[Effect of light of various spectral composition on kinetics of changes in a green leaf resistivity]

The kinetics of changes in the resistance of a green leaf by the action of exciting light was studied. It was shown that the illumination-induced changes in leaf conductance are mainly due to an elevation of temperature caused by the absorption of light energy. Based on the experimental results, the fraction of absorbed light energy converted into heat calculated under assumption that heating of the leaf across the thickness is uniform. It was found that the fraction of absorbed energy converted into heat does not depend on the intensity of radiation in the IR range and increases with decreasing intensity of photosynthetically active radiation. An explanation of the phenomenon is proposed, which is based on that in reality the heating of the leaf across the thickness is nonhomogeneous and this inhomogeneity of heating becomes more pronounced upon photoinduced changes in absorption resulting from a decrease in photosynthetically active radiation. It was shown that nonphotochemical fluorescence quenching does not substantially affect the leaf conductance at intensities of photosynthetically active radiation not higher than 200 Wt/m2.