The Interaction between Osmotic- and Pressure-induced Water Flow in Plant Roots

Abstract

This paper presents a general model for coupled solute and water flow through plant roots based on the thermodynamics of irreversible processes. The model explains in a straight- forward manner such experimentally observed phenomena as changes in root resistance, increased solute flux, and apparent negative resistance, which have been reported for root systems under the influence of a hydrostatic pressure gradient. These apparent anomalies are explained on the basis of the inter- action between the osmotic and hydrostatic driving forces and the well known "sweeping away" or dilution effect. We show that with a constant hydraulic conductivity the only features necessary to explain these phenomena are some type of mem- brane or membranelike structure and a mechanism for actively accumulating solutes.