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1.
In anoxic salt marsh sediments of Sapelo Island, GA, USA, the vertical distribution of CH4 production was measured in the upper 20 cm of surface sediments in ten locations. In one section of high marsh sediments,
the concentration and oxidation of acetate in sediment porewaters and the rate and amount of14C acetate and14CO2 incorporation into cellular lipids of the microbial population were investigated. CH4 production rates ranged from <1 to 493 nM CH4 gram sediment−1 day−1 from intact subcores incubated under nitrogen. Replacement with H2 stimulated the rate of methane release up to nine fold relative to N2 incubations. Rates of lipid synthesis from CO2 averaged 39.2 ×10−2nanomoles lipid carbon cm3 sediment−1 hr−1, suggesting that CO2 may be an important carbon precursor for microbial membrane synthesis in marsh sediments under anoxic conditions. Qualitative
measurements of lipid synthesis rates from acetate were found to average 8.7 × 10−2 nanomoles. Phospholipids were the dominant lipids synthesized by both substrates in sediment cores, accounting for an average
of 76.6% of all lipid radioactivity. Small amounts of ether lipids indicative of methanogenic bacteria were observed in cores
incubated for 7 days, with similar rates of synthesis for both CO2 and acetate. The low rate of ether lipid synthesis suggests that either methanogen lipid biosynthesis is very slow or that
methanogens represent a small component of total microbial lipid synthesis in anoxic sediments.
present address: The University of Maryland,, Chesapeake Biological Laboratory, Box 38, Solomons, MD 20688, USA 相似文献
2.
The abundance and distribution of dissolved CH4 were determined from 1987–1990 in Lake Fryxell, Antarctica, an amictic, permanently ice-covered lake in which solute movement
is controlled by diffusion. CH4 concentrations were < 1 υM in the upper oxic waters, but increased below the oxycline to 936 μM at 18 m. Sediment CH4 was 1100 μmol (1 sed)−1 in the 0–5 cm zone. Upward flux from the sediment was the source of the CH4, NH4
+, and DOC in the water column; CH4 was 27% of the DOC+CH4 carbon at 18 m. Incubations with surficial sediments indicated that H14CO3
− reduction was 0.4 μmol (1 sed)−1 day−1 or 4× the rate of acetate fermentation to CH4. There was no measurable CH4 production in the water column. However, depth profiles of CH4, NH4, and DIC normalized to bottom water concentrations demonstrated that a significant CH4 sink was evident in the anoxic, sulfate-containing zone of the water column (10–18 m). The δ13CH4 in this zone decreased from −72 % at 18 m to −76% at 12 m, indicating that the consumption mechanism did not result in an
isotopic enrichment of 13CH4. In contrast, δ13CH4 increased to −55 % at 9 m due to aerobic oxidation, though this was a minor aspect of the CH4 cycle. The water column CH4 profile was modeled by coupling diffusive flux with a first order consumption term; the best-fit rate constant for anaerobic
CH4 consumption was 0.012 yr−1. On a total carbon basis, CH4 consumption in the anoxic water column exerted a major effect on the flux of carbonaceous material from the underlying sediments
and serves to exemplify the importance of CH4 to carbon cycling in Lake Fryxell. 相似文献
3.
This study provides some results about microbial activity in salt marsh sediments. Microbial activity was determined by profiling
extracellular enzyme activities in three Tagus estuary marshes and in two sediments horizons: surface layer (0–2 cm) and depth
(8–10 cm). Five enzymatic activities were examined (β-glucosidase, cellulase, alkaline phosphatase, potential nitrification and nitrate reductase). All extracellular enzymatic
activities were highest in the surface layer and decreased with depth. β-glucosidase and alkaline phosphatase prevailed both in surface sediments (1150 and 1200 ηmol h−1 g−1, respectively) and in deeper sediments (150 and 200 ηmol h−1 g−1, respectively). Microbial activities differed significantly between salt marshes. The marsh location in the estuary seemed
to contribute to these differences: marshes located in the proximity of urbanised and industrial areas had higher microbial
activities. 相似文献
4.
Catabolic diversity of periphyton and detritus microbial communities in a subtropical wetland 总被引:1,自引:0,他引:1
The catabolic diversity of wetland microbial communities may be a sensitive indicator of nutrient loading or changes in environmental
conditions. The objectives of this study were to assess the response of periphyton and microbial communities in water conservation
area-2a (WCA-2a) of the Everglades to additions of C-substrates and inorganic nutrients. Carbon dioxide and CH4 production rates were measured using 14 days incubation for periphyton, which typifies oligotrophic areas, and detritus,
which is prevalent at P-impacted areas of WCA-2a. The wetland was characterized by decreasing P levels from peripheral to
interior, oligotrophic areas. Microbial biomass and N mineralization rates were higher for oligotrophic periphyton than detritus.
Methane production rates were also higher for unamended periphyton (80 mg CH4-C kg−1 d−1) than detritus (22 mg CH4-C kg−1 d−1), even though the organic matter content was higher for detritus (80%) than periphyton (69%). Carbon dioxide production for
unamended periphyton (222 mg CO2-C kg−1 d−1) was significantly greater than unamended detritus (84 mg CO2-C kg−1 d−1). The response of the heterotrophic microbial community to added C-substrates was related to the nutrient status of the wetland,
as substrate-induced respiration (SIR) was higher for detritus than periphyton. Amides and polysaccharides stimulated SIR
more than other C-substrates, and methanogenesis was greater contributor to SIR for periphyton than detritus. Inorganic P
addition stimulated CO2 and CH4 production for periphyton but not detritus, indicating a P limitation in the interior areas of WCA-2a. Continued nutrient
loading into oligotrophic areas of WCA-2a or enhanced internal nutrient cycling may stimulate organic matter decomposition
and further contribute to undesirable changes to the Everglades ecosystem caused by nutrient enrichment. 相似文献
5.
Flowthrough reactor flasks are described that allow continuous low-level nutrient input to mixed anoxic sediments without dilution of the sediment. The flasks were tested by simulating sulfate inputs into sediments collected from a freshwater eutrophic lake. After an initial 2-day adaptation within the reactor system, rates of methane production and sulfate consumption were constant for the duration of a 12-day incubation. A sulfate input rate of 0.15 mmol liter of sediment−1 day−1 resulted in an equivalent rate of sulfate removal, which was unaffected by inputs of acetate (1.0 mmol liter of sediment−1 day−1). The rate of methane production in control reactors, 0.18 mmol liter of sediment−1 day−1, was doubled by the addition of acetate, whereas sulfate consumption was only stimulated by additions of high concentrations of sulfate plus acetate (1.5 and 1.0 mmol liter of sediment−1 day−1, respectively). The reactor system appears to be effective in maintaining the balance between sulfate reduction and methane production in freshwater sediments and is potentially useful for study of the response of sediment populations to varying inputs of naturally occurring substrates, selected inhibitors, or xenobiotic compounds. 相似文献
6.
Species composition affects the carbon turnover and the formation and emission of the greenhouse gas methane (CH4) in wetlands. Here we investigate the individual effects of vascular plant species on the carbon cycling in a wetland ecosystem.
We used a novel combination of laboratory methods and controlled environment facilities and studied three different vascular
plant species (Eriophorum vaginatum, Carex rostrata and Juncus effusus) collected from the same wetland in southern Sweden. We found distinct differences in the functioning of these wetland sedges
in terms of their effects on carbon dioxide (CO2) and CH4 fluxes, bubble emission of CH4, decomposition of 14C-labelled acetate into 14CH4 and 14CO2, rhizospheric oxidation of CH4 to CO2 and stimulation of methanogenesis through root exudation of substrate (e.g., acetate). The results show that the emission
of CH4 from peat–plant monoliths was highest when the vegetation was dominated by Carex (6.76 mg CH4 m−2 h−1) than when it was dominated by Eriophorum (2.38 mg CH4 m−2 h−1) or Juncus (2.68 mg CH4 m−2 h−1). Furthermore, the CH4 emission seemed controlled primarily by the degree of rhizospheric CH4 oxidation which was between 20 and 40% for Carex but >90% for both the other species. Our results point toward a direct and very important linkage between the plant species
composition and the functioning of wetland ecosystems and indicate that changes in the species composition may alter important
processes relating to controls of and interactions between greenhouse gas fluxes with significant implications for feedback
mechanisms in a changing climate as a result. 相似文献
7.
Substrates for Sulfate Reduction and Methane Production in Intertidal Sediments 总被引:16,自引:12,他引:4 下载免费PDF全文
The activity of and potential substrates for methane-producing bacteria and sulfate-reducing bacteria were examined in marsh, estuary, and beach intertidal sediments. Slow rates of methane production were detected in all sediments, although rates of sulfate reduction were 100- to 1,000-fold higher. After sulfate was depleted in sediments, the rates of methane production sharply increased. The addition of methylamine stimulated methanogenesis in the presence of sulfate, and [14C]methylamine was rapidly converted to 14CH4 and 14CO2 in freshly collected marsh sediment. Acetate, hydrogen, or methionine additions did not stimulate methanogenesis. [methyl-14C]methionine and [2-14C]acetate were converted to 14CO2 and not to 14CH4 in fresh sediment. No reduction of 14CO2 to 14CH4 occurred in fresh sediment. Molybdate, an inhibitor of sulfate reduction, inhibited [2-14C]acetate metabolism by 98.5%. Fluoracetate, an inhibitor of acetate metabolism, inhibited sulfate reduction by 61%. These results suggest that acetate is a major electron donor for sulfate reduction in marine sediments. In the presence of high concentrations of sulfate, methane may be derived from novel substrates such as methylamine. 相似文献
8.
The flux of CO2 and CH4 from lakes and rivers in arctic Alaska 总被引:5,自引:2,他引:3
Partial pressures of CO2 and CH4 were measured directly or calculated from pH and alkalinity or DIC measurements for 25 lakes and 4 rivers on the North Slope
of Alaska. Nearly all waters were super-saturated with respect to atmospheric pressures of CO2 and CH4. Gas fluxes to the atmosphere ranged from −6.5 to 59.8 mmol m−2 d−1 for CO2 and from 0.08 to 1.02 mmol m−2 d−1 for CH4, and were uncorrelated with latitude or lake morphology. Seasonal trends include a buildup of CO2 and CH4 under ice during winter, and often an increased CO2 flux rate in August due to partial lake turnover. Nutrient fertilization experiments resulted in decreased CO2 release from a lake due to photosynthetic uptake, but no change in CO2 release from a river due to the much faster water renewal time. In lakes and rivers the groundwater input of dissolved CO2 and CH4 is supplemented by in-lake respiration of dissolved and particulate carbon washed in from land. The release of carbon from
aquatic systems to the atmosphere averaged 24 g C m−2 y−1, and in coastal areas where up to 50% of the surface area is water, this loss equals frac 1/5 to 1/2 of the net carbon accumulation
rates estimated for tundra. 相似文献
9.
Abstract
In acidic mining-impacted lake sediments, the microbial reduction of Fe(III) is the dominant electron-accepting process, whereas
the reduction of sulfate seems to be restricted to a narrow sediment zone of elevated pH and lower amounts of total and reactive
iron. To evaluate the microbial heterogeneity and the commensal interactions of the microbial community, the flow of supplemental
carbon and reductant was evaluated in four different zones of the sediment in anoxic microcosms at the in situ temperature of 12°C. Substrate consumption, product formation, and the potential to reduce Fe(III) and sulfate were similar
with both upper and lower sediment zones. In the upper acidic iron-rich sediment zone, the rate of Fe(II) formation 204 nmol
ml−1 d−1 was enhanced to 833 nmol ml−1 d−1 and 462 nmol ml−1 d−1 by supplemental glucose and H2, respectively. Supplemental lactate and acetate were not consumed under acidic conditions and decreased the rate of Fe(II)
formation to 130 nmol ml−1 d−1 and 52 nmol ml−1 d−1, respectively. When the pH of the upper sediment increased above pH 5, acetate-dependent reduction of sulfate was initiated
even though the pool of Fe(III) was not depleted. In deeper sediment zones with elevated pH, the rapid consumption of acetate
was always coincident to a decrease in the concentration of sulfate and soluble Fe(II), indicating the formation of Fe(II)
sulfides. Although the reduction of Fe(III) was still an ongoing process in deeper sediment zones, the formation of Fe(II)
was only slightly enhanced by the consumption of glucose or cellobiose, but not by H2 or acetate. H2-utilizing acetogens seemed to be involved in the consumption of H2. These collective results indicated (i) that the reduction of Fe(III) predominated over the reduction of sulfate as long
as the sediment remained acidic and carbon-limited, and (ii) that the sulfate-reducing microbiota in this heterogeneous sediment
were better adapted to the geochemical gradients present than were other neutrophilic dissimilatory Fe(III) reducers.
Received: 17 February 2000; Accepted: 22 June 2000; Online Publication: 28 August 2000 相似文献
10.
Anaerobic bioconversion of cellulose by Ruminococcus albus, Methanobrevibacter smithii, and Methanosarcina barkeri 总被引:1,自引:0,他引:1
A system is described that combines the fermentation of cellulose to acetate, CH4, and CO2 by Ruminococcus albus and Methanobrevibacter smithii with the fermentation of acetate to CH4 and CO2 by Methanosarcina barkeri to convert cellulose to CH4 and CO2. A cellulose-containing medium was pumped into a co-culture of the cellulolytic R. albus and the H2-using methanogen, Mb. smithii. The effluent was fed into a holding reservoir, adjusted to pH 4.5, and then pumped into a culture of Ms. barkeri maintained at constant volume by pumping out culture contents. Fermentation of 1% cellulose to CH4 and CO2 was accomplished during 132 days of operation with retention times (RTs) of the Ms. barkeri culture of 7.5–3.8 days. Rates of acetate utilization were 9.5–17.3 mmol l−1 day−1 and increased with decreasing RT. The K
s for acetate utilization was 6–8 mM. The two-stage system can be used as a model system for studying biological and physical
parameters that influence the bioconversion process. Our results suggest that manipulating the different phases of cellulose
fermentation separately can effectively balance the pH and ionic requirements of the acid-producing phase with the acid-using
phase of the overall fermentation.
Received: 7 December 1999 / Received revision: 28 April 2000 / Accepted: 19 May 2000 相似文献
11.
Algesten G Sobek S Bergström AK Jonsson A Tranvik LJ Jansson M 《Microbial ecology》2005,50(4):529-535
We measured sediment production of carbon dioxide (CO2) and methane (CH4) and the net flux of CO2 across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were
made in situ under ambient light conditions. The flux of CO2 between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m−2 day−1 from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated
to dissolved organic carbon (DOC) concentration in the water (r2 = 0.61). The net flux of CO2 across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed
layer (r2 = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration.
Lakes with DOC concentrations <5.6 mg L−1 had net consumption of CO2 in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic
(<2.6 mg L−1) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In
addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water
column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources. 相似文献
12.
One-carbon metabolism in methanogens: evidence for synthesis of a two-carbon cellular intermediate and unification of catabolism and anabolism in Methanosarcina barkeri 总被引:18,自引:15,他引:3 下载免费PDF全文
One-carbon metabolic transformations associated with cell carbon synthesis and methanogenesis were analyzed by long- and short-term 14CH3OH or 14CO2 incorporation studies during growth and by cell suspensions. 14CH3OH and 14CO2 were equivalently incorporated into the major cellular components (i.e., lipids, proteins, and nucleic acids) during growth on H2-CO2-methanol. 14CH3OH was selectively incorporated into the C-3 of alanine with decreased amounts fixed in the C-1 and C-2 positions, whereas 14CO2 was selectively incorporated into the C1 moiety with decreasing amounts assimilated into the C-2 and C-3 atoms. Notably, 14CH4 and [3-14C]alanine synthesized from 14CH3OH during growth shared a common specific activity distinct from that of CO2 or methanol. Cell suspensions synthesized acetate and alanine from 14CO2. The addition of iodopropane inhibited acetate synthesis but did not decrease the amount of 14CH3OH or 14CO2 fixed into one-carbon carriers (i.e., methyl coenzyme M or carboxydihydromethanopterin). Carboxydihydromethanopterin was only labeled from 14CH3OH in the absence of hydrogen. Cell extracts catalyzed the synthesis of acetate from 14CO (~1 nmol/min per mg of protein) and an isotopic exchange between CO2 or CO and the C-1 of pyruvate. Acetate synthesis from 14CO was stimulated by methyl B12 but not by methyl tetrahydrofolate or methyl coenzyme M. Methyl coenzyme M and coenzyme M were inhibitory to acetate synthesis. Cell extracts contained high levels of phosphotransacetylase (>6 μmol/min per mg of protein) and acetate kinase (>0.14 μmol/min per mg of protein). It was not possible to distinguish between acetate and acetyl coenzyme A as the immediate product of two-carbon synthesis with the methods employed. 相似文献
13.
Greenhouse gas fluxes from the eutrophic Temmesjoki River and its Estuary in the Liminganlahti Bay (the Baltic Sea) 总被引:2,自引:0,他引:2
Hanna Silvennoinen Anu Liikanen Jaana Rintala Pertti J. Martikainen 《Biogeochemistry》2008,90(2):193-208
We studied concentrations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in the eutrophic Temmesjoki River and Estuary in the Liminganlahti Bay in 2003–2004 and evaluated the atmospheric fluxes
of the gases based on measured concentrations, wind speeds and water current velocities. The Temmesjoki River was a source
of CO2, CH4 and N2O to the atmosphere, whereas the Liminganlahti Bay was a minor source of CH4 and a minor source or a sink of CO2 and N2O. The results show that the fluxes of greenhouse gases in river ecosystems are highly related to the land use in its catchment
areas. The most upstream river site, surrounded by forests and drained peatlands, released significant amounts of CO2 and CH4, with average fluxes of 5,400 mg CO2–C m−2 d−1 and 66 mg CH4–C m−2 d−1, and concentrations of 210 μM and 345 nM, respectively, but N2O concentrations, at an average of 17 nM, were close to the atmospheric equilibrium concentration. The downstream river sites
surrounded by agricultural soils released significant amounts of N2O (with an average emission of 650 μg N2O–N m−2 d−1 and concentration of 22 nM), whereas the CO2 and CH4 concentrations were low compared to the upstream site (55 μM and 350 nM). In boreal regions, rivers are partly ice-covered
in wintertime (approximately 5 months). A large part of the gases, i.e. 58% of CO2, 55% of CH4 and 36% of N2O emissions, were found to be released during wintertime from unfrozen parts of the river. 相似文献
14.
Richard D. Bowden Mark S. Castro Jerry M. Melillo Paul A. Steudler John D. Aber 《Biogeochemistry》1993,21(2):61-71
Fluxes of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) between soils and the atmosphere were measured monthly for one year in a 77-year-old temperate hardwood forest following
a simulated hurricane blowdown. Emissions of CO2 and uptake of CH4 for the control plot were 4.92 MT C ha−1 y−1 and 3.87 kg C ha−1 y−1, respectively, and were not significantly different from the blowdown plot. Annual N2O emissions in the control plot (0.23 kg N ha−1 y−1) were low and were reduced 78% by the blowdown. Net N mineralization was not affected by the blowdown. Net nitrification
was greater in the blowdown than in the control, however, the absolute rate of net nitrification, as well as the proportion
of mineralized N that was nitrified, remained low. Fluxes of CO2 and CH4 were correlated positively to soil temperature, and CH, uptake showed a negative relationship to soil moisture. Substantial
resprouting and leafing out of downed or damaged trees, and increased growth of understory vegetation following the blowdown,
were probably responsible for the relatively small differences in soil temperature, moisture, N availability, and net N mineralization
and net nitrification between the control and blowdown plots, thus resulting in no change in CO2 or CH4 fluxes, and no increase in N2O emissions. 相似文献
15.
In this work, the main environmental factors determining the functioning of the microbial community of the alkaline low-mineralized Lake Beloe during the annual cycle were studied. High numbers of phototrophic and heterotrophic microorganisms (up to 107 cells/mL) and high rates of bacterial processes of organic matter (OM) production and destruction were observed. The highest rate of dark CO2 assimilation (up to 0.43 mg C dm−3 day−1), as well as the peak intensities of the terminal processes of sulfate reduction and methanogenesis (up to 1.81 mg S dm−3 day−1 and 0.96 μL CH4 dm−3 day−1, respectively), detected at the end of summer, were comparable to the rates of these processes detected in the bottom sediments of most soda lakes of the Transbaikal Region. Principal Component Analysis (PCA) allowed us to estimate the effect of environmental factors on the functioning of the microbial community of the alkaline Lake Beloe. Four main components, explaining 98% of variations, were detected. The first one (PC1) explained 63.5% of the seasonal variations and represented the temperature factor consisting of the temperatures of air, water, and bottom sediments. Water temperature and pH were the main contributors to the second component (PC2) and determine 26.2% of the seasonal variations. The PC3 (silt temperature and the concentration of organic matter) and PC4 (salt concentration) components were less important and explained only 6.5 and 2.2% of the variations, respectively. 相似文献
16.
Manabu Fukui Jungin Suh Yoshitaka Yonezawa Yoshikuni Urushigawa 《Ecological Research》1997,12(2):201-209
To clarify the anaerobic microbial interactions in the process of carbon mineralization in marine eutrophic environments,
the microbial sulfate reduction and methane production rates were examined in coastal marine sediments of Ise Bay, Japan,
in autumn 1990. Sulfate reduction rates (51–210 nmol ml−1 day−1 at 24°C) were much higher than the methane production ones (<1.78 nmol ml−1 day−1) in the surface sediments (top 2 cm) at the six stations surveyed (water depth: 10.7–23.3 m). Substrates for sulfate-reducing
bacteria (SRB) were estimated after the addition of a specific inhibitor for SRB (20 mmol l−1 molybdate) into the sediment slurry, from the substrate accumulation rates. In the presence of the inhibitor, sulfate reduction
was completely stopped and volatile fatty acids (mainly acetate) were accumulated, although hydrogen was not. Methane production
occurred markedly accompanied by consumption of the accumulated acetate from the third day after the addition of molybdate.
The maximum rate of methane production was 1.2–1.9 μmol ml−1 day−1, which was similar to those in highly polluted freshwater sediments such as the Tama River, Tokyo, Japan. These results show
that acetate is a common major substrate for sulfate reduction and methane production, and SRB competitively inhibit potential
acetoclastic methanogenesis in coastal sediments. Methanogens may potentially inhabit the sediments at low levels of population
density and activity. 相似文献
17.
The Impact of Nitrogen Placement and Tillage on NO, N2O, CH4 and CO2 Fluxes from a Clay Loam Soil 总被引:4,自引:0,他引:4
Xuejun J. Liu Arvin R. Mosier Ardell D. Halvorson Fusuo S. Zhang 《Plant and Soil》2006,280(1-2):177-188
To evaluate the impact of N placement depth and no-till (NT) practice on the emissions of NO, N2O, CH4 and CO2 from soils, we conducted two N placement experiments in a long-term tillage experiment site in northeastern Colorado in 2004.
Trace gas flux measurements were made 2–3 times per week, in zero-N fertilizer plots that were cropped continuously to corn
(Zea mays L.) under conventional-till (CT) and NT. Three N placement depths, replicated four times (5, 10 and 15 cm in Exp. 1 and 0,
5 and 10 cm in Exp. 2, respectively) were used. Liquid urea–ammonium nitrate (UAN, 224 kg N ha−1) was injected to the desired depth in the CT- or NT-soils in each experiment. Mean flux rates of NO, N2O, CH4 and CO2 ranged from 3.9 to 5.2 μg N m−2 h−1, 60.5 to 92.4 μg N m−2 h−1, −0.8 to 0.5 μg C m−2 h−1, and 42.1 to 81.7 mg C m−2 h−1 in both experiments, respectively. Deep N placement (10 and 15 cm) resulted in lower NO and N2O emissions compared with shallow N placement (0 and 5 cm) while CH4 and CO2 emissions were not affected by N placement in either experiment. Compared with N placement at 5 cm, for instance, averaged
N2O emissions from N placement at 10 cm were reduced by more than 50% in both experiments. Generally, NT decreased NO emission
and CH4 oxidation but increased N2O emissions compared with CT irrespective of N placement depths. Total net global warming potential (GWP) for N2O, CH4 and CO2 was reduced by deep N placement only in Exp. 1 but was increased by NT in both experiments. The study results suggest that
deep N placement (e.g., 10 cm) will be an effective option for reducing N oxide emissions and GWP from both fertilized CT-
and NT-soils. 相似文献
18.
Quantification of methane oxidation in the rhizosphere of emergent aquatic macrophytes: defining upper limits 总被引:6,自引:2,他引:4
Rates of rhizospheric methane oxidation were evaluated by aerobic incubations of subcores collected in flooded anoxic soils
populated by emergent macrophytes, by greenhouse whole plant incubations, and by CH4 stable isotopic analysis. Subcore incubations defined upper limits for rhizospheric methane oxidation on an areal basis which
were equal to or greater than emission rates. These rates are considered upper limits because O2 did not limit CH4 uptake as is likely to occur in situ. The ratio of maximum potential methane oxidation (MO) to methane emission (ME) ranged from 0.7 to 1.9 in Louisiana rice
(Oryza sativa), from 1.0 to 4.0 in a N. Florida Sagittaria lancifolia marsh, and from 5.6 to 51 in Everglades Typha domingensis and Cladium jamaicense areas. Methane oxidation/methane emission ratios determined in whole plant incubations of Sagittaria lancifolia under oxic and anoxic conditions ranged from 0.5 to 1.6. Methane oxidation activity associated with emergent aquatic macrophytes
was found primarily in fine root material. A weak correlation was observed between live root biomass and CH4 uptake in Typha. Rhizomes showed small or zero rates of methane uptake and no uptake was associated with plant stems. Methane stable isotope
data from a S. lancifolia marsh were as follows: CH4 emitted from plants: −61.6 ± 0.3%; CH4 within stems: −42.0 ± 0.2%; CH4 within sedimentary bubbles: −51.7 ± 0.3%). The 13C enrichment observed relative to emitted CH4 could be due to preferential mobilization of CH4 containing the lighter isotope and/or the action of methanotrophic bacteria. 相似文献
19.
Formation of Methane and Carbon Dioxide from Dimethylselenide in Anoxic Sediments and by a Methanogenic Bacterium 总被引:7,自引:6,他引:1 下载免费PDF全文
Anaerobic San Francisco Bay salt marsh sediments rapidly metabolized [14C]dimethylselenide (DMSe) to 14CH4 and 14CO2. Addition of selective inhibitors (2-bromoethanesulfonic acid or molybdate) to these sediments indicated that both methanogenic and sulfate-respiring bacteria could degrade DMSe to gaseous products. However, sediments taken from the selenium-contaminated Kesterson Wildlife Refuge produced only 14CO2 from [14C]DMSe, implying that methanogens were not important in the Kesterson samples. A pure culture of a dimethylsulfide (DMS)-grown methylotrophic methanogen converted [14C]DMSe to 14CH4 and 14CO2. However, the organism could not grow on DMSe. Addition of DMS to either sediments or the pure culture retarded the metabolism of DMSe. This effect appeared to be caused by competitive inhibition, thereby indicating a common enzyme system for DMS and DMSe metabolism. DMSe appears to be degraded as part of the DMS pool present in anoxic environments. These results suggest that methylotrophic methanogens may demethylate methylated forms of other metals and metalloids found in nature. 相似文献
20.
Effects of Elevated Atmospheric CO2 Concentrations on CH4 and N2O Emission from Rice Soil: An Experiment in Controlled-environment Chambers 总被引:1,自引:0,他引:1
The effects of elevated concentrations of atmospheric CO2 on CH4 and N2O emissions from rice soil were investigated in controlled-environment chambers using rice plants growing in pots. Elevated
CO2 significantly increased CH4 emission by 58% compared with ambient CO2. The CH4 emitted by plant-mediated transport and ebullition–diffusion accounted for 86.7 and 13.3% of total emissions during the flooding
period under ambient level, respectively; and for 88.1 and 11.9% of total emissions during the flooding period under elevated
CO2 level, respectively. No CH4 was emitted from plant-free pots, suggesting that the main source of emitted CH4 was root exudates or autolysis products. Most N2O was emitted during the first 3 weeks after flooding and rice transplanting, probably through denitrification of NO3− contained in the experimental soil, and was not affected by the CO2 concentration. Pre-harvest drainage suppressed CH4 emission but did not cause much N2O emission (< 10 μg N m−2 h−1) from the rice-plant pots at both CO2 concentrations. 相似文献