The influence of NaCl salinity and hypoxia on aspects of growth in Trifolium species

The effects of salinity and hypoxia on growth, nutritive value, and ion relations were evaluated in 38 species of Trifolium and 3 check legume species (Trifolium fragiferum, Trifolium michelianum, and Medicago sativa) under glasshouse conditions, with the aim of identifying species that may be suitable for saline and/or waterlogged conditions. In the first set of experiments, plants were grown hydroponically at four NaCl concentrations (0, 40, 80, and 160mM NaCl) and harvested after exposure to these treatments for 4 weeks. NaCI concentrations up to 160mM reduced dry matter production in most species; however, there were differences in salt tolerance among species, with T. argutum, T. diffusum, T. hybridum, and T. ornithopodioides performing well under the saline conditions (dry matter production was reduced by less than 20%). Concentrations of Na + and Cl - in the shoots increased with increasing salinity levels, and species again differed in their capacity to limit the uptake of these ions. Dry matter digestibility at 0 mM ranged from 49.8% (T. palaestinum) to 74.0% (T. vesiculosum) and decreased with increasing NaCI concentrations. A second set of experiments evaluated the tolerance of Trifolium species to hypoxic conditions in the glasshouse. Shoot growth, and to a lesser extent root growth, were reduced in all Trifolium species when plants were exposed to stagnant, non-aerated conditions for 28 days, but T. michelianum, T. resupinatum, T. squamosum, T. nigrescens, T. ornithopodioides, T. salmoneum, and T. fragiferum were the least affected species. All species acclimated to the oxygen-depleted conditions by increasing the gas-filled porosity in the roots. This study has provided information that will assist in the identification of forage species for saline and/or waterlogged areas.