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Tobiašová E., Barančíková G., Gömöryová E., Makovníková J., Skalský R., Halas J., Koco Š., Tarasovičová Z., Takáč J., Špaňo M. Soil organic matter (SOM) plays an important role in the soil aggregation and vice versa, its incorporation into the soil aggregates is one of the mechanisms of soil organic carbon stabilization. In this study the influence of labile carbon fractions on the fractions of dry-sieved (DSA) and wet-sieved (WSA) macro-aggregates and the relationship between the content of total organic carbon (TOC) and its labile fractions in the soil and in the fractions of macro-aggregates were determined. The experiment included six soil types (Eutric Fluvisol, Mollic Fluvisol, Haplic Chernozem, Haplic Luvisol, Eutric Cambisol, Rendzic Leptosol) in four ecosystems (forest, meadow, urban, and agro-ecosystem). In the case of DSA, the contents of labile fractions of carbon, in particular cold water extractable organic carbon (CWEOC) and hot water extractable organic carbon (HWEOC), had a higher impact on the proportions of larger fractions of macro-aggregates (3-7 mm), while in the case of WSA, the impact of labile fractions of carbon, mainly labile carbon (C L ) oxidizable with KMnO 4 , was higher on the proportions of smaller fractions of aggregates (0.25-1 mm). The WSA size fraction of 0.5-1 mm seems an important indicator of changes in the ecosystems and its amounts were in a negative correlation with C L (r = -0.317; P < 0.05) and HWEOC (r = -0.356; P < 0.05). In the WSA and DSA size fractions 0.5-1 mm, the highest variability in the contents of TOC and C L was recorded in the forest ecosystem > meadow ecosystem > urban ecosystem > agro-ecosystem. The higher were the inputs of organic substances into the soil, the greater was the variability in their incorporation into the soil aggregates. The influence of the content of TOC and its labile forms on their contents in the DSA and WSA was different, and the contents of TOC and C L in the aggregates were more significantly affected by the C L content than by water soluble carbon. In the case of WSA fractions, their carbon content was more affected in the 1-2 mm than in 0.5-1 mm fraction.

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Organic matter is an essential soil component determining its physical, chemical and biological properties. Both in arable fields and in forest ecosystems, the key source of organic matter is plant material at various stages of decomposition and processing, living and dead soil organisms, as well as their excrement [1]. The effect of respective plant materials on organic matter balance in those ecosystems is not the same. The problem concerns the quantity and the quality of the material introduced to soil [2-7]. In forests the chemical composition of the plant litter reaching soil depends on the tree stand species and the habitat. The highest differences in the chemical composition were observed between deciduous and coniferous vegetation.