Predicting how life will respond to climate change today requires understanding how life changed with climate in the past. Biological change ultimately reflects evolution. My research in evolutionary biology examines how key plant traits change with climate.
As sessile organisms, individual plants and fungi are especially vulnerable to climate change. When conditions get too hot or dry, successful offspring have to find new places or ways of living. Their adaptations, as organisms that drive the carbon cycle, can feedback to the climate system. The history of life and climate records several dramatic episodes. Every mass extinction has been associated with rapid climate change. Some followed important physiological innovations by plants or microbes; all transformed life by pruning away broad swaths of diversity. The current mass extinction is unique because the adaptation driving change did not occur in a tree or fungus, but rather, among the diverse cultures of a peculiar ape (that’s us). Nevertheless, we can expect the history of life’s tumultuous relationship with climate to inform the future.
Over the past two million years, earth has cycled in and out of ice ages more than 20 times. Relatively warm conditions today followed much colder conditions just 20,000 years ago. Plants that are rare now may have enjoyed much more success then. Specifically, some rare plants that only grow in unusually cold locations today, like alpine plants near mountain snowpack, probably grew extensively along vast continental glaciers in the past. However, not all rare plants are climate refugees. Some may have originated very recently through local adaptation to the unique habitats where they grow. These alternative hypotheses, make different predictions for how adaptive traits, genetic variation and habitats align.
This small group of mostly North American herbaceous plants includes both rare and widespread species that are very difficult to tell apart. Most rare species are adapted to moist cliffs and have patchy distributions that coincide with their uncommon habitats. They could be relicts, like alpine plants, or given the complex evolutionary dynamics in the group (including a credible hypothesis that one species developed from an unfertilized gamete) they could be local ecotypes. Using population genetic data, I showed that one rare eastern species is likely a relict, while another is probably an ecotype (Oberle and Schaal 2011). The ecotype exchanges genes with a widespread relative despite a chromosomal barrier (Oberle et al. 2012). These patterns in the eastern United States may also apply to plants from the west and many other unrelated species groups with similarly complex patterns.
The first plants to gain a foothold on land had an unlikely ally: microscopic fungi growing in their roots. While many familiar fungi are plant pathogens, these mycorrhizal fungi are beneficial, giving plants important minerals from the soil in exchange for carbohydrates. Partnered plants and fungi break down rocks so effectively that they influence many exchanges between land, sea and air, including carbon cycling. As enduring and ubiquitous as this relationship may be (400 million years and 80% of plant species), it has interesting variability. Some plants form partnerships with very different fungi, while other plants have adaptations that exclude fungi altogether. These alternatives are associated with some major differences in climatic gradients and biogeochemical cycles. Working with colleagues on a large database, I helped show that transitions to the most common mycorrhizal state are favored over evolutionary time (Maherali et al. in press). To explain why other states persist, we showed that the most common association does poorly with extreme temperatures and in very nutrient rich soils (Maherali et al. in prep).
While Dodecatheon occurs in only a single north Florida glade, the state is filled with rare and unusual species. With students and collaborators at Marie Selby Botanical Garden, I am working to improve conservation of Florida’s unique flora, especially its epiphytic plants. I am also interested in using population genetics to uncover the recent history of Florida’s mangroves, which store so much carbon that they can actually build islands that rise with the sea.
In addition to further work on the evolution of mycorrhizae, including their impacts on plant soil feedback, I am interest in examining the evolutionary history of other plant traits which influence their sensitivity to global change, including salt tolerance and isoprene production.
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