The effect of geocryological conditions and soil properties on the spatial variation in the CO<Subscript>2</Subscript> emission from flat-topped peat mounds in the isolated permafrost zone of Western Siberia

The active layer thickness, CO2 emission, and contents of organic substances (including the total organic carbon, labile carbon, and the carbon of microbial biomass) in the soils of flat-topped peat mounds in the area of the Nadym Experimental Station in the north of Western Siberia (experimental site CALM R1) are characterized by considerable spatial variability. The low values of the CО₂ emission are confined to the microelevations on the peatland surface. The high values of the emission (>200 mg CO₂/(m² h)) are typical of the soils with the highest content of the carbon of microbial biomass and the lowest content of the labile organic carbon. The soils of elevated flat-topped peat mounds statistically differ from the soils of waterlogged mires in the contents of total, labile, and microbial carbon and in the CO₂ emission values. Though the soils of elevated flat-topped peat mounds are characterized by the high content of the carbon of microbial biomass (4260 ± 880 mg С/kg soil), the CO₂ emission from them is low (158 ± 23 mg CO₂/(m² h)), which is explained by the structure of microbial communities in the cryogenic soils and by the effect of specific hydrothermic conditions.     

Long‐term carbon loss and CO2‐C release of drained peatland soils in northeast Germany

Peatlands are common in many parts of the world. Draining and other changes in the use of peatlands increase atmospheric CO₂ concentration. If we are to make reliable quantitative predictions of that effect, we need good information on the CO₂ emission rates from peatlands. The present study uses two different methods for predicting CO₂‐C release of peatland soils: (i) a 40‐year field investigation of balancing organic carbon stocks and (ii) short‐term CO₂‐C release rates from laboratory experiments. To estimate long‐term losses of peat, and its resulting C input to the atmosphere, we combined highly detailed maps of surface topography and its changes, and the organic C contents and bulk densities of a drained peatland from different years. Short‐term CO₂‐C release rates were measured in the laboratory by incubating soil samples from several soil horizons at various temperatures and soil moistures. We then derived nonlinear CO₂‐C production functions, which we incorporated into a numerical simulation model (HYDRUS). Using HYDRUS, we calculated daily soil water components and CO₂‐release for (i) real‐climate data from 1950 to 2003 and (ii) a climate scenario extending to 2050, including an increase in temperature of 2°C and 20% less rainfall during the summer half year, i.e. from April to September inclusive. From our field measurements, we found a mean annual decrease of 0.7 cm in the thickness of the peat. Large losses (> 1.5 cm year^?1) occurred only during periods when groundwater levels were low (i.e. a deep water‐table). The annual CO₂‐C release results in a mean loss from the peat of about 700 g CO₂‐C m^?2, mostly as a direct contribution to the atmosphere. Both methods produced very similar results. The model scenarios demonstrated that CO₂‐C loss is mainly controlled by the groundwater (i.e. water‐table) depth, which controls subsurface aeration. A local climate scenario estimated a c. 5% increase of CO₂‐C losses within the next 50 years.     

Carbon dynamics in Appalachian peatlands of West Virginia and Western Maryland

Abundant production of organic matter that decomposes slowly under anaerobic conditions can result in substantial accumulation of soil organic matter in wetlands. Tedious means for estimating production and decomposition of plant material, especially roots, hampers our understanding of organic matter dynamics in such systems. In this paper, I describe a study that amended typical estimates for both production and decomposition of organic matter by measuring net flux of carbon dioxide (CO₂) over the peat surface within a conifer swamp, a sedge-dominated marsh, and a bog in the Appalachian Mountain region of West Virginia and western Maryland, USA. The sites are relatively productive, with net primary production (NPP) of 30 to 82.5 mol C m^?2 yr^?1, but peat deposits are shallow with an average depth of about 1 m. In summer, all three sites showed net CO₂ flux from the atmosphere to the peat during the daytime (?20.0 to ?30.5 mmol m^?2 d^?1), supported by net photosynthesis, which was less than net CO₂ flux from the peat into the atmosphere at nighttime (39.2 to 84.5 mmol m^?2 d^?1), supported by ecosystem respiration. The imbalance between these estimates suggests a net loss of carbon (C) from these ecosystems. The positive net CO₂ flux seems to be so high because organic matter decomposition occurs throughout the peat deposit — and as a result concentrations of dissolved inorganic carbon (DIC) in peat pore waters reached 4,000 Μmol L^?1 by late November, and concentrations of dissolved organic carbon (DOC) in peat pore waters reached 12,000 Μmol L^?1. Comparing different approaches revealed several features of organic matter dynamics: (i) peat accretion in the top 30 cm of the peat deposit results in a C accumulation rate of about 15 mmol m^?2 d^?1; however, (ii) the entire peat deposit has a negative C balance losing about 20 mmol m^?2 d^?1.     

Estimating the carbon stock of a blanket peat region using a peat depth inference model

At the global scale peatlands are an important soil organic carbon (SOC) pool. They sequester, store and emit carbon dioxide and methane and have a large carbon content per unit area. In Ireland, peatlands cover between 17% and 20% of the land area and contain a significant, but poorly quantified amount of SOC. Peatlands may function as a persistent sink for atmospheric CO₂. In Ireland the detailed information that is required to calculate the peatland SOC pool, such as peat depth, area and carbon density, is inconsistent in quality and coverage. The objective of this research was to develop an improved method for estimating the depth of blanket peat from elevation, slope and disturbance data to allow more accurate estimations of the SOC pool for blanket peatlands. The model was formulated to predict peat depth at a resolution of 100 ha (1 km²). The model correctly captured the trend and accounted for 58 to 63% of the observed variation in peat depth in the Wicklow Mountains on the east coast of Ireland. Given that the surface of a blanket peatland masks unknown undulations at the mineral/peat interface this was a successful outcome. Using the peat depth model, it was estimated that blanket peatland in the Wicklow Mountains contained 2.30 Mt of carbon. This compares to the previously published values ranging from 0.45 Mt C to 2.18 Mt C.     

Isotope (C and C) analysis of deep peat CO2 using a passive sampling technique

We developed and tested a new method to collect CO₂ from the surface to deep layers of a peatland for radiocarbon analysis. The method comprises two components: i) a probe equipped with a hydrophobic filter that allows entry of peat gases by diffusion, whilst simultaneously excluding water, and, ii) a cartridge containing zeolite molecular sieve that traps CO₂ passively. We field tested the method by sampling at depths of between 0.25 and 4 m at duplicate sites within a temperate raised peat bog. CO₂ was trapped at a depth-dependent rate of between ∼0.2 and 0.8 ml d⁻¹, enabling sufficient CO₂ for routine ¹⁴C analysis to be collected when left in place for several weeks. The age of peatland CO₂ increased with depth from modern to ∼170 BP for samples collected from 0.25 m, to ∼4000 BP at 4 m. The CO₂ was younger, but followed a similar trend to the age profile of bulk peat previously reported for the site (Langdon and Barber, 2005). δ¹³C values of recovered CO₂ increased with depth. CO₂ collected from the deepest sampling probes was considerably ¹³C-enriched (up to ∼+9‰) and agreed well with results reported for other peatlands where this phenomenon has been attributed to fermentation processes. CO₂ collected from plant-free static chambers at the surface of the mire was slightly ¹⁴C-enriched compared to the contemporary atmosphere, suggesting that surface CO₂ emissions were predominantly derived from carbon fixed during the post-bomb era. However, consistent trends of enriched ¹³C and depleted ¹⁴C in chamber CO₂ between autumn and winter samples were most likely explained by an increased contribution of deep peat CO₂ to the surface efflux in winter. The passive sampling technique is readily portable, easy to install and operate, causes minimal site disturbance, and can be reliably used to collect peatland CO₂ from a wide range of depths.     

Influence of water depth and soil amelioration on greenhouse gas emissions from peat soil columns

Recently, large areas of tropical peatland have been converted into agricultural fields. To be used for agricultural activities, peat soils need to be drained, limed and fertilized due to excess water, low nutrient content and high acidity. Water depth and amelioration have significant effects on greenhouse gas (GHG) production. Twenty-seven soil samples were collected from Jabiren, Central Kalimantan, Indonesia, in 2014 to examine the effect of water depth and amelioration on GHG emissions. Soil columns were formed in the peatland using polyvinyl chloride (PVC) pipe with a diameter of 21 cm and a length of 100 cm. The PVC pipe was inserted vertically into the soil to a depth of 100 cm and carefully pulled up with the soil inside after sealing the bottom. The treatments consisting of three static water depths (15, 35 and 55 cm from the soil surface) and three ameliorants (without ameliorant/control, biochar+compost and steel slag+compost) were arranged using a randomized block design with two factors and three replications. Fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) from the soil columns were measured weekly. There was a linear relationship between water depth and CO₂ emissions. No significant difference was observed in the CH₄ emissions in response to water depth and amelioration. The ameliorations influenced the CO₂ and N₂O emissions from the peat soil. The application of biochar+compost enhanced the CO₂ and N₂O emissions but reduced the CH₄ emission. Moreover, the application of steel slag+compost increased the emissions of all three gases. The highest CO₂ and N₂O emissions occurred in response to the biochar+compost treatment followed by the steel slag-compost treatment and without ameliorant. Soil pH, redox potential (Eh) and temperature influenced the CO₂, CH₄ and N₂O fluxes. Experiments for monitoring water depth and amelioration should be developed using peat soil as well as peat soil–crop systems.     

Sheep excreta cause no positive priming of peat-derived CO2 and N2O emissions

Large areas of peatlands in Germany and the Netherlands are affected by drainage and high nitrogen deposition. Sheep grazing is a common extensive management activity on drained peatlands, in particular on nature protection areas. However, input of easily mineralisable material such as sheep excrements could enhance degradation of soil organic carbon (C_org), thereby increasing the effect of these ecosystems on national GHG budgets. Thus, a microcosm experiment on the influence of sheep excreta on GHG emissions from a histic Gleysol with strongly degraded peat was set up. The ¹⁵N and ¹³C stable isotope tracer technique was used to partition sources of CO₂ and N₂O. Labeled sheep faeces and urine were obtained by feeding enriched material. Undisturbed soil columns were treated with surface application of urine, faeces or mixtures of both in different label combinations to distinguish between direct effects and possible priming effects. Incubation was done under stable temperature and precipitation conditions. Fluxes as well as ¹⁵N and ¹³C enrichment of N₂O and CO₂, respectively, were measured for three weeks. Addition of sheep excreta increased emission of total CO₂ in proportion to the added carbon amounts. There was no CO₂ priming in the peat. No effect on CH₄ and N₂O was observed under the aerobic experimental conditions. The N₂O–N source shifted from peat to excreta, which indicates negative priming, but priming was not significant. The results indicate that sheep excreta do not significantly increase GHG emissions from degraded peat soils. Considering the degraded peatland preserving benefits, sheep grazing on peatlands affected by drainage and high nitrogen deposition should be further promoted.     

The influence of temperature and water table position on carbon dioxide and methane emissions from laboratory columns of peatland soils

Laboratory columns (80 cm long, 10 cm diameter) of peat were constructed from samples collected from a subarctic fen, a temperate bog and a temperate swamp. Temperature and water table position were manipulated to establish their influence on emissions of CO₂ and CH₄ from the columns. A factorial design experiment revealed significant (P < 0.05) differences in emission of these gases related to peat type, temperature and water table position, as well as an interaction between temperature and water table. Emissions of CO₂ and CH₄ at 23°C were an average of 2.4 and 6.6 times larger, respectively, than those at 10°C. Compared to emissions when the columns were saturated, water table at a depth of 40 cm increased CO₂ fluxes by an average of 4.3 times and decreased CH₄ emissions by an average of 5.0 times. There were significant temporal variations in gas emissions during the 6-week experiment, presumably related to variations in microbial populations and substrate availability. Using columns with static water table depths of 0, 10, 20, 40 and 60 cm, CO₂ emissions showed a positive, linear relation with depth, whereas CH₄ emissions revealed a negative, logarithmic relation with depth. Lowering and then raising the water table from the peat surface to a depth of 50 cm revealed weak evidence of hysteresis in CO₂ emissions between the falling and rising water table limbs. Hysteresis (falling > rising limb) was very pronounced for CH₄ emissions, attributed to a release of CH₄ stored in porewater and a lag in the development of anaerobic conditions and methanogenesis on the rising limb. Decreases in atmospheric pressure were correlated with abnormally large emissions of CO₂ and CH₄ on the falling limb. Peat slurries incubated in flasks revealed few differences between the three peat types in the rates of CO₂ production under aerobic and anaerobic conditions. There were, however, major differences between peat types in the rates of CH₄ consumption under aerobic incubation conditions and CH₄ production under anaerobic conditions (bog > fen > swamp), which explain the differences in response of the peat types in the column experiment.     

Limited effects of six years of fertilization on carbon mineralization dynamics in a Minnesota fen

Peatlands, including fens, are important ecosystems in the context of the global carbon cycle. Future climate change and other anthropogenic activities are likely to increase nutrient loading in many peatland ecosystems and a better understanding of the effects of these nutrients on peatland carbon cycling is necessary. We investigated the effects of six years of nitrogen and phosphorus fertilization, along with liming, on carbon mineralization dynamics in an intermediate fen in northern Minnesota. Specifically, we measured CO₂ and CH₄ emission from intact peat cores, as well as CH₄ production and CH₄ consumption at multiple depths in short-term laboratory incubations. Despite increased nitrogen and phosphorus availability in the upper 5 cm of peat, increased pH, and clear shifts in the vegetation community, fertilization and liming had limited effects on microbial carbon cycling in this fen. Liming reduced the net flux of CO₂ approximately 3-fold compared to the control treatment, but liming had no effect on CH₄ emissions from intact cores. There were no nutrient effects on CO₂ or CH₄ emissions from intact cores. In all treatments, rates of CH₄ production increased with depth and rates of CH₄ consumption were highest near the in situ water-table level. However, nutrient and liming had no effect on rates of CH₄ production or CH₄ consumption at any depth. Our results suggest that over at least the intermediate term, the microbial communities responsible for soil carbon cycling in this peatland are tolerant to wide ranges of nutrient concentrations and pH levels and may be relatively insensitive to future anthropogenic nutrient stress.     

Nitrous oxide emission derived from soil organic matter decomposition from tropical agricultural peat soil in central Kalimantan,Indonesia

Our previous research showed large amounts of nitrous oxide (N₂O) emission (>200?kg?N?ha^?1?year^?1) from agricultural peat soil. In this study, we investigated the factors influencing relatively large N₂O fluxes and the source of nitrogen (N) substrate for N₂O in a tropical peatland in central Kalimantan, Indonesia. Using a static chamber method, N₂O and carbon dioxide (CO₂) fluxes were measured in three conventionally cultivated croplands (conventional), an unplanted and unfertilized bare treatment (bare) in each cropland, and unfertilized grassland over a three-year period. Based on the difference in N₂O emission from two treatments, contribution of the N source for N₂O was calculated. Nitrous oxide concentrations at five depths (5–80?cm) were also measured for calculating net N₂O production in soil. Annual N fertilizer application rates in the croplands ranged from 472 to 1607?kg?N?ha^?1?year^?1. There were no significant differences in between N₂O fluxes in the two treatments at each site. Annual N₂O emission in conventional and bare treatments varied from 10.9 to 698 and 6.55 to 858?kg?N?ha^?1?year^?1, respectively. However, there was also no significant difference between annual N₂O emissions in the two treatments at each site. This suggests most of the emitted N₂O was derived from the decomposition of peat. There were significant positive correlations between N₂O and CO₂ fluxes in bare treatment in two croplands where N₂O flux was higher than at another cropland. Nitrous oxide concentration distribution in soil measured in the conventional treatment showed that N₂O was mainly produced in the surface soil down to 15?cm in the soil. The logarithmic value of the ratio of N₂O flux and nitrate concentration was positively correlated with water filled pore space (WEPS). These results suggest that large N₂O emission in agricultural tropical peatland was caused by denitrification with high decomposition of peat. In addition, N₂O was mainly produced by denitrification at high range of WFPS in surface soil.     

The contribution of plant roots to CO2 fluxes from organic soils

The CO₂ released in soil respiration is formed from organic matter which differs in age and stability, ranging from soluble root exudates to more persistent plant remains. The contribution of roots, a relatively fast component of soil cycling, was studied in three experiments. (1) Willows were grown in a greenhouse and CO₂ fluxes from the substrate soil (milled peat) and from control peat were measured. (2) CO₂ fluxes from various peatland sites were measured at control points and points where the roots were severed from the plants. (3) CO₂ fluxes in cultivated grassland established on peatland were measured in grassy subsites and in subsites where the growth of grass was prevented by regular tilling. The root-derived respiration followed the typical annual phenology of the vegetation, being at its maximum in the middle and late summer. All the experiments gave similar results, root-derived respiration accounting for 35–45% of total soil respiration in the middle and late summer at sites with an abundant vegetation. The root-derived respiration from the virgin peatland sites correlated well with the tree biomass, and also partly with the understorey vegetation, but in the drained sites the root effect was greater, even in the presence of less understorey vegetation than at virgin subsites.     

Characterization of diffusivity‐based oxygen transport in Arctic organic soil

Arctic terrestrial ecosystems are characterized by large deposits of near‐surface soil organic carbon in poorly drained areas. Recent changes in Arctic regions such as warming and changes in water balance have adverse effects on the dynamics of near‐surface oxygen, leading to a potential increase in oxidation of near‐surface carbon and emission of CO₂. This study investigated oxygen diffusivity characteristics, in both gaseous and liquid phases, in the upper 10 cm of an organic soil profile from a peatland in Disko, West Greenland (69°N). Two commonly used methods for calculating diffusivity of gaseous‐phase oxygen were applied and discussed to select the most appropriate method for highly porous media, for example peat soil. We measured diffusivity of gaseous‐phase oxygen with a one‐chamber diffusion set‐up in soil at different air contents (mimicking draining), and described it numerically with a previously developed parametric diffusivity model. We obtained precise measurements of liquid‐phase oxygen diffusivity along a depth profile (0–2 cm) in water‐saturated peat soil with a diffusivity microsensor coupled to a micromanipulator. The results show that the choice of an appropriate diffusivity model is critical for predicting oxygen diffusivity in organic soil and that diffusivity in mineral soil is not representative for organic soil. Furthermore, the importance of the non‐linear functionality between water saturation and diffusivity is demonstrated. This highlights the importance of measuring and modelling oxygen diffusivity rather than relying on measurements of observed water content in future studies of CO₂ and CH₄ dynamics in Arctic soil systems subject to climate changes.     

Carbon emission flux and storage in the degraded peatlands of the Zoige alpine area in the Qinghai–Tibetan Plateau

The Zoige alpine peatlands cover approximately 4,605 km² of the Qinghai–Tibetan Plateau and are considered to constitute the largest plateau peatland on the Eurasian continent. However, the Zoige alpine peatlands are undergoing major degradation because of human activities and climate change, which would cause uncertainty in the budget of greenhouse gases (CH₄ and CO₂) and carbon (C) storage in global peatlands. This study simultaneously investigates the CH₄ and CO₂ emission fluxes and C storage at three typical sites with respect to the peatland degradation gradient: peatland, wet meadow and dry meadow. Results show that peatland degradation would increase the CO₂ emission and decrease the CH₄ emission. Moreover, the average C emission fluxes were 66.05, 165.78 and 326.56 mg C m^?2 hr^?1 for the peatland, wet meadow and dry meadow, respectively. The C storage of the vegetation does not considerably differ among the three sampling sites. However, when compared with the peatland (1,088.17 t C ha^?1), the soil organic C storage decreases by 420 and 570 t C ha^?1 in case of wet and dry meadows, respectively. Although the C storage in the degraded peatlands decreases considerably, it can still represent a large capacity of C sink. Therefore, the degraded peatlands in the Zoige alpine area must be protected and restored to mitigate regional climate change.     

Radiocarbon analysis of methane emitted from the surface of a raised peat bog

We developed a method to determine the radiocarbon (¹⁴C) concentration of methane (CH₄) emitted from the surface of peatlands. The method involves the collection of ∼9 L of air from a static gas sampling chamber which is returned to the laboratory in a foil gas bag. Carbon dioxide is completely removed by passing the sample gas firstly through soda lime and then molecular sieve. Sample methane is then combusted to CO₂, cryogenically purified and subsequently processed using routine radiocarbon methods. We verified the reliability of the method using laboratory isotope standards, and successfully trialled it at a temperate raised peat bog, where we found that CH₄ emitted from the surface dated to 195–1399 years BP. The new method provides both a reliable and portable way to ¹⁴C date methane even at the low concentrations typically associated with peatland surface emissions.     

Carbon dioxide emission from the soil surface in a bilberry-sphagnum pine forest of the Middle Taiga

The dynamics of the carbon dioxide emissions from the surface of a gleyic iron-illuvial sandy peat podzolic soil under a mature bilberry-sphagnum pine forest were studied during the growing seasons of 2008–2010. The maximum rates of the CO₂ emission were observed in late July-early August, and the minimum rates were in October. In the hot summer of 2010, an additional maximum was observed in June. A close positive correlation existed between the intensity of the CO₂ emission and the soil temperature (r = 0.71, α = 0.05), whereas no significant correlation was found between the CO₂ emission and the soil water content. The coefficient of multiple correlation between the rate of the CO₂ emission and the hydrothermic soil characteristics reached 0.57 (at α = 0.05). The total CO₂ emission from the soil surface during the growing season was estimated at 68–100 g of C m^?2.     

淡水湿地不同围垦土壤非耕季节呼吸速率差异

选择何种湿地利用方式,使得土壤固碳能力及CO₂气体排放受到的影响最小,是合理利用湿地、减少温室气体排放的关键所在,湿地土壤呼吸不仅受环境条件的影响,还受土壤本身性状的影响。以皖江地区为研究区域,利用定位试验对天然湿地及不同围垦利用方式下土壤在非耕季节CO₂排放通量、大气温度及表层土壤温度进行测定,并对其土壤TOC含量进行分析。结果表明,CO₂排放通量:水稻田[700.70 mg/(m²·h)]> 旱地[433.80 mg/(m²·h)]> 天然湿地[302.66 mg/(m²·h)],天然湿地土壤TOC含量明显高于围垦旱地及水稻田(0-30 cm),说明天然湿地较围垦旱地和水稻田对大气中CO₂浓度贡献最小,能存储更多的碳。探讨了CO₂排放通量与温度的相关性,得出3种土壤类型CO₂排放通量与大气温度和表层土壤温度均呈正相关关系。     

Emission of CO2 from the surface of oligotrophic bogs with due account for their microrelief in the southern taiga of European Russia

The results of studying the carbon dioxide fluxes from the soil’s surface during three years taking into account the microrelief are summarized. More precise estimates were obtained for the annual CO₂ emission from the oligotrophic peat bogs differing in vegetation and waterlogging in the southern taiga of European Russia. The maximum differences in the rates of the CO₂ emission related to the microrelief elements are characteristic of the treeless ridge-pool complex, where the hollows (without vegetation) emitted CO₂ twice less than the flat areas and thrice less than the hummocks. In the forest bogs, the differences related to the microrelief were significantly lower. In the areas with the ridge-pool microrelief, the weighted average (for 3 years) CO₂ emission was 436 g C/m² per year; in the better drained natural dwarf shrub-cotton grass-sphagnum pine forest, 930; and in the drained pine forest, 1292 g C/m² per year. The share of the CO₂ amount emitted in the cold period (November–April) amounted to 10% of its annual flux from the peat soils of the ridge-pool complex and 17 and 24%, respectively, in the natural and drained pine forests.     

Absorption and emission of CO2 by ponded water of a paddy field

In the daytime, the CO₂ concentration in the air close to the water surface of a ponded paddy field was lowest and it increased with the distance above the water surface, while an inverse relation was observed in the nighttime. On the other hand, the pH of the ponded water changed significantly throughout a day and was expected to affect atmospheric CO₂ in the vicinity of the water surface, because the solubility of CO₂ in water depends on the pH. In this study, we investigated the relationship between the changes in the pH of the ponded water and the response of the CO₂ concentration in the air above the water. The pH of the ponded water of the paddy field increased in the daytime and decreased in the nighttime, so that the water was alkaline in the daytime and weakly acidic in the nighttime. We found that the daily changes in the atmospheric CO₂ concentration gradient almost corresponded to the daily changes in pH. The increase of the pH of the ponded water in the daytime was due to the absorption of dissolved CO₂ by photosynthetic bacteria and micro-algae within the ponded water. Furthermore, we compared the pH with RpH, defined as the pH at which the CO₂ concentration of the water is in equilibrium with that of the air, to determine whether CO₂ was absorbed by or emitted from the ponded water. In the daytime, the pH value of the ponded water was higher than that of the RpH, and the water could therefore absorb CO₂ , whereas during the nighttime, since the pH value of the ponded water was lower than that of the RpH, the water was expected to emit CO₂. These results show that the ponded water absorbed CO₂ from the air above the water surface in the daytime and emitted CO₂ in the nighttime.     

CO<Subscript>2</Subscript> Emission and Organic Carbon Pools in Soils of the Northern Taiga Ecosystems of Western Siberia under Different Geocryological Conditions

Statistical analysis of a vast body of data collected during five field seasons (2011–2015) was performed to characterize the biological activity of soils in the northern taiga ecosystems of Western Siberia. Automorphic forest soils, hydromorphic (oligotrophic bog) soils, and semihydromorphic (flat-topped and large peat mounds) soils were characterized. Statistically significant differences of average levels of CO₂ emission from the soils were identified at the ecosystem level. The CO₂ emission from podzols of automorphic forest ecosystems at the peak of the growing season (205 ± 30 to 410 ± 40 mg CO₂/(m² h)) was significantly higher than the emission from semihydromorphic soils of peat mounds (70 ± 20 to 116 ± 10 mg CO₂/(m² h)). The presence and depth of permafrost was a significant factor that affected ecosystem diversity and biological activity of northern taiga soils. Statistically significant differences in the total, labile, and microbial carbon pools were observed for the studied soils. Labile and microbial carbon pools in the organic layer (10 cm) of forest podzols amounted to 0.19 and 0.66 t/ha, respectively; those in the organic layer (40 cm) of peat cryozems of flat-topped peat mounds reached 1.24 and 3.20 t/ha, and those in the oligotrophic peat soils (50 cm) of large peat mounds were 2.76 and 1.35 t/ha, respectively. The portion of microbial carbon in the total carbon pool (C_micr/C_tot, %) varied significantly; according to the values of this index, the soils were arranged into the following sequence: oligotrophic peat soil < peat cryozem < podzol.     

Direct experimental evidence for the contribution of lime to CO2 release from managed peat soil

Liming is a common management practice used to achieve optimum pH for plant growth in agricultural soils. Addition of lime to the soil, however, may cause CO₂ release when the carbonates in lime dissolve in water. Although lime may thereby constitute a significant carbon source, especially under acidic soil conditions, experimental data on the CO₂ release are lacking so far. We conducted a split-plot experiment within a cut-away peatland cultivated with a bioenergy crop (reed canary grass, Phalaris arundinacea L.) with lime and fertilizer treatments to determine effects of lime on the CO₂ emissions from soil and to better understand mechanisms underlying liming effects. Carbon dioxide release was measured over two growing seasons in the field after liming, and complementary laboratory studies were conducted. To differentiate CO₂ derived from lime and biotic respiration the δ¹³C of CO₂ released was determined and the two-pool mixing model was applied. The results showed that lime may contribute significantly to CO₂ release from the soil. In the laboratory, more than 50% of CO₂ release was attributable to lime-carbonates during short-term incubation. Lime-derived CO₂ emissions were much lower in the field, and were only detected during the first (2–4) months after the application. However, a maximum of 12% of monthly CO₂ emissions from the cultivated peatland originated from the lime. Biotic respiration rates were similar in limed and unlimed soils, suggesting that higher pH did not, at least in the short-term, increase carbon losses from cultivated peat soils. Additional fertilization and acidification did not contribute to further CO₂ release from the lime. According to our first estimations about one sixth of the lime applied would be released as CO₂ from the managed peatland, with all lime-derived emissions occurring during the first year of application (equivalent to about 4.6% of the total annual CO₂ losses from the soil in the first year). This suggests that the mass-balance approach as proposed by the IPCC Tier 1 methodology, which assumes that all carbon in lime ends up as CO₂ in the atmosphere, overestimates the emissions from lime. Our study further shows that there is a great risk to overestimate heterotrophic microbial activity in limed soils by measuring the CO₂ release without separating abiotic and biotic CO₂ production.