Effects of Forest Reclamation on Carbon Stocks and Respiration in Soils of Natural and Technogenic Ecosystems of Southern Karelia

The paper presents the results of studies on soil carbon stock dynamics, CO₂emissions and soil microbial respiration during post-industrial succession upon reforestation of a sand and gravel pit in southern Karelia. The soils of the territories of different reforestation options were studied in July 2021 and 2022. In 1991, annual Scots pine (Pinus sylvestris L.) seedlings were planted on the plots: 1) in sand and gravel mineral soil (SP 1, SP 2); 2) in peat-improved substrate (SP 3). Natural soils (Entic Podzol) of an undisturbed lingonberry-type pine forest (SP 4) served as the control. Soil total (organic) carbon, microbial activity (by using the basal and substrate-induced respiration method in the laboratory), and CO₂emission from the soil surface (under field conditions) were determined. The assessment of the properties of post-industrial soils revealed the similarity of the studied parameters in replantozem SP 3 and podzolized podbur SP 4, which indicates a positive effect of peat-enriched substrate on the recovery of the soil and vegetation cover of the sand and gravel pit. The higher values of the carbon stocks (6–10-fold) and CO₂fluxes (2–4-fold) from the surface of the replantozem (Umbric Leptosol (Novic)) SP 3 relative to those in psammozems (Skeletic Leptosol) of SP 1 and SP 2 are due to intensive organic matter accumulation processes and the application of peat substrate rich in nutrients and plant diaspores during planting. SP 1 and SP 2 had the lowest values of soil carbon stocks, CO₂emissions, microbial activity, simultaneously with low stand productivity as compared to SP 3 and SP 4. To make more accurate predictions of the dynamics of the said parameters of disturbed soils, it is necessary to take into account their spatial and temporal variability.