LIQUID ION-EXCHANGER MICROELECTRODES USED TO STUDY SOIL SOLUTE CONCENTRATIONS NEAR PLANT-ROOTS

A technique for using Na+ liquid ion exchanger (Na+-LIX) microelectrodes to accurately measure, repetitively, and in a nondestructive fashion, Na+ concentrations in the soil solution at single points is described. The method has been used to examine solute (NaCl) accumulation in proximity to single roots of lupine (Lupinus angustifolius L.) and radish (Raphanus sativus L.) plants subjected to two levels of transpirational demand and five soil solute concentrations. The results obtained indicate that, at soil water contents corresponding to matric water potentials > -140 kPa, back diffusion of solute significantly counteracts the tendency for solute accumulation at root surfaces during transpiration.