Influences of elevated atmospheric CO₂ and water stress on photosynthesis and fluorescence of loblolly pine, red maple, and sweetgum
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Changes in light harvesting ability and other physiological responses could int1uence the competitive outcomes of tree species in a future elevated CO2 atmosphere. Photosynthetic light response curves were constructed with a closed photosynthesis system (LI-COR, Inc. Lincoln, NB) in order to investigate the effect of growth in elevated CO2 (746 Î¼l-1) and ambient CO2 (379 Î¼l-1) on light responses, and seedlings were allowed to dry out to examine physiological changes to water stress. While drying out, photosynthesis was measured with a closed system (LI-COR, Inc. Lincoln, NB) and fluorescence was measured with a portable fluorescence measurement system (P.K. Morgan Instruments, Inc Andover, MA). No species showed significant increases In quantum yields or decreases in light-compensation points as a result of elevated CO2. Photosynthesis declined in all species due to water but seedlings grown in elevated C02 maintained photosynthesis longer. Loblolly pine and red maple grown in e1evated CO2 showed signs of photosynthetic acclimation. Photochemical efficiency of PSII declined with water stress in loblolly pine. Red maple and sweetgum showed no relationship between photochemical efficiency of PSII and simulated drought. Growth in elevated C02 did not influence this response in loblolly pine, but sweetgum started with a lower photochemical efficiency or PSII which increased significantly.
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