Investigation of Growth Indices and Gas Exchanges in Two Cultivars of Sweet William (Dianthus barbatus) under Salinity Stress

 Salinity stress impairs the absorption of elements such as potassium, leads to decrease in water and minerals, or due to an increase in Na+ effects the absorption of other elements. Salinity of water and soil is one of the obstacles to the expansion of agriculture in most part of the world. Salinity causes several physiological and morphological changes in plants and affects growth and photosynthesis. Salinity stress also affects the absorption of nutrients, and finally the plants sensitivity to stress increases. High concentrations of Nacl in rhizosphere reduce the water potential and cause physiological drought stress. In addition, salinity stress can cause ion toxicity and imbalance, which can damage the plant. Salinity stress has been shown to reduce plant biomass by decreasing photosynthetic capacity and chlorophyll content. As stress increases, stomatal conductance and CO2 assimilation decrease, which both negatively impact photosynthesis and lead to a decrease in plant growth. Dianthus is an annual or perennial plant that produces velvety flowers in various colors. Due to its resistance to cold and wide range of colors, it is commonly used in landscaping. However, limited research has been conducted on the response of Dianthus to environmental stress, making it important to investigate its behavior under such conditions.

 This research was conducted at greenhouse of municipality of Khomein, Iran. The statistical design was used in the factorial experiment based on CRD. Experimental factors included salinity stress (0, 10, 20, 30, 40, 50, 60, 70, 80, 90 mM) and cultivars (Barbarin and Diana). After preparing the seeds, it is first disinfected using sodium hypochlorite and then planted in plastic pots containing soil, sand and manure. At the end of the experiment, morphological traits, stomatal conductance, photosynthesis rate, Na+, K+ and Na+/K+ was also examined. Gas exchanges were measured using an exchange measuring device (LCA4, ADC Bioscientific,Ltd., Hoddesdon, England). At the time of measuring gas exchanges, the temperature under chamber was 26-29 C and relative humidity was 58-62%. (stomatal conductivity is based on mmol/m2/s and photosynthesis in µmol/m2/s). To measure the concentration of Na+ and K+, the leaf first turned to ash (at 550 C). Then 5 ml of hydrochlorid was added to dissolve the sample and the volume of the filtered solution was reduced to 50 ml with distilled water and the concentration of Na+ and K+ was measured with flame meter. In order to measure the fresh weight of leaves and roots, plant components were separated. Fresh weight was recorded with a scale and then samples were placed in the oven (for 48 h) and weighted again to measure dry weight. Leaf area was measured with a leaf guuge device (A30325) and plant height and root length using a ruler. Statistical analysis of data was performed using Mini Tab and Excel software.

 Results showed that salinity stress generally affected the growth of both carnation cultivars and reduced vegetative and reproductive growth. According to the results obtained from the study, fresh and dry weight of shoot, root and leaves, root length, plant height, stem diameter, diameter and number of flower, lateral shoot number, stomatal conductance, photosynthesis rate, K+ concentration in Diana and Barbarin cultivars decreased with increasing salinity level. Na+ concentration and Na+/K+ increased with increasing salinity and these two traits were higher in Diana than Barbarin cultivar, which indicates lower resistance of Diana cultivar. The plant's first response to stress is to reduce its leaf area, which reduces the supply of photosynthetic material to the growing parts and consequently hinders growth and flowering. Salinity stress and high osmotic potential in the rhizosphere greatly affect photosynthesis as they decrease pore conductivity. Moreover, excessive absorption of Na+ can interfere with the absorption of other elements, thereby restricting plant growth. Potassium (K+) is an essential inorganic molecule that plays a crucial role in increasing plant resistance to stress. It helps in maintaining turbidity, promoting cell development, and regulating stomatal function. In this study, salinity stress affected the growth and yield of both carnation cultivars, and with increasing stress, all morphological traits decreased. This stress also reduce photosynthesis by reducing stomatal conductance and subsequently reduce other growth characteristics. Growth reduction was observed at high salinity stress concentrations in both cultivars. However, barbarin cultivar showed higher resistance than Diana