| Summary: | Nivicolous myxomycete assemblages were surveyed in the northwest of the Great Caucasian ridge (Teberda state reserve), in the southern Khibiny Mountains (Kola peninsula), near Vaskelovo settlement (Leningrad oblast) and in Valamo Island (Karelia). In result we registered 46 species and 9 intraspecific taxa from 9 genera and 4 families of 3 orders. We report 39 species as new for Russia. To confirm the assignment of specimens (found in the Teberda reserve) to morphospecies, we obtained independently from determination 145 partial sequences of the 18S SSU rRNA gene from 35 taxa of Lamproderma, Meriderma, Physarum and Diderma, which turned out to represent 58 genotypes. Most of the taxa represented by more than one sequence had several genotypes, with an average of 1.7 genotypes per taxon. Except for three taxonomically difficult groups of species, partial SSU sequences did well correspond with the respective morphospecies and where similar or identical to sequences of specimens from the European Alps, making this marker a good candidate for barcoding in myxomycetes. Alpha diversity and taxonomic structure of myxomycete assemblages change regularly along altitudinal and latitudinal gradients and on different substrates. These parameters increase from lowland to mountain landscapes and from boreal forest to alpine meadows in the Northwest Caucasus. In temperate climate of the Northwest Caucasus species richness and diversity increase along the altitudinal gradient from subalpine crooked communities to treeless alpine meadows. In contrary, in the Arctic we registered a reverse trend - species richness and diversity decrease from subalpine crooked forests to alpine communities of mountain tundra. The intensity of sporulation in nivicolous myxomycetes depends on a combination of climatic factors not only during the spring snowmelt, but also throughout the year. For the successful growth of the population of amoebae and formation of fruit bodies in spring a combination of the following parameters is necessary: formation ...
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