Poster: Global change

Abs # 24: Physiological and growth responses of temperate forest tree saplings to altered carbon environments.

Presenter:	McGrath, Justin M, jmcgrat4@bradley.edu
Authors	McGrath, Justin M (A)   Mellor, Nathan J (A)   Morris, Sherri J (A)   McConnaughay, Kelly D (A)
Affiliations:	(A): Bradley University

Atmospheric CO₂ concentrations are increasing from current concentrations of 360 ppm to 800 ppm by the end of the century. Increases in CO₂ concentration can increase photosynthesis (A) through increased rates of carboxylation and decreases in photorespiration. There is typically a down regulation of one or more photosynthetic processes that limits increases in A. We examined the physiological responses of maple and sycamore saplings to current and elevated CO₂. Plants were grown in growth chambers on a regulated day-night cycle. We measured photosynthetic light and internal carbon dioxide response curves, chlorophyll content, specific leaf area, height-diameter relationships, and above-ground biomass after five months of growth. Sycamores had significantly higher in situ A than maples. There was a significant decrease in maximum rates of electron transport (J_max) and carboxylation (V_c,max), and a significant increase in light-acclimated respiration (R_d) in elevated CO₂. Although not significant, the inflection point between J_max- and V_c,max-limited A decreased in maples grown in elevated CO₂. These responses are typical of down-regulation in plants grown in elevated CO₂. Sycamores in elevated CO₂ also showed a decrease in chlorophyll content and had smaller height/diameter ratios than those grown in current CO₂. These changes in height-diameter relationships indicate that more mass is being allocated to support than height. Biomass was also greater in plants grown in elevated CO₂. Understanding controls on carbon gain and partitioning informs prediction regarding plant, and ultimately ecosystem, carbon storage. In light of increases in global CO₂ concentrations, this information would be useful in developing land-management techniques that increase carbon storage.