To investigate interaction effects of salinity and nitrogen on growth, mineral composition and salinity tolerance of LEMON SEEDLINGS, a greenhouse experiment with four sodium chloride concentrations (0, 250, 500 and 1000 mg kg soil) and four nitrogen levels (0, 50, 100, and 200 mg kg-1-1 soil ammonium sulfate) was carried out. Experiment was conducted in a completely randomized design with three replications. Sodium and chloride ions in plant tissues were increased to toxic levels with increase in salinity which resulted in a significant reduction of plant dry weight. Nitrogen consumption up to 100 mg kg soil increased plant dry weight. As the concentration of sodium chloride was increased, the improvement effect of nitrogen on plant growth was decreased. Although nitrogen had no considerable effect on sodium concentration in root and shoot, it made a decrease in chloride concentration in shoot and an increase in root concentration of this element. Salinity decreased essential nutrients concentration in plant shoot. Therefore, it can be concluded that adverse effect of salinity is to some extent due to reduction of required elements to suboptimal ranges in plant tissues. -1 Nitrogen improved the adverse effects of salinity on plant nutrients by increasing their concentration in plant tissues. Therefore it can be inferred that part of the ameliorative effects of nitrogen on salinity adverse effects is related to the maintenance of essential nutrient concentrations in plant tissues. The results of the present study indicate that nitrogen can be applied in amounts higher than optimal level to reduce the harmful effects of salinity.

The impact of different concentration of zinc (Zn) and boron (B) on growth and mineral composition of LEMON SEEDLINGS (Citrus Aurantifolia L.) was studied under greenhouse conditions. We used five concentration levels of B (0, 2.5, 5, 10 and 20 mg g-1 soil) and three of Zn (0, 5 and 10 mg g-1 soil). Fresh and dry plant weights of the control treatment were strongly decreased with B levels higher than 5 mg g-1 of soil. In above mentioned B levels, LEMON SEEDLINGS displayed slight to severe B toxicity symptoms. Zn treatments reduced B accumulation and the associated inhibitory effect on plant growth. Increased B level in soils enhanced the concentration of B in plant shoots to a greater extent in the absence of applied Zn. The effectiveness of Zn for the reduction of B accumulation and toxicity decreased as the level of applied B was increased. In a comparison of Zndeficient and Zn-treated soils, plant root and shoot analysis for B indicated an increased transport of B in the absence of Zn. The best plant production was achieved when 2.5 and 10 mg g-1 soil of B and Zn were applied simultaneously. This combination was associated with the highest uptake of Zn, nitrogen (N), phosphorous (P), potassium (K), iron (Fe), manganese (Mn) and copper (Cu), suggesting that the combination resulted to a suitable condition in which plants had a well-balanced nutritional status. While B application increased nutrients accumulation in plant shoot, the role of Zn was a dilution effect or antagonistic relationship. The results of this study indicated that supplemental Zn has potential and practical importance in the control of B absorption and toxicity in soil where plants are grown under Zn deficiency and B toxicity.