MINERALIZATION OF ORGANIC PHOSPHORUS BY VESICULAR ARBUSCULAR MYCORRHIZAL FUNGI

The potential of the mycorrhizal fungus, Glomus etunicatum, to mineralize organic P was studied in an artificial growth medium amended with various organic P sources. Plant growth and P uptake by non-mycorrhizal plants was improved by glycerophosphate and AMP, but amendment with phytic acid, RNA, ATP or CMP did not affect plant growth. In contrast, mycorrhizal plants benefitted from amendment by each of the P sources. Growth and P uptake by mycorrhizal plants exceeded that by non-mycorrhizal plants for all P sources except AMP. In a subsequent study, organic P-32 (cytidine 3'- and 5'-diphosphate) was added to a sterilized prairie soil to compare uptake of P-32 by mycorrhizal and non-mycorrhizal plants. Uptake of P-32 from the organic P-32 source was 500- to 6000-fold higher in mycorrhizal plants than in non-mycorrhizal plants. Mycorrhizal plants were also larger and had greater total P uptake than non-mycorrhizal plants. Addition of soil microorganisms in the form of non-sterile sievings had no effect on dry weight of mycorrhizal or non-mycorrhizal plants at any P concentration, but significantly increased P uptake by mycorrhizal plants.