PLANT PHYSIOLOGY , Vol 105, Issue 3 1007-1013, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Dependence of the Extent and Direction of Average Stomatal Response in Zea mays L. and Phaseolus vulgaris L. on the Frequency of Fluctuations in Environmental Stimuli
Z. G. Cardon, J. A. Berry and I. E. Woodrow
Department of Biological Sciences, Stanford University, Stanford, California 94305 (Z.G.C.)
Stomatal responses to fluctuating light and CO2 were investigated in Zea
mays and Phaseolus vulgaris. Slow-moving stomata can affect carbon gain and
water loss by plants during light flecks, under dynamic cloud cover, during
alternating windy and calm air conditions (which influence CO2
concentrations and humidity immediately around leaves in plant canopies),
at natural CO2 vents, or in growth chambers with imperfect CO2 control. It
was found that the frequency of constant-amplitude fluctuations in light
and CO2 dramatically affected the time-averaged stomatal conductance in
both Zea and Phaseolus. During oscillations in light, average stomatal
conductance was driven either above or below that observed at steady state
at the average light level, depending on the frequency of the oscillations.
Under oscillating CO2, the departure of average stomatal conductance away
from that observed at steady state at the average CO2 level was also
frequency dependent in both species. Upon cessation of oscillations and
return of light or CO2 to the stable median level, stomatal conductance
also returned to a steady state, matching that before oscillations were
initiated. This work shows that fluctuations in light and CO2, and equally
important, their frequency, can be critical in determining time-averaged
stomatal conductance under unstable environmental conditions.
