Abstracts |
Disturbance of vegetation and soil may change the
species composition of arbuscular mycorrhizal fungi (AMF), which
may in turn affect plant species responses to AMF. Seasonal
tropical forest in Mexico is undergoing rapid conversion to
early-successional forest because of increased wildfire and may
require restoration. The responses of six early- and
late-successional tree species were tested using early- and
late-successional AMF inoculum. The plants were germinated in
the shadehouse and received three inoculum treatments: (1) soil
from a two-year-old burned site, (2) soil froth a mature forest
site, or (3) uninoculated controls. They were transplanted as
seedlings to a site prepared by burning, and their growth was
measured from September 1997 to November MOO. All six species
had the greatest growth response to early-seral inoculum, but
the response to late-seral inoculum varied. Two tree species,
Ceiba pentandra and Guazuma ulmifolia, were smallest with
late-seral inoculum, even smaller than the uninoculated. plants,
and the other species, Brosimum alicastrum, Havardia albicans,
Acacia pennatula, and Leucaena leucocephala, had intermediate
growth with late-seral inoculum. Of these, Brosimum, Havardia,
and Ceiba occur in late-successional forest, and the others are
early seral. Of the several growth measurements (height, cover,
biomass, stem diameter), stem-diameter responses to inoculum
were still significantly different into the third year for four
of the species. The uninoculated plants became infected by
residual inoculum in the burned experimental site within three
months of transplanting, yet mycorrhizal responses persisted.
The treatment, size differences may be due to different species
composition of the inocula. The early-seral inoculum was
dominated by small-spored Glomus spp., while the late-seral
inoculum had a higher density of large-spored Gigasporaceae. The
latter are known from greenhouse experiments to promote a
smaller plant-growth response than Glomus. Mature forest trees
may withstand the carbon drain from Gigasporaceae better than
establishing seedlings, so the growth patterns we observed with
inoculum source are consistent with a rapidly growing
successional forest, followed by slower-growing mature forest.
The results suggest that early-seral AMF should be used when
seedlings are inoculated for restoration, even for late-seral
tree species
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