Abstract: | Resistances to the flow of water through young potted appletrees were estimated by measuring the transpiration rate oftrees with and without root systems. Root system resistanceswere obtained by difference. Whole-plant resistances were ofthe order 10 x 1013 Pa s m3 and there was some evidencethat root resistances (Rr) varied with transpiration rate; theratio Rr:Rx (where Rx is resistance to water flow in the stemsystem) altered from 2:1 at relatively high transpiration ratesto 1:1 at lower rates. The trunk of a 9-year-old orchard tree (trunk diameter {smalltilde}7 cm, height {small tilde}2.5 m) was cut under water andestimates of the flow resistances in this tree were obtained.These were much lower than the resistances to flow in the pottedtrees. Capacitance (defined as the change in stored water content perunit change in plant water potential) values were calculatedfor the small trees and the large tree from measurements ofweight and water potential changes after the trees were removedfrom water. They were very similar on a weight basis (approx.2.0 x 108 kg kg1 Pa1). Leaf capacitancevalues ({small tilde}1 x 108 kg Pa1 m2)were also obtained. Stomatal conductances decreased with water potential and increasedwith short-wave radiation, but the relationships were not definitive.Estimates of boundary layer conductance in a greenhouse (verylow wind speeds) were of the same order ({small tilde}5 mm s1)as values obtained previously. |