Transformation of physicochemical properties and CO<sub>2</sub> emission of urban soils in the mountainous landscape of Sochi

Soils of two urban zones were studied: residential and park-recreational (conditionally background), formed in the conditions of mountainous relief of the city of Sochi (Black Sea coast of Russia). The recreational zone is the territory of the Sochi Arboretum Park. Here natural zonal soils – brown soils (Cambisols) and yellow soils (Acrisols) are distributed, in the residential zone structural-metamorphic abrasions (Technosols) are developed. The aim of the present work was to study the transformation of physicochemical properties of urban soils and their CO2 emission and to identify the factors influencing the intensity of CO2 emission in the urban landscapes of Sochi. Acid-base properties of soils of the residential zone (Technosols) and the composition of its main biogenic elements were transformed compared to the background under the influence of technogenesis. Alkalization of soils, increase of the sum of exchangeable bases and insignificant decrease of humus content are observed. Measurements of CO2 emission were made by the method of closed chambers using a portable infrared gas analyzer. On average, the intensity of carbon dioxide flux in the soils of the residential zone is 2.5% lower compared to the background. This is due to the transformation of the upper part of the urban soil profile as a result of construction of houses and cultivation of lawns. A high variability of CO2 emission in soils of urban landscapes was noted, averaging 48%. The main factors contributing to this pattern include: 1) soil domestication by introducing material from humus-accumulative horizons of chernozems, 2) seeding disturbed soils with lawn grasses. Minimal soil CO2 emission is observed in natural and natural-like biocenoses under woody vegetation. Assessment of the climate-forming role of urban soils of Sochi as a source/sink of greenhouse gases is possible taking into account all the factors mentioned above.