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Abstract
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Growth and yeild of plants in many parts of the world are limited by numerous biotic and abiotic environmental stresses. Salinity stress is one of the most important stresses and a decreasing factor in plant growth and production. Zeolite is a mineral with a high cation exchange capacity which is mainly consisted of aluminosilicate and can play a role in decreasing environmental stresses including salinity. Therefore, the present research has been conducted with the aim of investigating the effect of various zeolite levels on lettuce (Lactuca sativa) under salinity stress conditions in a soilless culture. The experiment was performed with a factorial method which included three factors of zeolite, salinity and varietiy (Shushan and Taftan) in a completely randomize design. After planting and settling the plants, salinity stress was applied at four to five-leaf stages, using NaCl in four concentrations of 0, 25, 50, and 75 mM along with nutrient solution. Zeolite was mixed with cocopite and perlite at different levels of 0, 5, 10, and 15% (V/V) and was used as part of the substrate. Morphological characteristics including leaf surface, number of leaves, chlorophyll index, wet weight and dry weights of shoots and roots were measured. Vitamin C, total protein, peroxidase, Proline, sodium, potassium, and phosphorus quantities of the leaves were measured. The results indicated that salinity stress leads into a decrease in all the morphological characteristics and also amount of chlorophyll index total and protein in the plant as well as the amount of nitrogen, phosphorus, potassium, calcium and magnesium of lettuce leaf. Moreover, by increasing the salinity, the amount of proline, vitamin C, peroxidase enzyme activity and sodium amount were increased in shoots. Use of zeolite in the substrate caused a decrease negative effect of salinity so that the maximum values of the mentioned growth characteristics and phosphorus and potassium values was related to 10% zeolite treat
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