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 × 10⁻⁶ and 6.1 × 10⁻⁶ centimeter per second per bar. Relationships between the root flow per unit leaf area at a pressure differential of 3 bars (QPL₃), as well as the total root system conductance (L_R), and plant size were also examined. Values for QPL₃ 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.