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Effects of salinisation of soil on emergence, growth, and physiological attributes of seedlings of the date palm (Phoenix dactylifera) 'Rati' (Palmaceae) were studied. A mixture of chlorides and sulfates of Na, K, Ca, and Mg was added to the soil and salinity was maintained at 4.3, 6.0, 8.2, 10.5, 12.8, and 14.6 dS m -1 . A negative relationship between percentage seed germination and salt concentration was obtained. Seedlings did not emerge when soil salinity exceeded 12.8 dS m -1 . Results suggested that this species is salt tolerant at the seed germination stage. Seedlings survived and grew up to a soil salinity of 12.8 dS m -1 and evidently this species is salt tolerant at the seedling stage as well. Elongation of stem and root was retarded by increasing salt stress. However, this species has a tendency for rapid root penetration and roots are able to extract water from dry saline soil (6.0% moisture) below the permanent wilting percentage. Among the tissues, young roots and leaf tissue were most tolerant, whereas stem tissue was most sensitive to salt stress. This species is a halophyte and adapted to salt stress conditions by the evolution of an osmoregulation mechanism. However, osmoregulation is effective for salt tolerance only to a limited range in the continuum of salt stress. The ability of this plant to thrive in dry regions is further conferred by the xeromorphic features of its leaves.

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Greenhouse experiments were conducted to assess the effects of salinization of soil on emergence, seedling growth, and mineral accumulation of Prosopis cineraria (Linn.) Druce (Mimosaceae). A mixture of chlorides and sulfates of sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg) was added to the soil and salinity was maintained at 5.1, 7.2, 9.3, 11.5, and 13.3 dS m −1 . A negative relationship between seedling emergence and salt concentration was obtained. Seedlings did not emerge when soil salinity exceeded 11.5 dS m −1 . Results suggested that this tree species is salt tolerant at seed germination and seedling stages. Elongation of stem and root was retarded by increasing salt stress. Young roots and stem were most tolerant to salt stress, followed by old roots and leaves. Leaf tissue exhibited maximum reduction in dry-mass production in response to increasing salt stress. However, production of young roots and death of old roots were found to be continuous and plants apparently use this process as an avoidance mechanism to remove excess ions and delay onset of ion accumulation in this tissue. Plants accumulated Na in roots and were able to regulate transfer of Na ions to leaves. Stem tissues were a barrier for translocation of Na from root to leaf. Moreover, K decreased in root tissues with increased salinization. Nitrogen (N) content significantly (P < 0.01) decreased in all tissues (leaf, stem, and root) in response to low water treatment and salinization of soil. Phosphorus (P) content significantly (P < 0.01) decreased while Ca increased in leaves as soil salinity increased. Changes in elements-accumulation patterns and the possible mechanisms for avoidance of Na toxicity in tissues and organism level are discussed.

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