Hailey Jaynes

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As anthropogenic activity increases the concentration of atmospheric carbon dioxide ([CO2]) and global temperatures, Canada’s boreal tree species are at risk of reduced growth. The exchange of CO2 and water between plants and the atmosphere is important for plant growth, as well as climate regulation. Leaves are the site of these exchanges, and therefore any structural changes in leaves due to environmental factors will impact these fluxes. Currently, there is little information available on the combined effects of elevated temperature and [CO2] on leaf anatomy. This study examined changes in stomatal size and density, palisade layer length, overall leaf thickness, and length of spongy mesophyll exposed to intracellular air space in Betula papyrifera (white birch) under elevated temperature and [CO2] as compared to ambient conditions. Plasticity among stomatal traits was observed in response to both temperature and [CO2], with an overall increase in stomatal capacity at elevated temperatures to increase transpiration and facilitate evaporative cooling. Combined with reduced spongy mesophyll length, this suggests that there is a trade-off between leaf cooling and water retention via adjustment of internal and external leaf traits. Based on the results obtained in this study, temperature may be more a more important environmental factors in determining leaf anatomy than [CO2]. Warming reduced palisade length at ambient [CO2], but unexpectedly this effect disappeared with elevated [CO2]. This is likely due to decreased efficiency in CO2 uptake at ambient [CO2] exacerbated by decreased spongy mesophyll cell length at elevated temperatures. Alternatively, there may be other factors at play, such as tradeoffs in leaf number, size and thickness based on carbon availability and temperature.