Alkalinity affects plant production in the arable lands of the arid and semiarid regions of the world. Irrigation water of high alkalinity may cause nutritional problems in cultivated horticultural plants, specifically chlorosis in young leaves resulting from the formation of Fe forms that are unavailable for plant uptake. Alkalinity may also be associated with deficiency of cooper (Cu), zinc (Zn), K, and phosphorus (P) resulting from low solubility (FAO, 2000).
Alkalinity in water is caused mainly by carbonate (CO32−) and HCO3−, which at high concentrations are detrimental for plant growth (Cartmill et al., 2007). Use of irrigation water of high alkalinity leads to increased pH of the growing medium because acidity is neutralized by HCO3− and CO32− (Valdez-Aguilar and Reed, 2007).
High alkalinity irrigation water results in reduced growth and nutrient deficiency symptoms in young leaves, reducing plant quality and marketability, and represents a significant challenge to ornamental horticultural production systems. Lisianthus [Eustoma grandiflorum (Raf.) Shinn.], a species native to the arid zones of the southern United States and northern México, is an ornamental plant of increasing demand. Valdez-Aguilar et al. (2013) reported that lisianthus can tolerate high salinity irrigation water as long as sodium and chloride are not the predominant ions.
Calcium has been reported in a number of studies as an ion that enhances plant tolerance to abiotic stress, including drought (Hassan and Aarts, 2011), salinity (Zhu, 2001), and excess boron (Siddiqui et al., 2013) by regulating the response reactions and developmental processes (Steinhorst and Kudla, 2013). However, there is limited information on the potential role of Ca in enhancing plant tolerance to alkalinity stress. Calcium is a structural element that constitutes the middle lamellae, wall, and membranes of plant cells; participates in cell division, extension, and compartmentalization; and regulates the action of hormones and signals (Marschner, 1995). Supplementation with increasing Ca has been suggested to increase plant tolerance to salinity stress (Epstein, 1998). Kaya et al. (2002) and Tuna et al. (2007) reported that increased Ca concentrations resulted in enhanced growth and yield of strawberry (Fragaria ×ananassa Duch.) and tomato (Solanum lycopersicon L.) plants, respectively, exposed to high salinity conditions. The present study was conducted to investigate if supplementary Ca enhances the response of lisianthus to high levels of HCO3−-induced alkalinity.
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