Micro-organisms can make a considerable contribution to the apparent absorption of inorganic nutrients by excised roots. The microbial component of uptake has been studied by comparing the absorption of phosphate and rubidium by seedling roots of barley grown prior to excision under sterile and non-sterile conditions.
Although relative to the quantities taken up by sterile roots more phosphate than rubidium was absorbed by micro-organisms, for both ions over the range 0.001-1.0 mM, the relationship between absorption and increasing external concentration followed the kinetics of a first order reversible reaction. No simple kinetic relationship could, however, be derived to describe the uptake of either phosphate or rubidium by the roots.
The significance of these findings is considered in the light of the postulate, derived from experiments under non-sterile conditions, that the absorption of ions by roots is mediated by two distinct‘carrier’mechanisms, one of which dominates at low and the other at high external concentrations. It is concluded that experiments designed to investigate the nature of the uptake process should be carried out under sterile conditions.