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1.
Relationships between CH4, CO2, and N2O emissions were studied in soil that had been freshly amended with large deposits of cattle wastes. Dynamics of CH4, CO2, and N2O 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 N2O and CH4 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 CH4; (ii) N2O is produced and emitted until the level of mineral N decreases, while the level of CH4 production is low; and (iii) production of CH4 is greater when N immobilization decreases the level of NO3− in soil. N2O emissions were relatively large during the first 3 weeks, then peaked (at ca. 4000 μg N2ON m−2 h−1) and soon decreased to almost zero; the changes were related to the mineral and soluble organic N content in soil. CH4 fluxes were large, though variable, in the first 2 months (600–3000 μg CH4C m−2 h−1) and were independent of C and N availability. Although time courses differed for CH4 and N2O, a negative relationship between N2O and CH4 emissions was not detected. Contrary to CH4 and N2O fluxes, CO2 emissions progressively increased to ca. 300 mg CO2C 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 CH4, N2O, and CO2. Addition of C to soil during anaerobic incubation increased the production and consumption of N2O and supported the emission of CH4. The results suggest that rapid denitrification significantly contributes to the exhaustion of oxidizing agents and helps create microsites supporting methanogenesis in otherwise N2O-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 CH4, CO2, and N2O emissions.  相似文献   

2.
Wetlands are major natural sources of greenhouse gases (GHGs). In central and southern Africa, one of the most extensive wetlands are dambos (seasonal wetlands) which occupy 20–25% of land area. However, there are very little data on GHG methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) emissions from dambos, and this study presents the first estimates from dambos in Zimbabwe. The objective was to evaluate the effects of catena positions; upland, dambo mid-slope and dambo bottom, on GHG emissions along an undisturbed dambo transect. Methane emissions were ?0.3, 29.5 and ?1.3 mg m?2 hr?1, N2O emission were 40.1, 3.9 and 5.5 µg m2 hr?1, while CO2 emissions were 2648.9, 896.2 and 590.1 mg m?2 hr?1 for upland, mid-slope and bottom catena, respectively. Our results showed that uplands were important sources of N2O and CO2, and a sink for CH4, while the dambo mid-slope position was a major source of CH4, but a weak source of CO2 and N2O. Dambo bottom catena was weak source GHGs. Overall, dambos were major sources of CH4 and weak sources of N2O and CO2.We concluded that, depending on catenal position, dambos can be major or minor sources of GHGs.  相似文献   

3.
We investigated spatial structures of N2O, CO2, and CH4 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 N2O, CO2, and CH4 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 N2O than natural forest soils in the adjacent province on Sumatra during the relatively dry season, while CO2 and CH4 emissions from the A. mangium soils were less than or consistent with those in the natural forest soils. Multiple spatial dependence of N2O fluxes within 3.2 m (1-m grids) and 35.0 m (10-m grids), and CO2 fluxes within 1.8 m (1-m grids) and over 65 m (10-m grids) was detected. From the relationship among N2O and CO2 gas fluxes, soil properties, and topographic elements, we suggest that the multiple spatial structures of N2O and CO2 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, CH4 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   

4.
Forest soils can be sources or sinks of greenhouse gases (GHGs) depending on soil attributes that affect biomass and activity of soil micro-organisms involved in GHGs fluxes. In this work, we tested the hypothesis that soil physical, chemical and microbiological attributes, under different forests ecosystems, affect the soil GHGs [nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4)] fluxes. The study was carried out in two locations in southern Brazil in 2019, with three experimental plots of 900 m2 in native forests of the Atlantic Forest biome and in loblolly pine (Pinus taeda) plantations. Air samples released from the soil surface were analysed for concentration and flux of CO2, N2O and CH4. Soil samples were analysed for chemical attributes, density (Ds), soil microporosity (MiPs), soil macroporosity (MaPs), total porosity (TP), water-filled pore space (WFPS), microbial biomass carbon (MB-C), basal respiration (BR), microbial (qMic) and metabolic (qCO2) quotient and activities of soil urease and β-glucosidase enzymes. The seasons influenced the CO2 and N2O emissions, probably because of the changes in seasonal conditions. However, native forests consumed more CH4 than pine plantations. Meanwhile, the native forests presented soils with lower Ds (average 21.5% lower), more TP (average 12.5% higher) and more moisture (average 33% higher), which improved the microbiological attributes of the soil (20% to 60% more MB-C, 67% higher urease activity and 30% higher β-glucosidase activity) compared with pine plantations. Native forests contributed more intensely to CH4 consumption than pine plantations because they present better physical, chemical and microbiological soil conditions. Therefore, it is possible that forestry practices that improve soil physical attributes are likely to contribute to increase CH4 consumption, and to reduce GHGs emissions in forest ecosystems.  相似文献   

5.
Greenhouse gases (GHGs) are produced during the composting process, but few studies have measured emissions from a full-scale windrow of composting green-waste. This is important for evaluating composting as a waste management option and for understanding how changes to current composting management practices could help reduce emissions. This study uses micrometeorological mass balance (MMB) and open flow-through chamber techniques to measure emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from a windrow of composting green-waste in Northern California. The MMB technique yielded mean upwind–downwind concentration differences over the study period that showed sourcing of all three GHGs. CO2 showed a stronger signal than CH4 and N2O. A strong diel pattern was found in the concentration differences at lower levels and fluxes of CO2, with substantial noise likely obscuring any possible daily patterns for CH4 and N2O. Fluxes normalized by the time since the previous turn event revealed an initial rapid rise in CO2 concentration differences (at lower levels) and fluxes, peaking close to 13?h after the turn event followed by a gradual decline. The same pattern was not as clear for the other two gases but overall declines in concentration differences and fluxes were apparent with increasing time since the previous turn event. Substantial differences between MMB and chamber calculated fluxes were found, due to both differences in the techniques as well as sampling frequency.  相似文献   

6.
We quantified spatial and temporal variations of the fluxes of nitrous oxide (N2O) and methane (CH4) and associated abiotic sediment parameters across a subtropical river estuary sediment dominated by grey mangrove (Avicennia marina). N2O and CH4 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. N2O fluxes from sediment ranged from an average of −4 μg to 65 μg N2O m−2 h−1 representing N2O sink and emission. CH4 emissions varied by several orders of magnitude from 3 μg to 17.4 mg CH4 m−2 h−1. Fluxes of N2O and CH4 differed significantly between sampling seasons, as well as between fringe and forest positions. In addition, N2O flux differed significantly between time of day of sampling. Higher bulk density and total carbon content in sediment were significant contributors towards decreasing N2O emission; rates of N2O emission increased with less negative sediment redox potential (Eh). Porewater profiles of nitrate plus nitrite (NOx−) suggest that denitrification was the major process of nitrogen transformation in the sediment and possible contributor to N2O production. A significant decrease in CH4 emission was observed with increasing Eh, but higher sediment temperature was the most significant variable contributing to CH4 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 CH4 emissions decreased significantly. On the basis of their global warming potentials, N2O and CH4 fluxes, expressed as CO2-equivalent (CO2-e) emissions, showed that CH4 emissions dominated in summer and autumn seasons (82-98% CO2-e emissions), whereas N2O emissions dominated in winter (67-95% of CO2-e emissions) when overall CO2-e emissions were low. Our study highlights the importance of seasonal N2O contributions, particularly when conditions driving CH4 emissions may be less favourable. For the accurate upscaling of N2O and CH4 flux to annual rates, we need to assess relative contributions of individual trace gases to net CO2-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 N2O and CH4 emissions.  相似文献   

7.
Peatlands play an important role in emissions of the greenhouse gases CO2, CH4 and N2O, which are produced during mineralization of the peat organic matter. To examine the influence of soil type (fen, bog soil) and environmental factors (temperature, groundwater level), emission of CO2, CH4 and N2O and soil temperature and groundwater level were measured weekly or biweekly in loco over a one-year period at four sites located in Ljubljana Marsh, Slovenia using the static chamber technique. The study involved two fen and two bog soils differing in organic carbon and nitrogen content, pH, bulk density, water holding capacity and groundwater level. The lowest CO2 fluxes occurred during the winter, fluxes of N2O were highest during summer and early spring (February, March) and fluxes of CH4 were highest during autumn. The temporal variation in CO2 fluxes could be explained by seasonal temperature variations, whereas CH4 and N2O fluxes could be correlated to groundwater level and soil carbon content. The experimental sites were net sources of measured greenhouse gases except for the drained bog site, which was a net sink of CH4. The mean fluxes of CO2 ranged between 139 mg m−2 h−1 in the undrained bog and 206 mg m−2 h−1 in the drained fen; mean fluxes of CH4 were between −0.04 mg m−2 h−1 in the drained bog and 0.05 mg m−2 h−1 in the drained fen; and mean fluxes of N2O were between 0.43 mg m−2 h−1 in the drained fen and 1.03 mg m−2 h−1 in the drained bog. These results indicate that the examined peatlands emit similar amounts of CO2 and CH4 to peatlands in Central and Northern Europe and significantly higher amounts of N2O.  相似文献   

8.
Soil oxygen (O2) availability influences nitrification and denitrification, the major biological processes responsible for nitrous oxide (N2O) production and emissions from soil. In this study O2-specific planar optodes were used to visualise O2 distribution with high spatial and temporal resolution in soils in which the same amount of solid fraction of pig manure had been distributed in three different ways (mixed, layered, single patch) and which were maintained at a water potential of −5 kPa (corresponding to 91% of water-filled pore space). In parallel, the greenhouse gas emissions (N2O, CO2 and CH4) from soil at high temporal resolution were monitored. At the end of the incubations, vertical profiles of mineral nitrogen (ammonium and nitrate) in the soil matrix were quantified. The optode results revealed that anoxia rapidly developed in zones with manure addition and gradually expanded to the entire soil during the 66-h experimental period. The anoxia in the soil developed more quickly as the heterogeneity of manure distribution decreased (from single patch to layered to mixed). The single patch distribution of manure solids delayed peak emission rates of both N2O and CO2, but stimulated the cumulative N2O emissions and reduced the cumulative CO2 fluxes. The faster the anoxia developed, the less the nitrification process appeared to contribute to N2O emissions. No treatment effects on CH4 emissions were observed. Combined high resolution imaging of O2 dynamics and measurements of N2O emission rates are essential to get a detailed understanding of how O2 availability regulates the distribution and coupling of denitrification and nitrification activity in soil. Such unique information on soil O2 dynamics could be used for further modelling and quantification of processes producing greenhouse gases from soil ecosystems.  相似文献   

9.
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, N2O, CH4 and CO2 fluxes were measured simultaneously in a winter barley field under the maize/barley rotation. The fluxes of NO and N2O from the control were very low, and N fertilization increased the emissions of NO and N2O. NO and N2O from N fertilization treatments showed different emission patterns: significant NO emissions but low N2O emissions in the winter season, and low NO emissions but significant N2O 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 N2O emissions. Fertilizer-derived NO-N and N2O-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. CH4 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 CH4 and resulted in positive emissions from the soil. CO2 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 CO2 emissions from the soil. N2O, CH4 and CO2 fluxes were positively correlated (P<0.01) with each other, whereas NO and CO2 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 CO2 stored in its aboveground parts from the soil-derived GWP in CO2 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 CO2 equivalent, respectively, in the barley season.  相似文献   

10.
We examined net greenhouse gas exchange at the soil surface in deciduous forests on soils with high organic contents. Fluxes of CO2, CH4 and N2O 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 CO2 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 CO2 m−2 yr−1). The average annual CH4 emission was almost 10 times larger at the undrained site (7.6±3.1 compared to 0.9±0.5 g CH4 m−2 yr−1 for the two drained sites). The average annual N2O emissions at the undrained site (0.1±0.05 g N2O 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 N2O m−2 yr−1). The temporal variation in forest floor CO2 release could be explained to a large extent by differences in groundwater table and air temperature, but little of the variation in the CH4 and N2O fluxes could be explained by these variables. The measured soil variables were only significant to explain for the within-site spatial variation in CH4 and N2O fluxes at the undrained swamp, and dark forest floor CO2 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 N2O 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   

11.
Elevated CO2 stimulates N2O emissions in permanent grassland   总被引：1，自引：1，他引：0  
To evaluate climate forcing under increasing atmospheric CO2 concentrations, feedback effects on greenhouse gases such as nitrous oxide (N2O) with a high global warming potential should be taken into account. This requires long-term N2O flux measurements because responses to elevated CO2 may vary throughout annual courses. Here, we present an almost 9 year long continuous N2O flux data set from a free air carbon dioxide enrichment (FACE) study on an old, N-limited temperate grassland. Prior to the FACE start, N2O emissions were not different between plots that were later under ambient (A) and elevated (E) CO2 treatments, respectively. However, over the entire experimental period (May 1998–December 2006), N2O emissions more than doubled under elevated CO2 (0.90 vs. 2.07 kg N2O-N ha−1 y−1 under A and E, respectively). The strongest stimulation occurred during vegetative growth periods in the summer when soil mineral N concentrations were low. This was surprising because based on literature we had expected the highest stimulation of N2O emissions due to elevated CO2 when mineral N concentrations were above background values (e.g. shortly after N application in spring). N2O emissions under elevated CO2 were moderately stimulated during late autumn–winter, including freeze–thaw cycles which occurred in the 8th winter of the experiment. Averaged over the entire experiment, the additional N2O emissions caused by elevated CO2 equaled 4738 kg CO2-equivalents ha−1, corresponding to more than half a ton (546 kg) of CO2 ha−1 which has to be sequestered annually to balance the CO2-induced N2O emissions. Without a concomitant increase in C sequestration under rising atmospheric CO2 concentrations, temperate grasslands may be converted into greenhouse gas sources by a positive feedback on N2O emissions. Our results underline the need to include continuous N2O flux measurements in ecosystem-scale CO2 enrichment experiments.  相似文献   

12.
Biochar produced from plant biomass through pyrolysis has been shown to be much more resistant to biodegradation in the soil as compared with the raw biomass, such as cereal straw that is routinely shredded and discharged on to farm fields in large amounts. Biochar application to soil has also been reported to decrease greenhouse gas (GHG) emissions, although the mechanisms are not fully understood. In this study, the emissions of three main GHGs (CO2, CH4, and N2O) and enzyme activities (urease, β-glycosidase, and dehydrogenase) were measured during a 100-day laboratory incubation of a Chernozemic soil amended with either straw or its biochar at rates of 0.67 and 1.68 % (based on the amount of C added) for the low and high rates, respectively. The biochar application dramatically reduced N2O emissions, but CO2 or CH4 emissions were not different, as compared with the un-amended soil. At the same C equivalent application rate, CO2 and N2O emission rates were greater while CH4 emission rates were lower in straw than in biochar application treatments. The activities of both the dehydrogenase and β-glycosidase significantly declined while that of urease significantly increased with the biochar as compared with the straw treatment. We conclude that pyrolysis of cereal straw prior to land application would significantly reduce CO2 and N2O emissions, in association with changed enzyme activities, while increasing the soil C pool through the addition of stable C in the form of biochar.  相似文献   

13.
It has been well documented that restored wetlands in the Prairie Pothole Region of North America do store carbon. However, the net benefit of carbon sequestration in wetlands in terms of a reduction in global warming forcing has often been questioned because of potentially greater emissions of greenhouse gases (GHGs) such as nitrous oxide (N2O) and methane (CH4). We compared gas emissions (N2O, CH4, carbon dioxide [CO2]) and soil moisture and temperature from eight cropland and eight restored grassland wetlands in the Prairie Pothole Region from May to October, 2003, to better understand the atmospheric carbon mitigation potential of restored wetlands. Results show that carbon dioxide contributed the most (90%) to net-GHG flux, followed by CH4 (9%) and N2O (1%). Fluxes of N2O, CH4, CO2, and their combined global warming potential (CO2 equivalents) did not significantly differ between cropland and grassland wetlands. The seasonal pattern in flux was similar in cropland and grassland wetlands with peak emissions of N2O and CH4 occurring when soil water-filled pore space (WFPS) was 40-60% and >60%, respectively; negative CH4 fluxes were observed when WFPS approached 40%. Negative CH4 fluxes from grassland wetlands occurred earlier in the season and were more pronounced than those from cropland sites because WFPS declined more rapidly in grassland wetlands; this decline was likely due to higher infiltration and evapotranspiration rates associated with grasslands. Our results suggest that restoring cropland wetlands does not result in greater emissions of N2O and CH4, and therefore would not offset potential soil carbon sequestration. These findings, however, are limited to a small sample of seasonal wetlands with relatively short hydroperiods. A more comprehensive assessment of the GHG mitigation potential of restored wetlands should include a diversity of wetland types and land-use practices and consider the impact of variable climatic cycles that affect wetland hydrology.  相似文献   

14.
Biologically derived emissions of carbon dioxide (CO2) and nitrous oxide (N2O) at 0 °C vary with soil depth during soil thawing. Micro-site soil properties, especially those which influence porosity and substrate availability, also vary with depth and may help explain gas emissions. Intact soil cores collected to a depth of 80 cm from an undisturbed prairie Mollisol in central North Dakota were uniformly subjected to distinct temperature steps during a simulated soil thaw (−15 to 5 °C) and sampled for CO2 and N2O emissions throughout the soil profile. Emission data were fit to a first order exponential equation (E = αeβT). Cores were then analyzed in 10 cm depth increments for micro-site properties including root length and mass, aggregation, and organic substrate availability (available, aggregate-protected and mineral-bound pools). Both CO2 and N2O emissions at 0 °C declined exponentially with depth. Emissions of CO2 and N2O at 0 °C were strongly related to root length (R2 = 0.80 and 0.76, respectively), root mass (R2 = 0.56 and 0.74), large macroaggregate mass (R2 = 0.63 and 0.54), and aggregate-protected organic matter (R2 > 0.57), while available organic matter was related to CO2 (R2 > 0.60) and not N2O. When CO2 and N2O emissions were normalized by available and aggregate-protected carbon pools, respectively, nutrient use efficiency increased significantly with depth. Results suggest CO2 and N2O emissions are (1) positively influenced by the rhizosphere and (2) differentially affected by substrate pool or location. CO2 emissions were more positively affected by available substrate, while N2O emissions were more positively affected by less labile, aggregate-protected substrate.  相似文献   

15.
The greenhouse gases CO2 and N2O emissions were quantified in a long-term experiment in northern France, in which no-till (NT) and conventional tillage (CT) had been differentiated during 32 years in plots under a maize–wheat rotation. Continuous CO2 and periodical N2O soil emission measurements were performed during two periods: under maize cultivation (April 2003–July 2003) and during the fallow period after wheat harvest (August 2003–March 2004). In order to document the dynamics and importance of these emissions, soil organic C and mineral N, residue decomposition, soil potential for CO2 emission and climatic data were measured. CO2 emissions were significantly larger in NT on 53% and in CT on 6% of the days. From April to July 2003 and from November 2003 to March 2004, the cumulated CO2 emissions did not differ significantly between CT and NT. However, the cumulated CO2 emissions from August to November 2003 were considerably larger for NT than for CT. Over the entire 331 days of measurement, CT and NT emitted 3160 ± 269 and 4064 ± 138 kg CO2-C ha−1, respectively. The differences in CO2 emissions in the two tillage systems resulted from the soil climatic conditions and the amounts and location of crop residues and SOM. A large proportion of the CO2 emissions in NT over the entire measurement period was probably due to the decomposition of old weathered residues. NT tended to emit more N2O than CT over the entire measurement period. However differences were statistically significant in only half of the cases due to important variability. N2O emissions were generally less than 5 g N ha−1 day−1, except for a few dates where emission increased up to 21 g N ha−1 day−1. These N2O fluxes represented 0.80 ± 0.15 and 1.32 ± 0.52 kg N2O-N ha−1 year−1 for CT and NT, respectively. Depending on the periods, a large part of the N2O emissions occurred was probably induced by nitrification, since soil conditions were not favorable for denitrification. Finally, for the period of measurement after 32 years of tillage treatments, the NT system emitted more greenhouses gases (CO2 and N2O) to the atmosphere on an annual basis than the CT system.  相似文献   

16.
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   

17.
The annual carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) dynamics were measured with static chambers on two organic agricultural soils with different soil characteristics. Site 1 had a peat layer of 30 cm, with an organic matter (OM) content of 74% in the top 20 cm. Site 2 had a peat layer of 70 cm but an OM content of only 40% in the top 20 cm. On both sites there were plots under barley and grass and also plots where the vegetation was removed. All soils were net sources of CO2 and N2O, but they consumed atmospheric CH4. Soils under barley had higher net CO2 emissions (830 g CO2-C m−2 yr−1) and N2O emissions (848 mg N2O-N m−2 yr−1) than those under grass (395 g CO2-C m−3 yr−1 and 275 mg N2O-N m−2 yr−1). Bare soils had the highest N2O emissions, mean 2350 mg N2O-N m−2 yr−1. The mean CH4 uptake rate from vegetated soils was 100 mg CH4-C m−3 yr−1 and from bare soils 55 mg CH4-C m−2 yr−1. The net CO2 emissions were higher from Site 2, which had a high peat bulk density and a low OM content derived from the addition of mineral soil to the peat during the cultivation history of that site. Despite the differences in soil characteristics, the mean N2O emissions were similar from vegetated peat soils from both sites. However, bare soils from Site 2 with mineral soil addition had N2O emissions of 2-9 times greater than those from Site 1. Site 1 consumed atmospheric CH4 at a higher rate than Site 2 with additional mineral soil. N2O emissions during winter were an important component of the N2O budget even though they varied greatly, ranging from 2 to 99% (mean 26%) of the annual emission.  相似文献   

18.
Forests are the largest C sink (vegetation and soil) in the terrestrial biosphere and may additionally provide an important soil methane (CH4) sink, whilst producing little nitrous oxide (N2O) when nutrients are tightly cycled. In this study, we determine the magnitude and spatial variation of soil–atmosphere N2O, CH4 and CO2 exchange in a Eucalyptus delegatensis forest in New South Wales, Australia, and investigate how the magnitude of the fluxes depends on the presence of N2-fixing tree species (Acacia dealbata), the proximity of creeks, and changing environmental conditions. Soil trace gas exchange was measured along replicated transects and in forest plots with and without presence of A. dealbata using static manual chambers and an automated trace gas measurement system for 2 weeks next to an eddy covariance tower measuring net ecosystem CO2 exchange. CH4 was taken up by the forest soil (?51.8 μg CH4-C m?2 h?1) and was significantly correlated with relative saturation (Sr) of the soil. The soil within creek lines was a net CH4 source (up to 33.5 μg CH4-C m?2 h?1), whereas the wider forest soil was a CH4 sink regardless of distance from the creek line. Soil N2O emissions were small (<3.3 μg N2O-N m?2 h?1) throughout the 2-week period, despite major rain and snowfall. Soil N2O emissions only correlated with soil and air temperature. The presence of A. dealbata in the understorey had no influence on the magnitude of CH4 uptake, N2O emission or soil N parameters. N2O production increased with increasing soil moisture (up to 50% Sr) in laboratory incubations and gross nitrification was negative or negligible as measured through 15N isotope pool dilution.The small N2O emissions are probably due to the limited capacity for nitrification in this late successional forest soil with C:N ratios >20. Soil–atmosphere exchange of CO2 was several orders of magnitude greater (88.8 mg CO2-C m?2 h?1) than CH4 and N2O, and represented 43% of total ecosystem respiration. The forest was a net greenhouse gas sink (126.22 kg CO2-equivalents ha?1 d?1) during the 2-week measurement period, of which soil CH4 uptake contributed only 0.3% and N2O emissions offset only 0.3%.  相似文献   

19.
Agricultural production in Turkey is not sustainable due to degradation and loss of croplands, rapid population growth, and inequitable economic growth (poverty and overconsumption). Degrading land uses and management practices disturb the life‐supporting biogeochemical cycles within croplands and between croplands and natural ecosystems by increasing emissions of greenhouse gases (GHGs: CO2, CH4, N2O, CFCs, and tropospheric O3), pollution of water, soil and air, loss of soil organic matter and biodiversity, erosion, salinization and desertification. Sustainability‐oriented management practices in croplands include maintenance of soil organic matter by conservation tillage and residue management, windbreaks, selection of crops ecologically adapted to local climate regimes, efficient crop rotation, enhancement of agrobiodiversity (e.g. intercropping and agroforestry), and adoption of proper drainage techniques. Implementation of these preventive and mitigative measures necessitates internalization of ecological principles into agricultural policy and management processes. This study explores the opportunities and limitations of agricultural sustainability in Turkey in a holistic manner. A multiple linear regression (MLR) model was developed to relate CO2 emissions to energy intensity (energy use/gross domestic product), affluence (gross domestic product/population) and population growth. Our MLR model with a high R2 of 97 per cent revealed that stabilization of human population growth, and increasing energy efficiency in economic growth are essential to decreasing GHG emissions and enhancing environmental quality. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

20.
CO2 and N2O are important greenhouse gases that are related to soil mineralization–immobilization turnover and nitrification. To explore the responses of CO2 and N2O emissions to N deposition in forests with different N transformation characteristics, CO2 and N2O fluxes were measured in two NH4NO3 fertilized plots. One plot was in a temperate pine plantation in Heilongjiang Liangshui National Nature Reserve (LS) with slow and minimally coupled mineralization–immobilization turnover and a high nitrification rate. The other plot was in a subtropical bamboo forest in the Fujian Daiyun Mountain National Nature Reserve (DY) in China with rapid and coupled mineralization–immobilization turnover but a low nitrification rate. The results showed that CO2 emissions in the DY with a high mineralization rate were greater than those in the LS. Cumulative CO2 emissions were significantly enhanced by N addition in DY, but in LS, they were not affected. The mean N2O fluxes in the control were 0.010 and 0.008 mg N m?2 hr?1 for LS and DY, respectively. High N addition stimulated N2O emissions in both LS and DY, but the response ratio for N2O flux in LS (8.6) was larger than that in DY (2.9). These results suggested that soils with rapid and coupled mineralization–immobilization turnover are beneficial to CO2 emissions and their positive response to N deposition. A high nitrification rate contributed to high N2O emissions and the sensitive response of N2O emissions to N deposition.  相似文献   

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