Effects of neutral salt and alkali on ion distributions in the roots, shoots, and leaves of two alfalfa cultivars with differing degrees of salt tolerance
The effects of neutral salt and alkali on the ion distribution were investigated in two alfalfa (Medicago sativa L.) cultivars, including Zhongmu 1, a high salt-tolerant cultivar, and Algonquin, a low salt-tolerant cultivar. The alkali stress expressed more serious growth inhibition than the neutral salt stress at the same Na+ concentration. Compared with Algonquin, Zhongmu 1 did not exhibit a higher alkali tolerance under the Na2CO3-NaHCO3 treatment with the low Na+ concentration (50 mmol L−1). The alkali increased the accumulation of Na+, Ca2+, and Mg2+ in the root and changed the Ca2+ and Mg2+ balance in the entire alfalfa plant. The salt and alkali stresses decreased the K+ and Fe3+ contents of the roots and leaves, the root Mn2+ content, and the shoot Zn2+ content, but they increased the Fe3+ accumulation of the shoots, the shoot and leaf Cu2+ contents, and the leaf Zn2+ content in both alfalfa cultivars. Based on the results obtained under the conditions of this experiment, we found that the salt and alkali stresses reduced the plant growth in both alfalfa cultivars, while the alkali caused a stronger stress than the neutral salt in alfalfa. Thus, we conclude that under hydroponic conditions, the deleterious effects of the alkali on plants are due to the distribution change of some trophic ion balance in the roots, shoots, and leaves of the plants by causing of Na+, CO32−, and/or HCO3− stresses.
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