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 bigelowii and Salix herbacea rich snowbed communities at four altitudes (600-900 m) above treeline in low and middle oroarctic belts, were examined for mycorrhiza and soil microbial activity. Eight plant species were common and characteristic across the gradient, all together 58 plant species were identified. Colonization percentage was 100 in the four ectomycorrhizal species, of which only S. herbacea characterizes snowbed communities. There was a trend in ericoid mycorrhizal species (all rare) of increased colonization with altitude. Twenty-three species had arbuscular mycorrhiza (AM), nine being heavily colonized, including Gnaphalium supinum and Sibbaldia procumbens, which were typical for snowbed communities. Veronica alpina, also a typical species, was moderately colonized. Average AM colonization varied little from 600 to 800 m, but at 900 m root colonization dropped significantly. This was due to weakly mycorrhizal Cardamine bellidifolia and Festuca ovina, which 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 Kiölen mountains in Scandinavia; Acaulospora scrobiculata was the most common. Seven species were nonmycorrhizal (NM), Carex bigelowii and Oxyria digyna being typical for snowbed communities. In addition, there were nine unexamined species which were most obviously NM, judged by related examined species. Basal respiration rate and microbial biomass as well as the metabolic quotient were highest at 700 m altitude, where also AM spore density was highest, and were only about one third at two highest altitudes compared to those at 700 m. Microbial parameters and mycorrhizal colonization did not show any relation with each other.