Influence of the geological and ecological conditions of the Vyatka Uval within the Republic of Mari El on the formation and transformation of organic matter in forest soils

The subject of the study is the organic matter of forest soils as a key element of biospheric processes that ensure ecosystem stability, carbon accumulation and biodiversity maintenance. The Vyatka Ridge area, characterized by young geological structures, dissected relief and access to the surface of Permian red-colored sediments, is a unique natural laboratory for studying the interaction of geological, soil and biological factors. The relevance of the study is due to the need to deepen knowledge about the mechanisms of organic matter destruction in the context of climate change and the increasing anthropogenic impact on forest biogeocenoses. The aim of the work is to identify patterns of formation, accumulation and transformation of organic matter in the forest litter of Vyatka Ridge under the influence of specific geological and environmental conditions. To achieve this goal, the following tasks were solved: characterization of morphological and biochemical parameters of litter in various phytocenoses, establishing the relationship between the granulometric composition of soils, the acidity of litter and the intensity of humification, comparative analysis of the data obtained with international studies in the field of carbon cycle and organic degradation. Selection was carried out according to GOST 17.4.3.01-2017, litter was selected in layers with subsequent determination of their capacity, reserve, and morphological structure. The granulometric composition of the soil-forming rocks was analyzed by a laser particle analyzer. The pH of the extracts, the content of (P₂o₅) and (K₂O) were measured using the Kirsanov method, as well as the intensity of co₂ emission by the gasometric method. Morphological analysis of the samples revealed significant variability in the thickness of forest litter: in coniferous phytocenoses 2-6 cm, in deciduous – 1-2 cm. The predominance of two-layer bedding of the "moder" type (75% of samples) is explained by the relatively rapid decomposition of organic matter on carbonate soils typical of Vyatka Ridge. Litter of the "pestilence" type, typical for acidic soils with delayed mineralization, was absent. The physico-chemical properties of the litter demonstrated a regular decrease in the organic matter content with depth: from 79-96% in the upper layer (O1) to 46-89% in the lower layer (O2). The acidity of the litter showed minimum pH values (4.2–5.0) in pine forests, maximum (5.8–6.0) in birch forests. Deficiency of mobile phosphorus (12-30 mg/100 g) and potassium (120-200 mg/100 g) was observed in the litter of pine forests on sandy soils, which is associated with the removal of elements into mineral horizons.