The deleterious effects of salinity on plant growth are attributed to a decrease in osmotic potential of the growing medium, specific ion toxicity and nutrient ion deficiency (Greenway and Munns 1980). The extent of plant growth depression under saline conditions varies with salt composition, salt concentration, the physiological stage of the plant when it is exposed to salinity, and the plant species (Sharma 1983).Inhibition of seed germination by salinity has been attributed to osmotic effects in barley cultivars (Bliss et al. 1986). Other studies with cereals suggest that salinityinduced reductions in germination and seedling growth are cau$ed by specific ion toxicity (Sharma 1983; Hampson and Simpson 1990a,b). The interaction of osmotic and specific ion effects may be significant, depending on plant species and the combination of cations and anions in a given salt (Redmann 1974;Ryan et al. 1975;Hardegree and Emmerich 1990

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Salinity-calcium interactions, which have been shown to be important in plants grown in dryland saline soils of the Canadian prairies, were studied in two species differing in salt tolerance. In solution culture, wheat showed a greater reduction in growth and a higher incidence of foliar Ca deficiency symptoms than barley when grown under M g S O 4 or Na2SO 4 plus M g S O 4 salt stress. Amendment of the saline solution with Ca to increase the Ca/(Na + Mg) ratio ameliorated the effects of salt, but more so in wheat than in barley. At least part of the difference in salt tolerance between the two species must therefore relate to species differences in the interaction of salinity and Ca nutrition. The greater response of wheat to Ca was not due to a lower Ca status in leaf tissue; on the contrary, although Ca amendments improved tissue Ca/(Na + Mg) ratios in both species, salinized wheat had equivalent or higher Ca content, and higher Ca/(Na + Mg) ratios than did barley. The higher Ca requirement of wheat is apparently specific to a saline situation; at low salinity, wheat growth was not reduced as extensively as that of barley as Ca/(Na + Mg) ratio was decreased. High night-time humidity dramatically improved wheat growth under saline conditions, but increasing the Ca concentration of the saline solution had no effect on growth in the high humidity treatment. Membrane leakage from leaf tissue of wheat grown under saline conditions was increased compared to tissue from non-saline plants. Plants grown in Ca-amended saline solutions showed no increase in membrane leakage. These results confirm the importance of Ca interaction with salinity stress, and indicate differences in species response.

Inhibition of seed germination in alfalfa varieties Rambler, Roamer, and Beaver by iso-osmotic potentials of different substrates varied widely. Sodium and potassium sulfate and sodium chloride were most inhibitory. Chlorides of potassium and magnesium and magnesium sulfate were least effective; mannitol and polyethylene glycol were intermediate. Ion toxicity was determined by measuring germination recovery after treatment with solutions containing equivalent weights of salt. No salts were toxic at 25 meq/liter. Sodium sulfate and magnesium chloride appeared highly toxic at 200 meq/liter; other salts were less toxic, with sodium chloride showing the least effect of all. All salts were highly toxic at 400 meq/liter. Germination recovery after treatment with polyethylene glycol and mannitol was good, clearly distinguishing osmotic and specific ion effects. Variety Beaver was the most tolerant of both the osmotic and toxic effects of salt.