Ecological assessment of seasonal dynamics of soil CO<sub>2</sub> fluxes and humus content of Podzoluvisols on the slope catena of the forest park at different levels of recreational load
The article presents the results of monitoring the spatial and temporal variability of the main diagnostic parameters of the humus state (humus content, soil CO<sub>2</sub> fluxes and carbon stock) of Podzoluvisols in conditions of typical for the northern part of Moscow urban forest “Forest Experimental Station” of the Russian State Agrarian University - Moscow Timiryazev Agricultural Academy, formed 160 years ago on the basis of a natural forest area, with the introduction of monocultural plantings of various tree species typical for subzones of southern taiga and mixed forests of the European part of Russia and Western Siberia. As the main unregulated and regulated factors of the spatio-temporal variability of the humus state of the studied soils, the following ones are considered: (a) their position in the mesorelief (the summit of the gentle moraine hill - the middle part of the slope - the lower part (foot) of the slope); (b) the forest composition; (c) the level of recreational load (estimated by the severity of the path network); (d) the state of the herbage (estimated by the index of the projective cover); (e) the topsoil bulk density; (e) the topsoil moisture; (g) the topsoil temperature. Three levels of recreational load are considered: minimal (background), medium and strong. Soil samples were taken during three seasons in 2021: in spring, summer and autumn - from a depth of 0-5, 5-10 and 10-15 cm. The intensity of the soil CO<sub>2</sub> flux, temperature and soil moisture were determined 2 times a month. The content of organic carbon in the topsoil and the topsoil bulk density - once a month. A mobile infrared gas analyzer (IRGA) Li-820 was used to analyze the CO<sub>2</sub> flux. For statistical data analysis - Excel and SPSS programs. The conducted studies revealed a pronounced seasonal dynamics of soil CO<sub>2</sub> fluxes and the content of humus (soil organic matter) in the upper horizons of the studied soils - with a clear differentiation according to the mesorelief forms and the level of recreational load. Summer maxima of CO<sub>2</sub> fluxes reach 35-40 g/m<sup>2</sup> per day, and by the end of October they fall in 3-5 times. The humus content in the topsoil horizons (A1 - A1A2 - A2) within the total analyzed thickness of 15 cm in most cases after the April maximum significantly decreases (by 0.5-0.7%) to the seasonal minimum in August. With an increase in recreational load, on the contrary, there is a gradual decrease in the humus content by 10-20 relative percent. The average intensity of soil CO<sub>2</sub> emissions increases downhill by 5-7 g/m<sup>2</sup> per day and decreases with increasing recreational load by 5-10 g/m<sup>2</sup> per day. The established regularities significantly clarify the existing ideas about the spatial and temporal variability of the diagnostic parameters of the humus state of Podzoluvisols in an urban forest park with a pronounced recreational load and allow for a more reasonable selection of background environmental monitoring objects with an analysis of greenhouse gases and soil carbon balance.