SOIL SOLUTION CHEMISTRY OF ECTOMYCORRHIZAL MATS IN FOREST SOIL

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.