DECOMPOSITION OF C-14-LABELED SUBSTRATES BY ECTOMYCORRHIZAL FUNGI IN ASSOCIATION WITH DOUGLAS-FIR

Ectomycorrhizas of Pseudotsuga menziesii (Mirb.) France were synthesiz ed in pure culture with Cenococcum geophilum Fr., Laccaria bicolor (Ma ire) Orton, Rhizopogon vinicolor Smith, or Suillus lakei (Murr.) Smith and Thiers. The mycorrhizal plants were grown in sterile vessels with peat/vermiculite plus C-14 labelled hemicellulose, cellulose, Douglas fir needles, or humic polymers as an organic substrate. The sum of th e C-14 respired and that found in the seedling after 240 d of growth w as used to quantify decomposition of the labelled substrates. All myco bionts released at least 20-30% of the C-14 in hemicellulose and all w ere able to release C-14 from cellulose and needles, except L. bicolor , which failed to release C-14 from needles. S. lakei released the lar gest amount of C-14 from cellulose. C. geophilum, S. lakei and R. vini color released similar amounts of C-14 from needles. Generally, substr ates could be ranked in terms of ease of breakdown by the ectomycorrhi zal fungi as follows: humic polymers < needles < cellulose < hemicellu lose.