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1.
利用静态箱-气相色谱法,研究了择伐和皆伐对小兴安岭落叶松-泥炭藓沼泽CH4、CO2、N2O排放的影响.结果表明:采伐改变了落叶松-泥炭藓沼泽CH4和N2O的季节排放规律,其中对照样地的CH4为夏季吸收、秋季排放,N2O夏秋季吸收;择伐样地的CH4和N2O在夏季集中排放;皆伐样地的CH4在夏秋季排放,N2O则在夏季吸收、秋季排放.但采伐对CO2季节排放规律的影响,均为夏季春季秋季.采伐改变了CH4、CO2和N2O的源汇功能,对照样地为CO2的排放源、CH4和N2O的弱吸收汇;采伐地的CO2排放量下降了1/4,并转化为N2O弱排放源,为CH4的弱排放源或强排放源.择伐样地温室效应贡献潜力较对照样地下降了24.5%,皆伐地则提高了3.2%. 相似文献
2.
水位是影响湿地温室气体排放的重要因子。采用静态箱-气相色谱法研究了模拟条件下不同水位(0、5、10 cm和20 cm)对芦苇湿地温室气体(CO_2、CH_4、N_2O)夏季昼夜通量变化的影响。结果表明,1)4种不同水位CO_2通量日变化均表现为昼低夜高,且白天为汇,夜间为源,整体均表现为CO_2的汇;不同水位CH_4通量日变化则均表现为昼高夜低,且整体上均表现为CH_4的源;N_2O通量总体上水淹后均表现为昼高夜低而0cm水位表现为昼低夜高;2)随着水位的增加CH_4和CO_2平均通量呈现先增加后降低的趋势,且10cm水位下CH_4和CO_2平均通量最高,N_2O通量则在5cm水位最高;3)通过相关性和主成分分析表明,气温、水温是土壤CH_4、N_2O通量日变化的主导因子,而土壤温度是CO_2日变化通量的主导因子,同时,土壤p H、Eh及水体p H、Eh是CO_2通量日变化的重要因子之一。 相似文献
3.
中高纬度森林地区由于气候条件变化剧烈,土壤温室气体排放量的估算存在很大的不确定性,并且不同碳氮气体通量的主控因子与耦合关系尚不明确。以长白山温带针阔混交林为研究对象,采用静态箱-气相色谱法连续4a(2005—2009年)测定土壤二氧化碳(CO2)、甲烷(CH4)和氧化亚氮(N2O)净交换通量以及温度、水分等相关环境因子。研究结果表明:温带针阔混交林土壤整体上表现为CO2和N2O的排放源和CH4的吸收汇。土壤CH4、CO2和N2O通量的年均值分别为-1.3 kg CH4hm-2a-1、15102.2 kg CO2hm-2a-1和6.13 kg N2O hm-2a-1。土壤CO2通量呈现明显的季节性规律,主要受土壤温度的影响,水分次之;土壤CH4通量的季节变化不明显,与土壤水分显著正相关;土壤N2O通量季节变化与土壤CO2通量相似,与土壤水分、温度显著正相关。土壤CO2通量和CH4通量不存在任何类型的耦合关系,与N2O通量也不存在耦合关系;土壤CH4和N2O通量之间表现为消长型耦合关系。这项研究显示温带针阔混交林土壤碳氮气体通量主要受环境因子驱动,不同气体通量产生与消耗之间存在复杂的耦合关系,下一步研究需要深入探讨环境变化对其耦合关系的影响以及内在的生物驱动机制。 相似文献
4.
We studied concentrations of carbon dioxide (CO 2), methane (CH 4) and nitrous oxide (N 2O) in the eutrophic Temmesjoki River and Estuary in the Liminganlahti Bay in 2003–2004 and evaluated the atmospheric fluxes
of the gases based on measured concentrations, wind speeds and water current velocities. The Temmesjoki River was a source
of CO 2, CH 4 and N 2O to the atmosphere, whereas the Liminganlahti Bay was a minor source of CH 4 and a minor source or a sink of CO 2 and N 2O. The results show that the fluxes of greenhouse gases in river ecosystems are highly related to the land use in its catchment
areas. The most upstream river site, surrounded by forests and drained peatlands, released significant amounts of CO 2 and CH 4, with average fluxes of 5,400 mg CO 2–C m −2 d −1 and 66 mg CH 4–C m −2 d −1, and concentrations of 210 μM and 345 nM, respectively, but N 2O concentrations, at an average of 17 nM, were close to the atmospheric equilibrium concentration. The downstream river sites
surrounded by agricultural soils released significant amounts of N 2O (with an average emission of 650 μg N 2O–N m −2 d −1 and concentration of 22 nM), whereas the CO 2 and CH 4 concentrations were low compared to the upstream site (55 μM and 350 nM). In boreal regions, rivers are partly ice-covered
in wintertime (approximately 5 months). A large part of the gases, i.e. 58% of CO 2, 55% of CH 4 and 36% of N 2O emissions, were found to be released during wintertime from unfrozen parts of the river. 相似文献
5.
Central European grasslands are characterized by a wide range of different management practices in close geographical proximity. Site‐specific management strategies strongly affect the biosphere–atmosphere exchange of the three greenhouse gases (GHG) carbon dioxide (CO 2), nitrous oxide (N 2O), and methane (CH 4). The evaluation of environmental impacts at site level is challenging, because most in situ measurements focus on the quantification of CO 2 exchange, while long‐term N 2O and CH 4 flux measurements at ecosystem scale remain scarce. Here, we synthesized ecosystem CO 2, N 2O, and CH 4 fluxes from 14 managed grassland sites, quantified by eddy covariance or chamber techniques. We found that grasslands were on average a CO 2 sink (−1,783 to −91 g CO 2 m −2 year −1), but a N 2O source (18–638 g CO 2‐eq. m −2 year −1), and either a CH 4 sink or source (−9 to 488 g CO 2‐eq. m −2 year −1). The net GHG balance (NGB) of nine sites where measurements of all three GHGs were available was found between −2,761 and −58 g CO 2‐eq. m −2 year −1, with N 2O and CH 4 emissions offsetting concurrent CO 2 uptake by on average 21 ± 6% across sites. The only positive NGB was found for one site during a restoration year with ploughing. The predictive power of soil parameters for N 2O and CH 4 fluxes was generally low and varied considerably within years. However, after site‐specific data normalization, we identified environmental conditions that indicated enhanced GHG source/sink activity (“sweet spots”) and gave a good prediction of normalized overall fluxes across sites. The application of animal slurry to grasslands increased N 2O and CH 4 emissions. The N 2O‐N emission factor across sites was 1.8 ± 0.5%, but varied considerably at site level among the years (0.1%–8.6%). Although grassland management led to increased N 2O and CH 4 emissions, the CO 2 sink strength was generally the most dominant component of the annual GHG budget. 相似文献
6.
Using molecular simulations, we studied a diverse collection of zeolite–imidazolate frameworks (ZIFs) to evaluate their performances in adsorption- and membrane-based gas separations. Molecular simulations were performed for both single-component gases (CH 4, CO 2, H 2 and N 2) and binary gas mixtures (CO 2/CH 4, CO 2/N 2, CO 2/H 2 and CH 4/H 2) to predict the intrinsic and mixture selectivities of ZIFs. These two selectivities were compared to discuss the importance of multi-component mixture effects on making predictions about the separation performance of a material. Gas separation performances of ZIFs were compared with other nanoporous materials and our results showed that several ZIFs can outperform well-known zeolites and metal–organic frameworks in CO 2 separations. Several other properties of ZIFs such as gas permeability, working capacity and sorbent selection parameter were computed to identify the most promising materials in adsorption- and membrane-based separation of CO 2/CH 4, CO 2/N 2, CO 2/H 2 and CH 4/H 2. 相似文献
7.
The effects of elevated concentrations of atmospheric CO 2 on CH 4 and N 2O emissions from rice soil were investigated in controlled-environment chambers using rice plants growing in pots. Elevated
CO 2 significantly increased CH 4 emission by 58% compared with ambient CO 2. The CH 4 emitted by plant-mediated transport and ebullition–diffusion accounted for 86.7 and 13.3% of total emissions during the flooding
period under ambient level, respectively; and for 88.1 and 11.9% of total emissions during the flooding period under elevated
CO 2 level, respectively. No CH 4 was emitted from plant-free pots, suggesting that the main source of emitted CH 4 was root exudates or autolysis products. Most N 2O was emitted during the first 3 weeks after flooding and rice transplanting, probably through denitrification of NO 3− contained in the experimental soil, and was not affected by the CO 2 concentration. Pre-harvest drainage suppressed CH 4 emission but did not cause much N 2O emission (< 10 μg N m −2 h −1) from the rice-plant pots at both CO 2 concentrations. 相似文献
8.
We investigated soil carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O) exchanges in an age‐sequence (4, 17, 32, 67 years old) of eastern white pine ( Pinus strobus L.) forests in southern Ontario, Canada, for the period of mid‐April to mid‐December in 2006 and 2007. For both CH 4 and N 2O, we observed uptake and emission ranging from ?160 to 245 μg CH 4 m ?2 h ?1 and ?52 to 21 μg N 2O m ?2 h ?1, respectively (negative values indicate uptake). Mean fluxes from mid‐April to mid‐December across the 4, 17, 32, 67 years old stands were similar for CO 2 fluxes (259, 246, 220, and 250 mg CO 2 m ?2 h ?1, respectively), without pattern for N 2O fluxes (?3.7, 1.5, ?2.2, and ?7.6 μg N 2O m ?2 h ?1, respectively), whereas the uptake rates of CH 4 increased with stand age (6.4, ?7.9, ?10.8, and ?23.3 μg CH 4 m ?2 h ?1, respectively). For the same period, the combined contribution of CH 4 and N 2O exchanges to the global warming potential (GWP) calculated from net ecosystem exchange of CO 2 and aggregated soil exchanges of CH 4 and N 2O was on average 4%, <1%, <1%, and 2% for the 4, 17, 32, 67 years old stand, respectively. Soil CO 2 fluxes correlated positively with soil temperature but had no relationship with soil moisture. We found no control of soil temperature or soil moisture on CH 4 and N 2O fluxes, but CH 4 emission was observed following summer rainfall events. LFH layer removal reduced CO 2 emissions by 43%, increased CH 4 uptake during dry and warm soil conditions by more than twofold, but did not affect N 2O flux. We suggest that significant alternating sink and source potentials for both CH 4 and N 2O may occur in N‐ and soil water‐limited forest ecosystems, which constitute a large portion of forest cover in temperate areas. 相似文献
9.
The magnitude, temporal, and spatial patterns of soil‐atmospheric greenhouse gas (hereafter referred to as GHG) exchanges in forests near the Tropic of Cancer are still highly uncertain. To contribute towards an improvement of actual estimates, soil‐atmospheric CO 2, CH 4, and N 2O fluxes were measured in three successional subtropical forests at the Dinghushan Nature Reserve (hereafter referred to as DNR) in southern China. Soils in DNR forests behaved as N 2O sources and CH 4 sinks. Annual mean CO 2, N 2O, and CH 4 fluxes (mean±SD) were 7.7±4.6 Mg CO 2‐C ha ?1 yr ?1, 3.2±1.2 kg N 2O‐N ha ?1 yr ?1, and 3.4±0.9 kg CH 4‐C ha ?1 yr ?1, respectively. The climate was warm and wet from April through September 2003 (the hot‐humid season) and became cool and dry from October 2003 through March 2004 (the cool‐dry season). The seasonality of soil CO 2 emission coincided with the seasonal climate pattern, with high CO 2 emission rates in the hot‐humid season and low rates in the cool‐dry season. In contrast, seasonal patterns of CH 4 and N 2O fluxes were not clear, although higher CH 4 uptake rates were often observed in the cool‐dry season and higher N 2O emission rates were often observed in the hot‐humid season. GHG fluxes measured at these three sites showed a clear increasing trend with the progressive succession. If this trend is representative at the regional scale, CO 2 and N 2O emissions and CH 4 uptake in southern China may increase in the future in light of the projected change in forest age structure. Removal of surface litter reduced soil CO 2 effluxes by 17–44% in the three forests but had no significant effect on CH 4 absorption and N 2O emission rates. This suggests that microbial CH 4 uptake and N 2O production was mainly related to the mineral soil rather than in the surface litter layer. 相似文献
10.
Background and aimsThe litter layer is a major source of CO2, and it also influences soil-atmosphere exchange of N2O and CH4. So far, it is not clear how much of soil greenhouse gas (GHG) emission derives from the litter layer itself or is litter-induced. The present study investigates how the litter layer controls soil GHG fluxes and microbial decomposer communities in a temperate beech forest. MethodsWe removed the litter layer in an Austrian beech forest and studied responses of soil CO2, CH4 and N2O fluxes and the microbial community via phospholipid fatty acids (PLFA). Soil GHG fluxes were determined with static chambers on 22 occasions from July 2012 to February 2013, and soil samples collected at 8 sampling events. ResultsLitter removal reduced CO2 emissions by 30 % and increased temperature sensitivity (Q10) of CO2 fluxes. Diffusion of CH4 into soil was facilitated by litter removal and CH4 uptake increased by 16 %. This effect was strongest in autumn and winter when soil moisture was high. Soils without litter turned from net N2O sources to slight N2O sinks because N2O emissions peaked after rain events in summer and autumn, which was not the case in litter-removal plots. Microbial composition was only transiently affected by litter removal but strongly influenced by seasonality. ConclusionsLitter layers must be considered in calculating forest GHG budgets, and their influence on temperature sensitivity of soil GHG fluxes taken into account for future climate scenarios. 相似文献
11.
Atmospheric concentrations of methane (CH 4) and nitrous oxide (N 2O) have increased over the last 150 years because of human activity. Soils are important sources and sinks of both potent greenhouse gases where their production and consumption are largely regulated by biological processes. Climate change could alter these processes thereby affecting both rate and direction of their exchange with the atmosphere. We examined how a rise in atmospheric CO 2 and temperature affected CH 4 and N 2O fluxes in a well‐drained upland soil (volumetric water content ranging between 6% and 23%) in a semiarid grassland during five growing seasons. We hypothesized that responses of CH 4 and N 2O fluxes to elevated CO 2 and warming would be driven primarily by treatment effects on soil moisture. Previously we showed that elevated CO 2 increased and warming decreased soil moisture in this grassland. We therefore expected that elevated CO 2 and warming would have opposing effects on CH 4 and N 2O fluxes. Methane was taken up throughout the growing season in all 5 years. A bell‐shaped relationship was observed with soil moisture with highest CH 4 uptake at intermediate soil moisture. Both N 2O emission and uptake occurred at our site with some years showing cumulative N 2O emission and other years showing cumulative N 2O uptake. Nitrous oxide exchange switched from net uptake to net emission with increasing soil moisture. In contrast to our hypothesis, both elevated CO 2 and warming reduced the sink of CH 4 and N 2O expressed in CO 2 equivalents (across 5 years by 7% and 11% for elevated CO 2 and warming respectively) suggesting that soil moisture changes were not solely responsible for this reduction. We conclude that in a future climate this semiarid grassland may become a smaller sink for atmospheric CH 4 and N 2O expressed in CO 2‐equivalents. 相似文献
12.
Northern peatlands accumulate atmospheric CO 2 thus counteracting climate warming. However, CH 4 which is more efficient as a greenhouse gas than CO 2, is produced in the anaerobic decomposition processes in peat. When peatlands are taken for forestry their water table is lowered by ditching. We studied long-term effects of lowered water table on the development of vegetation and the annual emissions of CO 2, CH 4 and N 2O in an ombrotrophic bog and in a minerotrophic fen in Finland. Reclamation of the peat sites for forestry had changed the composition and coverage of the field and ground layer species, and increased highly the growth of tree stand at the drained fen. In general, drainage increased the annual CO 2 emissions but the emissions were also affected by the natural fluctuations of water table. In contrast to CO 2, drainage had decreased the emissions of CH 4, the drained fen even consumed atmospheric CH 4. CO 2 and CH 4 emissions were higher in the virgin fen than in the virgin bog. There were no N 2O emissions from neither type of virgin sites. Drainage had, however, highly increased the N 2O emissions from the fen. The results suggest that post-drainage changes in gas fluxes depend on the trophy of the original mires. 相似文献
13.
Sheepfolds represent significant hot spot sources of greenhouse gases (GHG) in semi-arid grassland regions, such as Inner Mongolia in China. However, the annual contribution of sheepfolds to regional GHG emissions is still unknown. In order to quantify its annual contribution, we conducted measurements of carbon dioxide (CO 2), methane (CH 4) and nitrous oxide (N 2O) fluxes at two sheepfold sites in the Baiyinxile administrative region of Inner Mongolia for 1 year, using static opaque chamber and gas chromatography methods. Our data show that, at an annual scale, both sheepfolds functioned as net sources of CO 2, CH 4 and N 2O. Temperatures primarily determined the seasonal pattern of CO 2 emission; 60–84% of the CO 2 flux variation could be explained by temperature changes. High rates of net CH 4 emissions from sheepfold soils were only observed when animals (sheep and goats) were present. While nitrous oxide emissions were also stimulated by the presence of animals, pulses of N 2O emissions were also be related to rainfall and spring-thaw events. The total annual cumulative GHG emissions in CO 2 equivalents (CO 2: 1; CH 4: 25; and N 2O: 298) were quantified as 87.4?±?18.4 t ha ?1 for the sheepfold that was used during the non-grazing period (i.e., winter sheepfold) and 136.7?±?15.9 t ha ?1 used during the grazing period (i.e., summer sheepfold). Of the annual total GHG emissions, CH 4 release accounted for approximately 1% of emissions, while CO 2 and N 2O emissions contributed to approximately 59% and 40%, respectively. The total GHG emission factor (CO 2?+?CH 4?+?N 2O) per animal for the sheepfolds investigated in this study was 30.3 kg CO 2 eq yr ?1 head ?1, which translates to 0.3, 18.8 and 11.2 kg CO 2 eq yr ?1 head ?1 for CH 4, CO 2 and N 2O, respectively. Sheepfolds accounted for approximately 34% of overall N 2O emissions in the Baiyinxile administrative region, a typical steppe region within Inner Mongolia. The contribution of sheepfolds to the regional CO 2 or CH 4 exchange is marginal. 相似文献
14.
In this study, we investigated the adsorption and separation behaviours of CO 2, N 2 and CH 4 in ZIF-78 and ZIF-79 by means of grand canonical Monte Carlo methods. Our simulations indicate that preferential adsorption sites are mainly located at the regions where guest molecules can maximise interactions with the imidazolate (IM) linkers. The –NO 2 and –CH 3 functional groups are not the major binding sites that directly bind the guest molecules. Instead, they alter the electronic structure and polarity of the adjacent IM linkers to affect the adsorption behaviours. In addition, we found that the selectivity of CO 2 over N 2 or CH 4 is found to be dependent on the component fractions of CO 2/N 2 and CO 2/CH 4 mixtures. Specifically, the selectivity of CO 2 over N 2 increases with CO 2 composition fraction, while the trend for the selectivity of CO 2/CH 4 was opposite. 相似文献
15.
Soils provide the largest terrestrial carbon store, the largest atmospheric CO 2 source, the largest terrestrial N 2O source and the largest terrestrial CH 4 sink, as mediated through root and soil microbial processes. A change in land use or management can alter these soil processes such that net greenhouse gas exchange may increase or decrease. We measured soil–atmosphere exchange of CO 2, N 2O and CH 4 in four adjacent land‐use systems (native eucalypt woodland, clover‐grass pasture, Pinus radiata and Eucalyptus globulus plantation) for short, but continuous, periods between October 2005 and June 2006 using an automated trace gas measurement system near Albany in southwest Western Australia. Mean N 2O emission in the pasture was 26.6 μg N m −2 h −1, significantly greater than in the natural and managed forests (< 2.0 μg N m −2 h −1). N 2O emission from pasture soil increased after rainfall events (up to 100 μg N m −2 h −1) and as soil water content increased into winter, whereas no soil water response was detected in the forest systems. Gross nitrification through 15N isotope dilution in all land‐use systems was small at water holding capacity < 30%, and under optimum soil water conditions gross nitrification ranged between < 0.1 and 1.0 mg N kg −1 h −1, being least in the native woodland/eucalypt plantation < pine plantation < pasture. Forest soils were a constant CH 4 sink, up to −20 μg C m −2 h −1 in the native woodland. Pasture soil was an occasional CH 4 source, but weak CH 4 sink overall (−3 μg C m −2 h −1). There were no strong correlations ( R < 0.4) between CH 4 flux and soil moisture or temperature. Soil CO 2 emissions (35–55 mg C m −2 h −1) correlated with soil water content ( R < 0.5) in all but the E. globulus plantation. Soil N 2O emissions from improved pastures can be considerable and comparable with intensively managed, irrigated and fertilised dairy pastures. In all land uses, soil N 2O emissions exceeded soil CH 4 uptake on a carbon dioxide equivalent basis. Overall, afforestation of improved pastures (i) decreases soil N 2O emissions and (ii) increases soil CH 4 uptake. 相似文献
16.
场镇发展是西南山区城镇发展的重要模式,且大部分场镇沿河分布,快速城镇发展给河流水环境及生物地化过程带来了一系列影响,然而其对河流温室气体排放时空格局的影响及机制尚不清楚。选择流域场镇发展特征明显的黑水滩河为研究对象,于2014年9月、12月、2015年3月、6月,对流域内干、支流水体温室气体浓度及扩散通量进行分析,旨在阐明流域场镇式发展下河流温室气体排放时空特征及关键驱动因素。研究结果表明,黑水滩河干、支流水体年均二氧化碳分压(pCO_2)及甲烷(CH_4)、一氧化二氮(N_2O)浓度均处于过饱和状态,是大气温室气体的净排放源;流域内干、支流水体流经不同场镇区前后水体碳、氮、磷及叶绿素a含量均不同程度增加,从上游向下游呈现明显的污染累积;水体溶存pCO_2\\CH_4\\N_2O浓度及扩散通量在不同场镇前后也呈现显著增加的趋势,三种温室气体扩散通量平均增幅分别为25.88%、55.22%、99.64%;河流水体pCO_2与N_2O浓度及通量秋季高于其他季节,CH_4浓度及扩散通量春季最高,秋季次之,夏、冬季最低,温室气体浓度及排放的季节变化主要受温度和降雨格局共同影响。相关分析表明,pCO_2与水温和pH关系密切,而水体CH_4和N_2O浓度与水体碳、氮、磷等生源要素均呈显著的正相关关系,水体CH_4与N_2O浓度对生源要素输入极为敏感,流域场镇发展带来的河流污染负荷的增加可能对水体CH_4与N_2O排放产生明显的激发效应。本研究认为,山区河流流域内沿河串珠状场镇分布对河流水体生源要素及其他理化性质产生累积影响,进而改变了水体温室气体的产生与排放时空格局。 相似文献
17.
The first full greenhouse gas (GHG) flux budget of an intensively managed grassland in Switzerland (Chamau) is presented. The three major trace gases, carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O) were measured with the eddy covariance (EC) technique. For CO 2 concentrations, an open‐path infrared gas analyzer was used, while N 2O and CH 4 concentrations were measured with a recently developed continuous‐wave quantum cascade laser absorption spectrometer (QCLAS). We investigated the magnitude of these trace gas emissions after grassland restoration, including ploughing, harrowing, sowing, and fertilization with inorganic and organic fertilizers in 2012. Large peaks of N 2O fluxes (20–50 nmol m ?2 s ?1 compared with a <5 nmol m ?2 s ?1 background) were observed during thawing of the soil after the winter period and after mineral fertilizer application followed by re‐sowing in the beginning of the summer season. Nitrous oxide (N 2O) fluxes were controlled by nitrogen input, plant productivity, soil water content and temperature. Management activities led to increased variations of N 2O fluxes up to 14 days after the management event as compared with background fluxes measured during periods without management (<5 nmol m ?2 s ?1). Fluxes of CO 2 remained small until full plant development in early summer 2012. In contrast, methane emissions showed only minor variations over time. The annual GHG flux budget was dominated by N 2O (48% contribution) and CO 2 emissions (44%). CH 4 flux contribution to the annual budget was only minor (8%). We conclude that recently developed multi‐species QCLAS in an EC system open new opportunities to determine the temporal variation of N 2O and CH 4 fluxes, which further allow to quantify annual emissions. With respect to grassland restoration, our study emphasizes the key role of N 2O and CO 2 losses after ploughing, changing a permanent grassland from a carbon sink to a significant carbon source. 相似文献
18.
SUMMARY 1. The effects of increasing CO 2 and nitrogen loading and of a change in water table and temperature on littoral CH 4, N 2O and CO 2 fluxes were studied in a glasshouse experiment with intact sediment cores including vegetation (mainly sedges), taken from a boreal eutrophic lake in Finland. Sediments with the water table held at a level of 0 or at ?15 cm were incubated in an atmosphere of 360 or 720 p.p.m. CO 2 for 18 weeks. The experiment included fertilisation with NO 3– and NH 4+ (to a total 3 g N m ?2). 2. Changes in the water table and temperature strongly regulated sediment CH 4 and cCO 2 fluxes (community CO 2 release), but did not affect N 2O emissions. Increase in the water table increased CH 4 emissions but reduced cCO 2 release, while increase in temperature increased emissions of both CO 2 and CH 4. 3. The raised CO 2 increased carbon turnover in the sediments, such that cCO 2 release was increased by 16–26%. However, CH 4 fluxes were not significantly affected by raised CO 2, although CH 4 production potential (at 22 °C) of the sediments incubated at high CO 2 was increased. In the boreal region, littoral CH 4 production is more likely to be limited by temperature than by the availability of carbon. Raised CO 2 did not affect N 2O production by denitrification, indicating that this process was not carbon limited. 4. A low availability of NO 3– did severely limit N 2O production. The NO 3– addition caused up to a 100‐fold increase in the fluxes of N 2O. The NH 4+ addition did not increase N 2O fluxes, indicating low nitrification capacity in the sediments. 相似文献
19.
Rapid climate change and intensified human activities have resulted in water table lowering (WTL) and enhanced nitrogen (N) deposition in Tibetan alpine wetlands. These changes may alter the magnitude and direction of greenhouse gas (GHG) emissions, affecting the climate impact of these fragile ecosystems. We conducted a mesocosm experiment combined with a metagenomics approach (GeoChip 5.0) to elucidate the effects of WTL (?20 cm relative to control) and N deposition (30 kg N ha ?1 yr ?1) on carbon dioxide (CO 2), methane (CH 4) and nitrous oxide (N 2O) fluxes as well as the underlying mechanisms. Our results showed that WTL reduced CH 4 emissions by 57.4% averaged over three growing seasons compared with no‐WTL plots, but had no significant effect on net CO 2 uptake or N 2O flux. N deposition increased net CO 2 uptake by 25.2% in comparison with no‐N deposition plots and turned the mesocosms from N 2O sinks to N 2O sources, but had little influence on CH 4 emissions. The interactions between WTL and N deposition were not detected in all GHG emissions. As a result, WTL and N deposition both reduced the global warming potential (GWP) of growing season GHG budgets on a 100‐year time horizon, but via different mechanisms. WTL reduced GWP from 337.3 to ?480.1 g CO 2‐eq m ?2 mostly because of decreased CH 4 emissions, while N deposition reduced GWP from 21.0 to ?163.8 g CO 2‐eq m ?2, mainly owing to increased net CO 2 uptake. GeoChip analysis revealed that decreased CH 4 production potential, rather than increased CH 4 oxidation potential, may lead to the reduction in net CH 4 emissions, and decreased nitrification potential and increased denitrification potential affected N 2O fluxes under WTL conditions. Our study highlights the importance of microbial mechanisms in regulating ecosystem‐scale GHG responses to environmental changes. 相似文献
20.
Warming can accelerate the decomposition of soil organic matter and stimulate the release of soil greenhouse gases (GHGs), but to what extent soil release of methane (CH 4) and nitrous oxide (N 2O) may contribute to soil C loss for driving climate change under warming remains unresolved. By synthesizing 1,845 measurements from 164 peer‐reviewed publications, we show that around 1.5°C (1.16–2.01°C) of experimental warming significantly stimulates soil respiration by 12.9%, N 2O emissions by 35.2%, CH 4 emissions by 23.4% from rice paddies, and by 37.5% from natural wetlands. Rising temperature increases CH 4 uptake of upland soils by 13.8%. Warming‐enhanced emission of soil CH 4 and N 2O corresponds to an overall source strength of 1.19, 1.84, and 3.12 Pg CO 2‐equivalent/year under 1°C, 1.5°C, and 2°C warming scenarios, respectively, interacting with soil C loss of 1.60 Pg CO 2/year in terms of contribution to climate change. The warming‐induced rise in soil CH 4 and N 2O emissions (1.84 Pg CO 2‐equivalent/year) could reduce mitigation potential of terrestrial net ecosystem production by 8.3% (NEP, 22.25 Pg CO 2/year) under warming. Soil respiration and CH 4 release are intensified following the mean warming threshold of 1.5°C scenario, as compared to soil CH 4 uptake and N 2O release with a reduced and less positive response, respectively. Soil C loss increases to a larger extent under soil warming than under canopy air warming. Warming‐raised emission of soil GHG increases with the intensity of temperature rise but decreases with the extension of experimental duration. This synthesis takes the lead to quantify the ecosystem C and N cycling in response to warming and advances our capacity to predict terrestrial feedback to climate change under projected warming scenarios. 相似文献
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