Thursday, August 5, 2010: 10:50 AM
408, David L Lawrence Convention Center
Background/Question/Methods
Leaf mass per unit area (LMA) is often used to predict leaf photosynthetic potential, with leaves with greater LMA (e.g. thicker sun leaves) are to have greater photosynthetic potential than leaves with low LMA (e.g. thinner shade leaves). However, its accuracy may be complicated due to independent variation in the two main components, leaf thickness and leaf density, in response to variations in the abiotic environment. A model combining parameters of leaf morphology, internal anatomy, and orientation offers a different approach to predicting leaf photosynthetic potential along abiotic gradients. Studies have indicated that, on barrier islands, several stress factors (e.g. salt spray, sand abrasion, and overwash) decrease with distance from the ocean, resulting in distinct vegetation zonation along an abiotic gradient. The aim of the present study was to compare the accuracy of these two models for predicting photosynthetic potential using two common sand dune species occupying different spatial positions along a small-scale abiotic stress gradient To compare the relative accuracy of these two leaf form/function models in predicting photosynthetic performance, leaf external morphology, internal structure, orientation, and photosynthesis were measured over a growth season for these two species on Topsail Island, North Carolina, USA. In addition, abiotic factors (e.g. incident sunlight, air and soil temperature, and salt deposition) were measured to define microclimatic differences within each vegetation zone.
Results/Conclusions
Iva imbricata, which had a wider spatial zone of occurrence, had thick succulent leaves, upper and lower palisade layers, stomata on both leaf surfaces, and horizontal leaf orientation resulting in approximately eight times greater incident sunlight on the adaxial leaf surface during the day. In contrast, Hydrocotyle bonariensis, found only in microhabitats furthest from the high-tide limit, had multiple upper palisade layers, stomata on both leaf surfaces, and more inclined leaves over the growing season, resulting in approximately three to four times more incident sunlight on the adaxial surface. Measured LMA for I. imbricata was approximately twice that of H. bonariensis, but overall mean photosynthesis was similar for both species. Each species had characteristics predicted by the orientation/structure model, and corresponding photosynthesis values agreed with this model. However, mean seasonal LMA failed to provide accurate predictions for these species along the abiotic gradient. These results suggest that incorporating leaf internal anatomy, external morphology, and orientation properties may provide a more accurate estimation of photosynthetic potential for different species rather than differences in LMA alone.
Leaf mass per unit area (LMA) is often used to predict leaf photosynthetic potential, with leaves with greater LMA (e.g. thicker sun leaves) are to have greater photosynthetic potential than leaves with low LMA (e.g. thinner shade leaves). However, its accuracy may be complicated due to independent variation in the two main components, leaf thickness and leaf density, in response to variations in the abiotic environment. A model combining parameters of leaf morphology, internal anatomy, and orientation offers a different approach to predicting leaf photosynthetic potential along abiotic gradients. Studies have indicated that, on barrier islands, several stress factors (e.g. salt spray, sand abrasion, and overwash) decrease with distance from the ocean, resulting in distinct vegetation zonation along an abiotic gradient. The aim of the present study was to compare the accuracy of these two models for predicting photosynthetic potential using two common sand dune species occupying different spatial positions along a small-scale abiotic stress gradient To compare the relative accuracy of these two leaf form/function models in predicting photosynthetic performance, leaf external morphology, internal structure, orientation, and photosynthesis were measured over a growth season for these two species on Topsail Island, North Carolina, USA. In addition, abiotic factors (e.g. incident sunlight, air and soil temperature, and salt deposition) were measured to define microclimatic differences within each vegetation zone.
Results/Conclusions
Iva imbricata, which had a wider spatial zone of occurrence, had thick succulent leaves, upper and lower palisade layers, stomata on both leaf surfaces, and horizontal leaf orientation resulting in approximately eight times greater incident sunlight on the adaxial leaf surface during the day. In contrast, Hydrocotyle bonariensis, found only in microhabitats furthest from the high-tide limit, had multiple upper palisade layers, stomata on both leaf surfaces, and more inclined leaves over the growing season, resulting in approximately three to four times more incident sunlight on the adaxial surface. Measured LMA for I. imbricata was approximately twice that of H. bonariensis, but overall mean photosynthesis was similar for both species. Each species had characteristics predicted by the orientation/structure model, and corresponding photosynthesis values agreed with this model. However, mean seasonal LMA failed to provide accurate predictions for these species along the abiotic gradient. These results suggest that incorporating leaf internal anatomy, external morphology, and orientation properties may provide a more accurate estimation of photosynthetic potential for different species rather than differences in LMA alone.