Department of Plant Sciences

Groundnut and maize differ in their P-uptake efficiency. To investigate the reasons for this difference, groundnut and maize were grown in a flowing nutrient solution culture at constant P-concentrations of 0.2, 1 and 100 μM. To study the changes in plant growth and P-uptake with plant age and to calculate P-influx, four harvests were made. Phosphorus uptake kinetics of the roots, i.e. maximum influx, Michaelis constant and minimum soil solution concentration were estimated based on the rate of P-depletion from solution. At 1μM P, maize was more P-efficient producing up to 90% of its maximum yield as compared to groundnut with only 20% of maximum yield. A 3-times higher P-uptake was the reason for maize P-efficiency. In contrast, for groundnut at 1μM P, a net P-efflux was observed at some stages indicating a much higher P-requirement at root surface for maximum growth. Maize had a 6-times higher maximum influx and a 2-times higher Michaelis constant as compared to groundnut. The higher influx of maize was mainly because of higher Michaelis constant. Maize previously grown at low P-concentrations had a minimum soil solution concentration of 0.1μM, while groundnut had 0.2 and 0.6 μM. Furthermore, groundnut previously grown at 100μM was not able to absorb P even at 40μM. Acclimation to low P-concentrations in solution by increasing maximum influx or decreasing Michaelis constant was not evident in this study. Differences in P-uptake efficiency between groundnut and maize were mainly because of differences in P-uptake kinetics and to a lesser extent to the size of the root system.