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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 and relative growth rate between H. anomalus and parental species H. annuus and H. petiolaris. 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.
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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.
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