Geoscience Reference
In-Depth Information
Peat
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loving rhododendrons.
If you want to plant rhododendron, or other heathers, in your garden,
it is best to replace the ordinary soil with coarsely shredded unlimed peat. These plants thrive in
acidic soil and form a symbiosis with ericoid mycorrhizal fungi, which are experts at releasing
nitrogen-rich amino acids from peat and other organic material. Weeds require easily accessible
nitrogen and are rarely a problem in these conditions
highly acidic soil do so by protecting their roots through the secretion of sub-
stances that bind the aluminium ions.
Crowberry, blueberry, bearberry and other members of the heather family pre-
dominate in tundra environments, where the soil is acidic and nutrient-poor. They
have adapted to this environment by evolving thin, hairy roots that form dense lat-
tice networks in the organic topsoil. Cells in these hairy roots are full of fungal
hyphae of another mycorrhizal type than that found in grass and herbs. The myc-
orrhizal fungi found in members of the heather family secrete enzymes that release
nitrogen and phosphorus from complex organic compounds in the soil.
A few years ago I took part in an experiment in Abisko in which we added radi-
oactive carbon dioxide to tundra plants enclosed under plastic covers. The plants
absorbed the carbon dioxide through photosynthesis and the radioactive isotope
enabled us to observe the carbon on its journey down into the soil. I asked one of
my students to extract roots from the soil so we could analyse how much carbon
entered the fungal tissue that filled the cells, a task that proved virtually impos-
sible as the samples were enmeshed in spidery roots that were extremely difficult
to separate from the surrounding soil. Nevertheless, after many painstaking hours
under the microscope, we eventually developed enough samples and were able to
see that the fungi utilised the plant's photosynthetic products heavily during the
major part of the growing season.
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