Mineralization of organic phosphate by hyphal exudates of arbuscular mycorrhizal fungi

摘要

Increased phosphate uptake of plants by arbuscular mycorrhizal (AM) fungi is mainly due to the extension of external hyphae to soil. On the other hand, it is known that roots of some plant species release phosphatases into the soil and that they mineralize organic phosphate. In this study, we collected hyphal exudates of AM fungi in a compartmentalized pot culture and mulite ceramic tubes buried in the soil and clarified their ability to mineralize organic phosphate. Sterilized Andisol was packed in pots which were separated into root and hyphal compartments by a nylon net of 30 μm pore size. Seedlings of onion (Allium cepa L.) inoculated with AM fungi, Glomus versiforme or Gigaspora margarita were grown in a growth cabinet. Control pots were not inoculated. Mulite ceramic tubes were buried in the soil of each compartment before sowing and soil solution was collected when onion was colonized with AM fungi. Acid phosphatase activity in the solution was assayed.Onion plants were well colonized by both AM fungi. Adhesion of external hyphae to the surface of the tubes in both compartments were observed. AM colonization increased shoot phosphorus uptake and growth of onion. Acid phosphatase activity of soil solution collected from the hyphal and root compartments of inoculated plants was higher than that of uninoculated plants. Activity was different among fungal species. It is suggested that hyphal exudates can contribute to increased P uptake of mycorrhizal plants.