Relationships between Root System Water Transport Properties and Plant Size in Phaseolus.

Root system hydraulic conductivity (L(P)) was measured on Phaseolus plants of different ages and sizes. Data analysis showed that L(P) changed in a complex manner depending on plant size. As the plants increased in size, L(P) increased initially then gradually decreased followed by a final modest increase. Values for L(P) ranged between 0.8 x 10(-6) and 6.1 x 10(-6) centimeter per second per bar. Relationships between the root flow per unit leaf area at a pressure differential of 3 bars (QPL(3)), as well as the total root system conductance (L(R)), and plant size were also examined. Values for QPL(3) varied with plant size, somewhat like L(P). L(R) values continuously increased with plant size at rates which depended on the growth rate of the root surface area as well as L(P). Comparison of our data with the root conductivity constant (k(r)) of Taylor and Klepper (1975 Soil Sci, 120: 57-67) showed good agreement. The observations on Phaseolus were also confirmed for Glycine. Values for L(P) and k(r) of both species were within the same range.