A comparison of the reaction to a localized supply of phosphate in Plantago major, Plantago lanceolata and Plantago media

Plantago major ssp. major, P. lanceolata and P. media have been compared with respect to their ability to adapt themselves to a localized availability of phosphate. The growth and phosphorus content of plants of the three species,were followed during 4-5 weeks in a divided-roots-experiment where at the start of the experiment about 25% of the root mass received a complete nutrient solution and the remaining roots a solution without phosphate. The dry matter production of the treated plant is slightly depressed in P. major but unaffected in P. lanceolata and P. media. In all species the P-supplied roots of the treated plant show a stimulated relative growth rate and a stimulated rate of P-uptake. These stimulations are smallest in P. major which also shows the lowest rate of P-uptake in control plants uniformly supplied with a complete nutrient solution. These facts point to the need for a more uniform supply of phosphate to the root system of P. major relative to P. lanceolata and P. media, correlating well with the nutrient-rich habitat of P. major. The stimulated rate of uptake of phosphate after localization of the P-supply appears to be correlated with (a) lower P-concentration in the shoot, (b) lower P-concentration in the phloem and (c) lower concentration of inorganic phosphate in the root.