The acclimation of carnivorous round-leaved sundew (Drosera rotundifolia L.) to solar radiation

Round-leaved sundew (Drosera rotundifolia L.) is a carnivorous plant which inhabits nutrient-poor, moist, and sun-exposed areas such as peat bogs and sandpits. These habitats are threatened by succession which could lead to substantial shading of sundews. Nevertheless, D. rotundifolia can also grow in shaded environment within a layer of dwarf shrubs, indicating great photosynthetic plasticity whose mechanism still remains largely unknown. Therefore, the aim of this experiment was to investigate physiological responses involved in D. rotundifolia acclimation to different light levels. Photosynthetic pigment content, photochemical efficiency, and content of phenolic compounds were studied in plants acclimated to sunlight conditions (outdoor-growing plants) as well as in those acclimated to low-light conditions (indoor-growing plants) before and after sudden exposure to high-intensity solar radiation for 5 h per day during 7-day period. Outdoor-growing plants were larger in size, had higher F-v/F-0 ratio, reddish leaves, and they flowered. Also, they had higher content of phenolic compounds including flavonoids and anthocyanins, as well as higher Car/Chl ratio, while indoor-growing plants showed higher chlorophyll a and b content. There was no significant difference in the photochemical efficiency of PSII between indoor- and outdoor-growing plants. The indoor-growing plants that were exposed to solar radiation showed initial photoinhibition of photosynthesis. However, after 7-day exposure, the chlorophyll content significantly decreased while contents of carotenoids, flavonoids, and anthocyanins, as well as Car/Chl ratio increased, leading to the restoration of PSII activity. In conclusion, our results revealed that sundews can successfully acclimate to both low- and high-light intensities by changing content and composition of the photosynthetic pigments and phenolic compounds.