Fluxes of P and Ca into intact corn roots and their dependence on solution concentration and root age

Fluxes of Ca and P through intact corn roots growing in flowing, well stirred nutrient solutions, were determined. The flux of Ca increased linearily when the Ca concentration in the nutrient solution was raised up to 250 ppm Ca. An increase in the P concentration from 0.02 ppm to 0.4 ppm P resulted in a higher Ca flux at each Ca concentration. A P concentration of about 0.15 ppm was found to be the saturation concentration above which the P flux through the roots increased only slightly. A Ca concentration range of 100 to 200 ppm had no apparent effect on the P flux. The flux through a certain unit of root surface area for both Ca and P dropped to nearly zero after 150 hours of active absorption. It is suggested that this is connected with the decrease in the specific surface area of the root with age, which is proposed to be due to the suberization which was observed microscopically.