Ectomycorrhizal fungi associated with Arctostaphylos contribute to Pseudotsuga menziesii establishment

Chaparral on the central coast of California can occur as relatively stable patches of ectomycorrhizal Arctostaphylos directly adjacent to arbuscular mycorrhizal Adenostoma. Vegetation surveys and seedling survival assays sho w that Pseudotsuga establishes only in Arctostaphylos. We found no signific ant differences between Arctostaphylos and Adenostoma in allelopathy; light ; temperature; or soil NH4+, NO3-, or K. Arctostaphylos soils tended to be higher in phosphate and were lower in pH, Ca, Mg, Ni, and Cr than those fro m Adenostoma. After 1 year of growth of Pseudotsuga seedlings in an Arctost aphylos patch, 17 species of fungi colonized both Pseudotsuga and Arctostap hylos. Fifty-six of 66 seedlings were colonized by fungi that also colonize d Arctostaphylos within the same soil core. Forty-nine percent of the Pseud otsuga ectomycorrhizal biomass was colonized by fungi that were also associ ated with Arctostaphylos within the same core. Another 12% was colonized by fungi known to associate with Arctostaphylos from different cores. After 4 months of growth, Pseudotsuga seedlings in four of five Arctostaphylos plo ts were ectomycorrhizal and colonized by fungi in Russulaceae, Thelephorace ae, and Amanitaceae. Pseudotsuga seedlings in two of five Adenostoma plots were ectomycorrhizal but colonized by only two species of fungi in Thelepho raceae. These results provide compelling evidence that ectomycorrhizal fung i associated with Arctostaphylos contribute to Pseudotsuga seedling establi shment.