Soil solution chemistry of ectomycorrhizal mat soils

Ectomycorrhizal fungal mats are distinct features of Pacific northwest coniferous forestsand other forests throughout the world. Organic acids produced by these fungi may playan important role in nutrient availability and mineral weathering within the soil ecosystem.The dissolved chemical elements in soil solutions isolated from two ectomycorrhizal fungal (Hysterangium setchellii and Gautieria monticola) mat soils were compared with those fromadjacent soils with no visible mat development. The concentrations of dissolved constituentswere greater, in all cases, for the mat soils (Table 1).
Concentrations of cations, oxalate, dissolved organic carbon (DOC) and total N werealways greatest in mat soils with concentrations in G. monticola mat solutions usually beinghigher than in H. setchellii mat solutions. The chemical constituents showing the largestdifferences between mat and non-mat soils for both mat types included: Al, Fe, Mg, Mn,oxalate and DOC. The reduced pH and elevated oxalate and DOC concentrations in the matsoils suggest that organic acids produced by the fungal mat community accelerated weather-ing of the soil mineral phase causing an increase in pore-water cation concentrations. Theelevated C:N ratios in mat soil solutions may be caused by the input of organic acids bythe ectomycorrhizal fungus and/or by the selective removal of dissolved organic nitrogen bythe fungus resulting in an enrichment of DOC. This process may be responsible for releasingplant nutrients to be transported by the fungi to the host tree.