Phospholipid fatty acids analysis of the vertical distribution of microbial communities in eutrophic lake sediments

Vertical distribution of microbial communities in a eutrophic lake sediments of Lake Xuanwu was quantified by phospholipid fatty acids analysis and multivariate statistical analysis was employed to interprete the data. Principle component analysis of sediment characteristics parameters, including total nitrogen, total phosphorus, organic matters and pH produced clustering of sampling sites for two distinct groups. These groups corresponded with the two sampling stations and the levels of nutrient enrichment. Total phospholipid fatty acids concentration, which is indicative of microbial biomass, reduced with depth, however, the relative percentage of anaerobic prokaryotes increased. To assess changes of microbial community along depth, phospholipid fatty acids compositions were analyzed by cluster analysis. Distinct clusters were observed in different sampling stations. Canonical correspondence analysis was carried out to infer the relationship between sediment characteristics and microbial communities. Phospholipid fatty acids samples collected at the same sampling site clustered together. Canonical correspondence analysis revealed that the environmental parameter with the greatest bearing on the phospholipid fatty acids profiles was pH. This study proved the successful application of phospholipid fatty acids and multivariate analysis to investigate the relationship between environment factors and microbial community composition.     

Temperature induced decoupling of enzymatic hydrolysis and carbon remineralization in long-term incubations of Arctic and temperate sediments

Extracellular enzymatic hydrolysis of high-molecular weight organic matter is the initial step in sedimentary organic carbon degradation and is often regarded as the rate-limiting step. Temperature effects on enzyme activities may therefore exert an indirect control on carbon mineralization. We explored the temperature sensitivity of enzymatic hydrolysis and its connection to subsequent steps in anoxic organic carbon degradation in long-term incubations of sediments from the Arctic and the North Sea. These sediments were incubated under anaerobic conditions for 24 months at temperatures of 0, 10, and 20 °C. The short-term temperature response of the active microbial community was tested in temperature gradient block incubations. The temperature optimum of extracellular enzymatic hydrolysis, as measured with a polysaccharide (chondroitin sulfate), differed between Arctic and temperate habitats by about 8-13 °C in fresh sediments and in sediments incubated for 24 months. In both Arctic and temperate sediments, the temperature response of chondroitin sulfate hydrolysis was initially similar to that of sulfate reduction. After 24 months, however, hydrolysis outpaced sulfate reduction rates, as demonstrated by increased concentrations of dissolved organic carbon (DOC) and total dissolved carbohydrates. This effect was stronger at higher incubation temperatures, particularly in the Arctic sediments. In all experiments, concentrations of volatile fatty acids (VFA) were low, indicating tight coupling between VFA production and consumption. Together, these data indicate that long-term incubation at elevated temperatures led to increased decoupling of hydrolytic DOC production relative to fermentation. Temperature increases in marine sedimentary environments may thus significantly affect the downstream carbon mineralization and lead to the increased formation of refractory DOC.     

Biodegradation of C-labeled low molecular organic acids using three biometer methods

Low molecular weight organic acids (LMWOA) are produced in soil by various biological and chemical processes and can exhibit substantial metal complexing and dissolution capacity. The reactivity of these compounds in the soil environment is dependent on their non-complexed concentration in the soil solution. Adsorption of LMWOA has been shown to reduce their concentration in the soil solution; however, little is known about the reduction of LMWOA concentration due to microbial degradation. To examine the extent of microbial degradation in reducing LMWOA concentration in the soil solution, three-biometer methods were used: a soil biometer flask, an in-situ field biometer and a soil column biometer. Four soil horizons were used with each method. To each soil sample, 2.0×10⁻⁶ moles of organic acid containing 3.7×10⁴ Bq total activity was applied. The ¹⁴C-radiolabeled aliphatic and aromatic acids studied included oxalic, malonic, succinic, and phthalic acid. Evolved ¹⁴CO₂ was trapped in 0.5 mol l⁻¹ NaOH and measured using liquid scintillation counting. Labeled acids degraded rapidly within the first 5 days for the Ap1, Ap2, and BA horizons, with a generally slower rate of ¹⁴CO₂ evolution being observed for the Bt1 horizon. The % degradation of labeled acid was substantially greater for the soil biometer flask method, compared to the field and soil column biometer methods. The average % degradation for the soil biometer flask was 67% for all soil horizons and organic acids, compared to 14% for the field biometer and 13% for the soil column biometer. Results indicate that substantial microbial degradation of organic acids can occur within a relatively short time period and the biometer method selected can influence the % acid degraded. Based on primary results, the soil column biometer method better approximated microbial degradation under field conditions, as evaluated using the field biometer.     

Early diagenesis of organic matter in the water column and sediments: Microbial degradation and resynthesis of lipids in Lake Haruna

Particulate matter, sediment trap, and surface sediment samples collected in freshwater Lake Haruna were studied to understand early diageesis of organic materials in the water column and in bottom sediments. The samples were analyzed for biomarkers, including aliphatic and aromatic hydrocarbons, fatty alcohols, saturated and unsaturated fatty acids, β- and ω-hydroxyacids, and α,ω-dicar☐ylic acids. Decreases in concentrations of autochthonous saturated C₁₂–C₁₉ fatty acids and polyunsaturated C₁₈ acids relative to TOC occured with the settling of organic matter ot the lake bottom, whereas the amounts of terrestial saturated C₂₀–C₃₀ acids remained almost constant. Conversely, the concentrations of monosaturated fatty acids, branched chain fatty acids, and β- and ω-hydroxyacids, which are probably produced by microbial activity, increased. These results indicate that preferential degradation of algal lipids accompanies microbial resynthesis of lipids during settling, however, terrigenous lipids are relatively stable.     

Hydrogen isotopic fractionation in lipid biosynthesis by H2-consuming Desulfobacterium autotrophicum

We report hydrogen isotopic fractionations between water and fatty acids of the sulfate-reducing bacterium Desulfobacterium autotrophicum. Pure cultures were grown in waters with deuterium (D) contents that were systematically varied near the level of natural abundance (−37‰ ? δD ? 993‰). H₂ of constant hydrogen isotope (D/H) ratio was supplied to the cultures. The D/H ratios of water, H₂, and specific fatty acids were measured by isotope-ratio mass spectrometry. The results demonstrate that D. autotrophicum catalyzes hydrogen isotopic exchange between water and H₂, and this reaction is conclusively shown to approach isotopic equilibrium. In addition, variation in the D/H ratio of growth water accounts for all variation in the hydrogen isotopic composition of fatty acids. The D/H ratios of fatty acids from cultures grown on H₂/CO₂ are compared with those from a separate set of cultures grown on D-enriched formate, an alternative electron donor. This comparison rules out H₂ as a significant source of fatty acid hydrogen. Grown on either H₂/CO₂ or formate, D. autotrophicum produces fatty acids in which all hydrogen originates from water. For specific fatty acids, biosynthetic fractionation factors are mostly in the range 0.60 ? α_FA-water ? 0.70; the 18:0 fatty acid exhibits a lower fractionation factor of 0.52. The data show that α_FA-water generally increases with length of the carbon chain from C₁₄ to C₁₇ among both saturated and unsaturated fatty acids. These results indicate a net fractionation associated with fatty acid biosynthesis in D. autotrophicum that is slightly smaller than in another H₂-consuming bacterium (Sporomusa sp.), but much greater than in most photoautotrophs.     

Maturation related changes in the distribution of ester bound fatty acids and alcohols in a coal series from the New Zealand Coal Band covering diagenetic to catagenetic coalification levels

A rank series of lignites and coals of low to moderate maturation levels (vitrinite reflectance (R₀): 0.27–0.8%) from the New Zealand Coal Band were investigated using alkaline ester cleavage experiments to reveal compositional changes of ester bound components (fatty acids and alcohols) during increasing maturation. Ester bound alcohols are found to be present in highest amounts in the very immature lignite samples (R₀: 0.27–0.29%), but show a rapid decrease during early diagenesis. Ester bound fatty acids also show an initial exponential decrease during diagenesis, but reveal an intermittent increase during early catagenesis before decreasing again during main catagenesis. This intermittent increase was related to the short chain fatty acids. To obtain a maturity related signal and to eliminate facies related scattering in the amounts of fatty acids in the coal samples, the carbon preference index of fatty acids (CPI_FA) parameter is introduced here. For the long chain fatty acids (C₂₀–C₃₂) originating from terrigenous plant debris, the CPI_FA decreases with increasing maturity, showing a strong maturation related signal. During diagenesis, the same trend can be observed for the short chain fatty acids, but the intermittent increase in the amounts of short chain fatty acids is also accompanied by high CPI_FA values. This indicates less altered organic biomass at this advanced maturation level and is in contrast to the mature CPI_FA signal of the long chain fatty acids of the same samples. One possible reason for this discrepancy could be extremely different amounts of short and long chain fatty acids in the original source organic matter of these samples. However, another intriguing explanation could be the incorporation of immature bacterial biomass from deep microbial communities containing C₁₆ and C₁₈ fatty acids as main cell membrane components. Deep microbial life might be stimulated at this interval by the increasing release of thermally generated potential substrates from the organic matrix during early catagenesis. In contrast to the fatty acids, the high amounts of alcohols in the immature lignite samples are also visible in the alkene distribution from the open system pyrolysis experiments of the organic matrix before and after saponification.     

松粉热解脂肪酸生物标志物的特征及其地球化学意义

现代松粉的温－压热模拟实验中，产出的轻质烃和氯仿抽提物芳烃馏份的GC－MS分析均检出大量偶数碳优势明显的脂肪酸类分子生物标志物，轻烃主要为C16，C18烷酸及其甲，乙酯，芳烃组分相对比较复杂，包括饱和脂肪酸（酯），不饱和脂肪酸（酯）和脂肪酸内酯，前者碳数分布为C15－，C30，C16，C18碳酸（酯）相对丰度占绝对优势为特征，后者碳数分布为C20-C30,以C26，C28和C30脂肪酸内酯为主，在250℃以下样品中检测出相对丰度较高的不饱和C18碳酸（酯），脂肪酸酯化合物在极低的温度条件下便可排出，并分别在200－300℃和300－400℃之间形成两次产出高峰；花粉内质体中的游离态脂肪酸及不饱和脂肪酸形成低温阶段的第一次高峰；花粉壁脂质结构中的脂肪酸及饱和脂肪酸在较高温度阶段形成第二次高峰，原样及低温样品以脂肪酸酯为主，250℃及其以上温度条件下因水解产生较多的脂肪酸，随温率继续升高，脂肪酸酯易发生脱羰反应而生成链烷烃。400℃以后因强烈降解脂肪酸酯含量大大降低，这与350－450℃之间奇数碳优势正构烷烃在轻质烃和饱和烃中的大量产出相吻合，研究表明，植物花粉是沉积有机质中饱和及不饱和C16，C18脂肪酸酯的重要母源之一。     

Lipid biomarkers and carbon-isotopes of modern travertine deposits (Yellowstone National Park, USA): Implications for biogeochemical dynamics in hot-spring systems

Lipid biomarkers and ¹³C fractionation patterns were used to understand the dynamics of carbon cycling during microbial metabolisms in different environments of travertine precipitation (called facies) at Spring AT-1 on Angel Terrace in the Mammoth Hot Springs complex of Yellowstone National Park, USA. Microbial mats that encrust travertine deposits were collected for analyses of lipid biomarkers and carbon isotopes along the continuous drainage outflow system of Spring AT-1. The spring water exhibits a continuous temperature drop from 71°C in the vent at top to 24°C in the distal slope at bottom. Phospholipid fatty acids (PLFA) and glycolipid fatty acids (GLFA) exhibit distinctly different compositions in each of the facies, which are consistent with partitioning of the bacterial 16S rRNA gene sequences in the Spring AT-1 travertine facies (Fouke et al., 2003).The δ¹³C composition of total biomass within the microbial mats decreases from −16.1‰ in the vent to −23.5‰ in the distal slope. However, lower values occur in the pond (−26.0‰) and the proximal slope (−28.0‰) between the vent and the distal slope. Isotopic compositions of PLFA and GLFA have variations similar to those of total biomass. The average δ¹³C values of PLFA are −12.4 ± 5.2‰ (n = 10 individual fatty acids, same below) in the vent, −33.0 ± 3.1‰ (n = 11) in the pond, −33.7 ± 3.8‰ (n = 16) in the proximal slope, and −22.4 ± 3.4‰ (n = 10) in the distal slope; the average δ¹³C values of GLFA are −19.6 ± 3.0‰ (n = 3) in the vent, −30.4 ± 4.7‰ (n = 8) in the pond, −36.9 ± 2.8‰ (n = 12) in the proximal slope, and −27.9 ± 3.1‰ (n = 13) in the distal slope. In particular, fatty acids in the vent are enriched in ¹³C relative to the total biomass, which is consistent with the notion that the biosynthetic pathways of the extant microbial community in the vent may be dominated by Aquificales using the reversed tricarboxylic acid cycle. Fractionations between fatty acids and total biomass in the pond, the proximal slope and the distal slope suggest the involvement of other biosynthetic pathways for CO₂ fixation by extant microbial populations. The results indicate that lipid biomarkers provide valuable information on the changing diversity and activity of microbial communities in different depositional environments. Carbon-isotope fractionations, on the other hand, can provide insight into the operating biosynthetic pathways associated with different organisms in the changing environment. This integrated approach may serve as a powerful tool for identifying functional metabolism within a community and identify shifts in microbial community structure in modern hot-spring systems.     

Short chain ladderanes: Oxic biodegradation products of anammox lipids

Anammox, the microbial anaerobic oxidation of ammonium by nitrite to produce dinitrogen gas, has been recognized as a key process in both the marine and freshwater nitrogen cycles, and found to be a major sink for fixed inorganic nitrogen in the oceans. Ladderane lipids are unique anammox bacterial membrane lipids that have been used as biomarkers for anammox bacteria in recent and past environmental settings. However, the fate of ladderane lipids during diagenesis is as of yet unknown. In this study, we performed oxic degradation experiments (at 20-100 °C) with anammox bacterial biomass to simulate early diagenetic processes occurring in the water column and at the sediment-water interface. Abundances of C₁₈ and C₂₀ ladderane lipids decreased with increasing temperatures, testifying to their labile nature. The most abundant products formed were ladderane lipids with a shorter alkyl side chain (C₁₄ and C₁₆ ladderane fatty acids), which was unambiguously established using two-dimensional NMR techniques on an isolated C₁₄-[3]-ladderane fatty acid. The most pronounced production of these short-chain lipids was at 40 °C, suggesting that degradation of ladderane lipids was microbially mediated, likely through a β-oxidation pathway. An HPLC-MS/MS method was developed for the detection of these ladderane alteration products in environmental samples and positively tested on various sediments. This showed that the ladderanes formed during degradation experiments also naturally occur in the marine environment. Thus, short-chain ladderane lipids may complement the original longer-chain ladderane lipids as suitable biomarkers for the detection of anammox processes in past depositional environments.     

An absolute paleotemperature record from 10 to 6 Ka inferred from fluid inclusion D/H ratios of a stalagmite from Vancouver Island, British Columbia, Canada

By using continuous helium flow during the crushing of calcite speleothem samples, we are able to recover liberated inclusion waters without isotopic fractionation. A paleotemperature record for the Jacklah Jill Cave locality, Vancouver Island, BC, was obtained from a 30-cm tall stalagmite that grew 10.3-6.3 Ka ago, using δ¹⁸O values of the crushed calcite and of the inclusion water as inferred from its δD. It is found that the locality experienced mean annual temperature variations up to 11 °C over a 4-Ka period in the early Holocene. At the beginning of the period, local temperature quickly increased from a minimum of ∼1 °C to around 10 °C, but this early climate optimum, about 3 °C warmer than today, only lasted for ∼1200 years. About 8.6 Ka ago, temperature had declined to ∼7 °C, approximately the same as the modern cave temperature. Since then, the study area has experienced only minor temperature fluctuations, but there was a brief fall to ∼4 °C at around 7 Ka ago, which might be caused by a short lived expansion of local alpine glaciers. The long-term T-dependence of δD was 1.47‰/°C, identical to the value in modern precipitation.     

Natural-abundance radiocarbon as a tracer of assimilation of petroleum carbon by bacteria in salt marsh sediments

The natural abundance of radiocarbon (¹⁴C) provides unique insight into the source and cycling of sedimentary organic matter. Radiocarbon analysis of bacterial phospholipid lipid fatty acids (PLFAs) in salt-marsh sediments of southeast Georgia (USA)—one heavily contaminated by petroleum residues—was used to assess the fate of petroleum-derived carbon in sediments and incorporation of fossil carbon into microbial biomass. PLFAs that are common components of eubacterial cell membranes (e.g., branched C₁₅ and C₁₇, 10-methyl-C₁₆) were depleted in ¹⁴C in the contaminated sediment (mean Δ¹⁴C value of +25 ± 19‰ for bacterial PLFAs) relative to PLFAs in uncontaminated “control” sediment (Δ¹⁴C = +101 ± 12‰). We suggest that the ¹⁴C-depletion in bacterial PLFAs at the contaminated site results from microbial metabolism of petroleum and subsequent incorporation of petroleum-derived carbon into bacterial membrane lipids. A mass balance calculation indicates that 6-10% of the carbon in bacterial PLFAs at the oiled site could derive from petroleum residues. These results demonstrate that even weathered petroleum may contain components of sufficient lability to be a carbon source for biomass production by marsh sediment microorganisms. Furthermore, a small but significant fraction of fossil carbon is assimilated even in the presence of a much larger pool of presumably more-labile and faster-cycling carbon substrates.     

Quantitative reconstruction of climate variability during the Eemian (Merkinė) and Weichselian (Nemunas) in Lithuania

Little is known concerning climate changes in the Eastern Baltic region during the last interglacial–glacial cycle and in particular, climate changes during the Weichselian. In this study, a quantitative reconstruction of the mean January and July temperature for the Medininkai-117 site in Lithuania is presented. The reconstruction is based on pollen and plant macrofossils from this site, which reveal that the vegetation was characteristic of many northern Europe sites during the Eemian and Early Weichselian. Gradual evolution of the vegetation suggests that relatively uniform climate conditions existed during the Eemian. Our reconstructions support the view of a relatively stable Eemian, with short cooling phases of low amplitude. A strong increase in temperature was apparent during the beginning of the interglacial and decrease during the transition to the Weichselian. Reconstructed July temperatures of the Eemian interglacial were approximately 2 °C higher than today (18.5 °C; today: 16.2 °C) and were similar to today for January (− 5.2 °C; today: − 5.1 °C). July temperatures during the Early Weichselian were only ~ 2°C lower than during the Eemian, whereas the January temperatures gradually decreased. Winter temperatures were relatively high (above − 10 °C) during the Early Weichselian.     

Qualitative fatty acid and n-alkane stratigraphy of the Lake Turkana Basin,Kenya

In order to improve understanding of the stratigraphy of the Lake Turkana Basin, one of the important sites in the evolution of early man, this study evaluates the usefulness of organic biological marker compounds, n-alkanes and fatty acids, for correlation of isolated sedimentary strata.Eighty-five paleosol samples were collected from well-defined sedimentary horizons in two regions (Area 103 and Area 130) of the Koobi Fora area of Lake Turkana. Results indicate that most of the organic matter present was derived from terrestrial plant waxes. In sediments where extensive diagenesis has occurred, microbial input of organic matter may have been substantial. Algae were either not an important source of organic matter, or their marker compounds have been removed or altered by degradative processes.The fate of the original paleosol organic matter has been governed to some extent by weathering processes, especially in Area 130. Weathering decreased the amount of extractable lipids, particularly fatty acids and the low molecular weight alkanes (C₁₇C₂₀); produced or retained relatively large amounts of alkanes greater than C₂₁ within a unimodal distribution; and lowered CPI values. Consequently, stratigraphic correlation by unique alkane and fatty acid distributions has been confined to short distances (many meters).Both n-alkanes and fatty acids have been retained better by association with clay minerals than by sand matrices. The alkane distribution of sandstones differs from that of clay organics in having a narrower carbon chain length distribution and lower CPI values. In Area 103, where weathering was less severe, compositional variations with stratigraphic position indicate that lipid material has been retained within each of the facies examined.     

Major,trace element and stable isotope composition of water and muds precipitated from the hot springs of Bolivia: Are the waters of the spring's potential ore forming fluids?

The deposition of metal-rich black or reddish muds by many thermal springs in the Cordilleras and the Altiplano of Bolivia suggest that these geothermal waters may be related to those that once formed the world-class Bolivian tin, silver and gold mineralisation. The discharge temperatures of these springs are as high as 70 °C. According to δ¹⁸O, δD, tritium data and Ar/N₂ ratios these waters are predominantly of meteoric origin. Less than 10% of the discharging thermal water represents deep-seated metal-rich thermal brines of at least 530 °C according to carbon exchange between CO₂ and CH₄. These brines ascend along tectonic faults and mix with low-temperature meteoric water in surface-near aquifers. The meteoric component of the thermal water is recharged in the high Cordilleras with residence times exceeding 50 years. The chemical composition of the thermal water is dominated by the rather inefficient low-temperature leaching of the surface-near aquifer rocks by meteoric water. The small fraction of metal-rich hot deep-seated water is not able to increase the metal content of the water mix to a level sufficient to classify these thermal waters as ore-bearing. Surface-near leaching is supported, e.g., by the B/Li ratios of the spring water of the Western Cordillera and Caleras/Pulacayo in the Eastern Cordillera that correspond very closely to that of the easily leachable glassy inclusions of the outcropping andesitic lavas. The often remarkable metal content of the muds deposited by the springs originate from efficient scavenging of heavy metals by ferric oxyhydroxides. Under the given arid to semi-arid climate the muds are additionally enriched in metals by wind-transported dust. The present study does support a relation of the actual thermal waters with neither the classical subduction-related Upper Tertiary tin, silver and gold mineralisation nor the supposed younger Sb mineralisation of Bolivia.     

Comparing the activity of aluminum in two B horizons developed from volcanic ash deposits in Japan, dominated by short-range ordered aluminosilicates and crystalline clay minerals, respectively

Mechanisms controlling the activity of free aluminum (Al) in Bw1 horizons of soils developed from volcanic ash deposits in Japan were investigated by means of acid-base titrations and kinetic studies. In a Bw1 horizon, with a high content of acid-oxalate extractable Al, soil solution reached equilibrium with short-range ordered aluminosilicates in the order of days. Relatively fast kinetics of the release and precipitation of Al and Si indicate a high reactivity of short-range ordered aluminosilicates in the soil. In the Bw1 horizon of an adjacent soil, with a high content of crystalline clay minerals like halloysite and interlayered vermiculite, solution remained well undersaturated with respect to short-range ordered aluminosilicates and aluminum hydroxide. Apparent equilibrium with respect to halloysite occurred after more than 30 days. This halloysite ( (25 °C)) has a solubility that is less than that reported in the literature ( (25°C)). Our findings suggest that different reactive aluminosilicates may control the activity of free Al in sub-surface horizons of volcanic ash soils with different mineralogy.     

中国西部天山高山带冷生土壤及相关土壤的地貌发生学

The soil landscape relationship was investigated in the Upper Urumqi River Basin of the Tienshan Mountain Range, Xinjiang, China. Cryosols occurred in glaciated valleys and north-facing toeslopes at elevations above 3 000 m. Most cryosols developed in moraine are Aquiturbels. The microrelief is dominated by earth hummocks, thus the surface organic layers are either discontinuous or broken due to frost action. The Bg horizons are either gleyed or mottled and frost-churned organic matter is common in the lower Bg horizons. Stratified horizons and buried organic or A horizons are also common on gentle sloping or undulating moraines indicating the effects of gelifluction. Reticular structures formed in the lower active layers due to ice lens formation and freeze-thaw cycles. The active layer thickness ranges from 140～200 cm. The organic cryosols (Hemistels) occur in depressions and north-facing toeslopes with an active layer thickness ranging from 90～110 cm. Soils formed on south-facing slopes have a mollic epipedon 20～25 cm thick and a strong brown cambic horizon and are classified as Haplocryolls. The distribution of cryosols is smaller as compared with the extent of permafrost due to the depth requirement of permafrost in cryosol classification. However, the existence of permafrost at greater depth cannot be ignored in land use interpretations.     

Formation of Fe-Mn-Si oxide and nontronite deposits in hydrothermal fields on the Valu Fa Ridge, Lau Basin

Hydrothermal Fe-Mn-Si oxides and nontronite are pervasive in the Hine Hina, Vai Lili and Mariner hydrothermal fields along the central Valu Fa Ridge, Lau Basin. Morphometric and mineralogical analyses reveal that the iron-rich filaments are the most important constituents of these Fe-Mn-Si oxide deposits. Both the morphologies and chemical composition of the filaments indicate that neutrophilic Fe-oxidizing bacteria have played a key role in the formation of these deposits. A key process of the formation of these deposits is the creation of a complicated filamentous network in which a series of metabolic activities and passive sorption and nucleation processes occur. The precipitation of dissolved Si in unsaturated and saturated states leads to a “two-generation” growth model in the hydrothermal vents. The precipitation of amorphous opal occurs in a relatively narrow temperature range (41.1-42.9 °C) based on oxygen isotope analyses, indicating a fast precipitation rate of opal-A when conductive cooling of the hydrothermal fluid occurrs. Patchy nontronite in the Mariner fields is a product of the direct precipitation from hydrothermal fluids at a temperature of ∼87.9 °C, whereas the scattered nontronite at the Hine Hina field is the product of the replacement of hydrothermal Fe-Si oxides at a temperature of ∼46.2 °C.     

气候变暖对多年冻土区土壤有机碳库的影响

多年冻土区存储了大量土壤有机碳。气候变暖、 多年冻土退化导致其长期封存的有机碳逐渐或快速释放, 进入大气圈或水系统, 改变原有多年冻土区碳循环, 并可能显著加速气候变暖。通过综述气候变暖对多年冻土区碳库的影响研究进展, 主要包括多年冻土碳库储量、 降解机理及变化预测, 研究表明： 北半球多年冻土区的碳储量巨大, 但不确定性很高, 尤其是海底多年冻土和水合物碳库储量的评估; 多年冻土碳库对气候变暖的响应速度受土壤水热特性、 土壤有机质C/N比、 有机碳含量和微生物群落特征等多种环境因素的控制或影响; 目前, 关于北半球多年冻土碳库对气候变暖响应模拟结果说明, 多年冻土退化短期内不会导致经济和生产方面的灾难性后果。但是, 无论是针对多年冻土碳库评估, 还是多年冻土有机碳库对气候变暖的响应模拟研究结果, 都有较大的不确定性。未来多年冻土碳库变化的模拟和预测研究应更多考虑多年冻土快速退化和多年冻土区水合物分解, 如中小尺度热喀斯特的生态环境和碳的源汇效应。准确的多年冻土区有机碳排放模拟可为未来多年冻土碳与气候反馈的预估提供重要支持。     

Measurement of methanotroph and methanogen signature phosopholipids for use in assessment of biomass and community structure in model systems

Methanotrophic biomass and community structure were assessed for a soil column enriched with natural gas. An increase in microbial biomass, based on phospholipid ester-linked fatty acids (PLFA), was apparent for the natural gas-enriched column relative to a control column and untreated surface soil. Following GC-MS analyses of the derivatized monounsaturated fatty acids, the major component (22% of the PLFA) of the natural gas-enriched column was identified as 18·1Δ 10c. This relatively novel fatty acid has only been previously reported as a major component in methanotrophs. Its presence in the soil, together with other supportive evidence, implies that this microbial metabolic group makes a large contribution to the column flora. Other microbial groups were also recognized and differences compared between the soils analysed. A recently developed HPLC method for the separation and characterisation of archaebacterial phospholipid-derived signature di- and tetra-ether lipids was used to examine methane-producing digesters. With this technique, methanogenic biomasses of approximately 10¹¹ bacteria per g dry weight of digestor material were determined. Differences between ratios of diether to tetraether phospholipids were apparent for the digestors analysed, though the causes are at this stage unknown. Taken together, these two methods can be used to estimate methanotrophic and methanogenic contributions in both model systems and environmental samples.     

Microbial diversity in waters,sediments and microbial mats evaluated using fatty acid-based methods

The review summarises recent advances towards a greater comprehensive assessment of microbial diversity in aquatic environments using the fatty acid methyl esters and phospholipid fatty acids approaches. These methods are commonly used in microbial ecology because they do not require the culturing of micro-organisms, are quantitative and reproducible and provide valuable information regarding the structure of entire microbial communities. Because some fatty acids are associated with taxonomic and functional groups of micro-organisms, they allow particular groups of micro-organisms to be distinguished. The integration of fatty acid-based methods with stable isotopes, RNA and DNA analyses enhances our knowledge of the role of micro-organisms in global nutrient cycles, functional activity and phylogenetic lineages within microbial communities. Additionally, the analysis of fatty acid profiles enables the shifts in the microbial diversity in pristine and contaminated environments to be monitored. The main objective of this review is to present the use of lipid-based approaches for the characterisation of microbial communities in water columns, sediments and biomats.