Light regimen-induced variability of photosynthetic pigments and UV-B absorbing compounds in Luzula sylvatica from Arcto-Alpine tundra

The aim of this study was to evaluate the effects of different in situ light regimen on ecophysiological parameters of Luzula sylvatica leaves. Plants of L. sylvatica grown under natural sunny and shade conditions in arcto-alpine tundra were analyzed with respect to their leaf anatomy, content of photosynthetic pigments, UV absorbing compounds and phenanthrenoid compounds. Relationship between chlorophyll concentrations (Chl a+b ) and SPAD values was determined for sun and shade leaves measured repeatedly within summer and autumn seasons 2019 and 2020. Pooled data showed curvilinear Chl a+b to SPAD relationship with the highest Chl a+b and SPAD values found for shade leaves. Sun leaves had higher UV-B absorbing compounds contents than shade ones. The HPLC-DAD analysis revealed significant amount of soluble flavonoids in Luzula sylvatica leaves, amongst others the flavone-luteolin and its derivatives ( e.g. tentatively identified luteolin-methyl-glucoside and luteolin-glucoside). The accumulation of luteolin based compounds in sun acclimated leaves is also plausible explanation for the higher antioxidant activity determined in sun leaf extraxts. Such response of flavonoid metabolism may help L.S. to cope with excessive-light stress through UV-attenuation mechanism and ROS scavanging. Additionally, phenanthrenoid compounds contents in L. sylvatica leaves were determined. Altogether, 9 phenanthrenoid compounds were identified by HPLC-HRMS. Their content was markedly different (up to the factor of 5) between sun and shade leaves of L.sylvatica .