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LI-6400XT Literature: Customer Application Articles

Plant Ecophysiology Project at the University of Nebraska-Lincoln

What happens to plants when they are fedon by insects? This question has been the focus of the Plant Ecophysiology Project at the University of Nebraska-Lincoln's Department of Entomologyfor the past 15 years. Part of the question involves identifying mechanisms of yield loss in agronomic plants. LI-COR's Leaf Area Meters and LI-6400XT Portable Photosynthesis System have been used in a long series of field studies to help establish yield loss from defoliating pests in soybeans due to reductions in canopy light interception. Currently, the department is exploring the light interception hypothesis in other agronomic species, such as potato. "The practical application ofthis work is dramatically improved accuracy in our decision-making tools for coping with insect pests," says Professor Leon Higleyof the Department of Entomology.

student studying ecophysiology at the University of Nebraska-Lincoln

Another side to the question of insect influence on plants is how gas exchange is affected by insect injury. Many variables influence photosynthetic responses to insect feeding, including plant phenology, injury type, injury intensity, location of injury on the plant, and interactions with environmental factors. "The LI-6400 has been an invaluable tool in addressing this issue," says Higley.

Responses seen in single leaves must be compared with responses of whole plants and plant populations. "Despite the complexity of these relationships, our work and that of colleagues is leading to broad understandings of plant responses. Much of our research has focused on mechanisms underlying photosynthetic rate changes from chewing insects that rapidly remove leaf tissue, and the role of water stress in moderating these responses," says Higley. His department is currently focusing on mechanisms underlying rate reductions from sucking insects, like aphids. New advances in instrumentation, such as the 6400-40 Leaf Chamber Fluorometer, used in measuring leaf fluorescence, are proving invaluable for improving understanding of the immediate changes in photosynthetic integrity triggered by insect feeding.

Many entomology students at UNL are alsousing LI-COR instrumentation for their studies. Paul Nabity, an undergraduatestudent, used the LI-6400 to measure plant responses to artificialand naturally induced defoliation by an insect herbivore. He was ableto observe how an environmentally stressed plant was able to cope withadditional biotic stresses.

Rod Madsen, an M.S. student, took survey measurements on early season soybeans experiencing defoliation with the LI-6400. During the summer of 2002, he plans to characterize a disease-stressed soybean variety by implementing a series of light curves as the disease progresses. The disease, soybean mosaic virus, causes a wilting condition of the leaves limiting light interception and photosynthesis resulting in severe yield decline. "Data gathered from the study will help to provide new insights in understanding soybean physiological responses to both disease and defoliation stress," says Madsen.

ecophysiology project

Kevin Delaney, a Ph.D. student, has used the LI-6400 to examine the response of common milkweed to insect herbivory. Delaney has examined how other types of environmental stress (i.e., water stress and inter specific plant interference) affect a milkweed leaf's ability to tolerate insect feeding. He is currently exploring why common milkweed (but not other Ascelepias species) has reduced photosynthetic rates following insect injury, and why there is seasonal variability in milkweed photosynthetic responses to insect injury. "These are important issues," says Delaney, "because the most commonly observed response of plants to leaf feeding by insects is no change in photosynthetic rates on remaining tissues."

Tulio Macedo, a Ph.D. student, is using the 6400-40 Leaf ChamberFluorometer with the LI-6400 to elucidate the physiological modificationscoupled by plants when challenged by biotic stress. The simultaneous measurement of gas exchange and fluorescence allows Macedo to better understand responses of crop varieties to insects. "Using the Leaf Chamber Fluorometer, we are able to work faster in field and laboratory environments because we are only handling one instrument," he says.

Thanks to Dr. Leon Higley and his students, Department of Entomology, University of Nebraska-Lincoln, for contributing to this article.

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