Wood ash contains all the essential plant nutrients except nitrogen, and thus supports tree growth
especially on peatlands where mineral nutrients often are in short supply. Here we report the effects of
wood ash fertilization on the soil microbial community in a boreal drained peatland, characterized by
phospholipid fatty acid (PLFA) composition, and more specifically the fungal community, characterized
with PCR-DGGE fingerprinting and sequencing methods. We investigated the microbial communities in
unfertilized and ash-fertilized sample plots (loose wood ash 5000 or 15 000 kg ha1) 6 years after
fertilization. Microbial function measured as heterotrophic basal respiration increased over 30% in the
surface peat layer after wood ash fertilization, yet the result was statistically insignificant. The higher
amount of wood ash induced a shift in the microbial community in the surface peat layer (0e10 cm)
along with an increase in pH. A higher relative proportion of fungal-specific PLFA 18:2u6 and an
increased fungal:bacterial ratio indicated that fungi benefited from the higher amount of wood ash in the
topmost layer. Also, the lower amount of wood ash seemed to have stimulated actinobacteria. Our results
indicated that higher pH and extra nutrients due to wood ash fertilization promoted the appearance of
mycorrhizal and wood-decomposing fungi directly or via increased tree growth. We suggest that wood
ash as a fertilizer would be a natural and economical choice to improve the nutrient status of drained
peatlands used for forestry since it maintains the positive feedback between fungi and trees.