Bushra Alajoze(*) and Ghiath Alloush(1(
(1). Department of Soil and Water Sciences, Faculty of Agriculture, Tishreen University, Lattakia, Syria.
(*Corresponding Author, Bushra Alajoze: bushraa.alajoze@gmail.com)
Received: 12/09/2022 Accepted: 18/11/2022
Abstract:
A hydroponic experiment was conducted in a greenhouse during (April-May 2021) at Tishreen University (tomato, cv. Bestona F1) using Nutrient Culture System. The study included different (NO3–:NH4+) ratios (100:0, 75:25, 50:50, 25:75, 0:100). The experiment lasted for 24 days during which nutrient solutions were changed twice a week. At harvest, plants were separated into shoots and roots, and fresh samples were taken for measurements of nitrate reductase activity (NRA) both actual and potential). Subsamples of fresh roots were also taken for measurement of root length. The remaining shoots and roots were oven-dried and weighed. Total N and soluble NO3– and NH4+ in shoots and roots tissue were measured. N uptake values were used to calculate inflow (I, mg/m root length/day) and specific accumulation rate in the shoots (SAcR, mg/g shoot DM/day). The results have demonstrated that plants (100% NO3–) had better dry matter accumulation. Moreover, using the combination of 25:75 and 0:100 (NO3–:NH4+) decreased shoot dry matter by 36% and 75.5% respectively. The presence of 25% ammonium in the nutrient solution enhanced roots development reaching 260 m/plant, and was superior to (203-70 m/plant) in the 100% nitrate and 100% ammonium treatments, respectively. Nitrogen concentration ranged from 43-68 mg N/g DM in roots compared to 35-42 mg/g DM in the shoots. Nitrogen forms (NO3–:NH4+), and their ratios did not influence N translocation to the shoots (SAcR), which was consistent with Inflow rates. High free nitrate concentrations were in the in the shoots 100% nitrate treatment (1.25 mg NO3– -N/g DM), and decreased by 20% and 80% in the 25% and100% ammonium treatments, respectively. This may indicates that NO3- was not stored in the vacuoles. Nitrogen assimilation is an expression of nitrogen investments in biochemical processes in the plants, and may explain growth enhancement in NO3– -fed plants. NRA values were high in the roots of 100:0 (NO3–:NH4+) treatment, and decreases gradually with increasing NH4+ concentration in the nutrient solution up to 100% NH4+. Similarly, potential (NRA) was inhibited with increasing NH4+ in the nutrient solution, This is may be due to ammonium toxic to NR enzyme, or inhibition of formation of the enzyme in the presence of high NH4 concentrations..
Key words: Nutrient Culture, tomato, NO3 and NH4 nutrition, N uptake, N assimilation, Nitrate reductase enzyme.
Full paper in Arabic: pdf