A Bioassay for Comparing Phosphorus Availability in Soils

Publisher Website
Google Scholar
Abstract
A bioassay method, based on the uptake of 32P from 5 .times. 10-6 M phosphate solution during a 15 min period, was used to detect P deficiency in plants. The method was tested using birch (Betula verrucosa Ehrh.) and sycamore (Acer pseudoplatanus L.) seedlings grown in sand culture supplied with 1-100 .mu.g P ml-1, P deficient soils either unfertilized or fertilized (0.1 g P kg-1 soil), and a range of 25 soils varying from extremely deficient to adequate in available P content. There was a negative exponential relationship (r = 0.95) between P uptake by birch from the test solution and the concentration of P previously supplied in sand culture solution. Birch seedlings grown in fertilized soils took up less 32P from the bioassay solution than did those from unfertilized soils. Birch seedlings grown for 2 yr in phosphate-deficent soils took up greater amounts of 32P from the bioassay solution than did those grown in soils with adequate P. Eighty-two percent of the variation in P uptake by birch seedlings was accounted for by the extractable P content, the isotopically exchangeable P, the total P content and the phosphatase activity of the soils on which they were previously grown. Ninety-three percent of the variation was accounted for if the plant P content and the mycorrhizal development on roots systems were also included in the regression. The corresponding amounts of variation for sycamore seedlings, grown on the same soils, were 58 and 83%, respectively. The 32P uptake from the bioassay solution, by both sycamore and birch, was markedly inhibited by 5 .times. 10-3 M KCN in the bioassay solution, indicating that uptake was metabolically mediated. The results are discussed in relation to the study of P deficiency in plants, and P availability in soils.

This publication has 1 reference indexed in Scilit: