Arbuscular mycorrhizal fungi (AMF) are important microbial symbionts for plants especially when soil phosphorus (P) and nitrogen (N) are limited. Little is known about the distribution of AM hyphae in natural systems of tropical soils across landscapes and their association with different land uses. We studied mycorrhizal hyphal abundance in a wildlife grazed system, a livestock grazed system and under cultivated soils in and near Serengeti National Park, Tanzania. Samples of the upper 15 cm of soil beneath locally dominant plant species were collected. Hyphae were preserved on permanent slides and the length of hyphae per cubic centimeter of soil was calculated. Significant differences (p<0.001) in AM hyphal densities were observed across land use systems, as mean hyphal densities were 61.03±22.02, 52.89±16.41 and 47.9±22.65 m/cm3 for wildlife grazed system, livestock grazed system and croplands, respectively. There were significant correlations between soil P and N on AM hyphal densities that reflected a pattern of decreasing hyphal densities with increasing soil P and N across sites. These results are congruent with the functional equilibrium hypothesis, which predicts that plants allocate relatively more to belowground structures when they are more limited by belowground resources than by aboveground resources, because AMF densities were highest at the sites with the lowest soil resources.
Key words: Land use, mycorrhizal, hyphal, abundance, soil, Serengeti, Tanzania.