Efficiency of VAM hyphae in utilisation of organic phosphorus by wheat plants

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Abstract
In a pot experiment wheat (Triticum aestivum L.) was grown under axenic conditions in two soils differing in organic matter and phosphorus contents. The pots were separated by 30 .urn nylon nets and a 0.45 .urn membrane into five compartments, a central one for root growth, two adjacent to the central compartment for hyphal growth and two outer ones for control. The treatments consisted of sterilized soil, supply of organic (Na-phytate) or inorganic phosphorus (P) and of soil either non-inoculated or inoculated with Glomus mosseae. Shoot dry weight increased by mycorrhizal inoculation in the range between 2.2 and 4.5 g pot−1 depending on the soil and treatment. Organic P was depleted by V A-mycorrhizal hyphae throughout the hyphal compartment (15 mm). The maximum depletion was 106 mg kg−1 soil within a 0.5 mm distance from the root surface. The depletion of organic P depended on the soil type, hyphal length density, phosphatase activities and the amount of organic P present in the system. The maximum hyphal contribution to the hydrolysis of organic P was concentrated in the zone within 3 mm from the root surface. In the mycorrhizal treatment, shoot concentrations of P, Cu, and Zn increased. In general, a slight decrease in the Mn and Fe concentrations was noticed. A significant increase in the concentration of K in the mycorrhizal plants was observed only in the presence of organic P. Calcium and Mg concentrations were not affected by mycorrhizal inoculation. The results obtained clearly demonstrated that V A-mycorrhizal phosphatase is effective in the hydrolysis of Na-phytate and confirmed the important direct contribution of VAM hyphae to plant P, Cu, and Zn nutrition.