Occurrence of arbuscular mycorrhizal fungi in soils of early stages of a secondary succession of Atlantic Forest in South Brazil

Arbuscular mycorrhizal fungi (AMF) species diversity and mycorrhizal inoculum potential were assessed in areas representative of stages of secondary succession in the Brazilian Atlantic Rain Forest. Within each stage - pioneer, 'capoeirinha' and 'capoeirão'- four transects were established and three soil samples were taken along each transect. The plant community was dominated by Pteridium aquilinium in the pioneer stage, while Dodonaea viscosa and P. aquilinium were co-dominants in the 'capoeirinha' stage. In capoeirão, Miconia cinnamomifolia was dominant followed by Euterpe edulis. Total spore number per 100 g soil was significantly larger in the 'capoeirinha' stage than in the other stages, although the number of viable spores was similar among stages. Acaulosporaceae and Glomeraceae were the predominant families accounting for 83% of the total spores recovered. Of the 18 spore morphotypes, 10 were allocated to known species, with Acaulospora sp. and Glomus sp. being the dominants recovered in all samples. Simpson's index of diversity and evenness for AMF species were not significantly different among the successional stages and AMF species richness was negatively correlated with plant species richness. Soil from 'Capoeirinha" showed the highest inoculum potential (37%). Dominance of the mycorrhizal community by few sporulators and the relationship between plant and fungal diversity are discussed