Water quantity and quality are critical global issues. As the urban population increases, the competition for high-quality water among agriculture, industry, and domestic water users is becoming progressively intense. Water consumption in urban landscape irrigation increases with urban population expansion (Kjelgren et al., 2000; Qian et al., 2005). Using alternative water sources such as municipal reclaimed water to irrigate urban landscapes can significantly conserve potable water. Municipal reclaimed water is the only water source that increases with population growth (Qian et al., 2005). Many regions with water shortage problems have started to use municipal reclaimed water (also called recycled water) to irrigate golf courses, school yards, and landscapes (Fox et al., 2005; Gori et al., 2000; Jordan et al., 2001; Wu et al., 2001) and for agricultural and horticultural crop production (Dobrowolski et al., 2008; Safi et al., 2007; Shillo et al., 2002). However, reclaimed water frequently contains high salt levels that may cause damage or even death to sensitive plants if not managed properly. Therefore, screening and identifying salt-tolerant landscape plants is urgently needed to expand the use of alternative and reclaimed water for landscape irrigation and nursery production.
Soil salinity is typically high in arid and semiarid regions where temperatures are high and rainfall is low. Irrigation with poor-quality water exacerbates the soil salinity. Typical plant responses to soil salinity include reduced shoot and root growth rates, decreased leaf or shoot number (Munns, 2002), decreased gas exchange rates, foliar salt damage, and even death as salinity increases (Munns and Tester, 2008; Niu and Cabrera, 2010). The degree of these negative responses depends on species and the level of the salinity. Many researchers worldwide have conducted studies on salt tolerance of landscape plants in the past years (e.g., Fox et al., 2005; Gori et al., 2000; Jordan et al., 2001; Marosz, 2004; Niu and Cabrera, 2010; Niu and Rodriguez, 2006a, 2006b; Tanji et al., 2008; Wu et al., 2001; Zollinger et al., 2007). These studies indicate a wide range of salt tolerance existing among different species and cultivars within the same species.
Wildflowers are popular plants in water-wise, low-maintenance landscapes. Planting wildflowers in landscapes could reduce mowing costs and improve soil erosion and soil stabilization (Bretzel et al., 2009). Planting wildflowers in landscapes also increases aesthetic appearance by increasing diversity in colors and vegetation. Herbaceous wildflowers dominate meadows in arid regions of Australia and the western United States (Beran et al., 1999; Kjelgren et al., 2009; Pérez et al., 2010). However, little information is available on the salt tolerance of these herbaceous wildflowers.
To introduce wildflowers in landscapes where poor-quality water with high salinity may be used for irrigation, this study aimed to examine the growth and physiological [osmotic potential (ψS) and ion uptake] responses of six native wildflowers to a range of salinity levels in both greenhouse and shadehouse environments under semiarid conditions. The selected wildflowers included were Salvia farinacea (mealy cup sage), Berlandiera lyrata (chocolate daisy), Ratibida columnaris (Mexican hat), Oenothera elata (Hooker’s evening primrose), Zinnia grandiflora (plains zinnia), and Monarda citriodora (lemon horsemint). All these species are native to North America and thrive in well-drained soils with full sun conditions in southwestern United States and northern Mexico (Stubbendieck et al., 2003).
Bretzel, F., Pezzarossa, B., Carrai, C. & Malorgio, F. 2009 Wildflowers planting to reduce the management cost of urban gardens and roadsides Acta Hort. 813 263 270
Cameron, R.W.F., Wilkinson, S., Davies, W.J., Harrison-Murray, R.S., Dunstan, D. & Burgess, C. 2004 Regulation of plant growth in container-grown ornamentals through the use of controlled irrigation Acta Hort. 630 305 312
Dobrowolski J., O'Neill M., Duriancik L. & Throwe J. 2008 Opportunities and challenges in agricultural water reuse: Final report. USDA-CSREES
Fox, L.J., Grose, J.N., Appleton, B.L. & Donohue, S.J. 2005 Evaluation of treated effluent as an irrigation source for landscape plants J. Environ. Hort. 23 174 178
Gori, R., Ferrini, F., Nicese, F.P. & Lubello, C. 2000 Effect of reclaimed wastewater on the growth and nutrient content of three landscape shrubs J. Environ. Hort. 18 108 114
Hasegawa, P.M., Bressan, R.A., Zhu, J.-K. & Bohnert, H.J. 2000 Plant cellular and molecular responses to high salinity Annu. Rev. Plant Physiol. Plant Mol. Biol. 51 463 499
Jordan, L.A., Devitt, D.A., Morris, R.L. & Neuman, D.S. 2001 Foliar damage to ornamental trees sprinkler-irrigated with reuse water Irrig. Sci. 21 17 25
Kjelgren, R., Wang, L. & Joyce, D. 2009 Water deficit stress responses of three native Australian ornamental herbaceous wildflower species for water-wise landscapes HortScience 44 1358 1365
Marosz, A. 2004 Effect of soil salinity on nutrient uptake, growth, and decorative value of four ground cover shrubs J. Plant Nutr. 27 977 989
Native Plant Database 2012 (July) <http://www.wildflower.org>
Niu, G. & Cabrera, R.I. 2010 Growth and physiological responses of landscape plants to saline water irrigation: A review HortScience 45 1605 1609
Niu, G. & Rodriguez, D.S. 2008 Responses of growth and ion uptake of four rose rootstocks to chloride- or sulfate-dominated salinity J. Amer. Soc. Hort. Sci. 133 663 669
Niu, G., Rodriguez, D.S. & Wang, Y.T. 2007 Salinity and growing medium regulate growth, morphology and ion uptake of gaillardia aristata J. Environ. Hort. 25 89 94
Pérez, H.E., Adams, C.R., Kane, M.E., Norcini, J.G., Acomb, G. & Larsen, C. 2010 Awareness and interest in native wildflowers among college students in plant-related disciplines: A case study from Florida HortTechnology 20 368 376
Qian, Y.L., Fu, J.M., Klett, J. & Newman, S.E. 2005 Effects of long-term recycled wastewater irrigation on visual quality and ion concentrations of ponderosa pine J. Environ. Hort. 23 185 189
Safi, M.I., Fardous, A., Muddaber, M., El-Zuraiqim, S., Balaweneh, A., Al-Hadidi, L. & Bashabsheh, I. 2007 Long term effects of reclaimed water on rose and carnation cut flower crops in soil and soilless media J. Appl. Sci. 7 1191 1198
Shannon, M.C., Grieve, C.M. & Francois, L.E. 1994 Whole-plant response to salinity, p. 199–244. In: Wilkinson, R.E. (ed.). Plant environment interaction. Marcel Dekker, New York, NY
Stubbendieck, J.L., Hatch, S.L. & Landholt, L.M. 2003 North American wildland plants: A field guide. University of Nebraska Press, NE. p. 280–281
Tanji, K., Grattan, S., Grieve, C., Harivandi, A., Rollins, L., Shaw, D., Sheikh, B. & Wu, L. 2008 Salt management guide for landscape irrigation with recycled water in coastal southern California: A comprehensive literature review. <http://www.salinitymanagement.org>
U.S. Environmental Protection Agency 1983 Methods of chemical analysis of water and wastes (EPA-600/4-79-020). U.S. Gov. Print. Office, Washington, DC
Wu, L., Guo, X. & Harivandi, A. 2001 Salt tolerance and salt accumulation of landscape plants irrigated by sprinkler and drip irrigation systems J. Plant Nutr. 24 1473 1490
Zollinger, N., Koenig, R., Cerny-Koenig, T. & Kjelgren, R. 2007 Relative salinity tolerance of intermountain western United States native herbaceous perennials HortScience 42 529 534