Brown, K.J. , Havran, J. Christopher , Ballard, H. E. .
Water use efficiency trends in three Hawaiian Viola are tightly linked to geographic distribution.
The role of ecological speciation, and the influence of ecological niches on adaptive radiation, are timely topics in evolutionary biology. The Hawaiian Viola species are a group that has undergone repeated adaptive radiations across the Hawaiian archipelago. The geographic distribution of the Hawaiian violets on Moloka’i exhibit tight species restrictions to open bog (Viola maviensis, VIMA), cloud forest (V. robusta, VIRO), and dry forest habitats (V. tracheliifolia, VITR). These habitats represent discrete zones of plant water availability. Our objective was to investigate the interspecific physiological and anatomical adaptations of Viola water use efficiency (WUE) on Moloka’i. Our expectation was that the violets would exhibit increasing physiological and anatomical trends in WUE that closely match the gradients in water stress. In August 2006 field experiments were conducted on Moloka’i in the Nature Conservancy Kamakou Preserve in populations of VIRO, VIMA, and VITR. Leaf gas exchange measurements were made using LI-6400 and LI-1800 instruments. Leaves were sampled for midday xylem pressure potential, and the same leaves were used for lab analyses of: stomatal density, specific leaf area, and d13C. Stomatal pore length was largest in the bog violet VIMA (52 um) versus wet VIRO and dry forest VITR violets (17.2 and 16.3 um respectively). However, stomatal density per unit area was also different across the violets (VIMA 76.5 mm-2, VIRO 55.4, and VITR 132.3), resulting in the bog violet with a much more porous leaf. Leaf stomatal conductance and instantaneous WUE also followed these trends. Preliminary results suggest that a hybrid, V. x luciae (V. maviensis x V. robusta), displays intermediate WUE which influence its geographic distribution in the boundary between VIRO and VIMA. Patterns of WUE appear to explain the tight habitat fidelity of the Moloka’i violets.
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1 - Ohio University, Environmental and Plant Biology, 315 Porter Hall, Athens, OH, 45701, USA
2 - Ohio University, Department of Environmental and Plant Biology, Porter 315, Athens, OH, 45701, U.S.A.
3 - Ohio University, Department of Environmental & Plant Biology, Porter Hall, Richland Avenue, Athens, Ohio, 45701-2979, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Stevens 1/Hilton
Date: Tuesday, July 10th, 2007
Time: 11:00 AM