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.


Introduction
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 (F v /F m ) as a screening indicator of plant response to a particular stress factor.F v /F m represents effectiveness of light utilization under the standard conditions of CO 2 fixation and the quantum yield of photochemical processes (Björkman and Demming 1987).Reactions of F v /F m 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 (Φ PSII ) is a real yield of active PSII reaction centres in the processing of absorbed light energy.Φ PSII represents the light used in photochemistry (Genty et al., 1989;Schreiber, 2004).The impact of water stress caused a decrease of Φ PSII in woody plants (Peguero-Pina et al., 2008, Gallé et al., 2007).
Fluorescence decrease ratio (R FD ) 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 R FD values was observed by Pukacki and Kamińska-Rożek (2005).

IN URBAN AREAS AND LANDSCAPE
The stomatal conductance (g s ) of the leaves was used to monitor the reactions of stomata through water deficit impact.It is a very important defence mechanism against a loss of water (Tardieu andDavis, 1993, in Živčák, 2006).The impact of water deficit results in the closure of stomata and the decrease in photosynthesis.Lower values of stomatal conductance also represent adaptation of plants in extreme conditions (Živčák, 2006).
One of the crucial factors for plant growth is the accessibility of water in the soil.Plants have more adaptive mechanisms that help them to tolerate adverse environmental conditions.There has been quite a lot of research about the drought response of crops but also more testing of drought tolerant ornamental plant species is needed in the field of landscape architecture.The impact of water scarcity to ornamental and useful woody plant Cornus mas L. was tested.The aim of the evaluation was to investigate if there were any differences in the mean values of chlorophyll fluorescence parameters and stomatal conductance of the leaves on the plants in variants during the experiment with different levels of soil water supply.

Material and Methods
Within a pot experiment, physiological responses of plants in relation to water scarcity were monitored.The non-destructive methods of monitoring the impact of a lack of water in the soil to plants, measurement of leaf stomatal conductance and modulated chlorophyll fluorescence were chosen.
The one-year old seedlings (in the year 2013) of Cornus mas L. come from generative propagation.The two variants with different soil water supply in the 3 litre size pots were established.A half of plants were exposed to 30% of the soil water supply (a variant with reduced water content in the soil -a stress variant) and another part of the plants were further hydrated in 60% of the soil water supply (a control variant).The plants were cultivated into the substrate based on the white peat, enriched with the clay (20 kg/m 3 ), pH 5.5-6.5, with NPK fertilizer 14 : 10 : 18 (Klasmann TS3, Klasmann-Deilmann GmbH, Germany), under the polypropylene cover with 40% of shading.The experimental plants were grown in the differentiated water regime from June to September, for the total period of 151 days in the year 2013 and 154 days in the year 2014.Ten plants in the control variant and ten plants in the stress variant were used for the measurement.Chlorophyll fluorescence was measured on two leaves of each plant by the chlorophyll fluorometer Hansatech FMS 1 (Hansatech Instruments Ltd, United Kingdom) in the morning hours.The software Modfluor for the data analysis was used and 21 days period of measurements was set in the two years.The following characteristics of measurement protocol of the chlorophyll fluorescence were used: one second light pulses of red light with an intensity of 895 μmol/m 2 /s 1 , the intensity of actinic light 34 μmol/m 2 /s 1 and the saturation light pulse 10 000 μmol/m 2 /s 1 .These parameters were measured and also used for the statistical analysis: F v /F m , Φ PSII and R FD .
When measuring the leaf stomatal conductance, the Delta T leaf porometer AP4 (Delta-T Devices Ltd, United Kingdom) was used.The measurement of a loss of water vapour through the stomata took place before midday (best conditions for measurement were between 8:00-10:00 am because of stomata closure at the midday because of higher temperature and light intensity) on two leaves per plant.The leaf stomatal conductance was determined in mm/s 1 , together with the recording the current time, light intensity in μmol/ m 2 /s 1 and the current temperature in degrees Celsius.
For the mathematical and statistical analysis of the data, the one-way Anova and Kruskal-Wallis Test, P <0.05 were used.The statistical assessment of the data was conducted using the software Statgraphics Centurion XVII (StatPoint Technologies, USA, XV, licence number: 7805000000722).The differences in the monitored parameters in the woody plant Cornus mas L. with reference to different water content in the soil were tested.

Results and Discussion
F v /F m measurements results are presented by nonsignificant differences between two variants with different water supply in the soil.The mean value of F v /F m after 21 days of experiment duration time in the year 2013 was in the stress variant 0.77 and in the control variant 0.80.In the year 2014 after 84 days of treatment the mean value was 0.81 (stress variant) and 0.83 (control variant), (Table 1).It can be possible that 30% of water supply for Cornus mas L. was not the critical level of water stress.Cornic and Massacci (1996) define that metabolism processes are not affected in the moderate water stress and also the short period of water deficit does not affect the F v /F m (Papageorgiou and Govindjee, 2004).These findings confirm the results of other authors (Bjorkman and Deming 1987;Johnson et al., 1993, Kalaji et al., 2012) that values around 0.83 are optimal for the most of the plant species in non-stressed conditions.Also Roháček  (2002) states the value 0.832 ±0.004 as the constant value which is reached by a lot of different plant species under non-stressed conditions.The results in the woody plants Spiraea japonica L. ´Little Princess´ and Cornus stolonifera Michx.´Kelseyi´ (Šajbidorová, 2013) as well as in Pyrus pyraster L. and Sorbus domestica L. (Šajbidorová et al., 2015) confirm that this parameter is non-sensitive to water deficit.
On the other hand F v /F m and Φ PSII are considered by Maxwell and Johnson (2000) as sensitive indicators of plants to stress environmental conditions.Both parameters characterize the function of PSII that significantly reacts to any environmental impact (Swiatek et al., 2001).The values in plants in stressed conditions are rapidly declining, so the parameter is considered as an indicator of photoinhibition or other damage of PSII (Roháček, 2002).Water deficit decreased the F v /F m values in Acer rubrum L. and Acer × freemanii E. Murray (Bauerle and Dudley, 2003) and also in Fagus sylvatica L. (Gallé and Feller, 2007).Percival and Sheriffs (2002) identified drought tolerant, intermediate, sensitive and very sensitive woody plants based on the F v /F m measurement after dehydration.Φ PSII seems to be the significant parameter of the condition of drought stress in a model plant.Φ PSII is the real yield of active PSII reaction centres in the processing of absorbed light energy and reflects the actual state of the photosynthetic apparatus (Genty et al., 1989;Schreiber, 2004).
The values of Φ PSII of the stress variant were significantly lower in comparison to the control variant (Table 1).In the year 2013, a significant decrease (46%) in the values of Φ PSII in the control variant (0.13) in comparison to the stress variant (0.06) after 41 days of lower water supply in the soil was observed.In the year 2014, a reduction in the values of Φ PSII was more remarkable, a 72% decrease between the variants (the control variant 0.11 and the stress variant 0.08) after longer duration of the differentiated irrigation regime (for 84 days).The similar decline of Φ PSII was observed in Spiraea japonica L. ‚Little Princess´ and Cornus stolonifera Michx.´Kelseyi´ (Šajbidorová 2013).Gallé et al. (2007) found a decrease in the values of Φ PSII in the condition of water deficit in Quercus pubescens Willd., as well as Peguero-Pina et al. (2008) in Quercus coccifera L. Hillová (2016) considered that the measurement of Φ PSII is a fast and affordable method for sorting of herbaceous perennials into five main groups which not fully correspond with the traditional use of perennials sorting according to Hansen and Stahl (1993).
Within two years, the values of fluorescence decrease ratio (R FD ) were significantly lower in the stress variant for most of the period (Table 1).In the year 2013, after 41 days of a lower level of water supply the decrease (62%) from 1.42 in the control variant in comparison to 0.88 in  When assessing stomatal conductance in the year 2013, lower values in the stress variant after 41 days of a differentiated water regime were observed.In the year 2014, there were lower values in the stress variant for most of the period.A bigger difference was recorded between the two variants after a 42 days period (a decrease by 73%).At the end of the period, after 84 days, the decrease in the values was much lower (35%) (Table 1).The same results emphasize Hillová et al. (2016) on herbaceous perennials when drought stress led to a considerable decline in stomatal conductance.Galmés et al. (2007) observed a decline in stomatal conductance in ten Mediterranean species when water stress intensified.Zweifel et al. (2009) said that stomatal regulation is species-specific.Closed stomata reduce transpiration and also photosynthesis and total tree metabolism (Larcher, 2003).

Conclusion
Reliable information about drought tolerant ornamental woody plants and herbs in the field of landscape architecture is needed, with regards to global warming and specific environmental conditions in urban areas.Analysing plants' reactions to extreme environmental conditions by research is more effective in case of crops rather than ornamental plants.Testing of drought resistance could be also useful when selecting ornamental plants because of the need for low maintenance of public green spaces in urban areas.
Šajbidorová, V. -Lichtnerová, H. | Water Deficit Impact on Selected Physiological Parameters... Plants in Urban areas and landscaPe | 2018 | pp.64-68 PLANTS IN URBAN AREAS AND LANDSCAPE the stress variant was recorded.In the year 2014, after 84 days of lower water supply a significant decrease the values between the two different variants (stress = 0.83 and control = 1.42) was measured, which accounts for the decrease of 58%.Pukacki and Modrzyński (1998) considered the values of R FD ≥2.3 for plants in optimal conditions and the impact of stress factors may result in a decrease in values.Pukacki and Kamińska-Rożek (2005) evaluated the impact of drought in the soil on the plants of Picea abies L. After 42 days of water deficit there was observed a decrease in the values Rfd and F v / F m by 44% compared to control plants.
resistance of woody plants and herbs to drought has become the subject of various experiments.The paper presents the study of impact of the water scarcity on chlorophyll fluorescence and stomatal conductance of the woody plants Cornus mas L. The experiment was carried out on plants in two different water regimes (a control variant was maintained with soil water supply on 60% and a stress variant with soil water supply on 30%).Chlorophyll fluorescence was carried out by chlorophyll fluorometer in a 21 days´ period in two growing seasons of 2013 and 2014.The following chlorophyll fluorescence parameters were recorded: maximum quantum efficiency of PSII (F v / F m ), effective quantum yield of PSII (Φ PSII ) and chlorophyll fluorescence decrease ratio (R FD ).Stomatal conductance (g s ) was carried out by leaf porometer in 21 days period in two growing season, 2013 and 2014.By the results the water deficit represented by soil water supply on 30% does not affect the values of F v /F m .The values of Φ PSII and Rfd were significantly affected due to water deficit in the soil in a model plant.Limiting of the irrigation on model plants resulted in the reduction in the stomatal conductance (g s ). Studying

Table 1
The mean values of the analysed parameters and 95% LSD test for the studied taxa Cornus mas L. and for the two variants of the soil water supply (control/stress) in the year 2013.Values with the same letter are not significantly different

Table 2
The mean values of the analysed parameters and 95% LSD test for the studied taxa Cornus mas L. and for the two variants of the soil water supply (control/stress) in the year 2014.Values with the same letter are not significantly different Šajbidorová, V. -Lichtnerová, H. | Water Deficit Impact on Selected Physiological Parameters... Plants in Urban areas and landscaPe | 2018 | pp.64-68 IN URBAN AREAS AND LANDSCAPE