Survival and productivity of Douglas-fir [Pseudotsuga menziesii (Mirb.
) Franco] depend on close association between host trees and ectomycor
rhizal fungi. Two of these fungi, Hysterangium setchellii (Fischer) an
d Gautieria monlicola (Harkness), form extensive hyphal mats with the
roots of Douglas-fir and other conifers in the surface of the 'A' hori
zon, often at the interface between mineral oil and litter. The fungal
mat alters the chemistry and mineral nutrition of the soil microenvir
onment within the rhizosphere, producing conditions that favor increas
ed tree growth by increasing nutrient availability. Forest soils with
or without obvious ectomycorrhizal mats were sampled at two locations
in the Pacific Northwest. Cation and anion chemistry, dissolved organi
c carbon (DOC) and oxalate anions were analyzed. Mean concentrations o
f DOC, oxalate, PO4, SO4, H, Al, Fe, Cu, Mn and Zn were significantly
higher in mat than in non-mat soil solutions in both mat types and loc
ations and on both sampling dates. Significant statistical correlation
s between DOC or oxalate and PO4 indicate that organic acids influence
weathering and solubility of PO4 in the mat soils, Mean oxalate conce
ntrations were significantly lower in soil solutions from Hysterangium
mat soils than in those from Gautieria mat soils. Organic acids relea
sed to the rhizosphere by G. monitcola and H. setchellii may provide a
local weathering environment that increases availability of PO4, SO4
and trace nutrients.