Uptake of Organic Phosphorus by ArbuscularMycorrhizal Red Clover

The capacities of two arbuscular mycorrhizal (AM) fungi, Glomus mosseae and Glomus versderme, tomineralize added organic P were studied in a sterilized calcareous soil. Mycorrhizal (inoculated with eitherof the AM fungi) and non-mycorrhizal red clover (Trghlium pmtense L.) plants were grown for eight weeksin pots with upper root, central hyphal and lower soil compartments. The hyphal and soil compartmentsreceived either organic P (as Na-phytate) or inorganic P (as KH2PO4) at tbe rate of 50 mg P kg-1. No P wasadded to the root compartments. Control pots received no added P. Yields were higher in mycorrhizal than innon-mycorrhizal clover. Mycorrhizal inoculation doubled shoot P concentration and more than doubled totalP uptake of plaflts in P-amended soil, irrespective of the form of applied P. The mycorrhizal contributionto inorganic P uptake was 80% or 76% in plants inoculated with G. mosseae or G. verefforme, respectively.Corresponding va1ues were 74% and 82% when Na-phytate was applied. In the root compartments of themycorrhizal treatments, the proportion of root length infected, hyphal length density and phosphatase activitywere all higher when organic P was applied than when inorganic P was added.