• Ectomycorrhizal fungi;
  • Spruce colonisation;
  • Wood ash;
  • N fertilisation;
  • Competition;


Interactions between two ectomycorrhizal fungal species, Piloderma croceum Erikss. and Hjortst. and Piloderma sp. 1 (found to colonise spruce roots and wood ash granules in the field), were investigated in wood ash amended substrates. The comparative ability of these fungi to colonise roots of non-mycorrhizal spruce (Picea abies (L.) Karst.) seedlings was studied in relation to factorial combinations of wood ash and N fertilisation. Non-mycorrhizal spruce seedlings (bait seedlings) were planted together with spruce seedlings colonised by P. croceum or Piloderma sp. 1. The growth substrate was a sand–peat mixture with wood ash or no ash and supplied with two levels of N, so that four substrate combinations were obtained. Piloderma sp. 1 mycelia colonised around 60% of the fine roots of bait seedlings in ash treatments regardless of N level and around 20–26% in treatments without ash. P. croceum only colonised 8% of the root tips in the presence of ash but 56% of the root tips in the low-N treatment without ash. However, in the high-N treatment without ash the colonisation level was reduced to around 30%. Total numbers of root tips per seedling did not vary significantly between the treatments. Possible reasons for the competitive advantage of Piloderma sp. 1 in wood ash fertilised substrate are discussed.