Variations in Organic Carbon Content and Dehydrogenase Activity in Post-Agriculture Forest Soils: A Case Study in South-Western Pomerania  
[PERSON]  
1 Department of Soil Science and Land Reclamation, Poznan University of Life Sciences, Piatkowska 94, 60-649 Poznan, Poland; [EMAIL_ADDRESS]  
2 Department of Construction and Geogeninger  
and affecting soil microorganism activity and in consequence the rate of decomposition processes (increasing output). At the same time, higher biomass production and organic carbon accumulation occur in areas with higher amounts of rainfall [5; 6]. The content of the SOC is a result of dynamic equilibrium between the carbon input and output, which are affected by land use type, plant species, climate factors, soil properties, anthropogenic or natural disturbances [7; 8]. The rate of transformation of organic carbon compounds, accumulated in forest soils, will vary depending on their biochemical resistance to mineralization processes, as well as physicochemical availability [9; 10; 11]. Commonly SOC resources are partitioned into three fractions differing in decomposability and protection mechanisms: active, intermediate and stable. Chemically active forms of organic carbon include water-soluble forms, light fractions (density \(<\) 1.6-2.0 g\(\cdot\)cm\({}^{-3}\)), as well as a pool of compounds susceptible to microbial degradation, such as saccharides and proteins. The stable fraction consists of compounds resistant to mineralization processes, composed of condensed lignin-based aromatic rings, waxes, cutins or products of pyrogenic degradation of organic compounds. Unlike the active carbon pool, their decomposition time is measured in hundreds of years. The second factor determining resistance to degradation processes is the physical availability of these compounds to microorganisms [5; 9; 12]. Forms of carbon found inside soil aggregates are protected against both microbiological processes, soil enzymes, and partly against the inflow of molecular oxygen. Physical protection of the stable, residual fraction against mineralization processes involves the creation of bonds with the clay, silt fractions or with iron and aluminum oxides. These mineral-organic complexes are formed as a result of the formation of coordination bonds with ligands, bonds through cationic bridges or hydrogen bonds [11]. All these factors mean that determining SOC stocks is not an easy task, but extremely labor-intensive and time consuming. This task in forest ecosystems encounters additional difficulties related to the uneven supply of fresh debris to soils and the impact of past land use and historical disturbance legacies (fires, tree falling/ deforestation) on the current state of carbon resources [13]. Increasing emissions of CO\({}_{2}\) and other greenhouse gases into the atmosphere and, as a result, the progressive process of global warming has attracted the attention of many research institutions towards methods that reduce the rate of climate change [4; 14]. One of the strategies adopted is the sequestration of atmospheric carbon dioxide, understood as the process of transformation and accumulation of gaseous CO\({}_{2}\) in the form of stable compounds [4; 10; 15]. Forest ecosystems that accumulate carbon in the form of lignins and other polymers resistant to decay are an ideal environment--a \"trap\" for the atmospheric carbon pool. Wherein, carbon is accumulated not only in aboveground biomass but also in the surface layers of soil. The process of carbon sequestration in forest soils takes place in two ways: through the input and transformation of organic substances on the surface and the activity of the root system [1]. Litter decomposition is one of the main sources of SOC and thus the quality of the incoming organic substance (C:N ratio, content of lignin compounds, hemicelluloses, celluloses, proteins, etc.) will significantly affect the amount of sequestration of this element [7].