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1.
Abstract Recent emphasis on residue management in sustainable agriculture highlights the importance of elucidating the mechanisms of microbial degradation of cellulose. Cellulose decomposition and its associated microbial dynamics in soil were investigated in incubation experiments. Population dynamics of actinomycetes, bacteria, and fungi were monitored by direct counts. Populations of oligotrophic bacteria in cellulose-amended soil were determined by plate count using a low C medium containing 4 mg C liter−1 agar, and copiotrophs using a high C medium. Cumulative 14CO2 evolution from 14C-labeled cellulose was best described by a multiphasic curve in a 28-day incubation experiment. The initial phase of decomposition was attributed mainly to the activity of bacterial populations with a low oligotroph-to-copiotroph ratio, and the second phase mainly to fungal populations. An increase in oligotroph-to-copiotroph ratio coincided with the emergence of a rapid 14CO2 evolution stage. Streptomycin reduced 14CO2 evolution during the first phase and prompted earlier emergence of the second phase, compared to the control. Cycloheximide initially promoted 14CO2 evolution but subsequently had a lasting negative effect on 14CO2 evolution. Cycloheximide addition significantly increased bacterial biomass and resulted in substantially stronger oscillation of active bacterial populations, whereas it initially reduced, and then stimulated, active fungal biomass. The observed changes in 14CO2 evolution could not be explained by observed shifts in fungal and bacterial biomass, probably because functional groups of fungi and bacteria could not be distinguished. However, it was suggested that oligotrophic bacteria prompted activation of cellulolytic enzumes in fungi and played an important role in leading to fungal dominance of cellulose decomposition. Received: 2 October 1995; Accepted: 10 February 1996  相似文献   

2.
Growth kinetics of Aspergillus niger strain A.n./61 on a solid medium containing beet pulp were examined. Solid state fermentation was carried out in laboratory microfermenter (aerated packed columns). During the experiments the CO2 evolution, protein biosynthesis, as well as cellulose and sucrose utilization were determined. It was found that CO2 evolution evidently increased in the logarithmic phase, together with the protein biosynthesis. Between 30–32 h of culture CO2 evolution and protein content in product were the greatest. Subsequently, CO2 evolution decreased. During 28 h of culture, cellulose was slightly utilized, the strain using mainly sucrose. Intense utilization of cellulose was paralleled by a drop in CO2 evolution.  相似文献   

3.
Elevated atmospheric CO2 increases aboveground plant growth and productivity. However, carbon dioxide-induced alterations in plant growth are also likely to affect belowground processes, including the composition of soil biota. We investigated the influence of increased atmospheric CO2on bacterial numbers and activity, and on soil microbial community composition in a pasture ecosystem under Free-Air Carbon Dioxide Enrichment (FACE). Composition of the soil microbial communities, in rhizosphere and bulk soil, under two atmospheric CO2 levels was evaluated by using phospholipid fatty acid analysis (PLFA), and total and respiring bacteria counts were determined by epifluorescence microscopy. While populations increased with elevated atmospheric CO2 in bulk soil of white clover (Trifolium repens L.), a higher atmospheric CO2 concentration did not affect total or metabolically active bacteria in bulk soil of perennial ryegrass (Lolium perenne L.). There was no effect of atmospheric CO2 on total bacteria populations per gram of rhizosphere soil. The combined effect of elevated CO2 on total root length of each species and the bacterial population in these rhizospheres, however, resulted in an 85% increase in total rhizosphere bacteria and a 170% increase in respiring rhizosphere bacteria for the two plant species, when assessed on a per unit land area basis. Differences in microbial community composition between rhizosphere and bulk soil were evident in samples from white clover, and these communities changed in response to CO2 enrichment. Results of this study indicate that changes in soil microbial activity, numbers, and community composition are likely to occur under elevated atmospheric CO2, but the extent of those changes depend on plant species and the distance that microbes are from the immediate vicinity of the plant root surface.  相似文献   

4.
Effect of carbon dioxide concentration on microbial respiration in soil   总被引:6,自引:0,他引:6  
In order to assess the validity of conventional methods for measuring CO2 flux from soil, the relationship between soil microbial respiration and ambient CO2 concentration was studied using an open-flow infra-red gas analyser (IRGA) method. Andosol from an upland field in central Japan was used as a soil sample. Soil microbial respiration activity was depressed with the increase of CO2 concentration in ventilated air from 0 to 1000 ppmv. At 1000 ppmv, the respiration rate was less than half of that at 0 ppmv. Thus, it is likely that soil respiration rate is overestimated by the alkali absorption method, because CO2 concentration in the absorption chamber is much lower than the normal level. Metabolic responses to CO2 concentration were different among groups of soil microorganisms. The bacteria actinomycetes group cultivated on agar medium showed a more sensitive response to the CO2 concentration than the filamentous fungi group.  相似文献   

5.
Three widely used methods for measuring total soil CO2 evolution are evaluated, including the dynamic CO2 absorption method, the static CO2 absorption method and the closed chamber method. The study covers laboratory experiments. numerical experiments with a simulation model and field measurements. The results are used to perform an error analysis. The aim of this error analysis is to indicate the impact of each method on the CO2 dynamics during the measurement, and to select the most suitable method for frequent field usage.Laboratory experiments and simulation results show that the dynamic CO2 absorption method has the potential to absorb all CO2 evolving at the soil surface. The results also prove that the method has only a minor impact on the CO2 concentration-depth gradient and the CO2 efflux. The static CO2 absorption method underestimates the soil CO2 evolution, because the absorption velocity is too low, due to slow diffusion processes. Measurements with the closed-chamber method are based on an increasing concentration with time under a closed cover. However, the accumulation of gas alters the concentration gradient in the soil profile and thus causes a rapidly decreasing efflux during the measurement. A commonly used mathematical procedure, which corrects for the altered concentration gradient, does not yield the exact surface efflux, because the effect of increasing storage in the soil profile is not incorporated. Field measurements of CO2 evolution, using the closed-chamber method and the dynamic CO2 absorption method confirm the trends that have been predicted by the simulation model. The results of this study indicate that the dynamic CO2 absorption method is accurate. As it is cheap and simple, it is suitable for the study of temporal and spatial dynamics of CO2 evolution from the soil.  相似文献   

6.
Technique for Measuring 14CO2 Uptake by Soil Microorganisms In Situ   总被引:12,自引:10,他引:2       下载免费PDF全文
Uptake of 14CO2 in soils due to algae or sulfur-oxidizing bacteria was examined by incubation of soil samples with gaseous 14CO2 and subsequent chemical oxidation of biologically fixed radioactive isotope to 14CO2 for detection with a liquid scintillation counting system. The 14CO2 was added to the soil in the gas phase so that no alteration of the moisture or ionic strength of the soil occurred. Wet oxidation of radioactive organic matter was carried out in sealed ampoules, and the 14CO2 produced was transferred to a phenethylamine-liquid scintillation counting system with a simply constructed apparatus. The technique is inexpensive and efficient and does not require elaborate traps since several possible interfering factors were found to have no harmful effects. Experiments in coal mine regions and in geothermal habitats have demonstrated the ecological applicability of this technique for measurement of CO2 fixation by sulfur-oxidizing bacteria and soil algae.  相似文献   

7.
The eastern Tibetan Plateau has become increasingly warmer and drier since the 1990s. Such warming and drying has a great impact on ecosystem processes on the eastern Tibetan Plateau. To determine their combined effects on CO2 and N2O emission rates, we conducted a field manipulative experiment in an alpine meadow of the eastern Tibetan Plateau during the growing season of 2009. The experiment showed that warming manipulation increased soil temperature by 1?°C, and drying manipulation decreased soil water content by 6.8?%. We found that by counteracting the effect of low temperature in the area, experimental warming significantly increased soil microbial biomass, the number of bacteria, fungi, actinomycetes, ammonifying bacteria, nitrobacteria and denitrifying bacteria, and facilitated the emission rates of CO2 and N2O by 33.4 and 31.5?%, respectively. However, decreased precipitation further aggravated soil water stress and inhibited the numbers of these organisms, and reduced the emission rates of CO2 and N2O by 47.4 and 37.9?%, respectively. So decreased soil water content tended to offset the positive effect of warming. Compared to the positive effects of warming, decreased soil water content was shown in our study to have even greater impact on the eastern Tibetan Plateau during the growing season. Therefore, inhibition of CO2 and N2O emission rates (32.3 and 29.3?%, respectively) by warming and drying will intensify if the combined effects of these climatic trends persist in the region.  相似文献   

8.

Background

Microbial cellulose conversion by Clostridium thermocellum 27405 occurs predominantly through the activity of substrate-adherent bacteria organized in thin, primarily single cell-layered biofilms. The importance of cellulosic surface exposure to microbial hydrolysis has received little attention despite its implied impact on conversion kinetics.

Results

We showed the spatial heterogeneity of fiber distribution in pure cellulosic sheets, which made direct measurements of biofilm colonization and surface penetration impossible. Therefore, we utilized on-line measurements of carbon dioxide (CO2) production in continuous-flow reactors, in conjunction with confocal imaging, to observe patterns of biofilm invasion and to indirectly estimate microbial accessibility to the substrate’s surface and the resulting limitations on conversion kinetics. A strong positive correlation was found between cellulose consumption and CO2 production (R2?=?0.996) and between surface area and maximum biofilm activity (R2?=?0.981). We observed an initial biofilm development rate (0.46 h-1, 0.34 h-1 and 0.33 h-1) on Whatman sheets (#1, #598 and #3, respectively) that stabilized when the accessible surface was maximally colonized. The results suggest that cellulose conversion kinetics is initially subject to a microbial limitation period where the substrate is in excess, followed by a substrate limitation period where cellular mass, in the form of biofilms, is not limiting. Accessible surface area acts as an important determinant of the respective lengths of these two distinct periods. At end-point fermentation, all sheets were digested predominantly under substrate accessibility limitations (e.g., up to 81% of total CO2 production for Whatman #1). Integration of CO2 production rates over time showed Whatman #3 underwent the fastest conversion efficiency under microbial limitation, suggestive of best biofilm penetration, while Whatman #1 exhibited the least recalcitrance and the faster degradation during the substrate limitation period.

Conclusion

The results showed that the specific biofilm development rate of cellulolytic bacteria such as C. thermocellum has a notable effect on overall reactor kinetics during the period of microbial limitation, when ca. 20% of cellulose conversion occurs. The study further demonstrated the utility of on-line CO2 measurements as a method to assess biofilm development and substrate digestibility pertaining to microbial solubilization of cellulose, which is relevant when considering feedstock pre-treatment options.
  相似文献   

9.
It is vital to understand responses of soil microorganisms to predicted climate changes, as these directly control soil carbon (C) dynamics. The rate of turnover of soil organic carbon is mediated by soil microorganisms whose activity may be affected by climate change. After one year of multifactorial climate change treatments, at an undisturbed temperate heathland, soil microbial community dynamics were investigated by injection of a very small concentration (5.12 µg C g−1 soil) of 13C-labeled glycine (13C2, 99 atom %) to soils in situ. Plots were treated with elevated temperature (+1°C, T), summer drought (D) and elevated atmospheric carbon dioxide (510 ppm [CO2]), as well as combined treatments (TD, TCO2, DCO2 and TDCO2). The 13C enrichment of respired CO2 and of phospholipid fatty acids (PLFAs) was determined after 24 h. 13C-glycine incorporation into the biomarker PLFAs for specific microbial groups (Gram positive bacteria, Gram negative bacteria, actinobacteria and fungi) was quantified using gas chromatography-combustion-stable isotope ratio mass spectrometry (GC-C-IRMS).Gram positive bacteria opportunistically utilized the freshly added glycine substrate, i.e. incorporated 13C in all treatments, whereas fungi had minor or no glycine derived 13C-enrichment, hence slowly reacting to a new substrate. The effects of elevated CO2 did suggest increased direct incorporation of glycine in microbial biomass, in particular in G+ bacteria, in an ecosystem subjected to elevated CO2. Warming decreased the concentration of PLFAs in general. The FACE CO2 was 13C-depleted (δ13C = 12.2‰) compared to ambient (δ13C = ∼−8‰), and this enabled observation of the integrated longer term responses of soil microorganisms to the FACE over one year. All together, the bacterial (and not fungal) utilization of glycine indicates substrate preference and resource partitioning in the microbial community, and therefore suggests a diversified response pattern to future changes in substrate availability and climatic factors.  相似文献   

10.
The fate, as well as the consequence for plant nutrition, of the additional carbon entering soil under elevated CO2 is largely determined by the activity of soil microorganisms. However, most elevated CO2 studies have documented changes (generally increases) in microbial biomass and total infection by symbiotic organisms, which is only a first step in the understanding of the modification of soil processes. Using a Mediterranean model ecosystem, we complemented these variables by analyzing changes in enzymatic activities, hyphal lengths, and bacterial substrate assimilation, to tentatively identify the specific components affected under elevated CO2 and those which suggest changes in soil organic matter pools. We also investigated changes in the functional structures of arbuscular mycorrhizas. Most of the microbial variables assessed showed significant and substantial increase under elevated CO2, of the same order or less than those observed for root mass and length. The increase in dehydrogenase activity indicates that the larger biomass of microbes was accompanied by an increase in their activity. The increase in hyphal length (predominantly of saprophytic fungi), and xylanase, cellulase and phosphatase activities, suggests an overall stimulation of organic matter decomposition. The higher number of substrates utilized by microorganisms from the soil under elevated CO2 was significant for the amine/amide group. Total arbuscular and vesicular mycorrhizal infection of roots was higher under elevated CO2, but the proportion of functional structures was not modified. These insights into the CO2-induced changes in soil biological activity point towards potential areas of investigation complementary to a direct analysis of the soil organic matter pools.  相似文献   

11.
The effect of soil warming on CO2 and CH4 flux from a spruce–fir forest soil was evaluated at the Howland Integrated Forest Study site in Maine, USA from 1993 to 1995. Elevated soil temperatures (~5 °C) were maintained during the snow-free season (May – November) in replicated 15 × 15-m plots using electric cables buried 1–2 cm below the soil surface; replicated unheated plots served as the control. CO2 evolution from the soil surface and soil air CO2 concentrations both showed clear seasonal trends and significant (P < 0.0001) positive exponential relationships with soil temperature. Soil warming caused a 25–40% increase in CO2 flux from the heated plots compared to the controls. No significant differences were observed between heated and control plot soil air CO2 concentrations which we attribute to rapid equilibration with the atmosphere in the O horizon and minimal treatment effects in the B horizon. Methane fluxes were highly variable and showed no consistent trends with treatment.  相似文献   

12.
The effect of elevated CO2 on growth of wheat plants (Triticum aestivum cv. Minaret) and soil protozoan and bacterial populations was investigated in soil pots placed in open top chambers fumigated with ambient air or air enriched with CO2 (ambient + 320 l L–1 CO2). We harvested plants two times during the growing season and measured the biomass and the C and N content of roots and shoots. The soil was divided into bulk and rhizosphere soil and the number of bacteria (colony-forming units, CFU) and protozoa was determined. There was no effect of atmospheric CO2 content on the number of bacteria, but the total number of bacterivorous protozoa was higher in pots from the elevated CO2 treatment. This increase was mainly due to an increase in the number of protozoa in the bulk soil. Density of protozoa in the rhizosphere was not affected by elevated CO2. This suggests that the increase in protozoan numbers was a result of a general increase in rhizodeposition, presumably caused by increased root production, and not to an increased root exudation per root mass. After harvest, soil from the two treatments was incubated with and without roots and the respiration rate was estimated at intervals for 200 days. During the first 55 days, the specific root induced respiration rate was not affected by the CO2 level at which the plants had been grown, indicating that the quality of the easily decomposable components of the roots was not affected by CO2 level.  相似文献   

13.
生物垃圾好氧处理中的纤维素降解菌生长规律研究   总被引:2,自引:0,他引:2  
目的:研究了蔬菜垃圾好氧处理过程中,纤维素降解菌和半纤维素降解菌(细菌和真菌),纤维素酶活和半纤维素酶活,和有机物降解之间的变化规律。方法:用添加纤维素和半纤维素的牛肉膏蛋白胨培养基和查式培养基,分别培养计数纤维素降解细菌、真菌和半纤维素降解细菌、真菌;马福炉灼烧测有机物含量。结果:好氧处理的初始阶段中,前4d有机物日均降解率5.2%,后3d日均降解率2.2%。结论:半纤维素降解菌的数量比纤维素降解菌的多,半纤维素酶活力,也高于纤维素酶活力;微生物的变化情况为前6d产两种酶的微生物主要有细菌和真菌;从第6d开始真菌快速生长;至第7d真菌纤维素酶和半纤维素酶活力显著升高。  相似文献   

14.
Summary 14C-labelled substrates (glucose, hemicellulose, cellulose, maize straw, and barley straw) were incubated in 4 soils with clay contents of, 6, 12, 16 and 34%. After 2 years an average of 20% of the labelled C remained in the soils; 10% of this residual C was in biomass as determined by fumigation with CHCl3.Air-drying, C addition (unlabelled glucose), heating (80°C), and grinding of the soils accelerated the evolution of labelled CO2. Grinding and heating had the largest effect, increasing CO2 evolution during the first 10 days by a factor of 15 to 22 relative to untreated soil. Air-drying had the least effect; it increased the CO2 evolution 7 to 9 times. The accelerating effect was still measurable, during the third month of incubation when the CO2 evolution was 1.2 to 1.9 times that from untreated soil.The treatments also affected the labelled biomass; air-drying had the least effect, and grinding the most. Three months after these two treatments the biomass was 3/4 and 1/4, respectively, of the amount at the start.On the average the treatments in all four soils had the greatest affect on humified material originating from glucose, hemicellulose, and cellulose; the least effect was on material originating from straw.The addition of unlabelled glucose accelerated the evolution of labelled CO2–C in all four soils. The size of the effect on CO2 evolution and on the biomass was similar to that of air-drying.Grinding killed a larger percentage of the biomass in the sandy soil than in the soils with a high content of clay. The effect of the other treatments was largely the same in all four soils.The effect of the treatments towards the native biomass and humic matter was largely parallel to that on the labelled biomass.The observations are consistent with the view that the biomass as determined by fumigation with CHCl3 mainly consists of dormant organisms. CO2 production — the biological activity — was related to the amount of available organic material and not the size of the biomass.  相似文献   

15.
Dark, that is, nonphototrophic, microbial CO2 fixation occurs in a large range of soils. However, it is still not known whether dark microbial CO2 fixation substantially contributes to the C balance of soils and what factors control this process. Therefore, the objective of this study was to quantitate dark microbial CO2 fixation in temperate forest soils, to determine the relationship between the soil CO2 concentration and dark microbial CO2 fixation, and to estimate the relative contribution of different microbial groups to dark CO2 fixation. For this purpose, we conducted a 13C‐CO2 labeling experiment. We found that the rates of dark microbial CO2 fixation were positively correlated with the CO2 concentration in all soils. Dark microbial CO2 fixation amounted to up to 320 µg C kg?1 soil day?1 in the Ah horizon. The fixation rates were 2.8–8.9 times higher in the Ah horizon than in the Bw1 horizon. Although the rates of dark microbial fixation were small compared to the respiration rate (1.2%–3.9% of the respiration rate), our findings suggest that organic matter formed by microorganisms from CO2 contributes to the soil organic matter pool, especially given that microbial detritus is more stable in soil than plant detritus. Phospholipid fatty acid analyses indicated that CO2 was mostly fixed by gram‐positive bacteria, and not by fungi. In conclusion, our study shows that the dark microbial CO2 fixation rate in temperate forest soils increases in periods of high CO2 concentrations, that dark microbial CO2 fixation is mostly accomplished by gram‐positive bacteria, and that dark microbial CO2 fixation contributes to the formation of soil organic matter.  相似文献   

16.
The abundance and distribution of microorganisms and their potential for mineralizing polycyclic aromatic hydrocarbons (PAHs) were measured in subsurface sediment samples at two geographically separate buried coal-tar sites. At a relatively undisturbed forested site in the northeastern United States, metabolic adaptation to the PAHs was evident: Radiolabeled naphthalene and phenanthrene were converted to 14CO2 in core material from inside but not outside a plume of groundwater contamination. However, at the urban site in the midwestern United States these PAHs were mineralized in sediments from both contaminated and uncontaminated boreholes. Thus, clear qualitative evidence showing an adaptational response by the subsurface microbial community was not obtained at the urban site. Instead, subtler clues suggesting metabolic adaptation by subsurface microorganisms from the urban site were discerned by comparing lag periods and extents of 14CO2 production from radiolabeled PAHs added to samples from contaminated and uncontaminated boreholes. Despite slightly higher PAH mineralization activity in contaminated borehole samples, p-hydroxybenzoate was mineralized equally in all samples from the urban site regardless of location. No striking trends in the abundances of actinomycetes, fungi, and either viable or total bacteria were encountered. However, colonies of the soil bacterium, Bacillus mycoides, were detected on enumeration plates of several samples from unsaturated and saturated zones in both urban boreholes. Furthermore, other common soil bacteria, Myxococcus xanthus and Chromobacterium violaceum, were identified in samples from the uncontaminated urban borehole. The occurrence of bacteria usually restricted to surface soil, combined with the observation of fragments of building materials in many of the core samples, suggested that past excavation and backfilling operations may have caused mixing of surface soil with subsurface materials at the urban site. We speculate that this mixing, as well as non-coal-tar-derived sources of PAHs, contributed to the PAH-mineralizing activity present in the sediment samples from the uncontaminated urban borehole.  相似文献   

17.
Over the past decades, the tropical mountain rainforest of southern Ecuador has been threatened by conversion to cattle pastures. Frequently, these pastures are invaded by bracken fern and abandoned when bracken becomes dominant. Changes in land-use (forest–pasture–abandoned pasture) can affect soil microorganisms and their physiological responses with respect to soil carbon and nutrient cycling. In situ investigations on litter decomposition and soil respiration as well as biogeochemical characterization of the soil were carried out to identify the driving factors behind. The conversion of forest to pasture induced a pronounced increase in CO2–C effluxes to 12.2 Mg ha?1 a?1 which did not decrease after abandonment. Soil microbial activity and biomass showed a different pattern with lowest values at forest and abandoned pasture sites. With 3445 mg kg?1 (0–5 cm) microbial biomass carbon (MBC by CFE-method), the active pasture had a more than three times higher value than forest and abandoned pasture, which was among the highest in tropical pasture soils. A shift in the microbial community structure (phospholipid fatty acid, PLFA) was also induced by the establishment of pasture land; the relative abundance of fungi and Gram-negative bacteria increased. PLFA fingerprints of the forest organic layer were more similar to pasture than to forest mineral soil. Chemical properties (pH value, exchangeable cations) were the main factors influencing the respective microbial structure. Bracken-invasion resulted in a decrease in the quantity and quality of above- and belowground biomass. The lower organic substance and nutrient availability induced a significant decline in microbial biomass and activity. After pasture abandonment, these differences in soil microbial function were not accompanied by pronounced shifts in the community structure and in soil pH as was shown for the conversion to pasture. A disconnection between microbial structure and function was identified. Similar soil CO2–C effluxes between active and abandoned pasture sites might be explained by an underestimation of the effluxes from the active pasture site. All measurements were carried out between grass tussocks where fine-root density was about 2.6 times lower than below tussocks. Thus, lower proportions of root respiration were expected than below tussocks. Overall, soil microorganisms responded differently to changes in land-use from forest to pasture and from pasture to abandoned pasture resulting in pronounced changes of carbon and nutrient cycling and hence of ecosystem functioning.  相似文献   

18.
长期施肥对稻田土壤固碳功能菌群落结构和数量的影响   总被引:3,自引:0,他引:3  
微生物固碳在减缓全球气候变化、实现人类可持续发展方面具有重要的意义,通过揭示长期不同施肥制度对土壤固碳细菌的影响规律,可以为我国稻田土壤科学施肥,稻田固碳和温室气体减排的共轭双赢作用提供重要的理论依据。以湖南宁乡国家级稻田肥力变化长期定位试验为平台,采用PCR-克隆测序和实时荧光定量(Real-time)PCR技术,研究不施肥(CK),氮磷钾肥(NPK)和秸秆还田(NPKS)3种长期施肥制度对稻田土壤固碳细菌群落结构及数量的影响。通过分析固碳细菌cbbL基因文库发现,长期施肥导致土壤固碳细菌种群结构产生了明显差异,NPK和NPKS处理中兼性自养固碳菌群落优势增加而严格自养固碳菌生长受到抑制。LUBSHUFF软件统计分析显示cbbL基因文库在CK、NPK及NPKS处理间均存在显著性差异。 3种施肥处理的稻田土壤细菌cbbL基因拷贝数为3.35?108 —5.61?108每克土,施肥后,土壤细菌cbbL基因数量增加,其中NPKS处理cbbL数量最多,是CK处理的1.5倍左右。稀疏曲线则显示长期施化肥导致细菌cbbL基因多样性高于NPKS,而NPKS高于CK。上述结果表明了长期施肥对土壤固碳细菌群落结构,多样性及数量均有显著的影响。本研究结果可为深入探讨稻田土壤微生物固碳潜力及其影响机理提供有力的依据。  相似文献   

19.
The gases CO, CO2, and H2 were used as substrates in anaerobic fermentations producing organic acids. Various mixed bacterial sources were used, including sewage sludge digester effluent, rabbit feces, and soil. Nonsterile microorganism selection was carried out using CO2/H2 and CO/H2 as the primary carbon and energy sources. Cultures were grown in specially designed, high-pressure (to 70 psig) flasks. Methanogenic bacteria were eliminated from the cultures. Liquid products of the fermentations were acetic through caproic acids, with the even-numbered acids predominating. Carbon balances showed conclusively that acetic acid was formed from carbon contained in the CO or CO2 feed gas. Measurements made included rates of acid product formation, cell density, and degree of gas utilization. Limited characterization of the microorganisms was also performed. Production of organic acids by mixed culture inocula from CO2/H2 or CO/H2 had not been reported previously. Application of this work is to the production of organic chemicals from synthesis gas (SNG), produced by the gasification of fossil fuels (peat, lignite, and various ranks of coals), biomass (agricultural and forest residues, and various biomass crops grown expressly for energy recovery), and municipal solid waste.  相似文献   

20.
A method is described for the measurement of 14CO2 assimilation by microorganisms in soils. A determination involves exposing soil to 14CO2, pyrolyzing the exposed soil, trapping the organic pyrolysis products on a column of firebrick coated with CuO, combusting the trapped organics by heating, and measuring the radioactivity in the CO2 produced in the combustion. The detection of significant levels of 14C in the trapped organic fraction appears to be an unambiguous indication of biological activity. The 14CO2 which is adsorbed or exchanged into soils by nonbiological processes does not interfere. The method easily detects the 14CO2 fixed by 102 to 103 algae after light exposure for 3 to 24 hr. Assimilation of 14C is also demonstrable in dark-exposed soils containing 105 to 106 heterotrophic bacteria. Possible applications of the method in the biological exploration of Mars are discussed.  相似文献   

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