Journal of Experimental Botany, Vol 50, 383-390, Copyright © 1999 by Oxford University Press
D Thomas, D Eamus and D Bell
There are two principal aims in this first manuscript, first, to compare
five methods for calculating the marginal unit water cost of plant carbon
gain (
ARTICLES
Optimization theory of stomatal behaviour I. A critical evaluation of five methods of calculation
School of Biological and Environmental Sciences, and School of Mathematical and Physical Sciences, Northern Territory University, Darwin, NT Australia, 9090; Corresponding author e-mail: dane.thomas@ntu.edu.au
E/
A) of leaves of two Australian tropical tree
species, and second, to test the hypothesis that
E/
A of
tropical tree leaves is constant when leaf-to-air vapour pressure
difference (D) varies. Few differences in the absolute values of
E/
A or the form of the response were found between
species. However differences did exist between methods of calculation.
Importantly,
E/
A was rarely constant with changing D.
Stomatal limitations of net photosynthesis caused by a reduction in
internal carbon dioxide concentration as stomatal conductance declined
caused
E/
A to increase when D was increased. Some methods
are applicable to canopy scale field measurements whilst others could only
be used in laboratory settings where sufficient control of the environment
is possible. The best method of calculation of
E/
A varied
according to the criteria used to judge best. However, overall, despite the
large numbers of independent data sets required, Method 1 was judged best
for calculating
E/
A for individual leaves as, although it
relies on the largest number of independently derived relationships, it has
the fewest assumptions. Methods 2 and 3 were applicable to the field when a
number of simplifying assumptions were made.Key words:
Stomatal optimization theory, marginal unit water cost.
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