Nitrogen Fertilization Effect on Salt Tolerance of Fino 49 Lemon Trees Grafted on Two Contrasting Rootstocks

摘要

The influence of different nitrate concentrations in the nutrient solution on salt tolerance of two years-old Fino 49 lemons trees grafted on C. Macrophylla (Citrus Macrophylla wester, CM) or Sour orange (Citrus aurantium, SO) was investigated. Trees of Fino 49 lemon were watered during 12 weeks with 1/2 Hoagland nutrient solution containing 0 mmol/L NaCl (control treatment) or two salt treatments (50 mmol/L NaCl) contrasting in the nitrogen concentration in the nutrient solution; 1/2 Hoagland nutrient solution containing 7 mmol/L NO3- (S) or 1/2 Hoagland nutrient solution containing 14 mmol/L NO3-(S + N). At the end of the experiment, growth parameters, leaf mineral concentration, leaf water relation and leaf gas exchange were measured. Saline treatments reduced leaf growth similarly in trees on C. Macrophylla and Sour orange but trees on C. Macrophylla were more vigorous than trees on Sour orange regardless of salt treatment. Thus, based on the leaf dry weight, trees on C. Macrophylla had a higher salinity tolerance than those from Sour orange. On the other hand, trees on Sour orange had a lower leaf Cl- and Na+ concentration than those on C. Macrophylla. Additional nitrogen fertilization, S + N treatment, under saline condition decreased leaf Cl" concentration and increased leaf K + concentration relative to S treatment in trees on both rootstocks. However, salt tolerance was not improved with additional nitrogen fertilization as leaf growth reduction was similar in trees from S and S + N treatments. Leaf water potential was decreased by salt treatment but this reduction was higher in trees from N + S than those from S treatment. Thus, results above indicate that besides the Cl- and/or Na +ion toxicity, osmotic effect played an important role in the growth response of Fino 49 lemon to the salt stress. The gas exchange parameters, net assimilation of CO2 and stomatal conductance, were reduced in salinized trees relative to trees from control treatment, regardless salt treatment of rootstock.