Methane Fluxes from Alpine Wetlands of Zoige Plateau in Relation to Water Regime and Vegetation under Two Scales

Methane fluxes in alpine ecosystems remain insufficiently studied, especially in terms of the magnitude, temporal, and spatial patterns. To quantify the mean methane emission of alpine ecosystems, methane fluxes were measured among six ecosystems and microsites within each ecosystem at Zoige National Wetland Reserve. The average methane emission from Zoige Plateau was 2.25 mg CH₄ m^?2?h^?1, which fell into the range of methane emission rate reported by a number of studies in other alpine wetlands. Prevailing ecosystem types had important impacts on the methane flux on the landscape scale. In the wet ecosystems, the microsites had different methane emissions resulting from the differences in the depth of water table and associated vegetation characteristics. The identification of the microsites based on their vegetation characteristics thus allows upscaling of methane emissions in these ecosystems. However, in the dry ecosystems showing even methane uptake, the spatial variation in the methane fluxes was low and the vegetation has a poor predicative value for the methane fluxes. There, the soil porosity linked to the gas diffusion rate in soil would be the key factor explaining methane fluxes.     

Effect of nitrogen fertilization on methane and carbon dioxide production potential in relation to labile carbon pools in tropical flooded rice soils in eastern India

In an incubation experiment with flooded rice soil fertilized with different N amounts and sampled at different rice stages, the methane (CH₄) and carbon dioxide (CO₂) production in relation to soil labile carbon (C) pools under two temperature (35°C and 45°C) and moisture (aerobic and submerged) regimes were investigated. The field treatments imposed in the wet season included unfertilized control and 40, 80 and 120 kg ha^?1 N fertilization. The production of CH₄ was significantly higher (27%) under submerged compared to aerobic conditions, whereas CO₂ production was significantly increased under aerobic by 21% compared to submerged conditions. The average labile C pools were significantly increased by 21% at the highest dose of N (120 kg ha^?1) compared to control and was found highest at rice panicle initiation stage. But the grain yield had significantly responded only up to 80 kg ha^?1 N, although soil labile C as well as gaseous C emission was noticed to be highest at 120 kg ha^?1 N. Hence, 80 kg N ha^?1 is a better option in the wet season at low land tropical flooded rice in eastern India for sustaining grain yield and minimizing potential emission of CO₂ and CH₄.     

Effects of bamboo biochar application on global warming in paddy fields in Ehime prefecture,Southern Japan

Biochar application can reduce global warming via carbon (C) sequestration in soils. However, there are few studies investigating its effects on greenhouse gases in rice (Oryza sativa L.) paddy fields throughout the year. In this study, a year-round field experiment was performed in rice paddy fields to investigate the effects of biochar application on methane (CH₄) and nitrous oxide (N₂O) emissions and C budget. The study was conducted on three rice paddy fields in Ehime prefecture, Japan, for 2 years. Control (Co) and biochar (B) treatments, in which 2-cm size bamboo biochar (2 Mg ha^?1) was applied, were set up in the first year. CH₄ and N₂O emissions and heterotrophic respiration (Rh) were measured using a closed-chamber method. In the fallow season, the mean N₂O emission during the experimental period was significantly lower in B (67 g N ha^?1) than Co (147 g N ha^?1). However, the mean CH₄ emission was slightly higher in B (2.3 kg C ha^?1) than Co (1.2 kg C ha^?1) in fallow season. The water-filled pore space increased more during the fallow season in B than Co. In B, soil was reduced more than in Co due to increasing soil moisture, which decreased N₂O and increased CH₄ emissions in the fallow season. In the rice-growing season, the mean N₂O emission tended to be lower in B (?104 g N ha^?1) than Co (?13 g N ha^?1), while mean CH₄ emission was similar between B (183 kg C ha^?1) and Co (173 kg C ha^?1). Due to the C release from applied biochar and soil organic C in the first year, Rh in B was higher than that in Co. The net greenhouse gas emission for 2 years considering biochar C, plant residue C, CH₄ and N₂O emissions, and Rh was lower in B (5.53 Mg CO₂eq ha^?1) than Co (11.1 Mg CO₂eq ha^?1). Biochar application worked for C accumulation, increasing plant residue C input, and mitigating N₂O emission by improving soil environmental conditions. This suggests that bamboo biochar application in paddy fields could aid in mitigating global warming.     

Effects of temperature,glucose and inorganic nitrogen inputs on carbon mineralization in a Tibetan alpine meadow soil

High levels of available nitrogen (N) and carbon (C) have the potential to increase soil N and C mineralization. We hypothesized that with an external labile C or N supply alpine meadow soil will have a significantly higher C mineralization potential, and that temperature sensitivity of C mineralization will increase. To test the hypotheses an incubation experiment was conducted with two doses of N or C supply at temperature of 5, 15 and 25 °C. Results showed external N supply had no significant effect on CO₂ emission. However, external C supply increased CO₂ emission. Temperature coefficient (Q₁₀) ranged from 1.13 to 1.29. Significantly higher values were measured with C than with N addition and control treatment. Temperature dependence of C mineralization was well-represented by exponential functions. Under the control, CO₂ efflux rate was 425 g CO₂–C m^?2 year^?1, comparable to the in situ measurement of 422 g CO₂–C m^?2 year^?1. We demonstrated if N is disregarded, microbial decomposition is primarily limited by lack of labile C. It is predicted that labile C supply would further increase CO₂ efflux from the alpine meadow soil.     

Potential short-term effects of yak and Tibetan sheep dung on greenhouse gas emissions in two alpine grassland soils under laboratory conditions

Yak and Tibetan sheep graze extensively on natural grasslands in the Qinghai-Tibetan Plateau, and large amounts of excrement are directly deposited onto alpine grasslands. However, information on greenhouse gas (GHG) emissions from this excrement is limited. This study evaluated the short-term effects of yak and Tibetan sheep dung on nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂) emissions from alpine steppe soil at a water holding capacity (WHC) of 40 or 60 % and from alpine meadow soil at a WHC of 60 or 80 % under laboratory conditions. Cumulative N₂O emissions over a 15-day incubation period at low soil moisture conditions ranged from 111 to 232 μg N₂O–N kg soil^?1 in the yak dung treatments, significantly (P?<?0.01) higher than that of sheep dung treatments (28.7 to 33.7 μg N₂O–N kg soil^?1) and untreated soils (1.04–6.94 μg N₂O–N kg soil^?1). At high soil moisture conditions, N₂O emissions were higher from sheep dung than yak dung and non-treated soils. No significant difference was found between the yak dung and non-treated alpine meadow soil at 80 % WHC. Low N₂O emission in the yak dung treatment from relatively wet soil was probably due to complete denitrification to N₂. Yak dung markedly (P?<?0.001) increased CH₄ and CO₂ emissions, likely being the main source of these two gases. The addition of sheep dung markedly (P?<?0.001) elevated CO₂ emissions. Dung application significantly (P?<?0.01) increased global warming potential, particularly for alpine steppe soil. In conclusion, our findings suggest that yak and Tibetan sheep dung deposited on alpine grassland soils may increase GHG emissions.     

Regional evaluation of the spatio-temporal variation in soil organic carbon dynamics for rainfed cereal farming in northern Kazakhstan

Abstract

A regional evaluation of the soil organic carbon (SOC) dynamics for the chernozem zone in northern Kazakhstan is now vitally important for agricultural and environmental policy making. The objectives of the present study were: (1) to predict spatial and temporal variability in C input as crop residues using multi-temporal MODIS satellite images, (2) to clarify spatial and temporal variability in CO₂ emission as SOC output using geostatistics and model s, (3) to clarify spatial and temporal variability in the SOC budget using the results from (1) and (2). The mean growing-season C input as plant residues in cereal fields ranged from 0.9 to 1.4 Mg C ha^?1, with higher values in wet years. Carbon input as plant residues was higher in the northern part of the area than in the other parts. The average growing-season CO₂ emission ranged from 0.9 to 1.1 Mg C ha^?1, and was also higher in wet years than in dry years. In addition, more CO₂ was emitted in the northern part of this area. Accordingly the average growing-season C budget ranged from –0.2 to 0.3 Mg C ha^?1 and showed a negative correlation with air temperature during the crop-growing season. The 5-year C budget for different crop rotation systems ranged from –1.0 (3-year cropped cereal with 2-year bare fallow) to 0.4 (5-year continuous cereal cropped) Mg C ha^?1. These results indicate that fallow-based crop rotation systems are degradative with regard to the SOC budget in the studied area.     

Evaluation of greenhouse gas emissions in a Miscanthus sinensis Andersson-dominated semi-natural grassland in Kumamoto,Japan

Increasing greenhouse gas emissions from anthropogenic activities continue to be a mounting problem worldwide. In the semi-natural Miscanthus sinensis Andersson; grasslands of Aso, Kumamoto, Japan, which have been managed for thousands of years, we measured soil methane (CH₄) and nitrous oxide (N₂O) emissions before and after annual controlled burns. We estimated annual soil carbon (C) accumulation, and CH₄ and N₂O emissions induced by biomass burning in 2009 and 2010, to determine the impacts of this ecosystem and its management on global warming. Environmental factors affecting soil CH₄ and N₂O fluxes were unknown, with no effect of annual burning observed on short-term soil CH₄ and N₂O emissions. However, deposition of charcoal during burning may have enhanced CH₄ oxidation and N₂O consumption at the study site, given that emissions (CH₄: ?4.33 kg C ha^?1 yr^?1, N₂O: 0.17 kg N ha^?1 yr^?1) were relatively lower than those measured in other land-use types. Despite significant emission of CH₄ and N₂O during yearly burning events in early spring, the M. sinensis semi-natural grassland had a large annual soil C accumulation, which resulted in a global warming potential of ?4.86 Mg CO₂eq ha^?1 yr^?1. Consequently, our results indicate that long-term maintenance of semi-natural M. sinensis grasslands by annual burning can contribute to the mitigation of global warming.     

Life cycle inventory-based analysis of greenhouse gas emissions from arable land farming systems in Hokkaido,northern Japan

Abstract

To assess their impacts on net global warming, total greenhouse gas emissions (mainly CO₂, N₂O and CH₄) from agricultural production in arable land cropping systems in the Tokachi region of Hokkaido, Japan, were estimated using life cycle inventory (LCI) analysis. The LCI data included CO₂ emissions from on-farm and off-farm fossil fuel consumption, soil CO₂ emissions induced by the decomposition of soil organic matter, direct and indirect N₂O emissions from arable lands and CH₄ uptake by soils, which were then aggregated in CO₂-equivalents. Under plow-based conventional tillage (CT) cropping systems for winter wheat, sugar beet, adzuki bean, potato and cabbage, on-farm CO₂ emissions from fuel-consuming operations such as tractor-based field operations, truck transportation and mechanical grain drying ranged from 0.424 Mg CO₂ ha^?1 year^?1 for adzuki bean to 0.826 Mg CO₂ ha^?1 year^?1 for winter wheat. Off-farm CO₂ emissions resulting from the use of agricultural materials such as chemical fertilizers, biocides (pesticides and herbicides) and agricultural machines were estimated by input–output tables to range from 0.800 Mg CO₂ ha^?1 year^?1 for winter wheat to 1.724 Mg CO₂ ha^?1 year^?1 for sugar beet. Direct N₂O emissions previously measured in an Andosol field of this region showed a positive correlation with N fertilizer application rates. These emissions, expressed in CO₂-equivalents, ranged from 0.041 Mg CO₂ ha^?1 year^?1 for potato to 0.382 Mg CO₂ ha^?1 year^?1 for cabbage. Indirect N₂O emissions resulting from N leaching and surface runoff were estimated to range from 0.069 Mg CO₂ ha^?1 year^?1 for adzuki bean to 0.381 Mg CO₂ ha^?1 year^?1 for cabbage. The rates of CH₄ removal from the atmosphere by soil uptake were equivalent to only 0.020–0.042 Mg CO₂ ha^?1 year^?1. From the difference in the total soil C pools (0–20 cm depth) between 1981 and 2001, annual CO₂ emissions from the CT and reduced tillage (RT) soils were estimated to be 4.91 and 3.81 Mg CO₂ ha^?1 year^?1, respectively. In total, CO₂-equivalent greenhouse gas emissions under CT cropping systems in the Tokachi region of Hokkaido amounted to 6.97, 7.62, 6.44, 6.64 and 7.49 Mg CO₂ ha^?1 year^?1 for winter wheat, sugar beet, adzuki bean, potato and cabbage production, respectively. Overall, soil-derived CO₂ emissions accounted for a large proportion (64–76%) of the total greenhouse gas emissions. This illustrates that soil management practices that enhance C sequestration in soil may be an effective means to mitigate large greenhouse gas emissions from arable land cropping systems such as those in the Tokachi region of northern Japan. Under RT cropping systems, plowing after harvesting was omitted, and total greenhouse gas emissions from winter wheat, sugar beet and adzuki bean could be reduced by 18%, 4% and 18%, respectively, mainly as a result of a lower soil organic matter decomposition rate in the RT soil and a saving on the fuels used for plowing.     

No significant difference in N2O emission,fertilizer-induced N2O emission factor and CH4 absorption between anaerobically digested cattle slurry and chemical fertilizer applied timothy (Phleum pratense L.) sward in central Hokkaido,Japan

Abstract

Nitrous oxide (N₂O) and methane (CH₄) fluxes from a fertilized timothy (Phleum pratense L.) sward on the northern island of Japan were measured over 2?years using a randomized block design in the field. The objectives of the present study were to obtain annual N₂O and CH₄ emission rates and to elucidate the effect of the applied material (control [no nitrogen], anaerobically digested cattle slurry [ADCS] or chemical fertilizer [CF]) and the application season (autumn or spring) on the annual N₂O emission, fertilizer-induced N₂O emission factor (EF) and the annual CH₄ absorption. Ammonium sulfate was applied to the CF plots at the same application rate of NH₄-N to the ADCS plots. A three-way ANOVA was used to examine the significance of the factors (the applied material, the application season and the year). The ANOVA for the annual N₂O emission rates showed a significant effect with regard to the applied material (P?=?0.042). The annual N₂O emission rate from the control plots (0.398?kg N₂O-N ha^?1?year^?1) was significantly lower than that from the ADCS plots (0.708?kg N₂O-N ha^?1?year^?1) and the CF plots (0.636?kg N₂O-N ha^?1?year^?1). There was no significant difference in the annual N₂O emission rate between the ADCS and CF plots. The ANOVA for the EFs showed insignificance of all factors (P?>?0.05). The total mean?±?standard error of the EFs (fertilizer-induced N₂O-N emission/total applied N) was 0.0024?±?0.0007 (kg N₂O-N [kg N]^?1), which is similar to the reported EF (0.0032?±?0.0013) for well-drained uplands in Japan. The CH₄ absorption rates differed significantly between years (P?=?0.014). The CH₄ absorption rate in the first year (3.28?kg CH₄?ha^?1?year^?1) was higher than that in the second year (2.31?kg CH₄?ha^?1?year^?1), probably as a result of lower precipitation in the first year. In conclusion, under the same application rate of NH₄-N, differences in the applied materials (ADCS or CF) and the application season (autumn or spring) led to no significant differences in N₂O emission, fertilizer-induced N₂O EF and CH₄ absorption.     

北方泥炭地甲烷排放研究: 综述

Northern peatlands store a large amount of carbon and play a significant role in the global carbon cycle. Owing to the presence of waterlogged and anaerobic conditions, peatlands are typically a source of methane (CH₄), a very potent greenhouse gas. This paper reviews the key mechanisms of peatland CH₄ production, consumption and transport and the major environmental and biotic controls on peatland CH₄ emissions. The advantages and disadvantages of micrometeorological and chamber methods in measuring CH₄ fluxes from northern peatlands are also discussed. The magnitude of CH₄ flux varies considerably among peatland types (bogs and fens) and microtopographic locations (hummocks and hollows). Some anthropogenic activities including forestry, peat harvesting and industrial emission of sulphur dioxide can cause a reduction in CH₄ release from northern peatlands. Further research should be conducted to investigate the in fluence of plant growth forms on CH₄ flux from northern peatlands, determine the water table threshold at which plant production in peatlands enhances CH₄ release, and quantify peatland CH₄ exchange at plant community level with a higher temporal resolution using automatic chambers.     

Carbon loss in drained forestry peatlands in Finland,estimated by re‐sampling peatlands surveyed in the 1980s

The total area of boreal peatlands is about 3.5 million km² and they are estimated to contain 15–30% of the global soil carbon (C) storage. In Finland, about 60 000 km², or 60% of the original peatland area, has been drained, mainly for forestry improvement. We have studied C inventory changes on forestry‐drained peatlands by re‐sampling the peat stratum in 2009 at the precise locations of quantitative peat mass analyses conducted as part of peatland transect surveys during the 1980s. The old and new profiles were correlated mainly by their ignition residue stratigraphies; at each site we determined a reference level, identifiable in both profiles, and calculated the cumulative dry mass and C inventories above it. Comparison of a total of 37 locations revealed broad variation, from slight increase to marked decrease; on average the 2009 results indicate a loss of 7.4 (SE ± 2.5) kg m^?2 dry peat mass when compared with the 1980s values. Expressed on an annual basis, the results indicate an average net loss of 150 g C m^?2 year^?1 from the soil of drained forestry peatlands in the central parts of Finland. The C balance appeared not to correlate with site fertility (fertility classes according to original vegetation type), nor with post‐drainage timber growth.     

Effects of nitrogen and sulfur deposition on CH4 and N2O fluxes in high-altitude peatland soil under different water tables in the Tibetan Plateau

Abstract

The effects of nitrogen (N) and sulfur (S) deposition on methane (CH₄) and nitrous oxide (N₂O) emissions under low (10 cm below soil surface) and high (at soil surface) water tables were investigated in the laboratory. Undisturbed soil columns from the alpine peatland of the Tibetan Plateau were analyzed. CH₄ emission was higher and N₂O emission was lower at the high water table than those at the low water table regardless of nutrient application. Addition of N (NH₄NO₃ (ammonium nitrate), 5 g N m^?2) decreased CH₄ emission up to 57% and 50% at low and high water tables, respectively, but correspondingly increased N₂O emission by 2.5 and 10.4 times. Addition of S (Na₂SO₄ (sodium sulfate), 2.5 g S m^?2) decreased CH₄ and N₂O emission by 64% and 79% at the low water table, respectively, but had a slightly positive effect at the high water table. These results indicated that the responses of CH₄ and N₂O emissions to the S deposition depend on the water table condition in the high-altitude peatland.     

Above and Below Ground Measurements of Greenhouse Gases from Swine Effluent Amended Soil

Abstract

As a means of economic disposal and to reduce need for chemical fertilizer, waste generated from swine production is often applied to agricultural land. However, there remain many environmental concerns about this practice. Two such concerns, contribution to the greenhouse effect and stratospheric ozone depletion by gases emitted from waste‐amended soils, have not been thoroughly investigated. An intact core study at Auburn University (32 36′N, 85 36′W) was conducted to determine the source‐sink relationship of three greenhouse gases in three Alabama soils (Black Belt, Coastal Plain, and Appalachian Plateau regions) amended with swine waste effluent. Soil cores were arranged in a completely random design, and treatments used for each soil type consisted of a control, a swine effluent amendment (112 kg N ha^?1), and an ammonium nitrate (NH₄NO₃) fertilizer amendment (112 kg N ha^?1). During a 2‐year period, a closed‐chamber technique was used to determine rates of emission of nitrous oxide (N₂O)–nitrogen (N), carbon dioxide (CO₂)–carbon (C), and methane (CH₄)–C from the soil surface. Gas probes inserted into the soil cores were used to determine concentrations of N₂O‐N and CO₂‐C from depths of 5, 15, and 25 cm. Soil water was collected from each depth using microlysimeters at the time of gas collection to determine soil‐solution N status. Application of swine effluent had an immediate effect on emissions of N₂O‐N, CO₂‐C, and CH₄‐C from all soil textures. However, greatest cumulative emissions and highest peak rates of emission of all three trace gases, directly following effluent applications, were most commonly observed from sandier textured Coastal Plain and Appalachian Plateau soils, as compared to heavier textured Black Belt soil. When considering greenhouse gas emission potential, soil type should be a determining factor for selection of swine effluent waste disposal sites in Alabama.     

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.     

Nitrous oxide and methane emissions from grassland treated with bark- or sawdust-containing manure at different rates

On the main Japanese island of Honshu, bark or sawdust is often added to cattle excreta as part of the composting process. Dairy farmers sometimes need to dispose of manure that is excess to their requirements by spreading it on their grasslands. We assessed the effect of application of bark- or sawdust-containing manure at different rates on annual nitrous oxide (N₂O) and methane (CH₄) emissions from a grassland soil. Nitrous oxide and CH₄ fluxes from an orchardgrass (Dactylis glomerata L.) grassland that received this manure at 0, 50, 100, 200, or 300?Mg?ha^?1?yr^?1 were measured over a two-year period by using closed chambers. Two-way analysis of variance (ANOVA) was employed to examine the effect of annual manure application rates and years on annual N₂O and CH₄ emissions. Annual N₂O emissions ranged from 0.47 to 3.03?kg?N?ha^?1?yr^?1 and increased with increasing manure application rate. Nitrous oxide emissions during the 140-day period following manure application increased with increasing manure application rate, with the total nitrogen concentration in the manure, and with cumulative precipitation during the 140-day period. However, manure application rate did not affect the N₂O emission factors of the manure. The overall average N₂O emission factor was 0.068%. Annual CH₄ emissions ranged from ?1.12 to 0.01?kg?C?ha^?1?yr^?1. The annual manure application rate did not affect annual CH₄ emissions.     

增温与干旱双重变化对若尔盖泥炭CH4排放的影响

若尔盖泥炭地经历了长期人为排水,未来又面临着强烈的变暖干旱,会对泥炭地CH₄排放产生复杂影响。在若尔盖选取了近自然和长期人为排水两种泥炭地类型,采集1 m深泥炭柱,采用室内环境控制试验,设定不同的氧气、水分和温度条件,探索这两种典型泥炭地的泥炭CH₄排放对增温与干旱双重变化的响应差异。结果表明:(1)由于水位降低和泥炭有机物质量下降,长期排水泥炭地的中下层泥炭(20—80 cm)CH₄累积排放量显著低于近自然泥炭地。(2)两种泥炭地的表层和深层泥炭CH₄排放都对升温不敏感,而中下层泥炭的CH₄累积排放量从5℃到15℃显著增加。(3)模拟增温10℃同时干旱水位降低20 cm条件下,中层泥炭受到了温度、水分和氧气变化的叠加影响,CH₄排放变化最剧烈。(4)最终整个1 m深泥炭近自然泥炭地高温低水位的CH₄总排放量为(204.29±15.13)μg/gC,比其低温高水位显著升高66.43 μg/gC(约48%); 排水泥炭地高温低水位的CH₄总排放量为(75.64±9.41)μg/gC,比其低温高水位升高11.95 μg/gC(约19%)。综上,升温干旱气候会对若尔盖泥炭地的有机碳稳定性造成破坏性影响,会集中导致中层泥炭CH₄排放的剧烈变化,可能最终使本区域CH₄排放量显著提高。     

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.     

夏季休牧对高寒矮嵩草草甸温室气体排放的影响

以高寒矮嵩草草甸为研究对象,利用密闭箱－气相色谱法,对夏季休牧8a的围栏草地(休牧草地)和全年放牧的草地(放牧草地)的温室气体排放通量、土壤特性和生物量进行了对比研究。结果表明：与放牧草地相比,休牧草地植被盖度较之高41％,单位面积生物量较之高53％。同时,土壤特性也有较大不同;休牧草地的植被－土壤系统CO₂排放通量比放牧草地低20.7％,测定期间两者CO₂排放通量以每天每公顷排放C的质量计分别为30.7和38.7 kg·(hm²·d)^-1;试验期间高寒矮嵩草草甸植被－土壤系统是大气CH₄的弱汇,休牧后草地土壤对CH₄的吸收能力增强,休牧和放牧草地CH₄的平均吸收强度分别为28.1和21.9 g·(hm²·d)^-1;休牧草地土壤N₂O排放通量比放牧草地低,两者排放通量分别为4.5和7.6 g·(hm²·d)^-1。可见,夏季休牧措施降低了草地对大气中温室气体浓度增加的贡献。     

Influence of increasing temperature and nitrogen input on greenhouse gas emissions from a desert steppe soil in Inner Mongolia

We investigated the effect of increasing soil temperature and nitrogen on greenhouse gas (GHG) emissions [carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O)] from a desert steppe soil in Inner Mongolia, China. Two temperature levels (heating versus no heating) and two nitrogen (N) fertilizer application levels (0 and 100?kg?N?ha^?1?year^?1) were examined in a complete randomized design with six replications. The GHG surface fluxes and their concentrations in soil (0 to 50?cm) were collected bi-weekly from June 2006 to November 2007. Carbon dioxide and N₂O emissions were not affected by heating or N treatment, but compared with other seasons, CO₂ was higher in summer [average of 29.6 versus 8.6?mg carbon (C) m^?2?h^?1 over all other seasons] and N₂O was lower in winter (average of 2.6 versus 4.0?mg?N?m^?2?h^?1 over all other seasons). Desert steppe soil is a CH₄ sink with the highest rate of consumption occurring in summer. Heating decreased CH₄ consumption only in the summer. Increasing surface soil temperature by 1.3°C or applying 100?kg?ha^?1?year^?1 N fertilizer had no effect on the overall GHG emissions. Seasonal variability in GHG emission reflected changes in temperature and soil moisture content. At an average CH₄ consumption rate of 31.65?µg?C?m^?2?h^?1, the 30.73 million ha of desert steppe soil in Inner Mongolia can consume (sequestrate) about 85?×?10^6?kg CH₄-C, an offset equivalent to 711?×?10^6?kg CO₂-C emissions annually. Thus, desert steppe soil should be considered an important CH₄ sink and its potential in reducing GHG emission and mitigating climate change warrants further investigation.     

The impact of logging residue on soil GHG fluxes in a drained peatland forest

Northern peatlands contain substantial reservoirs of carbon (C). Forestry activities endanger the C storages in some of these areas. While the initial impacts of forestry drainage on peatland greenhouse gas (GHG) balance have been studied, the impacts of other silvicultural practices, e.g. logging residue (LR) retention or removal, are not known. We measured the CH₄, N₂O and CO₂ fluxes between peat soil and atmosphere with and without decomposing LR over three (2002–2004) seasons (May–Oct) following clearfelling in a drained peatland forest, along with the mass loss of LR. Seasonal average CO₂ efflux from plots with LR (3070 g CO₂ m⁻² season⁻¹) was twice as high as that from plots without LR (1447 g CO₂ m⁻² season⁻¹). Less than 40% of this difference was accounted for by the decay of logging residues (530 g CO₂ m⁻² season⁻¹), so the majority of the increased CO₂ efflux was caused by increased soil organic matter decomposition under the LR. Furthermore LR increased soil N₂O fluxes over 3-fold (0.70 g N₂O m⁻² season⁻¹), compared to plots without LR (0.19 g N₂O m⁻² season⁻¹), while no change in CH₄ emissions was observed. Our results indicate that LR retention in clearfelled peatland sites may significantly increase GHG emissions and C release from the soil organic matter C storage. This would make the harvesting of LR for biofuel more beneficial, in the form of avoided emissions. Further investigations of the sources of CO₂ under logging residues are, however, needed to confirm this finding.