Browsing by Author "Lipscomb, Mary Virginia"

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    The influence of water and light on the physiology and spatial distributions of three shrubs in the Southern Appalachian Mountains
    Lipscomb, Mary Virginia (Virginia Tech, 1986-06-11)
    In order to understand vegetational gradients which develop in response to environmental gradients, the physiological capabilities of each species must be examined in relation to the observed environmental gradient. The distributions of three temperate zone shrub species which occupy different positions on the spur ridges of Brush Mountain may be influenced by their tolerances to light and moisture. Greenhouse studies indicate that R. maximum has a 60 % reduction in photosynthesis at water potentials below -1.0 MPa. R. nudiflorum has only a 30 % reduction and K. latifolia has less than 10 % reduction. Seasonal pressure volume curve determinations, conductance measurements, and water potential measurements of plants in the natural environment indicated that photosynthesis is not affected by water potential in K. latifolia. R. maximum has a significant reduction in conductance during drought which may limit photosynthesis. R. nudiflorum appears to begin senescence prior to severe drought in this area. Greenhouse experiments of adaptability to increasing light intensity show that K. latifolia and R. nudiflorum can significantly increase their light saturation point and maximum rate of photosynthesis in high light environments. R. maximum does not increase its photosynthesis rate in high light environments and appears to undergo chloroplast degradation when grown in high irradiance. Gradient analysis of vegetation on Brush Mountain shows that R. maximum reaches its highest importance in low light, high moisture sites. K. latifolia is most important in low moisture, high irradiance sites. R. nudiflorum is infrequent in the study area but occurs mostly in moderate moisture and irradiance sites. The distributions of R. maximum and K. latifolia appear to match their experimentally determined physiological tolerances. The results for R. nudiflorum are inconclusive.
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    The response of four ericaceous shrub species to multiple environmental resource variation
    Lipscomb, Mary Virginia (Virginia Tech, 1991-01-15)
    Natural environments are often limiting to plant growth in more than one resource due to the simultaneous fluctuations in resource supply and demand. The mechanisms a species uses to acclimate to simultaneous resource variation may not be uniform among species of the same growth form. Four evergreen ericaceous shrubs responded individualistically to fluctuations in light and water in an experimental garden study. Rhododendron maximum and Kalmia latifolia were able to acclimate photosynthetically to high and low irradiance under both high and low water availability. Rhododendron catawbiense and R. minus showed significantly higher acclimation to high light in high water treatments. All four species were able to reduce their osmotic potential and water deficit at the turgor loss point seasonally, especially in low water treatments. Low soil water availability also reduced midday conductance and water potential in all four species. Rhododendron maximum and R. catawbiense were very conservative in their water use patterns. Rhododendron minus and K. latifolia exercised less stomatal control over water loss but did not appear to experience water stress under these treatment conditions. Rhododendron catawbiense was the most sensitive to low water availability and had the lowest turgor pressure of the four species. Daily carbon dioxide assimilation was highest in high light, high water. treatments and lowest in low light, low water treatments for all four species. During the two years of this study, these species did not show any consistent pattern of increased growth in the high light, high water treatments where carbon dioxide assimilation was highest. Since these species are native to low resource habitats, their abilities to significantly increase growth during periods of high resource availability may be less than that of plants adapted to high resource availability. The results of these experiments indicate that these four species of the same growth form respond differently to simultaneous fluctuations in light and water resources.