ECOLOGICAL AND EVOLUTIONARY CONSEQUENCES OF PLANT GROWTH ON SERPENTINE SOIL: EFFECTS OF SOIL METALS ON PLANT MORPHOLOGY, METAL ACCUMULATION, PLANT-POLLINATOR INTERACTIONS, AND POLLEN-PISTIL INTERACTIONS

摘要

Edaphic factors are a strong selective force in shaping both plant species distributions and the diversification of many lineages. Specifically, adaptation to novel soil environments can result in species-level changes in floral morphology, phenology, or chemistry, each of which may affect plant reproduction. However, whether floral chemical changes alter plant reproduction following colonization of novel soils is poorly described. In this work, I investigate the effects of soil chemistry on plant chemistry, plant-animal interactions, and pollen-pistil interactions using serpentine-adapted plant species to help determine the effects of the soil chemical environment on plant reproduction and reproductive isolation. I show that (1) plants accumulate soil metals into vegetative and reproductive organs, as well as into pollen and nectar, (2) floral metal accumulation deters generalist pollinators and filters natural pollinator communities, and (3) floral metal accumulation alters pollen grain germination. These findings have important implications for plant reproduction on metal-rich soils. For example, my research has identified two novel mechanisms through which serpentine soil chemistry may foster reproductive isolation between species or populations growing in disparate soil environments. First, floral metal accumulation may result in pollinator filtering. Specifically, closely related plant species occurring in sympatry that differ in floral metal accumulation may become reproductively isolated through reduced pollinator sharing. Second, floral metal accumulation may provide a mechanism through which gene flow is reduced between serpentine and non-serpentine populations by altering pollen germination and pollen-pistil compatibility. I found that elevated metal concentrations in the pistils of maternal plants limits pollen tube growth towards ovules in non-adapted species. Furthermore, my results suggest that using metal hyperaccumulating plants in phytoremediation should be considered with caution. While I found that generalist pollinators exhibited decreased visitation to Ni-enriched flowers, they still visited these flowers, and therefore likely ingested a potentially toxic resource. If bioaccumulation of heavy metals occurs in plant-pollinator systems near metal-contaminated soils, pollinator populations may become threatened. This study highlights the influence of the soil environment on plant ecological interactions and plant evolution, and elucidates the role of the edaphic factor on plant reproduction.