The role of arbuscular mycorrhizal fungi in the transfer of nutrients between white clover and perennial ryegrass

A glasshouse experiment was conducted in which N-15 was used as a tracer ap plied as ((NH4)-N-15)(2)SO4 to donor plants of white clover and perennial r yegrass. Nitrogen transfer via hyphae of arbuscular mycorrhizal fungi (AMF) or by other routes was studied by separating the root systems of the two p lant species, as donors and receivers, when growing in the same pot, with s elective mesh barriers of varying pore sizes in the presence and absence of AMF. Inoculation with AMF increased DM production and nitrogen (N) yield o f clover plants. Transfer of N-15 occurred between white clover and grass p lants but was independent of AMF. Pore size of the mesh barriers controlled the degree of N-15 enrichment in the grass, suggesting that transfer was m ediated by mass flow and/or diffusion. Additional experiments showed that g rass roots could pass through pores of 60-mu m diameter, and hyphal links c ould not be detected by autoradiography, thus supporting the conclusions of the tracer experiment. (C) 2000 Elsevier Science Ltd. All rights reserved.