SUMMARYThe intensity of vesicular-arbuscular mycorrhizal infection was assessed in the major vegetation types of east-central England. All of the most important species of grassland, scrub and woodland were mycorrhizal and each individual of any species normally carried a heavy VA infection. Members of the Gramineae were particularly heavily infected. In limestone grassland, infection extended to members of the Cyperaceae and Juncaceae. Infection levels were high throughout the year, the highest levels occurring in the most nutrient-stressed situations.Mycorrhiza develops soon after germination, often while seedlings are still in the cotyledon stage. Since numbers of viable Glomus type spores are low, infection is thought to arise from root to root contact rather than from spores. The ecological implications of the widespread infection are discussed.

SUMMARYThe effects of vesicular-arbuscular (VA) mycorrhizal association on the growth of Festuca ovina L. were assessed in soils sterilized by irradiation, in unsterilized soil, and in sand or sandpeat cultures with various nutrient additions.In irradiated soils, effects of mycorrhizal infection were masked by nutrient release which proceeded through the first 4 months of growth. However, 9 months after inoculation, significant increases of yield and phosphorus content occurred in the mycorrhizal plants. When the irradiated soil was recovered and re-used to grow a second crop, marked increases of yield and P content were observed in mycorrhizal plants. Growth in unsterilized field soil was very slow despite the fact that all the plants were heavily infected.In sand culture, mycorrhizal plants were not significantly larger than non-mycorrhizal controls when both were supplied with a full nutrient medium but differences between the two categories were evident when sand-peat mixtures were supplemented with dilute nutrient medium and water.The results are discussed in relation to the possible significance of mycorrhizal infection in the field.