ION COMPARTMENTATION IN SALINITY-STRESSED ALFALFA SEEDLINGS GROWING UNDER DIFFERENT TEMPERATURE REGIMES

The compartmentation of ions in salinity-stressed 6-week-old alfalfa s eedlings was investigated in two cultivars, Batini (moderately salinit y tolerant) and Hunter River (salinity sensitive). Both cultivars were grown under field conditions during the cool season (20-25 degrees C) and the warm season (35-46 degrees C). Two saline solutions (6.4 and 12.2 dS m(-1)) were prepared by dissolving the required quantity of Na Cl in half-strength Hoagland solution. Tap water (0.8 dS m(-1)) served as control. Plants were irrigated twice a week with saline solutions, commencing 3 weeks after seedling emergence. The seedlings were separ ated into leaf(including petiole), stem, and root after 6 weeks of gro wth and analysed for phosphorus (P), potassium (K), calcium (Ca), magn esium (Mg), sodium (Na), chloride (Cl), and micronutrients [copper (Cu ), boron (B), zinc (Zn), manganese (Mn), and iron (Fe)]. The concentra tion of P and K in the plant tissue increased with increase in tempera ture, while Ca and Mg concentrations were depressed. Increase in salin ity, in general, resulted in decreased accumulation of all ions, inclu ding micronutrients. Hunter River maintained the same pattern of ion c ompartmentation (root<stem<leaf) for Na and Cl, whereas in Batini a di fferent pattern was obtained for Na (stem<leaf<root). Since the compar tmentation pattern of ions in Batini is different for Na and not Cl, i t appears that compartmentation of Na may be an important factor in sa lt tolerance.