Water Deficit Impact on Selected Physiological Parameters of the Woody Plant Cornus mas L.

The urban environment is a natural habitat for plants. Only some species are able to survive in these extreme conditions (drought, salinity, high temperature, etc.). The plants were selected with focus on species with adequate properties. Nowadays, the plants with ornamental and useful character are becoming extremely popular, especially fruit species that can be grown also in unfavourable environmental conditions (Hričovský and Vargová, 2007). For these reasons, Cornus mas L. was set as a model plant. Cornus mas L. belongs to useful – ornamental shrubs that bear tasty fruits. It is used in ornamental horticulture thanks to its early flowering. The fruits of Cornus mas L. can be universally used both in a fresh and processed state as well as in the medicine. Evaluation of the reaction of plants to the physiological level, especially on the status of photosynthesis was chosen. The simple method of measurement of the photosystem II, which could be affected by stress factors, is the use of chlorophyll fluorescence techniques. Chlorophyll fluorescence technique has become popular among breeders, biotechnologists, plant physiologists, farmers, gardeners, foresters, ecophysiologists and environmentalists (Kalaji et al., 2016). The chlorophyll fluorescence signal is very rich in its content and very sensitive to changes in photosynthesis (Kalaji et al., 2014). Björkman and Demming (1987) consider the maximum quantum efficiency of PSII (Fv/Fm) as a screening indicator of plant response to a particular stress factor. Fv/Fm represents effectiveness of light utilization under the standard conditions of CO2 fixation and the quantum yield of photochemical processes (Björkman and Demming 1987). Reactions of Fv/Fm to drought by woody plants were recorded by Bauerle and Dudley (2003), Gallé and Feller (2007), Percival and Sheriffs (2002). The effective quantum yield of PSII (ΦPSII) is a real yield of active PSII reaction centres in the processing of absorbed light energy. ΦPSII represents the light used in photochemistry (Genty et al., 1989; Schreiber, 2004). The impact of water stress caused a decrease of ΦPSII in woody plants (Peguero-Pina et al., 2008, Gallé et al., 2007). Fluorescence decrease ratio (RFD) is considered to be the vitality index of the photosynthetic apparatus (Lichtenthaler and Babani 2000). Lower values are typical for plants in suboptimal conditions and the higher ones represent a higher photosynthetic activity and also adaptability of woody plants (Lichtenthaler et al., 2005). The decrease of RFD values was observed by Pukacki and Kamińska-Rożek (2005). WATER DEFICIT IMPACT ON SELECTED PHYSIOLOGICAL PARAMETERS OF THE WOODY PLANT CORNUS MAS L.