The McMurdo Dry Valleys comprise some 4,800km2 of ice-free terrain in east
Antarctica and this constitutes the coldest and most arid desert on Earth. The
ecosystem of the Dry Valleys is characterized by microbial processes since
environmental extremes severely limit higher plant and animal life. A major
international collaborative research effort co-ordinated by the International Center
for Terrestrial Antarctic Research (ICTAR), identified long-term study sites
representative of maritime and inland Dry Valleys environments. The maritime site,
Miers Valley, has been the subject of intensive multi-disciplinary study in recent
years, of which the work in this thesis is a part. Previous studies have identified
soil microbial communities and their putative functional roles, but lithic communities
have not been previously appreciated. This thesis reports aspects on the
biodiversity and ecology of lithic microbial communities in Miers Valley.
A survey of terrain revealed extensive weathered granite, but no porous
sandstone or limestone rocks more commonly associated with cryptoendolithic
communities (those colonizing pore spaces within rock substrates). Granite was
extensively colonized (30-100% of available substrate) by chasmoendolithic
microorganisms (colonizing cracks and fissures in weathered rock). Visual
examination of colonized rocks revealed a distinct zone of biomass 2-5mm below the
rock surface, and this was overlain by a weathered and friable matrix of rock.
Microscopy revealed a community dominated by diverse cyanobacterial
morphotypes, plus other unidentifiable microbes of varied morphology.
A quantitative approach to broad-scale community fingerprinting was adopted,
utilizing terminal restriction fragment length polymorphism (TRFLP) and sequence
based identifications of restriction fragments. The multi-domain approach
encompassed Archaea, Bacteria and Eukarya. The results revealed relatively low
species richness (0.6-1.8) for each domain with community richness estimates also
relatively low (<3). Nonetheless very clear and statistically supported patterns in
the occurrence of phylotypes within chasmolithic communities were related to aspect
(which strongly affects temperature and moisture availability in Dry Valleys
locations). The bacterial assemblages formed two groups (cold-dry south facing
slopes and valley floor moraine). The eukaryal assemblages also formed two
groups although here the moraine samples grouped with the warmer wetter north
facing slope and the cold-dry south facing slope assemblages formed a separate
group. The archaeal assemblages displayed no difference within different valley
terrain.
Extensive sequence based interrogation of community structure using clone
libraries revealed a community dominated by cyanobacteria, Actinobacteria,
Deinococci and putative lichens. These phyla are all known for their extreme
tolerance to desiccation and occurrence in arid landscapes. Phylogenetic analysis
revealed that these abundant taxa shared close affiliation with those from other
Antarctic refuge niches such as hypoliths and cryptoendoliths. The cyanobacteria
were mainly Oscillatoriales, but other genera such as Chroococcidiopsis and Nostoc
commonly recovered in hot desert lithic communities were generally absent. The
eukaryal community was dominated by chlorophyte algae, whilst the archaeal
phylotypes were a diverse collection spanning both euryachaeal and crenarchaeal
lineages.
Overall the data revealed the chasmoendolithic community in Miers Valley
was widespread and with relatively restricted diversity. The selection pressures
related to topology of the valley have resulted in different community structure
within the valley. / published_or_final_version / Biological Sciences / Master / Master of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/174557 |
| Date | January 2012 |
| Creators | Yung, Cheuk-man., 容卓敏. |
| Contributors | Pointing, SB |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B4784999X |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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