PHOSPHATASE-ACTIVITY IN THE RHIZOSPHERE AND HYPHOSPHERE OF VA MYCORRHIZAL WHEAT SUPPLIED WITH INORGANIC AND ORGANIC PHOSPHORUS

To examine the phosphatase activity of vesicular arbuscular (VA) mycorrhizal fungi in the rhizosphere and hyphosphere, mycorrhizal and non-mycorrhizal wheat (Triticum aestivum L.) were grown for 60 days in two sterilized soils in pots with five compartments, a central one for root growth (rhizosphere) and two adjacent on both sides next to the root compartment for hyphal growth (hyphosphere) and an outer compartment on both sides where root and hyphae could not penetrate. Compartmentation was accomplished by a 30 mum nylon net or a 0.45 mum membrane, in the two types of compartment, respectively. All compartments received a uniform concentration of phosphorus (200 P mg kg-1 soil), either in organic (Na phytate) or inorganic [Ca(H2PO4)2] form. Plants were inoculated with Glomus mosseae (Nicol & Gerd) Gerd & Trappe or remained uninfected. In the root compartment acid phosphatase activity was much higher than alkaline phosphatase activity, and both were slightly enhanced by mycorrhizal infection. Throughout the hyphal compartment, phosphatase activities were distinctly higher in the presence of mycorrhizal plants particularly with a supply of organic P which also increased the percentage of infected root length. Phosphatase activity was strongly correlated with hyphal length which was highest within 10 mm from the root surface. Mycorrhizal inoculation increased plant dry weight. P content and total P uptake irrespectively of P sources and soils. Of the total P uptake mycorrhizal contribution accounted for 24 33% with P supplied in inorganic form, and 48-59% with P supplied in organic form. The results demonstrate a stimulatory effect of organic P in the form of phytate on mycorrhizal infection and hyphal growth as well as the efficient use of phytate-P by phosphatase of mycorrhizal hyphae.