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Ecophysiology of Antarctic lichens

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Hovenden, Mark Joseph (1996) Ecophysiology of Antarctic lichens. PhD thesis, University of Tasmania.

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Abstract

The vegetation of the Windmill Islands oasis, Wilkes Land, continental Antarctica is dominated by lichens. Aspects of the ecology and physiology of lichens were studied during three summers and a winter period on the well vegetated Clark and Bailey Peninsulas in an attempt to explain patterns in lichen distribution. Most studies were done at a knoll on Clark Peninsula. This knoll has an extensive range of substratum nutrient levels and a variety of microhabitats, resulting in a variety of niches in a small area. At this site 29 identifiable species
of lichen occur in seven sociations, most dominated in varying degrees by the macrolichens Pseudephebe minuscula, Umbilicaria decussata, Usnea sphacelata and Usnea antarctica. The crustose lichen Buellia frigida dominates sites on exposed boulders and a separate suite of species inhabits dead and dying moss. There are a suite of species which are restricted to sites with high nutrient levels, although the distribution of the dominant species is relatively insensitive to substratum nutrition. Exposure limits all species to various extents, with all lichens being intolerant of late-lying snow.
The nitrogen and phosphate content of lichen thalli is clearly related to that of the substratum on which they are growing. Monthly sampling of Usnea sphacelata and Umbilicaria decussata from eight sites identified a consistent trend in thallus nitrogen content with %N increasing throughout the winter and then dropping sharply with the onset of the melt and increasing during the summer. Lichen integrity during the middle of winter and before and after an unusual winter event were assessed by investigating the distribution of mineral nutrients within the lichen thallus. Although the distribution of minerals in the thalli differed between species and sites there was no effect of month and therefore the unseasonal rewetting and subsequent refreezing had little effect on membrane integrity.
The most important time for lichen photosynthetic activity was early summer from late October to early December. The increasing temperatures and insolation at this time lead to a great deal of snow melt and hence an increase in the availability of free water. Humidity was therefore high so that activation of photosynthesis was possible through water vapour uptake alone. During the bulk of the summer lichens are photosynthetically inactive. At this time the air is too dry for lichens to absorb sufficient water from the atmosphere to initiate photosynthesis and hence they rely on direct moistening from summer snow falls and run off. The photosynthesis of the major species as a function of thallus water content was related to their observed distribution patterns.
Together, substratum nutrient levels, microclimate and photosynthetic characteristics of species can describe a great deal of the observed distribution patterns of lichens in the Windmill Islands.

Item Type: Thesis (PhD)
Keywords: Lichens
Copyright Holders: The Author
Copyright Information:

Copyright 1996 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1997. Includes bibliographical references

Date Deposited: 19 Dec 2014 02:57
Last Modified: 28 Nov 2016 06:32
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