Corylus avellana bark optical properties differ during and out of the vegetation season

Abstract

We compared different bark traits of the common hazel (Corylus avellana L.) in four different months during the vegetation season (September, November) and out of the vegetation season (January, February) to get an insight into the changes in bark morphological, biochemical, and optical properties. Since bark of woody plants contains a layer of chlorenchyma, which can harvest transmitted light and perform photosynthesis, we also measured bark potential photochemical efficiency of photosystem II. The values of the latter parameter decreased during the research period, ranging from 0.77 in September to 0.22 in February. This could be attributed to low temperatures. The shapes of the bark reflectance curves were similar between the four samplings, with a peak in red and pronounced reflectance in the near-infrared spectrum. However, the level of reflectance differed between the four samplings. Regarding the time of the season, we obtained the most pronounced changes in the green, yellow, and red reflectance spectra. Light reflectance in these regions was positively related with chlorophyll b and carotenoid contents, while it was negatively related with anthocyanins and UV-B–absorbing substances. Transmittance spectra showed less variability between the four samplings. Regarding the studied pigments, the most pronounced changes were obtained for anthocyanin and UV-B–absorbing substances contents, which decreased in accordance with decreasing environmental temperatures. On the contrary, the level of photosynthetic pigments remained high, thus enabling undisturbed primary metabolism.