MICROBIAL BIOMASS AND NUTRIENT CONCENTRATIONS IN HYPHAL MATS OF THE ECTOMYCORRHIZAL FUNGUS HYSTERANGIUM-SETCHELLII IN A CONIFEROUS FOREST SOIL

In western Oregon, the calcium oxalate-producing ectomycorrhizal fungus Hysterangium setchellii (Fischer) forms a symbiotic relationship with Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] resulting in fungal mats that range from 1 to 1.5 m dia and 7-10 cm thickness. Microbial biomass, extractable soil nutrients and nutrient concentration of hyphal tissue were measured in mat soils and adjacent non-mat soils. Extractable concentrations of N, P, K, Ca, Mg, Al, B, Cu, Fe, Mn and Zn were analyzed in H. seichellii hyphal tissue, mat soils, non-mat soils and mat soils with H. setchellii hyphae removed. Microbial biomass, and concentrations of most nutrients were greater in mat soils than in non-mat soils. Nutrients were incorporated primarily in the fungal tissue rather than on soil exchange sites. Extractable nutrients other than Cu were correlated with microbial biomass for combined data from mat and adjacent non-mat soils. Macronutrients other than N were positively correlated with Al + Fe concentration in mat soils, but showed negative correlations in the non-mat soils and in mat soils with hyphae removed. The inverse correlation of soil Al + Fe concentration to soil macronutrient concentration in non-mat soils may reflect greater leaching and lower retention of macronutrients in soils without H. setchellii mats. These results indicate that the ectomycorrhizal fungus H. setchellii is able to concentrate nutrients in hyphal tissue that are important to the growth and productivity of Douglas-fir forests.