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|Title:||Foliar damage and shoot growth changes resulting from exposure of eastern white pine seedlings to nightly acidic mists|
|Author(s):||Maurice, Charles Gerard|
|Doctoral Committee Chair(s):||Crang, Richard F.E.|
|Department / Program:||Plant Biology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
Agriculture, Plant Pathology
|Abstract:||Eastern white pine is an important coniferous forest species of the northeastern United States where nightly acidic mists may be a factor in the decline of highland forests. During 3 studies, experimental mists were applied nightly in order to simulate nocturnal misty conditions common in the forested highlands along the Appalachian Mountain Chain.
Under conditions of limited nutrient availability, acidic mists can serve as a supplemental source of nutrients and, thus, can enhance foliar growth; however, when nutrient availability is not limited, acidic mists do not affect current-year seedling heights, fascicle lengths, and needle transectional areas.
A direct relationship exists between mist acidity and both the initiation and the magnitude of foliar damage to eastern white pine seedlings, i.e. thresholds for visible foliar damage are 10 to 12 weeks at pH 2.6, 12 to 18 weeks at pH 3.6, and 18 to 24 weeks at pH 4.6 and damage gradients after 24 weeks of treatment consist of no lesions at pH 5.6, spot lesions at pH 4.6, spot and segment lesions at pH 3.6, and necrosis of entire needles at pH 2.6. Initially, foliar damage is localized in the form of tip chlorosis and small, distally-located chlorotic spots. With continued exposure, damage progresses along the needle lengths and inwardly toward the needle axes. Extrusion-bearing eruptions overlying subdermal resin ducts are visible near the foliar lesion centers via scanning electron microscopy.
Internally, the foliar lesions are characterized by the presence of extracellular exudate which through cytochemical analysis has been found to contain protein and complex polysaccharides and which is believed to originate from damaged plicate mesophyll cells. Damaged plicate mesophyll cells possess an increased starch presence in their chloroplasts, as well as an initial increase and subsequent marked decrease in cellular lipid content. Some of the ultrastructural features observed in the plicate mesophyll cells are similar to those observed by other authors working with sulfur-damaged conifer needles (i.e. few thylakoids per granum, more and less dense plastoglobuli, rounded chloroplasts, and cytoplasmic lipid-like inclusions) indicating that sulfate contained in the acidic mist is probably at least partially responsible for the foliar damage.
|Rights Information:||Copyright 1989 Maurice, Charles Gerard|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI8924893|