VESICULAR-ARBUSCULAR MYCORRHIZAL INOCULUM POTENTIAL AFFECTS THE GROWTH OF STRYPHNODENDRON-MICROSTACHYUM SEEDLINGS IN A COSTA-RICAN HUMAN TROPICAL LOWLAND

This study used a plant bioassay to investigate the vesicular-arbuscul ar mycorrhizal (VAM) inoculum potential of soil from three vegetation types (fern, secondary forest, and grass) in an abandoned pasture in t he tropical humid lowlands at La Selva, in northeastern Costa Rica. Gr owth, measured as seedling height, number of leaves, and total (above- and below-ground) biomass, of Stryphnodendron microstachyum Poepp. et Endl. (Synon. S. excelsum Harms) seedlings was significantly lower wh en grown in soil inoculum from the fern areas than in soil inoculum fr om the forest and grass areas. However, S. microstachyum seedlings gro wn in the fern inoculum had significantly greater VAM colonization tha n seedlings grown in the forest and grass inoculum. In addition, roots collected from a dominant plant species from each of the three vegeta tion types showed that the fern (Nephrolepsis biserrata) had significa ntly greater mycorrhizal colonization than the tree (Pentaclethra macr oloba (Willd.) Kuntze or the grass (Brachiaria spp.). The results of t his study suggest that differences in mycorrhizal inoculum potential a mong vegetation types and its effects on seedling growth may have impo rtant implications for the restoration and management of degraded land s.