Mineral nutrition in the tripartite interaction between <i>Frankia</i>, <i>Glomus</i> and <i>Alnus</i> at different soil phosphorus regimes

SUMMARY Phosphate uptake by a tripartite association involving Frankia, Glomus and Alnus was studied in containerized seedlings of Alnus nepalensis D. Don. The response of non‐mycorrhizal plants to P fertilization was more pronounced than their mycorrhizal counterparts. The yield of nodulated mycorrhizal plants was greater at low than at high P doses. At the highest P application, however, reduction in nodulation as well as nitrogenase activity was observed. Mycorrhizal infection was reduced by phosphate application, but markedly stimulated nodulation in Alnus seedlings. The nitrogen content of the nodule was higher than that of the shoot of nodulated mycorrhizal plants. Nodule dry weight, nitrogenase activity and nodule nitrogen content increased with increase in P application up to quantities typical of those in soil, after which it declined.