Preferential utilization of organic and inorganic sources of phosphorus by wheat plant

Abstract

On soils of low P supply organic P (Po) makes up a similar or even larger part in soil solution thaninorganic P (Pi). The ability of wheat (Triticum aestivum L., cv. Star) plants to hydrolyze and absorbthis Po in comparison to similar concentrations of Pi was studied. Four concentration levels of Pi andPo were obtained by extracting two soils with deionized water in a ratio of 1:1 and concentrating theresulting filtrate by freeze drying to different degrees. The concentration of Pi varied between 5 and36 lM and Po between 3 and 22 lM. Wheat seedlings were grown in these solutions for 12 and 24 hand acid and alkaline phosphatase activity determined. The reduction of Po concentration in solutionexpressed on a root length basis gave the rate of Po hydrolysis and the reduction in concentration of Piand Po gave the P inflow into the roots. No alkaline phosphatase activity was detected. The activity ofwheat root acid phosphatase increased with Po concentration in solution. Phosphorus uptake was 2 to 6fold higher from Pi than from Po at similar concentrations of both. The rate of uptake from Pi, theinflow, as well as the rate of hydrolysis of Po increased linearly with concentration but at similar con-centration the inflow was 2 to 4 times higher than the rate of Po hydrolysis. Results suggest that plantscan utilize Po after hydrolysis by phosphatase, but Pi is more important and preferentially used byplants; Po may be essential for plant nutrition especially in high P-fixing soils.