Effects of continuous optimal fertilization on belowground ectomycorrhizalcommunity structure in a Norway spruce forest

Studies of effects of fertilizer treatment on ectomycorrhizal fungal commun ity structure have predominantly been based on large, single additions of n itrogen. Studies involving chronic additions of nutrients in combination wi th irrigation are much less common. We used morphotyping to study effects o f balanced additions of a nutrient solution on ectomycorrhizal fungal commu nity structure in a 36-year-old stand of Picea abies (L.) Karst. Despite hi gh variability among individual samples, principal components analysis reve aled a clear shift in community structure in response to fertilization. Irr igated plots receiving only water did not differ significantly from untreat ed control plots. Mycorrhizal root tips colonized by Cenococcum geophilum F r. were significantly mon common in fertilized plots than in control plots. Possible responses by other ectomycorrhizal species were masked by high va riability. Over sixty morphotypes were distinguished, but there was no meas urable effect of either fertilizer or irrigation treatment on morphotype ri chness or total number of root tips.