Arbuscular mycorrhizal colonization increases with host density in a heathland community

. The relationship is examined here between Nardus stricta root length colonized (RLC) by arbuscular mycorrhizal (AM) fungi (% RLC) and vegetation composition in a heathland community. . Two approaches were taken: a field survey of AM colonization of Nardus at two contrasting locations (Glen Clunie and Glen Shee, UK) in relation to vegetation composition; and an 11-month bioassay of AM inoculum potential in Calluna vulgaris and Nardus swards using uncolonized Nardus transplants. . In the field survey, % RLC of Nardus was positively related to Nardus density. This relationship was strongest in Glen Clunie, probably because overall colonization levels were lower at the more fertile Glen Shee site. In the bioassay, Nardus transplants within Calluna swards developed little or no AM colonization, whereas those within Nardus swards had a mean RLC of 23%. . This is the first report that degree of AM colonization is related to host density in the field. isolated Nardus plants in Calluna swards might be disadvantaged compared with Nardus plants in Nardus swards because of lower of AM colonization.