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 μl-1) and ambient CO2 (379 μl-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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