PLANT PHYSIOLOGY , Vol 111, Issue 1 179-185, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Dynamics of Changing Intercellular CO2 Concentration (ci) during Drought and Determination of Minimum Functional ci
T. Brodribb
Department of Plant Science, University of Tasmania, P.O. Box 252C, Tasmania 7001, Australia
Nine conifer species with narrow (<5 mm), single-veined leaves were
selected for the purpose of examining changes in intercellular CO2
concentration (ci) during drought. Due to the leaf morphology of the study
plants, the confounding effects of nonhomogenous photosynthesis common to
most reticulate-veined angiosperms were largely avoided, giving a clear
picture of ci dynamics under increasing drought. A characteristic biphasic
response was observed in all species, with an initial stomatal control
phase resulting in a substantial reduction in ci as stomatal conductance
(gs) decreased. As gs reached low levels, a strong nonstomatal limitation
phase was observed, causing ci to increase as gs approached a minimum. This
nonstomatal phase was linked to a concomitant rapid decrease in the
fluorescence parameter quantum efficiency, indicating the onset of
nonreversible photoinhibition. The ratio of internal to atmospheric CO2
concentration (ci/ca) decreased from values of between 0.68 and 0.57 in
undroughted plants to a minimum, (ci/ca)min, which was well defined in each
species, ranging from 0.10 in Actinostrobus acuminatus to 0.36 in Acmopyle
pancheri. A high correlation was found to exist between (ci/ca)min and leaf
water potential measured at (ci/ca)min. Species developing high maximum
intrinsic water use efficiencies (low [ci/ca]min), such as A. acuminatus,
did so at lower leaf water potentials (-4.5 MPa) than more mesic species
(-1.75 MPa for A. pancheri). It is concluded that in the absence of patchy
stomatal closure, (ci/ca)min gives a good representation of the drought
tolerance of foliage.
