INFLUENCE OF AMMONIA IN NUTRIENT SOLUTION ON GROWTH AND METABOLISM OF CUCUMBER PLANTS

Shoot yield of cucumber plants grown 18 days in nutrient solution with 0.06 m M NH3 was decreased. Root yield was diminished at 0.09 m M NH3 The ammonia treatment caused heavy chlorosis increasing with age of leaves. This chlorosis was not due to any nutrient deficiency. Ammonia also influenced the morphology of roots. They were clearly shorter caused by a much smaller size of root cells. The decrease of yield was linked to a reduction of assimilation occurring not only after a long influence of ammonia lasting 14 days, but also within one hour after starting the NH3 treatment. The decline of assimilation was probably caused by a higher resistance of stomata against CO2 influx in leaf tissue as can be concluded from the observation that transpiration was decreased in the same way as assimilation. The effect of ammonia in nutrient solution could also be due to the occurrence of higher NH3 concentrations in leaf tissue, because both, pH of plant press sap as well as NH4 concentration of plant tissue, were increased. Furthermore, it is shown that the nitrate content of plant tissue was diminished by ammonia whereas ammonium and amide content were raised. Regulation of nitrate uptake of plants by means of ammonium and amide content of tissue is discussed. © 1979 Martinus Nijhoff.