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1.
We examined net greenhouse gas exchange at the soil surface in deciduous forests on soils with high organic contents. Fluxes of CO 2, CH 4 and N 2O were measured using dark static chambers for two consecutive years in three different forest types; (i) a drained and medium productivity site dominated by birch, (ii) a drained and highly productive site dominated by alder and (iii) an undrained and highly productive site dominated by alder. Although the drained sites had shallow mean groundwater tables (15 and 18 cm, respectively) their average annual rates of forest floor CO 2 release were almost twice as high compared to the undrained site (1.9±0.4 and 1.7±0.3, compared to 1.0±0.2 kg CO 2 m −2 yr −1). The average annual CH 4 emission was almost 10 times larger at the undrained site (7.6±3.1 compared to 0.9±0.5 g CH 4 m −2 yr −1 for the two drained sites). The average annual N 2O emissions at the undrained site (0.1±0.05 g N 2O m −2 yr −1) were lower than at the drained sites, and the emissions were almost five times higher at the drained alder site than at the drained birch site (0.9±0.35 compared to 0.2±0.11 g N 2O m −2 yr −1). The temporal variation in forest floor CO 2 release could be explained to a large extent by differences in groundwater table and air temperature, but little of the variation in the CH 4 and N 2O fluxes could be explained by these variables. The measured soil variables were only significant to explain for the within-site spatial variation in CH 4 and N 2O fluxes at the undrained swamp, and dark forest floor CO 2 release was not explained by these variables at any site. The between-site spatial variation was attributed to variations in drainage, groundwater level position, productivity and tree species for all three gases. The results indicate that N 2O emissions are of greater importance for the net greenhouse gas exchange at deciduous drained forest sites than at coniferous drained forest sites. 相似文献
2.
We evaluated the spatial structures of nitrous oxide (N 2O), carbon dioxide (CO 2), and methane (CH 4) fluxes in an Acacia mangium plantation stand in Sumatra, Indonesia, in drier (August) and wetter (March) seasons. A 60 × 100-m plot was established in an A. mangium plantation that included different topographical elements of the upper plateau, lower plateau, upper slope and foot slope. The plot was divided into 10 × 10-m grids and gas fluxes and soil properties were measured at 77 grid points at 10-m intervals within the plot. Spatial structures of the gas fluxes and soil properties were identified using geostatistical analyses. Averaged N 2O and CO 2 fluxes in the wetter season (1.85 mg N m −2 d −1 and 4.29 g C m −2 d −1, respectively) were significantly higher than those in the drier season (0.55 mg N m −2 d −1 and 2.73 g C m −2 d −1, respectively) and averaged CH 4 uptake rates in the drier season (−0.62 mg C m −2 d −1) were higher than those in the wetter season (−0.24 mg C m −2 d −1). These values of N 2O fluxes in A. mangium soils were higher than those reported for natural forest soils in Sumatra, while CO 2 and CH 4 fluxes were in the range of fluxes reported for natural forest soils. Seasonal differences in these gas fluxes appears to be controlled by soil water content and substrate availability due to differing precipitation and mineralization of litter between seasons. N 2O fluxes had strong spatial dependence with a range of about 18 m in both the drier and wetter seasons. Topography was associated with the N 2O fluxes in the wetter season with higher and lower fluxes on the foot slope and on the upper plateau, respectively, via controlling the anaerobic-aerobic conditions in the soils. In the drier season, however, we could not find obvious topographic influences on the spatial patterns of N 2O fluxes and they may have depended on litter amount distribution. CO 2 fluxes had no spatial dependence in both seasons, but the topographic influence was significant in the drier season with lowest fluxes on the foot slope, while there was no significant difference between topographic positions in the wetter season. The distributions of litter amount and soil organic matter were possibly associated with CO 2 fluxes through their effects on microbial activities and fine root distribution in this A. mangium plantation. 相似文献
3.
In temperate regions, climate change is predicted to increase annual mean temperature and intensify the duration and frequency of summer droughts, which together with elevated atmospheric carbon dioxide (CO 2) concentrations, may affect the exchange of nitrous oxide (N 2O) and methane (CH 4) between terrestrial ecosystems and the atmosphere. We report results from the CLIMAITE experiment, where the effects of these three climate change parameters were investigated solely and in all combinations in a temperate heathland. Field measurements of N 2O and CH 4 fluxes took place 1-2 years after the climate change manipulations were initiated. The soil was generally a net sink for atmospheric CH 4. Elevated temperature (T) increased the CH 4 uptake by on average 10 μg C m −2 h −1, corresponding to a rise in the uptake rate of about 20%. However, during winter elevated CO 2 (CO 2) reduced the CH 4 uptake, which outweighed the positive effect of warming when analyzed across the study period. Emissions of N 2O were generally low (<10 μg N m −2 h −1). As single experimental factors, elevated CO 2, temperature and summer drought (D) had no major effect on the N 2O fluxes, but the combination of CO 2 and warming (TCO 2) stimulated N 2O emission, whereas the N 2O emission ceased when CO 2 was combined with drought (DCO 2). We suggest that these N 2O responses are related to increased rhizodeposition under elevated CO 2 combined with increased and reduced nitrogen turnover rates caused by warming and drought, respectively. The N 2O flux in the multifactor treatment TDCO 2 was not different from the ambient control treatment. Overall, our study suggests that in the future, CH 4 uptake may increase slightly, while N 2O emission will remain unchanged in temperate ecosystems on well-aerated soils. However, we propose that continued exposure to altered climate could potentially change the greenhouse gas flux pattern in the investigated heathland. 相似文献
4.
We examined the effects of forest clearfelling on the fluxes of soil CO 2, CH 4, and N 2O in a Sitka spruce ( Picea sitchensis (Bong.) Carr.) plantation on an organic-rich peaty gley soil, in Northern England. Soil CO 2, CH 4, N 2O as well as environmental factors such as soil temperature, soil water content, and depth to the water table were recorded in two mature stands for one growing season, at the end of which one of the two stands was felled and one was left as control. Monitoring of the same parameters continued thereafter for a second growing season. For the first 10 months after clearfelling, there was a significant decrease in soil CO 2 efflux, with an average efflux rate of 4.0 g m −2 d −1 in the mature stand (40-year) and 2.7 g m −2 d −1 in clearfelled site (CF). Clearfelling turned the soil from a sink (−0.37 mg m −2 d −1) for CH 4 to a net source (2.01 mg m −2 d −1). For the same period, soil N 2O fluxes averaged 0.57 mg m −2 d −1 in the CF and 0.23 mg m −2 d −1 in the 40-year stand. Clearfelling affected environmental factors and lead to higher daily soil temperatures during the summer period, while it caused an increase in the soil water content and a rise in the water table depth. Despite clearfelling, CO 2 remained the dominant greenhouse gas in terms of its greenhouse warming potential. 相似文献
5.
To assess the impacts of yak excreta patches on greenhouse gas (GHG) fluxes in the alpine meadow of the Qinghai-Tibetan plateau, methane (CH 4), carbon dioxide (CO 2), and nitrous oxide (N 2O) fluxes were measured for the first time from experimental excreta patches placed on the meadow during the summer grazing seasons in 2005 and 2006. Dung patches were CH 4 sources (average 586 μg m −2 h −1 in 2005 and 199 μg m −2 h −1 in 2006) during the investigation period of two years, while urine patches (average −31 μg m −2 h −1 in 2005 and −33 μg m −2 h −1 in 2006) and control plots (average −28 μg m −2 h −1 in 2005 and −30 μg m −2 h −1 in 2006) consumed CH 4. The cumulative CO 2 emission for dung patches was about 36-50% higher than control plots during the experimental period in 2005 and 2006. The cumulative N 2O emissions for both urine and dung patches were 2.1-3.7 and 1.8-3.5 times greater than control plots in 2005 and 2006, respectively. Soil water-filled pore space (WFPS) explained 35% and 36% of CH 4 flux variation for urine patches and control plots, respectively. Soil temperature explained 40-75% of temporal variation of CO 2 emissions for all treatments. Temporal N 2O flux variation in urine patches (34%), dung patches (48%), and control (56%) plots was mainly driven by the simultaneous effect of soil temperature and WFPS. Although yak excreta patches significantly affected GHG fluxes, their contributions to the whole grazing alpine meadow in terms of CO 2 equivalents are limited under the moderate grazing intensity (1.45 yak ha −1). However, the contributions of excreta patches to N 2O emissions are not negligible when estimating N 2O emissions in the grazing meadow. In this study, the N 2O emission factor of yak excreta patches varied with year (about 0.9-1.0%, and 0.1-0.2% in 2005 and 2006, respectively), which was lower than IPCC default value of 2%. 相似文献
6.
Tropical savanna ecosystems are a major contributor to global CO 2, CH 4 and N 2O greenhouse gas exchange. Savanna fire events represent large, discrete C emissions but the importance of ongoing soil-atmosphere gas exchange is less well understood. Seasonal rainfall and fire events are likely to impact upon savanna soil microbial processes involved in N 2O and CH 4 exchange. We measured soil CO 2, CH 4 and N 2O fluxes in savanna woodland ( Eucalyptus tetrodonta/ Eucalyptus miniata trees above sorghum grass) at Howard Springs, Australia over a 16 month period from October 2007 to January 2009 using manual chambers and a field-based gas chromatograph connected to automated chambers. The effect of fire on soil gas exchange was investigated through two controlled burns and protected unburnt areas. Fire is a frequent natural and management action in these savanna (every 1-2 years). There was no seasonal change and no fire effect upon soil N 2O exchange. Soil N 2O fluxes were very low, generally between −1.0 and 1.0 μg N m −2 h −1, and often below the minimum detection limit. There was an increase in soil NH 4+ in the months after the 2008 fire event, but no change in soil NO 3−. There was considerable nitrification in the early wet season but minimal nitrification at all other times.Savanna soil was generally a net CH 4 sink that equated to between −2.0 and −1.6 kg CH 4 ha −1 y −1 with no clear seasonal pattern in response to changing soil moisture conditions. Irrigation in the dry season significantly reduced soil gas diffusion and as a consequence soil CH 4 uptake. There were short periods of soil CH 4 emission, up to 20 μg C m −2 h −1, likely to have been caused by termite activity in, or beneath, automated chambers. Soil CO 2 fluxes showed a strong bimodal seasonal pattern, increasing fivefold from the dry into the wet season. Soil moisture showed a weak relationship with soil CH 4 fluxes, but a much stronger relationship with soil CO 2 fluxes, explaining up to 70% of the variation in unburnt treatments. Australian savanna soils are a small N 2O source, and possibly even a sink. Annual soil CH 4 flux measurements suggest that the 1.9 million km 2 of Australian savanna soils may provide a C sink of between −7.7 and −9.4 Tg CO 2-e per year. This sink estimate would offset potentially 10% of Australian transport related CO 2-e emissions. This CH 4 sink estimate does not include concurrent CH 4 emissions from termite mounds or ephemeral wetlands in Australian savannas. 相似文献
7.
The effects of elevated CO 2 supply on N 2O and CH 4 fluxes and biomass production of Phleum pratense were studied in a greenhouse experiment. Three sets of 12 farmed peat soil mesocosms (10 cm dia, 47 cm long) sown with P. pratense and equally distributed in four thermo-controlled greenhouses were fertilised with a commercial fertiliser in order to add 2, 6 or 10 g N m −2. In two of the greenhouses, CO 2 concentration was kept at atmospheric concentration (360 μmol mol −1) and in the other two at doubled concentration (720 μmol mol −1). Soil temperature was kept at 15 °C and air temperature at 20 °C. Natural lighting was supported by artificial light and deionized water was used to regulate soil moisture. Forage was harvested and the plants fertilised three times during the basic experiment, followed by an extra fertilisations and harvests. At the end of the experiment CH 4 production and CH 4 oxidation potentials were determined; roots were collected and the biomass was determined. From the three first harvests the amount of total N in the aboveground biomass was determined. N 2O and CH 4 exchange was monitored using a closed chamber technique and a gas chromatograph. The highest N 2O fluxes (on average, 255 μg N 2O m −2 h −1 during period IV) occurred just after fertilisation at high water contents, and especially at the beginning of the growing season (on average, 490 μg N 2O m −2 h −1 during period I) when the competition of vegetation for N was low. CH 4 fluxes were negligible throughout the experiment, and for all treatments the production and oxidation potentials of CH 4 were inconsequential. Especially at the highest rates of fertilisation, the elevated supply of CO 2 increased above- and below-ground biomass production, but both at the highest and lowest rates of fertilisation, decreased the total amount of N in the aboveground dry biomass. N 2O fluxes tended to be higher under doubled CO 2 concentrations, indicating that increasing atmospheric CO 2 concentration may affect N and C dynamics in farmed peat soil. 相似文献
8.
The study was carried out at the experimental station of the Japan International Research Center for Agricultural Sciences to investigate gas fluxes from a Japanese Andisol under different N fertilizer managements: CD, a deep application (8 cm) of the controlled release urea; UD, a deep application (8 cm) of the conventional urea; US, a surface application of the conventional urea; and a control, without any N application. NO, N 2O, CH 4 and CO 2 fluxes were measured simultaneously in a winter barley field under the maize/barley rotation. The fluxes of NO and N 2O from the control were very low, and N fertilization increased the emissions of NO and N 2O. NO and N 2O from N fertilization treatments showed different emission patterns: significant NO emissions but low N 2O emissions in the winter season, and low NO emissions but significant N 2O emissions during the short period of barley growth in the spring season. The controlled release of the N fertilizer decreased the total NO emissions, while a deep application increased the total N 2O emissions. Fertilizer-derived NO-N and N 2O-N from the treatments CD, UD and US accounted for 0.20±0.07%, 0.71±0.15%, 0.62±0.04%, and 0.52±0.04%, 0.50±0.09%, 0.35±0.03%, of the applied N, respectively, during the barley season. CH 4 fluxes from the control were negative on most sampling dates, and its net soil uptake was 33±7.1 mg m −2 during the barley season. The application of the N fertilizer decreased the uptake of atmospheric CH 4 and resulted in positive emissions from the soil. CO 2 fluxes were very low in the early period of crop growth while higher emissions were observed in the spring season. The N fertilization generally increased the direct CO 2 emissions from the soil. N 2O, CH 4 and CO 2 fluxes were positively correlated ( P<0.01) with each other, whereas NO and CO 2 fluxes were negatively correlated ( P<0.05). The N fertilization increased soil-derived global warming potential (GWP) significantly in the barley season. The net GWP was calculated by subtracting the plant-fixed atmospheric CO 2 stored in its aboveground parts from the soil-derived GWP in CO 2 equivalent. The net GWP from the CD, UD, US and the control were all negative at −243±30.7, −257±28.4, −227±6.6 and −143±9.7 g C m −2 in CO 2 equivalent, respectively, in the barley season. 相似文献
9.
The aim of this study was to investigate the combined effects of soil moisture and temperature as well as drying/re-wetting and freezing/thawing on soil-atmosphere exchange of CO 2 and CH 4 of the four dominant land use/cover types (typical steppe, TS; sand dune, SD; mountain meadow, MM; marshland, ML) in the Xilin River catchment, China. For this purpose, intact soil cores were incubated in the laboratory under varying soil moisture and temperature levels according to field conditions in the Xilin River catchment. CO 2 and CH 4 fluxes were determined approximately daily, while soil CH 4 gas profile measurements at four soil depths (5 cm, 10 cm, 20 cm and 30 cm) were measured at least twice per week. Land use/cover generally had a substantial influence on CO 2 and CH 4 fluxes, with the order of CH 4 uptake and CO 2 emission rates of the different land use/cover types being TS ≥ MM ≥ SD > ML and MM > TS ≥ SD > ML, respectively. Significant negative soil moisture and positive temperature effects on CH 4 uptake were found for most soils, except for ML soils. As for CO 2 flux, both significant positive soil moisture and temperature effects were observed for all the soils. The combination of soil moisture and temperature could explain a large part of the variation in CO 2 (up to 87%) and CH 4 (up to 68%) fluxes for most soils. Drying/re-wetting showed a pronounced stimulation of CO 2 emissions for all the soils —with maximum fluxes of 28.4 ± 2.6, 50.0 ± 5.7, 81.9 ± 2.7 and 10.6 ± 1.2 mg C m −2 h −1 for TS, SD, MM and ML soils, respectively—but had a negligible effect on CH 4 fluxes (TS: −3.6 ± 0.2; SD: 1.0 ± 0.9; MM: −4.1 ± 1.3; ML: −5.6 ± 0.8; all fluxes in μg C m −2 h −1). Enhanced CO 2 emission and CH 4 oxidation were observed for all soils during thawing periods. In addition, a very distinct vertical gradient of soil air CH 4 concentrations was observed for all land use/cover types, with gradually decreasing CH 4 concentrations down to 30 cm soil depth. The changes in soil air CH 4 concentration gradients were in accordance with the changes of CH 4 fluxes during the entire incubation experiment for all soils. 相似文献
10.
Emissions of N 2O and CH 4 and CH 4 oxidation rates were measured from Lolium perenne swards in a short-term study under ambient (36 Pa) and elevated (60 Pa) atmospheric CO 2 at the Free Air Carbon dioxide Enrichment experiment, Eschikon, Switzerland. Elevated pCO 2 increased ( P<0.05) N 2O emissions from high N fertilised (11.2 g N m −2) swards by 69%, but had no significant effect on net emissions of CH 4. Application of 13C-CH 4 (11 μl l −1; 11 at.% excess 13C) to closed chamber headspaces in microplots enabled determination of rates of 13C-CH 4 oxidation even when net CH 4 fluxes from main plots were positive. We found a significant interaction between fertiliser application rate and atmospheric pCO 2 on 13C-CH 4 oxidation rates that was attributed to differences in gross nitrification rates and C and N availability. CH 4 oxidation was slower and thought to be temporarily inhibited in the high N ambient pCO 2 sward. The most rapid CH 4 oxidation of 14.6 μg 13C-CH 4 m −2 h −1 was measured in the high fertilised elevated pCO 2 sward, and we concluded that either elevated pCO 2 had a stimulatory effect on CH 4 oxidation or inhibition of oxidation following fertiliser application was lowered under elevated pCO 2. Application of 14NH 415NO 3 and 15NH 415NO 3 (10 at.% excess 15N) to different replicates enabled determination of the respective contributions of nitrification and denitrification to N 2O emissions. Inhibition of CH 4 oxidation in the high fertilised ambient pCO 2 sward, due to competition between NH 3 and CH 4 for methane monooxygenase enzymes or toxic effects of NH 2OH or NO 2− produced during nitrification, was hypothesised to increase gross nitrification (12.0 mg N kg dry soil −1) and N 2O emissions during nitrification (327 mg 15N-N 2O m −2 over 11 d). Our results indicate that increasing atmospheric concentrations of CO 2 may increase emissions of N 2O by denitrification, lower nitrification rates and either increase or decrease the ability of soil to act as a sink for atmospheric CH 4 depending on fertiliser management. 相似文献
11.
We investigated spatial structures of N 2O, CO 2, and CH 4 fluxes during a relatively dry season in an Acacia mangium plantation stand in Sumatra, Indonesia. The fluxes and soil properties were measured at 1-m intervals in a 1 × 30-m plot (62 grid points) and at 10-m intervals in a 40 × 100-m plot (55 grid points) at different topographical positions of the upper plateau, slope, and valley bottom in the plantation. Spatial structures of each gas flux and soil property were identified using geostatistical analysis. The means (±SD) of N 2O, CO 2, and CH 4 fluxes in the 10-m grids were 0.54 (±0.33) mg N m −2 d −1, 2.81 (±0.71) g C m −2 d −1, and −0.84 (±0.33) mg C m −2 d −1, respectively. This suggests that A. mangium soils function as a larger source of N 2O than natural forest soils in the adjacent province on Sumatra during the relatively dry season, while CO 2 and CH 4 emissions from the A. mangium soils were less than or consistent with those in the natural forest soils. Multiple spatial dependence of N 2O fluxes within 3.2 m (1-m grids) and 35.0 m (10-m grids), and CO 2 fluxes within 1.8 m (1-m grids) and over 65 m (10-m grids) was detected. From the relationship among N 2O and CO 2 gas fluxes, soil properties, and topographic elements, we suggest that the multiple spatial structures of N 2O and CO 2 fluxes are mainly associated with soil resources such as readily mineralizable carbon and nitrogen in a relatively dry season. The soil resource distributions were probably controlled by the meso- and microtopography. Meanwhile, CH 4 fluxes were spatially independent in the A. mangium soils, and the water-filled pore space appeared to mainly control the spatial distribution of these fluxes. 相似文献
12.
We quantified spatial and temporal variations of the fluxes of nitrous oxide (N 2O) and methane (CH 4) and associated abiotic sediment parameters across a subtropical river estuary sediment dominated by grey mangrove ( Avicennia marina). N 2O and CH 4 fluxes from sediment were measured adjacent to the river (“fringe”) and in the mangrove forest (“forest”) at 3-h intervals throughout the day during autumn, winter and summer. N 2O fluxes from sediment ranged from an average of −4 μg to 65 μg N 2O m −2 h −1 representing N 2O sink and emission. CH 4 emissions varied by several orders of magnitude from 3 μg to 17.4 mg CH 4 m −2 h −1. Fluxes of N 2O and CH 4 differed significantly between sampling seasons, as well as between fringe and forest positions. In addition, N 2O flux differed significantly between time of day of sampling. Higher bulk density and total carbon content in sediment were significant contributors towards decreasing N 2O emission; rates of N 2O emission increased with less negative sediment redox potential ( Eh). Porewater profiles of nitrate plus nitrite (NO x−) suggest that denitrification was the major process of nitrogen transformation in the sediment and possible contributor to N 2O production. A significant decrease in CH 4 emission was observed with increasing Eh, but higher sediment temperature was the most significant variable contributing to CH 4 emission. From April 2004 to July 2005, sediment levels of dissolved ammonium, nitrate, and total carbon content declined, most likely from decreased input of diffuse nutrient and carbon sources upstream from the study site; concomitantly average CH 4 emissions decreased significantly. On the basis of their global warming potentials, N 2O and CH 4 fluxes, expressed as CO 2-equivalent (CO 2-e) emissions, showed that CH 4 emissions dominated in summer and autumn seasons (82-98% CO 2-e emissions), whereas N 2O emissions dominated in winter (67-95% of CO 2-e emissions) when overall CO 2-e emissions were low. Our study highlights the importance of seasonal N 2O contributions, particularly when conditions driving CH 4 emissions may be less favourable. For the accurate upscaling of N 2O and CH 4 flux to annual rates, we need to assess relative contributions of individual trace gases to net CO 2-e emissions, and the influence of elevated nutrient inputs and mitigation options across a number of mangrove sites or across regional scales. This requires a careful sampling design at site-level that captures the potentially considerable temporal and spatial variation of N 2O and CH 4 emissions. 相似文献
13.
While experimental addition of nitrogen (N) tends to enhance soil fluxes of carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O), it is not known if lower and agronomic-scale additions of urea-N applied also enhance trace gas fluxes, particularly for semi-arid agricultural lands in the northern plains. We aimed to test if this were true at agronomic rates [low (11 kg N ha −1), moderate (56 kg N ha −1), and high (112 kg N ha −1)] for central North Dakota arable and prairie soils using intact soil cores to minimize disturbance and simulate field conditions. Additions of urea to cores incubated at 21 °C and 57% water-filled pore space enhanced fluxes of CO 2 but not CH 4 and N 2O. At low, moderate, and high urea-N, CO 2 fluxes were significantly greater than control but not fluxes of CH 4 and N 2O. The increases in CO 2 emission with rate of urea-N application indicate that agronomic-scale N inputs may stimulate microbial carbon cycling in these soils, and that the contribution of CO 2 to net greenhouse gas source strength following fertilization of semi-arid agroecosystems may at times be greater than contributions by N 2O and CH 4. 相似文献
14.
Sharp peaks in nitrous oxide (N 2O) fluxes under no-tillage in wet conditions appear to be related to near surface soil and crop cover conditions. Here we explored some of the factors influencing tillage effects on short-term variations in gas flux so that we could learn about the mechanisms involved. Field investigations revealed that a cumulative emission of 13 kg N 2O–N ha −1 over a 12-week period was possible under no-tillage for spring barley. We investigated how reducing crop cover and changing the structural arrangement of the water-filled pore space (WFPS) by short-term laboratory compaction influenced N 2O and carbon dioxide (CO 2) fluxes in upward and downward directions in core samples from tilled and untilled soil. Increasing the downward flux of N 2O within a soil profile by changing soil or moisture conditions may increase the likelihood of its further reduction to N 2 or dissolution. We took undisturbed cores from 3 to 8 cm depth, equilibrated them to −1 or −6 kPa matric potential, incubated them and measured N 2O and CO 2 fluxes from the upper and lower surfaces in a purpose-designed apparatus before and after compaction in an uniaxial tester. We also measured WFPS, air permeability, bulk density and air-filled porosity before and after compaction. Spring barley was tested in 1999 and winter barley in 2000.Fluxes of N 2O were from 1.5 to 35 times higher from no-tilled than ploughed even where the soil was of similar bulk density. Reduction of the crop cover increased CO 2 flux and could reduce N 2O flux. The effects of structural changes induced by laboratory compaction on the fluxes of N 2O and CO 2 were not influenced greatly by the tillage and crop cover treatments. Fluxes from the upper surfaces of cores (corresponding to 3 cm soil depth, upwards direction) could be up to 100 times greater (N 2O) or 8 times (CO 2) than from the lower surfaces (8 cm depth, downwards direction). These differences between surfaces were greatest when N 2O fluxes were very high in no-tilled soil (4.2 mg N 2O–N m −2 h −1) as occurred when WFPS exceeded 80% or became blocked with water, an effect that was increased by our compaction treatment. In general N 2O fluxes increased with WFPS. The production and emission of N 2O were strongly influenced by the soil physical environment, the magnitude of the water-filled pore space and continuity of the air-filled pore space in particular, produced in no-till versus plough cultivation. 相似文献
15.
Net ecosystem carbon dioxide exchange was measured in two contrasting peatlands in northern Alberta, Canada using the eddy covariance technique during the growing season (May–October). Sphagnum spp. made up approximately 66% of the total LAI (1.52 m 2 m −2) at the poor fen and the total N content of Sphagnum capitula was 7.8 mg g −1 at the peak of the growing season. In contrast, the dominant plant species at the extreme-rich fen site, the perennial sedge, Carex lasiocarpa, accounted for approximately 60% of the total LAI (1.09 m 2 m −2), and had leaf total N content of 19.3 mg g −1 at peak biomass. In addition, the peak aboveground biomass was higher at the poor fen (230.9 g m −2) than at the extreme-rich fen (157.1 g m −2). Both sites had maximum daily rates of net CO 2 uptake of approximately 5 μmol m −2 s −1, and typical nighttime rates of CO 2 loss of approximately 2 μmol m −2 s −1 during the peak of the growing season. Calculations of maximum photosynthetic and respiratory capacity were consistently higher at the extreme-rich fen. The poor fen was a net sink for CO 2 during 4 of the 6 months (peaking at 44 g C m −2 in July), while only slight net losses of CO 2 (3 g C m −2) occurred in May and September. In contrast, the extreme-rich fen was calculated to be a significant net sink for CO 2 only during 2 months of the growing season (peaking at 30 g C m −2 in August), while significant net losses of CO 2 occurred in May (8 g C m −2) and in October (13 g C m −2). The plant species at the poor fen site were active earlier and later in the growing season, while it took longer for C. lasiocarpa to develop leaf tissue, and leaf senescence and reduction in photosynthetic activity occurred earlier in the fall at the extreme-rich fen. When integrated over the 6-month growing season, the poor fen was a net sink (90 g C m −2) that was three times larger than the extreme-rich fen (31 g C m −2). The ratio of cumulative total ecosystem respiration to gross primary production was 0.7 at the poor fen and 0.9 at the extreme-rich fen. 相似文献
16.
Relationships between CH 4, CO 2, and N 2O emissions were studied in soil that had been freshly amended with large deposits of cattle wastes. Dynamics of CH 4, CO 2, and N 2O emissions were investigated with flux chambers from early April to late June 2011, during the 3 months following cattle overwintering at the site. This 81-day field study was supplemented with soil analyses of available C and N content and measurement of denitrification activity. In a more detailed field investigation, the daily time course of emissions was determined. The field research was complemented with a laboratory experiment that focused on the short-term time course of N 2O and CH 4 production in artificially created anoxic soil microsites. The following hypotheses were tested: (i) a large input of C (and N and other nutrients) in cattle manure creates conditions suitable for methanogenesis, and therefore overwintering areas can produce large amounts of CH 4; (ii) N 2O is produced and emitted until the level of mineral N decreases, while the level of CH 4 production is low; and (iii) production of CH 4 is greater when N immobilization decreases the level of NO 3− in soil. N 2O emissions were relatively large during the first 3 weeks, then peaked (at ca. 4000 μg N 2ON m −2 h −1) and soon decreased to almost zero; the changes were related to the mineral and soluble organic N content in soil. CH 4 fluxes were large, though variable, in the first 2 months (600–3000 μg CH 4C m −2 h −1) and were independent of C and N availability. Although time courses differed for CH 4 and N 2O, a negative relationship between N 2O and CH 4 emissions was not detected. Contrary to CH 4 and N 2O fluxes, CO 2 emissions progressively increased to ca. 300 mg CO 2C m −2 h −1 at the end of the field study and were closely related to air and soil temperatures. Diurnal measurements revealed significant correlations between temperature and emissions of CH 4, N 2O, and CO 2. Addition of C to soil during anaerobic incubation increased the production and consumption of N 2O and supported the emission of CH 4. The results suggest that rapid denitrification significantly contributes to the exhaustion of oxidizing agents and helps create microsites supporting methanogenesis in otherwise N 2O-producing upland soil. The results also indicate that accurate estimate of gas fluxes in animal-impacted grassland areas requires assessment of both diurnal and long-term changes in CH 4, CO 2, and N 2O emissions. 相似文献
17.
AbstractTo evaluate the hypothesis that plant-mediated oxygen supplies decrease methane (CH 4) production and total global warming potential (GWP) in a tropical peatland, the authors compared the fluxes and dissolved concentrations of greenhouse gases [GHGs; CH 4, carbon dioxide (CO 2) and nitrous oxide (N 2O)] and dissolved oxygen (DO) at multiple peatland ecosystems in Central Kalimantan, Indonesia. Study ecosystems included tropical peat swamp forest and degraded peatland areas that were burned and/or drained during the rainy season. CH 4 fluxes were significantly influenced by land use and drainage, which were highest in the flooded burnt sites (5.75 ± 6.66 mg C m ?2 h ?1) followed by the flooded forest sites (1.37 ± 2.03 mg C m ?2 h ?1), the drained burnt site (0.220 ± 0.143 mg C m ?2 h ?1), and the drained forest site (0.0084 ± 0.0321 mg C m ?2 h ?1). Dissolved CH 4 concentrations were also significantly affected by land use and drainage, which were highest in the flooded burnt sites (124 ± 84 μmol L ?1) followed by the drained burnt site (45.2 ± 29.8 μmol L ?1), the flooded forest sites (1.15 ± 1.38 μmol L ?1) and the drained forest site (0.860 ± 0.819 μmol L ?1). DO concentrations were influenced by land use only, which were significantly higher in the forest sites (6.9 ± 5.6 μmol L ?1) compared to the burnt sites (4.0 ± 2.9 μmol L ?1). These results suggest that CH 4 produced in the peat might be oxidized by plant-mediated oxygen supply in the forest sites. CO 2 fluxes were significantly higher in the drained forest site (340 ± 250 mg C m ?2 h ?1 with a water table level of ?20 to ?60 cm) than in the drained burnt site (108 ± 115 mg C m ?2 h ?1 with a water table level of ?15 to +10 cm). Dissolved CO 2 concentrations were 0.6–3.5 mmol L ?1, also highest in the drained forest site. These results suggested enhanced CO 2 emission by aerobic peat decomposition and plant respiration in the drained forest site. N 2O fluxes ranged from ?2.4 to ?8.7 μg N m ?2 h ?1 in the flooded sites and from 3.4 to 8.1 μg N m ?2 h ?1 in the drained sites. The negative N 2O fluxes might be caused by N 2O consumption by denitrification under flooded conditions. Dissolved N 2O concentrations were 0.005–0.22 μmol L ?1 but occurred at < 0.01 μmol L ?1 in most cases. GWP was mainly determined by CO 2 flux, with the highest levels in the drained forest site. Despite having almost the same CO 2 flux, GWP in the flooded burnt sites was 20% higher than that in the flooded forest sites due to the large CH 4 emission (not significant). N 2O fluxes made little contribution to GWP. 相似文献
18.
Here we present results from a field experiment in a sub-arctic wetland near Abisko, northern Sweden, where the permafrost is currently disintegrating with significant vegetation changes as a result. During one growing season we investigated the fluxes of CO 2 and CH 4 and how they were affected by ecosystem properties, i.e., composition of species that are currently expanding in the area ( Carex rotundata, Eriophorum vaginatum and Eriophorum angustifolium), dissolved CH 4 in the pore water, substrate availability for methane producing bacteria, water table depth, active layer, temperature, etc. We found that the measured gas fluxes over the season ranged between: CH 4 0.2 and 36.1 mg CH 4 m −2 h −1, Net Ecosystem Exchange (NEE) −1000 and 1250 mg CO 2 m −2 h −1 (negative values meaning a sink of atmospheric CO 2) and dark respiration 110 and 1700 mg CO 2 m −2 h −1. We found that NEE, photosynthetic rate and CH 4 emission were affected by the species composition. Multiple stepwise regressions indicated that the primary explanatory variables for NEE was photosynthetic rate and for respiration and photosynthesis biomass of green leaves. The primary explanatory variables for CH 4 emissions were depth of the water table, concentration of organic acid carbon and biomass of green leaves. The negative correlations between pore water concentration and emission of CH 4 and the concentrations of organic acid, amino acid and carbohydrate carbon indicated that these compounds or their fermentation by-products were substrates for CH 4 formation. Furthermore, calculation of the radiative forcing of the species expanding in the area as a direct result of permafrost degradation and a change in hydrology indicate that the studied mire may act as an increasing source of radiative forcing in future. 相似文献
19.
We quantified the relationship between water table position and CO 2 emissions by manipulating water table levels for two summers in microcosms installed in a Colorado subalpine fen. Water levels were manipulated in the microcosms by either adding water or removing water and ranged from +10 cm above the soil surface to 40 cm below the soil surface, with ambient water levels in the fen averaging +3 and +2 cm above the soil surface during 1998 and 1999, respectively. Microcosm installation had no significant effect on CO 2 efflux; the 2 year means of natural and reference CO 2 efflux were 205.4 and 213.9 mg CO 2-C m −2 h −1, respectively ( p=0.80). Mean CO 2 emissions were lowest at the highest water tables (water +6 to +10 cm above the soil surface), averaging 133.8 mg CO 2-C m −2 h −1, increased to 231.3 mg CO 2-C m −2 h −1 when the water table was +1 to +5 cm above the soil surface and doubled to 453.7 mg CO 2-C m −2 h −1, when the water table was 0-5 cm below the soil surface. However, further lowering of the water table had little additional effect on CO 2 emissions, which averaged 470.3 and 401.1 mg CO 2-C m −2 h −1 when the water table was 6-10 cm, and 11-40 cm beneath the soil surface, respectively. The large increase in CO 2 emissions as we experimentally lowered the water table beneath the soil surface, coupled with no increase in CO 2 emissions as we furthered lowered water tables beneath the soil surface, suggest the presence of an easily oxidized labile carbon pool near the soil surface. 相似文献
20.
PurposeThe purposes of this study were to analyse the spatiotemporal variations in greenhouse gas diffusive fluxes at the sediment–water interface of sewage-draining rivers and natural rivers, and investigate the factors responsible for the changes in greenhouse gas diffusive fluxes. Materials and methodsGreenhouse gas diffusive fluxes at the sediment–water interface of rivers in Tianjin city (Haihe watershed) were investigated during July and October 2014, and January and April 2015 by laboratory incubation experiments. The influence of environmental variables on greenhouse gas diffusive fluxes was evaluated by Spearman’s correlation analysis and a multiple stepwise regression analysis. Results and discussionSewage-draining rivers were more seriously polluted by human sewage discharge than natural rivers. The greenhouse gas diffusive fluxes at the sediment–water interface exhibited obvious spatiotemporal variations. The mean absolute value of the CO2 diffusive fluxes was seasonally variable with spring>winter>fall>summer, while the mean absolute values of the CH4 and N2O diffusive fluxes were both higher in summer and winter, and lower in fall and spring. The annual mean values of the CO2, CH4 and N2O diffusive fluxes at the sewage-draining river sediment–water interface were ??123.26?±?233.78 μmol m?2 h?1, 1.88?±?6.89 μmol m?2 h?1 and 1505.03?±?2388.46 nmol m?2 h?1, respectively, which were 1.22, 4.37 and 134.50 times those at the natural river sediment–water interface, respectively. The spatial variation of the N2O diffusive fluxes in the sewage-draining rivers and the natural rivers was the most significant. As a general rule, the more serious the river pollution was, the greater the diffusive fluxes of the greenhouse gases were. On average for the whole year, the river sediment was the sink of CO2 and the source of CH4 and N2O. There were positive correlations among the CO2, CH4 and N2O diffusive fluxes. The main influencing factor for CO2 and N2O diffusive fluxes was the water temperature of the overlying water; however, the key factors for CH4 diffusive fluxes were the Eh of the sediment and the NH4+-N of the overlying water. ConclusionsRiver sediment can be either a sink or a source of greenhouse gases, which varies in different levels of pollution and different seasons. Human sewage discharge has greatly affected the carbon and nitrogen cycling of urban rivers. 相似文献
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