High soil salinity is often problematic to turfgrass managers. Salinity causes osmotic stress (i.e., physiological drought), ion imbalance, and phytotoxicity and adversely affects plant growth and development (Qian and Harivandi, 2007), resulting in reduced visual quality and playability of the turfgrass. Many factors such as deficient precipitation, water percolation from high water tables, low-quality water (e.g., recycled water, well water, and salt water from sea water intrusion), and salts from fertilizers and deicer can result in high soil salinity (Wu and Lin, 1993). Various turfgrass species respond to soil salinity differently. For example, kentucky bluegrass is very sensitive to saline conditions, whereas creeping bentgrass shows moderate salinity sensitivity (Marcum, 2007). Tall fescue, perennial ryegrass, and zoysiagrass are moderately tolerant to salinity, whereas bermudagrass and alkaligrass are highly tolerant (Marcum, 2007).
Alkalinity (high pH) and salinity often coexist in nature, especially in sodic soils because of the hydrolysis of exchangeable sodium (Guerrero-Alves et al., 2002; Javid et al., 2011). Of the cultivated land worldwide (13.2 × 109 ha), ≈23% is affected by salinity and another 37% is affected by sodicity (Läuchli and Lüttge, 2002). More than 70% land in northeast China is covered by alkaline meadow and it is expanding (Kawanabe and Zhu, 1991). High soil pH (greater than 8.5) has been reported on more than 80% of the sodic soils in Australia (Rengasamy, 2002). Qian and Mecham (2005) reported that an increase of soil salinity, sodium content, and pH on golf fairways was observed after long-term (4 to 33 years) use of recycled water.
Previous research on salinity stress has been focused on the impact of neutral salts such as NaCl on plant growth and development (Dai et al., 2009; Zhang et al., 2011). Recent studies have demonstrated that the combined saline–alkaline conditions are more detrimental to plants than salinity alone (Javid et al., 2012; Li et al., 2010; Liu and Shi, 2010; Paz et al., 2012; Shi and Wang, 2005). Lower seed germination was observed in sheepgrass [Leymus chinensis (Trin.) Tzvel.], switchgrass (Panicum virgatum L.), and wheat (Triticum aestivum L.) under the combined saline–alkaline stress than salinity alone (Guo et al., 2010; Lin et al., 2014; Liu et al., 2014). Many seeds exposed to the combined saline–alkaline condition were not able to recover even after the stress was removed, suggesting that high pH may cause structural decomposition in seeds (Guo et al., 2010). Photosynthetic pigments, stomatal conductance, and net photosynthetic rates were significantly reduced in sunflower (Helianthus annuus L.) under saline–alkaline conditions, but not saline stress alone (Liu and Shi, 2010). In addition to the salinity injuries, alkalinity under saline–alkaline conditions may inhibit iron absorption and cause precipitation of calcium, magnesium, and phosphorus, thus interrupting ion homeostasis in plant cells (Javid et al., 2012). A higher Na+/K+ ratio was observed in various crops under the combined stress than salinity stress alone (Javid et al., 2012; Liu and Shi, 2010; Shi and Wang, 2005). Li et al. (2010) and Liu and Shi (2010) reported higher total organic acid production in plants under the combined saline–alkaline stress than the saline condition alone. Accumulation of organic acid contributes to osmotic adjustment under a stressful environment; however, it is energy-consuming resulting in reduced ability of ion regulation (Li et al., 2010; Liu and Shi, 2010). Furthermore, alkaline conditions may interfere with abscisic acid distribution between roots and the rhizosphere and its transportation within plant organs, resulting in root growth inhibition (Degenhardt et al., 2000; Javid et al., 2011).
To our knowledge, turfgrass responses to saline–alkaline conditions have not been evaluated. Therefore, this study was conducted to determine the effect of a saline–alkaline condition on turfgrass during seed germination, a critical period of turfgrass development and when plants are most likely to experience salt accumulation (Almansouri et al., 2001). Results will provide useful information to managers for selecting turfgrass species tolerant to saline–alkaline soil conditions and to breeders for screening and developing tolerant germplasms.
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