Formal Criteria for the Humus Status of Mountainous Peat Soils in Altitudinal Zones

Resumo

Cryogenic oligotrophic (Hyperdystric Cryic Fibric Histosols), oligomesotrophic (Dystric Fibric Histosols), mesoeutrophic (Oligeoeutric Fibric Histosols), and eutrophic (Hypereutric Fibric Histosols) peat soils were studied on the eastern slopes of the Kuznetsk Alatau Ridge (Republic of Khakassia). Their altitudinal differentiation was examined, and clustering according to the qualitative and quantitative composition of organic matter was performed. The most informative indicators of similarity and/or differences between the clusters were suggested. The group composition of organic matter was analyzed using acid and alkaline extractions. Multivariate statistical analyses (cluster, discriminant, and canonic) were applied for evaluation of the humus status. Indicators of organic matter status, which are significant for discrimination form two discriminant functions. Function 1 discriminates between the clusters (80%) and includes the indicators characterizing the depths of peat soil transformation: humification degree (∑HA + ∑FA), type of humus (C_HA/C_FA ratio), and ratio between the fractions of humic acids extracted by 0.02 N NaOH and 0.1 N NaOH (С_{0.02 n NaOH}/C_{0.1 n NaOH}). Function 1 clearly separates clusters of permafrost-affected oligotrophic peat soils of the alpine tundra zone (>1460 m a.s.l.) from oligo-mesotrophic peat soils of the subalpine zone (1087 m a.s.l.). Function 2 discriminates (at the 16% difference level) the clusters of peat soils of the forest zone—meso-eutrophic peat soils of the taiga zone (832 m a.s.l.) and eutrophic peat soils of the subtaiga–forest-steppe zone (622–573 m a.s.l.); it also includes hemicellulose and cellulose—characteristics of the initial state of peat-forming plants. The humus status of the mountainous peat soils corresponds to their diagnostics according to the base saturation and pH criteria and reflects a general pedogenetic trend in mountains: an increase in the humus content in soils with the altitude, which was earlier shown for mineral soils.