The effect of salinity on parameters of potassium and nitrate uptake of cotton

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Abstract
Salt damage to plants may be caused by competition in uptake between salt ions and nutritional ions. The effect of sodium chloride (NaCl) on nitrate (NO3), o‐phosphate (P), and potassium (K) uptake by cotton (Gossypium hirsutum L.) was measured. Plants were grown in nutrient cultures with added 0–450 mM NaCl for 41 days. Uptake of NO3, P, and K was measured according to their depletion in the solution with time, and measured root surface area. Net‐influx In in low external concentrations was assumed to obey the Hill equation: In =Imax.Cn/(Ka n+Cn), where C is concentration, Imax the value of In when C is infinite, Ka is the apparent Michaelis‐Menten coefficient, and n is the cooperativity index. The results showed a depression in Imax of K with increasing NaCl in the solution, accompanied by an increase in Ka and n. Nitrate Imax and n were not affected, but its Ka somewhat increased with NaCl concentration. All the three parameters for phosphate influx slightly increased in higher NaCl concentration. Mean influx of K and NO3 from relatively high concentrations increased with their concentration. Sodium chloride interfered with K uptake, at all K concentrations, but not to NO3 uptake rate. NaCl concentrations higher than 280 mM resulted in increased root radius and a sharp increase in influx of all the measured ions. It was concluded that the main salt disturbance to nutrient uptake in the measured cotton cultivar is by Na‐K competition, which indirectly affects NO3 uptake inhibition. A practical procedure is proposed to calculate uptake rate of saline ions by plants according to their amount in the plant and root growth.