Meeting Abstract

P2-7  Saturday, Jan. 5 15:30 – 17:30  Leaf-Level Carbon Dynamics of Trees with Various Phloem Loading Strategies in Elevated CO₂ Conditions PARK, MH*; GERSONY, JT; ROCKWELL, FE; HOLBROOK, NM; Harvard University; Harvard University; Harvard University; Harvard University mariapark@college.harvard.edu

Plants are integral to the functioning of the natural world. Vegetation accounts for a significant portion of global carbon fluxes into and out of the atmosphere, and the terrestrial carbon cycle’s existing equilibria could become skewed by climatic changes, such as temperature increases and drought. As atmospheric CO₂ levels rise, it is critical to expand and deepen our current comprehension of how trees will respond to this shifting environmental factor. To study the effects of elevated CO₂ on plant functioning, six tree species were selected based on their different strategies of loading sugars produced by photosynthesis into their phloem transport vasculature (phloem loading). We hypothesize that trees dependent on a sucrose concentration gradient to load sugars into the phloem (passive phloem loaders) will be less efficient in sugar export in conditions of higher atmospheric CO₂ concentrations. Over the course of 24 hours, rates of net photosynthesis were measured with the Li-Cor 6400, and leaf discs collected for their dry weight. These measurements allow calculation of net C balance and thus temporal patterns of sugar export into the phloem. The observation of relative rates of sugar export in this study will improve our understanding of how trees with different phloem loading types will respond to elevated atmospheric CO₂ concentrations.