We investigated the effect of elevated CO2 on the
growth and mycorrhizal colonization of three tree species native
to north-eastern American forests (Betula papyrifera
Marsh., Pinus strobus L. and Tsuga canadensis L. Carr).
Saplings of the tree species were collected from Harvard Forest,
Massachusetts, and grown in forest soil under
ambient (c. 375 ppm) and elevated (700 ppm) atmospheric CO2
concentrations for 27–35 wk.
In all three species there was a trend to increasing whole-plant, total-root
and fine-root biomass in elevated CO2,
and a significant increase in the degree of ectomycorrhizal colonization
B. papyrifera and P. strobus, but not in
T. canadensis. However, in T. canadensis the degree of
colonization with arbuscular mycorrhizas increased
significantly. In both the ambient and elevated environments, on the roots
of B. papyrifera and P. strobus 12
distinct ectomycorrhizal morphotypes were identified. Distinct changes
in the ectomycorrhizal morphotype
assemblage of B. papyrifera were observed under CO2
This change resulted in an increase in the
frequency of ectomycorrhizas with a higher incidence of emanating hyphae
rhizomorphs, and resulted in a
higher density of fungal hyphae in a root exclusion chamber.