Resistance to water movement through wheat root systems

Abstract

A three-layer electrical analogue model was used to calculate resistance to water movement through the roots of wheat plants growing in small weighing lysimeters. In one experiment the wheat was grown in two soil types; in a second experiment one soil type was used but different root systems were induced by controlling the water table before the start of the experimental period. Resistance calculations were based on hourly measurements of transpiration rate, leaf water potential and water uptake from three soil layers (qi), calculated from measurements of soil water potential at three depths. The number of main roots per stem (required for the model) and root surface area in each layer (Ai) were obtained from measurements of root lengths and diameters in soil cores taken at the end of each experiment. Estimates of the resistance to flow through stems led to estimates of ψ0), the water potential at the stem base, at any stem flow rate. Axial (main) root resistances (Rxi) were calculated from the Poiseuille equation. Values of the resistance to water movement through the roots in layer i were calculated from the set of equations describing uptake from each layer in terms of flow rates, potential gradients and resistances; these values, inserted in the solution for 1/10 from the set of three equations, yielded total root resistances (RT) and estimates of the effective soil moisture potential (^ψs) for the whole profile. (RT) ranged from 63.9 to 627.3 bar sec mm-3 (cf. stem resistance between 24 and 70 bar sec mm-3) and was inversely related to flow rate through the main roots, which indicated a constant potential drop (^ψs – ψ0) of about 10 bars, irrespective of soil type or root system. Radial root resistances, estimated as At(<ψsi – ψ0)/qi, ranged from 4.6 x 104 to 4.2 x 106 bar sec mm-l and were inversely related to qi. Inaccuracies in estimates of Rxi do not affect the results much and the model used is potentially valuable as a framework for field research.

Comparison of Root System Development in Two Rice Cultivars During Stress Recovery from Drought and the Plant Traits for Drought Resistance

“…Another possible explanation why the two cultivars differed in ET rate is the difference in water transport. Differences in water transport efficiency among species and cultivars may arise due to differences in root resistance to water transport (Seaton and Landsberg, 1978).…”

Water uptake and transport of soybeans as a function of rooting patterns

“…A quick examination shows that D's are close to 1.0 when the axial resistances are comparatively smaller than the radial resistances. For the case n=3, the solution is identical with that of Seaton and Landsberg (1978).…”

Leaf Water Potential of Weeds and Rice (Oryza sativa)

“…Presently, there is still a controversy as to where the largest resistances lie. Differences in the efficiency of water transport among species and cultivars may be due to differences in root resistance to water transport because roots offer the highest resistance to water flux through the plant (15). Large resistances in wheat (Triticum aestiuum L. 'Heron').…”