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.