Composition of coffee shade tree species and density of indigenous arbuscular mycorrhizal fungi (AMF) spores in Bonga natural coffee forest, southwestern Ethiopia

Abstract

The composition of coffee shade tree species and density of arbuscular mycorrhizal fungi (AMF) spores in Bonga natural coffee forest of southwestern Ethiopia were investigated. This study is the first report on AMF populations of Ethiopian natural coffee forests. The main purposes were to systematically identify the dominant coffee shade tree species, evaluate their densities and quantify and characterize populations of arbuscular mycorrhizal fungi particularly in the rhizosphere of coffee plants. Sample plots of 400 m2 with coffee plants and dominant shade tree species were selected. Sampling of soil was carried out at a depth of 0–15 cm from the rooting areas of shaded and unshaded coffee plants for analysis of some soil parameters and quantification of AMF spores. Nineteen dominant shade tree species belonging to 14 plant families were identified in considered 10 quadrates. In terms of their stand dominance, Millettia ferruginea (Hochst.) Baker had the highest frequency of occurrence (22.3%) followed by O. welwitschii Friis & P.S. Green (15.5%). High density (503 stems/ha) and/or percentage (66%) of Coffea arabica L. were recorded. All soil samples yielded AMF spores and the counts ranged from 4 to 67 spores 100 g 1 of dry soil. Notably higher mean counts of AMF spores were found under leguminous shade trees compared to non-leguminous ones. AMF spore counts were significantly positively correlated with coffee counts and available soil P content. Five genera of AMF were identified based on spore morphology. Glomus dominated members of Glomeromycota. The other genera found were Gigaspora, Acaulospora, Entrophospora and Scutellospora in order of occurrence. The present investigation has documented species richness among dominant coffee shade tree species along with a fair distribution of relevant numbers and types (genera) of AMF to stimulate coffee growth. Thus, Bonga natural coffee forest seems to be an ideal focal forest for in situ coffee genetic resources conservation and promotion of organic coffee production. # 2007 Elsevier B.V. All rights reserved. Keywords: Arbuscular mycorrhizal fungi spore density; Bonga natural coffee forest; Coffee shade tree species