The Hawaiian lobeliads (Campanulaceae) are one of the most spectacular examples of adaptive radiation in flowering plants, ranging from fully open to densely shaded microsites and from 500 to >12,000 mm annual rainfall. Prior research has provided a molecular phylogeny for this clade, documented the distribution of 11 representative species along a gradient of photon flux density (PFD), and demonstrated the adaptation to PFD of static and dynamic photosynthetic light responses and associated leaf traits via field and common-garden studies. Diversification in habitat has generally been accompanied by shifts in photosynthetic physiology that follow classic patterns of adaptation to sun vs. shade. However, light availability is almost inevitably correlated with variation in rainfall and evaporative demand, with the latter affected by differences in air temperature, relative humidity, and heat load in sunny vs. shady microsites. It is thus unclear - in Hawaiian lobeliads, or across land plants - the extent to which variation in photosynthetic responses and associated leaf traits along PFD gradients reflects adaptation to variation in light per se, moisture supply relative to demand, or both. Preliminary data suggest that light and moisture availability interact to shape photosynthetic light responses and associated leaf traits in lobeliads native to different habitats.
The research tests the hypothesis that the interaction of water with light availability critically influenced the path of physiological diversification and adaptive evolution in several Hawaiian lobeliads adapted to a range of light and moisture gradients. Experiments will characterize water relations under field conditions, including studies of leaf water potential, stomatal response to humidity, photosynthetic response to VPD, leaf hydraulic conductance and hydraulic vulnerability. Experiments in a common garden will be used to analyze ecological and evolutionary shifts in water relations, hydraulics, photosynthesis, associated leaf traits, and whole plant growth under common conditions. Finally, research will determine if evolutionary trends occur in physiological traits across broad environmental gradients in the Hawaiian Islands.
Findings will provide fundamental insights into the evolution of gas exchange strategies in land plants. By conducting such studies on closely related taxa in the context of an explicit phylogeny, important inferences will be drawn about evolutionary pathways for various traits, and the role of ecology vs. ancestry in shaping the characteristics of present-day species. Outreach activities include developing a module for the ESA's Teaching Issues and Experiments in Ecology; coordinating with the Volcano School of Arts and Sciences, and Kamehameha Schools Kea`au campus to develop a module on local plant adaptation for K-8 students; and providing summer research opportunities for undergraduate students from underrepresented groups through coordination with the UH-Hilo REU program & ESA SEEDS program.
