A Study of the Absorption and Utilization of Phosphate by Young Barley Plants

The effect of the external concentration on the distribution of phosphate absorbed by young barley plants was studied in experimental periods varying from 1 hour to 7days.The experimental were carried out in water culture with radioactive phosphorus as a tracer. The concentration of labelled phosphate supplied to the plants ranged from 0·0003 to over 30 p.p.m. P. When the external concentration of phosphate is reduced below 10 p.p.m. P, the proportion of the absorbed phosphate found in the shoots is markedly reduced. Plants which have been treated with low concentrations of phosphate lose recently absorbed phosphate to the outer medium when transferred to phosphate-free solutions. Plants treated with higher concentrations lose a smaller proportion of recently absorbed phosphate. Different balances of other nutrients do not affect the general relationship between the absorption and distribution of phosphate, though quantitative changes occur.It is concluded that the retention of phosphate in the roots induced by dilute media is a direct consequence of the small quantity of phosphate entering the roots and is not attributable to the effects of other ions which may be simultaneously absorbed.