Combined Effects of Carbon Dioxide, Sunfleck Duration, and Sunfleck Brightness on Photosynthetic Gas Exchange and Daily Carbon Assimilation by Aralia nudicaulis and Smilacina racemosa in the Forest Understory
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Walsh, Christina Kathleen
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Plants in the forest understory experience dynamic variation in both irradiance and naturally enriched CO2, but little is known about their interactive effects on photosynthesis, conductance, transpiration, and water use efficiency. Net carbon assimilation (A), stomatal conductance (g), transpiration (E), and water use efficiency (WUE) were measured for the herbaceous species Aralia nudicaulis and Smilacina racemosa to determine the individual and combined effects of elevated CO2 and sunfleck characteristics (brightness, duration, fluence) on photosynthetic gas exchange. Naturally-established plants were grown under simulated sunflecks in a greenhouse. Gas exchange was measured under steady-state conditions and in response to an array of sunflecks (0.5 to 8 minutes, 50 to 800 umol m-2 s-1) at both 400 and 500 ppm CO2. The results were combined with field PPF and CO2 data to estimate daily net A in a central MA forest under four scenarios: (normal versus enriched CO2) x (steady-state versus sunfleck responses). All four physiological variables increased significantly in Aralia in response to sunfleck duration, brightness, and fluence. For Smilacina, A and WUE increased significantly at elevated CO2, and A, g, E, and WUE all responded significantly to duration. The effect of brightness increased with duration for both species, especially for A and WUE. Estimated daily A varied from -0.00487 to 0.053983 mol m-2 day-1 between microsites, with substantial differences between the species. When averaged across the twelve microsites, there was no significant difference among the four methods. This work confirms the importance of quantifying species-specific responses to both sunflecks and enriched CO2 across heterogeneous understories.
Franklin and Marshall College Archives, Undergraduate Honors Thesis 2006
- F&M Theses Collection