COS 53-7
Back to the Future: Ancestral plants test assumptions in future growth trajectories

Wednesday, August 7, 2013: 10:10 AM
L100A, Minneapolis Convention Center
Rachel M. Gentile, Biological Sciences, University of Notre Dame, Notre Dame, IN
Marilia B.M. Figueiredo, Biological Sciences, University of Notre Dame, Notre Dame, IN
Jason S. McLachlan, Department of Biology, University of Notre Dame, Notre Dame, IN
Background/Question/Methods

Plant growth response to elevated [CO2] is difficult to predict because relationships between plant performance and atmospheric [CO2] are not static: ecosystem interactions, plant acclimation, and evolution also affect plant performance.  Ecosystem interactions and plant acclimation do alter plant performance under elevated [CO2], but the role of evolution in responses to rising [CO2] over a 100-year period is uncertain. We cannot fast-forward a century to investigate the trajectory of growth in elevated [CO2], but we can go “back in time” to measure plant response to rising [CO2] of the past and the present. Seeds from Schoenoplectus americanus, a dominant C3 salt marsh sedge of the Mid-Atlantic region, remain viable in sediments for up to 100 years. We germinated these old seeds and cloned out the plants, forming an “ancestral” population not adapted to current [CO2] levels, genetically and morphologically distinct from modern populations. To quantify the effect of genetic changes on plant growth predictions, we subjected the ancestral and a modern population to past (~290ppm) and current (~400ppm) [CO2] levels and measured growth throughout the two-month experiment.

Results/Conclusions

Results indicate that if the ancestral Schoenoplectus americanus population were used to predict the trajectory of growth in 400ppm [CO2] without accounting for genetic shifts in the population, the prediction would overestimate the stimulation of growth in the modern population by about 30%.  Ancestral plants had significantly more aboveground growth and stem density in 400ppm [CO2] than the modern population (p<0.05).  Modern plants also had reduced phenotypic plasticity in response to [CO2] compared to the ancestral plants, suggesting genetic accommodation as a mechanism for selection.  This study shows that genetic changes over a relatively short period (100 years) can significantly change the trajectory of growth as [CO2] continues to rise, which could alter how we think about projections for the future.