super-optimal stomatal conductance

Bill Williams bwilliam at
Tue Nov 17 13:14:42 EST 1992

One reasonable place to look for supra-optimal conductance might be in
plants from very hot environments but with ready access to plenty of
water, which they might use for evaporative cooling.  I participated in
a study of Mimulus species several years ago that appeared to
demonstrate that conductance was NOT super-optimal in these plants
(which met the above requirements), but that conclusion was not as
strong as it might have been.  We did, however, demonstrate that the
stomata had normal sensitivity to relative humidity

At the most recent conference of American Society of Plant
Physiologists (ASPP), Eduardo Zeiger and his colleagues presented a
series of papers about some cotton plants they'd been looking at.  They
are bred for maximum productivity in very hot, well-irrigated locations
in Arizona, and he found that they had increased stomatal conductance
and decreased leaf size in relation to cotton plants not so bred. 
Stomatal conductance in these plants increased with increasing air
temperature and so their response to VPD was presumably inverted
(Eduardo hadn't done the gas-exchange experiments to verify this at the
time, but he undoubtedly has by now).  This may well be a case of
"supra-optimal" conductance, but of course the plants were specifically
bred for maximum production in rather unusual circumstances.
William E. Williams, bwilliam at
Divison of Natural Sciences and Mathematics
St. Mary's College of Maryland
St. Mary's City, MD 20686

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