The Response of Ornamental Plants to Saline Irrigation Water

Salinity affects about one third of irrigated land, causing a significant reduction in crop productivity (Flowers & Yeo, 1995; Ravindran et al., 2007). For this reason researchers have paid considerable attention to this important environmental problem over the last decades. Few studies, however, have dealt specifically with ornamental plants used in landscapes, despite the fact that salt stress causes serious damage in these species (Cassaniti et al., 2009a; Marosz, 2004). Salinity is of rising importance in landscaping because of the increase of green areas in the urban environment where the scarcity of water has led to the reuse of wastewaters for irrigation (McCammon et al., 2009; Navarro et al., 2008). Salinity is also a reality in coastal gardens and landscapes, where plants are damaged by aerosols originating from the sea (Ferrante et al., 2011) and in countries where large amounts of de-icing salts are applied to roadways during the winter months (Townsend & Kwolek, 1987). Although water is used for purposes other than irrigation, “a landscape may serve as a visual indicator of water use to the general public due to its visual exposure” (Thayer, 1976). While in the past only good quality water (in some States of the USA, homeowners used approximately 60% of potable water to irrigate landscapes; Utah Division of Water Resources, 2003) was used for landscaping and/or floriculture (Tab. 1), nowadays the ecological sensitivity widely diffused in landscape management and planning (Botequilla Leitão & Ahern, 2002) determines the need to explore alternative water sources for irrigation. Landscape water conservation consequently requires making choices of plant species able to tolerate salt stress in order to allow the use of low quality water. Alternative water sources might be recycled water, treated municipal effluent and brackish groundwater, all of which generally have higher levels of salts compared with potable waters (Niu et al., 2007b). Treated effluent may also contain nutrients essential for plant growth; if water quality is good (not too saline), treated effluent can improve plant growth and reduce fertilizer requirements (Gori et al., 2000; Quist et al., 1999); application of industrial and municipal wastewater to land can be an environmentally safe water management strategy (Rodriguez, 2005; Ruiz et al., 2006). The potential physical, chemical or biological problems that are associated with effluent water applied to edible crops (Kirkam, 1986) are of lesser concern for landscape plant production (Gori et al., 2000).