Fertilisation of coniferous forest soil with wood ash (5 t ha-1) was demonstrated to affect microbial biomass (on the basis of phospholipid fatty acid analysis). Fungi reacted more sensitively to wood ash treatment than bacteria, which was reflected by decreasing fungal-to-bacterial phospholipid fatty acid ratios (Baath et al. 1995). Because ectomycorrhizal fungi are known to play an important role in the nutrient supply of trees, Hagerberg and Wallander (2002) investigated the effect of wood ash amendment on a Norway spruce forest floor and revealed an increase in ectomycor — rhizal biomass. The ectomycorrhizal fungus Piloderma sp. was found to frequently colonise granulated wood ash in a wood-ash-fertilised spruce forest, suggesting a direct impact on nutrient mobilisation (Mahmood et al. 2001, 2002). Piloderma sp. was moreover assumed to affect short-term storage of Ca derived from wood ash granules, whereas no effect on P storage or release was discovered (Hagerberg et al. 2005). Gaitnieks et al. (2005) reported a positive effect of wood ash (6 t ha-1) on Suillus sp. when it was applied prior to planting of Scots pine seedlings; this was accompanied by increased root and needle biomass of the seedlings.

In a long-term study on different forest sites, wood ash fertilisation (5-8 t ha-1) led to increased CO2 production caused by enhanced microbial activity but did not influence N2O emissions, although nitrification and denitrification may have been affected by wood ash application (Maljanen et al. 2006a, b). This effect was shown by Ozolincius et al. (2006) in a Pinus sylvestris stand in Lithuania, revealing an increase of ammonifying, nitrifying and denitrifying microorganisms after wood ash application (1.25-5 t ha-1). In contrast, Saarsalmi et al. (2010) did not find changes in net nitrification when investigating the effect of wood ash (3 t ha-1) combined with N (0.15 t ha-1) on soil microbial processes in two coniferous stands in Finland 15 years after application.