首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The photoassimilate flow in an intact plant stem was imaged in real-time and its dynamics was quantitatively described using the Positron Emitting Tracer Imaging System (PETIS). Radioactive 11CO2 was fed to a leaf of an intact broad bean ( Vicia faba L.) plant, together with air containing an ambient concentration of non-radioactive carrier CO2 gas. Movies of flow of the 11C-labeled photoassimilates in the plant body were captured with PETIS. Here we demonstrate that the average flow speeds and the distribution ratios of photoassimilates in the respective nodes and internodes of the observed stem can be estimated by the transfer function analysis, one of the mathematical modeling methods. We also estimated the changes in the spatial distribution of the average flow speeds in the same stem when the fed leaf was exposed to enriched carrier CO2 gas.  相似文献   

2.
Abstract

Real-time images of nitrogen fixation in an intact nodule of hydroponically cultured soybean (Glycine max [L] Merr.) were obtained. In the present study, we developed a rapid method to produce and purify 13N-labeled radioactive nitrogen gas (half life: 9.97?min). 13N was produced from a 16O (p, α) 13N nuclear reaction. The target chamber was filled with CO2 and irradiated for 10?min with protons at an energy of 18.3?MeV and an electric current of 5?μA, which was delivered from a cyclotron. All CO2 in the collected gas was absorbed and removed with powdered soda-lime in a syringe and replaced with helium gas. The resulting gas was injected into gas chromatography and separated and a 35?mL fraction, including the peak of [13N]-nitrogen gas, was collected by monitoring the chromatogram. The obtained gas was mixed with 10?mL of O2 and 5?mL of N2 and used in the tracer experiment. The tracer gas was fed into the underground part of intact nodulated soybean plants and serial images of the distribution of 13N were obtained non-invasively using a positron-emitting tracer imaging system (PETIS). The rates of nitrogen fixation of the six test plants were estimated to be 0.17?±?0.10?μmol N2?h?1 from the PETIS image data. The decreasing rates of assimilated nitrogen were also estimated to be 0.012?±?0.011?μmol?N2?h?1. In conclusion, we successfully observed nitrogen fixation in soybean plants with nodules non-invasively and quantitatively using [13N]N2 and PETIS.  相似文献   

3.
We describe an automated gas sampling system for monitoring trace gas fluxes from soils. The sampling system allows automated collection of gas samples in glass vials using a syringe pump connected to an automated static chamber installed in the field. The gas samples are transferred to a laboratory and then analyzed using a gas chromatography system. Comparisons between manual and automated sampling of standard gases showed good agreement ( r 2 = 0.99996 for N2O, r 2 = 0.999 for CH4 and r 2 = 0.998 for CO2). In a field test, replicated flux measurements using two chambers generally showed good agreement. The sampling system allows frequent and long-term monitoring of fluxes under a wide range of weather conditions (tested temperatures ranged from –6.5 to 40°C; 127 mm day−1 max precipitation). The major advantages of the system are its increased portability, ease of operation and cost effectiveness compared with on-line automated sampling/analytical systems.  相似文献   

4.
Abstract. Land disposal of sewage sludge in the UK is set to increase markedly in the next few years and much of this will be applied to grassland. Here we applied high rates of digested sludge cake (1–1.5×103 kg total N ha−1) to grassland and incorporated it prior to reseeding. Using automated chambers, nitrous oxide (N2O) and carbon dioxide (CO2) fluxes from the soil were monitored 2–4 times per day, for 6 months after sludge incorporation. Peaks of N2O emission were up to 1.4 kg N ha−1 d−1 soon after incorporation, and thereafter were regularly detected following significant rainfalls. Gas emissions reflected diurnal temperature variations, though N2O emissions were also strongly affected by rainfall. Although emissions decreased in the winter, temperatures below 4 °C stimulated short, sharp fluxes of both CO2 and N2O as temperature increased. The aggregate loss of nitrogen and carbon over the measurement period was up to 23 kg N ha−1 and 5.1 t C ha−1. Losses of N2O in the sludge-amended soil were associated with good microbial conditions for N mineralization, and with high carbon and water contents. Since grassland is an important source of greenhouse gases, application of sewage sludge can be at least as significant as fertilizer in enhancing these emissions.  相似文献   

5.
To evaluate the atmospheric load of reactive gaseous nitrogen in the fast-developing Eastern China region, we compiled inventories of nitrous oxide (N2O), nitrogen oxide (NOx) and ammonia (NH3) emissions from a typical rural catchment in Jiangsu province, China, situated at the lower reach of the Yangtze River. We considered emissions from synthetic N fertilizer, human and livestock excreta, decomposition of crop residue returned to cropland and residue burning, soil background and household energy consumption. The results showed that, for the 45.5 km2 catchment, the annual reactive gaseous emission was 279 ton N, of which 7% was N2O, 16% was NOx and 77% was NH3. Synthetic N fertilizer application was the dominant source of N2O and NH3 emissions and crop residue burning was the dominant source of NOx emission. Sixty-seven percent of the total reactive gaseous N was emitted from croplands, but on a per unit area basis, NOx and NH3 emissions in residential areas were higher than in croplands, probably as a result of household crop residue burning and extensive human and livestock excreta management systems. Emission per capita was estimated to be 18.2 kg N year−1 in the rural catchment, and emission per unit area was 56.9 kg N ha−1year−1 for NH3 + NOx, which supports the observed high atmospheric N deposition in the catchment. Apparently, efficient use of N fertilizer and biological utilization of crop straw are important measures to reduce reactive gases emissions in this rural catchment.  相似文献   

6.
Fixation and transfer of nitrogen by white clover to ryegrass   总被引：4，自引：0，他引：4  
Abstract. 15N2 was used in a sealed controlled environment chamber to investigate the transfer of fixed nitrogen from white clover to perennial ryegrass growing in soil in pots. There was no difference in the 15N content of roots and shoots of clover plants after exposure to 15N. No labelled fixed nitrogen was detected in ryegrass plants growing with the clover plants for a period of 129 days. There was therefore no evidence of rapid direct transfer (excretion) of fixed nitrogen from clover to ryegrass.  相似文献   

7.
The present study investigated the nitrogen balance in swine manure composting to evaluate the effect of nitrite (     ) accumulation, which induces nitrogenous emissions, such as N2O, during compost maturation. During active composting, most N losses result from NH3 emission, which was 9.5% of the initial total nitrogen (TNinitial), after which,     began to accumulate as only ammonia-oxidizing bacteria proliferated. After active composting, the addition of mature swine compost (MSC), including nitrite-oxidizing bacteria (NOB), could prevent     accumulation and reduce N2O emission by 70% compared with the control in which     accumulated as a result of delayed growth of indigenous NOB. Total N2O emissions in the control and in the treatment of MSC addition (MA) were 9.3% and 3.0% of TNinitial, respectively, whereas N losses as the sum total of NH3 and N2O over the whole period were 19.0% (control) and 12.8% (MA) of TNinitial, respectively. However, the difference in total N losses was markedly greater than that measured as NH3 and N2O, which were 27.8% (control) and 13.3% (MA) of TNinitial, respectively. These results demonstrated that the magnitude of nitrogen losses induced by     accumulation is too large to ignore in the composting of swine manure.  相似文献   

8.
An introduction to the global nitrogen cycle   总被引：22，自引：0，他引：22  
Abstract. Current estimates are tabulated for the quantities of nitrogen circulating in the global nitrogen cycle. Five gases, NH3, N2O, NO, NO2 and N2, dominate the movement of nitrogen between the earth's surface and the atmosphere. The input of combined nitrogen to the land surface of the earth is tentatively estimated at 290 million tonnes per year, a total which includes 74 million tonnes from fertilizers. Known outputs from land (as gaseous NH3, N2O and NOX, and as inorganic nitrogen carried to the sea by rivers) are much less, totalling 130 million tonnes per year. Emissions of N2 gas probably account for most of the difference. There has been an increase in the use of nitrogen of about 5% per year over the last ten years. The demand for fertilizer nitrogen is likely to continue to grow if the population of the world continues to increase.  相似文献   

9.
Greenhouse gas emissions from farmed organic soils: a review   总被引：14，自引：0，他引：14  
Abstract. The large boreal peatland ecosystems sequester carbon and nitrogen from the atmosphere due to a low oxygen pressure in waterlogged peat. Consequently they are sinks for CO2 and strong emitters of CH4. Drainage and cultivation of peatlands allows oxygen to enter the soil, which initiates decomposition of the stored organic material, and in turn CO2 and N2O emissions increase while CH4 emissions decrease. Compared to undrained peat, draining of organic soils for agricultural purposes increases the emissions of greenhouse gases (CO2, CH4, and N2O) by roughly 1t CO2 equivalents/ha per year. Although farmed organic soils in most European countries represent a minor part of the total agricultural area, these soils contribute significantly to national greenhouse gas budgets. Consequently, farmed organic soils are potential targets for policy makers in search of socially acceptable and economically cost-efficient measures to mitigate climate gas emissions from agriculture. Despite a scarcity of knowledge about greenhouse gas emissions from these soils, this paper addresses the emissions and possible control of the three greenhouse gases by different managements of organic soils. More precise information is needed regarding the present trace gas fluxes from these soils, as well as predictions of future emissions under alternative management regimes, before any definite policies can be devised.  相似文献   

10.
Abstract. Grassland is a major source of nitrous oxide (N2O) and methane (CH4) emissions in the UK, resulting from high rates of fertilizer application. We studied the effects of substituting mineral fertilizer by organic manures and a slow-release fertilizer in silage grass production on greenhouse gas emissions and soil mineral N content in a three-year field experiment. The organic manures investigated were sewage sludge pellets and composted sewage sludge (dry materials), and digested sewage sludge and cattle slurry (liquid materials). The organic manures produced N2O and carbon dioxide (CO2) consistently from time of application up to harvest. However, they mitigated N2O emissions by around 90% when aggregate emissions of 15.7 kg N ha−1 from NPK fertilizer were caused by a flux of up to 4.9 kg N ha−1 d−1 during the first 4 days after heavy rainfall subsequent to the NPK fertilizer application. CH4 was emitted only for 2 or 3 days after application of the liquid manures. CH4 and CO2 fluxes were not significantly mitigated. Composting and dried pellets were useful methods of conserving nutrients in organic wastes, enabling slow and sustained release of nitrogen. NPK slow-release fertilizer also maintained grass yields and was the most effective substitute for the conventional NPK fertilizer for mitigation of N2O fluxes.  相似文献   

11.
Fluxes of the greenhouse gases methane (CH4) and nitrous oxide (N2O) from histosolic soils (which account for approximately 10% of Swedish agricultural soils) supporting grassley and barley production in Sweden were measured over 3 years using static chambers. Emissions varied both over area and time. Methane was both produced and oxidized in the soil: fluxes were small, with an average emission of 0.12 g CH4 m−2 year−1 at the grassley site and net uptake of −0.01 g CH4 m−2 year−1 at the barley field. Methane emission was related to soil water, with more emission when wet. Nitrous oxide emissions varied, with peaks of emission after soil cultivation, ploughing and harrowing. On average, the grassley and barley field had emissions of 0.20 and 1.51 g N2O m−2 year−1, respectively. We found no correlation between N2O and soil factors, but the greatest N2O emission was associated with the driest areas, with < 60% average water-filled pore space. We suggest that the best management option to mitigate emissions is to keep the soil moderately wet with permanent grass production, which restricts N2O emissions whilst minimizing those of CH4.  相似文献   

12.
Summary A clear understanding of the short-term decomposition and fate of crop residues is necessary to predict the availability of mineral N in soil. The fate of 13 C15N-labelled wheat straw in a silty soil (Typic Hapludalf) was studied using particle size fractionation and in situ incubation in which the equivalent of 8 t dry matter per ha of straw was incorporated into the soil over 574 days. Soil samples were separated into five particle-size fractions by wet sieving after disruption of aggregates. The weight, C and N contents, and 13C and 15N atom excess of each fraction were determined. Straw-derived C disappeared rapidly from the > 2000-μm fraction with an estimated half-life of 53 'normalized' days (equivalent of 10°C and −0−01 MPA water potential). Straw-derived C appeared to be only temporarily stored in the intermediate fractions (1000–2000 and 200–1000 pm). The maximum net 13C accumulation in the 50–200-μm fraction was 4·4% of added 13C. Straw-derived C accumulated most rapidly and preferentially in the 50-μm fraction, which stabilized after 265 days and accounted for 70% of the residual 13C on day 574. Although there was more residual 15N than 13C, the distributions and kinetics of the two isotopes in the fractions were similar.  相似文献   

13.
Reduction of nitrous oxide (N2O) is an autonomous respiratory pathway. Nitrous oxide is an alternative electron acceptor to O2 when intensive biological activity and reduced diffusivity result in an O2 deficit. Hypoxic or anoxic micro sites may form even in well-aerated soils, and provide a sink for N2O diffusing through the gas-filled pore space. We reproduced similar in vitro conditions in suboxic (0.15% O2) flow-through incubation experiments with samples from a Stagnosol and from a Histosol. Apparent half-saturation constants ( k m) for N2O reduction were similar for both soils and were, on average, 3.8 μmol mol−1 at 5°C, 5.1 μmol mol−1 at 10°C, and 6.9 μmol mol−1 at 20°C. Respiration of N2O was estimated to contribute a maximum proportion of 1.7% to total respiration in the Stagnosol (pH 7.0) and 0.9% in the Histosol (pH 2.9).  相似文献   

14.
Abstract. Formulation of nitrogen balances on farms requires accurate information on all inputs of the nutrient. N2-fixation by legumes, particularly forage legumes, is an important input which is difficult to measure. Simple regression models have been established from the literature for predicting N2-fixation by grass–white clover ( Trifolium repens ) mixtures using dry matter yields.
Linear relationships were obtained between the N2- fixation (Nfix) and the extra dry matter production of mixed swards (Md) compared with pure grass swards. Nitrogen fixation was given by Nfix= A + 0.067Md where A is the intercept having a value of 6.8 for cut swards and -168.1 for grazed swards. A common slope was adopted because the F statistics showed that slopes fitted separately were not significantly different. The value of the negative intercept represents the supply of N to the grazed sward from soil and excreta-derived N. The regression equation for the cut sward gave reasonable predictions (r2= 0.953) of values of N2-fixed for experimental data not used in establishing the relationship. For grazed grass, the approach over-estimated the N2- fixation by an average of 15%.  相似文献   

15.
Abstract. The success of organic cropping systems depends on symbiotic N2 fixation by leguminous crops, and it is important to explore new management systems to improve the nitrogen input through N2 fixation. During two growing seasons the possible advantage of growing fababean ( Vicia faba L.) in ridges was studied in comparison to the traditional method on flat soil. Differences in soil physical parameters resulted in a significantly greater microbial activity and a deeper root system at the flowering stage when grown in the ridge than on the flat. Consequently, the amount of fixed N at flowering was significantly greater in ridges than in flat soil. However, during the period from flowering until harvest, when the major part of the N uptake and N2 fixation took place, the differences between the treatments disappeared. Average values for the growing season of fluorescein diacetate hydrolysis, arylamidase activity and arylsulphatase activity were significantly greater in the ridge than on the flat, and the microbial biomass-C, derived from substrate induced respiration (SIR), was on average 232 and 223 μg C g−1 soil in the ridge and on the flat, respectively. Measured total-N uptake, including root N (0–30 cm depth), ranged from 206 to 247 kg N ha−1, of which 182–201 kg N ha−1 was fixed N. From 154 to 173 kg N ha−1 was removed in grain resulting in a soil-N balance of +28 kg N ha−1 in both years. However, by including estimates of total root N and rhizodeposition-N the soil-N balance ranged from +52 to +62 kg N ha−1.  相似文献   

16.
Decomposition in a peaty soil improved for pastoral agriculture   总被引：1，自引：0，他引：1  
Abstract. The rates of CO2 production and decomposition of 13C-enriched Lolium perenne leaves and roots in soil from the surface five cm of two upland stagnohumic gley soils were measured in laboratory experiments. One of the soils had been limed (pH 6.8) 13 years earlier. The other was unlimed (pH 3.7). Liming increased the rate of CO2 release from soil to which no L. perenne had been added. About 30% of the 13C in L. perenne leaves remained in both limed and unlimed soil after 224 days. By contrast, less 13C-remained in the limed soil amended with L. perenne roots (44%) than in the limed soils (55%). Although the daily rate of CO2 from the plant material-amended soils was initially greater in the improved than in the unimproved soil, it subsequently declined more rapidly.  相似文献   

17.
The contribution of an earthworm species ( Amynthas vittatus ) to the increase of the nitrogen content of soil was examined. Three specimens of adult earthworms were introduced into 300 g of soil (Gray Lowland soil, silty clay) supplemented with 1% carboxymethyl cellulose in a container and incubated for 32 d at 22°C in the dark. The contents of total-N, NH4-N and NO3-N, and the population of aerobic nitrogen-fixing bacteria in soil significantly increased after incubation with the earthworms, while the natural abundance of 15N (δ15N) in soil decreased. The amount of nitrogen in the earthworms did not decrease during the incubation in the microcosm. Both acetylene reduction activity of the microcosm and incorporation of 15N to soil from atmospheric 15N2 were significantly enhanced by the introduction of the earthworms into soil, though the observed increment of nitrogen in soil was much higher than the estimated one based on the nitrogen-fixing activity. The results obtained in the present study indicated that the earthworms increased the nitrogen content of soil, presumably due to the enhancement of the nitrogen-fixing activity of the soil from the microcosm by the earthworms.  相似文献   

18.
The N recovery from 15N-labeled swine manure compost and rice bran with or without simultaneous application of unlabeled cattle manure compost was examined in a paddy field with direct-seeded rice during a 1-year period (1 crop season). In all the 15N-labeled materials including (15NH4)2SO4, the processes of N recovery from the 15N materials by rice plants were different between the plots with and without application of cattle manure compost. At the tillering stage, the N recovery rates from the 15N materials in the plots with application of cattle manure compost were significantly lower than those in the plots without application of cattle manure compost. These recovery rates, however, became close and no significant differences were observed at the maturity stage. Thus, simultaneous application of cattle manure compost could impede the N recovery from swine manure compost, rice bran as well as (NH4)2SO4.  相似文献   

19.
Emissions of nitrous oxide (N2O) and nitrogen gas (N2) from denitrification were measured using the acetylene inhibition method on drained and undrained clay soil during November 1980-June 1981. Drainage limited denitrification to about 65% of losses from undrained soil. Emissions from the undrained soil were in the range 1 to 12 g N ha–1 h–1 while those from the drained soil ranged from 0.5 to 6 g N ha–1 h–1 giving estimated total losses (N2O + N2) of 14 and 9 kgN ha–1.
Drainage also changed the fraction of nitrous oxide in the total denitrification product. During December, emissions from the drained soil (1.8±0.6 gN ha–1 h–1) were composed entirely of nitrous oxide, but losses from the undrained soil (2.7 ± 1.1 g N ha–1 h–1) were almost entirely in the form of nitrogen gas (the fraction of N2O in the total loss was 0.02). In February denitrification declined in colder conditions and the emission of nitrous oxide from drained soil declined relative to nitrogen gas so that the fraction of N2O was 0.03 on both drainage treatments. The delayed onset of N2O reduction in the drained soil was related to oxygen and nitrate concentrations. Fertilizer applications in the spring gave rise to maximum rates of emission (5–12g N ha–1 h–1) with the balance shifting towards nitrous oxide production, so that the fraction of N2O was 0.2–0.8 in April and May.  相似文献   

20.
Impacts of land management on fluxes of trace greenhouse gases   总被引：8，自引：0，他引：8  
Abstract. Land use change and land management practices affect the net emissions of the trace gases methane (CH4) and nitrous oxide (N2O), as well as carbon sources and sinks. Changes in CH4 and N2O emissions can substantially alter the overall greenhouse gas balance of a system. Drainage of peatlands for agriculture or forestry generally increases N2O emission as well as that of CO2, but also decreases CH4 emission. Intermittent drainage or late flooding of rice paddies can greatly diminish the seasonal emission of CH4 compared with continuous flooding. Changes in N2O emissions following land use change from forest or grassland to agriculture vary between climatic zones, and the net impact varies with time. In many soils, the increase in carbon sequestration by adopting no-till systems may be largely negated by associated increases in N2O emission. The promotion of carbon credits for the no-till system before we have better quantification of its net greenhouse gas balance is naïve. Applying nitrogen fertilizers to forests could increase the forest carbon sink, but may be accompanied by a net increase in N2O; conversely, adding lime to acid forest soils can decrease the N2O emission.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号