Beskydy 2016, 9, 31-40
Photosynthetic response of mountain grassland species to drought stress is affected by UV-induced accumulation of epidermal flavonols
Interactive effects of drought and ultraviolet (UV) radiation on CO2 assimilation rate and accumulation of epidermal flavonols were studied in two herbs (Hypericum maculatum and Rumex obtusifolius) and two grasses (Agrostis capillaris and Holcus mollis) under field conditions of Beskydy Mts. The main objective of this study was to evaluate a protective role of epidermal flavonols against drought stress. Experimental shelters were used to manipulate amount of incident precipitation and UV radiation intensity for 12 weeks (May–July). The light-saturated CO2 assimilation rate (Amax) and the content of epidermal flavonols were regularly measured at intervals of 2–3 weeks during the entire period. Drought-induced reduction of Amax was enhanced by high UV intensity in R. obtusifolius, whereas in other species UV radiation reduced a negative effect of drought. Generally, drought increased flavonol content in leaves as compared to non-stressed plants. Similarly, high UV intensities increased the flavonol content in control plants, but not in drought-stressed ones. Regression analysis between the flavonol content and Amax revealed a positive correlation especially for A. capillaris and R. obtusifolius. In both species, a separation of these relationships was observed as the result of water availability. Thus lower Amax were observed at the same flavonol content in drought-stressed plants when compared to control, well-watered counterparts. We conclude that UV-induced accumulation of epidermal flavonols can alleviate negative impacts of summer drought on photosynthesis, particularly in species with slower ontogeny like H. maculatum and A. capillaris.
Keywords
Agrostis capillaris, CO2 assimilation, drought stress, flavonols, grassland, Holcus mollis, Hypericum maculatum, precipitation, Rumex obtusifolius, UV radiation.
Funding
This work was supported by the Ministry of Education, Youth and Sports of CR within the National Sustainability Program I (NPU I), grant number LO1415.
