SIZE, DISTRIBUTION AND BIOMASS OF GENETS IN POPULATIONS OF SUILLUS-BOVINUS (L, FR) ROUSSEL REVEALED BY SOMATIC INCOMPATIBILITY

The spatial distribution of genets in the ectomycorrhizal fungus Suill us bovinus (L.:Fr.) Roussel were studied in somatic incompatibility pa irings of isolates from five Scots pine (Pinus sylvestris L.) stands d iffering in forest history and age. With increasing forest age, the si ze of genets increased while the number of genets and production of sp orocarps per unit area decreased. There was an estimated 700-5700 gene ts ha(-1) in younger forests and 30-120 ha(-1) in older ones. The maxi mum size of genets was 1.7-5.3 m in the younger forest and to 17.5 m i n the older ones. The production of sporocarps per unit area decreased with increasing forest age. Furthermore, production of sporocarps inc reased nonlinearly with the size of the genet, suggesting that genets become fragmented. Ergosterol measurements indicated that the fungal b iomass of one genet consisted of 20-45% sporocarps and 55-80% mycorrhi za, not including extramatrical mycelia. Mycorrhizal aggregations in s oil were mapped in two 5 m(2) areas and, based on somatic incompatibil ity tests, all were found to belong to the same genet as sporocarps pr esent above ground. Production of spores per sporocarp was estimated t o be 1.1-12.8 x 10(8). The observations are discussed in terms of popu lation ecology.