The freezing tolerance of populations of the fodder species Atriplex halimus L. and Atriplex canescens (Pursh.) Nutt (Chenopodiaceae) from different locations in Algeria was investigated, in relation to plant provenance and leaf cation con- centrations. For two populations of A. halimus, the effect of increased soil salinity (addition of NaCl) on tolerance was determined. Tolerance was determined in leaf electrolyte leakage assays and by assessment of visual damage, after expo- sure to temperatures between -5 and -25ºC. There was significant correlation (P<0.005) between freezing tolerance and the leaf sap concentrations of Na and Na+K, tolerance being improved markedly by soil salinisation, but no relationship between tolerance and the soil salinity or minimum winter temperatures of the original sites of the populations. It is concluded that, for these halophytic species, the soil salinity (supply of ionic osmolytes) at cold-winter sites will be of great importance regarding the likely freezing damage.
The current findings, together with previous results, indicate that for A. halimus and A. canescens, soil salin- ity (i.e. the supply of ionic osmolytes) is an important factor determining freezing tolerance via its influence on tissue cation accumulation. This will be useful when selecting cold-winter sites suitable for plantations of these two species, of value for their fodder supply under semi-arid and/or saline conditions.