Sequential (S) and equal-time (ET) methods were applied to assess the temperature sensitivity of respiration of peat soils in different terrestrial ecosystems: southern tundra, northern taiga, and mixed coniferous–broadleaved forests. The Q10 values varied widely (1.3–4.8) and in case of the ET method decreased from northern to temperate latitudes. In the cold range (5–15°С), Q10 increased from the southern tundra (3.5) to the northern taiga (4.8) and then sharply decreased in the zone of mixed forests (2.5). Meanwhile, warm range (15–25°С) showed a clear decline of Q10 from northern to temperate latitudes: southern tundra (2.6) > northern taiga (1.6) > coniferous–broadleaved forests (1.3). Application of the S method resulted in low variability of Q10 values. Our results demonstrate a higher temperature sensitivity of the respiration of peat soils in northern latitudes as compared to that in the temperate zone. The Q10 values obtained in this study can be useful for calibration of regional carbon cycle datasets that consider the contribution of peat soils.

Soils are the largest terrestrial reservoir of organic carbon, and so even small changes in soil carbon stocks can have significant effects on the atmosphere and climate. To select effective strategies to mitigate climate change, predictions of how soils will respond to future changes in climate and land use are needed. Achieving meaningful predictions requires a deep understanding of the highly complex, open, multicomponent soil organic matter system. One of the most effective methods for predicting the dynamics of soil organic matter is mathematical modeling. Process-oriented (physically based) models make it possible to present the basic concepts about the mechanisms that determine the behavior of this system in a mathematically formalized form and conduct a quantitative analysis. The uncertainty of the forecasts depends on the level of development of the theory explaining the dynamics of soil organic matter, the models representing it and their experimental support. This review examines the achievements of the last decade in modeling the role of microorganisms in the stabilization of soil organic matter, the concept of soil saturation with organic carbon, and temperature control, as well as the development of reactive transport models describing the dynamics of organic carbon in the soil profile and the representation of the dynamics of soil organic matter in global climate models. Unsolved problems associated with the high variability in the structure of new generation soil organic matter dynamics models are discussed.

— The assessment of carbon stocks in soils of coniferous and broadleaved forests, agrocenoses, fallow lands, and floodplains has been performed for the territory of the Chashnikovo Agrobiological Station of Moscow State University. The typology of litter horizons, the contents of plant detritus in the them, and the ratio of the thicknesses of litter subhorizons have been determined as indicators of the organic matter decomposition intensity. For mineral soil profile, total organic carbon stocks in the layers of 0–30 and 0–100 cm layers and the stock of biologically active carbon in the layer of 0–20 cm layer have been determined. Maximum organic matter accumulation in litters and moderate accumulation in mineral profile is typical of soddy-podzolic soils (Retisols) under coniferous forests. The litter carbon stocks in spruce forests differ by almost an order of magnitude depending on the position in the tessera. Minimum carbon accumulation in litters is characteristic of the soils of upland and floodplain meadows. Alluvial soils of floodplain meadows are characterized by the highest stock of total carbon, as well as carbon of biologically active soil organic matter. The potential of CO 2 production by soil determined the structural and functional litter characteristics and the stock of biologically active organic matter in the upper (0–20 cm) soil layer depend on several factors: vegetation type, hydromorphism degree, and agricultural use at present and in the past. Soils of coniferous forests in comparison with soils of broadleaved forests are characterized by lower rates of litter decomposition due to the biochemical features of plant remains and are assumed to have a lower potential for CO 2 production. Soils of natural herbaceous ecosystems, especially floodplain meadows, are characterized by the maximum potential production of carbon dioxide due to intense decomposition of plant residues and high stock of biologically active organic matter carbon.

Within the territory of MSU Agrobiostation “Chashnikovo”, assessment of carbon stock for soil, typical for coniferous-broad-leaved forests subzone – coniferous forests, small-leaved forests, agrocenoses, fallow lands and floodplain meadows – was given. The next indexes were studied for litters: typology, stock, detritus content and ratio of sub-horizons thickness (deposit) – these indexes are indicators of organic matter decomposition intensity. For mineral soil profile, the assessment of general organic carbon stock in 0–30 and 0–100 cm layers, as well as stock of biologically active carbon in 0–20 cm layer (by calculation according to the content of total carbon), are given. Maximum organic matter accumulation in litters and moderate accumulation – in mineral profile, was obtained for coniferous forests soddy-podzolic soils. The litter carbon stock value in spruce forests differ by almost 10 times, depending on location in tessera. Minimal carbon accumulation by litters is obtained for meadow ecosystem soils – upland meadows as well as flood-plain meadows. Alluvial soils of flood-plain meadows are characterized by highest stock of general carbon, as well as carbon of biologically active soil organic matter. Potential of CO2 production by soil, determined by data, including structural and functional litter indexes and organic matter biologically active carbon stock (0–20 cm layer), depends on combination of row of factors: vegetation type, hydromorphism degree, and agricultural use character in present or past. Coniferous forest soils comparing with small-leaved forest soils are characterized by less rate of litter decomposing due to plant remains biochemical features, thereby these soils are assumed to less CO2 production potential. Soils of natural grass ecosystems, especially flood-plain meadows, are characterized by maximal potential production of carbon dioxide, resulting from intensive plant residues decomposition and high stock of biologically active organic matter carbon.

Within the territory of MSU Agrobiostation “Chashnikovo”, assessment of carbon stock for soil, typical for coniferous-broad-leaved forests subzone – coniferous forests, small-leaved forests, agrocenoses, fallow lands and floodplain meadows – was given. The next indexes were studied for litters: typology, stock, detritus content and ratio of sub-horizons thickness (deposit) – these indexes are indicators of organic matter decomposition intensity. For mineral soil profile, the assessment of general organic carbon stock in 0–30 and 0–100 cm layers, as well as stock of biologically active carbon in 0–20 cm layer (by calculation according to the content of total carbon), are given. Maximum organic matter accumulation in litters and moderate accumulation – in mineral profile, was obtained for coniferous forests soddy-podzolic soils. The litter carbon stock value in spruce forests differ by almost 10 times, depending on location in tessera. Minimal carbon accumulation by litters is obtained for meadow ecosystem soils – upland meadows as well as flood-plain meadows. Alluvial soils of flood-plain meadows are characterized by highest stock of general carbon, as well as carbon of biologically active soil organic matter. Potential of CO2 production by soil, determined by data, including structural and functional litter indexes and organic matter biologically active carbon stock (0–20 cm layer), depends on combination of row of factors: vegetation type, hydromorphism degree, and agricultural use character in present or past. Coniferous forest soils comparing with small-leaved forest soils are characterized by less rate of litter decomposing due to plant remains biochemical features, thereby these soils are assumed to less CO2 production potential. Soils of natural grass ecosystems, especially flood-plain meadows, are characterized by maximal potential production of carbon dioxide, resulting from intensive plant residues decomposition and high stock of biologically active organic matter carbon.

Permafrost degradation due to climate warming is currently observed in the northeastern part of European Russia. Peat plateaus underlain by permafrost cover only about 20% of the Russian European cryolithozone but contain almost 50% of soil organic carbon stocks (SOC), which are considered to be vulnerable to microbial mineralization after permafrost thaw. The current study was performed at three key sites of peat plateaus located along the southern permafrost limit. SOC decomposition was studied by aerobic and anaerobic incubation experiments, conducted at 4 °C over a period of 1301 days. The CO2 production was measured in peat samples at three key sites from the active layer (AL), transitional layer (TL), permafrost layer (PL), and at one site from the deep permafrost layer (DPL), which is in contact with mineral soil at 3.7 m depth. During the experiment, the initial СО2 respiration rates significantly differed in the samples AL, TL and PL in all key sites. However, at each site in the majority of samples the CO2 respiration rates were 2-5 times aerobically higher than anaerobically. In anaerobic conditions, in all sites, the СО2 respiration rate in PL was the lowest, higher in TL and the highest in AL in all 3 sites. Projections of CO2 aerobically production for 80 years represent 1.44 ± 0.11, 6.31 ± 0.47, 30.64 ± 17.98% of initial permafrost carbon from the samples of Inta 1, Inta 11 and Kolva respectively. But under anaerobical conditions estimates are close and indicate insignificant amounts 0.30…1.90% of carbon release over a period of 80 years. We suggest that even under ideal conditions of the incubation experiment, without considering ecological inertia under natural conditions, while also permafrost temperature is close to zero, greenhouse gas release from initial SOC is significantly less than estimated.

Wetland ecosystems play a significant role in organic carbon conservation; one meter layer of peat soils store over 30 percent of terrestrial organic carbon (Lal, 2008). Ecosystems have different sensitivity to climate change in different nature zones (IPCC, 2014) due to various moisture and temperature regime. The aim in this work is to define effect of temperature and moisture on mineralization rate in peat soils in Northern and Southern taiga. The samples of Cryic Histosol (WRB, 2014) were taken from Northern Taiga (65°18'52" N, 72°52'32" E). The samples of Fibric Histosol (WRB, 2014) were taken from Southern Taiga (55°40'04" N 36°42'49" E). In laboratory conditions, samples were brought to certain soil moisture (SM): 30, 60, 80, 100 % (Gritsch, 2015), temperature of incubation was ranging from 5 to 25 ◦C (equal-time method). In all the cases basal respiration (BR) was growing with increasing of temperature. Samples of Cryic Histosol are more sensitive to changes both in temperature and moisture. BR varies from 0.58 ±0.26 (30% SM and 5 ◦C) to 13.53±0.22 mg C-CO2/g/h (100% SM and 25 ◦C). Q10 coefficient varies from 4.64 to 2.82 respectively (this coefficient demonstrates differences in the temperature sensitivity of soil respiration (Kirschbaum, 1995)). For samples of Fibric Histosol BR varies from 0.75±0.01 (30% SM and 5 ◦C) to 6.14±0.26 mg C-CO2/g/h (100% SM and 25 ◦C). Q10 coefficient varies from 2.70 to 2.18 respectively. Influence of moisture and temperature on biological activity in all of the cases was statistically confirmed, but interaction of factors is significant only for Cryic Histosol. According to the results, Cryic Histosol is more sensitive to temperature and moisture change, than Fibric Histosol. Peat soils in the northern area are subjected to more rapid organic carbon mineralization after a change of hydrothermal regime, than southern peat soils. In conclusion, Q10 coefficient variation indicates that soils with low soil moisture are more sensitive to temperature changes.

Soils play an important role in the biogeochemical carbon cycle; therefore, in connection with the problem of global climate change, special attention is paid to the assessment of soil organic matter reserves. The accumulation of organic matter in soil is the result of combined effects of many factors that regulate the processes of its transformations, which determines its high spatial variability. The degree of soil moisture is one of the leading factors that affect organic carbon reserves in soils. The moisture factor is of particular importance, when assessing carbon stocks in soils of the forest zone, which accounts for 70% of the area of all semihydromorphic soils in Russia. According to published data, the organic carbon reserves in semihydromorphic forest soils are several times higher than in automorphic ones. Information about the variability of carbon stocks in forest soils and its dependence on moisture conditions is needed to refine regional estimates of organic carbon stocks in soils in the forest zone of Russia. In this paper, we discuss the results of a comparative statistical analysis of the variability of organic carbon stocks in automorphic and semihydromorphic forest soils. Information from two sources, that is, a database of organic carbon in soils of forest ecosystems in European Russia [8] and the soil-geographical database of Russia, was used to estimate the stocks of soil carbon and to calculate the quantitative parameters of their variability. The data were collected into a single array, which contains the characteristics of 289 soil profiles of forest ecosystems, including 201 pits of automorphic soils and 88 pits of semihydromorphic soils. The results of statistical analysis show that organic carbon stocks (including litter) in semihydromorphic soils are characterized by higher variability, as shown by a larger range of changes, interquartile range, and higher standard deviations. The contribution of the organic horizon to the total variability of carbon stocks in soils of forest ecosystems with increased moisture is the greatest. The standard deviation for this is seven times higher in semihydromorphic soils than in automorphic ones, while the differences for a 1-m-thick soil layer are four times higher.

Peatland soils in permafrost area are among the major components of global carbon cycle. In the case of predicted climate change, they may act as a significant source of greenhouse gases efflux. A four-year transplantation experiment (transplantation of soil cores of 20 cm in height and 10 cm in diameter to other natural positions) with the peat horizon was arranged to assess the temperature sensitivity of CO2 efflux from palsa peatlands in the north of Western Siberia. The rise in temperature by 7°С caused a positive feedback (30–70%) of CO2 efflux (measured by the closed chamber method) from transplanted soils as compared with the control. Temperature dependence of CO2 efflux from transplanted soils had the highest value (R2 = 0.8) in the first two years as a result of maximum contrast of temperature conditions between sites and decreased in the next two years. On the contrary, the temperature sensitivity of CO2 efflux from transplanted soils showed a high value during most of observations (Q10 = 3–6) thus indicating the increased rate of organic matter mineralization in peat soils of permafrost area for a long (four years) period. Our results might be useful for calibration of regional carbon cycle data sets that consider the contribution of organic permafrost-affected soils.

Results of the comparison of organic carbon stocks in the automorphic and semihydromorphic forest soils are discussed. The database includes information on 289 soil profiles in the forest zone of European Russia. On the average, the total organic carbon pool (including forest litter) in semihydromorphic soils is three times higher than that in automorphic soils. The difference decreases with an increase in the thickness of the considered soil layer from 3.2 times for the layer of 0–30 cm to 2.6 times for the layer of 0–100 cm. The greatest difference in carbon stocks is noted for the organic horizons; in semihydromorphic soils, the carbon storage in them averages 73 ± 8.2 t C/ha; in automorphic soils, it is seven times smaller. The neglect of the contribution of semihydromorphic soils results in underestimation of the total soil organic carbon stock of the region. The degree of underestimation depends on the soil cover pattern of particular areas and on the thickness of the considered soil layer. Calculations made for Karelia show that the underestimation of organic carbon stocks in various landscapes ranges from 10 to 40%. For the total area of this republic, it is estimated at 22, 19, and 13% for the soil layers of 0–30, 0–50, and 0–100 cm, respectively. A comparative analysis of known pedotransfer functions for calculating soil bulk density shows that the best results (RMSE = 0.15; R 2 = 0.36) for mineral horizons of forest soils in European Russia are provided by the pedotransfer function suggested by O.V. Chestnykh and D.G. Zamolodchikov.

The results of the four-year study of the temperature regime of soils of three common landscapes of northern taiga in Western Siberia, located in the area of discontinuous permafrost, are presented. The soils of lumpy peatlands are characterized by mild permafrost annual regime with very cold summer and moderately cold winter. Temperature regime of the forest soils may be characterized as cold long-time seasonally freezing mild with very cold summer and moderately cold winter. The soils of the investigated region are functioning in conditions of the narrow range of temperatures: at the depth of 20 cm for the soils of all of the landscapes, the temperatures vary within the range of -2.5 to 0°С. This occurs due to their high moisture, low thermal conductivity, specificities of snow cover regime and the freezing effect of permafrost rocks. Annual temperature soil indices are characterized by the weak correlation to the mean annual specificities of air temperature regime. We discovered the direct correlation of annual soil temperature regime and the dynamics of the snow cover (with average and maximal thickness, and thawing date), and with winter N-factor (surface temperature index), and accumulative positive temperatures. Since isolating activity of the vegetation is significantly lower than that of snow (summer N- factors 0.7-0.9), annual fluctuations of summer air temperatures will significantly affect the temperature regime of soils and geo-cryologic situation of the region in general.

Contemporary (corresponding to the modern state of ecosystems and land use) and prehistoric (for hypothetic intact natural ecosystems similar to modern virgin ecosystems) stocks of organic carbon were assessed for model regions of southern taiga, forest-steppe and steppe in European Russia. The comparison of these stocks enabled an assessment of the integral result of the multidirectional changes in land use that occurred in the studied regions over the historical period. The carbon stocks were determined using a unified cartographic basis, data on taxonomy and texture of soil units, modern land use types and the type and age structure of reconstructed and contemporary vegetation. The results obtained indicate that the modern carbon pool has reduced by 24% compared to the potential prehistoric one in the Kostroma Region and Rostov Region (southern taiga and steppe zones, respectively) and by 37% in the Kursk Region (forest-steppe zone). It was also demonstrated that the contribution of soil to the total organic carbon stock increases southwards, from southern taiga to dry steppe, from 51 to 95% during the prehistoric period and from 62 to 96% currently. The study results show that forestry and agriculture increase the contribution of soil to maintaining the region’s carbon budget.

In the course of studies in typical forest ecosystems of the northern, middle, and southern taiga of Western Siberia performed at the peak of the growing season, the spatial variation of soil CO2 emissions and their relationships with the content of extractable and microbial soil carbon and soil hydrothermic parameters were estimated. The studied parameters of the soil carbon cycle are characterized by the high spatial variability in all the studied ecosystems. This fact indicates the need for a detailed investigation of the greenhouse gas soil emission in all ecosystems typical of a given natural zone. There is a statistically significant difference between the soils of the green-moss pine forests and the soils of the lichen pine forest of the northern taiga. In the green-moss pine forest, the carbon content of microbial biomass is 1.5 times higher (195 ± 24 and 127 ± 16 mg C/kg soil, respectively), the content of extractable carbon is 4 times higher (157 ± 25 and 41 ± 5 mg C/kg of soil, respectively), and the CO2 emission is 1.7 times higher (324 ± 20 and 190 ± 10 mg CO2/(m2 h), respectively) than those in the lichen pine forest. In the northern taiga zone, carbon dioxide emissions from soils in the green-moss pine forests are largely determined by the soil temperature; the role of soil moisture is less significant. In the soils of lichen pine forests, the CO2 emission is mainly controlled by the content of extractable carbon. Significant factors influencing the soil СО2 emission in forest ecosystems of the taiga zone are the content of extractable and microbial carbon and hydrothermic parameters of the soils.

An assessment of the state of soil invertebrate complex, litter horizons, and soddy-podzolic soils (Albic Retisols) in Moscow forest parks ("Bitsevskii Forest" and "Losinyi Ostrov") as a function of the level of recreational loads is presented. A clear pattern has been established for the deterioration of the soil invertebrates as the recreational load increases. This occurs as a result of changes in their habitat conditions, largely due to changes in the soil water regime and soil invertebrate feeding conditions. The abundance, biomass and diversity of soil invertebrates decrease by a factor of 2-2.5 under the influence of the recreational load. The condition of soil invertebrates is a sensitive indicator, which depends on the conditions of their habitat and is mainly determined by changes in the characteristics of the litter and soil properties.

Palsa peatland soils are known as significant terrestrial storage of the Earth’s soil carbon. The response of these soils to changing climate may result in a strong feedback to global carbon balance. In laboratory, we investigated the effect of rising temperatures on the upper (T1) and lower (T2) horizons of Turbic Histic Cryosols using sequential (S) and equal-time (ET) methods. The S method was applied to estimate the response of organic carbon mineralization rate (R) to sequential temperature increase from 5 to 30°C; the ET method was used to study the response of the basal (microbial) respiration rate to equal-time incubation at 5, 15, and 25°C. The Q10 coefficient was calculated. In the T1 horizon, both methods (S and ET) demonstrated a positive response of respiration to the rise in temperature. The respiration intensity increased by 91 and 84%, respectively. In the T2 horizon, it increased by 93 and 91%, respectively. However, despite the overall positive response of soil respiration to the rise in temperature, the Q10 values demonstrated differences in the temperature sensitivity of soil respiration. These values were maximal in the cold (5–15°C) range for both horizons. For most of temperature ranges, Q10 was higher for T2 than for T1. For the T1 horizon and S method, Q10 slightly varied (2.7–3.0), whereas in the case of the ET method, it decreased by 3.3 times from the cold (4.9) to the warm 15–25°C (1.5) temperature range. For the T2 horizon, the S method also did not cause significant shifts in Q10 (3.0–3.5); the ET method caused a decrease in Q10 by 1.5 times from the cold (4.3) to the warm (2.8) temperature range. To sum up, the ET method leads to a wider variation of Q10 values in comparison with the S method thus indicating its better applicability for temperature sensitivity studies with palsa peatland soils under laboratory conditions.