Carbon and energy yields in prebiotic syntheses using atmospheres containing CH4, CO and CO2

Yields based on carbon are usually reported in prebiotic experiments, while energy yields (moles cal-1) are more useful in estimating the yields of products that would have been obtained from the primitive atmosphere of the earth. Energy yields for the synthesis of HCN and H2CO from a spark discharge were determined for various mixtures of CH4, CO, CO2, H2, H2O, N2 and NH3. The maximum yields of HCN and H2CO from CH4, CO, and CO2 as carbon sources are about 4 X 10(-8) moles cal-1.     

Prebiotic synthesis in atmospheres containing CH4, CO,and CO2

The prebiotic synthesis of organic compounds using a spark discharge on various simulated primitive earth atmospheres at 25 degrees C has been studied. Methane mixtures contained H2 + CH4 + H2O + N2 + NH3 with H2/CH4 molar ratios from 0 to 4 and pNH3 = 0.1 torr. A similar set of experiments without added NH3 was performed. The yields of amino acids (1.2 to 4.7% based on the carbon) are approximately independent of the H2/CH4 ratio and whether NH3 was present, and a wide variety of amino acids are obtained. Mixtures of H2 + CO + H2O + N2 and H2 + CO2 + H2O + N2, with and without added NH3, all gave about 2% yields of amino acids at H2/CO and H2/CO2 ratios of 2 to 4. For a H2/CO2 ratio of 0, the yield of amino acids is extremely low (10(-3)%). Glycine is almost the only amino acid produced from CO and CO2 model atmospheres. These results show that the maximum yield is about the same for the three carbon sources at high H2/carbon ratios, but that CH4 is superior at low H2/carbon ratios. In addition, CH4 gives a much greater variety of amino acids than either CO or CO2. If it is assumed that an abundance of amino acids more complex than glycine was required for the origin of life, then these results indicate the requirement for CH4 in the primitive atmosphere.     

Organic syntheses from CH4−N2 atmospheres: Implications for Titan

Numerous experiments have already been performed, simulating the evolution of gaseous mixtures containing CH₄ when submitted to energy flux. From their results, it appears that a variety of organic compounds, including unsaturated hydrocarbons and nitriles such as HCN, can be synthesized into noticeable amounts from CH₄–N₂ mixtures. In particular, systematic studies of the influence of the composition of the mixture on the nature and amount of synthesized compounds show that organic volatile nitriles, and particularly cyanoacetylene and cyanogen, are formed only in media rich in nitrogen. Those nitriles have been identified very recently in the atmosphere of Titan, and thus, data from such laboratory experiments may provide important indirect information on the organic chemistry occuring at the periphery of this satellite of Saturn. However, during these experiments, there is a continuous formation and accumulation of molecular hydrogen, which does not occur in the atmosphere of Titan, because of H₂ escape. In order to reassess the data already available from this type of laboratory studies, experiments on CH₄–N₂ atmospheres, with and without H2 escape, have been recently performed. The influence of this parameter on the chemical evolution of the atmosphere and on the nature and relative quantities of organic compounds has been studied.After reviewing these experiments, implications of the obtained results on the organic chemistry at the periphery of Titan are discussed.Paper presented at the 6th College Park Colloquium, October 1981.     

Biomass fast pyrolysis in a fluidized bed reactor under N2, CO2, CO, CH4 and H2 atmospheres

Biomass fast pyrolysis is one of the most promising technologies for biomass utilization. In order to increase its economic potential, pyrolysis gas is usually recycled to serve as carrier gas. In this study, biomass fast pyrolysis was carried out in a fluidized bed reactor using various main pyrolysis gas components, namely N₂, CO₂, CO, CH₄ and H₂, as carrier gases. The atmosphere effects on product yields and oil fraction compositions were investigated. Results show that CO atmosphere gave the lowest liquid yield (49.6%) compared to highest 58.7% obtained with CH₄. CO and H₂ atmospheres converted more oxygen into CO₂ and H₂O, respectively. GC/MS analysis of the liquid products shows that CO and CO₂ atmospheres produced less methoxy-containing compounds and more monofunctional phenols. The higher heating value of the obtained bio-oil under N₂ atmosphere is only 17.8 MJ/kg, while that under CO and H₂ atmospheres increased to 23.7 and 24.4 MJ/kg, respectively.     

Linking Belowground Carbon Allocation to Anaerobic CH4 and CO2 Production in a Forested Peatland,New York State

Heterotrophic soil microorganisms rely on carbon (C) allocated belowground in plant production, but belowground C allocation (BCA) by plants is a poorly quantified part of ecosystem C cycling, especially, in peat soil. We applied a C balance approach to quantify BCA in a mixed conifer-red maple (Acer rubrum) forest on deep peat soil. Direct measurements of CH₄ and CO₂ fluxes across the soil surface (soil respiration), production of fine and small plant roots, and aboveground litterfall were used to estimate respiration by roots, by mycorrhizae and by free-living soil microorganisms. Measurements occurred in two consecutive years. Soil respiration rates averaged 1.2 bm μmol m^{? 2} s^{? 1} for CO₂ and 0.58 nmol m^{? 2} s^{? 1} for CH₄ (371 to 403 g C m^{? 2} year^{? 1}). Carbon in aboveground litter (144 g C m^{? 2} year^{? 1}) was 84% greater than C in root production (78 g C m^{? 2} year^{? 1}). Complementary in vitro assays located high rates of anaerobic microbial activity, including methanogenesis, in a dense layer of roots overlying the peat soil and in large-sized fragments within the peat matrix. Large-sized fragments were decomposing roots and aboveground leaf and twig litter, indicating that relatively fresh plant production supported most of the anaerobic microbial activity. Respiration by free-living soil microorganisms in deep peat accounted for, at most, 29 to 38 g C m^{? 2} year^{? 1}. These data emphasize the close coupling between plant production, ecosystem-level C cycling and soil microbial ecology, which BCA can help reveal.     

Partitioning of CH4 and CO2 Production Originating from Rice Straw,Soil and Root Organic Carbon in Rice Microcosms

Flooded rice fields are an important source of the greenhouse gas CH₄. Possible carbon sources for CH₄ and CO₂ production in rice fields are soil organic matter (SOM), root organic carbon (ROC) and rice straw (RS), but partitioning of the flux between the different carbon sources is difficult. We conducted greenhouse experiments using soil microcosms planted with rice. The soil was amended with and without ¹³C-labeled RS, using two ¹³C-labeled RS treatments with equal RS (5 g kg⁻¹ soil) but different δ¹³C of RS. This procedure allowed to determine the carbon flux from each of the three sources (SOM, ROC, RS) by determining the δ¹³C of CH₄ and CO₂ in the different incubations and from the δ¹³C of RS. Partitioning of carbon flux indicated that the contribution of ROC to CH₄ production was 41% at tillering stage, increased with rice growth and was about 60% from the booting stage onwards. The contribution of ROC to CO₂ was 43% at tillering stage, increased to around 70% at booting stage and stayed relatively constant afterwards. The contribution of RS was determined to be in a range of 12–24% for CH₄ production and 11–31% for CO₂ production; while the contribution of SOM was calculated to be 23–35% for CH₄ production and 13–26% for CO₂ production. The results indicate that ROC was the major source of CH₄ though RS application greatly enhanced production and emission of CH₄ in rice field soil. Our results also suggest that data of CH₄ dissolved in rice field could be used as a proxy for the produced CH₄ after tillering stage.     

Bioconversion of organic carbon to CH4 and CO2

The activities of populations in complex anaerobic microbial communities that perform complete bioconversion of organic matter to CH₄ and CO₂ are reviewed. Species of eubacteria produce acetate, H₂, and CO₂ from organic substrates, and methanogenic species of archaebacteria transform the acetate, H₂, and CO₂ to CH₄. The characteristics and activities of the methanogenic bacteria are described. The impact of the use of H₂ by methanogens on the fermentations that produce acetate, H₂, and CO₂ and the importance of syntrophy in complete bioconversion are discussed.     

Soil-atmosphere exchange of CH4, CO2, NOx,and N2O in the Colorado shortgrass steppe under elevated CO2

In late March 1997, an open-top-chamber (OTC) CO₂ enrichment study was begun in the Colorado shortgrass steppe. The main objectives of the study were to determine the effect of elevated CO₂ (720 mol mol^–1) on plant production, photosynthesis, and water use of this mixed C₃/C₄ plant community, soil nitrogen (N) and carbon (C) cycling and the impact of changes induced by CO₂ on trace gas exchange. From this study, we report here our weekly measurements of CO₂, CH₄, NO_x and N₂O fluxes within control (unchambered), ambient CO₂ and elevated CO₂ OTCs. Soil water and temperature were measured at each flux measurement time from early April 1997, year round, through October 2000. Even though both C₃ and C₄ plant biomass increased under elevated CO₂ and soil moisture content was typically higher than under ambient CO₂ conditions, none of the trace gas fluxes were significantly altered by CO₂ enrichment. Over the 43 month period of observation NO_x and N₂O flux averaged 4.3 and 1.7 in ambient and 4.1 and 1.7 g N m^–2 hr ^–1 in elevated CO₂ OTCs, respectively. NO_x flux was negatively correlated to plant biomass production. Methane oxidation rates averaged –31 and –34 g C m^–2 hr^–1 and ecosystem respiration averaged 43 and 44 mg C m^–2 hr^–1 under ambient and elevated CO₂, respectively, over the same time period.     

Comparison analysis on the energy efficiencies and biomass yields in microbial CO2 fixation

CO₂ fixation by a hydrogen-oxidizing bacterium, Cupriavidus necator, was evaluated in a packed bed bioreactor under a constant flow rate of gas mixtures (H₂, O₂, CO₂). The overall energy efficiency depends on the efficiencies of CO₂ fixation into carbohydrate and the reduced carbon into biomass and bioproducts, respectively. The efficiencies varied with the limiting gas substrate. Under O₂ limitation, the efficiency (20–30%) of CO₂ fixation increased with time and was higher than the overall efficiency (12–18%). Under H₂ limitation, the efficiency of CO₂ fixation declined with time while the biomass yield was quite similar to that under O₂ limitation. A cellular metabolic model was suggested for the lithoautotrophic growth of C. necator, including CO₂ fixation into carbohydrate followed by the main metabolic pathway of reduced carbon. Under CO₂ limitation, most H₂ energy was wasted, resulting in a very low biomass yield. Under a dual limitation of O₂ and nitrogen, biosynthesis of poly(3-hydroxybutyrate) was triggered, and the energy efficiency or yield of biopolyester was lower than those of microbial cell mass. Compared with a green microalga Neochloris oleoabundans that produces lipid under nutrient limitation, C. necator exhibited a much higher (3–6 times) energy efficiency in producing biomass and bioproducts from CO₂.     

Fluxes of N2O,CH4 and CO2 on afforested boreal agricultural soils

After drainage of natural boreal peatlands, the decomposition of organic matter increases and peat soil may turn into a net source of CO₂ and N₂O, whereas CH₄ emission is known to decrease. Afforestation is a potential mitigation strategy to reduce greenhouse gas emission from organic agricultural soils. A static chamber technique was used to evaluate the fluxes of CH₄, N₂O and CO₂ from three boreal organic agricultural soils in western Finland, afforested 1, 6 or 23 years before this study. The mean emissions of CH₄ and N₂O during the growing seasons did not correlate with the age of the tree stand. All sites were sources of N₂O. The highest daily N₂O emission during the growing season, measured in the oldest site, was as high as 29 mg N₂O m^–2d^–1. In general, organic agricultural soils are sinks for methane. Here, the oldest site acted as a small sink for methane, whereas the two youngest afforested organic soils were sources for methane with maximum emission rates (up to 154 mg m^–2d^–1) similar to those reported for minerogenous natural peatlands. Soil respiration rates decreased with the age of the forest. The high soil respiration in the younger sites, probably resulted from the high biomass production of herbs, could create soil anaerobiosis and increase methane production. Our results show that afforestation of agricultural peat soils does not abruptly terminate the N₂O emissions during the first two decades, and afforestation can even enhance methane emission for a few years. The carbon accumulation in the developing tree stand can partly compensate the carbon loss from soil.     

Diurnal Oscillations in Gas Production (O2, CO2, CH4, and N2) in Soil Monoliths

Soil cores (35 cm long, 7 cm diameter) from the Macaulay Land Use Research Institute's Sourhope Research Station in the Scottish Borders were kept and monitored at constant temperature (18± 1°C) for gas production using a 1.6 mm diameter stainless steel probe fitted with a membrane inlet and connected to a quadrupole mass spectrometer. This provided a novel method for on-line, real time monitoring of soil gas dynamics. In closed-system headspace experiments, O₂ and CO₂ (measured at m/z values 32 and 44, respectively) showed anti-phase diurnal fluctuations in low-intensity simulated daylight and under a light-dark (LD, 12:12 h) regime. O₂ increased during periods of illumination and decreased in the dark. The inverse was true for CO₂ production. Ar (m/z = 40) concentration and temperature (°C) remained constant throughout the experiments. The same phase-related oscillations, in CO₂ and O₂ concentrations, were observed at 2 and 5 cm depth in soil cores. The O₂ concentration did not oscillate diurnally at 10 cm depth. In below-ground experiments, CH₄ (m/z = 15) concentration showed diurnal cycles at 2, 5 and 10 cm depth. The CH₄ production had the same diurnal phase cycle as CO₂ but with lower amplitude. Evidence of below-ground diurnal oscillations in N₂ (m/z = 28) concentration was provided at 5 cm depth. The scale of production and consumption of gases associated with soil-atmosphere interactions and below-ground processes, are shown to be a multifaceted output of several variables. These include light, circadian-controlled physiological rhythms of plants and microbes, and the interactions between these organisms.     

Diurnal Oscillations in Gas Production (O2, CO2, CH4, and N2) in Soil Monoliths

Soil cores (35 cm long, 7 cm diameter) from the Macaulay Land Use Research Institute's Sourhope Research Station in the Scottish Borders were kept and monitored at constant temperature (18± 1°C) for gas production using a 1.6 mm diameter stainless steel probe fitted with a membrane inlet and connected to a quadrupole mass spectrometer. This provided a novel method for on-line, real time monitoring of soil gas dynamics. In closed-system headspace experiments, O₂ and CO₂ (measured at m/z values 32 and 44, respectively) showed anti-phase diurnal fluctuations in low-intensity simulated daylight and under a light-dark (LD, 12:12 h) regime. O₂ increased during periods of illumination and decreased in the dark. The inverse was true for CO₂ production. Ar (m/z = 40) concentration and temperature (°C) remained constant throughout the experiments. The same phase-related oscillations, in CO₂ and O₂ concentrations, were observed at 2 and 5 cm depth in soil cores. The O₂ concentration did not oscillate diurnally at 10 cm depth. In below-ground experiments, CH₄ (m/z = 15) concentration showed diurnal cycles at 2, 5 and 10 cm depth. The CH₄ production had the same diurnal phase cycle as CO₂ but with lower amplitude. Evidence of below-ground diurnal oscillations in N₂ (m/z = 28) concentration was provided at 5 cm depth. The scale of production and consumption of gases associated with soil-atmosphere interactions and below-ground processes, are shown to be a multifaceted output of several variables. These include light, circadian-controlled physiological rhythms of plants and microbes, and the interactions between these organisms.     

Effects of CO2, CH4 and N2 on growth and nutrition of rice seedlings

Summary Flooded soils, which accumulate gaseous products of anaerobic fermentation, are often associated with poor rice plant growth. In the present experiment the effects of CO₂, CH₄, N₂, and air on rice seedling growth and nutrition were evaluated. Nutrient culture techniques were used to avoid secondary soil effects normally experienced.Carbon dioxide gas in the root zone of rice reduced seedling growth significantly, whereas CH₄ and N₂ had no significant effect. Methane gave no stimulatory benefits, unlike results reported by some earlier workers. Of three major nutrient elements studied, P uptake was affected more than N or K. Phosphorus uptake was significantly reduced in leaves and sheaths by all three gases, but was significantly increased in roots. This suggests an immobilization mechanism affecting P in roots, and since CO₂, CH₄, and N₂ behaved similarly in contrast to air, a lack of oxygen in the root system is suspected as the causal mechanism rather than toxic effects of gases. Effects on N and K uptake were minimal and insignificant.Contribution from the Department of Agronomy and Range Science, University of California, Davis, California 95616.Contribution from the Department of Agronomy and Range Science, University of California, Davis, California 95616.     

植物对沼泽湿地生态系统CO2和CH4排放的影响

利用静态暗箱/气相色谱法于2003~2005年在生长季对三江平原小叶章(Calamagrostis angustifolia)沼泽化草甸和毛果苔草(Carexlasiocarpa)沼泽地区CO2和CH4的排放通量进行野外对比观测实验。结果表明:2003~2005年生长季小叶章草甸土壤-植物系统CO2排放通量分别是土壤CO2排放通量的1.65、2.06和2.01倍,毛果苔草沼泽土壤-植物系统CO2排放通量分别是土壤CO2排放通量的2.58、2.27和4.21倍,表明沼泽湿地土壤-植物系统CO2排放通量的主要贡献者是植物地上部分的呼吸作用,且3个生长季小叶章草甸CO2排放通量均显著大于毛果苔草沼泽,主要是由于植物生物量的差异以及土壤微生物活性的不同。2003~2005年植物生长季,小叶章草甸土壤-植物系统CH4排放通量分别是土壤的4.84、3.55和6.45倍,毛果苔草沼泽土壤-植物系统CH4排放通量分别是土壤的2.60、1.25和3.22倍,且3个生长季小叶章草甸和毛果苔草沼泽CH4排放通量均具有显著差异,这主要是由于水位的差异以及植物对CH4排放能力的不同造成的。     

Spatial and temporal variations of dissolved gases (CH4, CO2, and O2) in peat cores

Spatial and temporal variations in the concentrations of dissolved gases (CH₄, CO₂, and O₂) in peat cores were studied using membrane inlet mass spectrometry (MIMS). Variations in vertical gas profiles were observed between random peat cores taken from hollows on the same peat bog. Methane concentrations in profiles (0–30 cm) generally increased with depth and reached maximum values in the range of 200–450 m CH₄ below about 13-cm depth. In some profiles, a peak of dissolved methane was observed at 7-cm depth. Oxygen penetrated to approximately 2-cm depth in the hollows. The sampling probe was used to continuously monitor CH₄, CO₂, and O₂ concentrations at fixed depths in peat cores over periods of several days. The concentration of dissolved CO₂ and O₂ at 1-cm depth oscillated over a 24-h period with the maximum of CO₂ concentration corresponding with the minimum of 0₂. Diurnal variations in CO₂ but not CH₄ were measured at 15-cm depth; dissolved CO₂ levels decreased during daylight hours to a constant minimum concentration of 4.85 mm. This report also describes the application of MIMS for the measurement of gaseous diffusion rates in peat using an inert gas (argon); the value of D, the diffusion coefficient, was 2.07 × 10^–8 m² s^–1. Correspondence to: D. Lloyd     

N2O排放规律及其影响因子

采用野外静态箱-气相色谱法,研究了小兴安岭典型阔叶林沼泽生长季节土壤CO2、CH4和N2O排放季节变化规律、源/汇功能及主要影响因子。结果表明：①苔草沼泽、毛赤杨沼泽和白桦沼泽生长季节土壤CO2、CH4、N2O排放分别集中在夏季、夏秋季、春夏季,平均排放通量依次为514.63、487.89、382.27 mgm-2h-1,1.88、1.03、0.04 mgm-2h-1,58.61、11.73、3.70µgm-2h-1。②三者生长季节土壤CO2排放通量与气温和0~20 cm土壤温度均呈显著正相关;苔草沼泽CH4排放通量与30~40 cm土壤温度呈显著正相关,毛赤杨沼泽CH4排放通量与地表温度呈显著负相关;白桦沼泽N2O排放通量与地表温度呈显著正相关。苔草沼泽N2O排放与水位呈显著负相关;毛赤杨沼泽CH4排放与水位呈显著正相关;白桦沼泽CO2排放与水位呈显著负相关。③三者生长季节土壤均为CO2、CH4、N2O排放源（17.56、13.76、18.53 thm-2;67.54、37.05、1.30 kghm-2;0.13、2.11、0.42 kg.hm-2）,三者CO2排放量相近（5.5%~21.6%）;苔草沼泽为CH4的强排放源,毛赤杨沼泽为中排放源,白桦沼泽为弱排放源;毛赤杨沼泽为N2O的强排放源,白桦沼泽为中排放源,苔草沼泽为弱排放源。     

Dynamics of dissolved O2, CO2, CH4, and N2O in a tropical coastal swamp in southern Thailand

We studied the distribution of dissolved O₂, CO₂, CH₄, and N₂O in a coastal swamp system in Thailand with the goal to characterize the dynamics of these gases within the system. The gas concentrations varied spatially and seasonally in both surface and ground waters. The entire system was a strong sourcefor CO₂ and CH₄, and a possible sink for atmospheric N₂O. Seasonal variation in precipitation primarily regulated the redox conditions in the system. However, distributions of CO₂, CH₄, and N₂O in the river that received swamp waters were not always in agreement with redox conditions indicated by dissolvedO₂ concentrations. Sulfate production through pyriteoxidation occurred in the swamp with thin peat layerunder aerobic conditions and was reflected by elevatedSO ₄ ^2– /Cl^– in the river water. When SO ₄ ^2– /Cl^– was high, CO₂ and CH₄ concentrations decreased, whereas the N₂O concentration increased. The excess SO ₄ ^2– in the river water was thus identified as a potential indicator for gas dynamics in this coastal swamp system.