Abstract
Several investigations were carried out to elucidate the effects of high salt concentrations and osmotic pressure of rooting medium on the growth, water uptake and osmotic pressure of root sap of cucumber seedlings in water and sand cultures.
In addition, the specific difference in ability to stand the high salt concentrations was examined using cucumber, eggplant, tomato and peper plants grown in gravel cultures as test plants.
The results obtained may be summarized as follows:
Growth of cucumber seedlings was significantly suppressed when grown in rooting media of both KNO3 solutions and balanced nutrient solutions at the osmotic pressure of 2.5 to 3.0atm, and it was severely depressed when the osmotic pressure of both solution was raised to 4.0 to 4.5atm.
In an experiment where cucumbers were grown for several days in growth media to which polyethylene glycol added to change its osmotic pressure without any change in nutrient concentrations, depression of growth occurred, and transpiration rate was decreased at the osmotic pressure of higher than 1.8atm. Osmotic pressure of root sap of cucumber plants grown in 2.4atm pressure medium was about 2atm higher than the one of those grown in the standard medium of 0.6atm pressure.
In another experiment, adaptation of cucumber plants to high osmotic pressure of growth medium was observed, when it was raised stepwise from 0.6 through 1.8 and 3.0 to 4.2atm at two day intervals with polyethylene glycol and by increasing the concentration of valanced nutrient solutions respectively. This phenomenom was more remarkable when polyethylene glycol was used to increase the osmotic pressure.
Cucumbers were the most sensitive to high salt concentrations, followed by tomatoes. Eggplants and peppers showed higher ability to tolerate them.
