Seasonal variation and distribution at different soil depths of arbuscular mycorrhizal fungi spores in a tropical sclerophyllous shrubland

Limited information is available for the diversity of arbuscular mycorrhizal fungi (AMF) in most tropical soils. To assess the biodiversity of AMF in a sclerophyllous shrubland ecosystem, an exhaustive collection of spores from soil collected in the Venezuelan Guayana was undertaken. Spores were collected from the first 15 cm of soil, four times throughout the year, and at four different depths during dry and wet seasons. A total of 50 AMF morphotypes were collected in the field, and 2 more were isolated from pot cultures. There was a reduction in spore density with soil depth, although richness of spores remained the same up to a depth of 45 cm. Spore density and richness based on soil cores were higher in the dry season than in the rainy season. Only 24% of the AMF morphotypes present could be identified to species level, since most of them did not fit published descriptions available. It is important to perform an exhaustive sampling of spores in the different seasons throughout the year and at different soil depths to obtain an accurate view of AMF spore diversity associated with a particular ecosystem.