Tuesday, August 7, 2007: 1:30 PM
Santa Clara I, San Jose Hilton
Oaks depend on ectomycorrhizal fungi. As oak woodlands regenerate or expand, seedlings must encounter mycorrhizal inoculum. According to the Janzen-Connell hypothesis, seeds dispersed greater distances from parent plants have a better chance of survival because they escape seed and seedling predators; however, the requirement for ectomycorrhizal inoculum limits the distance at which seedlings can survive. The problem for oaks is two-fold: acorns must be carried away from parent trees, and mycorrhizal inocula must reach seedling roots. The question is how ectomycorrhizal inoculum reaches seedlings. Quercus garryana mycorrhizal associations include hypogeous fungi. Small mammals eat hypogeous sporocarps depositing spores in fecal pellets. Our goal was to assess availability of ectomycorrhizal inoculum as a function of distance from mature oaks and to determine the potential of small mammals to disperse mycorrhizal inoculum. We trapped animals at distances from mature oaks and examined fecal pellets for spores. We planted seeds at trap sites to probe available mycorrhizal inoculum. We compared mycorrhizal communities on roots of saplings with those of mature trees. We found that small mammals enter traps up to 35 m from mature trees, particularly in shrublands rather than grasslands. Spores of hypogeous fungi were found in fecal pellets at distances up to 35 m from mature trees where hypogeous fungi form fruiting bodies. On sapling roots distant from mature trees, mycorrhizas included hypogeous and epigeous species. This spring we will excavate seedlings to test whether mycorrhizal inoculum declines in species richness with increasing distance from mature oaks and whether the fungal species in small mammal fecal pellets occur as ectomycorrhizas on seedlings. Dispersal of mycorrhizal inoculum affects restoration of oak habitats, natural regeneration of oak communities, and possibilities for range expansion with global warming.
