Mineralization of organic phosphorus by vesicular-arbuscular mycorrhizal fungi

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