Distribution of arbuscular mycorrhizal fungi spores in soils of smallholder agroforestry and monocultural coffee systems in southwestern Ethiopia

Arbuscular mycorrhizal fungi (AMF) are associated with the root system of coffee (Coffea arabica L.) plants, but their distribution in smallholder agroforestry and monocultural coffee systems is not well known. This study investigates the spatial distribution of AMF spores in a field study in southwestern Ethiopia. Soil samples from different depths (0–50 cm) were collected under the tree canopies of Acacia abyssinica, Albizia gummifera, Ficus sur, Ficus vasta and randomly selected unshaded coffee plants at different sampling points (canopy base, radius, edge and outside canopy). Significantly higher AMF spore densities were recorded at canopy bases and at 0–30 cm soil depth. Spore populations were found to belong to five genera: Acaulospora, Entrophospora, Glomus, Gigaspora and Scutellospora, with Glomus and Acaulospora dominating. Sampling points, sites and depths, shade tree species and shade tree/coffee plant age affected AMF spore density. Agroforestry practices including the use of leguminous shade trees effectively maintained AMF numbers in soils even at depth compared with unshaded coffee plants (monocultures).