Vertical distribution of mycorrhizal colonization, root hairs, and belowground biomass in three contrasting sites from the Tropical high Mountains, Merida, Venezuela

Very little is known about the distribution and abundance of mycorrhizae in the high Tropical mountains. The objective of the present study was to determine whether soil drainage and soil depth in a toposequence in a Venezuelan paramo affect the extent of mycorrhizal colonization, percentage root hairs, and belowground biomass of unknown species randomly sampled from the study sites. Well-drained soils in the shrub-rosette site (SR) during the dry season were less fertile and mycorrhizal colonization was the highest (69.4 +/- 2.5%) compared to the more poorly drained pasture soils, located in topographically low situations, which were more fertile but with a lower mycorrhizal colonization and more root hairs. A low diffusion of oxygen in the poorly drained soils of the humid pasture (HP), which remained wet throughout the year, may explain the abrupt decline in mycorrhizal colonization. Vertical distribution of belowground biomass and mycorrhizal colonization suggest that nutrients are mainly distributed in the surface soil layer.