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Significant or trivial: Fungi in Polar Ecosystems

Periodic Reporting for period 1 - F-Pole (Significant or trivial: Fungi in Polar Ecosystems)

Reporting period: 2016-09-01 to 2018-08-31

The overall objective of the project F-POLE was to study the diversity and distribution of marine-derived fungi in polar ecosystems, to relate these findings to environmental parameters and to begin to assess their overall importance for these ecosystems. Fungi are major components of the Earth’s biosphere, playing a pivotal role as decomposers and recyclers of nutrients across different environments. Information on the fungal biology and ecology in marine environments is, however, limited. Previous studies indicate a distinct diversity, including chytrids (fungi with swimming tails), which can affect algae and zooplankton communities. This interaction is thought to be a product of the parasitic lifestyle of many chytrids or their role as a food source. On account of these aspects, chytrids can be important components of aquatic ecosystems with a potential to shape capacity and function at the base of the food web. Investigations within this project were therefore focused on the diversity and distribution of this fungal group.
Environmental samples have been taken during summer in the Arctic Ocean and the Southern Ocean, respectively. During the project, different water depths, covering the surface water, the chlorophyll max (where the major phytoplankton groups reside) and the under-ice water were sampled and DNA was extracted for characterization. Two phylogenetic informative markers were sequenced in order to study the marine fungal community (ITS2 region) as well as the wider microbial eukaryotic community (V4 region). This approach allowed for the identification of putative distribution patterns. Furthermore, relationships between marine-derived fungal community structures and environmental parameters were elucidated using statistical tests.
Preliminary results of this project revealed a high diversity of unclassified marine fungi, particular in high Arctic regions. Comparisons with chytrid sequence data from public databases originating from different oceanographic regions showed a close phylogenetic relationship between chytrids from cold-water environments compared to those originating from temperate oceanographic regions. This finding suggests a potential biogeographic distribution of chytrids. To evaluate potential environmental factors, influencing fungal community structure and distribution, different parameters have been tested. The data revealed an effect for sea ice concentration and salinity. In terms of chytrids, this groups was mainly recovered in ‘low saline’, sea ice melt influenced sampling sites. Microbe-microbe co-association analyses, indicated a correlation between certain diatom species and chytrid prevalence. The results of this study are submitted for publication in a peer review journal.
Overall, the project provided a comprehensive dataset of environmental DNA barcodes of marine-derived fungi from polar regions and thus contributed substantially to the research community by complementing important information on chytrid diversity and distribution. Our work demonstrates that in the Arctic Ocean, chytrids can be important components of the polar ecosystem, particularly in the fresher summer surface waters. Hence, under continuous sea ice retreat and surface water freshening our data imply an altered chytrid diversity and distribution hinting at a wider ecosystem change.