Nitrogen addition changed macromycete sporocarp production and below-ground ectomycorrhizal species composition in a Norway spruce stand

Martina Peter (1), François Ayer (2), Simon Egli (2)
(1) INRA Centre de Nancy, UMR INRA-UHP 1136 Interactions Arbres/Micro-organismes, 54280 CHAMPENOUX
(2) Swiss Federal Research Institute WSL, Zuercherstr. 111, 8903 BIRMENSDORF, Switzerland

The effects of simulated N deposition on the ectomycorrhizal and total macrofungal community in a subalpine Picea abies stand were investigated by adding 150 kg N ha-1year-1 as ammonium nitrate as a long-term fertilizer. Ectomycorrhizal diversity was studied 1) above-ground in terms of sporocarp production, including three years of re-cording before N addition, and 2) below-ground by PCR-RFLP analysis of the ITS region of rDNA extracted from single mycorrhizal root tips before and after one and two years of fertilization in treated and control plots.
Sporocarp surveys revealed a strong impact of increased N input on the ectomycorrhizal community by drastically decreasing species diversity already one year after the start of N addition, whereas the saprobic fungal community was not affected. The impact of N ad-dition on below-ground ectomycorrhizal diversity was less pronounced. No change in the number of ectomycorrhizal taxa and Simpson's index of diversity was found. How-ever, ordi-nation analysis as well as comparison of similarities among control and treated plots in-dicated a change in below-ground species composition two years after N addition. Significant changes in abundances of single species were observed in fertilized plots. Eleven out of 25 species which produced conspicuous sporocarps in the six years of survey were identi-fied on the root system. These species accounted for approx. 25% of all sampled root tips. At least 44% of all ectomycorrhizas, comprising nine different RFLP-types, were formed by spe-cies belonging to the Thelephoraceae and Corticiaceae, taxa which produce in-con-spicuous sporocarps. Our data indicate that the abundance of these species on the root system increases at higher N concentrations, whereas the abundance of species which pro-duce fewer sporocarps after N input decreases.