EFFECTS OF N-FREE FERTILIZATION ON ECTOMYCORRHIZA COMMUNITY STRUCTUREIN NORWAY SPRUCE STANDS IN SOUTHERN SWEDEN

The application of N-free fertilizer (i.e. lime combined with nutrient s such as P, Ca, K and Mg) has been suggested as one way of compensati ng for nitrogen-caused eutrophication and losses of base cations due t o atmospheric pollution. To study the effects of such a treatment on m ycorrhizal fungi, fine-root samples were collected from the LFH-layer in four Norway spruce stands in southern Sweden. One stand was part of a larger experiment (Skogaby) and had four replicates. It was fertili zed twice in 1988-89 (P:K:Ca:Mg:S 48:43:218:46:75 kg ha(-1)), and samp ling was carried out once yearly during 1991-93. The other three stand s were fertilized once in 1988-89 (P:K:Ca:Mg:S125:62:33:12:54 kg ha(-1 )) and sampled in 1992. Ectomycorrhizal fine-roots were classified int o morphotypes on the basis of the structure and colours of their exter nal hyphae and fungal mantle. The fungal biomass was estimated in 1992 using ergosterol analysis. In Skogaby, N-free fertilizer had no appar ent effects on fungal biomass or on the total number of ECM types. Sim ilar results were obtained for the other three stands. Previously repo rted 50% reductions in sporocarp production on the fertilized plots at Skogaby can probably be explained by a decrease in carbon allocation to the roots and by a decline in the abundance of a single morphotype which accounted for 3% of the total number of root tips, but ca. 30% o f the sporocarp biomass in the control plots in the present study. It is concluded that moderate levels of N-free fertilization are not like ly to drastically affect the community structure of the dominating ect omycorrhizal fungi. This result should be interpreted with some cautio n, however, since it remains to be determined whether the fertilizer t reatments affect the function of the nutrient-absorbing soil mycelium of the mycorrhizal fungi.