RELATIONSHIPS BETWEEN ROOT-SYSTEM WATER TRANSPORT PROPERTIES AND PLANT SIZE IN PHASEOLUS

Root system hydraulic conductivity (Lp) was measured on Phaseolus [cv. Ouray] plants of different ages and sizes. Lp changed in a complex manner depending on plant size. As the plants increased in size, Lp increased initially then gradually decreased followed by a final modest increase. Values for Lp ranged between 0.8 .times. 10-6 and 6.1 .times. 10-6 cm/s 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 (LR), and plant size were also examined. Values for QPL3 varied with plant size, somewhat like Lp. LR values continuously increased with plant size at rates which depended on the growth rate of the root surface area as well as Lp. Comparison of data with the root conductivity constant (kr) of Taylor and Klepper showed good agreement. The observations on Phaseolus were also confirmed for Glycine max cv. Ransom. Values for Lp and kr of both species were within the same range.