Salinity is a serious environmental problem worldwide, especially in arid and semi-arid regions. It is estimated that ≈800 million ha of arable lands are currently affected by salinity stress (Food and Agriculture Organization of the United Nations, 2008). The chemical compositions in water and salt-affected soils vary with sources and locations. Sodium chloride (NaCl), sodium sulfate (Na2SO4), calcium chloride (CaCl2), calcium sulfate (CaSO4), magnesium chloride (MgCl2), magnesium sulfate (MgSO4), potassium chloride (KCl), and sodium carbonate (Na2CO3) all contribute to salinity stress; however, NaCl is the most prevalent salt (Taiz and Zeiger, 2015). Dissolved salts in the root zone can cause low water potential, thereby limiting the water available to plants. Furthermore, high concentrations of ions that accumulate in plant tissue, particularly sodium (Na+) and chloride (Cl-), can cause specific ion effects on plant growth and development, nutrient uptake and imbalance, and plant photosynthesis (Grattan and Grieve, 1999; Taiz and Zeiger, 2015).
Aesthetically appealing landscapes are needed to meet the demand of rapidly growing urban populations for high-quality living environments. Landscape irrigation will consume large quantities of fresh water that are already low in many regions. Alternative waters such as brackish groundwater and treated and reclaimed sewage effluent (reclaimed water) can provide additional water for landscape use (Tanji et al., 2008). These alternative waters are saline with varying chemical compositions and typically contain 1 to 7 g·L−1 total dissolved salts (TDS) (Glenna et al., 2009). If there is no opportunity to drain the accumulated salts, then they can quickly build and injure salt-sensitive species. Practices like improving drainage, maintaining a leaching fraction, monitoring salt concentrations in reclaimed water, and using salt-tolerant plant species are needed to reduce salinity stress (Niu and Cabrera, 2010).
Japanese spirea is an ideal landscape plant for border, foundation, and mass plantings. It has a dense, compact habit with large clusters of pink or white flowers that bloom in late spring and summer. It is an ornamental plant for gardeners in Utah and the intermountain western United States that offers a wide range of sizes and cultivars. ‘Galen’ japanese spirea has rich pink flowers, purple-red new growth in spring, and blue-green foliage in summer (Morton Arboretum, 2018). ‘Minspi’ japanese spirea is a low-growing shrub with splashy green, yellow, and cream variegated leaves and bright pink flowers (Proven Winners, 2018a). ‘NCSX1’ japanese spirea was introduced by Proven Winners (Monrovia, 2018a). It is an exceptional low-growing shrub with purple flowers and bright candy apple red foliage that emerges in spring and then matures to a bold yellow foliage. ‘NCSX2’ japanese spirea is a shrub with green foliage and red flowers (Proven Winners, 2018b). ‘SMNSJMFP’ japanese spirea has pink flowers and green foliage (Spring Meadow Nursery, 2018). ‘Tracy’ japanese spirea is a patented cultivar discovered by Timothy Wood from an open pollination of ‘Wilma’ fritsch spirea (Spiraea fritschiana) as the female parent and japanese spirea as the male parent (Monrovia, 2018b). It produces massive pink flowers and orange foliage in spring, deep yellow in the summer, and golden orange in autumn. ‘Yan’ japanese spirea has pink flowers and vibrant gold foliage (Morton Arboretum, 2018).
Research-based information regarding spirea salt tolerance is limited. The salt tolerance of japanese spirea has been reported in extension articles. For example, japanese spirea and bumalda japanese spirea (Spiraea ×bumalda) are listed as shrubs tolerant to saline soils and salt spray (Appleton et al., 2015). Bumalda japanese spirea is sensitive to salt spray (Beckerman and Lerner, 2009), whereas japanese spirea has moderate tolerance to salt spray (Jull, 2009). However, these inconsistent reports are based on anecdotal observations without defined thresholds for salt tolerance categories. Therefore, it is necessary to perform additional research to investigate their salt tolerance and to select salt-tolerant japanese spirea for landscape use. In this study, seven spirea cultivars were irrigated with saline water to mimic reclaimed water irrigation. Plant morphological and physiological responses to salt stress were evaluated to determine differences in salt tolerance among cultivars.
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Monrovia 2018b Double Play® Big Bang™ spirea: Spiraea japonica ‘Tracy'. Plant Patent #21,588. 7 Nov. 2018. <https://www.monrovia.com/plant-catalog/plants/3040/double-play-big-bang-spirea/>
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Proven Winners 2018a Double Play® Painted Lady® spirea. 7 Nov. 2018. <https://www.provenwinners.com/plants/spiraea/double-play-painted-lady-spirea-spiraea-japonica>
Proven Winners 2018b Double Play® Doozie® spirea. 7 Nov. 2018. <https://www.provenwinners.com/plants/spiraea/double-play-doozie-spirea-spiraea-x>
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