Rippin, Martin (2018). Biological Soil Crust Microalgae and Cyanobacteria - Key Players in Polar and Alpine Ecosystems. PhD thesis, Universität zu Köln.

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The Polar Regions and alpine zones are extremely hostile environments due to prevailing low temperatures, high levels of solar radiation and extreme seasonality. Water is almost exclusively present as ice and snow, thus, unavailable for organisms. These conditions restrict the vegetational cover to be sparse or completely absent. However, the soil surface is not barren but mostly covered by biological soil crusts (BSCs). These crusts are complex aggregations of different organisms, such as Cyanobacteria and other prokaryotes, eukaryotic microalgae, bryophytes, Fungi, lichens and a versatile microfauna, occurring in varying portions. Biocrusts are integral parts of cold ecosystems as they contribute extensively to primary production and nitrogen fixation. Furthermore, BSCs are important ecosystem engineers that prevent soil loss, change hydrological patterns, albedo, and increase soil fertility. Global change is a major threat to these communities as it leads to alterations in biodiversity amplified by an invasion of non-indigenous species. Hence, studying and monitoring BSCs is essential to recognize shifts in community structures early on and predict future scenarios. Reliable methodologies are the basis for sound results and conclusions. Extracting nucleic acids from BSC samples successfully is highly dependent on, for instance, soil properties. Soil often contains high amounts of humics, which can interfere with enzymatic reactions and should be removed. In this thesis, it was found that an extraction method based on a cetyl trimethylammonium bromide performed superior to commercial kits. All BSC isolates processed with this protocol yielded high-quality nucleic acids. Thus, this procedure and variations of it were used in the course of this project. Biodiversity assessment is crucial to unravel the complexity of communities such as biocrusts. However, cultivating and examining individual organisms has several limitations and will only reveal a small fraction of the actual biodiversity. Molecular methods may overcome these limitations to a certain degree as total DNA or RNA is extracted from the sample and analyzed. In this thesis, five different BSCs were studied, four from Svalbard, Norway, in the Arctic and one from Livingston Island, a part of the Antarctic Peninsula. All five BSCs were in a late successional stage with bryophytes being most dominant. Moreover, Cyanobacteria exhibited a high relative abundance, while microalgae appeared to be diverse but only present at a low relative abundance. The genera Chloromonas (Chlorophyceae), Coccomyxa, Dictyochlorop- sis, Elliptochloris, Leptosira (Trebouxiophyceae), Spumella (Chrysophyceae) and Nostoc (Cyanobacteria) were detected in all samples suggesting an ubiquitous distribution. Especially, Nostoc may be an important keystone species in Polar Regions which may be further investigated in future studies. Furthermore, the presence of sulfur Bacteria indicates that BSCs are involved in sulfur cycling. Overall, the combination of cultivation based and molecular approaches provides a more comprehensive picture of BSC communities. As mentioned above, BSC organisms have to cope with extreme conditions such as water scarcity, which can cause desiccation. The ability to tolerate water deprivation and adapt to it was studied in an alpine strain of Zygnema circumcarinatum (Zygnematophyceae). Similar to land plants, Zygnema increases the transcript pool of early light-induced proteins, aquaporins, reactive oxygen species scavengers and chaperones such as late embryogenesis abundant proteins. Additionally, transcriptional changes in the carbohydrate and lipid metabolism suggest accumulation of sucrose and membrane modifications, respectively. In conclusion, the integration of physiological, cell-biological and omic approaches is a promising way to get extensive insights into the biodiversity and ecology of biological soil crusts. The outcome can be merged to shed light on present community patterns and functionality, and help to generate predictions models for future developments.

Item Type: Thesis (PhD thesis)
Translated title:
Mikroalgen und Cyanobakterien aus biologischen Bodenkrusten als wichtige Akteure in polaren und alpinen ÖkosystemenGerman
CreatorsEmailORCIDORCID Put Code
Rippin, Martinmartin.rippin@uni-koeln.deUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-81885
Date: 16 February 2018
Language: English
Faculty: Faculty of Mathematics and Natural Sciences
Divisions: Faculty of Mathematics and Natural Sciences > Department of Biology > Botanical Institute
Subjects: Natural sciences and mathematics
Life sciences
Uncontrolled Keywords:
Biological soil crusts; Cyanobacteria; Microalgae; Polar Regions; Svalbard; Livingston Island; Metatranscriptomics; Metabarcoding; TranscriptomicsEnglish
Date of oral exam: 9 April 2018
NameAcademic Title
Becker, BurkhardProf. Dr.
Bonkowski, MichaelProf. Dr.
Kroth, PeterProf. Dr.
Refereed: Yes


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