Optical technologies are very useful for monitoring plant vitality and the effects of stress conditions on plant photosynthetic capabilities. We reviewed articles and publications that report on the optical properties of leaves and bark of different plant species, radiation conditions and stress effects on the plant. In the experimental part, we performed four sets of measurements of the optical properties of the hazel bark and, in the first two sets, also on the leaves during leafing. We were interested in how the optical properties change during leafing and when the plant sheds its leaves. In addition to measurements of optical properties, we also performed biochemical research to determine the amount of chlorophyll, carotenoids, anthocyanins and UV-absorbing substances. We also used a microscope to measure certain anatomical parameters of the bark. Finally, we statistically processed the results to determine if there are associations between the optical, biochemical, and structural properties we measured on our hazel samples. We found that there were statistically significant differences between the sets of bark reflectance measurements, but there were none between transmittance. The reflectance graphs of the bark and leaves differ from each other, especially in second set of measurements. Certain structural and biochemical properties thus influenced the reflectance and transmittance spectra of the bark. The decrease in air temperature caused a decrease in potential photochemical efficiency.
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