Water and soil salinization are global problems and are more severe in water-scarce areas such as arid and semiarid regions, where groundwater is the primary source of water. The increasing population has intensified the competition for high-quality water supply among urban and agricultural water users. Therefore, using alternative water sources such as municipal reclaimed water to irrigate nursery crops and landscape plants has drawn considerable attention (Grieve, 2011). Reclaimed water carries relatively high levels of soluble salts, which negatively affect plant growth and development and impose foliar salt injury on sensitive plants (Niu and Cabrera, 2010; Veatch-Blohm et al., 2014). The salinity of groundwater, which is a primary water source for nursery crops in some areas, varies with location and rainfall (Niu and Cabrera, 2010). Overuse of groundwater leads to decline of water table and increases salinity (Smith et al., 2016). Therefore, information on salt tolerance of nursery and landscape crops is necessary to prevent salt damage and maintain aesthetically appealing landscapes.
Berberis thunbergii (japanese barberry) is a species native to Japan and eastern Asia, although widely naturalized in China and North America (Wikipedia, The Free Encyclopedia, 2017). It is a multibranched dense shrub that can grow up to 2.5 m tall with shiny green to burgundy alternate leaves along its thorny stems (Dirr, 1998). It has solitary yellow flowers that bloom from March to April and produces round or elliptical red berries (Dirr, 1998). Japanese barberry is a widely grown landscape plant that was awarded the prestigious Royal Horticultural Societies Annual Award of Garden Merit in 1993 (Davis Landscape Architecture, 2017). In the United States, an estimated $30 million in barberry plants are sold annually (U.S. Department of Agriculture, 2009). Previous breeding efforts have led to numerous cultivars that offer different foliage colors (yellow, dark red to violet, or variegated foliage) and forms (erect growth or dwarf size) (Dirr, 1998). For example, B. thunbergii var. atropurpurea ‘Concorde’ is extremely slow growing with a compact habit and small deep red or purple leaves that hold color in heat (Dirr, 1998). Berberis thunbergii var. atropurpurea ‘Helmond Pillar’ is a distinct upright with fastigiate form and reddish purple leaves that usually grows up to 1.5 m tall and 0.6 m wide forming a slow-growing column (Dirr, 1998). Berberis thunbergii var. atropurpurea ‘Rose Glow’ can grow about 1.5–1.8 m tall and produces new foliage in rose-pink mottled with deeper red-purple splotches that gradually mature to a deep reddish purple (Dirr, 1998).
Salt tolerance of barberry species has been reported in extension articles. For example, Beckerman and Lerner (2009) reported that Berberis species are sensitive or have intermediate tolerance to aerial salt spray, whereas they are sensitive to soil salinity. On the list of salt-tolerant plants compiled by Chalet Nursery (2013), Berberis species have high aerial salt tolerance and low soil salt tolerance. Berberis thunbergii has poor soil salt tolerance (Gilman, 2014) and high tolerance to aerial salt spray (Jull, 2009). Berberis koreana also has high tolerance to aerial salt spray (Jull, 2009), but its tolerance to soil salinity is yet to be determined. Berberis julianae and Berberis bealei have moderate salt tolerance (Glen et al., 2004; Harrison, 2009). However, these reports are mostly based on anecdotal observations without defined thresholds for categories of salt tolerance. Only a few research-based studies have been conducted to evaluate the responses of barberry plants to salinity. Monk and Wiebe (1961) reported that B. thunbergii was not salt tolerant based on the study in salinized field plots. Berberis thunbergii is listed as a very salt-sensitive plant because a 25% growth reduction occurred when the EC of a saturation extract of growing medium was 1.8 dS·m−1, whereas Berberis ×mentorensis is listed as a salt-sensitive plant tolerating a saturation extract of EC up to 3–4 dS·m−1 (Costello et al., 2003; Handreck and Black, 2002). Two-year-old seedlings of B. thunbergii ‘Atropurpurea’ showed no significant difference in annual growth when irrigated with tap water, tap water containing 3.3 g·L−1 NaCl, 6.0 g·L−1 CaCl2, or 10.5 g·L−1 Na2CO3 for eight times at 7-d intervals (Marosz, 2012).
Given that salt tolerance varies considerably among species and even cultivars within a species, a systematic study is needed to investigate the salt tolerance of different barberry cultivars. The objectives of this study were to evaluate the relative salt tolerance of eight barberry cultivars in a greenhouse study using the parameters of shoot growth, visual quality, chlorophyll content, PI, and mineral concentration in response to elevated salinity of irrigation solution.
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