SHIFTS IN MYCORRHIZA AND MICROBIAL ACTIVITY ALONG AN OROARCTIC ALTITUDINAL GRADIENT IN NORTHERN FENNOSCANDIA

Roots of 42 plant species, collected in northern Finland from Carex bi gelowii and Salix herbacea rich snowbed communities at four altitudes (600-900 m) above treeline in low and middle oroarctic belts, were exa mined for mycorrhiza and soil microbial activity. Eight plant species were common and characteristic across the gradient, all together 58 pl ant species were identified. Colonization percentage was 100 in the fo ur ectomycorrhizal species, of which only S. herbacea characterizes sn owbed communities. There was a trend in ericoid mycorrhizal species (a ll rare) of increased colonization with altitude. Twenty-three species had arbuscular mycorrhiza (AM), nine being heavily colonized, includi ng Gnaphalium supinum and Sibbaldia procumbens, which were typical for snowbed communities. Veronica alpina, also a typical species, was mod erately colonized. Average AM colonization varied little from 600 to 8 00 m, but at 900 m root colonization dropped significantly. This was d ue to weakly mycorrhizal Cardamine bellidifolia and Festuca ovina, whi ch grew only at higher altitudes. If these two species were excluded, there were no differences in average AM colonization among altitudes, e.g. colonization in G. supinum, S. procumbens, and V. alpina did not differ among altitudes. Seven AM fungal species were identified, none of which has been reported before from the Kiolen mountains in Scandin avia; Acaulospora scrobiculata was the most common. Seven species were nonmycorrhizal (NM), Carer bigelowii and Oxyria digyna being typical for snowbed communities. In addition, there were nine unexamined speci es which were most obviously NM, judged by related examined species. B asal respiration rate and microbial biomass as well as the metabolic q uotient were highest at 700 m altitude, where also AM spore density wa s highest, and were only about one third at two highest altitudes comp ared to those at 700 m. Microbial parameters and mycorrhizal colonizat ion did not show any relation with each other.