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Abstract:
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Effects of above-ground herbivory on shortterm
plant carbon allocation were studied using maize
(Zea mays) and a generalist lubber grasshopper (Romalea
guttata). We hypothesized that above-ground herbivory
stimulates current net carbon assimilate allocation
to below-ground components, such as roots, root exudation
and root and soil respiration. Maize plants 24 days
old were grazed (c. 25-50% leaf area removed) by caging
grasshoppers around individual plants and 18 h later
pulse-labelled with 14CO2. During the next 8 h, ~4C assimilates
were traced to shoots, roots, root plus soil respiration,
root exudates, rhizosphere soil, and bulk soil
using carbon-14 techniques. Significant positive relationships
were observed between herbivory and carbon allocated
to roots, root exudates, and root and soil respiration,
and a significant negative relationship between herbivory
and carbon allocated to shoots. No relationship
was observed between herbivory and 14C recovered from
soil. While herbivory increased root and soil respiration,
the peak time for ~4CO2 evolved as respiration was not
altered, thereby suggesting that herbivory only increases
the magnitude of respiration, not patterns of translocation
through time. Although there was a trend for lower
photosynthetic rates of grazed plants than photosynthetic
rates of ungrazed plants, no significant differences were
observed among grazed and ungrazed plants. We conclude
that above-ground herbivory can increase plant
carbon fluxes below ground (roots, root exudates, and rhizosphere respiration), thus increasing resources (e.g.,
root exudates) available to soil organisms, especially microbial
populations. |
