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Effect of Leaf Angle and Orientation on Photosynthesis and Water Relations in Silphium terebinthinaceum

Marian Smith and Drew Ullberg
American Journal of Botany
Vol. 76, No. 12 (Dec., 1989), pp. 1714-1719
Stable URL: http://www.jstor.org/stable/2444470
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Effect of Leaf Angle and Orientation on Photosynthesis and Water Relations in Silphium terebinthinaceum
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Abstract

Leaf angle and orientation were measured for 217 leaves from two populations of Silphium terebinthinaceum Jacq., a prairie forb with large, unlobed leaves. Seventy-five percent of leaves measured had an angle of deviation from horizontal of more than 60⚬, and 60% were oriented within 15⚬ of North. Incident Photon Flux Density (PFD), leaf temperature, photosynthesis, stomatal conductance to CO2, internal CO2 concentration, transpiration, and water use efficiency (WUE) were measured on 67 pairs of leaves with the axes oriented in either a North-South (N-S) or East-West (E-W) direction. Leaves with axes oriented N-S intercepted higher levels of PFD during morning and afternoon and exhibited higher diurnal rates of photosynthesis and WUE. Leaf temperature was reduced in N-S leaves during midday as compared to E-W leaves, and was lower in vertical leaves than in those in a horizontal position. Therefore, it was concluded that leaf orientation and verticality enhance carbon gain and minimize water loss-characteristics which may have adaptive significance in a hot, stressful prairie environment.

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