Photosynthetic responses and leaf variability in sassafras.
Item
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Title
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Photosynthetic responses and leaf variability in sassafras.
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Identifier
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AAI9000021
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identifier
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9000021
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Creator
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de Soyza, Amrita Giles.
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Contributor
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Adviser: Dwight T. Kincaid
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Date
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1989
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, General | Biology, Botany | Biology, Plant Physiology
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Abstract
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A field study was carried out to investigate whether spatial and temporal variability in leaf form has functional and adaptive meaning in terms of net photosynthesis in Sassafras albidum. Leaves with entire margins predominated at the proximal and distal nodes of shoots while lobed leaves were most common at the intermediate nodes and had the greatest surface area.;Greatest chlorophyll (mg g{dollar}\sp{lcub}-1{rcub}{dollar} and g m{dollar}\sp{lcub}-2{rcub}){dollar} occurred in leaves of the intermediate nodes except during the latter part of the growing season, when leaves of the distal nodes had the greatest chlorophyll contents. A similar pattern was seen with leaf nitrogen content.;Greatest net photosynthetic rates occurred in leaves of the intermediate nodes (nodes 6-9; maximum of 14.53 {dollar}\mu{dollar}mol m{dollar}\sp{lcub}-2{rcub}{dollar}s{dollar}\sp{lcub}-1{rcub}{dollar}). Statistically significant differences in net photosynthesis were rarely found between leaves with entire margins and leaves with lobes. I conclude that the nodal position of a leaf is more important than leaf shape in determining the photosynthetic capacity of a leaf. Similarly, significant differences were rarely found in stomatal conductance, transpiration or water use efficiency among leaf shapes. Midday xylem water potential (which ranged from {dollar}-{dollar}0.95 mPa on June 10 to {dollar}-{dollar}1.68 mPa on August 18) also showed no statistically significant differences among leaf shapes.;A study of the effect of leaf size and shape on convectional heat loss using illuminated leaf models with integrated thermocouples, showed that lobed leaves had lower temperatures and shorter time constants than leaves with entire margins of the same surface area. While direct relationships between leaf form and leaf function were not established, the predominance of lobed leaves at the intermediate nodes which have the greatest capacity for photosynthesis and the greatest surface area, suggested that leaf lobing plays a role in maintaining these leaves at temperatures conducive to favourable water relations and high net photosynthesis rates.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
