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1.
Methane (CH4) uptake by soil can possibly be suppressed more in regions with heavy summer precipitation, such as those under the East Asian monsoon climate, as compared to that in regions with a dry summer. In order to determine how precipitation patterns affect seasonal and spatial variations in CH4 fluxes in temperate forest soils, such fluxes and selected environmental variables were measured on different parts of a hill slope in a cypress forest in central Japan. On the upper and middle parts of the slope, CH4 uptake was observed throughout the year, and the uptake rates increased slightly with soil temperature and decreased with soil water content. The CH4 flux predicted using data for the middle and upper parts of the slope ranged from −1.12 to −0.83 kg-CH4 ha−1 y−1 (i.e. CH4 uptake by soil) and from −2.30 to −2.04 kg-CH4 ha−1 y−1, respectively. In contrast, in the relatively wet lower part of the slope near an in-stream wetland, large CH4 emissions (>2 mg-CH4 m−1 d−1) were observed during the rainy summer. In this wetter plot, the soil functioned as a net annual CH4 source in a rainy year. Hence the variation in CH4 flux with a change in soil water conditions and soil temperature on the lower part of the slope contrasted to that on the upper and middle parts of the slope. The predicted CH4 flux for this lower plot ranged from −0.45 kg-CH4 ha−1 y−1 in a dry year to 1.80 kg-CH4 ha−1 y−1 in a rainy year. Our results suggest that consideration of the soil water conditions across a watershed is important for estimating the CH4 budgets for entire forest watershed, particularly in regions subject to a wet summer.  相似文献   

2.
Afforestation and reforestation of pastures are key land-use changes in New Zealand that help sequester carbon (C) to offset its carbon dioxide (CO2) emissions under the Kyoto Protocol. However, relatively little attention has been given so far to associated changes in trace gas fluxes. Here, we measure methane (CH4) fluxes and CO2 production, as well as microbial C, nitrogen (N) and mineral-N, in intact, gradually dried (ca. 2 months at 20 °C) cores of a volcanic soil and a heavier textured, non-volcanic soil collected within plantations of Pinus radiata D. Don (pine) and adjacent permanent pastures. CH4 fluxes and CO2 production were also measured in cores of another volcanic soil under reverting shrubland (mainly Kunzea var. ericoides (A. Rich) J. Thompson) and an adjacent pasture. CH4 uptake in the pine and shrubland cores of the volcanic soils at field capacity averaged about 35 and 14 μg CH4-C m−2 h−1, respectively, and was significantly higher than in the pasture cores (about 21 and 6 μg CH4-C m−2 h−1, respectively). In the non-volcanic soil, however, CH4-C uptake was similar in most cores of the pine and pasture soils, averaging about 7-9 μg m−2 h−1, except in very wet samples. In contrast, rates of CO2 production and microbial C and N concentrations were significantly lower under pine than under pasture. In the air-dry cores, microbial C and N had declined in the volcanic soil, but not in the non-volcanic soil; ammonium-N, and especially nitrate-N, had increased significantly in all samples. CH4 uptake was, with few exceptions, not significantly influenced by initial concentrations of ammonium-N or nitrate-N, nor by their changes on air-drying. A combination of phospholipid fatty acid (PLFA) and stable isotope probing (SIP) analyses of only the pine and pasture soils showed that different methanotrophic communities were probably active in soils under the different vegetations. The C18 PLFAs (type II methanotrophs) predominated under pine and C16 PLFAs (type I methanotrophs) predominated under pasture. Overall, vegetation, soil texture, and water-filled pore space influenced CH4-C uptake more than did soil mineral-N concentrations.  相似文献   

3.
We examined the effects of forest clearfelling on the fluxes of soil CO2, CH4, and N2O in a Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation on an organic-rich peaty gley soil, in Northern England. Soil CO2, CH4, N2O 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 CO2 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 CH4 to a net source (2.01 mg m−2 d−1). For the same period, soil N2O 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, CO2 remained the dominant greenhouse gas in terms of its greenhouse warming potential.  相似文献   

4.
The eddy flux of methane (CH4) was measured over 14 months above a restored wetland in western Denmark. The average annual daily CH4 flux was 30.2 mg m−2 d−1, but the daily emission rates varied considerably over time. Several factors were identified that explained some of this variation. (1) Grazing cattle moving through the source area of the eddy flux mast increased the measured emission rates by one order of magnitude during short time periods. (2) Friction velocity exerted a strong control on the CH4 flux whenever there were water pools on the surface. (3) An exponential response of the daily CH4 flux to soil temperature at 20 cm depth was found for most of the study period, but not for parts of the summer season that coincided with a low water level in the river flowing through the wetland. (4) Additional variations in the CH4 emission rates were related to the spatial heterogeneity of the source area. This area covered not only different plant communities but also a gravel road and a river surface, and it had a microtopography that visibly induced a large spatial variability in the wetness of the top soil. It is shown that the control mechanisms for the methane emission from restored wetlands are more complex than those reported for natural wetlands, since they include both management activities and slow adaptive processes related to changes in vegetation and hydrology. On the basis of eddy fluxes of carbon dioxide measured at the same site it is finally demonstrated that the variability in the CH4 fluxes strongly affects the greenhouse gas sink strength of the restored wetland.  相似文献   

5.
We measured methane (CH4) emissions from the stem surfaces of mature Fraxinus mandshurica var. japonica trees in a floodplain forest. Flux measurements were conducted almost monthly from May to October 2005, and positive CH4 fluxes were detected throughout the study period, including the leafless season. The mean CH4 flux was 176 and 97 μg CH4 m−2 h−1 at the lower (15 cm above the ground) and upper (70 cm above the ground) stem positions, respectively. The CH4 concentration was lower in soil gas than in ambient air to a depth of at least 40 cm. One possible source of CH4 emitted from the stems might be the dissolved CH4 in groundwater; maximum concentrations were 10,000 times higher than atmospheric CH4 concentrations. Our results suggest that CH4 transport from the submerged soil layer to the atmosphere may occur through internal air spaces in tree bodies.  相似文献   

6.
Methane oxidation in forest soils removes atmospheric CH4. Many studies have determined methane uptake rates and their controlling variables, yet the microorganisms involved have rarely been assessed simultaneously over the longer term. We measured methane uptake rates and the community structure of methanotrophic bacteria in temperate forest soil (sandy clay loam) on a monthly basis for two years in South Korea. Methane uptake rates at the field site did not show any seasonal patterns, and net uptake occurred throughout both years. In situ uptake rates and uptake potentials determined in the laboratory were 2.92 ± 4.07 mg CH4 m−2 day−1 and 51.6 ± 45.8 ng CH4 g−1 soil day−1, respectively. Contrary to results from other studies, in situ oxidation rates were positively correlated with soil nitrate concentrations. Short-term experimental nitrate addition (0.20-1.95 μg N g−1 soil) significantly stimulated oxidation rates under low methane concentrations (1.7-2.0 ppmv CH4), but significantly inhibited oxidation under high methane concentrations (300 ppmv CH4). We analyzed the community structures of methanotrophic bacteria using a DNA-based fingerprinting method (T-RFLP). Type II methanotrophs dominated under low methane concentrations while Type I methanotrophs dominated under high methane concentrations. Nitrogen addition selectively inhibited Type I methanotrophic bacteria. Overall, the results of this study indicate that the effects of inorganic N on methane uptake depend on methane concentrations and that such a response is related to the dissimilar activation or inhibition of different types of methanotrophic bacteria.  相似文献   

7.
The effect of aluminium on methane oxidation was examined from incubation experiments involving the addition of several concentrations of Al solution (0.1, 0.2, 0.5, 1, 3 and 5 mM) to two soil samples that possessed different CH4 oxidation potential. Atmospheric CH4 oxidation activity was inhibited by the addition of as little as 0.1 mM Al solution (approximately 0.5 μg of Al per gram dry weight soil) to a forest soil that contained low water-soluble Al and possessed a high CH4 oxidation potential. Our results indicate that Al inhibition of CH4 oxidation activity is concentration-dependant after a certain time and the inhibition increases gradually over time until at least 96 h have elapsed. We also found that relatively small amounts of Al additions, such as 10-20 μg per gram dry weight of soil, halved the CH4 oxidation rate compared to the control, regardless of the original CH4 oxidation potential of the soil. Since the Al concentrations used in our experiment are often observed in forest soils, we can assume that Al acts as an important inhibitor of CH4 oxidation in forest soils under natural conditions. The sharp falls and a continuous decrease in CH4 oxidation rate in other forest samples with the addition of deionized water implies that the water-soluble Al contained in soils contributes to the inhibition of CH4 oxidation rate. This result suggests that precipitation causes a relatively prolonged inhibition of CH4 oxidation in soils containing a high concentration of water-soluble Al.  相似文献   

8.
Methane oxidation in temperate soils: effects of inorganic N   总被引：1，自引：0，他引：1  
Additions of inorganic nitrogen (N) to an oak soil with significant potential for methane (CH4) oxidation resulted in differential reduction in CH4 oxidation capacity depending on N species added. Nitrate, rather than nitrite or ammonium, proved to be the strongest inhibitor of CH4 oxidation in oak soil. Both high (CH4 at 10 μl l−1) and low (CH4 at 5 ml l−1) affinity CH4 oxidation in oak soil was completely inhibited at a nitrate concentration similar to that present in an alder soil from the same experimental site. The alder soil showed no capacity for low affinity CH4 oxidation. A ‘low nitrate’ forest soil (oak) showed high affinity, low capacity CH4 oxidation upto around 1 ml l−1 CH4, above which both high and low affinity CH4 oxidation became apparent following a lag phase, indicating either an induced high affinity uptake mechanism or the existence of distinct low affinity and high affinity methanotroph populations. High affinity CH4 oxidation became saturated at CH4 concentrations >500 μl l−1, while low affinity CH4 oxidation became saturated at ∼30 ml l−1 CH4. In a ‘high nitrate’ forest soil (alder), CH4 oxidation appeared to be due to high affinity CH4 oxidation only and became undetectable at CH4 concentrations >5 ml l−1.  相似文献   

9.
Northern wetlands are critically important to global change because of their role in modulating atmospheric concentrations of greenhouse gases, especially CO2 and CH4. At present, continuous observations for CO2 and CH4 fluxes from northern wetlands in Asia are still very limited. In this paper, two growing season measurements for CO2 flux by eddy covariance technique and CH4 flux by static chamber technique were conducted in 2004 and 2005, at a permanently inundated marsh in the Sanjiang Plain, northeastern China. The seasonal variations of CO2 exchange and CH4 flux and the environmental controls on them were investigated. During the growing seasons, large variations in net ecosystem CO2 exchange (NEE) and gross ecosystem productivity (GEP) were observed with the range of −4.0 to 2.2 (where negative exchange is a gain of carbon from the atmosphere) and 0-7.6 g C m−2 d−1, respectively. Ecosystem respiration (RE) displayed relatively smooth seasonal pattern with the range of 0.8-4.2 g C m−2 d−1. More than 70% of the total GEP was consumed by respiration, which resulted in a net CO2 uptake of 143 ± 9.8 and 100 ± 9.2 g C m−2 for the marsh over the growing seasons of 2004 and 2005, respectively. A significant portion of the accumulated NEE-C was lost by CH4 emission during the growing seasons, indicating the great potential of CH4 emission from the inundated marsh. Air temperature and leaf area index jointly affected the seasonal variation of GEP and the seasonal dynamic of RE was mainly controlled by soil temperature and leaf area index. Soil temperature also exerted the dominant influence over variation of CH4 flux while no significant relationship was found between CH4 emission and water table level. The close relationships between carbon fluxes and temperature can provide insights into the response of marsh carbon exchange to a changing climate. Future long term flux measurements over the freshwater marsh ecosystems are undoubtedly necessary.  相似文献   

10.
Methane uptake to soil was examined in individual chambers at three small forest catchments with different treatments, Control, Limed and Nitrex sites, where N-deposition was experimentally increased. The catchments consisted of both well-drained forest and wet sphagnum areas, and showed uptake of CH4 from the ambient air. The lowest CH4 uptakes were observed in the wet areas, where the different treatments did not influence the uptake rate. In the well-drained areas the CH4 uptakes were 1.6, 1.4 and 0.6 kg ha–1 year–1 for the Limed, Control and Nitrex sites, respectively. The uptake of methane at the well-drained Nitrex site was statistically smaller than at the other well-drained catchments. Both acidification and increase in nitrogen in the soil, caused by the air-borne deposition, are the probable cause for the reduction in the methane uptake potential. Uptake of methane was correlated to soil water content or temperature for individual chambers at the well-drained sites. The uptake rate of methane in soil cores was largest in the 0- to 10-cm upper soil layer. The concentration of CH4 in the soil was lower than the atmospheric concentration up to 30 cm depth, where methane production occurred. Besides acting as a sink for atmospheric methane, the oxidizing process in soil prevents the release of produced methane from deeper soil layers reaching the atmosphere. Received: 27 September 1996  相似文献   

11.
We describe experiments to better understand how CH4 oxidation rates by different methanotroph communities respond to changing CH4 concentrations. We used a novel system of automatically monitored chambers to investigate the response of CH4 oxidation rates in a New Zealand pasture and adjacent pine forest soil exposed to varying atmospheric CH4 concentrations.Type II methanotrophs that dominate CH4 oxidation in the forest soil became progressively saturated as CH4 concentrations rose from ambient (1.8 ppmv) to 570 ppmv, as shown by a decrease in uptake efficiency from 20% to 2% removal. By contrast, CH4 oxidation in the pasture soil where Type I methanotrophs dominate increased in proportion to the increase in CH4 inlet concentration, oxidising about 2% of the inlet CH4 flux throughout. Modelling based on Michaelis-Menten kinetics revealed that low-affinity (Type I) methanotrophs were solely responsible for CH4 oxidation in pasture soils, whereas high affinity (Type II) methanotrophs only contributed about 10% of the CH4 oxidation in the forest soil. Increased aeration status using a soil–perlite (1:1) mixture doubled CH4 oxidation rates at both ambient (1.8 ppmv) and 40 ppmv atmospheric CH4. A similar volcanic soil previously exposed for 8 y to high CH4 fluxes from a landfill had removal efficiencies consistently above 95% for atmospheric CH4 concentrations up to 7500 ppmv when the CH4 oxidation rate was7000 μg CH4 kg−1soil h−1.  相似文献   

12.
To compare factors that control methane flux in forest soils, we studied three equal-aged Japanese cypress (Chamaecyparis obtusa) forests in Chubu district, central Japan. The three sites are located at different altitudes: 630 m (SET), 1010 m (INB), and 1350 m (OSK). Methane was absorbed at every site. The highest uptake rate was observed in the middle-altitude soil (INB, 5.89 mg CH4 m−2 d−1), which was the only site where methane uptake rate was correlated with air and soil surface temperatures. Methane flux in the field was not correlated with water content, inorganic N content, or water-soluble organic carbon. C/N ratio was correlated with methane flux (r=0.64,p<0.001). The results suggest that some organic inhibitors might be produced through decomposition of organic matter. There was a negative correlation between methane uptake rate and water-soluble Al (r=−0.63,p<0.001). Inhibition of methane consumption by 1 and 5 mM Al solutions was observed in laboratory incubation. This result suggests that water-soluble Al may be a factor controlling methane uptake. Multiple regression with a backward-elimination procedure identified three variables that were significantly associated with methane flux in the field (p<0.05): air temperature, C/N ratio, and the concentration of water-soluble Al.  相似文献   

13.
Tree species can affect the sink and source strength of soils for atmospheric methane and nitrous oxide. Here we report soil methane (CH4) and nitrous oxide (N2O) fluxes of adjacent pure and mixed stands of beech and spruce at Solling, Germany. Mean CH4 uptake rates ranged between 18 and 48 μg C m?2 hour?1 during 2.5 years and were about twice as great in both mixed and the pure beech stand as in the pure spruce stand. CH4 uptake was negatively correlated with the dry mass of the O horizon, suggesting that this diminishes the transport of atmospheric CH4 into the mineral soil. Mean N2O emission was rather small, ranging between 6 and 16 μg N m?2 hour?1 in all stands. Forest type had a significant effect on N2O emission only in one mixed stand during the growing season. We removed the O horizon in additional plots to study its effect on gas fluxes over 1.5 years, but N2O emissions were not altered by this treatment. Surprisingly, CH4 uptake decreased in both mixed and the pure beech stands following the removal of the O horizon. The decrease in CH4 uptake coincided with an increase in the soil moisture content of the mineral soil. Hence, O horizons may maintain the gas diffusivity within the mineral soil by storing water which cannot penetrate into the mineral soil after rainfall. Our results indicate that conversion of beech forests to beech–spruce and pure spruce forests could decrease soil CH4 uptake, while the long‐term effect on N2O emissions is expected to be rather small.  相似文献   

14.
Methane fluxes were measured monthly over a year from tropical peatland of Sarawak, Malaysia using a closed-chamber technique. The CH4 fluxes in forest ecosystem ranged from −4.53 to 8.40 μg C m−2 h−1, in the oil palm ecosystem from −32.78 to 4.17 μg C m−2 h−1 and in the sago ecosystem from −7.44 to 102.06 μg C m−2 h−1. A regression tree approach showed that CH4 fluxes in each ecosystem were related to different underlying environmental factors. They were relative humidity for forest and water table for both sago and oil palm ecosystems. On an annual basis, both forest and sago were CH4 source with an emission of 18.34 mg C m−2 yr−1 for forest and 180 mg C m−2 yr−1 for sago. Only oil palm ecosystem was a CH4 sink with an uptake rate of −15.14 mg C m−2 yr−1. These results suggest that different dominant underlying environmental factors among the studied ecosystems affected the exchange of CH4 between tropical peatland and the atmosphere.  相似文献   

15.
In boreal forests, canopy-scale emissions of biogenic volatile organic compounds (BVOCs) are rather well characterised, but knowledge of ecosystem-scale BVOC emissions is still inadequate. We used adsorbent tubes to measure BVOCs from a boreal Scots pine (Pinus sylvestris L.) forest floor in southern Finland and analysed the compounds with a gas chromatograph-mass spectrometer. The most abundant compound group was the monoterpenes (averaging 5.04 μg m−2 h−1), in which α-pinene, Δ3-carene and camphene contributed over 90% of the emissions. Emissions of other terpenoids (isoprene and sesquiterpenes) were low (averaging 0.05 and 0.04 μg m−2 h−1, respectively). BVOC emissions from the forest floor varied seasonally, peaking in early summer and autumn, with most of the compounds following similar patterns. The emission pattern was sustained throughout the measurement period, suggesting that the main sources of the emissions remained more or less stable. We compared the BVOC fluxes with environmental parameters such as temperature, precipitation and PAR, and with fluxes of other trace gases (CO2, CH4, N2O), as well as with ground vegetation photosynthesis and with litter input. Several of these parameters were correlated with the presence of BVOCs. The sources of soil BVOC emissions are very poorly understood, but our results suggest, that changes in litter quantity and quality, soil microbial activity and the physiological stages of plants are linked with changes in BVOC fluxes.  相似文献   

16.
The effects of elevated CO2 supply on N2O and CH4 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, CO2 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 CH4 production and CH4 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. N2O and CH4 exchange was monitored using a closed chamber technique and a gas chromatograph. The highest N2O fluxes (on average, 255 μg N2O 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 N2O m−2 h−1 during period I) when the competition of vegetation for N was low. CH4 fluxes were negligible throughout the experiment, and for all treatments the production and oxidation potentials of CH4 were inconsequential. Especially at the highest rates of fertilisation, the elevated supply of CO2 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. N2O fluxes tended to be higher under doubled CO2 concentrations, indicating that increasing atmospheric CO2 concentration may affect N and C dynamics in farmed peat soil.  相似文献   

17.
Methane emissions from soils are the net result of two processes: methane (CH4) production and CH4 oxidation. In order to understand how both processes respond to environmental changes, it is necessary to distinguish between CH4 production and oxidation. In bacterial cultures and small soil samples, difluoromethane (CH2F2) was found to inhibit CH4 oxidation reversibly, without affecting CH4 production. Hence, CH2F2 allows the study of CH4 production directly and of CH4 oxidation indirectly. To our knowledge, however, the inhibitory effect of CH2F2 within soil columns has not yet been evaluated. We therefore tested which CH2F2 concentration is needed for complete inhibition of CH4 oxidation in reconstructed 28 cm high peat soil columns under different water levels (WL). We found that soil columns require considerably higher headspace CH2F2 concentrations for complete inhibition of CH4 oxidation than small soil samples. Inhibition remained complete until ca. 24 h after CH2F2 exposure. Then, the inhibitory effect diminished. The time needed for the inhibitory effect to disappear depended on WL; at a low WL of −15 cm, the inhibitory effect declined slowly and oxidation rates recovered by 90% only after 12 days. At WL = −5 cm, CH4 oxidation recovered much faster (90% recovery after ca. 3 days). Last, CH2F2 addition significantly decreased the N2O emissions, whereas CO2 emissions remained unaltered.  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 CO2 and CH4 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 CH4 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: CH4 0.2 and 36.1 mg CH4 m−2 h−1, Net Ecosystem Exchange (NEE) −1000 and 1250 mg CO2 m−2 h−1 (negative values meaning a sink of atmospheric CO2) and dark respiration 110 and 1700 mg CO2 m−2 h−1. We found that NEE, photosynthetic rate and CH4 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 CH4 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 CH4 and the concentrations of organic acid, amino acid and carbohydrate carbon indicated that these compounds or their fermentation by-products were substrates for CH4 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.
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 (CO2) concentrations, may affect the exchange of nitrous oxide (N2O) and methane (CH4) 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 N2O and CH4 fluxes took place 1-2 years after the climate change manipulations were initiated. The soil was generally a net sink for atmospheric CH4. Elevated temperature (T) increased the CH4 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 CO2 (CO2) reduced the CH4 uptake, which outweighed the positive effect of warming when analyzed across the study period. Emissions of N2O were generally low (<10 μg N m−2 h−1). As single experimental factors, elevated CO2, temperature and summer drought (D) had no major effect on the N2O fluxes, but the combination of CO2 and warming (TCO2) stimulated N2O emission, whereas the N2O emission ceased when CO2 was combined with drought (DCO2). We suggest that these N2O responses are related to increased rhizodeposition under elevated CO2 combined with increased and reduced nitrogen turnover rates caused by warming and drought, respectively. The N2O flux in the multifactor treatment TDCO2 was not different from the ambient control treatment. Overall, our study suggests that in the future, CH4 uptake may increase slightly, while N2O 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   

20.
ABSTRACT

Emission of methane (CH4), a major greenhouse gas, from submerged paddy soils is generally reduced by introducing intermittent drainage in summer, which is a common water management in Japan. However, such a practice is not widely conducted in Hokkaido, a northern region in Japan, to prevent a possible reduction in rice grain yield caused by cold weather. Therefore, the effects of intermittent drainage on CH4 emission and rice grain yield have not been investigated comprehensively in Hokkaido. In this study, we conducted a three-year field experiment in Hokkaido and measured CH4 and nitrous oxide (N2O) fluxes and rice grain yield to elucidate whether the reduction in CH4 emission can be achieved in Hokkaido as well as other regions in Japan. Four experimental treatments, namely, two soil types [soils of light clay (LiC) and heavy clay (HC) textures] and two water management [continuous flood irrigation (CF), and intermittent drainage (ID)], were used, and CH4 and N2O fluxes were measured throughout the rice cultivation periods from 2016 to 2018. Cumulative CH4 emissions in 2016 were markedly low, suggesting an initially low population of methanogens in the soils presumably due to no soil submergence or crop cultivation in the preceding years, which indicates a possible reduction in CH4 emission by introducing paddy-upland crop rotation. Cumulative CH4 emissions in the ID-LiC and ID-HC plots were 21–91% lower than those in the CF-LiC and CF-HC plots, respectively, whereas the cumulative N2O emissions did not significantly differ between the different water managements. The amount of CH4 emission reduction by the intermittent drainage was largest in 2018, with a comparatively long period of the first drainage for 12 days in summer. Rice grain yields did not significantly differ between the different water managements for the entire 3 years, although the percentage of well-formed rice grains was reduced by the intermittent drainage in 2018. These results suggest that CH4 emission from paddy fields can be reduced with no decrease in rice grain yield by the intermittent drainage in Hokkaido. In particular, the first drainage for a long period in summer is expected to reduce CH4 emission markedly.  相似文献   

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