NITROGEN AND DROUGHT EFFECTS ON ECTOMYCORRHIZAE OF NORWAY SPRUCE [PICEA-ABIES L. (KARST.)]

Effects of N addition and drought on ectomycorrhizae of Norway spruce trees were investigated in an outdoor pot lysimeter study. Three level s of N were applied as ammonium nitrate in irrigation water for five y ears; ambient rainwater (NO) and 5 (N5) and 15 (N15) times this N conc entration. Mean annual N addition during the five years corresponded t o 5, 27 and 82 kg.ha(-1).y(-1) for the N0, N5 and N15 treatments, resp ectively. During the third and fifth growth seasons two levels (length s) of drought were artificially induced in addition to a watered contr ol. Soil cores taken from each pot lysimeter were analyzed for mycorrh izal colonization and ectomycorrhizae were categorized according to ma croscopic morphology. Drought decreased mycorrhizal colonization signi ficantly. There was a significant interaction of drought and N effects on reduction of the mycorrhizal colonization. Although all of the myc orrhiza types were influenced by drought, only Cenococcum geophilum sh owed a significant change. N treatment alone did not show any signific ant effect either on mycorrhizal colonization or mycorrhizal types.