Table IV.

Comparison of the estimated values for various root water flow parameters from the concentric membrane model and the values measured with the root pressure probe

The L_r of roots with an average length of 120 mm was calculated from Equation 2, assuming that all of the root length, except 5 mm at the apex, was absorbing water and that all radial water flow occurred through the cell-to-cell flow path. The Lp_r was calculated from Equation 3 using the same assumptions. To compare the linear regressions between L_r and root length, the length of the concentric membranes was varied to coincide with the range of root length segments measured with the root pressure probe. n/a, Not applicable.

Parameter	Type of Value	Narrow-Leafed Lupin	Yellow Lupin	Wheat
Root diameter (μm)		1,537	1,050	660
No. of cell layers including endodermis		11	9	6
Lr for 120-mm-long root (m3 s−1 MPa−1 × 10−11)	Predicted	3.0	2.1	1.9
	Measured	3.4	2.3	2.5
Regression coefficient for Lr versus root length (m2 s−1 MPa−1 × 10−11)	Predicted	26.0	18.4	16.2
	Measured	43.3	19.2	0.68a
Root length when Lr = 0 (mm)	Predicted	5	5	5
	Measured	40.5	2.1	n/a
Lpr (m s−1 MPa−1 × 10−8)	Predicted	5.4	5.6	7.8
	Measured	6.0	5.9	10.6
P (predicted versus measured Lpr)		0.106	0.271	0.015
Reduction in Lpr after 50 μm HgCl2 (%)	Predicted	33	85	77
	Measured	10	14	41

^aRegression does not significantly deviate from zero (P = 0.937).