexity the role of different host species for emergence of Lyme disease remains controversial. Here, by analysing long-term data on incidence in humans over a broad geographical scale in Norway, we show that both high spatial and temporal deer population density increase Lyme disease incidence. However, the trajectories of deer population sizes play an overall limited role for the recent emergence of the disease. Our study suggests that managing deer populations will have some effect on disease incidence, but that Lyme disease may nevertheless increase as multiple drivers are involved.

• Nilsson, R. Henrik; Hyde, Kevin D.; Pawlowska, Julia; Ryberg, Martin; Tedersoo, Leho; Aas, Anders Bjørnsgard; Alias, Siti A.; Alves, Artur; Anderson, Cajsa Lisa; Antonelli, Alexandre; Arnold, A. Elizabeth; Bahnmann, Barbara; Bahram, Mohammad; Bengtsson-Palme, Johan; Berlin, Anna; Branco, Sara; Chomnunti, Putarak; Dissanayake, Asha; Drenkhan, Rein; Friberg, Hanna; Frøslev, Tobias Guldberg; Halwachs, Bettina; Hartmann, Martin; Henricot, Beatrice; Jayawardena, Ruvishika; Jumpponen, Ari; Kauserud, Håvard; Koskela, Sonja; Kulik, Tomasz; Liimatainen, Kare; Lindahl, Björn D.; Lindner, Daniel; Liu, Jian-Kui; Maharachchikumbura, Sajeewa; Manamgoda, Dimuthu; Martinsson, Svante; Neves, Maria Alice; Niskanen, Tuula; Nylinder, Stephan; Pereira, Olinto Liparini; Pinho, Danilo Batista; Porter, Teresita M.; Queloz, Valentin; Riit, Taavi; Sánchez-García, Marisol; de Sousa, Filipe; Stefanczyk, Emil; Tadych, Mariusz; Takamatsu, Susumu; Tian, Qing; Udayanga, Dhanushka; Unterseher, Martin; Wang, Zheng; Wikee, Saowanee; Yan, Jiye; Larsson, Ellen; Larsson, Karl-Henrik; Kõljalg, Urmas & Abarenkov, Kessy (2014). Improving ITS sequence data for identification of plant pathogenic fungi. Fungal diversity.  ISSN 1560-2745.  67(1), s 11- 19 . doi: 10.1007/s13225-014-0291-8

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• Aas, Anders Bjørnsgard (2013). The role of B. anthracis in the soil microbiome.
• Carlsen, Tor; Aas, Anders Bjørnsgard; Lindner, D; Vrålstad, Trude; Schumacher, Trond & Kauserud, Håvard (2012). Don't make a mista(g)ke: is tag switching an overlooked source of error in amplicon pyrosequencing studies?. Fungal ecology.  ISSN 1754-5048.  5(6), s 747- 749 . doi: 10.1016/j.funeco.2012.06.003 Show summary

  High throughput sequencing has become a powerful tool for fungal ecologists to explore the diversity and composition of fungal communities. However, various biases and errors are associated with the new sequencing techniques that must be handled properly. We here provide evidence for a source of error that has not yet been taken into account. During amplicon pyrosequencing we incorporate tags in both ends of the amplicons, which allows us to check for tag coherence after sequencing. In several studies we have observed that a small proportion of the resulting sequences possess novel tag combinations. Our observations cannot be explained by primer contamination or PCR chimaeras. This indicates that some DNA fragments switch tags during laboratory setup. If not controlled for, this will cause numerous false positives in downstream analyses. In most amplicon pyrosequencing studies of fungal communities, amplicons are typically tagged in one end only. We suggest that amplicons should be tagged in both ends before pyrosequencing to control for tag switching.

• Aas, Anders Bjørnsgard; Carlsen, Tor; Kauserud, Håvard; Mysterud, Atle & Vrålstad, Trude (2010). The effects of animal grazing on species richness and composition of fungal endophytes in a perennial grass. Show summary

  Virtually all land plants host fungal endophytes. However, the composition and diversity of fungal endophytes growing in a range of wild grasses serving as food sources for grazing animals remains largely unexplored. Avenella flexuosa, a perennial grass of the family Poaceae, is abundant in the cold temperate regions of Europe. In alpine habitats of Norway, this grass accounts for ~30% of the diet for about 2.1 million domestic sheep (Ovis aries) that are released for summer grazing yearly. The aim of the present study was to investigate the effect of grazing on the species diversity and composition of endophytes appearing in A. flexuosa in an alpine habitat in Norway. Plants were sampled from plots exposed to grazing (80 sheep per km2) as well as control plots (no grazing). The study area is part of a long-term study measuring the effects of grazing on alpine ecosystems, and has been closely monitored and exposed to controlled grazing pressure for seven years prior to sampling. The presence of fungal endophytes was assessed with traditional culturing methods followed by ITS sequence identification. In parallel, grass bulk samples were screened for total fungal diversity using 454 pyrosequencing. The results of the study will be presented

• Aas, Anders Bjørnsgard; Vrålstad, Trude; Carlsen, Tor; Kauserud, Håvard & Mysterud, Atle (2010). Diversity and species composition of fungal endophytes in Avenella flexuosa under different sheep grazing regimes.

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