Leaf Conductance in Relation to Rate of CO(2) Assimilation: II. Effects of Short-Term Exposures to Different Photon Flux Densities.

When photon flux density incident on attached leaves of Zea mays L. was varied from the equivalent of 0.12 of full sunlight to full sunlight, leaf conductance to CO(2) transfer, g, changed in proportion to the change in rate of CO(2), assimilation, A, with the result that intercellular partial pressure of CO(2) remained almost constant. The proportionality was the same as that previously found in g and A measured at one photon flux density in plants of Zea mays L. grown at different levels of mineral nutrition, light intensities, and ambient partial pressures of CO(2). In shade-grown Phaseolus vulgaris L. plants, A as photon flux density was increased from about 0.12 up to about 0.5 full sunlight, the proportionality being almost the same in plants grown at low and at high light intensity.When photon flux density incident on the adaxial and abaxial surfaces of the isolateral leaves of Eucalyptus pauciflora Sieb. ex Spreng was varied, g and A also varied proportionally. The leaf conductance in a particular surface was affected by the photon flux density at the opposite surface to a greater extent than was expected on the basis of transmittance. The results indicated that stomata may, in some way, be sensitive to the photon flux absorbed within the leaf as a whole.