The Effect of Forest Plantations on Carbon Dioxide Emission from Soils in the Volga and Don Regions

The formation of an organic carbon pool in soil is determined by the balance of incoming and outgoing fluxes. The incoming fluxes are associated with the processes of dying off and further transformation of the organic matter of plants, while the outgoing fluxes are primarily formed by the processes of organic matter destruction, although in many ecosystems the removal of carbon with water flows is also important. Heterotrophic destruction of soil organic matter, together with roots respiration, forms the emission of carbon dioxide from the soil. Comparing the emission values in different habitats makes it possible to draw conclusions about the nature of the factors that control the degradation processes in the soil. Measurements of carbon dioxide emissions from the soil were carried out by the chamber method in the second half of August 2020–2021 at five sites in the Voronezh, Volgograd, Astrakhan, Samara and Rostov regions. The work was carried out on pairs of plots covered with herbaceous vegetation and forest plantations. Emission of carbon dioxide from soil in forest stands was significantly higher (2.99 ± 0.26 g C m –2 ) compared to treeless areas (2.20 ± 0.11 g C m –2 ) ( P < 0.01). A statistical analysis of the correlation between emission values and soil temperature at a depth of 10 cm, volumetric soil moisture in the 0–7 cm layer, and the normalised difference vegetation index (NDVI) of vegetation cover was carried out. Humidity and NDVI were found to be significant emission factors, while temperature was not significant. The results obtained in this work and available in other scientific publications allowed us to conclude that the emission of carbon dioxide, as a rule, increased after the conversion of grass to tree cover. However, an increase in emissions was not accompanied by a loss of soil carbon stock, which either remained constant or increased slightly. An increase in NDVI indicated an increase in net primary production in forest plantations, that is, the modified ecosystem became a carbon sink with the totality of phytomass and soil pools. This pattern of change in carbon stocks and fluxes, even in carbon-rich arid soils, makes ambitious plans to create protective forest plantations to enhance carbon sequestration meaningful.