Decomposition of 14C‐labelled substrates by ectomycorrhizal fungi in association with Douglas fir

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Abstract
Ectomycorrhizas of Pseudotsuga menziesii (Mirb.) Franco 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 14C labelled hemicellulose, cellulose, Douglas fir needles, or humic polymers as an organic substrate. The sum of the 14C 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 14C in hemicellulose and all were able to release 14C from cellulose and needles, escept L. buolttr, which failed to release 14C from needles. S. lakei released the largest amount of 14C from cellulose. C. geophilum, S. lakei and R. filticolor released similar amounts of 14C from needles. Generally, substrates could be ranked in terms of ease of breakdown by the ectomycorrhizal fungi as follows: humic polymers < needles < cellulose < hemicellulose.