『Abstract
An electron microprobe and petrographic microscope were used
to study the biota-rock interface beneath higher-plant communities
and lichens, as well as unvegetated surfaces, on Hawaiian basalt
flows ranging from a few years to several thousand years in age
and currently receiving moderate to extremely high annual rainfall.
We find dramatic (order of magnitude minimum) acceleration of
weathering rates beneath vascular plants on the youngest flows
relative to adjacent non- or primitively-vegetated controls, notably
rocks colonized by the common fruticose lichen Stereocaulon
vulcani. Bulk dissolution of plagioclase accounts for most
of the weathering observed beneath higher plants on these young
basalts. Analysis of older flows under mature forests reveals
that chemical weathering beneath vascular plant communities continues
unabated for thousands of years after initial colonization. Moreover,
such weathering is not limited to exterior basalt surfaces but
is commonly found adjacent to joints and vesicles within the rock,
where it is often associated with fine (sub-2 mm diameter) plant
roots. Plagioclase dissolution was also observed on lichen-encrusted
and unvegetated flows a few hundred to thousands of years in age,
but it was typically much less advanced than beneath higher plants
and rarely extended more than several millimeters from exterior
rock surfaces. Chemical denudation rates on older flows with higher
plants are at minimum ten times greater than those with only lichens
or microbiota in the environments studied. If S. vulcani
and associated microflora resemble the terrestrial precursors
to vascular plant communities, then the results of studies such
as this have implications for the history of atmospheric CO2 and the Earth's climate.』
1. Introduction
2. Field area and methods
3. General observations
3.1. Modes of chemical weathering
3.2. The effect of vascular plants
3.3. Lichens and microbiota in the absence of higher plants
4. Discussion and conclusions
Acknowledgements
References