Elevated CO₂ concentration and nitrogen fertilisation effects on N₂O and CH₄ fluxes and biomass production of Phleum pratense on farmed peat soil     

Riitta Kettunen  Sanna Saarnio  Jouko Silvola 《Soil biology & biochemistry》2005,37(4):739-750

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   

CH₄ oxidation and N₂O emissions at varied soil water-filled pore spaces and headspace CH₄ concentrations     

M.I. Khalil  E.M. Baggs 《Soil biology & biochemistry》2005,37(10):1785-1794

Emission of N₂O and CH₄ oxidation rates were measured from soils of contrasting (30-75%) water-filled pore space (WFPS). Oxidation rates of ¹³C-CH₄ were determined after application of 10 μl ¹³C-CH₄ l⁻¹ (10 at. % excess ¹³C) to soil headspace and comparisons made with estimates from changes in net CH₄ emission in these treatments and under ambient CH₄ where no ¹³C-CH₄ had been applied. We found a significant effect of soil WFPS on ¹³C-CH₄ oxidation rates and evidence for oxidation of 2.2 μg ¹³C-CH₄ d⁻¹ occurring in the 75% WFPS soil, which may have been either aerobic oxidation occurring in aerobic microsites in this soil or anaerobic CH₄ oxidation. The lowest ¹³C-CH₄ oxidation rate was measured in the 30% WFPS soil and was attributed to inhibition of methanotroph activity in this dry soil. However, oxidation was lowest in the wetter soils when estimated from changes in concentration of ¹²⁺¹³C-CH₄. Thus, both methanogenesis and CH₄ oxidation may have been occurring simultaneously in these wet soils, indicating the advantage of using a stable isotope approach to determine oxidation rates. Application of ¹³C-CH₄ at 10 μl ¹³C-CH₄ l⁻¹ resulted in more rapid oxidation than under ambient CH₄ conditions, suggesting CH₄ oxidation in this soil was substrate limited, particularly in the wetter soils. Application of and (80 mg N kg soil⁻¹; 9.9 at.% excess ¹⁵N) to different replicates enabled determination of the respective contributions of nitrification and denitrification to N₂O emissions. The highest N₂O emission (119 μg ¹⁴⁺¹⁵N-N₂O kg soil⁻¹ over 72 h) was measured from the 75% WFPS soil and was mostly produced during denitrification (18.1 μg ¹⁵N-N₂O kg soil⁻¹; 90% of ¹⁵N-N₂O from this treatment). Strong negative correlations between ¹⁴⁺¹⁵N-N₂O emissions, denitrified ¹⁵N-N₂O emissions and ¹³C-CH₄ concentrations (r=−0.93 to −0.95, N₂O; r=−0.87 to −0.95, denitrified ¹⁵N-N₂O; P<0.05) suggest a close relationship between CH₄ oxidation and denitrification in our soil, the nature of which requires further investigation.  相似文献   

Denitrification in grass swards is increased under elevated atmospheric CO₂     

E.M Baggs  M RichterG Cadisch  U.A Hartwig 《Soil biology & biochemistry》2003,35(5):729-732

Emissions of N₂O and N₂ were measured from Lolium perenne L. swards under ambient (36 Pa) and elevated (60 Pa) atmospheric CO₂ at the Swiss free air carbon dioxide enrichment experiment following application of 11.2 g N m⁻² as ¹⁵NH₄¹⁵NO₃ or ¹⁴NH₄¹⁵NO₃ (1 at.% excess ¹⁵N). Total denitrification (N₂O+N₂) was increased under elevated pCO₂ with emissions of 6.2 and 19.5 mg ¹⁵N m⁻² measured over 22 d from ambient and elevated pCO₂ swards, respectively, supporting the hypothesis that increased belowground C allocation under elevated pCO₂ provides the energy for denitrification. Nitrification was the predominant N₂O producing process under ambient pCO₂ whereas denitrification was predominant under elevated pCO₂. The N₂-to-N₂O ratio was often higher under elevated pCO₂ suggesting that previous estimates of gaseous N losses based only on N₂O emissions have greatly underestimated the loss of N by denitrification.  相似文献   

Seasonal variation and fire effects on CH₄, N₂O and CO₂ exchange in savanna soils of northern Australia     

Stephen J. Livesley  Samantha GroverLindsay B. Hutley  Hizbullah JamaliKlaus Butterbach-Bahl  Benedikt FestJason Beringer  Stefan K. Arndt 《Agricultural and Forest Meteorology》2011,151(11):1440-1452

Tropical savanna ecosystems are a major contributor to global CO₂, CH₄ and N₂O 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 N₂O and CH₄ exchange. We measured soil CO₂, CH₄ and N₂O 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 N₂O exchange. Soil N₂O 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 NH₄⁺ in the months after the 2008 fire event, but no change in soil NO₃⁻. There was considerable nitrification in the early wet season but minimal nitrification at all other times.Savanna soil was generally a net CH₄ sink that equated to between −2.0 and −1.6 kg CH₄ 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 CH₄ uptake. There were short periods of soil CH₄ emission, up to 20 μg C m⁻² h⁻¹, likely to have been caused by termite activity in, or beneath, automated chambers. Soil CO₂ fluxes showed a strong bimodal seasonal pattern, increasing fivefold from the dry into the wet season. Soil moisture showed a weak relationship with soil CH₄ fluxes, but a much stronger relationship with soil CO₂ fluxes, explaining up to 70% of the variation in unburnt treatments. Australian savanna soils are a small N₂O source, and possibly even a sink. Annual soil CH₄ flux measurements suggest that the 1.9 million km² of Australian savanna soils may provide a C sink of between −7.7 and −9.4 Tg CO₂-e per year. This sink estimate would offset potentially 10% of Australian transport related CO₂-e emissions. This CH₄ sink estimate does not include concurrent CH₄ emissions from termite mounds or ephemeral wetlands in Australian savannas.  相似文献   

Short-term effects of clearfelling on soil CO₂, CH₄, and N₂O fluxes in a Sitka spruce plantation     

Argyro Zerva 《Soil biology & biochemistry》2005,37(11):2025-2036

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   

Seasonal changes in the spatial structures of N₂O, CO₂, and CH₄ fluxes from Acacia mangium plantation soils in Indonesia     

Ryota Konda  Seiichi Ohta  Joko Heriyanto 《Soil biology & biochemistry》2010,42(9):1512-1522

We evaluated the spatial structures of nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄) 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 N₂O and CO₂ 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 CH₄ 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 N₂O fluxes in A. mangium soils were higher than those reported for natural forest soils in Sumatra, while CO₂ and CH₄ 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. N₂O fluxes had strong spatial dependence with a range of about 18 m in both the drier and wetter seasons. Topography was associated with the N₂O 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 N₂O fluxes and they may have depended on litter amount distribution. CO₂ 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 CO₂ fluxes through their effects on microbial activities and fine root distribution in this A. mangium plantation.  相似文献   

Fluxes of CO₂, CH₄ and N₂O from drained organic soils in deciduous forests     

K. von Arnold  M. Nilsson  P. Weslien 《Soil biology & biochemistry》2005,37(6):1059-1071

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   

NO, N₂O, CH₄ and CO₂ fluxes in winter barley field of Japanese Andisol as affected by N fertilizer management     

Haiyan Chu  Yasukazu Hosen  Kazuyuki Yagi 《Soil biology & biochemistry》2007,39(1):330-339

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   

Can a mixed stand of N₂-fixing and non-fixing plants restrict N₂O emissions with increasing CO₂ concentration?     

Riitta Kettunen  Sanna Saarnio  Jouko Silvola 《Soil biology & biochemistry》2007,39(10):2538-2546

Initial effects of elevated atmospheric CO₂ concentration on N₂O fluxes and biomass production of timothy/red clover were studied in the laboratory. The experimental design consisted of two levels of atmospheric CO₂ (ca. 360 and 720 μmol CO₂ mol⁻¹) and two N fertilisation levels (5 and 10 g N m⁻²). There was a total of 36 mesocosms comprising sandy loam soil, which were equally distributed in four thermo-controlled greenhouses. In two of the greenhouses, the CO₂ concentration was kept at ambient concentration and in the other two at doubled concentration. Forage was harvested and the plants fertilised three times during the basic experiment, followed by harvest, a fertilisation with the double amount of nitrogen and rise of water level. Under elevated CO₂, harvestable and total aboveground dry biomass production of a mixed Trifolium/Phleum stand was increased at both N treatments compared to ambient CO₂. The N₂O flux rates under ambient CO₂ were significantly higher at both N treatments during the early growth of mixed Phleum/Trifolium mesocosms compared to the N₂O flux rate under elevated CO₂. However, when the conditions were favourable for denitrification at the end of the experiment, i.e. N availability and soil moisture were high enough, the elevated CO₂ concentration enhanced the N₂O efflux.  相似文献   

Fluxes of CO₂, CH₄, and N₂O in an alpine meadow affected by yak excreta on the Qinghai-Tibetan plateau during summer grazing periods   总被引：1，自引：0，他引：1  

Xingwu Lin  Shiping Wang  Xiuzhi Ma  Caiyun Luo  Gaoming Jiang 《Soil biology & biochemistry》2009,41(4):718-725

To assess the impacts of yak excreta patches on greenhouse gas (GHG) fluxes in the alpine meadow of the Qinghai-Tibetan plateau, methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O) 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 CH₄ 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 CH₄. The cumulative CO₂ emission for dung patches was about 36-50% higher than control plots during the experimental period in 2005 and 2006. The cumulative N₂O 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 CH₄ flux variation for urine patches and control plots, respectively. Soil temperature explained 40-75% of temporal variation of CO₂ emissions for all treatments. Temporal N₂O 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 CO₂ equivalents are limited under the moderate grazing intensity (1.45 yak ha⁻¹). However, the contributions of excreta patches to N₂O emissions are not negligible when estimating N₂O emissions in the grazing meadow. In this study, the N₂O 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   

N₂O emissions and product ratios of nitrification and denitrification as affected by freezing and thawing     

Pål Tore Mørkved  Peter Dörsch  Lars Reier Bakken 《Soil biology & biochemistry》2006,38(12):3411-3420

Agricultural soils contribute significantly to atmospheric nitrous oxide (N₂O). A considerable part of the annual N₂O emission may occur during the cold season, possibly supported by high product ratios in denitrification (N₂O/(N₂+N₂O)) and nitrification (N₂O-N/(NO₃⁻-N+NO₂⁻-N)) at low temperatures and/or in response to freeze-thaw perturbation. Water-soluble organic materials released from frost-sensitive catch crops and green manure may further increase winter emissions. We conducted short-term laboratory incubations under standardized moisture and oxygen (O₂) conditions, using nitrogen (N) tracers (¹⁵N) to determine process rates and sources of emitted N₂O after freeze-thaw treatment of soil or after addition of freeze-thaw extract from clover. Soil respiration and N₂O production was stimulated by freeze-thaw or addition of plant extract. The N₂O emission response was inversely related to O₂ concentration, indicating denitrification as the quantitatively prevailing process. Denitrification product ratios in the two studied soils (pH 4.5 and 7.0) remained largely unaltered by freeze-thaw or freeze-thaw-released plant material, refuting the hypothesis that high winter emissions are due to frost damage of N₂O reductase activity. Nitrification rates estimated by nitrate (NO₃⁻) pool enrichment were 1.5-1.8 μg NO₃-N g⁻¹ dw soil d⁻¹ in freeze-thaw-treated soil when incubated at O₂ concentrations above 2.3 vol% and one order of magnitude lower at 0.8 vol% O₂. Thus, the experiments captured a situation with severely O₂-limited nitrification. As expected, the O₂ stress at 0.8 vol% resulted in a high nitrification product ratio (0.3 g g⁻¹). Despite this high product ratio, only 4.4% of the measured N₂O accumulation originated from nitrification, reaffirming that denitrification was the main N₂O source at the various tested O₂ concentrations in freeze-thaw-affected soil. N₂O emission response to both freeze-thaw and plant extract addition appeared strongly linked to stimulation of carbon (C) respiration, suggesting that freeze-thaw-induced release of decomposable organic C was the major driving force for N₂O emissions in our soils, both by fuelling denitrifiers and by depleting O₂. The soluble C (applied as plant extract) necessary to induce a CO₂ and N₂O production rate comparable with that of freeze-thaw was 20-30 μg C g⁻¹ soil dw. This is in the range of estimates for over-winter soluble C loss from catch crops and green manure plots reported in the literature. Thus, freeze-thaw-released organic C from plants may play a significant role in freeze-thaw-related N₂O emissions.  相似文献   

Contribution of nitrification and denitrification to N₂O emissions from urine patches     

Mette S. Carter 《Soil biology & biochemistry》2007,39(8):2091-2102

Urine deposition by grazing livestock causes an immediate increase in nitrous oxide (N₂O) emissions, but the responsible mechanisms are not well understood. A nitrogen-15 (¹⁵N) labelling study was conducted in an organic grass-clover sward to examine the initial effect of urine on the rates and N₂O loss ratio of nitrification (i.e. moles of N₂O-N produced per moles of nitrate produced) and denitrification (i.e. moles of N₂O produced per moles of N₂O+N₂ produced). The effect of artificial urine (52.9 g N m⁻²) and ammonium solution (52.9 g N m⁻²) was examined in separate experiments at 45% and 35% water-filled pore space (WFPS), respectively, and in each experiment a water control was included. The N₂O loss derived from nitrification or denitrification was determined in the field immediately after application of ¹⁵N-labelled solutions. During the next 24 h, gross nitrification rates were measured in the field, whereas the denitrification rates were measured in soil cores in the laboratory. Compared with the water control, urine application increased the N₂O emission from 3.9 to 42.3 μg N₂O-N m⁻² h⁻¹, whereas application of ammonium increased the emission from 0.9 to 6.1 μg N₂O-N m⁻² h⁻¹. In the urine-affected soil, nitrification and denitrification contributed equally to the N₂O emission, and the increased N₂O loss resulted from a combination of higher rates and higher N₂O loss ratios of the processes. In the present study, an enhanced nitrification rate seemed to be the most important factor explaining the high initial N₂O emission from urine patches deposited on well-aerated soils.  相似文献   

Spatial and temporal variability in CH₄ and N₂O fluxes from a Scottish ombrotrophic peatland: Implications for modelling and up-scaling     

Kerry J. Dinsmore  Ute M. Skiba  Robert M. Rees 《Soil biology & biochemistry》2009,41(6):1315-1323

Peatlands typically exhibit significant spatial heterogeneity which can lead to large uncertainties when catchment scale greenhouse gas fluxes are extrapolated from chamber measurements (generally <1 m²). Here we examined the underlying environmental and vegetation characteristics which led to within-site variability in both CH₄ and N₂O emissions and the importance of such variability in up-scaling. We also consider within-site variation in the controls of temporal dynamics. Net annual emissions (and coefficients of variation) for CH₄ and N₂O were 1.06 kg ha⁻¹ y⁻¹ (300%) and 0.02 kg ha⁻¹ y⁻¹ (410%), respectively. The riparian zone was a significant CH₄ hotspot contributing ∼12% of the total catchment emissions whilst covering only ∼0.5% of the catchment area. In contrast to many other studies we found smaller CH₄ emissions and greater uptake in chambers containing either sedges or rushes. We also found clear differences in the drivers of temporal CH₄ dynamics across the site, e.g. water table was important only in chambers which did not contain aerenchymous plants. We suggest that depending on the heterogeneity of the site, flux models could be improved by incorporating a number of spatially distinct sub-models, rather than a single model parameterized using whole-catchment averages.  相似文献   

Emission of N₂O, N₂ and CO₂ from soil fertilized with nitrate: effect of compaction, soil moisture and rewetting     

R. Ruser  H. Flessa  G. Schmidt  J.C. Munch 《Soil biology & biochemistry》2006,38(2):263-274

Soil compaction and soil moisture are important factors influencing denitrification and N₂O emission from fertilized soils. We analyzed the combined effects of these factors on the emission of N₂O, N₂ and CO₂ from undisturbed soil cores fertilized with (150 kg N ha⁻¹) in a laboratory experiment. The soil cores were collected from differently compacted areas in a potato field, i.e. the ridges (ρ_D=1.03 g cm⁻³), the interrow area (ρ_D=1.24 g cm⁻³), and the tractor compacted interrow area (ρ_D=1.64 g cm⁻³), and adjusted to constant soil moisture levels between 40 and 98% water-filled pore space (WFPS).High N₂O emissions were a result of denitrification and occurred at a WFPS≥70% in all compaction treatments. N₂ production occurred only at the highest soil moisture level (≥90% WFPS) but it was considerably smaller than the N₂O-N emission in most cases. There was no soil moisture effect on CO₂ emission from the differently compacted soils with the exception of the highest soil moisture level (98% WFPS) of the tractor-compacted soil in which soil respiration was significantly reduced. The maximum N₂O emission rates from all treatments occurred after rewetting of dry soil. This rewetting effect increased with the amount of water added. The results show the importance of increased carbon availability and associated respiratory O₂ consumption induced by soil drying and rewetting for the emissions of N₂O.  相似文献   

The inhibitory effect of difluoromethane on CH₄ oxidation in reconstructed peat columns and side-effects on CO₂ and N₂O emissions at two water levels     

S. Vicca  H. Flessa  I.A. Janssens 《Soil biology & biochemistry》2009,41(6):1117-1123

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   

Land use effects on gross nitrogen mineralization, nitrification, and N₂O emissions in ephemeral wetlands     

Angela Bedard-Haughn  Amanda L. Matson  Dan J. Pennock 《Soil biology & biochemistry》2006,38(12):3398-3406

Stable ¹⁵N isotope dilution and tracer techniques were used in cultivated (C) and uncultivated (U) ephemeral wetlands in central Saskatchewan, Canada to: (1) quantify gross mineralization and nitrification rates and (2) estimate the relative proportion of N₂O emissions from these wetlands that could be attributed to denitrification versus nitrification-related processes. In-field incubation experiments were repeated in early May, mid-June and late July. Mean gross mineralization and nitrification rates (10.3 and 3.1 mg kg⁻¹ d⁻¹, respectively) did not differ between C and U wetlands on any given date. Despite these similarities, the mean NH₄⁺ pool size in the U wetlands (17.2 mg kg⁻¹) was two to three times that of the C wetlands (6.7 mg kg⁻¹) whereas the mean NO₃⁻ pool size in U wetlands (2.2 mg kg⁻¹) was less than half that of C wetlands (5.8 mg kg⁻¹). Mean N₂O emissions from the C wetlands decreased from 112.8 to 17.0 ng N₂O m² s⁻¹ from May to July, whereas mean U-wetland N₂O emissions ranged only from 31.8 to 51.1 ng N₂O m² s⁻¹ over the same period. This trend is correlated to water-filled pore space in C wetlands, demonstrating a soil moisture influence on emissions. Denitrification is generally considered the dominant emitter of N₂O under anaerobic conditions, but in the C wetlands, only 49% of the May emissions could be directly attributed to denitrification, decreasing to 29% in July. In contrast, more than 75% of the N₂O emissions from the U wetlands arose from denitrification of the soil NO₃⁻ pool throughout the season. These land use differences in emission sources and rates should be taken into consideration when planning management strategies for greenhouse gas mitigation.  相似文献   

Nitrous oxide production by nitrification and denitrification in soil aggregates as affected by O₂ concentration     

K Khalil  P Renault 《Soil biology & biochemistry》2004,36(4):687-699

Nitrous oxide emitted by soils can be produced either by denitrification in anoxic conditions or by nitrification in presence of O₂. The relative importance of the two processes, particularly under varied partial pressures of O₂, is not always known. This paper focuses on the influence of O₂ concentration on N₂O production by nitrification and denitrification in an arable Orthic Luvisol. Soil aggregates (2-3 mm size), water unsaturated, received 116 mg N kg⁻¹ as ammonium sulphate labelled with ¹⁵N and were incubated during 14 days at different O₂ partial pressures: 0, 0.35, 0.76, 1.5, 4.3 and 20.4 kPa. A ¹⁵N tracing technique was used to quantify nitrification and denitrification rates. ¹⁵N₂O and ¹⁵N₂ were measured. Oxygen pressure appeared to strongly influence both nitrification and denitrification rates and also N₂O emissions. Nitrification rates were reduced by a factor of 6-9 when O₂ decreased from 20.4 to 0.35 kPa. They were highly correlated with O₂ consumption rates. Denitrification mainly occurred in complete anoxic conditions. The proportion of N₂O emitted by denitrification was estimated by two independent methods: one based on ¹⁵N tracing using isotope composition of NH₄, NO₃ and N₂O, the other based on the measurement of the ¹⁵N₂O:¹⁵N₂ ratio. The two methods gave close results. The highest N₂O emissions were obtained under complete anoxic conditions and were due to denitrification. However, N₂O emissions almost as important were obtained at day 14 with 1.5 kPa O₂ pressure, and they were due to nitrification. Nitrification was the main source of N₂O at O₂ concentrations greater than 0.35 kPa. The amounts of N₂O-N emitted by nitrification were linearly related to the amounts of N nitrified, but the slope of the regression was highly dependent on O₂ concentration: it varied from 0.16 to 1.48% when O₂ concentration was reduced from 20.4 to 0.76 kPa. Emissions of N₂O by nitrification may then be quite significant if nitrification occurs at a reduced O₂ concentration.  相似文献   

Emission of CO₂, CH₄ and N₂O from lakeshore soils in an Antarctic dry valley     

E.G. Gregorich  D.W. Hopkins  A.D. Sparrow  P. Novis  P. Rochette 《Soil biology & biochemistry》2006,38(10):3120-3129

We measured soil profile concentrations and emission of CO₂, CH₄ and N₂O from soils along a lakeshore in Garwood Valley, Antarctica, to assess the extent and biogeochemical significance of biogenic gas emission to C and N cycling processes. Simultaneous emission of all three gases from the same site indicated that aerobic and anaerobic processes occurred in different layers or different parts of each soil profile. The day and location of high gas concentrations in the soil profile corresponded to those having high gas emission, but the pattern of concentration with depth in the soil profile was not consistent across sites. That the highest gas concentrations were not always in the deepest soil layer suggests either limited production or gas diffusion in the deeper layers. Emission of CO₂ was as high as 47 μmol m⁻² min⁻¹ and was strongly related to soil temperature. Soil respiration differed significantly according to location on the lakeshore, suggesting that factors other than environmental variables, such as the amount and availability of O₂ and nutrients, play an important role in C mineralization processes in these soils. High surface emission (maximum: 15 μmol m⁻² min⁻¹) and profile gas concentration (maximum: 5780 μL L⁻¹) of CH₄ were at levels comparable to those in resource-rich temperate ecosystems, indicating an active indigenous population of methanogenic organisms. Emission of N₂O was low and highly variable, but the presence of this gas and NO₃ in some of the soils suggest that denitrification and nitrification occur there. No significant relationships between N₂O emission and environmental variables were found. It appears that considerable C and N turnover occurs in the lakeshore soils, and accurate accounting will require measurements of aerobic and anaerobic mineralization. The production and emission of biogenic gases confirm the importance of these soils as hotspots of biological activity in the dry valleys and probable reservoirs of biological diversity.  相似文献   

Influence of warming and enchytraeid activities on soil CO₂ and CH₄ fluxes     

M.J.I. Briones  J. Poskitt 《Soil biology & biochemistry》2004,36(11):1851-1859

To determine the sum of ‘direct’ and ‘indirect’ effects of climatic change on enchytraeid activity and C fluxes from an organic soil we assessed the influence of temperature (4, 10 and 15 °C incubations) on enchytraeid populations and soil CO₂ and CH₄ fluxes over 116 days. Moisture was maintained at 60% of soil dry weight during the experimental period and measurements of enchytraeid biomass and numbers, and CO₂ and CH₄ fluxes were made after 3, 16, 33, 44, 65, 86 and 116 days. Enchytraeid population numbers and biomass increased in all temperature treatments with the greatest increase produced at 15 °C (to over threefold initial values by day 86). Results also showed that enchytraeid activity increased CO₂ fluxes by 10.7±4.5, 3.4±4.0 and 26.8±2.6% in 4, 10 and 15 °C treatments, respectively, with the greatest CO₂ production observed at 15 °C for the entire 116 day incubation period (P<0.05). The soil respiratory quotient analyses at lower temperatures (i.e. 4-10 °C) gave a Q₁₀ of 1.7 and 1.9 with and without enchytraeids, respectively. At temperatures above 10 °C (i.e. 10-15 °C) Q₁₀ significantly increased (P<0.01) and was 25% greater in the presence of enchytraeids (Q₁₀=3.4) than without (Q₁₀=2.6). In contrast to CO₂ production, no significant relationships were observed between net CH₄ fluxes and temperature and only time showed a significant effect on CH₄ production (P<0.01).Total soil CO₂ production was positively linked with enchytraeid biomass and mean soil CO₂-C production was 77.01±6.05 CO₂-C μg mg enchytraeid tissue⁻¹ day⁻¹ irrespective of temperature treatment. This positive relationship was used to build a two step regression model to estimate the effects of temperature on enchytraeid biomass and soil CO₂ respiration in the field. Predictions of potential CO₂ production were made using enchytraeid biomass data obtained in the field from two upland grassland sites (Sourhope and Great Dun Fell at the Moor House Nature Reserve, both in the UK). The findings of this work suggest that a 5 °C increase in atmospheric temperature above mean ambient temperature could have the potential to produce a significant increase in enchytraeid biomass resulting in a near twofold increase in soil CO₂ release from both soil types. The interaction between temperature and soil biology will clearly be an important determinant of soil respiration responses to global warming.  相似文献   

Temporal and spatial dynamics of soil solution C and N concentrations during Lolium perenne L. sward establishment and the effects of elevated CO₂ and N additions     

P.W. Hill  D.L. Jones  J.F. Farrar 《Soil biology & biochemistry》2006,38(6):1290-1297

There is now clear evidence for a prolonged increase in atmospheric CO₂ concentrations and enrichment of the biosphere with N. Understanding the fate of C in the plant-soil system under different CO₂ and N regimes is therefore of considerable importance in predicting the environmental effects of climate change and in predicting the sustainability of ecosystems. Swards of Lolium perenne were grown from seed in a Eutric Cambisol at either ambient (ca. 350 μmol mol⁻¹) or elevated (700 μmol mol⁻¹) atmospheric pCO₂ and subjected to two inorganic N fertilizer regimes (no added N and 70 kg N ha⁻¹ month⁻¹). After germination, soil solution concentrations of dissolved organic C (DOC), dissolved inorganic N (DIN), dissolved organic N (DON), phenolics and H⁺ were measured at five depths down the soil profile over 3 months. The exploration of soil layers down the soil profile by roots caused transient increases in soil solution DOC, DON and phenolic concentrations, which then subsequently returned to lower quasi-stable concentrations. In general, the addition of N tended to increase DOC and DON concentrations while exposure to elevated pCO₂ had the opposite effect. These treatment effects, however, gradually diminished over the duration of the experiment from the top of the soil profile downwards. The ambient pCO₂ plus added N regime was the only treatment to maintain a notable difference in soil solution solute concentration, relative to other treatments. This effect on soil solution chemistry appeared to be largely indirect resulting from increased plant growth and a decrease in soil moisture content. Our results show that although plant growth responses to elevated pCO₂ are critically dependent upon N availability, the organic chemistry of the soil solution is relatively insensitive to changes in plant growth once the plants have become established.  相似文献