Spatial separation of males and females should be a significant disadvantage in organisms that are not mobile. However, spatial separation is common in plants with separate sexes. This project will integrate field, greenhouse, and molecular approaches to rigorously test hypotheses for mechanisms causing spatial separation of the sexes in the wetland grass Distichlis spicata (saltgrass). The study takes advantage of novel molecular techniques to identify saltgrass seedlings as male or female, then follows the fates of both genders in an integrated set of experiments that will evaluate the mechanisms and consequences of competition for limited resources by males and females of the same species in a variety of habitats. Additionally, the experiments will test whether the soil biota plays a significant role in the different plant-soil associations of males and females. The proposed research will have significant impacts on wetland conservation, resource management, and student training. Sea levels are projected to rise for the foreseeable future. Understanding how male and female plants of saltgrass compete will allow researchers to anticipate the effects of rising sea levels on this important salt marsh species. The proposed research also has applied value, because saltgrass and related species are used in agronomy and environmental restoration. The project will also provide support for two graduate and 12 undergraduate students. Undergraduates will be recruited through outreach to local community colleges to increase recruitment of underrepresented groups via targeted internships.
My lab is interested in determining how environmental stress affects sexual reproduction in plants. Specifically, this project was aimed at rigorously testing hypotheses for evolutionary mechanisms responsible for ecological niche divergence between males and females in the wetland grass Distichlis spicata. This grass species has separate male and female individuals, and they occupy different ecological niches in the salt marsh. Female plants occur lower in the salt marsh near the ocean, while males occur higher in the marsh. This pattern of spatial segregation of male and female individuals is common in plants with separate sexes and difficult to explain as it appears to reduce sexual reproduction and the production of seeds. Understanding the pattern will help explain how evolution shapes plant reproductive systems, particularly for plant species with separate sexes. No previous studies have used manipulative experiments to determine the ecological causes of this pattern. We used transplant experiments in the salt marsh and controlled greenhouse experiments to determine the ecological and physiological factors responsible for spatial segregation of the sexes in D. spicata. Our results suggest that male and female plants interact differently with mycorrhizal fungal mutualists, mutualists which occur in the majority of plants species and are important in nutrient and water acquisition. We suggest that sex-specific interactions of D. spicata with mycorrhizal fungi are important in explaining why the sexes are able to occupy different ecological niches, particularly with respect to water availability. Our work also suggests that competition between males and females is greater than competition within a sex (between females or between males) and that this increased inter-sexual competition may partially explain why the sexes segregate into separate niches. Our work supports a growing body of research suggesting that belowground ecological interactions (particularly interactions between plants and fungi) can be critical to structuring communities.
