Effects of continuous optimal fertilization on belowground ectomycorrhizal community structure in a Norway spruce forest.

Studies of effects of fertilizer treatment on ectomycorrhizal fungal community structure have predominantly been based on large, single additions of nitrogen. Studies involving chronic additions of nutrients in combination with irrigation are much less common. We used morphotyping to study effects of balanced additions of a nutrient solution on ectomycorrhizal fungal community structure in a 36-year-old stand of Picea abies (L.) Karst. Despite high variability among individual samples, principal components analysis revealed a clear shift in community structure in response to fertilization. Irrigated plots receiving only water did not differ significantly from untreated control plots. Mycorrhizal root tips colonized by Cenococcum geophilum Fr. were significantly more common in fertilized plots than in control plots. Possible responses by other ectomycorrhizal species were masked by high variability. Over sixty morphotypes were distinguished, but there was no measurable effect of either fertilizer or irrigation treatment on morphotype richness or total number of root tips.