Solubilisation and colonisation of wood ash by ectomycorrhizal fungi isolated from a wood ash fertilised spruce forest

In Sweden application of granulated wood ash has been suggested as a method to supplement nutrient loss resulting from harvesting of forest residues for bioenergy production. Mycelia of two ectomycorrhizal fungi Piloderma sp. 1 and Ha-96-3, were commonly found to colonise ash granules in a wood ash fertilised spruce forest. Thirty-eight fungal isolates were selected from 10 taxa to investigate the possible role of different ectomycorrhizal fungi in nutrient mobilisation from ash. The taxa were Cenococcum geophilum Fr., Piloderma croceum Erikss. and Hjortst., Piloderma sp. 1, Thelephora terrestris (Ehrenb.) Fr., Tylospora fibrillosa Donk, and five unidentified species, all originating from a wood ash fertilised spruce forest. The isolates were tested for their ability to solubilise tricalcium phosphate (TCP) or hardened wood ash (HWA) in vitro. Ha-96-3, P. croceum and Piloderma sp. 1 were the only taxa which solubilised TCP. Abundant calcium oxalate crystals were formed in TCP and HWA plates with Piloderma sp. 1. Ha-96-3 and two isolates of P. croceum produced intermediate amounts of crystals. Ha-96-1 and T. fibrillosa produced low amounts of crystal but no crystal formation was observed by any of the other isolates. Piloderma sp. 1 from HWA plates had significantly higher concentrations of P, compared to P. croceum or Ha-96-3. Piloderma sp. 1 and P. croceum were further tested for their ability to colonise wood ash in microcosms containing intact mycorrhizal associations. After 7 months Piloderma sp. 1 colonised ash amended patches with a dense, mat like mycelium, whereas P. croceum mycelia avoided the ash patches. Possible differences between these fungi in patterns of carbon allocation were investigated by labelling seedlings with 14CO(2). Piloderma sp. 1 mycelia allocated significantly more 14C to ash patches than P. croceum. P. croceum allocated relatively more 14C to control patches than to the ash patches. The possible role of ectomycorrhizal fungi in mobilisation of nutrients from wood ash is discussed.