We studied the optical properties of common reed leaves (Phragmites australis), the influence of anatomical and biochemical characteristics on light reflectance and transmittance and the differences in characteristics between the leaves of different age. We also determined the content of phytoliths in leaves and their influence on reflectance and transmittance. Plants were collected in reed stands at Lake Cerknica. We have measured the concentration of chlorophyll a and b, carotenoids, anthocyanins and UV-absorbing compounds, the structural properties of the leaves, and their optical properties in the range of 280 to 880 nm. The leaves differed the most in the thickness of the cuticle and mesophyll and the number of stomata. Biochemical parameters differ the most in old leaves, sampled in July. The content of phytoliths in old and young leaves was very similar. The leaves differed the most in June and July. Curves of reflectance and transmittance spectra have similar shape irrespective of the age of the leaves. We measured relatively low reflectance and transmittance in the ultraviolet and visible part of the spectrum and a relatively high reflectance and transmittance in the NIR range. The RDA analysis revealed that the reflectance spectra are the most affected by the content of carotenoids, chlorophyll a, the length of prickle hairs, the length of the stomata and the thickness of the mesophyll, while the transmittance spectra are affected by the number of stomata in the upper epidermis and the thickness of the upper epidermis. The most pronounced difference between the June and July leaves is evident in the NIR region, as leaves sampled in June had significantly lower reflectance.
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