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

A glasshouse experiment was conducted in which 15N was used as a tracer applied as (15NH4)2SO4 to donor plants of white clover and perennial ryegrass. Nitrogen transfer via hyphae of arbuscular mycorrhizal fungi (AMF) or by other routes was studied by separating the root systems of the two plant species, as donors and receivers, when growing in the same pot, with selective mesh barriers of varying pore sizes in the presence and absence of AMF. Inoculation with AMF increased DM production and nitrogen (N) yield of clover plants. Transfer of 15N occurred between white clover and grass plants but was independent of AMF. Pore size of the mesh barriers controlled the degree of 15N enrichment in the grass, suggesting that transfer was mediated by mass flow and/or diffusion. Additional experiments showed that grass roots could pass through pores of 60-microm diameter, and hyphal links could not be detected by autoradiography, thus supporting the conclusions of the tracer experiment.