Environmental and Experimental Botany 77 (2012) 175–184 Contents lists available at SciVerse ScienceDirect Environmental and Experimental Botany journa l h omepa g e: www.elsevier.com/locate/envexpbot Comparisons of annual pasture legumes in growth, ion regulation and root porosity demonstrate that Melilotus siculus has exceptional tolerance to combinations of salinity and waterlogging Natasha Lea Teakle a,b,∗ , Scott Bowman b , Edward G. Barrett-Lennard a,c , Daniel Real b,c,d , Timothy David Colmer b a Centre for Ecohydrology, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia b School of Plant Biology, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia c Department of Agriculture and Food Western Australia, 3 Baron-Hay Court, South Perth, WA 6151, Australia d Future Farm Industries CRC, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia a r t i c l e i n f o Article history: Received 6 July 2011 Received in revised form 14 November 2011 Accepted 23 November 2011 Keywords: Pasture legume Salinity tolerance Waterlogging tolerance Sodium Chloride Melilotus a b s t r a c t Annual pasture legumes with high tolerance of combined salinity and waterlogging are needed for saline areas in many rain-fed agricultural regions. Melilotus siculus is an annual legume from saline marshy areas of the Mediterranean with potential use in saline pastures and, based on descriptions of its native habitat, was hypothesised to tolerate combined salinity and waterlogging. Experiments compared M. siculus to Trifolium michelianum and Medicago polymorpha, other annual pasture legumes with reported salt or waterlogging tolerances, with 0–450 mM NaCl in hydroponics or in sand culture. Tolerance to combined salinity and waterlogging was also evaluated at 150, 400 and 550 mM NaCl in a stagnant deoxygenated nutrient solution. M. siculus was substantially more salt tolerant than the other two species. At 450 mM NaCl, shoot DM of M. siculus was 30% of control, compared with only 15% for the other species. M. siculus was also the most tolerant species to combined salinity and stagnant treatment, and produced new leaves even after 14 d in stagnant nutrient solution with 550 mM NaCl (∼ sea water salinity). In comparison, T. michelianum and M. polymorpha only survived up to 5 d in stagnant solution with 400 mM NaCl. Even at only 150 mM NaCl in stagnant solution, shoot DM was just 30% of control for T. michelianum and M. polymorpha, compared to 60% for M. siculus. Tolerance to combined salinity and waterlogging was associated with higher root porosity and regulation of shoot Na + and Cl - , with the more tolerant M. siculus having similar shoot Na + and Cl - concentrations for both aerated-saline and stagnant-saline treatments. In summary, M. siculus is a pasture legume that can grow at high salinity (up to 550 mM) even when in combination with waterlogging, as root porosity and associated O 2 transport presumably enables continued regulation by the roots of Na + and Cl - entry under these dual stress conditions. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The increasing spread of salinity is impacting on agricultural production, with about 800 Mha of land estimated to be salt affected, covering more than 6% of the world’s land area (FAO, 2008). Exacerbating the problem, waterlogging also frequently occurs in saline areas, reducing aeration of soil and hence O 2 supply to roots, which inhibits respiration (Datta and de Jong, ∗ Corresponding author at: School of Plant Biology (M084), The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia. Tel.: +61 8 6488 2220; fax: +61 8 6488 1108. E-mail addresses: natasha.teakle@uwa.edu.au (N.L. Teakle), bowmas@live.com.au (S. Bowman), ed.barrett-lennard@agric.wa.gov.au (E.G. Barrett-Lennard), daniel.real@agric.wa.gov.au (D. Real), timothy.colmer@uwa.edu.au (T.D. Colmer). 2002; Smedema and Shiati, 2002; Rengasamy et al., 2003; Bennett et al., 2009). Salinity and waterlogging interact adversely to reduce production of crops and pastures, as very few species used in agriculture can tolerate the combination of both stresses (Barrett- Lennard, 2003). Annual pasture legumes are particularly sensitive to combined salinity and waterlogging (Bennett et al., 2009); there- fore saline soils in regions of the world with Mediterranean climates are often nitrogen deficient and pasture production on such land can be very limited (Mara ˜ nón et al., 1989; Bordeleau and Prévost, 1994; Zahran, 1999; Rogers et al., 2005; Bennett et al., 2009). New pasture legumes are needed for saline land, as few species can tolerate the combined stresses of salinity and waterlog- ging (Barrett-Lennard, 2003; Bennett et al., 2009). Species with moderate tolerance to salinity or waterlogging include Trifolium michelianum Savi. (balansa clover) and Medicago polymorpha L. (burr medic). Field and glasshouse experiments have demonstrated that T. michelianum is tolerant to waterlogging, but only has low to 0098-8472/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2011.11.020