Physiological and genetic responses of sugar maple (Acer saccharum) and aspen (Populus tremuloides) to long-term, interacting exposures of elevated carbon dioxide and ozone

Anthropogenic activities and land use change after pre-industrialization has led to increase in greenhouse gases in the atmosphere. In our study we focused on long-term interacting effects of two major greenhouse gases carbon dioxide (CO₂) and ozone (O₃) on northern hardwood species, aspen and maple. Aspen is a pioneer species and sugar maple is late-successional shade-tolerant species. In a long-term physiological study, we documented the variable physiological response of both the species when exposed to elevated CO₂ and O₃. Higher rates of photosynthesis were seen in aspen compared to maple with elevated CO₂. In aspen, these effects were offset when exposed to combined gases, however a similar response was not observed in maple. The physiology of sun and shade maple seedlings growing under variable light environment did not vary significantly. Aspen growing under elevated CO₂ retained canopy for a longer period of time with early bud break and delayed senescence than when exposed to elevated O₃. Extension of the growing season under elevated CO₂ was validated by another independent canopy study, using litter traps. Molecular studies were performed using high density arrays to seek explanation for physiological response in aspen under elevated CO₂ and O₃, aspen growing under elevated CO₂, had higher expression of genes related to photosynthesis whereas reduced transcripts under elevated O₃. In the case of O₃ higher transcripts of defense related genes was observed.