The highest peak on Rila Mountain is Moussala (2925 m a. s. l.). Its climate conditions depend on the geographic location, peculiarities of relief, and atmospheric circulation, and a specific microclimate is formed. In alpine regions, conditions become extremely variable with the increase in altitude. Plants that are growing in alpine conditions are exposed to the combined impact of environmental factors such as altitude, prolonged UV irradiation, low temperature, etc. This study aims to compare and assess whether the pigment content of wild-growing species at Moussala peak changes in the two following years. As plant material was used following species: Saxifraga cymosa Waldst & Kit (Saxifragaceae), Anthemis carpatica Waldst. & Kit. ex Willd. (Asteraceae), Geum repens (Rosaceae), Doronicum columnae Ten.(Asteraceae), Achillea clusiana L. (Asteraceae), Allium sibiricum L. (Liliaceae) and Festuca valida (R.Uechtr.) Pénzes (Poaceae). Plants were collected from Moussala Peak in July-August, in two successive growing seasons of 2020 and 2021. Data for the average daily value of “Erythemal UV irradiance” response (UVE) for the experimental site at Rila Mountain (2925 m a. s. l.) were measured with a UV sensor. Average daily values for July and August are calculated. Photosynthetic pigment content was applied as an endpoint. It was obtained that genotype response varies depending on the environmental conditions of the studied year. Data for UV irradiation at Moussala peak for a period of two following years 2020-2021 show insignificant change. Radiation conditions at Moussala peak show that both years differed in UVE response, but this small change of UV irradiation for one year is probably insignificant. The levels of total chlorophylls, chl. a, chl. b and total carotenoids for most of the studied alpine plants measured for 2021 were insignificantly higher in comparison with those measured for 2020. Only for S. cymosa were evaluated significantly higher pigment levels in 2021 than those in 2020. The chlorophyll a/b ratio was stable for all studied wild species growing at this altitude. The chlorophyll a/b ratio also varies depending on the studied genotype and different radiation conditions of the years studied. Our preliminary data indicate a change in pigment content depending on the different environmental conditions in the respective years and alpine plants examined. Data for radiation conditions at Moussala peak show that both years differed in UVE response, but this small change of UV irradiation for one year is probably insignificant. Changes in pigment content in some of the studied alpine genotypes propose different adaptive strategies to overcome the environmental stress at this altitude. Because alpine conditions at Moussala peak are related to the various impacts of extreme environmental factors on the pigment content of plants, further studies are needed to understand the mechanisms of interaction of factors and plant response in the long-term aspect of time.

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Tsveta Angelova, Nikolai Tyutyundzhiev, Christo Angelov, Svetla Gateva, Gabriele Jovtchev, "Assessment of pigment content on wild growing plants in moussala peak", RAD Conf. Proc, vol. 6, 2022, pp. 1-7, http://doi.org/10.21175/RadProc.2022.01