HORTSCIENCE 55(2):224–230. 2020. https://doi.org/10.21273/HORTSCI14460-19 and Saha, 2014). Plants under drought stress tend to reduce leaf size, stimulate leaf abscis- sion, enhance root growth, and limit photo- Morphological and Physiological synthesis (Taiz et al., 2015). Some plants can maintain water balance under drought condi- Responses of Cornus alba to Salt tions through osmotic adjustment (Farooq et al., 2008). The fact that drought resistance and Drought Stresses under varies among plant species warrants further investigation to evaluate plant responses to drought conditions and select drought-tolerant Greenhouse Conditions plants for landscape use. Qiang Liu Soil salinity is also a global issue and is College of Life Sciences and Technology, Central South University of caused partially by human activities such as irrigation with poor quality water and poor Forestry and Technology, 498 South Shaoshan Road, Changsha, Hunan soil drainage, which result in excess soluble 410004, China; and Hunan Academy of Forestry, 658 South Shaoshan Road, salts in the soil. It is estimated that 20% of Changsha, Hunan 410004, China the irrigated lands in the world are currently affected by salinity stress (Taiz et al., 2015). Youping Sun Salinity induces a series of metabolic dys- Department of Plants, Soils and Climate, Utah State University, 4820 Old functions in plants, including specific ion Main Hill, Logan, UT 84322 toxicity, nutrient imbalance, decreased pho- tosynthesis, and enzyme dysfunction (Munns James Altland and Tester, 2008). The extent of adverse U.S. Department of Agriculture, Agricultural Research Service, Application impact of salinity on plant physiological Technology Research Unit, 1680 Madison Avenue, Wooster, OH 44691 processes depends on the rate and duration of salinity stress. Salinity stress can damage Genhua Niu various physiological and chemical processes Texas A&M AgriLife Research Center at Dallas, Texas A&M University, and even kill the plant. Salt-tolerant plants can withstand the adverse effects of high 17360 Coit Road, Dallas, TX 75252 salinity without severe foliar salt damage Additional index words. drought tolerance, salt tolerance, tatarian dogwood, volumetric water and significant reductions in growth and yield content (Grieve et al., 2008). The ability to tolerate salinity stress varies among plant species and Abstract. Tatarian dogwood (Cornus alba) is an ornamental shrub with white fruits, genotypes. Evaluating plant species com- creamy-white flowers, and red stems in fall through late winter and is widely used in monly used in landscape for salt tolerance residential landscape, public parks, and botanical gardens. Two greenhouse experiments may aid in identifying salt-tolerant plants for were conducted to characterize the survival, morphological, aesthetic, and physiological landscape use. responses of tatarian dogwood seedlings to salinity and drought stresses. In Expt. 1, Tatarian dogwood (Cornus alba)isa tatarian dogwood seedlings grown in three soilless growing substrates (Metro-Mix 360, member of dogwood family (Cornaceae) that 560, and 902) were irrigated with a nutrient solution at an electrical conductivity (EC) of is native to Siberia, northern China, and 1.2 dS·mL1 (control) or saline solution (by adding calculated amount of sodium chloride Korea (Zhang et al., 2013). It has been intro- and calcium chloride) at an EC of 5.0 or 10.0 dS·mL1 once per week for 8 weeks. Results duced to North America and Europe because showed that substrate did not influence the growth of tatarian dogwood seedling. All of its high cold hardiness and resistance to air plants irrigated with saline solutions at an EC of 10.0 dS·mL1 died, whereas those pollution (Konarska, 2011). Tatarian dog- irrigated with saline solutions at an EC of 5.0 dS·mL1 exhibited severe foliar salt damage wood is a popular ornamental shrub with with an average visual score of 1.0 (on a scale of 0 to 5, with 0 = dead and 5 = excellent white fruits, creamy-white flowers, and red without foliar salt damage). Compared with the control, saline solutions at an EC of 5.0 stems in fall through late winter (Dirr, 2009). dS·mL1 reduced plant height and shoot dry weight (DW) by 50.8% and 55.2%, It is widely used in residential landscape, respectively. Relative chlorophyll content [soil plant analysis development (SPAD) public parks, and botanical gardens. reading], chlorophyll fluorescence (Fv/Fm), and net photosynthesis rate (Pn) also de- The morphological and physiological re- creased when plants were irrigated with saline solutions at an EC of 5.0 and 10.0 dS·mL1. sponses to abiotic stress vary with species in Leaf sodium (Na+) concentration of tatarian dogwood seedlings irrigated with saline dogwood family (Hinckley et al., 1980; solutions at an EC of 5.0 and 10.0 dS·mL1 increased 11 and 40 times, respectively, Renault, 2005). Red-osier dogwood (Cornus compared with the control, whereas chloride (Cl-) concentration increased 25 and 33 stolonifera) has been reported to be moder- times, respectively. In Expt. 2, tatarian dogwood seedlings were irrigated at a substrate ately resistant to salt stress in a number of volumetric water contents (volume of water/volume of substrate, VWC) of 15%, 20%, investigations (Davis et al., 2014; Mustard 25%, 30%, 35%, 40%, or 45% using a sensor-based automated irrigation system for 60 and Renault, 2004; Renault and Affifi, 2009). days. Results showed that drought stress decreased plant growth of tatarian dogwood In a greenhouse study, the changes in the cell seedlings with a reduction of 71%, 85%, and 87% in plant height, leaf area, and shoot wall composition and elasticity of red-osier DW, respectively, when VWC decreased from 45% to 15%, but all plants survived at dogwood (Cornus sericea) under drought all VWC treatments. Significant reductions of photosynthesis (Pn), stomatal conductance stress were attributed to the delay in breaking (gS), transpiration rate (E), and water potential were also found in plants at a VWC of 15%, bud (Mustard and Renault, 2006). Dale et al. compared with other VWCs. However, SPAD readings and Fv/Fm of tatarian dogwood (2003) found that water deficit enhanced the seedlings were similar among the VWCs. In conclusion, tatarian dogwood seedlings were freeze-tolerance of red-osier dogwood. Flow- sensitive to the salinity levels tested in this study but could survive at all tested substrate ering dogwood (Cornus florida) has been volumetric water contents and exhibited resistance to drought conditions. reported to grow well in moderately com- pacted soil (Day et al., 2000). Water scarcity is one of the severe envi- arid and arid regions, which receive only 13 to However, little is known regarding the ronmental constraints to plant growth and 76 cm of precipitation annually, and the tolerance of salt and drought stresses of development. On a global basis, approxi- remaining two-thirds of lands are occasionally tatarian dogwood. Therefore, the purpose of mately one-third of lands are located in semi- exposed to drought conditions (Bhattacharjee this study was to characterize the survival, 224 HORTSCIENCE VOL. 55(2) FEBRUARY 2020 morphological, aesthetic, and physiological 15–5–15 Ca-Mag Special; ICL Specialty Fer- using a portable photosynthesis system with responses of tatarian dogwood seedlings to tilizers, Dublin, OH) to reverse osmosis (RO) an automatic universal PLC6 broad leaf cu- salinity and drought stresses. water, and the resulting EC was 1.2 dS·m–1. vette (CIRAS-2; PP Systems, Amesbury, The saline solution at an EC of 5.0 dS·m–1 was MA) 1 d before the first and second harvest. Materials and Methods prepared by adding 1.20 g·L–1 sodium chloride Relative chlorophyll content (SPAD reading) (NaCl) and 1.16 g·L–1 calcium chloride was also measured using a handheld chloro- Plant materials (CaCl2) to the nutrient solution, and the saline phyll meter (measured as the optical density; Tatarian dogwood seeds (F.W. Schu- solution at an EC of 10.0 dS·m–1 was prepared Minolta Camera Co., Osaka, Japan). Mean- macher Co., Sandwich, MA) in wet sands were by adding 2.84 g·L–1 NaCl and 2.70 g·L–1 while, to examine the effect of elevated stratified at 4 °C for 2 months starting from CaCl2 to the nutrient solution. The pH of all salinity on leaf photosynthetic apparatus, min- Dec. 2015. In February, 2016, seedlings were solutions was adjusted to 6.6 using potassium imal fluorescence (F0), maximum fluorescence transplanted into 10-cm pots with a soilless hydroxide (KOH). Both nutrient and saline (Fm), the maximal photochemical efficiency of growing substrate (45% to 55% canadian solutions were prepared in 100-L tanks with PSII (Fv/Fm,Fv =Fm –F0), were measured sphagnum peatmoss, vermiculite, composted EC confirmed using an EC meter (LAQUA using a chlorophyll fluorescence system bark, dolomite limestone, 0.0001% silicon di- Twin; Horiba, Ltd., Kyoto, Japan) before irri- (Pocket PEA; Hansatech, Norfolk, UK). oxide (SiO2) (Metro-Mix 360 RSI; SunGro gation. From 14 June to 17 Aug. 2016, treat- Mineral analysis. Leaves at the first har- Horticulture, Agawam, MA). These seedlings ment solutions were applied manually roughly vest were separated from the stem to analyze were used for both salinity and drought studies. once per week for 8 weeks. A total of 1.0 L Na+,Cl-, calcium (Ca2+), potassium (K+), treatment solution was applied to each plant phosphorus (P), zinc (Zn2+), iron (Fe3+), sul- Salinity study (Expt. 1) each time, resulting in a leaching fraction of fur (S), copper (Cu2+), magnesium (Mg2+), Growing substrates. Three soilless grow- 35%. Between treatment solution irriga- and boron (B) concentrations. Leaves were ing substrates (Metro-Mix 360, Metro-Mix tions, plants were irrigated with 500 mL of ground to pass a 40-mesh screen with a 560, Metro-Mix 902; SunGro Horticulture, nutrient solution whenever the substrate sur- stainless Wiley mill (Thomas Scientific, Agawam, MA) were used in this study.