Effect of CO 2 elevation and UV-A radiation on growth responses of Zinnia , Petunia , Coxcomb , and Marigold

In order to evaluate the effect of CO2 elevation and UV radiation on growth responses of zinnia, petunia, coxcomb, and marigold, a study was conducted in 2015 at Arsanjan Islamic Azad University, Iran. The experimental design was factorial arranged in completely randomized design with three replications. Treatments were included four ornamental species (zinnia, petunia, coxcomb, and marigold), CO2 concentration at two levels (350 and 700 ppm), and UV radiation at two levels (with and without UV radiation). Results showed that elevating of CO2 concentration from 350 ppm to 700 ppm increased morphological and physiological characters of C3 plants, especially marigold. Meanwhile, increasing CO2 concentration from 350 ppm to 700 ppm, decreased effects of UV damage on plants’ morphological and physiological characters. The highest leaf number, shoot dry mass, plant height and water use efficiency of C4 plant (coxcomb flower) were observed at 350 ppm of CO2 concentration without UV radiation while, the highest leaf number, shoot dry mass and leaf pigments of C3 plants (zinnia, petunia, and marigold flower) were obtained at 700 ppm of CO2 concentration without UV radiation. The results showed that the activity of catalase and peroxidase enzymes under UV radiation was increased in all of plants. Overall, it is concluded that, the recognition of plants resistant to UV radiation and high levels of CO2 concentration in the future may be better for environmental production and distribution as ornamental plants in town landscapes, where ecophysiological traits should be considered.


INTRODUCTION
Nowadays, unstable symptoms on the Earth such as environmental pollution and species extinction caused by increased emissions of greenhouse gases, in combination with changes in solar radiations intensity appeared to be unavoidable (Xing, 2009;Ziska and Blumenthal, 2010).Morphological traits and physiological processes of plants are affected by different climate change aspects such as CO 2 elevation, high temperature, ultra violet (UV) radiation, and quantity and dispersal of rainfall (Fuhrer, 2003).It is reported that climate changes has affected flowering initiation, physiology, water relations, ions absorption, photosynthesis and respiration of plants (Mortensen, 1987).
CO 2 plays an important role in process of global warming and climate changes (Holden and Hoyer, 2005).The level of CO 2 in the atmosphere is rising at an unprecedented rate, has increased from 280 ppm at the beginning of the industrial revolution to 380 ppm today, and is expected to double pre-industrial levels sometime during this century (Hennessy et al., 2008;Karl et al., 2009).Generally, CO 2 elevation could increase net photosynthesis of potted plants, cut flowers, and vegetables (Croonenborghs et al., 2009).Significant increase of water use efficiency (WUE) and decrease of stomatal conductance were observed in plants treated by CO 2 elevation (Lincoln and Couvet, 1989;Prior et al., 2011).Kamali et al. (2011) reported that CO 2 elevation from 380 to 1050 ppm could increase shoot and root dry mass, height, number of leaves and leaf area of coxcomb (Celosia argentea L.).Shoor et al. (2010) showed that increasing CO 2 level to 700 ppm could accelerate marigold (Tagetes patula L.) flowering time.
Plants, as sessile organisms that require sunlight for growth and development, are inevitably exposed to UV wavelengths (200-400 nm), which represent almost 7 % of the electromagnetic radiation emitted from the sun.Plants responses to ozone layer destruction and high UV radiation include widespread range of bio-chemical, physiological, morphological, and anatomical changes (Zhang et al., 2003).High doses of UV radiation may damage macromolecules, including DNA and proteins, and induce the production of reactive oxygen species (ROS), affecting photosynthetic pigments, cell membrane integrity and viability (Horii et al., 2007).Rahimzadeh et al. (2011) reported that UV-A radiation decreased shoot dry mass, protein, and chlorophyll content of savory (Satureja hortensis L.).Kazemi Ghale et al. (2011) showed that in radish plants treated with UV radiation photosynthesis rate decreases due to leaf area reduction, leaf thickness increases, and observes bio-chemical changes of chlorophyll pigments.Golbazhagh et al. ( 2010) reported the reduction of sunflower growth such as shoot dry mass, root length, and leaf area caused by increasing exposure time of different doses of UV-A radiation.Sarikhani (2013) showed that the UV-A radiation reduced peppermint yield.Also, antioxidant and secondary metabolite activity increased when peppermint was treated by UV-A radiation.
By considering the climatic changes the objective of this research was to determine the influence of CO 2 elevation and UV-A radiation on morphological and physiological properties of zinnia, petunia, coxcomb, and marigold .Study of climate changes effect on zinnia, petunia, coxcomb, and marigold production, quality, and marketable properties are very important because these plants are widespread ornamental species.

MATERIALS AND METHODS
In order to evaluate the effect of CO 2 elevation and UV-A radiation on morphological and physiological parameters of zinnia (Zinnia elegans Jacq.), petunia (Petunia x hybrida 'Grandiflorus'), coxcomb (Celosia cristata L.), and Mexican marigold (Tagetes erecta L.) a study was conducted in 2015 at Islamic Azad University, Arsanjan branch, Iran (53° 19' E, 29° 55' N and 1690 m).The Experimental design was factorial arranged in completely randomized design with three replications.Treatments included plant species (zinnia, petunia, coxcomb, and marigold), CO 2 concentration at two levels (ambient CO 2 (350 ppm) and elevated CO 2 (700 ppm)), and UV radiation at two levels (with and without UV-A radiation).
The experiment was conducted in two environmentally controlled growth chambers with four compartments to apply CO2 and UV-A treatments, with the mean air temperature of 25/14 °C (day/night) and relative humidity of 75 (day) and 60 % (night).At the beginning of the experiment, five seeds were planted in 5 cm deep of each of the 48 pots (18 cm height and 14 cm diameter) filled with a silty-loam soil with 1.16 % organic matter, 15 to 18 % sand, 50 to 56 % silt, 10 to 15 % clay and pH of 7.5.After seed germination, seedlings were thinned to one per pot at the four-leaf stage.Then, half of the pots were moved into the ambient CO 2 chamber and the other half, into the elevated CO 2 chamber.Pots were uniformly irrigated (EC = 0.78 ds m -1 of water) every 3 days.Half of the pots in the chambers was exposed by UV-A radiation (5 min per days) from fluorescent tubes (T9 Black light blue fluorescent-Schwan Company), used to produce UV-A radiation.They were installed at 50 height from each pot.
Measured traits were leaf number, shoot dry mass, plant height, water use efficiency, chlorophyll-a and carotenoid content, and activity of catalase and peroxidase enzymes.In order to the assessment leaf pigments content, 20 ml aceton (80 %) was mixed with 0.5 g of leaf fresh mass, then, the mixture was centrifuged (with 3000 rpm for 10 min).Then, leaf pigments were determined by spectrophotometer (UV2100 Plus model -USA) device (wavelength 470 and 663 nm) (Arnon, 1967).
In order to measure activity of catalase and peroxidase, 5 ml of potassium phosphate buffer (100 m mol and pH 7.5) was blend with 0.5 g of leaf fresh mass, then, the mixture was centrifuged (with 12000 rpm for 60 min).Afterwards, activity of catalase and peroxidase were determined using method described by Pereia et al. (2002) and Fielding and Hall (1978) , respectively.All data were submitted to an analysis of variance (ANOVA) and Duncan test was used to verify the significant differences among treatment means at the 5 % probability level (Little and Jackson, 1978).

RESULTS AND DISCUSSION
Effect of CO 2 and species interaction was significant on leaves' number, shoot dry mass, plant height, water use efficiency, chlorophyll a, activity of catalase and peroxidase (Table1).Results showed that the highest leaf number and shoot dry mass were observed in coxcomb flower + ambient CO 2 (Figure1 (a) and (b)).
The highest WUE was obtained in coxcomb flower + ambient CO 2 (Figure1 (d)) and the highest catalase activity was achieved in coxcomb flower + elevated CO 2 (Figure1 (g)).
Results showed that the highest plant height was observed in Zinnia + elevated CO 2 (Figure1 (c)) also, the highest chlorophyll a was achieved in marigold + ambient CO 2 (Figure1 (e)) while, the highest peroxidase activity were achieved in petunia + ambient CO 2 (Figure1 (h)).Generally, the highest leaf number and shoot dry mass were observed in coxcomb in comparison to the C 3 plants due to quickly establishment and better use of soil nutrients by coxcomb seedlings (Hammer et al., 2005;Wortman et al., 2011).Shoor et al. (2010) reported that elevating CO 2 concentration to 700 ppm could be increased marigold height (approximately 50 %) as a result improved plant photosynthesis capacity and allocated more assimilates to vegetative growth.It seems that elevating CO 2 concentration improved WUE due to high CO 2 concentration into inter-cellular space and transpiration reduction by stomatal closer (Fuhrer, 2003).Furthermore, increasing chlorophylla and carotenoid pigments by elevated CO 2 had significant role in photosynthesis rate and photosystem II protection for improving radiation absorption and increasing photosynthesis capacity (Mavrogianopoulos et al., 1999;Joseph et al., 2008).Miri and Rastegar (2012) showed that elevated CO 2 could increase chlorophyll index (approximately 6 to 30 %) in soybean, lambsquarters, panicum, and pigweed.
In addition, shoot dry mass, WUE, chlorophyll a, catalase and peroxidase activity were significantly influenced by UV-A radiation and species interaction (Table 1).According to results, morphological and physiological parameters showed a reduction as affected by UV-A radiation.The highest leaf number, shoot dry mass, and WUE, and chlorophyll a were observed in coxcomb and marigold , respectively, without UV-A radiation (Figure 2 (a), ( ).Meanwhile, the catalase activity in all plants increased by UV-A radiation (Figure 2 (g)).It seems that in plant subjected to UV-A radiation less transfer of photosynthetic assimilate occurred due to reduction of photosynthesis capacity (Balouchi et al., 2008).Reduction in growth and development and reduction of cell division also was observed by UV-A radiation (Smirnoff and Wheelev, 2000;Gao et al., 2003).But, plants response differently to UV-A radiation as affected by species and environmental factors such as plant water status, photosynthetically active radiation (PAR), and nutrients availability (Mark and Tevini, 1996;Balouchi et al., 2009).
In general, results showed that shoot dry mass, plant height, WUE, chlorophyll a and carotenoid pigments, and catalase activity were significantly influenced by CO 2 concentration, UV-A radiation, and plant species (Table 1).
The highest leaf number and shoot dry mass were obtained in coxcomb + ambient CO 2 + without UV-A radiation (Figure 3 (a) and (b)).Also, the highest WUE was observed in coxcomb + at elevated CO 2 + without UV-A radiation (Figure 3 (d)).Meanwhile, the highest plant height was achieved in Zinnia + elevated CO 2 + without UV-A radiation (Figure3 (c)).According to our research, results showed that UV-A radiation could decrease growth parameters of plant species due to its impact on photosynthesis capacity, but, elevating CO 2 could lead to improve photosynthesis capacity and high assimilate transfer to vegetative growth (Ziska and McClung, 2008;Croonenborghs et al., 2008;He et al., 2013).
Table 1: The summary of the source of variation and the mean square of shoot dry mass (g per plant), leaf number (per plant), water use efficiency (g l -1 ), chlorophyll a and carotenoid (mg g -1 ), catalase and peroxidase activity (u mol g  It seems that elevating CO 2 concentration could increase growth of C 3 plants (zinnia, petunia, and marigold) in comparison to the C 4 ones (coxcomb ) due to a better use of environmental sources for growth and development.However, UV-A radiation reduced plant growth parameters, but, increasing CO 2 concentration could reduce destructive effects of UV-A radiation on analysed plants species.It is concluded that, the highest growth parameters of zinnia, petunia, and marigold were achieved under elevated CO 2 without UV-A radiation, but, the highest growth parameters of coxcomb were obtained in ambient CO 2 without UV-A radiation.

Figure 1 :Figure 2 :Figure 3 :
Figure 1: The effect of flower species and CO 2 concentration interaction on leaf number (a), shoot dry mass (b), plant height (c), water use efficiency (d), chlorophyll a content (e), carotenoid content (f), catalase activity (g), and peroxidase activity (h).(According to standard error, the means with same overlap not significant) -1 min -1 )