POTASSIUM AND PHOSPHATE-UPTAKE OF CUCUMBER PLANTS AT DIFFERENT AMMONIA SUPPLY

Experiments on cucumber plants grown in nutrient solution were conducted in order to study long and short time effects of ammonia on growth, nutrient element uptake and respiration of roots. Shoot yield and potassium concentration in tissue of plants treated 18 days with varied ammonia concentration were decreased. However, it was not assumed that K deficiency caused the yield reduction. The ammonia effect on K content was more pronounced in roots than in shoots. The decreased K concentration of plant tissue was linked to a diminished ability of plant roots to absorb potassium. The maximum rate of potassium uptake was lowered by ammonia during both, long- and short-time treatment. The results indicated that the NH3 influence on potassium uptake was due to effects on metabolism and permeability of roots because changes of K uptake rate occurred immediately after starting the NH3 treatment. Furthermore, it is shown that ammonia inhibited respiration of roots. During the short-time treatment net potassium efflux of roots was observed at higher NH3 concentrations. The extent of K efflux depended on K concentration of both, root tissue and nutrient solution. Pretreating the plants for 12 hours with ammonia also resulted a decline in K uptake rate. However, plant roots subjected to ammonia concentrations up to 0.09 m M completely recovered during 24 hours after removing the NH3 treatment whereas at higher NH3 concentrations only a partial recovery occurred. Furthermore, it was shown that ammonia also influenced P uptake by plant roots. © 1979 Martinus Nijhoff.