The Effect of Soil Moisture and Rubidium Concentration on Diffusion and Uptake of Rubidium‐86

An autoradiographic technique was used to study the effect of soil moisture and Rb concentration on Rb 86 diffusion and uptake by corn plants. Changes in soil moisture influenced the rate of diffusion, rate of root elongation, and the incidence of root hairs. The self‐diffusion of Rb 86 was linearly correlated (R 2 = 0.89) positively with soil mositure, Rb concentration, and interaction of these two factors. The correlation of Rb 86 uptake from the soil was positively correlated with Rb 86 diffusion values approximated from measurements made of the depleted areas about the roots. When the root diameter used in the calculation included the length of the root hairs, the r 2 was 0.70 and when the root hairs were not included the r 2 was 0.56. The correlation of uptake with the values of Dp/b from self‐diffusion studies gave an r 2 of 0.99. Uptake by roots without root hairs was linearly correlated (r 2 = 0.98) with soil moisture, Rb concentration, and their interaction. Since the uptake relationships were similar whether or not the roots possessed root hairs, it was concluded that moisture's effect on rate of diffusion was of greater significance in its effect on Rb 86 uptake than was its effect on root hair incidence in these experiments.