Diurnal Changes in Volume and Solute Transport Coefficients of Phaseolus Roots

Volume (J(v)) and solute (J(s)) fluxes through Phaseolus root systems were observed over a 24-hour period. The volume flux was varied in a pressure chamber by altering the hydrostatic pressure in 10 steps, from 0 to 0.41 megapascals. All root systems showed strong diurnal peaks in volume flux. The five transport coefficients (sigma, omega, J(s) (*), L(p), and pi(*)) were estimated from a nonlinear least squares algorithm. Analysis of the data revealed that all the coefficients exhibited a diurnal rhythm. When the total differential of the volume flux was considered it was possible to show that the diurnal changes in volume flux were due to a complex interaction between the diurnally shifting coefficients with the role of each highly dependent on the level of volume flux. At low volume fluxes, omega, J(s) (*), and pi(*) accounted for nearly all the diurnal change in volume flux. At high volume fluxes, however, the major influence shifted to L(p) and pi(*), while omega and J(s) (*) became relatively unimportant. Thus, pi(*) was the only coefficient of interest across the entire range of J(v) and appeared to be the single most important one in determining the diurnal rhythm of J(v) under conditions of a constant applied pressure.