Anders Aas
Research Scientist
Authors
Synnøve Smebye Botnen Marie Louise Davey Anders Aas Tor Carlsen Ella Thoen Einar Heegaard Unni Vik Philipp Dresch Sunil Mundra Ursula Peintner Andy F. S. Taylor Håvard KauserudAbstract
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.
Abstract
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.
Authors
Atle Mysterud William Ryan Easterday Vetle Malmer Stigum Anders Aas Erling Meisingset Hildegunn ViljugreinAbstract
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.
