Evolutionary Ecophysiology of Helianthus anomalus:
One comparison that is often done in ecophysiological research is to examine physiological characteristics of closely related species to test hypotheses about which plant traits confer a selective advantage in a given environment.  In our lab, we use the Helianthus hybrid system to look at the evolution of ecophysiological traits.  This is an ideal system for this type of work because the same two parental species, H. annuus and H. petiolaris, hybridized to form three stable hybrid species, H. anomalus, H. deserticola, and H. paradoxus.  All three hybrid species occur in extreme habitats relative to the parental species and the phenotypes of the parents are known, so we are able to examine how selection in novel environments has led to changes in physiological traits. 

Current work in our lab focuses on the evolution of the hybrid sunflower Helianthus anomalus, which is endemic to active sand dunes in the southwestern US.  We would like to determine which ecophysiological traits are responsible for the ability of H. anomalus to colonize its unique habitat and what genetic mechanisms are responsible for these ecologically important traits.  Preliminary data suggest that the scarcity of nutrients in the soil and the presence of water deep in the dunes are important factors in the evolution of H. anomalus.  As a major component of this research, we are examining differences in stress-induced gene expression in H. anomalus compared to its parental species to target ecologically important genes.  Additionally, we are continuing to work on species-level differences in ecophysiology between H. anomalus and parental species H. annuus and H. petiolaris.  Beau Brouillette is the graduate student in the lab whose project focuses on this area, and active collaborators are the Knapp and Burke labs at UGA and the Rieseberg lab at the University of British Columbia. 

Because H. annuus is the progenitor of cultivated sunflower, there is potential for the use of H. anomalus to be used in breeding and genetic engineering projects aimed at improving crops.  Additionally, our work will lead to a more clear understanding of the process of adaptation to stressful habitats.

Evolutionary and ecological responses of plant populations to the coastal dune environment:
 This research focuses on understanding the ecological and evolutionary responses of plant populations to selective pressures in the extremely dynamic coastal dune habitat.  Coastal dune communities are well established model systems for ecological research, due to the dynamic nature of dune habitat and the zonation patterns of the vegetation.  To a certain degree, vegetation zonation reflects successional change; however, environmental conditions vary greatly within the range of a single species.  Coastal dune plants are characterized by a long, narrow, fragmented distribution.  How and whether this unusual geographic distribution, combined with microenvironmental factors, affects the underlying genetic structure of populations is largely unknown since little genetic work has been conducted on coastal dune species.  Understanding patterns of population differentiation in response to environmental variation is crucial for successful restoration and conservation efforts. 
Our research focuses on two coastal dune species, Uniola paniculata, essential for stabilizing dune habitats, and Cakile edentula, a widespread annual colonizer.  We will use environmental sampling, plant trait measurements, and field and lab experiments to (1) to characterize the interacting dune environmental factors that drive plant trait variation; (2) to determine whether plant populations exhibit local adaptation along an environmental gradient; and (3) to assess whether genetic variation among plant populations corresponds to the environmental characterization, using comparisons of genetic divergence at neutral marker loci and quantitative traits. 

While coastal dunes are frequently disturbed habitats, dune habitats now face encroaching development and environmental change.  The maintenance of healthy coastal dune plant populations is essential for preventing massive beach erosion and protecting interior land against storm damage.  Recent work in the newly developing field of conservation physiology indicates that understanding of physiological functioning will help us to identify important predictor traits for successful restoration efforts and determine causal mechanisms underlying conservation problems.  Our research integrates methods from evolutionary ecology, ecophysiology, and genetics, to inform our understanding at multiple scales, from the whole plant level to the population level.  This research is being led by graduate student Cara Gormally.

Nighttime transpiration in C3 and C4 plants:
Water is a key limiting factor for plant growth and productivity worldwide.  Researches strive to understand plants water regulation and apply this knowledge to tasks such as crop management and predicting human impacts to the environment.  Plants loose water through open stomata and it is widely accepted that plants regulate stomatal aperture to maximize photosynthetic carbon gain while minimizing water loss and xylem cavitation.  C3 and C4 plants fix carbon during the day and lose water from leaves as an unavoidable cost of getting CO2 to the site of carboxylation.  At night these plants were expected to close their stomata, minimizing water loss when carbon gain was not occurring, and allowing plants to rehydrate.  However, challenging this widely held paradigm, our data and literature reviews demonstrate that substantial nighttime stomatal conductance (g) and transpiration (E) are a widespread phenomenon in C3 and C4 plants.

Our broad objective is to investigate potential benefits, consequences and adaptive significance of the unexpectedly large magnitude of nighttime g and E found in many plants. First, using four diverse focal species we are determining if resource availability affects nighttime g and E.  Soil and plant water status, nutrient availability, plant nutrient status, and VPD are being manipulated and nighttime g and E quantified in controlled environment and field experiments. Second, we will determine if and under what conditions there is a net beneficial effect of high nighttime g and E on resource uptake and interactions (water, nutrients, carbon) and plant performance (growth, reproductive output).  Nighttime E will be manipulated in controlled environment and field experiments and effects on resource acquisition, growth, and reproduction measured.Third, at the evolutionary scale, high nighttime g and E are expected to be more prevalent in taxa from water abundant but low nutrient environments.  Close relatives native to diverse habitats within eight diverse taxonomic groups will be assessed for nighttime g and E in common environments.  This project is led by Ava Howard and Lisa Donovan in collaboration with Jim Richards, Mairgareth Caird and Krishna Nemali.

Our studies are fundamental to understanding the importance of nighttime stomatal regulation for water loss, nutrient acquisition, and plant growth.  Our work provides the foundation for assessing ecological consequences of nighttime plant water loss and improving crop water management. 

Plant-soil predawn disequilibrium

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