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1.
Background and aimsStudies have found significant differences in methane (CH4) emissions among rice cultivars; however, it is unclear whether this difference is related to radial oxygen loss (ROL) from the roots.MethodsBased on a 2-year in situ field study and solution culture experiments on 16 rice cultivars, we investigated CH4 emission levels and their dependence on ROL.ResultsWe detected significant differences in CH4 emission and ROL among rice cultivars. The lowest and highest CH4 emission levels were 4.10 and 7.35 g m?2 for early rice, and 14.36 and 23.33 g m?2 for late rice, respectively. The maximum and minimum ROL values were 3.77 and 1.73 mmol plant?1 h?1 for early rice, and 4.18 and 2.08 mmol plant?1 h?1 for late rice, respectively. Seasonal total CH4 emission was negatively correlated with ROL in the early rice season (p?<?0.01), and (p?<?0.01) in the late rice season. ROL was positively correlated with the number of roots per plant (RN), root tips per plant (RT), and root volume per plant (RV).ConclusionsWe suggest that ROL can be used as a predictive index for CH4 emissions. RN, RT, and RV were the most important factors influencing ROL in rice cultivars. 相似文献
2.
The soil of the former Lake Texcoco is a saline alkaline environment where anthropogenic drainage in some areas has reduced salt content and pH. Potential methane (CH 4) consumption rates were measured in three soils of the former Lake Texcoco with different electrolytic conductivity (EC) and pH, i.e. Tex-S1 a >18 years drained soil (EC 0.7 dS m ?1, pH 8.5), Tex-S2 drained for ~10 years (EC 9.0 dS m ?1, pH 10.3) and the undrained Tex-S3 (EC 84.8 dS m ?1, pH 10.3). An arable soil from Alcholoya (EC 0.7 dS m ?1, pH 6.7), located nearby Lake Texcoco was used as control. Methane oxidation in the soil Tex-S1 (lowest EC and pH) was similar to that in the arable soil from Alcholoya (32.5 and 34.7 mg CH 4 kg ?1 dry soil day ?1, respectively). Meanwhile, in soils Tex-S2 and Tex-S3, the potential CH 4 oxidation rates were only 15.0 and 12.8 mg CH 4 kg ?1 dry soil day ?1, respectively. Differences in CH 4 oxidation were also related to changes in the methane-oxidizing communities in these soils. Sequence analysis of pmoA gene showed that soils differed in the identity and number of methanotrophic phylotypes. The Alcholoya soil and Tex-S1 contained phylotypes grouped within the upland soil cluster gamma and the Jasper Ridge, California JR-2 clade. In soil Tex-S3, a phylotype related to Methylomicrobium alcaliphilum was detected. 相似文献
3.
Microbial oxidation in aerobic soils is the primary biotic sink for atmospheric methane (CH 4), a powerful greenhouse gas. Although tropical forest soils are estimated to globally account for about 28% of annual soil CH 4 consumption (6.2 Tg CH 4 year ?1), limited data are available on CH 4 exchange from tropical montane forests. We present the results of an extensive study on CH 4 exchange from tropical montane forest soils along an elevation gradient (1,000, 2,000, 3,000 m) at different topographic positions (lower slope, mid-slope, ridge position) in southern Ecuador. All soils were net atmospheric CH 4 sinks, with decreasing annual uptake rates from 5.9 kg CH 4–C ha ?1 year ?1 at 1,000 m to 0.6 kg CH 4–C ha ?1 year ?1 at 3,000 m. Topography had no effect on soil atmospheric CH 4 uptake. We detected some unexpected factors controlling net methane fluxes: positive correlations between CH 4 uptake rates, mineral nitrogen content of the mineral soil and with CO 2 emissions indicated that the largest CH 4 uptake corresponded with favorable conditions for microbial activity. Furthermore, we found indications that CH 4 uptake was N limited instead of inhibited by NH 4 +. Finally, we showed that in contrast to temperate regions, substantial high affinity methane oxidation occurred in the thick organic layers which can influence the CH 4 budget of these tropical montane forest soils. Inclusion of elevation as a co-variable will improve regional estimates of methane exchange in these tropical montane forests. 相似文献
4.
Global warming is associated with the continued increase in the atmospheric concentrations of greenhouse gases; carbon dioxide, methane (CH 4) and nitrous oxide. Wetlands constitute the largest single natural source of atmospheric CH 4 in the world contributing between 100 and 231 Tg year ?1 to the total budget of 503–610 Tg year ?1, approximately 60 % of which is emitted from tropical wetlands. We conducted diffusive CH 4 emission measurements using static chambers in river channels, floodplains and lagoons in permanent and seasonal swamps in the Okavango Delta, Botswana. Diffusive CH 4 emission rates varied between 0.24 and 293 mg CH 4 m ?2 h ?1, with a mean (±SE) emission of 23.2 ± 2.2 mg CH 4 m ?2 h ?1 or 558 ± 53 mg CH 4 m ?2 day ?1. These emission rates lie within the range reported for other tropical wetlands. The emission rates were significantly higher ( P < 0.007) in permanent than in seasonal swamps. River channels exhibited the highest average fluxes at 31.3 ± 5.4 mg CH 4 m ?2 h ?1 than in floodplains (20.4 ± 2.5 mg CH 4 m ?2 h ?1) and lagoons (16.9 ± 2.6 mg CH 4 m ?2 h ?1). Diffusive CH 4 emissions in the Delta were probably regulated by temperature since emissions were highest (20–300 mg CH 4 m ?2 h ?1) and lowest (0.2–3.0 mg m ?2 h ?1) during the warmer-rainy and cooler winter seasons, respectively. Surface water temperatures between December 2010 and January 2012 varied from 15.3 °C in winter to 33 °C in summer. Assuming mean inundation of 9,000 km 2, the Delta’s annual diffusive emission was estimated at 1.8 ± 0.2 Tg, accounting for 2.8 ± 0.3 % of the total CH 4 emission from global tropical wetlands. 相似文献
5.
The primary objective of this study was to clarify the influence of crop plants on atmospheric methane (CH 4) in an agriculture-dominated landscape in the Upper Midwest of the United States. Measurements were carried out at two contrasting scales. At the plant scale, CH 4 fluxes from soybean and corn plants were measured with a laser-based plant chamber system. At the landscape scale, the land surface flux was estimated with a modified Bowen ratio technique using measurements made on a tall tower. The chamber data revealed a diurnal pattern for the plant CH 4 flux: it was positive (an emission rate of 0.4?±?0.1 nmol m ?2 s ?1, average of soybean and corn, in reference to the unit ground area) during the day, and negative (an uptake rate of ?0.8?±?0.8 nmol m ?2 s ?1) during the night. At the landscape scale, the flux was estimated to be 14.8 nmol m ?2 s ?1 at night and highly uncertain during the day, but the available references and the flux estimates from the equilibrium methods suggested that the CH 4 flux during the entire observation period was similar to the estimated nighttime flux. Thus, soybean and corn plants have a negligible role in the landscape-scale CH 4 budget. 相似文献
6.
A laboratory incubation study conducted to assess the temporal variation of CH 4 oxidation during soil reduction processes in a flooded soil ecosystem. A classical sequence of microbial terminal electron accepting process observed following NO 3 ? reduction, Fe 3+ reduction, SO 4 2? reduction and CH 4 production in flooded soil incubated under initial aerobic and helium-flushed anaerobic conditions. CH 4 oxidation in the slurries was influenced by microbial redox process during slurry reduction. Under aerobic headspace condition, CH 4 oxidation rate (k) was stimulated by 29 % during 5 days (NO 3 ? reduction) and 32 % during both 10 days (Fe 3+) and 20 days (early SO 4 2? reduction) over unreduced slurry. CH 4 oxidation was inhibited at the later methanogenic period. Contrastingly, CH 4 oxidation activity in anaerobic incubated slurries was characterized with prolonged lag phase and lower CH 4 oxidation. Higher CH 4 oxidation rate in aerobically incubated flooded soil was related to high abundance of methanotrophs ( r?=?0.994, p?<?0.01) and ammonium oxidizers population ( r?=?0.184, p?<?0.05). Effect of electron donors NH 4 +, Fe 2+, S 2? on CH 4 oxidation assayed to define the interaction between reduced inorganic species and methane oxidation. The electron donors stimulated CH 4 oxidation as well as increased the abundance of methanotrophic microbial population except S 2? which inhibited the methanotrophic activity by affecting methane oxidizing bacterial population. Our result confirmed the complex interaction between methane-oxidizing microbial groups and redox species during sequential reduction processes of a flooded soil ecosystem. 相似文献
7.
Paddy field, being a man-made wetland, is recognized as one of the major sources of global methane (CH 4) emission. Since China has the second-largest area of rice cultivation in the world, it is important to develop valid and reliable strategies to reduce CH 4 emission and sustain rice productivity in Chinese paddy fields. In this study, we applied steel slag fertilizer, a by-product of steel industry with a high concentration of active iron (Fe), at rates of 0, 2, 4, and 8 Mg ha ?1 in subtropical rice ( Oryza sativa L.) paddy fields in China to assess the effect of steel slag amendment on CH 4 emissions as well as rice growth and yield characteristics. Results showed that the Fe concentrations in paddy soils significantly increased with the application levels of steel slag fertilizer. Steel slag amendment in paddy fields largely reduced the CH 4 production rate, resulting in a decrease in the overall CH 4 emission rate. In response to the applications of steel slag at a rate of 2, 4 and 8 Mg ha ?1, total CH 4 emission during rice cultivation decreased by 26.6, 43.3 and 49.3 %, respectively. Furthermore, steel slag amendment had a significant, positive effect on the rice grain yield and the percentage of ripened grain, most probably due to the increased availability of inorganic nutrients such as silicate and manganese. Our results suggest that steel slag can be an effective soil amendment for reducing CH 4 emissions as well as increasing rice productivity in subtropical paddy fields in China. 相似文献
8.
Anthropogenic nutrient inputs fuel eutrophication and hypoxia ([O2]?<?2 mg L?1), threatening coastal and near shore environments across the globe. The world’s second largest anthropogenic coastal hypoxic zone occurs annually along the Louisiana (LA) shelf. Springtime loading of dissolved inorganic nitrogen (DIN) from the Mississippi River, combined with summertime stratification and increased water residence time on the shelf, promotes establishment of an extensive hypoxic zone that persists throughout the summer. We investigated the patterns of pelagic denitrification and methane (CH4) oxidation along the LA shelf. Microbial activity rates were determined along with concentrations of dissolved nutrients and greenhouse gases, nitrous oxide (N2O) and CH4, during summer in 2013, 2015, and 2016. We documented denitrification rates up to 1900 nmol N L?1 d?1 and CH4 oxidation rates as high as 192 nmol L?1 d?1 in hypoxic waters characterized by high concentrations of N2O (range: 1 to 102 nM) and CH4 (range: 3 to 641 nM). Ecosystem scaling estimates suggest that pelagic denitrification could remove between 0.1 and 47% of the DIN input from the Mississippi River, whereas CH4 oxidation does not function as an effective removal process with CH4 escaping to the atmosphere. Denitrification and CH4 oxidizing bacteria within the LA shelf hypoxic zone were largely unable to keep up with the DIN and CH4 inputs to the water column. Rates were variable and physiochemical dynamics appeared to regulate the microbial removal capacity for both nitrate/nitrite and CH4 in this ecosystem. 相似文献
9.
Aims Effects of different soil amendments were investigated on methane (CH 4) emission, soil quality parameters and rice productivity in irrigated paddy field of Bangladesh. Methods The experiment was laid out in a randomized complete block design with five treatments and three replications. The experimental treatments were urea (220 kg ha ?1) + rice straw compost (2 t ha ?1) as a control, urea (170 kg ha ?1) + rice straw compost (2 t ha ?1) + silicate fertilizer, urea (170 kg ha ?1) + sesbania biomass (2 t ha ?1 ) + silicate fertilizer, urea (170 kg ha ?1) + azolla biomass (2 t ha ?1) + cyanobacterial mixture 15 kg ha ?1 silicate fertilizer, urea (170 kg ha ?1) + cattle manure compost (2 t ha ?1) + silicate fertilizer. Results The average of two growing seasons CH 4 flux 132 kg ha ?1 was recorded from the conventional urea (220 kg ha ?1) with rice straw compost incorporated field plot followed by 126.7 (4 % reduction), 130.7 (1.5 % reduction), 116 (12 % reduction) and 126 (5 % reduction) kg CH 4 flux ha ?1 respectively, with rice straw compost, sesbania biomass, azolla anabaena and cattle manure compost in combination urea and silicate fertilizer applied plots. Rice grain yield was increased by 15 % and 10 % over the control (4.95 Mg ha ?1) with silicate plus composted cattle manure and silicate plus azolla anabaena, respectively. Soil quality parameters such as soil organic carbon, total nitrogen, microbial biomass carbon, soil redox status and cations exchange capacity were improved with the added organic materials and azolla biofertilizer amendments with silicate slag and optimum urea application (170 kg ha ?1) in paddy field. Conclusion Integrated application of silicate fertilizer, well composted organic manures and azolla biofertilizer could be an effective strategy to minimize the use of conventional urea fertilizer, reducing CH 4 emissions, improving soil quality parameters and increasing rice productivity in subtropical countries like Bangladesh. 相似文献
10.
Small lakes in northern latitudes represent a significant source of CH 4 to the atmosphere that is predicted to increase with warming in the Arctic. Yet, whole-lake CH 4 budgets are lacking as are measurements of δ 13C-CH 4 and δ 2H-CH 4. In this study, we quantify spatial variability of diffusive and ebullitive fluxes of CH 4 and corresponding δ 13C-CH 4 and δ 2H-CH 4 in a small, Arctic lake system with fringing wetland in southwestern Greenland during summer. Net CH 4 flux was highly variable, ranging from an average flux of 7 mg CH 4 m ?2 d ?1 in the deep-water zone to 154 mg CH 4 m ?2 d ?1 along the lake margin. Diffusive flux accounted for ~8.5 % of mean net CH 4 flux, with plant-mediated and ebullitive flux accounting for the balance of the total net flux. Methane content of emitted ebullition was low (mean ± SD 10 ± 17 %) compared to previous studies from boreal lakes and wetlands. Isotopic composition of net CH 4 emissions varied widely throughout the system, with δ 13C-CH 4 ranging from ?66.2 to ?55.5 ‰, and δ 2H-CH 4 ranging from ?345 to ?258 ‰. Carbon isotope composition of CH 4 in ebullitive flux showed wider variation compared to net flux, ranging from ?69.2 to ?49.2 ‰. Dissolved CH 4 concentrations were highest in the sediment and decreased up the water column. Higher concentrations of CH 4 in the hypoxic deep water coincided with decreasing dissolved O 2 concentrations, while methanotrophic oxidation dominated in the epilimnion based upon decreasing concentrations and increasing values of δ 13C-CH 4 and δ 2H-CH 4. The most depleted 13C- and 2H-isotopic values were observed in profundal bottom waters and in subsurface profundal sediments. Based upon paired δ 13C and δ 2H observations of CH 4, acetate fermentation was likely the dominant production pathway throughout the system. However, isotopic ratios of CH 4 in deeper sediments were consistent with mixing/transition between CH 4 production pathways, indicating a higher contribution of the CO 2 reduction pathway. The large spatial variability in fluxes of CH 4 and in isotopic composition of CH 4 throughout a single lake system indicates that the underlying mechanisms controlling CH 4 cycling (production, consumption and transport) are spatially heterogeneous. Net flux along the lake margin dominated whole-lake flux, suggesting the nearshore littoral area dominates CH 4 emissions in these systems. Future studies of whole-lake CH 4 budgets should consider this significant spatial heterogeneity. 相似文献
11.
Most studies of greenhouse gas fluxes from forest soils in the coastal rainforest have considered carbon dioxide (CO 2), whereas methane (CH 4) has not received the same attention. Soil hydrology is a key driver of CH 4 dynamics in ecosystems, but the impact on the function and distribution of the underlying microbial communities involved in CH 4 cycling and the resultant net CH 4 exchange is not well understood at this scale. We studied the growing season variations of in situ CH 4 fluxes, microbial gene abundances of methanotrophs (CH 4 oxidizers) and methanogens (CH 4 producers), soil hydrology, and nutrient availability in three typical forest types across a soil moisture gradient. CH 4 displayed a spatial variability changing from a net uptake in the upland soils (3.9–46 µmol CH 4 m ?2 h ?1) to a net emission in the wetter soils (0–90 μmol CH 4 m ?2 h ?1). Seasonal variations of CH 4 fluxes were related to soil hydrology in both upland and wet soils. Thus, in the upland soils, uptake rates increased with the decreasing soil moisture, whereas CH 4 emission was inversely related to the water table depth in the wet soils. Spatial variability of CH 4 exchange was related to the abundance of genes involved in CH 4 oxidation and production, but there was no indication of a temporal link between microbial groups and CH 4 exchange. Our data show that the abundances of genes involved in CH 4 oxidation and production are strongly influenced by soil moisture and each other and grouped by the upland–wetland classification but not forest type. 相似文献
12.
Atmospheric CO 2 and CH 4 exchange in peatlands is controlled by water table levels and soil moisture, but impacts of short periods of dryness and rainfall are poorly known. We conducted drying-rewetting experiments with mesocosms from an ombrotrophic northern bog and an alpine, minerotrophic fen. Efflux of CO 2 and CH 4 was measured using static chambers and turnover and diffusion rates were calculated from depth profiles of gas concentrations. Due to a much lower macroporosity in the fen compared to the bog peat, water table fluctuated more strongly when irrigation was stopped and resumed, about 11 cm in the fen and 5 cm in the bog peat. Small changes in air filled porosity caused CO 2 and CH 4 concentrations in the fen peat to be insensitive to changes in water table position. CO 2 emission was by a factor of 5 higher in the fen than in the bog mesocosms and changed little with water table position in both peats. This was probably caused by the importance of the uppermost, permanently unsaturated zone for auto- and heterotrophic CO 2 production, and a decoupling of air filled porosity from water table position. CH 4 emission was <0.4 mmol m ?2 day ?1 in the bog peat, and up to >12.6 mmol m ?2 day ?1 in the fen peat, where it was lowered by water table fluctuations. CH 4 production was limited to the saturated zone in the bog peat but proceeded in the capillary fringe of the fen peat. Water table drawdown partly led to inhibition of methanogenesis in the newly unsaturated zone, but CH 4 production appeared to continue after irrigation without time-lag. The identified effects of irrigation on soil moisture and respiration highlight the importance of peat physical properties for respiratory dynamics; but the atmospheric carbon exchange was fairly insensitive to the small-scale fluctuations induced. 相似文献
13.
The response of methanotrophic bacteria capable of oxidizing atmospheric CH 4 to climate warming is poorly understood, especially for those present in Arctic mineral cryosols. The atmospheric CH 4 oxidation rates were measured in microcosms incubated at 4 °C and 10 °C along a 1‐m depth profile and over a range of water saturation conditions for mineral cryosols containing type I and type II methanotrophs from Axel Heiberg Island (AHI), Nunavut, Canada. The cryosols exhibited net consumption of ~2 ppmv CH 4 under all conditions, including during anaerobic incubations. Methane oxidation rates increased with temperature and decreased with increasing water saturation and depth, exhibiting the highest rates at 10 °C and 33% saturation at 5 cm depth (260 ± 60 pmol CH 4 gdw ?1 d ?1). Extrapolation of the CH 4 oxidation rates to the field yields net CH 4 uptake fluxes ranging from 11 to 73 μmol CH 4 m ?2 d ?1, which are comparable to field measurements. Stable isotope mass balance indicates ~50% of the oxidized CH 4 is incorporated into the biomass regardless of temperature or saturation. Future atmospheric CH 4 uptake rates at AHI with increasing temperatures will be determined by the interplay of increasing CH 4 oxidation rates vs. water saturation and the depth to the water table during summer thaw. 相似文献
14.
Background and aims The rice production is experiencing a shift from conventionally seedling-transplanted (TPR) to direct-seeded (DSR) cropping systems in Southeast Asia. Besides the difference in rice crop establishment, water regime is typically characterized as water-saving moist irrigation for DSR and flooding-midseason drainage-reflooding and moist irrigation for TPR fields, respectively. A field experiment was conducted to quantify methane (CH 4) and nitrous oxide (N 2O) emissions from the DSR and TPR rice paddies in southeast China. Methods Seasonal measurements of CH 4 and N 2O fluxes from the DSR and TPR plots were simultaneously taken by static chamber-GC technique. Results Seasonal fluxes of CH 4 averaged 1.58 mg m ?2 h ?1 and 1.02 mg m ?2 h ?1 across treatments in TPR and DSR rice paddies, respectively. Compared with TPR cropping systems, seasonal N 2O emissions from DSR cropping systems were increased by 49 % and 46 % for the plots with or without N application, respectively. The emission factors of N 2O were estimated to be 0.45 % and 0.69 % of N application, with a background emission of 0.65 and 0.95 kg N 2O-N ha ?1 under the TPR and DSR cropping regimes, respectively. Rice biomass and grain yield were significantly greater in the DSR than in the TPR cropping systems. The net global warming potential (GWP) of CH 4 and N 2O emissions were comparable between the two cropping systems, while the greenhouse gas intensity (GHGI) was significantly lower in the DSR than in the TPR cropping systems. Conclusions Higher grain yield, comparable GWP, and lower GHGI suggest that the DSR instead of conventional TPR rice cropping regime would weaken the radiative forcing of rice production in terms of per unit of rice grain yield in China, and DSR rice cropping regime could be a promising rice development alternative in mainland China. 相似文献
15.
Rice is staple food of half of mankind and paddy soils account for the largest anthropogenic wetlands on earth. Ample of research is being done to find cultivation methods under which the integrative greenhouse effect caused by emitted CH 4 and N 2O would be mitigated. Whereas most of the research focuses on quantifying such emissions, there is a lack of studies on the biogeochemistry of paddy soils. In order to deepen our mechanistic understanding of N 2O and CH 4 fluxes in rice paddies, we also determined NO 3 ? and N 2O concentrations as well as N 2O isotope abundances and presence of O 2 along soil profiles of paddies which underwent three different water managements during the rice growing season(s) in (2010 and) 2011 in Korea. Largest amounts of N 2O (2 mmol m ?2) and CH 4 (14.5 mol m ?2) degassed from the continuously flooded paddy, while paddies with less flooding showed 30–60 % less CH 4 emissions and very low to negative N 2O balances. In accordance, the global warming potential (GWP) was lowest for the Intermittent Irrigation paddy and highest for the Traditional Irrigation paddy. The N 2O emissions could the best be explained (* P < 0.05) with the δ 15N values and N 2O concentrations in 40–50 cm soil depth, implying that major N 2O production/consumption occurs there. No significant effect of NO 3 ? on N 2O production has been found. Our study gives insight into the soil of a rice paddy and reveals areas along the soil profile where N 2O is being produced. Thereby it contributes to our understanding of subsoil processes of paddy soils. 相似文献
16.
There is an ongoing discussion of the possible effects of nitrogen (N) application on methane (CH 4) emission from rice fields. However, the Intergovernmental Panel on Climate Change (IPCC) methodologies for estimating the national inventory of CH 4 emission from paddy rice production do not consider the effects of N addition. To assess the lack of knowledge about N addition effects on inventory estimates, we recently launched a multi-site observation campaign in major rice cultivation regions of China. The observations showed that, across various climate zones, the application of ammonium-based fertilizers at the commonly-adopted levels for fields in China (150 or 250 kg N ha ?1) generally inhibited accumulative CH 4 emission during rice season (by 28–30% on average) as compared to no N addition. An increase in application from the moderate level of 150 kg N ha ?1 to the high rate of 250 kg N ha ?1 did not significantly modify CH 4 emission. Our results suggest that disregarding the effect of N fertilization by the IPCC methodologies may not significantly bias CH 4 inventory estimates of China. In regions with much lower N addition levels, however, disregarding the effect of N fertilization may result in the underestimation of regional CH 4 emission, since these emissions were mainly derived from studies in regions with relatively high N addition rates. 相似文献
17.
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 CH 4 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 O 2 did not limit CH 4 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 CH 4 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: CH 4 emitted from plants: −61.6 ± 0.3%; CH 4 within stems: −42.0 ± 0.2%; CH 4 within sedimentary bubbles: −51.7 ± 0.3%). The 13C enrichment observed relative to emitted CH 4 could be due to preferential mobilization of CH 4 containing the lighter isotope and/or the action of methanotrophic bacteria. 相似文献
18.
Background and aims The effects of tillage and N fertilization on CO 2 and CH 4 emissions are a cause for concern worldwide. This paper quantifies these effects in a Mediterranean dryland area. Methods CO 2 and CH 4 fluxes were measured in two field experiments. A long-term experiment compared two types of tillage (NT, no-tillage, and CT, conventional intensive tillage) and three N fertilization rates (0, 60 and 120 kg N ha ?1). A short-term experiment compared NT and CT, three N fertilization doses (0, 75 and 150 kg N ha ?1) and two types of fertilizer (mineral N and organic N with pig slurry). Aboveground and root biomass C inputs, soil organic carbon stocks and grain yield were also quantified. Results The NT treatment showed a greater mean CO 2 flux than the CT treatment in both experiments. In the long-term experiment CH 4 oxidation was greater under NT, whereas in the short-term experiment it was greater under CT. The fertilization treatments also affected CO 2 emissions in the short-term experiment, with the greatest fluxes when 75 and 150 kg organic N ha ?1 was applied. Overall, the amount of CO 2 emitted ranged between 0.47 and 6.0 kg CO 2?equivalent kg grain ?1. NT lowered yield-scaled emissions in both experiments, but these treatment effects were largely driven by an increase in grain yield. Conclusions In dryland Mediterranean agroecosystems the combination of NT and medium rates of either mineral or organic N fertilization can be an appropriate strategy for optimizing CO 2 and CH 4 emissions and grain yield. 相似文献
19.
Dissolved CH 4 concentrations in the Belgian coastal zone (North Sea) ranged between 670 nmol l ?1 nearshore and 4 nmol l ?1 offshore. Spatial variations of CH 4 were related to sediment organic matter (OM) content and gassy sediments. In nearshore stations with fine sand or muddy sediments, the CH 4 seasonal cycle followed water temperature, suggesting methanogenesis control by temperature in these OM-rich sediments. In offshore stations with permeable sediments, the CH 4 seasonal cycle showed a yearly peak following the chlorophyll- a spring peak, suggesting that in these OM-poor sediments, methanogenesis depended on freshly produced OM delivery. This does not exclude the possibility that some CH 4 might originate from dimethylsulfide (DMS) or dimethylsulfoniopropionate (DMSP) or methylphosphonate transformations in the most offshore stations. Yet, the average seasonal CH 4 cycle was unrelated to those of DMS(P), very abundant during the Phaeocystis bloom. The annual average CH 4 emission was 126 mmol m ?2 y ?1 in the most nearshore stations (~4 km from the coast) and 28 mmol m ?2 y ?1 in the most offshore stations (~23 km from the coast), 1260–280 times higher than the open ocean average value (0.1 mmol m ?2 y ?1). The strong control of CH 4 by sediment OM content and by temperature suggests that marine coastal CH 4 emissions, in particular in shallow areas, should respond to future eutrophication and warming of climate. This is supported by the comparison of CH 4 concentrations at five stations obtained in March 1990 and 2016, showing a decreasing trend consistent with alleviation of eutrophication in the area. 相似文献
20.
During two intensive field campaigns in summer and autumn 2004 nitrogen (N 2O, NO/NO 2) and carbon (CO 2, CH 4) trace gas exchange between soil and the atmosphere was measured in a sessile oak ( Quercus petraea (Matt.) Liebl.) forest in Hungary. The climate can be described as continental temperate. Fluxes were measured with a fully automatic measuring system allowing for high temporal resolution. Mean N 2O emission rates were 1.5 μg N m −2 h −1 in summer and 3.4 μg N m −2 h −1 in autumn, respectively. Also mean NO emission rates were higher in autumn (8.4 μg N m −2 h −1) as compared to summer (6.0 μg N m −2 h −1). However, as NO 2 deposition rates continuously exceeded NO emission rates (−9.7 μg N m −2 h −1 in summer and −18.3 μg N m −2 h −1 in autumn), the forest soil always acted as a net NO
x
sink. The mean value of CO 2 fluxes showed only little seasonal differences between summer (81.1 mg C m −2 h −1) and autumn (74.2 mg C m −2 h −1) measurements, likewise CH 4uptake (summer: −52.6 μg C m −2 h −1; autumn: −56.5 μg C m −2 h −1). In addition, the microbial soil processes net/gross N mineralization, net/gross nitrification and heterotrophic soil respiration as well as inorganic soil nitrogen concentrations and N 2O/CH 4 soil air concentrations in different soil depths were determined. The respiratory quotient (ΔCO 2 resp ΔO 2 resp−1) for the uppermost mineral soil, which is needed for the calculation of gross nitrification via the Barometric Process Separation (BaPS) technique, was 0.8978 ± 0.008. The mean value of gross nitrification rates showed only little seasonal differences between summer (0.99 μg N kg −1 SDW d −1) and autumn measurements (0.89 μg N kg −1 SDW d −1). Gross rates of N mineralization were highest in the organic layer (20.1–137.9 μg N kg −1 SDW d −1) and significantly lower in the uppermost mineral layer (1.3–2.9 μg N kg −1 SDW d −1). Only for the organic layer seasonality in gross N mineralization rates could be demonstrated, with highest mean values in autumn, most likely caused by fresh litter decomposition. Gross mineralization rates of the organic layer were positively correlated with N 2O emissions and negatively correlated with CH 4 uptake, whereas soil CO 2 emissions were positively correlated with heterotrophic respiration in the uppermost mineral soil layer. The most important abiotic factor influencing C and N trace gas fluxes was soil moisture, while the influence of soil temperature on trace gas exchange rates was high only in autumn. 相似文献
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