In arid and semiarid regions, high-quality water supply is often limited and soil salinity is often high as a result of low rainfall and high evapotranspiration. With a rapid increase in urban populations, the intense competition for high-quality water among agriculture, industry, and recreational users has promoted the use of alternative water sources for irrigating landscapes in arid and semiarid regions. Alternative water, primarily municipal-treated effluents (also called reclaimed water), has higher salinity compared with that of potable water. In coastal regions, seawater intrusion results in high soil salinity, whereas deicing salts also increase soil salinity in northern areas. Thus, tolerant plants are needed for these regions.
The relative salinity tolerance among multiple cultivars or species is often assessed based on survival rate, growth, and yield. Mineral analysis and other physiological responses to salinity help to understand the mechanisms of salinity tolerance (Carter and Grieve, 2006; Niu and Cabrera, 2010). Salinity reduces the ability of plants to take up water, and this quickly causes reductions in growth rate along with a suite of metabolic changes identical to those caused by water stress (Marschner, 1995; Munns, 2002). Increasing salinity stress as a result of higher salinity and/or extended time exposure to salinity generally leads to foliar salt injury. For ornamental plants, being compact and free of foliar damage is more important compared with maximum growth. Many researchers have used visual ratings as one of the parameters to assess salinity tolerance (Cameron et al., 2004; Fox et al., 2005; Niu et al., 2008, 2012; Zollinger et al., 2007).
Sodium chloride is usually the primary salt in salinized soils and low-quality irrigation water. Ions of Na+ and Cl– are often excessively absorbed by plants under salinity conditions, which reduce the uptake of other nutrients such as Ca2+ and K+. Most salt-tolerant plants have better ability to exclude Na+ and/or Cl– to prevent their accumulation or limit the transport of these ions to shoots (Munns and Tester, 2008; Niu and Cabrera, 2010). Therefore, the shoot or leaf Na+ and/or Cl– concentrations are often used to examine the salt tolerance of a plant and the mechanism of salt tolerance along with other parameters. For example, R. × fortuniana had higher Na+ exclusion ability than R. multiflora and R. odorata, as evidenced by lower Na+ concentrations in stems and leaves (Niu et al., 2008).
Garden rose (Rosa spp.) is one of the most economically important and popular ornamental plants in the world. Rose has been traditionally categorized as a salt-sensitive species with salt injury reported within a range of 0.5 to 3 dS·m−1 EC, depending on species and cultivar, cultural medium, leaching fraction, and environmental conditions (Urban, 2003). However, our previous research indicated that rose rootstocks R. fortuniana, R. multiflora, R. odorata, and ‘Dr. Huey’ could tolerate moderate salinity (EC up to 4.0 dS·m−1) with acceptable growth reduction and aesthetic appearance (Niu et al., 2008; Niu and Rodriguez, 2008). Other researchers also reported that yield and quality of roses did not decrease when irrigated with drainage recycled water at EC of 3.5 dS·m−1 provided that an appropriate rootstock and aerated medium were used (Cabrera, 2003; Raviv et al., 1998). More information on salt tolerance for greenhouse cut roses is available (Bernstein et al., 2006; Cabrera, 2003; de Vries, 2003; Fernández-Falcón et al., 1986; Hughes and Hanan, 1978; Wahome et al., 2001) as compared with garden roses, especially self-rooted roses. The objectives of this study were to compare the relative salt tolerance of selected garden roses, which are commonly used in southern regions, and to determine the mineral nutrition of these roses when irrigated with nutrient solution with increasing salinity.
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