NITROGEN IN ECTOMYCORRHIZAL MAT AND NON-MAT SOILS OF DIFFERENT-AGE DOUGLAS-FIR FORESTS

In an attempt to determine how stand age and mat-forming fungi affect N chemistry in forest soils, soils with or without ectomycorrhizal mat s were collected from five Douglas-fir Pseudotsuga menziesii (Mirb.) Franco! forest stands, age 2-450 yr, in the Oregon Cascade Mountains. A number of chemical and biological variables were measured in these s oils, including: soil organic matter (SOM), pH, total N, inorganic N, extractable NH4+ and NO3-, fungal hyphal length, numbers of bacteria, and labile C and N. Total soil N and labile N both were significantly greater in old-growth soils than in other soils, suggesting that fores t soils become enriched in organic N with age. Labile C concentrations were higher in mat than in non-mat soils of all age classes but were significantly higher only in the older stands. This finding suggests t hat ectomycorrhizal mat communities affect soil N with age both by sel ectively removing organic N and by producing compounds with high C:N r atios.