Current Research

Research in our laboratory is currently focused in two areas: 1) the physiological basis for inter- and intra-specific variation in response to elevated atmospheric carbon dioxide levels, and 2) delineating the physiological and ecological tolerance limits of the rare elements of the Atlantic Coastal Plain flora in Nova Scotia.

Arabidopsis h The first project attempts to explain the often diverse effects of elevated carbon dioxide on plant growth and development. We use a range of different species as model systems including Arabidopsis because of the wealth of information that has accumulated on its developmental pathways. This work contributes to our understanding of how natural populations will evolve, as well as what traits we should select for in managed populations in a future high carbon dioxide world.   

The Atlantic Coastal Plain flora contains many of Nova Scotia’s rare and endangered species. The rarest of these species are limited to a small number of low nutrient wetlands. This habitat is under threat due to land use changes, cottage development, construction of dams, and eutrophication. The second project attempts to understand why the rare elements are so limited in their distribution. In particular, our focus has been on understanding the relationship between growth and hydrological regime using both correlative and experimental approaches. A detailed understanding of the impact of the hydrological regime on these species will allow us better predict the impacts of development on these species and may allow us to ameliorate damage that has already occurred.
Euthania spp. Sabatia kennedyana Sisyrinchium montanum Coreopsis rosea Hydrocotyle umbellata Rhexia virginica
Holly Lightfoot 2009
Atlantic Coastal Plain Wildflowers

 

Students (past and present)

 

Publications

 

Examples of Recently Completed Studies

Effect of rising atmospheric carbon dioxide concentrations on time of flowering
A number of studies in North America, Europe and elsewhere have revealed that there have been consistent changes in flowering times in recent years, flowering being hastened in most species, but delayed in others, particularly those that flower late in the season. These changes have been widely interpreted as a consequence of global warming, but associated with global warming are changes in a range of other environmental variables such as carbon dioxide concentration that may also have effects upon phenology. Our laboratory has demonstrated that flowering is hastened by elevated carbon dioxide in long-day species and is either delayed or unaffected in short-day species. Further, using a realistic global change scenario we have shown that the direct effect of carbon dioxide on flowering phenology is at least as important as the effect of rising temperatures. This study sheds light on why observed changes in phenology are so variable among species allowing us to predict which species may or may not respond. 		Helianthus annuus

 

Interactions between carbon dioxide concentration and developmental pathways
We have explored the basis for the interaction between carbon dioxide and photoperiod on flowering using Arabidopsis mutants deficient in particular loci in the developmental pathway that senses photoperiod and induces flowering. Elevated carbon dioxide had an effect mediated by the photoreceptors, cryptochrome 2 and PHYTOCHROME B under short-days, and by the gigantea gene under long-days that increased the number of leaves required for bud formation, and an effect mediated by floWERING locus T in both long- and short-days that reduced the number of leaves required. Elevated carbon dioxide also affected flowering by increasing the rate of leaf production. It would appear that the effect of elevated carbon dioxide on time of flowering in Arabidopsis is actually the net result of a positive effect on growth rate, and both positive and negative effects on the developmental pathways that affect leaf number at flowering. These results explain why the effect of elevated carbon dioxide on flowering varies depending upon photoperiod and other environmental conditions.

Picea glauca H Selection for an enhanced growth response to elevated Carbon Dioxide
It has been demonstrated in a number of species that there is a great deal of variation among genotypes in the extent to which elevated carbon dioxide stimulates growth (i.e. significant genotype X carbon dioxide interactions).  This has led some researchers to suggest that there may be selection for an enhanced growth response as carbon dioxide concentrations continue to rise. Such selection could significantly alter current predictions regarding the impact of elevated carbon dioxide on plant growth and carbon sequestration.  However, the presence of a genotype X carbon dioxide interaction is a necessary, but not sufficient condition for the evolution for an enhanced growth response. In Picea glauca, we found that elevated carbon dioxide
resulted in anywhere from a 19 to 94% increase in growth.  We used the tools of quantitative genetics to demonstrate that despite this genotype X carbon dioxide interaction, there is unlikely to be selection for an enhanced growth response as the variance accounted for by the interaction was insignificant relative to the variation accounted for by genotype and the genetic correlation between performance at the two carbon dioxide levels was not significantly different from one. 

The impact of hydrological fluctuations on the Coastal Plain flora
The Atlantic Coastal Plain flora is a group of wetland species that includes a large proportion of Nova Scotia’s rare and endangered species, several of which are also nationally or globally endangered. Lakes with a large watershed area tend to have the highest density of Coastal Plain species due to their wide fluctuations in water level. These are also the lakes that are the most attractive for the construction of dams for generating hydroelectricity. Changes in the water fluctuation regime brought about by dam construction have had catastrophic consequences for the Coastal Plain flora in several instances. The reason for this decline is not entirely clear as a number of these lakes continue to exhibit wide fluctuations in water levels. Using a combination of field surveys, experimental transplants, and greenhouse studies, we have shown that time of flooding can be as critical as extent of flooding in determining plant success. For example, at least some of the species cannot survive temperatures below -4 °C; therefore, if the plants are not flooded before temperatures drop below this point, they cannot survive. Results will be useful in remediation of Coastal Plain habitat on managed lakes and in assessing the effect of climate change on these species.

Impact of bloom harvesting on the population dynamics of sea lavender
Sea lavender is a long-lived herbaceous perennial found in the salt marshes of eastern North America. Its blooms are harvested on a commercial basis by the floral industry. Anecdotal reports suggested that the level of harvest was increasing and that some populations of this species were in decline in Nova Scotia. We collected detailed demographic data on seeds, seedlings and adults in various size categories, and experimentally assessed the effect of bloom removal on subsequent survival and growth in the field over a five year period. These data were used to construct a stage-structured population growth model. The model was used to estimate population growth rates at various harvest levels and to estimate the maximum sustainable harvest		 Limonium carolinianum

 

 

Phytotron Phytoremediation
Phytotron at the KC Irving Center Experimental Garden Plots at KC Irving Center