Soil respiration (SR) is one of the largest fluxes in the global carbon cycle. The temperature sensitivity of SR (often termed as Q₁₀) is a principal parameter for evaluating the feedback intensity between soil carbon efflux and global warming. The present study aimed to estimate the seasonal and interannual dynamics of the temperature sensitivity of SR based on a long-term 24-year series of measurements in two temperate forest ecosystems in European Russia. The study was conducted in a mature mixed forest with sandy Entic Podzol and in a secondary deciduous forest with loamy Haplic Luvisol. The SR rate was measured continuously from December 1997 to November 2021 at 7–10-day intervals using the closed chamber method. Sandy Entic Podzol demonstrated a higher temperature sensitivity of SR in comparison with loamy Entic Luvisol. The Q₁₀ values for both soils in dry years were 1.3–1.4 times lower than they were in the years with normal levels of humidity. For both types of soil, we observed a significant positive correlation between the Q₁₀ values and wetness indexes. The interannual variability of Q₁₀ values for SR in forest soils was 18%–40% depending on the calculation approach and levels of aridity/humidity over the growing season. The heterogeneous Q₁₀ values should be integrated into SR and C balance models for better predictions.

Soil health is the basis of ecological and food security for humanity. Among the informative indicators of soil health are microbiological indicators based on the intensity of the carbon dioxide release from the soil. The reaction of the microbial community of Haplic Chernozem Loamic, Haplic Arenosols Eutric, and Haplic Cambisols Eutric to contamination with oxides and nitrates of Ag, Bi, Tl, and Te at doses of 0.5, 1, 3, 10, and 30 derived specific permissible concentrations (SPC) was analyzed in the conditions of a vegetation experiment (the exposure period was 10 days). One derived concentration is assumed to be equal to three background concentrations of the element in the soil. The carbon content of microbial biomass in Haplic Chernozem varied between the experimental options from 6 to 218 mg/kg of soil; in Haplic Arenosols, from 3 to 349 mg/kg of soil; and in Haplic Cambisols, from 7 to 294 mg/kg of soil. Microbial biomass was a more sensitive indicator of contamination by the studied pollutants than basal soil respiration. A decrease in specific microbial respiration was found when Haplic Cambisols were contaminated with Ag, Bi, Te, and Tl oxides. Te and Tl nitrates had a significant toxic effect on each type of soil. At the maximum dose of Tl and Te nitrate, a decrease in basal soil respiration of 56–96% relative to the control and an increase in the metabolic coefficient by 4–6 times was found. The toxicity series of heavy metals averaged for all types of soils in terms of microbiological activity was established: Bi > Ag > Te > Tl (oxides) and Te > Tl > Ag > Bi (nitrates). Nitrates of the elements were more toxic than oxides. Soil toxicity due to Ag, Bi, Tl, and Te contamination was dependent on soil particle size distribution, organic matter content, and soil structure. A series of soil sensitivity to changes in microbial biomass and basal soil respiration when contaminated with the studied pollutants: Haplic Arenosols > Haplic Chernozems > Haplic Cambisols. When diagnosing and assessing the health of soils contaminated with Ag, Bi, Tl, and Te, it is advisable to use indicators of soil microbiological activity.

Climate warming has led to more frequent soil freeze–thaw (FT) events in high-latitude and high-altitude regions, leading to significant pulse releases of greenhouse gasses (GHGs) such as nitrous oxide (N₂O) and carbon dioxide (CO₂) into the atmosphere. These pulse emissions exhibit unpredictable spatiotemporal variability, which are influenced by soil type, soil moisture and FT temperature. This study employed controlled laboratory experiments to investigate the effects of varying FT intensities (−10 °C/10 °C, −5 °C/5 °C, and a control at 0 °C/0 °C) and soil moisture levels (30%, 60%, and 90% water-filled pore space, WFPS) on the dynamics of soil N₂O and CO₂ emissions (measured daily), and the availability of carbon and nitrogen, microbial biomass, and enzyme activities (measured weekly) in the soils collected from two forest stands in the Changbai mountains of northeast China, a broadleaf and Korean pine (Pinus koraiensis Sieb. et Zucc.) mixed forest (BKPF) and an adjacent secondary white birch (Betula platyphylla Suk.) forest (WBF), where FT events frequently occur. Our findings reveal that a high FT intensity (−10 °C/10 °C) significantly increased N₂O and CO₂ emissions from BKPF and WBF soils. With increasing soil moisture, soil CO₂ emissions peaked at 60% WFPS, while soil N₂O emissions were the highest at 90% WFPS. Notably, pulse emissions of N₂O were particularly intense under a high FT intensity and high moisture (i.e., 90% WFPS) in WBF soils, persisting for nearly 8 days during FT cycles. The emissions of N₂O and CO₂ under varying FT and moisture conditions are intricately regulated by soil substrate dynamics, including dissolved organic carbon, nitrogen mineralization, and nitrate concentrations. The results improve the understanding of the high variability of soil GHG emissions during the FT process and its underlying mechanisms, which are inadequately considered in current ecological and land surface process models. Consequently, it would contribute valuable insights into the interaction between soil GHG emissions and climate change in high-latitude and high-altitude zones.

Soil respiration (SR) is a main component of the carbon cycle in terrestrial ecosystems, and being strongly affected by changes in the environment, it is a good indicator of the ecosystem’s ability to cope with climate change. This research aims to find better empirical SR models using 25-year-long SR monitoring in two forest ecosystems formed on sandy Entic Podzol and loamy Haplic Luvisol. The following parameters were considered in the examined models: the mean monthly soil or air temperatures (T_soil or T_air), the amount of precipitation during the current (P) and the previous (PP) months, and the storage of soil organic carbon (SOC). The weighted non-linear regression was used for model parameter estimations for the normal, wet, and dry years. To improve the model resolutions by magnitude, we controlled the slope and intercept of the linear model comparison between the measured and modeled data through the change in R₀—SR at zero soil temperature. The mean bias error (MBE), root-mean-square error (RMSE), and determination coefficient (R²) were used for the estimation of the goodness of model performances. For the sandy Entic Podzol, it is more appropriate to use the models dependent on SOC (TPPC). While for the loamy Haplic Luvisol, the Raich–Hashimoto model (TPPrh) with the quadratic T_soil or T_air dependency shows the better results. An application of T_soil for the model parameterization gives better results than T_air: the TPPC model was able to adequately describe the cold-period SR (T_soil ≤ 2 °C); the TPPrh model was able to avoid overestimations of the warm-period SR (T_soil > 2 °C). The TPPC model parameterized with T_soil can be used for the quality control of the cold-period SR measurements. Therefore, we showed the importance of accounting for SOC and the water-holding ability when the optimal SR model is chosen for the analysis.

Precipitation and temperature regimes are the key factors that regulate the rate of decomposition of soil organic matter in terrestrial ecosystems. The aim of this study was to assess the effect of the duration of dry periods in summer and different depths of snow cover in winter on heterotrophic soil respiration. The studies were carried out as part of a two-year field simulation experiment on gray soil (Haplic Luvisol) under the temperate continental climate (south of Moscow oblast). Three variants were forecasted: (1) simulation of mild weather with uniform irrigation of the soil in summer and the absence of freezing in winter, (2) simulation of two summer dry periods lasting 1–2 months with natural winter snow cover (control), (3) simulation of extreme weather with one long (~3 months) dry period in summer and complete removal of snow cover in winter. Heterotrophic soil respiration was measured by the closed chamber method on bare fallow during two years of continuous experiment and one year after its completion. Median values of heterotrophic soil respiration for the entire period of the experiment in the three above-mentioned variants of the experiment were 38, 27 and 19 mg C/(m² × h), respectively. Two short dry periods led to an increase in heterotrophic soil respiration by 7–10%, which is associated both with the drying and rewetting cycles of the soil and with an increase in the mean summer temperature of a 20-cm soil layer by 1.5°C. The prolonged dry period caused a decrease in heterotrophic soil respiration by 12–16% as a result of low soil moisture content. Soil freezing led to a strong decrease in winter heterotrophic soil respiration, which reached 34–55% in the control variant and 57–72% when the snow cover was removed. The frosty period (November–March) contributed 25–34% and 14–19% without and with soil freezing, respectively, to the annual CO₂ flux from the soil. It was concluded that the lack of soil freezing caused by an increase in the depth of snow cover led to a more significant change in the annual heterotrophic soil respiration than the lack of precipitation in the summer season.

Respiration of soil heterotrophs—mainly of bacteria and fungi—is a substantial part of carbon balance in terrestrial ecosystems, which tie up organic matter decomposition with the rise of atmospheric CO₂ concentration. Deep understanding and prediction of seasonal and interannual variation of heterotrophic and autotrophic components of CO₂ efflux from soil is limited by the lack of long-term, full-year measurements. To better understand the impact of current climate changes on CO₂ emissions from soils in the mixed forest and mowed grassland, we measured CO₂ efflux every week for 2 years. Heterotrophic (SOM-derived + leaf litter) and root-associated (root with rhizosphere microorganisms) components were partitioned by the root exclusion method. The total CO₂ efflux from soil was averaged 500 g C m⁻² yr⁻¹ in the forest and 650 g C m⁻² yr⁻¹ in the grassland, with shares of the no-growing cold season (Nov–Mar) of 22% and 14%, respectively. The heterotrophic component of CO₂ efflux from the soil averaged 62% in the forest and 28% in the grassland, and it was generally stable across seasons. The redistribution of the annual precipitation amounts as well as their deficit (droughts) reduced soil respiration by 33–81% and heterotrophic respiration by 24–57% during dry periods. This effect was more pronounced in the grassland (with an average decline of 56% compared to 39% in the forest), which is related to lower soil moisture content in the grassland topsoil during dry periods.