EFFECTS OF HIGH-NITROGEN CONCENTRATIONS ON ECTOMYCORRHIZAL STRUCTURE AND GROWTH OF SEEDLINGS OF PICEA-ABIES (L) KARST

High nitrogen concentrations are known to affect ectomycorrhizas and e ctomycorrhizal fungi in field and laboratory experiments. Using NH4+ a s a nitrogen source in the growth pouch system, a variety of structura l modifications were documented on first order lateral roots of Picea abies (L.) Karst. seedlings. Root cells increased in size and number a t high levels of NH4+, resulting in a hypertrophic appearance of roots in both uncolonized seedlings and in those inoculated with mycelia of the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull. ex St. Ama ns) Quel. A fungal mantle surrounded short roots of inoculated seedlin gs, and the outer walls of epidermal and cortical cells were often thi ckened when in contact with fungal hyphae. No Hartig net developed, al though intracellular penetration of fungal hyphae into epidermal and c ortical cells frequently occurred. At moderate NH4+ concentrations, Ha rtig net development was incomplete, but occasional intracellular pene tration of Hartig net hyphae into epidermal and cortical cells occurre d. The addition of high levels of NH4+ after ectomycorrhizal developme nt resulted in ectomycorrhizas with distinctly altered apical structur es. None of the various NH4+ concentrations resulted in significantly different plant dry weights after two months of exposure, either with or without fungal inoculation. After four months, dry weight, root len gth and branching indices were higher in both inoculated plants and th ose exposed to high nitrogen. The root/shoot ratio and number of short roots per seedling were high with fungal inoculation. Shoot nitrogen levels after two and four months and the Ca levels after 4 months were higher with increasing NH4+ in the nutrient solution. Other mineral e lements were not influenced by nitrogen concentrations and fungal inoc ulation.