objectives of the proposed research are to determine how elevated
atmospheric CO2 affects plant-herbivore interactions in complex and simple communities,
and to quantify the photosynthetic competence of leaves following
herbivory. The projected increase
in CO2 caused by human activities alters the chemical and structural
characteristics of leaves. These
changes, such as increases in leaf starch content or decreases in
nitrogen, reduce the quality of foliage as a food source.
Folivores may respond by increasing consumption to compensate for
poor food quality; however, this response is highly variable and depends
in part on the availability alternative food sources. Using Free-Air CO2 Enrichment (FACE) technology, we will investigate how projected
changes in atmospheric CO2 affect leaf quality and the feeding behavior of folivorous
arthropods in natural settings.
employs vertical vent pipes extending through the plant canopy to
precisely control atmospheric
levels in plots within an otherwise intact ecosystem.
The control and treatment plots are contiguous with the surrounding
ecosystem, and open to the full suite of folivores and their predators.
In North Carolina, the amount of herbivory and the population
dynamics of the major folivorous arthropods will be compared for 14
hardwood species growing in the naturally occurring understory of a pine
plantation under ambient (~360 ml/l) and elevated (~560 ml/ l)
the level expected in 2050. We
hypothesize that the total amount of herbivory by generalists will not
change in this complex community as they choose nearby species whose
foliage quality has not responded to elevated
Parallel measurements will be made in Illinois where a soybean
monoculture will be grown under elevated
with FACE. In this system we
expect per capita herbivory to increase as leaf quality decreases for all
plants. In North Carolina and
Illinois, measurements of leaf structure and chemistry will be paired with
measurements of herbivory and arthropod population dynamics to determine
induces compensatory feeding by specific herbivores or if the population
size or community structure of herbivores is altered.
the exception of severe outbreaks, it is generally accepted that herbivory
has a relatively minor effect on ecosystem productivity.
This view rests on measurements of the amount of leaf tissue
removed by herbivores but does not consider the photosynthetic competence
of the remaining leaf tissue. We
recently built a novel fluorescence imaging system that provides detailed
maps of the component reactions of photosynthesis across the surfaces of
intact leaves. Preliminary results indicate that photosynthesis is inhibited at
substantial distances from the area of leaf tissue removed, suggesting
that simply measuring the loss of leaf tissue greatly underestimates the
damage by herbivores. Using this
instrument we will test the hypothesis that different feeding guilds of
arthropods (chewers, suckers, gall formers) will differentially affect
remaining leaf tissue in forest trees and soybean.
These new measurements of the effect of herbivory on photosynthesis
together with the experiments on the effects of elevated
on herbivory will provide new insights into how plant-herbivore
interactions will alter ecosystem productivity in a future high-CO2