Soil Nematode Communities of Typical Biocenoses in the Republic of Altai

The first data on soil nematodes of coniferous forest and steppe biocenoses in the Republic of Altai were presented, thus making it possible to establish relationships between characteristics of nematode communities and vegetation features. Overall, 49 taxa of soil nematodes belonging to 31 families and nine orders were found. The results showed the highest value of nematode taxonomic diversity lying in larch forest, compared to the lowest in steppe biocenoses. The nematode population density and biomass were similarly high in the soil of forest biocenoses, but significantly exceeded those in the steppe. Variations in the eco-trophic structure of soil nematode communities among the study biocenoses were revealed. In the pine forest with Pinus sibirica , bacterial feeders and nematodes associated with plants prevailed in the soil, this being typical of various types of pine forest, compared to bacterial feeders, plant parasites, and fungal feeders which dominated in the larch forest. Nematode communities in steppe soils showed specific features and differed markedly from those in forest biocenoses, the community structure being incomplete, with dominance of fungal feeders and/or omnivores. Based on the ecological indices (Structure index SI, Enrichment index EI) calculated for nematode communities and the state of the food web described, the soil ecosystems of forest biocenoses were assessed as undisturbed, with complex food webs and a moderate level of soil organic matter enrichment. The steppe biocenosis formed by chee grass Stipa splendens , on the contrary, was characterized by SI and EI values indicating a simplified and unstable food web associated with degraded soil ecosystems under the influence of unfavorable environmental factors (climatic or anthropogenic). This shows the possible effect of extreme conditions on soil nematodes formed in the steppe of the Kosh-Agachskii region. The CI (Channel index) values of the predominant pathway of organic matter decomposition in the soil varied depending on the type of biocenosis. In Siberian stone pine and larch forests, low CI values were found, indicating the active participation of bacteria in the decomposition of organic matter in the soil. This is not typical of forest biocoenoses of other zones (for example, coniferous forests of Karelia), where soil fungi dominate in the decomposition of organic matter. In this study, a similar situation was observed in the steppe biocenosis, where the CI values were high and indicate the dominance of soil fungi in the processes of organic matter decomposition.