Soil organic matter (SOM) concentration and composition are essential properties that
affect most functions and ecosystem services. The relationship between soil and environmental
covariates regarding SOM concentration and composition in various pools is not completely
understood. This study aimed to identify the most influential drivers of SOM stabilization,
focusing on arable lands in Hungary. Hungary is an ideal area for investigating SOM
variability because it is at the meeting point of the three main climate effects that
trigger a wide range of soil, land use, and topographical conditions. Overall, 87
soil samples were taken from the topsoil (2–20 cm) and fractionated (<20 µm) to separate
the mineral phase-associated organic carbon (MAOC) and bulk pools. MAOC concentration
varied on a wide range (0.5–14.1 %) and was the function of bulk SOM aromaticity and
slope steepness, rather than land use, climatic conditions, or soil properties, indicating
that MAOC is also affected by decomposition if the bulk OM is less available for the
microbiome. Land use, especially in forest topsoils, reflects the elemental composition
of the OM, focusing on the variations of residue composition. In contrast, aromaticity
is rather related to soil and climate properties, suggesting increased relevance of
transformation processes. As a consequence, SOM composition varies on a wide range
in the topsoil, however, the lack of a definite trend at the county level suggests
the complexity of the system and highlights the role of local circumstances.
