Effects of salt stress on concentration of nitrogen, phosphorus, potassium, calcium, magnesium, and sodium in leaves, shoots, and roots of six olive cultivars

The effect of salt stress on the concentrations of nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) in the young and mature leaves, the shoots, and the roots of six major Greek olive cvs (Koroneiki, Mastoidis, Kalamon, Amphissis, Kothreiki, and Megaritiki) was investigated on self-rooted one-year-old plants. The treatments, consisting of 0, 25, 50, 100, and 200mM NaCl in half-strength Hoagland nutrient solution; were applied for five months. After the end of the experiment, destructive samples were collected and analyzed for N, P, K, Ca, Mg, and Na. In the no-NaCl controls, significant differences in the concentration of mineral elements in the tissues of the tested cultivars were found. The higher concentrations of mineral nutrients occurred in the roots and the lower ones in stems, with the only exception of N and in part of K (Koroneiki and Amphissis), where the lower values were found in the roots. Between cultivars, the differences in the concentration of mineral elements were more clear in the stems and to a lesser degree in the roots than in young or mature leaves. In salinized plants, over all cultivars and treatments, Na %d.m. in young leaves, mature leaves, shoot, and roots increased 14, 18, 11, and 6 times, respectively. In all cultivars, the higher Na %d.m., was recorded in the roots followed by shoots, mature, and young leaves with the exception of the salt sensitive Amphissis, which had the higher Na %d.m. (0.758 +/- 0.03) in mature leaves. Potassium percent dropped in all organs as a result of the saline treatments. The concentrations of root N, K, Ca, and Mg decreased in all cultivars while root P was not affected. Besides, the concentration of Na + K and the K/Na ratio dropped sharply in all tissues. Shoot N and P increased in all cvs, but in the salt tolerant Kalamon. Young leaves showed a tendency for lower N and P, but the drop in Ca and Mg was important and started at the first salinity level (25 mM NaCl) in all cvs. In mature leaves, N and P changes were cultivar dependent while Ca and Mg also dropped.