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

Ectomycorrhizas of Pseudotsuga menziesii (Mirb.) France were synthesized in pure culture with Cenococcum geophilum Fr., Laccaria bicolor (Maire) 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 the C-14 respired and that found in the seedling after 240 d of growth was used to quantify decomposition of the labelled substrates. All mycobionts released at least 20-30% of the C-14 in hemicellulose and all were able to release C-14 from cellulose and needles, except L. bicolor, which failed to release C-14 from needles. S. lakei released the largest amount of C-14 from cellulose. C. geophilum, S. lakei and R. vinicolor released similar amounts of C-14 from needles. Generally, substrates could be ranked in terms of ease of breakdown by the ectomycorrhizal fungi as follows: humic polymers < needles < cellulose < hemicellulose.