Seasonal dynamics of the content of photosynthetic pigments in the leaves of ornamental forms of Berberis thunbergii DC. in the conditions of arid Steppe of Ukraine

Abstract

Aims. Analysis of the seasonal dynamics of the content and ratio of photosynthetic pigments in the leaves of the varicolored decorative forms of Japanese barberry (Berberis thunbergii DC.) in the conditions of the arid Steppe of Ukraine. Methods. The object of research was Berberis thunbergii and its decorative forms with different leaf colors ('Red Rocket', 'Superba', 'Bagatelle', 'Golden Ring', 'Harleguin', 'Pow Wow', 'Bananza Gold', 'Aurea '), growing in the collection of the botanical garden of Kherson State University. The content of chlorophyll a and b and the amounts of carotenoids were studied in the leaves of one- and two-year-old shoots, which were collected for analysis monthly, starting from May to October 2017–21. Standard methods were used to determine the pigment amount (Wellburn, 1994). Measurements were carried out using an SF-2000 spectrophotometer at wavelengths of 665 and 649 µm for chlorophylls a and b and 480 µm for carotenoids. Statistical analyses were carried out in MS Excel 2007. Results. During May–October, the seasonal dynamics of the content of photosynthetic pigments in the leaves of decorative forms of B. thunbergii were investigated. In green- and purple-leaved forms, the maximum amount of chlorophyll and carotenoids occurred in the first half of the growing season, and in yellow-leaved forms—in the autumn months. Purple- and yellow-leaved forms in almost all observation periods were in most cases inferior to green-leaved forms in terms of chlorophyll content. From the middle of summer, a decrease in the amount of chlorophyll b in purple- and green-leaf forms begins. The contents of chlorophyll and carotenoids in the leaves of two-year-old shoots in most variants of the experiment were significantly higher than in one-year-old leaves. The maximum values of the ratio of chlorophyll a/b, and chlorophyll/carotenoids were established in most forms in the middle of the growing season. Lack of moisture in the soil and air, and high temperatures lead to a decrease in the content of chlorophyll, and carotenoids in the middle of the growing season. This can be seen as the effects of prolonged drought. Conclusions. The established peculiarities of the seasonal dynamics of photosynthetic pigments in the leaves of colorful decorative forms of B. thunbergii indicate that their pigment apparatus is form-specifically adapted to the arid conditions of the Steppe with excessively high positive temperatures. Since chlorophyll is associated with light-harvesting complexes, its content decreases within the leaves of plants in extreme drought conditions, which can lead to a decrease in photosynthetic CO₂ fixation and inhibition of plant growth.