To provide more species for landscapes where poor-quality irrigation water is used, salt tolerance of commonly used landscape plants should be characterized. Nine ornamental species, including six herbaceous and three woody, were irrigated with nutrient solution at electrical conductivity (EC) of 1.2 dS·m−1 (control) or saline solution at EC of 5.0 or 10.0 dS·m−1 (EC 5 or EC 10) for 8 weeks and their growth and physiological responses were determined. Although growth was reduced in orange peel jessamine (Cestrum ‘Orange Peel’) and mexican hummingbird bush (Dicliptera suberecta) as salinity increased, no obvious signs of stress or injury were observed, indicating that orange peel jessamine and mexican hummingbird bush were the most salt tolerant. Flame acanthus (Anisacanthus quadrifidus var. wrightii), rock rose (Pavonia lasiopetala), and ‘Dark knight’ bluebeard (Caryopteris ×clandonensis ‘Dark Knight’) had more growth reduction than that of orange peel jessamine and mexican hummingbird bush with minimal or no foliar damage in EC 5 and slight foliar damage in EC 10. Cardinal flower (Lobelia cardinalis) and mexican false heather (Cuphea hyssopifolia) exhibited mortality rates of 30% and 20%, severe foliar damage, and greater than 70% reduction in leaf area and dry weight in EC 10 compared with their respective controls. Although the growth reductions in butterfly blue (Scabiosa columbaria) were not as great as cardinal flower and mexican false heather, 40% of butterfly blue plants were dead with moderate foliar damage in EC 10. Therefore, cardinal flower, mexican false heather, and butterfly blue plants were considered as moderately salt sensitive. Eastern red columbine (Aquilegia canadensis) was the most salt sensitive among the species investigated with moderate foliar damage in EC 5 and all plants died in EC 10. Four out of the nine species tested had significant differences in net photosynthetic rate (Pn), stomatal conductance (g s), and/or relative chlorophyll content between the control and EC 10, and the difference varied with species. Shoot ion concentrations of the nine ornamentals were also affected by salinity levels and varied among species.
Shasha Wu, Youping Sun, and Genhua Niu
Shasha Wu, Youping Sun, Genhua Niu, James Altland, and Raul Cabrera
Asteraceae is one of the largest plant families with many important garden ornamental species. Salt tolerance of 10 aster perennials was evaluated in a greenhouse experiment, including the following: damianita (Chrysactinia mexicana), gregg’s mistflower (Eupatorium greggii), shasta daisy (Leucanthemum ×superbum ‘Becky’), blackfoot daisy (Melampodium leucanthum), lavender cotton (Santolina chamaecyparissus), aromatic aster (Symphyotrichum oblongifolium), copper canyon daisy (Tagetes lemmonii), four-nerve daisy (Tetraneuris scaposa), skeleton-leaf goldeneye (Viguiera stenoloba), and zexmenia (Wedelia texana). Plants were irrigated with nutrient solution at electrical conductivity (EC) of 1.2 dS·m−1 (control) or saline solutions at EC of 5.0 or 10.0 dS·m−1 (EC 5 or EC 10) for 5 weeks. Upon termination, growth parameters, foliar salt damage, relative chlorophyll content [Soil-Plant Analysis Development (SPAD) readings], and mineral concentration were measured. Gregg’s mistflower, skeleton-leaf goldeneye, and lavender cotton were the most salt-tolerant species with less reductions in shoot dry weight (DW) in both EC 5 and EC 10. Considering the relatively severe foliar salt damage (visual quality score of 3.1 and 2.7 at EC 5; 2.4 and 1.6 at EC 10) and mortality rate (10% and 40%) in EC 10, aromatic aster and zexmenia should be avoided where poor quality water may be used for irrigation. Gregg’s mistflower and skeleton-leaf goldeneye had relatively lower leaf sodium (Na) concentrations suggesting that both species can selectively exclude Na. Damianita and the four daisies, i.e., blackfoot daisy, copper canyon daisy, four-nerve daisy, and shasta daisy, were salt sensitive as evidenced by their greater growth reduction, foliar salt damage, and high Na and chlorine (Cl) accumulation in leaves, and should be avoided in landscapes where poor quality water may be used for irrigation.