EFFICIENCY OF VAM HYPHAE IN UTILIZATION OF ORGANIC PHOSPHORUS BY WHEAT PLANTS

In a pot experiment wheat (Triticum aestivum L.) was grown under axeni c conditions in two soils differing in organic matter and phosphorus c ontents. The pots were separated by 30 mu m nylon nets and a 0.45 mu m membrane into five compartments, a central one for root growth, two a djacent to the central compartment for hyphal growth and two outer one s for control. The treatments consisted of sterilized Soil, supply of organic (Na-phytate) or inorganic phosphorus (P) and of soil either no n-inoculated or inoculated with Glomus mosseae. Shoot dry weight incre ased 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 VA -mycorrhizal hyphae throughout the hyphal compartment (15 mm). The max imum depletion was 106 mg kg(-1) soil within a 0.5 mm distance from th e root surface. The depletion of organic P depended on the soil type, hyphal length density, phosphatase activities and the amount, of organ ic P present in the system. The maximum hyphal contribution to the hyd rolysis 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 concentrati on of K in the mycorrhizal plants was observed only in the presence of organic P. Calcium and Mg concentrations were not affected by mycorrh izal inoculation. The results obtained clearly demonstrated that VA-my corrhizal phosphatase is effective in the hydrolysis of Wa-phytate and confirmed the important direct contribution of VAM hyphae to plant P, Cu, and Zn nutrition.