Journal of Experimental Botany, Vol 50, 9-13, Copyright © 1999 by Oxford University Press
D Robinson and A Fitter
Various claims have been made about the ecological significance of
plant-to-plant carbon movement through common mycorrhizal networks (CMNs).
Most suggest that resource competition among interconnected plants should
be less important than previously thought. If true, that would profoundly
alter our perception of how plants interact among themselves and with their
environment. However, there are difficulties in quantifying the amounts of
resource transferred via CMNs, ensuring that transfer is genuinely through
hyphae, not soil, and understanding its control. Carbon movement has not
been quantified in many of the published studies. Where it has, its likely
functional role has not been clarified. Some recent, well-publicized
research suggests that carbon transferred to trees via an ectomycorrhizal
(EcM) network may be physiologically and ecologically important. Our view,
however, is that the evidence for this remains equivocal. Appropriate
controls for the possibility of carbon transfer via soil were not used
under field conditions. In laboratory experiments, controls failed to
clarify the role of EcM links in carbon transfer. To resolve some areas of
uncertainty, abundances of 13C have been measured to
estimate carbon transfers via an arbuscular mycorrhizal (AM) network
connecting grasses and forbs of the same or different species. Permeable
barriers to roots and hyphae allowed any direct carbon transfer via soil to
be detected. Large amounts of carbon (typically 10% of that in roots) were
transferred between linked plants via the CMN. Transferred carbon was never
transported into shoots of 'receiver' plants. It remained in roots,
probably inside fungal structures and, therefore, unavailable to the plants
into which it was apparently transferred. Carbon transfer via an AM network
does not allow 'resource sharing' among linked plants. It is probably
irrelevant to the botanical components of a community, but it may be
fundamental for fungal members. The 'mycocentric' view is that fungal
structures within roots are parts of extended mycelia through which fungi
move carbon according to their own carbon demands, not those of their
autotrophic hosts.Keywords: Arbuscular mycorrhiza,
carbon, common mycorrhizal network, ectomycorrhiza.
ARTICLES
The magnitude and control of carbon transfer between plants linked by a common mycorrhizal network
Cellular and Environmental Physiology Department, Scottish Crop Research Institute, Dundee DD2 5DA, UK; Department of Biology, University of York, PO Box 373, York YO10 5YW, UK; Corresponding author; Fax: +44 1382 562 426; E-mail: d.robinson@scri.sari.ac.uk
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