Seasonal and spatial distribution of roots and arbuscular mycorrhizal fungi under live fences ofAcacia laetaandAcacia melliferain Sénégal

Abstract

Soils were sampled around live fences of A. laeta and A. mellifera plots in an experimental research site of the Senegalese Institute of Agricultural Research at Bambey, Senegal. They were collected before and after the rainy season at three distances (1 m, 3 m and 5 m) and two depths (0-25 cm and 25-50 cm). Roots were extracted using the wet sieving method and their concentrations were evaluated. Arbuscular mycorrhizal colonization (% of total roots length) was assessed after staining and observation under a compound microscope. Spores were extracted from soils by sucrose centrifugation and counted under the microscope. Root concentrations (cm per 100 g of dry soil) were greater on A. mellifera than on A. laeta for all seasons, distances and depths. For each species studied, root concentrations were greater at 1m from the live fence and at 0-25 cm of depth. The intensity of mycorrhizal colonization was greater on A. mellifera (66%) than on A. laeta (42%). For both tree species level of colonization was higher after the rainy season but A. laeta root colonization seems to be more affected by rain than in the case of A. mellifera . Mycorrhizal colonisation was not affected by distance from the live fence or by soil depth. Spore number (in 100 g of dry soil) was generally low (37.5 spores) and did not vary between seasons and between distances. Spores were more numerous under A. mellifera fence (42.43 per 100 g dry soil) than under A. laeta fence (33.28 per 100 g dry soil). Its number decreased from 0-25 cm to 25-50 cm depth. Generally, positive coefficient correlations were higher between root concentration and root infection than between root concentration and spore number. Low correlation was also found between infection and spore number. Given its numerous qualities, A. mellifera appears to be more promising in live fences than A. laeta . Keywords : Acacia , arbuscular mycorrhizas, live fences, roots, spores Southern African Forestry Journal Vol. 207 2006: 41-46