Use of alternative water sources such as municipal reclaimed water for landscape and nursery irrigation is of increasing importance (Yeager et al., 2010). Increased population results in increased demand for freshwater. On the other hand, population growth inevitably increases the production of municipal wastewater. Treated municipal wastewater has already been used for irrigation of landscapes and nursery crops in water-scarce regions for decades (Dobrowolski et al., 2008; Morgan et al., 2008; Tanji et al., 2008; Yeager et al., 2010). However, reclaimed water contains higher salt concentrations than potable water, and the elevated salinity can cause salt damage on salt-sensitive plants (Niu and Cabrera, 2010).
Salinity decreases soil water potential and thereby makes water less available to plants (Munns, 2002). Typical plant responses to salinity include stunted plant growth and foliar injury such as leaf edge burn, scorch, necrosis, and premature defoliation (LeCompte et al., 2017; Munns, 2002; Niu and Cabrera, 2010). Salinity may also induce a series of metabolic dysfunctions in plants, including absorption of excessive Na and Cl, resulting in nutrient imbalance, and inhibition of plant photosynthesis and stomatal conductance (gs) (Munns and Tester, 2008). Information on salt tolerance of commonly used landscape plants is still limited.
The 10 ornamental taxa selected for this study are commonly used for commercial and residential landscapes. Chaenomeles speciosa (‘Orange Storm’ and ‘Pink Storm’) is a thorny deciduous or semi-evergreen shrub native to eastern Asia. Diervilla rivularis (‘G2X885411’, ‘G2X88544’, and ‘Smndrsf’) is a flowering shrub in the honeysuckle family and native to the eastern United States. Forsythia ×intermedia ‘Mindor’ is an ornamental deciduous shrub well adapted to temperature changes and is widely planted in gardens and parks. Hibiscus syriacus is a species of flowering plant in the Malvaceae family native to Asia. Hydrangea macrophylla (‘Smhmtau’ and ‘Smnhmsigma’) is a species of flowering plant in the family of Hydrangeaceae native to Japan. Parthenocissus quinquefolia, native to eastern and central North America, is a species of flowering plant in the family Vitaceae. The salt tolerance of these taxa is unknown.
To increase the plant selection option for areas where alternative waters may be used for irrigation, evaluation of salt tolerance for popular landscape plants is necessary. The purposes of this study were to compare the relative salt tolerance of the previously described 10 ornamental taxa by quantifying the growth, morphological, and physiological responses to a range of salinity in a greenhouse study.
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