Can elevated CO2 and ozone shift the genetic composition of aspen (Populus tremuloides) stands?

Background/Question/Methods

The world’s forests are currently exposed to increasing concentrations of CO₂ and ozone.  Both pollutants can potentially exert a selective effect on plant populations.  This in turn may lead to changes in ecosystem properties such as carbon sequestration.  Here we report how elevated CO₂ and ozone affect the genetic composition of a woody plant population via altered survival.  Using data from the Aspen FACE experiment (in which aspen clones were grown in factorial combinations of CO₂ and O₃), we develop a hierarchical Bayesian model of survival.  We also examine how survival differences between clones could affect pollutant responses in the next generation given a range of assumptions about the heritability of pollutant responses and the distribution of reproductive success. 

Results/Conclusions

Our model predicts that the relative abundance of the tested clones, given equal initial abundance, would shift under either elevated CO₂ or O₃ due to changing survival rates.  Survival was strongly affected by growth responses, which differed significantly between clones.  Selection could noticeably decrease O₃ sensitivity in the next generation, leading to a less negative average growth response, depending on the heritability of growth responses and the distribution of seed production. The response to selection by CO₂, however, is likely to be small regardless of heritability.  Our results suggest that changing atmospheric composition could shift the genotypic composition and average pollutant responses of tree populations over moderate timescales in ways that may affect carbon sequestration.