Soil respiration (SR) is one of the largest fluxes in the global carbon cycle, exceeding anthropogenic CO2 emission by more than an order of magnitude. Estimation of the heterotrophic component of SR is necessary to assess the carbon balance on the ecosystem and on the regional, national, and global scales. Within the framework of the most important national innovation project “Development of a System of Ground-based and Remote Monitoring of Carbon Pools and Greenhouse Gas Fluxes on the Territory of the Russian Federation,” the first Russian national network is organized to monitor CO2 emission from soils and other linked parameters. The SR values and the relationship with the temperature of the upper 5- to 10-cm layer of soil (TS) are analyzed for the first time on the territory of Russia based on methodologically identical field measurements conducted simultaneously in the summer period (June–August 2023) at 75 monitoring sites in the different ecosystems in the main Russian bioclimatic zones from the tundra to the semidesert. The positive effect of soil temperature on the mean summer SR rate and the maximum monthly SR values is observed in the interval of mean TS from 10 to 20°C. Among the ecosystems studied, the lowest SR values are recorded in tundra and bog ecosystems, while the highest values are in the forest–steppe. Amongst the forest ecosystems, the lowest SR rates are characteristic of larch forests, while the highest SR values are observed in broadleaved forests of the forest–steppe zone. To clarify the regularities obtained, it is necessary to expand studies in all bioclimatic zones, but mainly in agrocenoses, tundra, and steppe ecosystems.

The temperature sensitivity (Q(10)) of C mineralization was studied in soils of two types: gray forest (Phaeozem, forest glade ecosystem) and soddy-podzolic (Retisol), dead soil cover pine ecosystem). It is shown that the temperature sensitivity is higher in the forest glade than in the pine forest and increases down the soil profile. Soil depth was found to be the strongest determinant of Q(10) variation. Application of nitrogen (NH4NO3) raised Q(10) in the upper soil horizons, and application of glucose, on the contrary, lowered Q(10) in both ecosystems. The effect of glucose addition was most pronounced in the lower horizons. The combined application of glucose and nitrogen affected Q(10), as well as the addition of glucose alone, indicating that the availability of a readily degradable substrate is a stronger factor influencing temperature sensitivity than nitrogen. The data obtained permitted predicting the change in the contribution of the heterotrophic component of CO2 emission from soils during global warming, as well as the increasing influx of root exudates, phytodetritus, and exogenous nitrogen into the soil.

Basal respiration is one of the key indicators of soil C mineralization. Temperature sensitivity (Q10) of basal respiration is important for predicting changes in C mineralization due to warming. A modified methodology of Q10 determination is proposed. Soil samples were incubated at 25°C with periodic short-term (2 h) decline of temperature to 15°C and high-frequency measurements of CO2 production rates. The temperature sensitivity is estimated as the average rate of CO2 production at 25°C (before and after temperature decline) divided by the rate of CO2 production at 15°C. With this method we demonstrated that glucose addition most strongly affects the Q10 values at low temperature ranges (20–10°C), while temperature range affects Q10 stronger than the glucose additions. The negative effect of soil moisture on Q10 of basal respiration was demonstrated: the Q10 values decreased with increasing soil moisture.

Seasonal dynamics of CO2 efflux from gray forest soil have been studied using collars inserted to different depths in order to estimate the contributions and interaction of soil autotrophs and heterotrophs. The depth of collar insertion has proved to have an effect on CO2 efflux only in periods of the highest biological activity. It has also been shown for the first time that the level of competition between soil autotrophs and heterotrophs depends mainly on tree species rather than on soil type.

Mycorrhizal ingrowth collars were used to study the effect of tree species on the seasonal dynamics of carbon dioxide flux from three major sources of soil respiration: (1) plant roots, (2) mycorrhizal hyphae, and (3) microorganisms. Distinct seasonality in carbon transport to mycorrhizae was revealed, with its highest values being observed during the second half of the growing season. The annual amount of C transferred through mycorrhizae did not differ between the two tree species, and the contribution of mycorrhizae to soil surface CO2 emission was about 20%.