Soil solution chemistry of ectomycorrhizal mats in forest soil

Survival and productivity of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] depend onclose association between host trees and ectomycorrhizal fungi. Two of these fungi, Hysterangium setchellii(Fischer) and Gautieria monticola (Harkness), form extensive hyphal mats with the roots of Douglas-firand other conifers in the surface of the 'A' horizon, often at the interface between mineral oil and litter.The fungal mat alters the chemistry and mineral nutrition of the soil microenvironment within therhizosphere, producing conditions that favor increased tree growth by increasing nutrient availability.
Forest soils with or without obvious ectomycorrhizal mats were sampled at two locations in the PacificNorthwest. Cation and anion chemistry, dissolved organic carbon (DOC) and oxalate anions wereanalyzed. Mean concentrations of DOC, oxalate, PO4, SO4, H, Al, Fe, Cu, Mn and Zn were significantlyhigher in mat than in non-mat soil solutions in both mat types and locations and on both sampling dates.Significant statistical correlations between DOC or oxalate and PO4 indicate that organic acids influenceweathering and solubility of PO4 in the mat soils. Mean oxalate concentrations were significantly lowerin soil solutions from Hysterangium mat soils than in those from Gautieria mat soils. Organic acids releasedto the rhizosphere by G. monitcola and H. setchellii may provide a local weathering environment thatincreases availability of PO,, SO4 and trace nutrients.