Below-ground distribution and persistence of an ectomycorrhizal fungus

In most studies, the distribution of the mycelia of ectomycorrhizal fungi in forest soils has been inferred from areas occupied by fruit bodies. Here, we investigated the below-ground spatio-temporal distribution of Hebeloma cylindrosporum by polymerase chain reaction quantification of a specific DNA sequence present in DNA extracted from soil. Soil samples were collected in a Pinus pinaster stand located in a campsite where fruit bodies of H. cylindrosporum had been mapped from 1990 to 2000. In samples collected underneath fruit bodies, DNA of H. cylindrosporum was always detected in large amounts. However, this DNA was often undetectable in the absence of fruit body even 1 yr after their disappearance. This result was supported by the failure to identify mycorrhizas of this species on seedlings planted in soil samples collected in places where fruit bodies were present 1 yr before sampling. This pattern suggests a recolonization of the site each year by H. cylindrosporum basidiospores in 'receptive' patches of ground created either by the local elimination of competitors or by local nutrient enrichments, which could frequently occur in a campsite. Our results demonstrate that an ectomycorrhizal species can be completely eliminated from the roots within 1 yr and does not necessarily contribute to the next generation of mycorrhizas.