Abundance of endomycorrhizas and root-surface microorganisms on three grasses grown separately and in mixtures

Three grasses of acid, infertile soils,Agrostis tenuis, Deschampsia flexuosa and Festuca ovina were grown in pots separately and in two-species mixtures. After 8 months the abundance of internal mycorrhizal infection and of bacteria and fungi on the root surfaces was determined by microscopic examination of stained root segments.Abundance of bacteria, fungi and mycorrhizas all differed between “host” species. Abundance of bacteria was not affected by which other grass species (“partner”) was present, but fungal abundance was consistently lowest when the partner species was Agrostis and highest when it was Festuca. As a result, in two-species mixtures fungal abundance was always intermediate between the two corresponding monoculture values. Mycorrhizal infection was also influenced by the partner species, but in a less regular manner.