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 forestsoils, soils with or without ectomycorrhizal mats were collected from five Douglas-fir [Pseudotsugamenziesii (Mirb.) Franco] forest stands, age 2-450 yr, in the Oregon Cascade Mountains. A number ofchemical and biological variables were measured in these soils, including: soil organic matter (SOM), pH,total N, inorganic N, extractable NH4 and NO3, fungal hyphal length, numbers of bacteria, and labileC and N. Total soil N and labile N both were significantly greater in old-growth soils than in other soils,suggesting that forest soils become enriched in organic N with age. Labile C concentrations were higherin mat than in non-mat soils of all age classes but were significantly higher only in the older stands. Thisfinding suggests that ectomycorrhizal mat communities affect soil N with age both by selectively removingorganic N and by producing compounds with high C:N ratios.