The light fraction of soil organic matter (LF) has a rapid turnover and may be potentially metal-enriched, but the interaction between this pool of organic matter and trace elements has not been well studied. The present study aimed to investigate changes in LF content and its effect on heavy metals distribution and extractability in long-term contaminated soil by smelting activity. An incubation experiment was conducted on a surface horizon of Brunic Arenosol sampled from the previously-existing sanitary zone of Głogów smelter, for 450 days. The contaminated soil was divided into three combinations: with the addition of either triticate straw (at the dose of 4.5 Mg ha^-1) or pig manure (at the dose of 40 Mg ha^-1) or without any “foreign” organic materials (nil). The LF (ρ > 1.7 g cm^-3) occurred to be metal-enriched and despite its low content (5.49%—nil, 7.18%—straw and 7.29%—manure combination) in the bulk soil, it was observed that initially Cd, Cu, Pb and Zn stock reached 16.2%, 11.9%, 18.0% and 32.3%, respectively. Incubation conditions where mineralization processes dominate led to a decrease in the LF share by about 12.6% in nil and 31.4–39.8% in the combinations with organic amendments. In consequence, the DOC (dissolved organic carbon) concentration doubled and metal distribution had changed. The increase in water-soluble (F1) fraction was observed for all metals, additionally for Cu, Pb, Zn in exchangeable fraction (F2) and in carbonate bound (F3) fraction for Cd and Zn. These results support the view that changes in the LF content may play a key role in controlling trace metals mobility, especially in long-term contaminated soil.

Temperate forest soils of Europe are regarded as an important sink of carbon and thought to have potential to sequester CO₂ from atmosphere. However, there are insufficient data not only on organic carbon (OC) content in forest soils and its temporal changes but also on microbiological activity and especially their relationship to carbon turnover. In this study seven research plots were located on afforested land in the north-western part of Poland in Tuczno Forest District (Western Pomerania) in order to examine seasonal variation in OC content and dehydrogenases activity (DHA) during 2012–2016. Based on the studies conducted, statistically significant seasonal variation of the OC content was observed. Higher amounts of OC in the A horizon were observed during spring and autumn seasons and lower in summer. However, no seasonal variation on OC content was observed in the organic horizon (O horizon). Although DHA is thought to exhibit strong seasonal variability, no seasonal variation on DHA was observed. However, a statistically significant difference was observed among studied years (2012–2016), a sharp drop of DHA was noted from spring 2014. Statistical analyses revealed that OC content in soils was a function of forest stand age and progressing acidification of soil. Moreover, OC content in O horizon was negatively correlated with soil moisture and DHA, suggesting that periods with higher microbial activity lead to lower accumulation of carbon in the O horizon. During 2012–2016 only for the O horizon was an increase in OC content was observed.

The purpose of this work is to determine seasonal changes in the organic carbon content in the mineral topsoil horizon of the Dystric Brunic Arenosols currently used as forest. In addition, the influence of forest age on the soil organic carbon (SOC) content in the A horizon was analyzed. The paper presents the results of studies on temporal changes in the SOC content in the mineral surface horizon of 55-year-old (Sk2) and 13-year-old forest (Sk5) in 2013 and 2014. Soil samples were collected from A horizon once a month between April 2013 and March 2015. Based on the conducted studies, clear seasonal differentiation of the SOC content was observed. Higher contents of SOC in the A horizon of the analyzed soils occurred in the autumn and winter months, and were lower in spring and summer. For Sk2 soil, higher SOC values were observed in autumn and then in winter, which on average were 11.08 g·kg⁻¹ and 9.61 g·kg⁻¹ respectively, while lower in spring and summer (8.85 g·kg⁻¹ and 8.83 g·kg–1 respectively). Also in the mineral topsoil horizon of Sk5 soil, higher SOC contents were recorded in autumn and winter (8.07 g·kg⁻¹ and 7.27 g·kg⁻¹ respectively), and lower in spring and summer (6.19 g·kg⁻¹ and 6.57 g·kg⁻¹ respectively). The periodicity of SOC content in plots studied was related to the seasonality of precipitation and temperature. The research also showed that the age of the forest stand influences significantly the content of organic carbon in the A horizon. Higher content of SOC was observed in the A horizon of the 55 years old forest stand (average 9.69 g·kg⁻¹) than on the 13 years old (7.02 g·kg⁻¹).

Land use changes inevitably lead to changes in the carbon stocks stored in the soil. However, despite numerous studies investigating soil organic carbon (SOC) dynamics following the afforestation of post-agricultural lands, findings remain diverse and often inconclusive. In this study, the effect of stand age on the carbon content and stock in Scots pine (Pinus sylvestris) stands located in the Dfb-climate zone was investigated. Five research plots, characterized by similar soil types, geological structures, and tree cover, but differing in stand age (14-, 27-, 37-, 55-, 90-year-old stands), were selected. Additionally, one plot was located at arable soil as a reference. The soil was sampled from both organic and mineral horizons. The content of organic carbon in the organic horizion increased with years that passed from afforestation and amounted to 234.0, 251.6, 255.0, 265.0 and 293.0 g·kg⁻¹ in 14-, 27-, 37-, 55- and 90-year-old stands, respectively. Such a pattern was also observed in the upper mineral horizons where the contents of SOC gradually increased from 7.27 g·kg⁻¹ up to 17.1 g·kg⁻¹. In the organic horizon, the stock of OC increased significantly with stand age up to 55 years after afforestation, while in the former plough layer, SOC stocks were found to slowly increase with stand age. The afforested soils, with the organic horizon, reached levels of carbon stocks observed on arable land after 17 years. Notably, the SOC stock in the mineral A horizon reach this level after 83 years. The obtained results indicate that in the years immediately following afforestation, SOC content is notably higher in arable soils compared to forest soils. However, as stand age increases, the SOC contents of upper horizons in forest soils surpass those of comparable agricultural soils. The observed SOC variability pinpoints the necessity of long-term monitoring in forest ecosystems in order to better understand the temporal dynamics of carbon turnover and to optimize afforestation strategies for long-term carbon sequestration.