『Abstract
Sandstone samples from Vingen, western Norway have been analysed
to find whether different lichen taxa may explain variations in
the degree of weathering at this site. The samples were analysed
by highperformance thin-layer chromatography (HPTLC)/thin-layer
chromatography (TLC), scanning electron microscopy (SEM), X-ray
diffraction (XRD) and X-ray fluorescence spectroscopy (XRF), followed
by descriptive statistics and principal component analysis (PCA).
The study of the weathering rinds beneath four lichens indicates
differences in weathering effect between the studied taxa. Those
rinds beneath Ophioparma ventosa, and to a lesser extend
Pertusaria corallina, are in general deeper and show a
higher degree of mineral dissolution and crumbling of the rock
surface, compared to Fuscidea cyathoides and Ochrolechia
tartarea. A very high concentration of fungal hyphae within
the weathering rind beneath O. ventosa and P. corallina,
compared to the other two taxa, may be the cause of the increased
biophysical and biochemical weathering. O. ventosa and
F. cyathoides contain similar amounts of oxalate, which
also in general are much higher than for P. corallina and
O. tartarea. The studied taxa also contain different lichen
compounds. Differences in content of lichen compounds seem thus
to be a more likely explanation for the variations in chemical
weathering, than differences in oxalic acid production.
In addition to biological mediated physical and chemical weathering,
the water holding capacity of lichens may increase the chemical
dissolution and frost wedging of rock surfaces. The thallus and
the endolithic fungal hyphae bind the partly fragmented rock surfave
and protect it from abrasion and erosion. However, when the thallus
dies, loose mineral grains and fragments from the upper lichen-mineral
interface will be removed and a new surface will be exposed and
available for colonization and biodegradation. It is thus likely
that lichens enhance weathering rates, except at locations with
extremely high abrasion, where they may protect the surface.
Keywords: Endolithic hyphae; Lichen compounds; Lichen taxa; Oxalate;
Sandstone; Weathering』
『要旨
ノルウェー西部のVingenからの砂岩試料について、異なる地衣類分類群によりこの場所の風化度の変動を説明できるかどうかを知るために、分析を行った。試料は、高速薄層クロマトグラフィー(HPTLC)/薄層クロマトグラフィー(TLC)、走査電顕(SEM)、X線回折(XRD)、および蛍光X線分光(XRF)により分析し、統計処理と主成分解析を続けて行った。
4種の地衣類の下の風化殻の研究から、研究した分類群間で風化への影響が違うことが示された。 Ophioparma ventosa
および程度は劣るがPertusaria corallina の下の風化殻は、Fuscidea cyathoides
および Ochrolechia tartarea に比べて、一般に深く、岩石表面の鉱物溶解と破壊の程度も大きい。他の2つの分類群に比べて、O.
ventosa および P. corallina の下の風化殻内の菌糸の濃度が非常に高いのは、生物物理学的および生物化学的風化が原因であろう。O.
ventosa および F. cyathoides は同じような量のシュウ酸を含み、それはまたP.
corallina および O. tartarea よりも一般に非常に多い。研究した分類群はまた異なる地衣類成分を含む。したがって、地衣類成分の含有量の違いは、シュウ酸生産の違いよりも、化学風化の変動について説明しやすそうに思われる。
生物が仲介する物理および化学風化に加えて、地衣類が水を保持する能力は、岩石表面の化学溶解および凍結割れを増加させるだろう。葉状体および岩石内菌糸は部分的に崩壊した岩石表面を縛りつけ、摩耗および浸食から保護する。しかし、葉状体が死ぬと、地衣類−鉱物界面上部からゆるんだ鉱物粒子や破片が取り除かれるであろうし、新しい表面が露出して、コロニーの形成や生物浸食に適するようになる。したがって、地衣類が風化速度を促進することはありそうである、ただし極端に摩耗が激しくて、地衣類が表面を保護しているような場所は除くが。』
1. Introduction
2. Materials and methods
2.1. Study site and sampling
2.2. Taxonomic identification
2.3. Analytical methods
2.3.1. Scanning electron microscopy (SEM)
2.3.2. X-ray diffraction (XRD)
2.3.3. X-ray fluorescence spectroscopy (XRF)
2.4. Statistical methods
3. Results
3.1. Unweathered bedrock
3.1.1. Variation in unweathered rock composition within and
between taxa
3.2. Weathered bedrock
3.2.1. Variation in weathered rock composition within taxa
3.2.2. Variation in weathered rock composition between taxa
3.3. The lichen-mineral interface
4. Discussion
4.1. Chemical weathering by lichens
4.2. Physical weathering by lichens
5. Conclusions
Acknowledgements
References