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1.
In order to identify the effects of land-use/cover types, soil types and soil properties on the soil-atmosphere exchange of greenhouse gases (GHG) in semiarid grasslands as well as provide a reliable estimate of the midsummer GHG budget, nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes of soil cores from 30 representative sites were determined in the upper Xilin River catchment in Inner Mongolia. The soil N2O emissions across all of the investigated sites ranged from 0.18 to 21.8 μg N m-2 h-1, with a mean of 3.4 μg N m-2 h-1 and a coefficient of variation (CV, which is given as a percentage ratio of one standard deviation to the mean) as large as 130%. CH4 fluxes ranged from -88.6 to 2,782.8 μg C m-2 h-1 (with a CV of 849%). Net CH4 emissions were only observed from cores taken from a marshland site, whereas all of the other 29 investigated sites showed net CH4 uptake (mean: -33.3 μg C m-2 h-1). CO2 emissions from all sites ranged from 3.6 to 109.3 mg C m-2 h-1, with a mean value of 37.4 mg C m-2 h-1 and a CV of 66%. Soil moisture primarily and positively regulated the spatial variability in N2O and CO2 emissions (R2?=?0.15–0.28, P?<?0.05). The spatial variation of N2O emissions was also influenced by soil inorganic N contents (P?<?0.05). By simply up-scaling the site measurements by the various land-use/cover types to the entire catchment area (3,900 km2), the fluxes of N2O, CH4 and CO2 at the time of sampling (mid-summer 2007) were estimated at 29 t CO2-C-eq d-1, -26 t CO2-C-eq d-1 and 3,223 t C d-1, respectively. This suggests that, in terms of assessing the spatial variability of total GHG fluxes from the soils at a semiarid catchment/region, intensive studies may focus on CO2 exchange, which is dominating the global warming potential of midsummer soil-atmosphere GHG fluxes. In addition, average GHG fluxes in midsummer, weighted by the areal extent of these land-use/cover types in the region, were approximately -30.0 μg C m-2 h-1 for CH4, 2.4 μg N m-2 h-1 for N2O and 34.5 mg C m-2 h-1 for CO2.  相似文献   

2.
《Global Change Biology》2018,24(5):1843-1872
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 (CO2), nitrous oxide (N2O), and methane (CH4). The evaluation of environmental impacts at site level is challenging, because most in situ measurements focus on the quantification of CO2 exchange, while long‐term N2O and CH4 flux measurements at ecosystem scale remain scarce. Here, we synthesized ecosystem CO2, N2O, and CH4 fluxes from 14 managed grassland sites, quantified by eddy covariance or chamber techniques. We found that grasslands were on average a CO2 sink (−1,783 to −91 g CO2 m−2 year−1), but a N2O source (18–638 g CO2‐eq. m−2 year−1), and either a CH4 sink or source (−9 to 488 g CO2‐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 CO2‐eq. m−2 year−1, with N2O and CH4 emissions offsetting concurrent CO2 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 N2O and CH4 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 N2O and CH4 emissions. The N2O‐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 N2O and CH4 emissions, the CO2 sink strength was generally the most dominant component of the annual GHG budget.  相似文献   

3.
Wetlands can influence global climate via greenhouse gas (GHG) exchange of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Few studies have quantified the full GHG budget of wetlands due to the high spatial and temporal variability of fluxes. We report annual open‐water diffusion and ebullition fluxes of CO2, CH4, and N2O from a restored emergent marsh ecosystem. We combined these data with concurrent eddy‐covariance measurements of whole‐ecosystem CO2 and CH4 exchange to estimate GHG fluxes and associated radiative forcing effects for the whole wetland, and separately for open‐water and vegetated cover types. Annual open‐water CO2, CH4, and N2O emissions were 915 ± 95 g C‐CO2 m?2 yr?1, 2.9 ± 0.5 g C‐CH4 m?2 yr?1, and 62 ± 17 mg N‐N2O m?2 yr?1, respectively. Diffusion dominated open‐water GHG transport, accounting for >99% of CO2 and N2O emissions, and ~71% of CH4 emissions. Seasonality was minor for CO2 emissions, whereas CH4 and N2O fluxes displayed strong and asynchronous seasonal dynamics. Notably, the overall radiative forcing of open‐water fluxes (3.5 ± 0.3 kg CO2‐eq m?2 yr?1) exceeded that of vegetated zones (1.4 ± 0.4 kg CO2‐eq m?2 yr?1) due to high ecosystem respiration. After scaling results to the entire wetland using object‐based cover classification of remote sensing imagery, net uptake of CO2 (?1.4 ± 0.6 kt CO2‐eq yr?1) did not offset CH4 emission (3.7 ± 0.03 kt CO2‐eq yr?1), producing an overall positive radiative forcing effect of 2.4 ± 0.3 kt CO2‐eq yr?1. These results demonstrate clear effects of seasonality, spatial structure, and transport pathway on the magnitude and composition of wetland GHG emissions, and the efficacy of multiscale flux measurement to overcome challenges of wetland heterogeneity.  相似文献   

4.
Wetlands are important sources of methane (CH4) and sinks of carbon dioxide (CO2). However, little is known about CH4 and CO2 fluxes and dynamics of seasonally flooded tropical forests of South America in relation to local carbon (C) balances and atmospheric exchange. We measured net ecosystem fluxes of CH4 and CO2 in the Pantanal over 2014–2017 using tower‐based eddy covariance along with C measurements in soil, biomass and water. Our data indicate that seasonally flooded tropical forests are potentially large sinks for CO2 but strong sources of CH4, particularly during inundation when reducing conditions in soils increase CH4 production and limit CO2 release. During inundation when soils were anaerobic, the flooded forest emitted 0.11 ± 0.002 g CH4‐C m?2 d?1 and absorbed 1.6 ± 0.2 g CO2‐C m?2 d?1 (mean ± 95% confidence interval for the entire study period). Following the recession of floodwaters, soils rapidly became aerobic and CH4 emissions decreased significantly (0.002 ± 0.001 g CH4‐C m?2 d?1) but remained a net source, while the net CO2 flux flipped from being a net sink during anaerobic periods to acting as a source during aerobic periods. CH4 fluxes were 50 times higher in the wet season; DOC was a minor component in the net ecosystem carbon balance. Daily fluxes of CO2 and CH4 were similar in all years for each season, but annual net fluxes varied primarily in relation to flood duration. While the ecosystem was a net C sink on an annual basis (absorbing 218 g C m?2 (as CH4‐C + CO2‐C) in anaerobic phases and emitting 76 g C m?2in aerobic phases), high CH4 effluxes during the anaerobic flooded phase and modest CH4 effluxes during the aerobic phase indicate that seasonally flooded tropical forests can be a net source of radiative forcings on an annual basis, thus acting as an amplifying feedback on global warming.  相似文献   

5.
Crop residues like corn (Zea mays L.) stover perform important functions that promote soil health and provide ecosystem services that influence agricultural sustainability and global biogeochemical cycles. We evaluated the effect of corn stover removal from a no-till, corn-soybean (Glycine max (L.) Merr) rotation on soil greenhouse gas (GHG; CO2, N2O, CH4) fluxes, crop yields, and soil organic carbon (SOC) dynamics. We conducted a 4-year study using replicated field plots managed with two levels of corn stover removal (none; 55 % stover removal) for four complete crop cycles prior to initiation of ground surface gas flux measurements. Corn and soybean yields were not affected by stover removal with yields averaging 7.28 Mg ha?1 for corn and 2.64 Mg ha?1 for soybean. Corn stover removal treatment did not affect soil GHG fluxes from the corn phase; however, the treatment did significantly increase (107 %, P?=?0.037) N2O fluxes during the soybean phase. The plots were a net source of CH4 (~0.5 kg CH4-C ha?1 year?1 average of all treatments and crops) during the generally wet study duration. Soil organic carbon stocks increased in both treatments during the 4-year study (initiated following 8 years of stover removal), with significantly higher SOC accumulation in the control plots compared to plots with corn stover removal (0–15 cm, P?=?0.048). Non-CO2 greenhouse gas emissions (945 kg CO2-eq ha?1 year?1) were roughly half of SOC (0–30 cm) gains with corn stover removal (1.841 Mg CO2-eq ha?1 year?1) indicating that no-till practices greatly improve the viability of biennial corn stover harvesting under local soil-climatic conditions. Our results also show that repeated corn stover harvesting may increase N loss (as N2O) from fields and thereby contribute to GHG production and loss of potential plant nutrients.  相似文献   

6.
Large Greenhouse Gas Emissions from a Temperate Peatland Pasture   总被引:2,自引:0,他引:2  
Agricultural drainage is thought to alter greenhouse gas emissions from temperate peatlands, with CH4 emissions reduced in favor of greater CO2 losses. Attention has largely focussed on C trace gases, and less is known about the impacts of agricultural conversion on N2O or global warming potential. We report greenhouse gas fluxes (CH4, CO2, N2O) from a drained peatland in the Sacramento-San Joaquin River Delta, California, USA currently managed as a rangeland (that is, pasture). This ecosystem was a net source of CH4 (25.8 ± 1.4 mg CH4-C m−2 d−1) and N2O (6.4 ± 0.4 mg N2O-N m−2 d−1). Methane fluxes were comparable to those of other managed temperate peatlands, whereas N2O fluxes were very high; equivalent to fluxes from heavily fertilized agroecosystems and tropical forests. Ecosystem scale CH4 fluxes were driven by “hotspots” (drainage ditches) that accounted for less than 5% of the land area but more than 84% of emissions. Methane fluxes were unresponsive to seasonal fluctuations in climate and showed minimal temporal variability. Nitrous oxide fluxes were more homogeneously distributed throughout the landscape and responded to fluctuations in environmental variables, especially soil moisture. Elevated CH4 and N2O fluxes contributed to a high overall ecosystem global warming potential (531 g CO2-C equivalents m−2 y−1), with non-CO2 trace gas fluxes offsetting the atmospheric “cooling” effects of photoassimilation. These data suggest that managed Delta peatlands are potentially large regional sources of greenhouse gases, with spatial heterogeneity in soil moisture modulating the relative importance of each gas for ecosystem global warming potential.  相似文献   

7.
We investigated soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) 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 CH4 and N2O, we observed uptake and emission ranging from ?160 to 245 μg CH4 m?2 h?1 and ?52 to 21 μg N2O 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 CO2 fluxes (259, 246, 220, and 250 mg CO2 m?2 h?1, respectively), without pattern for N2O fluxes (?3.7, 1.5, ?2.2, and ?7.6 μg N2O m?2 h?1, respectively), whereas the uptake rates of CH4 increased with stand age (6.4, ?7.9, ?10.8, and ?23.3 μg CH4 m?2 h?1, respectively). For the same period, the combined contribution of CH4 and N2O exchanges to the global warming potential (GWP) calculated from net ecosystem exchange of CO2 and aggregated soil exchanges of CH4 and N2O was on average 4%, <1%, <1%, and 2% for the 4, 17, 32, 67 years old stand, respectively. Soil CO2 fluxes correlated positively with soil temperature but had no relationship with soil moisture. We found no control of soil temperature or soil moisture on CH4 and N2O fluxes, but CH4 emission was observed following summer rainfall events. LFH layer removal reduced CO2 emissions by 43%, increased CH4 uptake during dry and warm soil conditions by more than twofold, but did not affect N2O flux. We suggest that significant alternating sink and source potentials for both CH4 and N2O 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   

8.
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 (CO2), methane (CH4), and nitrous oxide (N2O) were measured with the eddy covariance (EC) technique. For CO2 concentrations, an open‐path infrared gas analyzer was used, while N2O and CH4 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 N2O 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 (N2O) fluxes were controlled by nitrogen input, plant productivity, soil water content and temperature. Management activities led to increased variations of N2O 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 CO2 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 N2O (48% contribution) and CO2 emissions (44%). CH4 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 N2O and CH4 fluxes, which further allow to quantify annual emissions. With respect to grassland restoration, our study emphasizes the key role of N2O and CO2 losses after ploughing, changing a permanent grassland from a carbon sink to a significant carbon source.  相似文献   

9.
温带针阔混交林土壤碳氮气体通量的主控因子与耦合关系   总被引:3,自引:0,他引: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   

10.
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 CO2, CH4, and N2O 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 N2O sources and CH4 sinks. Annual mean CO2, N2O, and CH4 fluxes (mean±SD) were 7.7±4.6 Mg CO2‐C ha?1 yr?1, 3.2±1.2 kg N2O‐N ha?1 yr?1, and 3.4±0.9 kg CH4‐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 CO2 emission coincided with the seasonal climate pattern, with high CO2 emission rates in the hot‐humid season and low rates in the cool‐dry season. In contrast, seasonal patterns of CH4 and N2O fluxes were not clear, although higher CH4 uptake rates were often observed in the cool‐dry season and higher N2O 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, CO2 and N2O emissions and CH4 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 CO2 effluxes by 17–44% in the three forests but had no significant effect on CH4 absorption and N2O emission rates. This suggests that microbial CH4 uptake and N2O production was mainly related to the mineral soil rather than in the surface litter layer.  相似文献   

11.
We studied concentrations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) 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 CO2, CH4 and N2O to the atmosphere, whereas the Liminganlahti Bay was a minor source of CH4 and a minor source or a sink of CO2 and N2O. 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 CO2 and CH4, with average fluxes of 5,400 mg CO2–C m−2 d−1 and 66 mg CH4–C m−2 d−1, and concentrations of 210 μM and 345 nM, respectively, but N2O 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 N2O (with an average emission of 650 μg N2O–N m−2 d−1 and concentration of 22 nM), whereas the CO2 and CH4 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 CO2, 55% of CH4 and 36% of N2O emissions, were found to be released during wintertime from unfrozen parts of the river.  相似文献   

12.
Rapid, precise, and globally comparable methods for monitoring greenhouse gas (GHG) fluxes are required for accurate GHG inventories from different cropping systems and management practices. Manual gas sampling followed by gas chromatography (GC) is widely used for measuring GHG fluxes in agricultural fields, but is laborious and time‐consuming. The photo‐acoustic infrared gas monitoring system (PAS) with on‐line gas sampling is an attractive option, although it has not been evaluated for measuring GHG fluxes in cereals in general and rice in particular. We compared N2O, CO2, and CH4 fluxes measured by GC and PAS from agricultural fields under the rice–wheat and maize–wheat systems during the wheat (winter), and maize/rice (monsoon) seasons in Haryana, India. All the PAS readings were corrected for baseline drifts over time and PAS‐CH4 (PCH4) readings in flooded rice were corrected for water vapor interferences. The PCH4 readings in ambient air increased by 2.3 ppm for every 1000 mg cm?3 increase in water vapor. The daily CO2, N2O, and CH4 fluxes measured by GC and PAS from the same chamber were not different in 93–98% of all the measurements made but the PAS exhibited greater precision for estimates of CO2 and N2O fluxes in wheat and maize, and lower precision for CH4 flux in rice, than GC. The seasonal GC‐ and PAS‐N2O (PN2O) fluxes in wheat and maize were not different but the PAS‐CO2 (PCO2) flux in wheat was 14–39% higher than that of GC. In flooded rice, the seasonal PCH4 and PN2O fluxes across N levels were higher than those of GC‐CH4 and GC‐N2O fluxes by about 2‐ and 4fold, respectively. The PAS (i) proved to be a suitable alternative to GC for N2O and CO2 flux measurements in wheat, and (ii) showed potential for obtaining accurate measurements of CH4 fluxes in flooded rice after making correction for changes in humidity.  相似文献   

13.
The magnitude of greenhouse gas (GHG) flux rates may be important in wet and intermediate wet forest soils, but published estimates are scarce. We studied the surface exchange of methane (CH4) and nitrous oxide (N2O) from soil along toposequences in two temperate deciduous forest catchments: Strødam and Vestskoven. The soil water regime ranged from fully saturated to aerated within the catchments. At Strødam the largest mean flux rates of N2O (15 μg N2O-N m?2 h?1) were measured at volumetric soil water contents (SWC) between 40 and 60% and associated with low soil pH compared to smaller mean flux rates of 0-5 μg N2O-N m?2 h?1 for drier (SWC < 40%) and wet conditions (SWC > 80%). At Vestskoven the same response of N2O to soil water content was observed. Average CH4 flux rates were highly variable along the toposequences (?17 to 536 μg CH4-C m?2 h?1) but emissions were only observed above soil water content of 45%. Scaled flux rates of both GHGs to catchment level resulted in emission of 322 and 211 kg CO2-equivalents ha?1 year?1 for Strødam and Vestskoven, respectively, with N2O contributing the most at both sites. Although the wet and intermediate wet forest soils occupied less than half the catchment area at both sites, the global warming potential (GWP) derived from N2O and CH4 was more than doubled when accounting for these wet areas in the catchments. The results stress the importance of wet soils in assessments of forest soil global warming potentials, as even small proportions of wet soils contributes substantially to the emissions of N2O and CH4.  相似文献   

14.
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 (CO2), methane (CH4) and nitrous oxide (N2O) 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 CO2, CH4 and N2O. Temperatures primarily determined the seasonal pattern of CO2 emission; 60–84% of the CO2 flux variation could be explained by temperature changes. High rates of net CH4 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 N2O emissions were also be related to rainfall and spring-thaw events. The total annual cumulative GHG emissions in CO2 equivalents (CO2: 1; CH4: 25; and N2O: 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, CH4 release accounted for approximately 1% of emissions, while CO2 and N2O emissions contributed to approximately 59% and 40%, respectively. The total GHG emission factor (CO2?+?CH4?+?N2O) per animal for the sheepfolds investigated in this study was 30.3 kg CO2 eq yr?1 head?1, which translates to 0.3, 18.8 and 11.2 kg CO2 eq yr?1 head?1 for CH4, CO2 and N2O, respectively. Sheepfolds accounted for approximately 34% of overall N2O emissions in the Baiyinxile administrative region, a typical steppe region within Inner Mongolia. The contribution of sheepfolds to the regional CO2 or CH4 exchange is marginal.  相似文献   

15.
Human activities have substantially enhanced the availability of important nutrient elements such as nitrogen (N), phosphorus (P), and potassium (K) in ecosystems worldwide. However, how the concurrent increase in all of these nutrients will affect greenhouse gas (that is, CO2, N2O, CH4) levels remains unknown. In a temperate steppe of northern China, a 2-year field experiment was conducted to examine the effects of multi-nutrient additions on GHG fluxes from 2009 to 2010. Four levels of annual nutrient loads were mimicked: 0 g NPK (control), 15.5 g P m?2 and 19.5 g K m?2 as KH2PO4 (PK), 10 g N m?2 as NH4NO3 plus PK (10N + PK), and 20 g N m?2 plus PK (20N + PK) per year. The results show that multi-nutrient additions led to significant increases in net primary production (NPP) and soil temperature (ST), a significant decrease in soil moisture (SM) in 2010, and no significant changes in other soil parameters. Seasonal patterns differed greatly for different GHG fluxes in response to different nutrient treatments, largely as a result of differences in influential factors. The 10N + PK treatment significantly increased CO2 uptake, whereas the 20N + PK treatment significantly decreased CO2 uptake. The application of P and K without additional N significantly enhanced CH4 uptake, whereas the two N + PK treatments significantly enhanced N2O emissions. Significant positive, linear relationships were found between cumulative CO2 uptake and soil total nitrogen (TN), microbial biomass carbon, and microbial biomass nitrogen, whereas significant negative, linear relationships were found with NPP, SM, and the C/N ratio. Significant positive, linear relationships were found between cumulative N2O emission and ST, TN, NPP, and total organic carbon, whereas no relationships were found between cumulative CH4 uptake and any soil parameters. CO2 flux was related to N2O flux temporally, to a certain extent, for all the treatments. In the control, N2O flux showed a negative, linear relationship with CH4 flux, whereas no regular relationships were detected between CO2 and CH4 fluxes in any treatment. Our findings imply that increasing nutrient deposition will change the magnitude, patterns, and relationships among GHG uptakes and emissions in the future.  相似文献   

16.
Indigenous broadleaf plantations are increasingly developing as a prospective silvicultural management approach for substituting in place of large pure conifer plantations in subtropical China. However, little information is known about the effects of tree species conversion on soil-atmosphere greenhouse gas (GHG) exchanges. Four adjacent monospecific plantations were selected in subtropical China to examine the effects of tree species on soil-atmosphere exchanges of N2O, CH4 and CO2. One coniferous plantation was composed of Pinus massoniana (PM), and the three broadleaf plantations were Castanopsis hystrix (CH), Michelia macclurei (MM) and Mytilaria laosensis (ML). We found that mean soil N2O and CO2 emissions in the PM plantation were 4.34 μg N m?2?h?1 and 43.25 mg C m?2?h?1, respectively, lower than those in the broadleaf plantations (>5.25 μg N m?2?h?1 and >56.38 mg C m?2?h?1). The PM plantation soil had higher mean CH4 uptake (39.03 μg C m?2?h?1) than the broadleaf plantation soils (<32.67 μg C m?2?h?1). Variations in soil N2O emissions among tree species could be primarily explained by the differences in litter C:N ratio and soil total N stock. Differences in soil CH4 uptake among tree species could be mostly attributed to the differences in mean soil CO2 flux and water filled pore space (WFPS). Litter C:N ratio could largely account for variations in soil CO2 emissions among tree species. This study confirms that there is no GHG benefit of converting PM plantation to broadleaf plantations in subtropical China. Therefore, the future strategy of tree species selection for substituting in place of large coniferous plantations in subtropical China needs to consider the potential effects of tree species on soil-atmosphere GHG exchanges.  相似文献   

17.
Constructed wetlands (CWs) are efficient at removing excessive nutrients from wastewaters. However, this removal often results in the flux of important greenhouse gases (GHG), such as nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) that could mitigate the environmental benefits of CWs. We studied the efficiency of artificial aeration and 2 different macrophyte species (Phragmites australis, Typha angustifolia) on the removal and transformations of nitrogen and GHG gas flux using CW mesocosms supplied with 60 L m?2 d?1 of wastewater. Removal of total nitrogen (TN) and dissolved organic nitrogen (DON) was generally high in all beds but resulted in a net production of oxidized nitrogen (NOy) in aerated CW mesocosms as compared to ammonium (NH4+) in non-aerated units. Aerated units emitted less N2O when planted with P. australis or left unplanted. Aerated beds and planted mesocosms had lower CH4 fluxes than non-aerated units and unplanted beds, respectively. Our study suggests that planted systems with artificial aeration have the overall best performances in that they lead to a reduction of GHG flux and promote the release of NOy over NH4+ in their effluents.  相似文献   

18.
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   

19.
S Hashimoto 《PloS one》2012,7(8):e41962
Soil greenhouse gas fluxes (particularly CO2, CH4, and N2O) play important roles in climate change. However, despite the importance of these soil greenhouse gases, the number of reports on global soil greenhouse gas fluxes is limited. Here, new estimates are presented for global soil CO2 emission (total soil respiration), CH4 uptake, and N2O emission fluxes, using a simple data-oriented model. The estimated global fluxes for CO2 emission, CH4 uptake, and N2O emission were 78 Pg C yr−1 (Monte Carlo 95% confidence interval, 64–95 Pg C yr−1), 18 Tg C yr−1 (11–23 Tg C yr−1), and 4.4 Tg N yr−1 (1.4–11.1 Tg N yr−1), respectively. Tropical regions were the largest contributor of all of the gases, particularly the CO2 and N2O fluxes. The soil CO2 and N2O fluxes had more pronounced seasonal patterns than the soil CH4 flux. The collected estimates, including both the previous and the present estimates, demonstrate that the means of the best estimates from each study were 79 Pg C yr−1 (291 Pg CO2 yr−1; coefficient of variation, CV = 13%, N = 6) for CO2, 21 Tg C yr−1 (29 Tg CH4 yr−1; CV = 24%, N = 24) for CH4, and 7.8 Tg N yr−1 (12.2 Tg N2O yr−1; CV = 38%, N = 11) for N2O. For N2O, the mean of the estimates that was calculated by excluding the earliest two estimates was 6.6 Tg N yr−1 (10.4 Tg N2O yr−1; CV = 22%, N = 9). The reported estimates vary and have large degrees of uncertainty but their overall magnitudes are in general agreement. To further minimize the uncertainty of soil greenhouse gas flux estimates, it is necessary to build global databases and identify key processes in describing global soil greenhouse gas fluxes.  相似文献   

20.
梁东哲  赵雨森  曹杰  辛颖 《生态学报》2019,39(21):7950-7959
为研究大兴安岭重度火烧迹地在不同恢复方式下林地土壤CO2、CH4和N2O排放特征及其影响因素,采用静态箱/气相色谱法,在2017年生长季(6月-9月)对3种恢复方式(人工更新、天然更新和人工促进天然更新)林地土壤温室气体CO2、CH4、N2O通量进行了原位观测。研究结果表明:(1)3种恢复方式林地土壤在生长季均为大气CO2、N2O的源,CH4的汇;生长季林地土壤CO2排放通量大小关系为人工促进天然更新((634.40±246.52)mg m-2 h-1) > 人工更新((603.63±213.22)mg m-2 h-1) > 天然更新((575.81±244.12)mg m-2 h-1),3种恢复方式间无显著差异;人工更新林地土壤CH4吸收通量显著高于人工促进天然更新;天然更新林地土壤N2O排放通量显著高于其他两种恢复方式。(2)土壤温度是影响3种恢复方式林地土壤温室气体通量的关键因素;土壤水分仅对人工更新林地土壤N2O通量有极显著影响(P < 0.01);3种恢复方式林地土壤CO2通量与大气湿度具有极显著的响应(P < 0.01);土壤pH仅与天然更新林地土壤CO2通量显著相关(P < 0.05);土壤全氮含量仅与人工促进天然更新林地土壤CH4通量显著相关(P < 0.05)。(3)基于100年尺度,由3种温室气体计算全球增温潜势得出,人工促进天然更新(1.83×104 kg CO2/hm2) > 人工更新(1.74×104 kg CO2/hm2) > 天然更新(1.67×104 kg CO2/hm2)。(4)阿木尔地区林地土壤年生长季CO2和N2O排放量为8.85×106 t和1.88×102 t,CH4吸收量为1.05×103 t。  相似文献   

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