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1.
At high latitudes, winter climate change alters snow cover and, consequently, may cause a sustained change in soil frost dynamics. Altered winter soil conditions could influence the ecosystem exchange of carbon dioxide (CO2) and, in turn, provide feedbacks to ongoing climate change. To investigate the mechanisms that modify the peatland CO2 exchange in response to altered winter soil frost, we conducted a snow exclusion experiment to enhance winter soil frost and to evaluate its short‐term (1–3 years) and long‐term (11 years) effects on CO2 fluxes during subsequent growing seasons in a boreal peatland. In the first 3 years after initiating the treatment, no significant effects were observed on either gross primary production (GPP) or ecosystem respiration (ER). However, after 11 years, the temperature sensitivity of ER was reduced in the treatment plots relative to the control, resulting in an overall lower ER in the former. Furthermore, early growing season GPP was also lower in the treatment plots than in the controls during periods with photosynthetic photon flux density (PPFD) ≥800 μmol m?2 s?1, corresponding to lower sedge leaf biomass in the treatment plots during the same period. During the peak growing season, a higher GPP was observed in the treatment plots under the low light condition (i.e. PPFD 400 μmol m?2 s?1) compared to the control. As Sphagnum moss maximizes photosynthesis at low light levels, this GPP difference between the plots may have been due to greater moss photosynthesis, as indicated by greater moss biomass production, in the treatment plots relative to the controls. Our study highlights the different responses to enhanced winter soil frost among plant functional types which regulate CO2 fluxes, suggesting that winter climate change could considerably alter the growing season CO2 exchange in boreal peatlands through its effect on vegetation development.  相似文献   

2.
The impact of changes in winter soil frost regime on soil CO2 concentration and its atmospheric exchange in a boreal Norway spruce forest was investigated using a field‐scale soil frost manipulation experiment. The experiment comprised three treatments: deep soil frost, shallow soil frost and control plots (n= 3). Winter soil temperatures and soil frost distribution were significantly altered by the different treatments. The average soil CO2 concentrations during the growing season were significantly lower in plots with deep soil frost than in plots with shallow soil frost. The average CO2 soil–atmosphere exchange rate exhibited the same pattern, and differences in soil respiration rates among the treatments were statistically significant. Both the variation in soil CO2 concentration and the CO2 soil–atmosphere exchange rate could statistically be explained by the differences in the maximum soil frost depth during the previous winter. A response model for growing season soil respiration rates suggests that every 1 cm change in winter soil frost depth will change the emission rates by ca. 0.01 g CO2 m?2 day?1, corresponding to 0.2–0.5% of the estimated net ecosystem productivity (NEP). This suggests that the soil frost regime has a significant influence on the C balance of the system, because interannual variations in soil frost up to 60 cm have been recorded at the site. We conclude that winter climate conditions can be important in controlling C balances in northern terrestrial ecosystems, and also that indirect effects of the winter season must be taken into account, because these can affect the prevailing conditions during the growing season.  相似文献   

3.
王怡萌  段磊磊  陈聪  王铭  王升忠  赵婧 《生态学报》2023,43(11):4583-4593
泥炭地水文条件影响泥炭地生物地球化学循环,控制和维持着泥炭地生态系统的结构和功能,是泥炭地生态恢复的重要前提。然而,目前关于恢复泥炭地土壤碳排放对不同水位的响应尚不明确。以长白山区天然(NP)、退耕(DP)及实施不同水文管理的恢复泥炭地(低水位(LR)、高水位(HR)与高低交替水位(H-LR))为研究对象,采用静态箱-气相色谱法对研究区泥炭地进行生长季(6-10月)土壤CO2、CH4排放监测。结果表明:温度和水位变化是研究区泥炭地土壤CO2、CH4排放季节变化的主控因子。H-LR受水位控制的影响,生长季土壤CO2排放速率波动剧烈,其它水位管理恢复区土壤CO2排放速率呈单峰型排放模式,且均与近地表温度呈指数相关(P<0.05)。除HR外,土壤CO2排放速率与水位呈显著负相关(P<0.05)。生长季,研究区HR土壤CH4排放速率呈双峰型,H-LR与NP的土壤CH4排放呈单峰型,与近地表温度呈指数相关(P<0.05),LR水位与CH4排放速率显著正相关(P<0.05)。研究区不同水位管理恢复泥炭地土壤碳排放差异显著,虽然HR的土壤CO2-C累积碳排放量显著低于其它水位恢复区,但其土壤CH4-C累积碳排放量和综合增温潜势显著高于其它水位恢复区(P<0.05)。LR的累积碳排放量显著低于退化泥炭地,且其综合增温潜势最低。因此,建议在泥炭地恢复初期将低水位管理作为短期策略,以更好地恢复泥炭地碳汇功能,减弱其增温潜势。  相似文献   

4.
Rich fens are common boreal ecosystems with distinct hydrology, biogeochemistry and ecology that influence their carbon (C) balance. We present growing season soil chamber methane emission (FCH4), ecosystem respiration (ER), net ecosystem exchange (NEE) and gross primary production (GPP) fluxes from a 9‐years water table manipulation experiment in an Alaskan rich fen. The study included major flood and drought years, where wetting and drying treatments further modified the severity of droughts. Results support previous findings from peatlands that drought causes reduced magnitude of growing season FCH4, GPP and NEE, thus reducing or reversing their C sink function. Experimentally exacerbated droughts further reduced the capacity for the fen to act as a C sink by causing shifts in vegetation and thus reducing magnitude of maximum growing season GPP in subsequent flood years by ~15% compared to control plots. Conversely, water table position had only a weak influence on ER, but dominant contribution to ER switched from autotrophic respiration in wet years to heterotrophic in dry years. Droughts did not cause inter‐annual lag effects on ER in this rich fen, as has been observed in several nutrient‐poor peatlands. While ER was dependent on soil temperatures at 2 cm depth, FCH4 was linked to soil temperatures at 25 cm. Inter‐annual variability of deep soil temperatures was in turn dependent on wetness rather than air temperature, and higher FCH4 in flooded years was thus equally due to increased methane production at depth and decreased methane oxidation near the surface. Short‐term fluctuations in wetness caused significant lag effects on FCH4, but droughts caused no inter‐annual lag effects on FCH4. Our results show that frequency and severity of droughts and floods can have characteristic effects on the exchange of greenhouse gases, and emphasize the need to project future hydrological regimes in rich fens.  相似文献   

5.
Fluxes of N2O,CH4 and CO2 on afforested boreal agricultural soils   总被引:3,自引:0,他引:3  
After drainage of natural boreal peatlands, the decomposition of organic matter increases and peat soil may turn into a net source of CO2 and N2O, whereas CH4 emission is known to decrease. Afforestation is a potential mitigation strategy to reduce greenhouse gas emission from organic agricultural soils. A static chamber technique was used to evaluate the fluxes of CH4, N2O and CO2 from three boreal organic agricultural soils in western Finland, afforested 1, 6 or 23 years before this study. The mean emissions of CH4 and N2O during the growing seasons did not correlate with the age of the tree stand. All sites were sources of N2O. The highest daily N2O emission during the growing season, measured in the oldest site, was as high as 29 mg N2O m–2d–1. In general, organic agricultural soils are sinks for methane. Here, the oldest site acted as a small sink for methane, whereas the two youngest afforested organic soils were sources for methane with maximum emission rates (up to 154 mg m–2d–1) similar to those reported for minerogenous natural peatlands. Soil respiration rates decreased with the age of the forest. The high soil respiration in the younger sites, probably resulted from the high biomass production of herbs, could create soil anaerobiosis and increase methane production. Our results show that afforestation of agricultural peat soils does not abruptly terminate the N2O emissions during the first two decades, and afforestation can even enhance methane emission for a few years. The carbon accumulation in the developing tree stand can partly compensate the carbon loss from soil.  相似文献   

6.
The moss layer transfer technique removes the top layer of vegetation from donor sites as a method to transfer propagules and restore degraded or reclaimed peatlands. As this technique is new, little is known about the impacts of moss layer transfer on vegetation and carbon fluxes following harvest. We monitored growing season carbon dioxide (CO2) and methane (CH4) fluxes as well as plant communities at donor sites and neighbouring natural peatland sites in an ombrotrophic bog and minerotrophic fen in Alberta, Canada from which material was harvested between 1 and 6 years prior to the study. Plant recovery at all donor sites was rapid with an average of 72% total plant cover one growing season after harvest at the fen and an average of 87% total plant cover two growing seasons after harvest at the bog. Moss cover also returned, averaging 84% 6 years after harvest at the bog. The majority of natural peatlands in western Canada are treed and tree recruitment at the donor sites was limited. Methane emissions were higher from donor sites compared to natural sites due to the high water table and greater sedge cover. Carbon budgets suggested that the donor fen and bog sites released higher CO2 and CH4 over the growing season compared to adjacent natural sites. However, vegetation re-establishment on donor sites was rapid, and it is possible that these sites will return to their original carbon-cycle functioning after disturbance, suggesting that donor sites may recover naturally without implementing management strategies.  相似文献   

7.
Boreal peatlands have significant emissions of non-methane biogenic volatile organic compounds (BVOCs). Climate warming is expected to affect these ecosystems both directly, with increasing temperature, and indirectly, through water table drawdown following increased evapotranspiration. We assessed the combined effect of warming and water table drawdown on the BVOC emissions from boreal peatland microcosms. We also assessed the treatment effects on the BVOC emissions from the peat soil after the 7-week long experiment. Emissions of isoprene, monoterpenes, sesquiterpenes, other reactive VOCs and other VOCs were sampled using a conventional chamber technique, collected on adsorbent and analyzed by GC–MS. Carbon emitted as BVOCs was less than 1% of the CO2 uptake and up to 3% of CH4 emission. Water table drawdown surpassed the direct warming effect and significantly decreased the emissions of all BVOC groups. Only isoprene emission was significantly increased by warming, parallel to the increased leaf number of the dominant sedge Eriophorum vaginatum. BVOC emissions from peat soil were higher under the control and warming treatments than water table drawdown, suggesting an increased activity of anaerobic microbial community. Our results suggest that boreal peatlands could have concomitant negative and positive radiative forcing effects on climate warming following the effect of water table drawdown. The observed decrease in CH4 emission causes a negative radiative forcing while the increase in CO2 emission and decrease in reactive BVOC emissions, which could reduce the cooling effect induced by the lower formation rate of secondary organic aerosols, both contribute to increased radiative forcing.  相似文献   

8.
In North America, mulching of vacuum-harvested sites combined with blocking of the drainage system is widely used for peatland restoration to accelerate Sphagnum establishment. However, peat extraction in fen peatlands or exposure of deeper minerotrophic peat layers results in soil chemistry that is less suitable for re-establishment of Sphagnum moss. In this situation, restoration of plant species characteristic of minerotrophic peatlands is desirable to return the site to a carbon accumulating system. In these cases, it may be worthwhile to maintain spontaneously revegetating species as part of restoration if they provide desirable ecosystem functions. We studied the role of six spontaneously recolonizing vegetation communities for methane (CH4) emissions and pore water CH4 concentration for two growing seasons (2008 and 2009) at an abandoned minerotrophic peatland in southeastern Quebec. We then compared the results with bare peat and adjacent natural fen vegetation. Communities dominated by Eriophorum vaginatum, Carex aquatilis and Typha latifolia had CH4 flux an order of magnitude greater than other cutover vegetation types and natural sites. In contrast, Scirpus atrocinctus and Equisetum arvense had CH4 emission rates lower than natural hollow vegetation. We found seasonal average water table and vegetation volume had significant correlation with CH4 flux. Water table and soil temperature were significantly correlated with CH4 flux at plots where the water table was near or above the surface. Pore water CH4 concentration suggests that CH4 is being produced at the cutover peatland and that low measured fluxes likely result from substantial oxidation of CH4 in the unsaturated zone. Understanding ecosystem functions of spontaneously recolonizing species on cutover fens can be used to help make decisions about the inclusion of these communities for future restoration measures.  相似文献   

9.
湿地是大气甲烷(CH_4)的主要排放源,而有关放牧对湿地CH_4排放的影响特征仍未得到足够的报道。因此,通过静态箱法,研究了放牧对四川省若尔盖高原湿地CH_4排放的影响,CH_4气体通过快速温室气体分析仪测量。结果表明:放牧样地和围栏内样地生长季CH_4排放量为(31.32±19.57)g/m~2和(30.31±23.46)g/m~2,它们之间无差异显著;但是集中放牧期间(7—9月),放牧样地(21.01±12.35)g/m~2较围栏内样地显著增加了CH_4排放量为54.3%。2014年生长季期间通过刈割植物模拟放牧表明两种刈割强度CH_4排放量为(5.01±5.37)g/m~2和(4.69±5.99)g/m~2,较未刈割样地(1.15±1.89)g/m~2增加了335.9%和308.0%,其原因可能是放牧或者刈割减少地表植物生物量,降低植物高度,缩短了CH_4排放的路径距离。该结果可为我国高原湿地保护与管理决策提供基础数据支撑。  相似文献   

10.
In high‐latitude regions, carbon dioxide (CO2) emissions during the winter represent an important component of the annual ecosystem carbon budget; however, the mechanisms that control the winter CO2 emissions are currently not well understood. It has been suggested that substrate availability from soil labile carbon pools is a main driver of winter CO2 emissions. In ecosystems that are dominated by annual herbaceous plants, much of the biomass produced during the summer is likely to contribute to the soil labile carbon pool through litter fall and root senescence in the autumn. Thus, the summer carbon uptake in the ecosystem may have a significant influence on the subsequent winter CO2 emissions. To test this hypothesis, we conducted a plot‐scale shading experiment in a boreal peatland to reduce the gross primary production (GPP) during the growing season. At the growing season peak, vascular plant biomass in the shaded plots was half that in the control plots. During the subsequent winter, the mean CO2 emission rates were 21% lower in the shaded plots than in the control plots. In addition, long‐term (2001–2012) eddy covariance data from the same site showed a strong correlation between the GPP (particularly the late summer and autumn GPP) and the subsequent winter net ecosystem CO2 exchange (NEE). In contrast, abiotic factors during the winter could not explain the interannual variation in the cumulative winter NEE. Our study demonstrates the presence of a cross‐seasonal link between the growing season biotic processes and winter CO2 emissions, which has important implications for predicting winter CO2 emission dynamics in response to future climate change.  相似文献   

11.
We conducted plant species removals, air temperaturemanipulations, and vegetation and soil transplants inAlaskan wet-meadow and tussock tundra communities todetermine the relative importance of vegetation typeand environmental variables in controlling ecosystemmethane (CH4) and carbon dioxide (CO2) flux. Plastic greenhouses placed over wet-meadow tundraincreased air temperature, soil temperature, and soilmoisture, but did not affect CH4 or CO2 flux(measured in the dark). By contrast, removal ofsedges in the wet meadow significantly decreased fluxof CH4, while moss removal tended to increaseCH4 emissions. At 15 cm depth, pore-waterCH4 concentrations were higher in sedge-removalthan in control plots, suggesting that sedgescontribute to CH4 emissions by transportingCH4 from anaerobic soil to the atmosphere, ratherthan by promoting methanogenesis. Inreciprocal-ecosystem transplants between thewet-meadow and tussock tundra communities, CH4and CO2 emissions were higher overall in thewet-meadow site, but were unrelated to transplantorigin. Methane flux was correlated with localvariation in soil temperature, thaw depth, andwater-table depth, but the relative importance ofthese factors varied through the season. Our resultssuggest that future changes in CH4 and CO2flux in response to climatic change will be morestrongly mediated by large-scale changes in vegetationand soil parameters than by direct temperature effects.  相似文献   

12.
Calcium sulfate, a common soil amendment was applied at rates of 0, 1,000 and 2,000 kg ha-1 to flooded rice plots treated with urea-N (128 kg ha-1). Experimental plots were drill-seeded with Toro-2, a mid-season long-grain rice cultivar, and CH4 emissions were measured over the first cropping season. Over the 70 d sampling season, the low and high rate of CaSO4 reduced CH4 evolution 29 and 46%, respectively, compared to control plots. No significant correlation between soil temperature (0, 5, 10 cm depths) and CH4 emission was observed.  相似文献   

13.
Tropical peatlands are vital ecosystems that play an important role in global carbon storage and cycles. Current estimates of greenhouse gases from these peatlands are uncertain as emissions vary with environmental conditions. This study provides the first comprehensive analysis of managed and natural tropical peatland GHG fluxes: heterotrophic (i.e. soil respiration without roots), total CO2 respiration rates, CH4 and N2O fluxes. The study documents studies that measure GHG fluxes from the soil (n = 372) from various land uses, groundwater levels and environmental conditions. We found that total soil respiration was larger in managed peat ecosystems (median = 52.3 Mg CO2 ha?1 year?1) than in natural forest (median = 35.9 Mg CO2 ha?1 year?1). Groundwater level had a stronger effect on soil CO2 emission than land use. Every 100 mm drop of groundwater level caused an increase of 5.1 and 3.7 Mg CO2 ha?1 year?1 for plantation and cropping land use, respectively. Where groundwater is deep (≥0.5 m), heterotrophic respiration constituted 84% of the total emissions. N2O emissions were significantly larger at deeper groundwater levels, where every drop in 100 mm of groundwater level resulted in an exponential emission increase (exp(0.7) kg N ha?1 year?1). Deeper groundwater levels induced high N2O emissions, which constitute about 15% of total GHG emissions. CH4 emissions were large where groundwater is shallow; however, they were substantially smaller than other GHG emissions. When compared to temperate and boreal peatland soils, tropical peatlands had, on average, double the CO2 emissions. Surprisingly, the CO2 emission rates in tropical peatlands were in the same magnitude as tropical mineral soils. This comprehensive analysis provides a great understanding of the GHG dynamics within tropical peat soils that can be used as a guide for policymakers to create suitable programmes to manage the sustainability of peatlands effectively.  相似文献   

14.
Rice cultivation is an important anthropogenic source of atmospheric methane (CH4), the emission of which is affected by management practices. Many field measurements have been conducted in major rice‐producing countries in Asia. We compiled a database of CH4 emissions from rice fields in Asia from peer‐reviewed journals. We developed a statistical model to relate CH4 flux in the rice‐growing season to soil properties, water regime in the rice‐growing season, water status in the previous season, organic amendment and climate. The statistical results showed that all these variables significantly affected CH4 flux, and explained 68% of the variability. Organic amendment and water regime in the rice‐growing season were the top two controlling variables; climate was the least critical variable. The average CH4 fluxes from rice fields with single and multiple drainages were 60% and 52% of that from continuously flooded rice fields. The flux from fields that were flooded in the previous season was 2.8 times that from fields previously drained for a long season and 1.9 times that from fields previously drained for a short season. In contrast to the previously reported optimum soil pH of around neutrality, soils with pH of 5.0–5.5 gave the maximum CH4 emission. The model results demonstrate that application of rice straw at 6 t ha?1 before rice transplanting can increase CH4 emission by 2.1 times; when applied in the previous season, however, it increases CH4 emission by only 0.8 times. Default emission factors and scaling factors for different water regimes and organic amendments derived from this work can be used to develop national or regional emission inventories.  相似文献   

15.
At the southern margin of permafrost in North America, climate change causes widespread permafrost thaw. In boreal lowlands, thawing forested permafrost peat plateaus (‘forest’) lead to expansion of permafrost‐free wetlands (‘wetland’). Expanding wetland area with saturated and warmer organic soils is expected to increase landscape methane (CH4) emissions. Here, we quantify the thaw‐induced increase in CH4 emissions for a boreal forest‐wetland landscape in the southern Taiga Plains, Canada, and evaluate its impact on net radiative forcing relative to potential long‐term net carbon dioxide (CO2) exchange. Using nested wetland and landscape eddy covariance net CH4 flux measurements in combination with flux footprint modeling, we find that landscape CH4 emissions increase with increasing wetland‐to‐forest ratio. Landscape CH4 emissions are most sensitive to this ratio during peak emission periods, when wetland soils are up to 10 °C warmer than forest soils. The cumulative growing season (May–October) wetland CH4 emission of ~13 g CH4 m?2 is the dominating contribution to the landscape CH4 emission of ~7 g CH4 m?2. In contrast, forest contributions to landscape CH4 emissions appear to be negligible. The rapid wetland expansion of 0.26 ± 0.05% yr?1 in this region causes an estimated growing season increase of 0.034 ± 0.007 g CH4 m?2 yr?1 in landscape CH4 emissions. A long‐term net CO2 uptake of >200 g CO2 m?2 yr?1 is required to offset the positive radiative forcing of increasing CH4 emissions until the end of the 21st century as indicated by an atmospheric CH4 and CO2 concentration model. However, long‐term apparent carbon accumulation rates in similar boreal forest‐wetland landscapes and eddy covariance landscape net CO2 flux measurements suggest a long‐term net CO2 uptake between 49 and 157 g CO2 m?2 yr?1. Thus, thaw‐induced CH4 emission increases likely exert a positive net radiative greenhouse gas forcing through the 21st century.  相似文献   

16.
Eddy covariance measurements of methane (CH4) net flux were made in a boreal fen, typical of the most abundant peatlands in western Canada during May–September 2007. The objectives of this study were to determine: (i) the magnitude of diurnal and seasonal variation in CH4 net flux, (ii) the relationship between the temporally varying flux rates and associated changes in controlling biotic and abiotic factors, and (iii) the contribution of CH4 emission to the ecosystem growing season carbon budget. There was significant diurnal variation in CH4 emission during the peak of the growing season that was strongly correlated with associated changes in solar radiation, latent heat flux, air temperature and ecosystem conductance to water vapor. During days 181–215, nighttime average CH4 efflux was only 47% of the average midday values. The peak value for daily average CH4 emission rate was approximately 80 nmol m?2 s?1 (4.6 mg CH4 m?2 h?1), and seasonal variation in CH4 flux was strongly correlated with changes in soil temperature. Integrated over the entire measurement period [days 144–269 (late May–late September)], the total CH4 emission was 3.2 g CH4 m?2, which was quite low relative to other wetland ecosystems and to the simultaneous high rate of ecosystem net CO2 sequestration that was measured (18.1 mol CO2 m?2 or 217 g C m?2). We estimate that the negative radiative forcing (cooling) associated with net carbon storage over the life of the peatland (approximately 2200 years) was at least twice the value of positive radiative forcing (warming) caused by net CH4 emission over the last 50 years.  相似文献   

17.
Northern peatlands constitute a significant source of atmospheric methane (CH4). However, management of undisturbed peatlands, as well as the restoration of disturbed peatlands, will alter the exchange of CH4 with the atmosphere. The aim of this systematic review and meta‐analysis was to collate and analyze published studies to improve our understanding of the factors that control CH4 emissions and the impacts of management on the gas flux from northern (latitude 40° to 70°N) peatlands. The analysis includes a total of 87 studies reporting measurements of CH4 emissions taken at 186 sites covering different countries, peatland types, and management systems. Results show that CH4 emissions from natural northern peatlands are highly variable with a 95% CI of 7.6–15.7 g C m?2 year?1 for the mean and 3.3–6.3 g C m?2 year?1 for the median. The overall annual average (mean ± SD) is 12 ± 21 g C m?2 year?1 with the highest emissions from fen ecosystems. Methane emissions from natural peatlands are mainly controlled by water table (WT) depth, plant community composition, and soil pH. Although mean annual air temperature is not a good predictor of CH4 emissions by itself, the interaction between temperature, plant community cover, WT depth, and soil pH is important. According to short‐term forecasts of climate change, these complex interactions will be the main determinant of CH4 emissions from northern peatlands. Drainage significantly (p < .05) reduces CH4 emissions to the atmosphere, on average by 84%. Restoration of drained peatlands by rewetting or vegetation/rewetting increases CH4 emissions on average by 46% compared to the original premanagement CH4 fluxes. However, to fully evaluate the net effect of management practice on the greenhouse gas balance from high latitude peatlands, both net ecosystem exchange (NEE) and carbon exports need to be considered.  相似文献   

18.
Boreal peatlands contain approximately 500 Pg carbon (C) in the soil, emit globally significant quantities of methane (CH4), and are highly sensitive to climate change. Warming associated with global climate change is likely to increase the rate of the temperature‐sensitive processes that decompose stored organic carbon and release carbon dioxide (CO2) and CH4. Variation in the temperature sensitivity of CO2 and CH4 production and increased peat aerobicity due to enhanced growing‐season evapotranspiration may alter the nature of peatland trace gas emission. As CH4 is a powerful greenhouse gas with 34 times the warming potential of CO2, it is critical to understand how factors associated with global change will influence surface CO2 and CH4 fluxes. Here, we leverage the Spruce and Peatland Responses Under Changing Environments (SPRUCE) climate change manipulation experiment to understand the impact of a 0–9°C gradient in deep belowground warming (“Deep Peat Heat”, DPH) on peat surface CO2 and CH4 fluxes. We find that DPH treatments increased both CO2 and CH4 emission. Methane production was more sensitive to warming than CO2 production, decreasing the C‐CO2:C‐CH4 of the respired carbon. Methane production is dominated by hydrogenotrophic methanogenesis but deep peat warming increased the δ13C of CH4 suggesting an increasing contribution of acetoclastic methanogenesis to total CH4 production with warming. Although the total quantity of C emitted from the SPRUCE Bog as CH4 is <2%, CH4 represents >50% of seasonal C emissions in the highest‐warming treatments when adjusted for CO2 equivalents on a 100‐year timescale. These results suggest that warming in boreal regions may increase CH4 emissions from peatlands and result in a positive feedback to ongoing warming.  相似文献   

19.
Recently, plant-derived methane (CH4) emission has been questioned because limited evidence of the chemical mechanism has been identified to account for the process. We conducted an experiment with four treatments (i.e. winter-grazed, natural alpine meadow; naturally restored alpine meadow eight years after cultivation; oat pasture and bare soil without roots) during the growing seasons of 2007 and 2008 to examine the question of CH4 emission by plant communities in the alpine meadow. Each treatment consumed CH4 in closed, opaque chambers in the field, but two types of alpine meadow vegetation reduced CH4 consumption compared with bare soil, whereas oat pasture increased consumption. This result could imply that meadow vegetation produces CH4. However, measurements of soil temperature and water content showed significant differences between vegetated and bare soil and appeared to explain differences in CH4 production between treatments. Our study strongly suggests that the apparent CH4 production by vegetation, when compared with bare soil in some previous studies, might represent differences in soil temperature and water-filled pore space and not the true vegetation sources of CH4.  相似文献   

20.
Thawing permafrost in the sub‐Arctic has implications for the physical stability and biological dynamics of peatland ecosystems. This study provides an analysis of how permafrost thawing and subsequent vegetation changes in a sub‐Arctic Swedish mire have changed the net exchange of greenhouse gases, carbon dioxide (CO2) and CH4 over the past three decades. Images of the mire (ca. 17 ha) and surroundings taken with film sensitive in the visible and the near infrared portion of the spectrum, [i.e. colour infrared (CIR) aerial photographs from 1970 and 2000] were used. The results show that during this period the area covered by hummock vegetation decreased by more than 11% and became replaced by wet‐growing plant communities. The overall net uptake of C in the vegetation and the release of C by heterotrophic respiration might have increased resulting in increases in both the growing season atmospheric CO2 sink function with about 16% and the CH4 emissions with 22%. Calculating the flux as CO2 equivalents show that the mire in 2000 has a 47% greater radiative forcing on the atmosphere using a 100‐year time horizon. Northern peatlands in areas with thawing sporadic or discontinuous permafrost are likely to act as larger greenhouse gas sources over the growing season today than a few decades ago because of increased CH4 emissions.  相似文献   

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