Investigating the Function of the Xanthophyll Cycle in the Sand Dune Herb Hydrocotyle bonariensis

Presentation given at the 79th Annual Meeting of the Association of Southeastern Biologists. Coastal sand dunes are abiotically stressful environments for native plant species. During the growth season, plants are exposed to multiple stress factors, including high incident sunlight that is most pronounced during midday. Thus, native sand dune species likely have mechanisms to safely dissipate excess absorbed light energy. Hydrocotyle bonariensis is a large-leaf clonal herb common to Georgia’s sand dunes and has been shown to increase leaf inclination over the growing season to avoid high incident sunlight, resulting in increased photosynthetic efficiency. However, these studies suggest that there may be additional mechanisms used by H. bonariensis to avoid negative effects of excess light absorption. The xanthophyll cycle is a series of pigment conformational changes that has been shown to reduce the risk of photoinhibition, or decreased photosynthetic efficiency, in plants in high light habitats. The purpose of this study was to investigate the relationship between photosynthetic efficiency (measured as leaf chlorophyll content and chlorophyll fluorescence) and the xanthophyll cycle in response to incident sunlight for H. bonariensis. Specifically, chlorophyll fluorescence was measured for naturally inclined leaves and experimental leaves restrained in a horizontal position in June, August, and September 2017. Leaf samples were then collected and are currently being analyzed for leaf chlorophyll content and xanthophyll pigment concentrations. The final results are expected to elucidate the relationship between photosynthetic efficiency and xanthophyll cycle activity. The results of this experiment will further clarify the avoidance and tolerance mechanisms exhibited by this species in response to high light in the sand dune habitat.