Herbivore-specific elicitation of photosynthesis by mirid bug salivary secretions in the wild tobacco Nicotiana attenuata.

Herbivory is thought to be detrimental to plant fitness and commonly results in a metabolic shift in the plant: photosynthetic processes are typically down-regulated, while resource allocation to defenses is increased in herbivore-attacked plants, resulting in fitness costs of induced plant responses. Wild tobacco, Nicotiana attenuata, attacked by Tupiocoris notatus mirid bugs becomes resistant against more damaging herbivores through mirid-induced direct and indirect defenses. However, mirid-induced resistance and tissue loss do not result in a reduction of plant fitness.

Combined effects of elevated CO2 and natural climatic variation on leaf spot diseases of redbud and sweetgum trees.

Atmospheric CO(2) concentrations are predicted to double within the next century and alter climate regimes, yet the extent that these changes will affect plant diseases remains unclear. In this study conducted over five years, we assessed how elevated CO(2) and interannual climatic variability affect Cercospora leaf spot diseases of two deciduous trees. Climatic data varied considerably between the five years and altered disease expression.

Foliage of oaks grown under elevated CO2 reduces performance of Antheraea polyphemus (Lepidoptera: Saturniidae).

To understand how the increase in atmospheric CO2 from human activity may affect leaf damage by forest insects, we examined host plant preference and larval performance of a generalist herbivore, Antheraea polyphemus Cram., that consumed foliage developed under ambient or elevated CO2. Larvae were fed leaves from Quercus alba L.

Comparison of photosynthetic damage from arthropod herbivory and pathogen infection in understory hardwood saplings.

Arthropods and pathogens damage leaves in natural ecosystems and may reduce photosynthesis at some distance away from directly injured tissue. We quantified the indirect effects of naturally occurring biotic damage on leaf-level photosystem II operating efficiency (Phi(PSII)) of 11 understory hardwood tree species using chlorophyll fluorescence and thermal imaging. Maps of fluorescence parameters and leaf temperature were stacked for each leaf and analyzed using a multivariate method adapted from the field of quantitative remote sensing.

Elevated CO2 reduces leaf damage by insect herbivores in a forest community.

By altering foliage quality, exposure to elevated levels of atmospheric CO(2) potentially affects the amount of herbivore damage experienced by plants. Here, we quantified foliar carbon (C) and nitrogen (N) content, C : N ratio, phenolic levels, specific leaf area (SLA) and the amount of leaf tissue damaged by chewing insects for 12 hardwood tree species grown in plots exposed to elevated CO(2) (ambient plus 200 microl l(-1)) using free-air CO(2) enrichment (FACE) over 3 yr. The effects of elevated CO(2) varied considerably by year and across species.

Insect herbivory in an intact forest understory under experimental CO2 enrichment.

Human-induced increases in atmospheric CO(2) concentration have the potential to alter the chemical composition of plant tissue, and thereby affect the amount of tissue consumed by herbivorous arthropods. At the Duke Forest free-air concentration enrichment (FACE) facility in North Carolina (FACTS-1 research facility), we measured the amount of leaf tissue damaged by insects and other herbivorous arthropods during two growing seasons in a deciduous forest understory continuously exposed to ambient (360 microl l(-1)) and elevated (approximately 560 microl l(-1)) CO(2) conditions. In 1999, there was a significant interaction between CO(2) and species such that winged elm ( Ulmus alata) showed lower herbivory in elevated CO(2) plots, whereas red maple (Acer rubra) and sweetgum (Liquidambar styraciflua) did not.

Radiation-use efficiency of a forest exposed to elevated concentrations of atmospheric carbon dioxide.

We compared radiation-use efficiency of growth (epsilon;), defined as rate of biomass accumulation per unit of absorbed photosynthetically active radiation, of forest plots exposed to ambient (approximately 360 micro l l-1) or elevated (approximately 560 micro l l-1) atmospheric CO2 concentration ([CO2]). Large plots (30-m diameter) in a loblolly pine (Pinus taeda L.) plantation, which contained several hardwood species in the understory, were fumigated with a free-air CO2 enrichment system.

The nitrogen budget of a pine forest under free air CO enrichment.

Elevated concentrations of atmospheric CO increase plant biomass, net primary production (NPP) and plant demand for nitrogen (N). The demand for N set by rapid plant growth under elevated CO could be met by increasing soil N availability or by greater efficiency of N uptake. Alternatively, plants could increase their nitrogen-use efficiency (NUE), thereby maintaining high rates of growth and NPP in the face of nutrient limitation.

Forest carbon balance under elevated CO.

Free-air CO enrichment (FACE) technology was used to expose a loblolly pine (Pinus taeda L.) forest to elevated atmospheric CO (ambient + 200 µl l). After 4 years, basal area of pine trees was 9.