Short-Term Dynamics of CO₂ Emission and Carbon Content in Urban Soil Structures in the Steppe Zone

Сonstructed Technosols are an important component of urban green infrastructure whose role in the carbon balance of urban ecosystems remains poorly understood. The dynamics of carbon stocks and CO₂ emissions of soil structures depend on both bioclimatic conditions and the parameters of the construction – the substrates used, the composition and thickness of the layers. The carbon stock dynamics and CO₂ emission were studied on constructozems of different composition established at the “Experimental Station for Study of Soil Constructs” in the Botanical Garden of the Southern Federal University (Rostov-on-Don). The station consists of 15 self-contained sites, which present 5 different variants of soil constructions created using substrates traditionally used for landscaping and beautification tasks in the cities of the steppe zone. The Haplic Chernozems, located on a placor plot in the vicinity of the Experimental Station, was studied as a background area. Monitoring studies over two seasons (from September 2020 to December 2022) allowed the seasonal dynamics of organic and inorganic carbon content and CO₂ emissions to be compared for the different soil design options in comparison with the background. In all constructions created on the basis of humus-accumulative horizons of chernozems, a marked dependence of CO₂ emission on air (at p < 0.05 for construction 2 r = 0.76, construction 3 – r = 0.82, construction 4 – r = 0.76, construction 5 – r = 0.49) and soil (at p < 0.05 for construction 2 r = 0.58, construction 3 – r = 0.74, construction 4 – r = 0.75, construction 5 – r = 0.68) and soil (at p < 0.05 for construction 2 r = 0.58, construction 3 – r = 0.74, construction 4 – r = 0.75, construction 5 – r = 0.68) was noted. The biomass stocks of lawn grasses growing on the constructions were determined, and a positive correlation between the CO₂ emission and the growth of the above–ground biomass (for construction 2 a moderate correlation (r = 0.48, p < 0.05), for constructions 3 and 4 a marked correlation (r = 0.5, p < 0.05; r = 0.68, p < 0.05), and for construction 5 a high correlation (r = 0.75, p < 0.05) was noted. The dynamics of the stock of various forms of carbon in the first year of operation of the structures were studied. Based on the comparison of carbon fluxes and stocks, it is shown that lawn ecosystems in the early stages of constructozem cannot be considered as net carbon stock sites in the temperate continental climate of Rostov-on-Don.