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1.
The observation that a fraction of organic matter produced in marine systems evades the concerted efforts of microbial communities and is buried in sediments suggests that there are ‘speed bumps’ in carbon degradation pathways that impede microbially driven remineralization processes. The initial step in degradation of macromolecules, extracellular enzymatic hydrolysis, is often stated to be ‘the’ rate-limiting step in carbon remineralization. Experimental investigations described here, however, demonstrate that at least in certain cases, microbes produce extracellular enzymes on time scales of hours to tens of hours in response to substrate addition, and hydrolysis is extremely rapid. If enzymatic hydrolysis can be rapid, what factors slow or stop organic matter degradation? A lack of the correct inducer to initiate enzyme production, and/or a lack of the correct organism to produce the required enzyme, may result in a complete lack of hydrolysis in certain environments—a barricade, rather than a speed bump. Preliminary evidence supporting this hypothesis includes a comparison of polysaccharide hydrolysis in seawater and sediments, which demonstrates that the spectrum of enzymes active in seawater and sediments are fundamentally different. Furthermore, a survey of enzyme activities in surface waters from a range of locations suggests that pelagic microbial communities also differ widely in their abilities to express specific extracellular enzymes. Trans-membrane transport through porins is yet another potential location of structure-related selectivity.Our efforts to identify speed bumps and barricades are hampered by our inability to structurally characterize in sufficient detail the macromolecular structures present in marine systems. Furthermore, assessments of organic matter ‘quality’ from a chemical perspective do not necessarily accurately reflect the availability of organic carbon to microbial communities. For these communities, in fact, ‘quality’ may be a variable, which depends on the enzymatic and uptake capabilities of community members. To begin to assess substrate structure and quality from a microbial perspective, we will have to combine specific knowledge of macromolecular structures with detailed investigations of the enzymatic and transport capabilities of heterotrophic marine microbes. 相似文献
2.
The activities of extracellular enzymes that initiate the microbial remineralization of high molecular weight organic matter were investigated in the water column and sandy surface sediments at two sites in the northeastern Gulf of Mexico. Six fluorescently labeled polysaccharides were hydrolyzed rapidly in the water column as well as in permeable sediments. This result contrasts with previous studies carried out in environments dominated by fine-grained muds, in which the spectrum of enzymes active in the water column is quite limited compared to that of the underlying sediments. Extracts of Spirulina, Isochrysis, and Thalassiosira were also used to measure hydrolysis rates in water from one of the sites. Rates of hydrolysis of the three plankton extracts were comparable to those of the purified polysaccharides. The broad spectrum and rapid rates of hydrolysis observed in the water column at both sites in the northeastern Gulf of Mexico may be due to the permeable nature of the sediments. Fluid flux through the sediments is sufficiently high that the entire 1.5 m deep water column could filter though the sediments on timescales of a few days to two weeks. Movement of water through sediments may also transport dissolved enzymes from the sediment into the water column, enhancing the spectrum as well as the rate of water column enzymatic activities. Such interaction between the sediments and water column would permit water column microbial communities to access high molecular weight substrates that might otherwise remain unavailable as substrates. 相似文献
3.
The dynamics of high molecular weight organic matter in marine systems are influenced by molecular conformation, interactions with surfaces and susceptibility to enzymatic hydrolysis, parameters that are difficult to observe experimentally. Here we use electron paramagnetic resonance spectroscopy (EPR) and spin-labeled (SL-) polysaccharides to monitor the sorption of SL-polysaccharides to natural sediment surfaces and to montmorillonite and to observe decreases in polysaccharide size due to enzymatic hydrolysis. SL-pullulan, SL-xylan and SL-maltoheptaose all sorbed rapidly to muddy sediments but not to sandy sediments. SL-pullulan and SL-maltoheptaose also both sorbed to montmorillonite; however, SL-pullulan reached substantially greater final surface loadings than did SL-maltoheptaose. Using EPR has the advantages of being rapid (spectra can be acquired in 100 seconds), non-destructive and functional in complex media, including sediment slurries, muddy water or other optically opaque samples, permitting investigation of the interactions between biomacromolecules, extracellular enzymes and mineral surfaces in aquatic environments. 相似文献
4.
The extent to which marine organic matter is associated with surfaces and the consequences of such associations for organic matter remineralization are the focus of considerable attention. Since extracellular enzymes operating outside microbial cells are required to hydrolyze organic macromolecules to sizes sufficiently small for substrate uptake, the effects of surface interactions–on enzymes as well as on substrates–for hydrolytic activity also require investigation. We used a simplified laboratory system consisting of a free (dissolved) polysaccharide (pullulan) and the same polysaccharide tethered to agarose beads to restrict mobility, plus the corresponding free enzyme (pullulanase) and the same enzyme sorbed to montmorillonite (Mte), to investigate systematically the consequences of surface associations of enzymes and of substrates on hydrolytic activity. Changes in substrate molecular weight were monitored with time to measure the course of enzymatic hydrolysis. Although hydrolysis of free substrate was nearly complete after 2 min incubation with the free enzymes, the sorbed enzymes also effectively hydrolyzed free substrate, and the data suggest that they retained activity longer in solution compared to the free enzymes. Sorbed enzymes progressively hydrolyzed the free substrate from > 50 kD to lower molecular weights during a 24 h incubation, with a final product distribution on average showing only 1.4% and 10.3% of substrate still in the > 50 kD and 10 kD size classes, while 46.6%, 29.3%, and 12.5% of substrate was in the 4 kD, monomer, and free tag size classes, respectively. This product distribution was very similar to that of the free substrate/free enzyme experiment. Tethering the substrate to agarose beads led to lower substrate release (2–3% of total substrate after 98 h incubation) into solution compared to the free substrate case. For tethered substrates, the state of the enzyme (free or sorbed) measurably affected the molecular weight distribution of the hydrolysis products, with free enzymes producing a higher fraction of high molecular weight hydrolysis products (28.7 ± 5.4% of substrate > 50 kD at the end of the incubation) compared to sorbed enzymes (11.6 ± 2.8% of substrate > 50 kD at the end of the incubation.) Tethered substrates were also hydrolyzed in a sediment slurry from surface sediments from Cape Lookout Bight, North Carolina; 0.1% of total substrate was released by enzymes naturally present in 1 cm3 of sediment after 144 h incubation, demonstrating that the enzymes naturally present in marine sediments are also capable of accessing tethered substrates. These investigations suggest that surface associations of enzymes in marine systems may extend the active lifetime of such enzymes, providing an opportunity for hydrolysis over longer periods of time and producing a different size spectrum of hydrolysis products relative to free enzymes. Furthermore, in well-mixed systems, surface-associated enzymes can hydrolyze substrates whose mobility is restricted, highlighting the importance of processes such as resuspension and bioturbation on organic matter remineralization. 相似文献
5.
《Marine Chemistry》2001,73(3-4):319-332
The accumulation of dissolved organic matter (DOM) at the air–sea interface is controlled by dynamic physical processes at the boundary between ocean and atmosphere. Much of the DOM concentrated in the surface microlayer is thought to be protein or glycoprotein. Enzymatic hydrolysis of these and other biopolymers is an important step in the microbial uptake of dissolved and particulate organic matter in many aquatic environments. We employed a sensitive fluorescence technique to investigate differences between extracellular enzymatic peptide hydrolysis in the sea surface microlayer and corresponding subsurface water from Stony Brook Harbor, NY. We separated the microlayer from its underlying water and thus measured hydrolysis potential rather than an in-situ process. Peptide turnover was always faster in the microlayer than in subsurface waters. This was confirmed by allowing a new surface film to form on subsurface water; hydrolysis was still faster in the new surface film. In a year-long study, we found the relative difference between turnover times in the surface film and subsurface waters to vary greatly with season. While rate constants of peptide hydrolysis were generally higher in both microlayer and bulk water samples in spring/summer than in fall/winter, the difference in activity between the two environments was greatest in winter. Enhanced hydrolysis in the sea surface microlayer is likely due to the greater concentrations of DOM in the microlayer. Seasonal changes in distribution of hydrolytic activity between surface film and subsurface water probably reflect seasonal variation in the mechanisms of DOM enrichment, which depend on water temperature, substance and energy fluxes across the water–air boundary, activity of aquatic organisms and other seasonal variables. 相似文献
6.
In aquatic environments extracellular enzymes are bound to microbial cells or exist in a free and adsorbed state. Various
filters have been used to fractionate these enzymatic activities, but enzymes may be readily adsorbed onto some materials,
and such adsorption can induce errors in the estimation of enzymatic activity. In this study we examined three filters to
determine the most suitable filter for fractionation when estimating proteolytic enzyme activity in seawater. We found that
the polycarbonate Nuclepore membrane, widely used for size fractionation because of its pore-size accuracy, was the most favorable
for this purpose, even though it adsorbed slightly more enzymes than the low-protein-binding polyethersulfone membrane. We
also found that trypsin-and chymotrypsin-type enzymes were more easily adsorbed than aminopeptidases. 相似文献
7.
This paper presents a review of the past decade's highlights of research on the isolation and characterisation of particulate
organic matter (POM) in the world's oceans. The emphasis is on chemical studies but, in keeping with the growing interdisciplinary
nature of marine science, advances in other disciplines are also discussed, particularly those in biological sciences. Increasing
evidence for the importance of picoplankton, bacteria and viruses as POM constituents is highlighted, including the recent
recognition of large populations of autotrophic bacteria able to harvest light for energy. The transport of POM to bottom
waters was thought to be largely confined to large, rapidly sinking faecal pellets. However, recent studies have highlighted
the importance of organic aggregates and flocs formed by diatoms such as Rhizosolenia and other microalgae. Ascending particles have also been discovered, many of which are lipid-rich. Several studies have shown
that resuspension of bottom sediments and lateral advection of material from continental shelves can lead to anomalously high
particle fluxes measured in sediment traps moored in deep water. Many new approaches for characterizing POM have emerged,
such as pyrolysis gas chromatography-mass spectrometry and direct temperature-resolved mass spectrometry for analysis of higher
molecular weight materials and biopolymers. Lipid biomarker techniques have also advanced, exciting new possibilities being
raised by the ability to measure stable and radioactive carbon isotopes for individual compounds. The techniques of molecular
biology, such as the polymerase chain reaction (PCR), are being increasingly applied to provide complementary information
to more conventional microscopy and flow cytometry on the identity of organisms in the sea. The combination of these techniques
with advanced chemical analysis methods promises to greatly increase our knowledge of the origins, transport and fate of organic
matter in the oceans.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
单体分子放射性碳同位素分析在海洋科学及环境科学研究中的应用 总被引：3，自引：1，他引：2
单体分子放射性碳同位素分析(CSRA)是近十几年来发展起来的一项新兴的分析手段,将所需的单体分子(生物标志物)从复杂的环境样品基质中分离并富集,再进行加速质谱仪(AMS)的放射性碳(14C)测定。这种分子水平的放射性碳同位素测定技术能够揭示出总有机质同位素组成的异质性,为解释有机碳的来源、迁移和转化等提供了新型的手段。在海洋科学研究中,单体分子放射性碳同位素分析已应用于计算碳在全球各储库的逗留时间并揭示和定量估算化石源有机碳的输入、指示沉积物的搬运过程、示踪微生物的代谢途径、改进沉积物年代学等;在环境科学研究中,单体分子放射性碳同位素分析可用于有毒物质(如多环芳烃)的源解析,示踪有机污染环境中微生物的代谢途径等。伴随着单体分子分离技术的改进及AMS灵敏度的提高,CSRA技术的应用会更加广泛。 相似文献
9.
南海沉积物细菌胞外蛋白酶在家族水平上的多样性 总被引：2，自引：0，他引：2
海洋产蛋白酶细菌及其分泌的胞外蛋白酶在降解有机氮以推动海洋氮循环进行方面发挥着重要作用，但目前对这二者多样性的认识非常有限。本研究自南海沉积物中筛选得到90株产蛋白酶细菌，并通过N-端氨基酸序列，分析了其胞外蛋白酶在家族水平上的多样性。16S rRNA基因序列分析的结果表明，筛选的产蛋白酶细菌均属于Gammaproteobacteria纲，且大多数属于Alteromonadales目和Vibrionales目的不同属。对其中14株菌株的14个胞外蛋白酶的N-端氨基酸序列分析表明，所有这些蛋白酶属于金属蛋白酶的M4家族或丝氨酸蛋白酶的S8家族。本研究提供了海洋沉积物产蛋白酶细菌在类群及其胞外蛋白酶在类型上的新细节，这将有助于全面了解微生物酶促降解海洋沉积物有机氮的过程和机理。 相似文献
10.
R. Danovaro N. Della Croce A. Dell&#x;Anno A. Pusceddu 《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(12):1411-1420
The Atacama trench, the deepest ecosystem of the southern Pacific Ocean (ca. 8000 m depth) was investigated during the Atacama Trench International Expedition. Sediments, collected at three bathyal stations (1040–1355 m depth) and at a hadal site (7800 m) were analyzed for organic matter quantity and biochemical composition (in terms of phytopigments, proteins, carbohydrates and lipids), bacterial abundance, biomass and carbon production and extracellular enzymatic activities. Functional chlorophyll-a (18.0±0.10 mg m−2), phytodetritus (322.2 mg m−2) and labile organic carbon (16.9±4.3 g C m−2) deposited on surface sediments at hadal depth (7800 m) reached concentrations similar to those encountered in highly productive shallow coastal areas. High values of bacterial C production and aminopeptidase activity were also measured (at in situ temperature and 1 atm). The chemical analyses of the Atacama hadal sediments indicate that this trench behaves as a deep oceanic trap for organic material. We hypothesize that, despite the extreme physical conditions, benthic microbial processes might be accelerated as a result of the organic enrichment. 相似文献
11.
海水胞外酶活性可以指示有机物的分布特征以及微生物的营养状况。我们测定了2017年3月25日至4月15日黄海和东海44个大面站以及2018年4月28日至29日胶州湾湾口附近海域10个站位表层海水中的8种胞外酶活性并研究了其分布特征。2017年春季黄、东海表层海水中碱性磷酸酶和脂肪酶活性较高，高值区出现在苏北沿岸和南黄海中部，碱性磷酸酶与磷酸盐浓度之间呈正相关。其余6种酶(肽酶、几丁质酶、纤维素酶、α-D-葡萄糖苷酶、β-D-半乳糖苷酶、木糖苷酶)活性高值区出现在长江口以东的外海，东海的β-D-半乳糖苷酶、木糖苷酶平均酶活性显著高于黄海。8种酶活性平均值排列顺序由大到小为:碱性磷酸酶、脂肪酶、肽酶、几丁质酶、α-D-葡萄糖苷酶、β-D-半乳糖苷酶、纤维素酶、木糖苷酶，其中α-D-葡萄糖苷酶和β-D-半乳糖苷酶的活性基本一致。2018年春季胶州湾附近海域海水中碱性磷酸酶、脂肪酶、木糖苷酶活性分布为近岸高于远岸，几丁质酶活性为近岸低于远岸。8种酶活性平均值排列顺序由大到小为:碱性磷酸酶、脂肪酶、肽酶、木糖苷酶、α-D-葡萄糖苷酶、β-D-半乳糖苷酶、几丁质酶、纤维素酶，其中几丁质酶和纤维素酶的活性基本一致。黄海的碱性磷酸酶和脂肪酶平均酶活性均显著高于东海和胶州湾附近海域。糖类水解酶(几丁质酶、纤维素酶、α-D-葡萄糖苷酶、β-D-半乳糖苷酶、木糖苷酶)平均酶活性在黄海最低。本文的结果对于理解中国近海海水有机碳的分布、浮游植物及异养细菌对有机碳的降解具有重要意义。 相似文献
12.
The molecular size distribution of humic substances has been investigated in two recent sediment samples of different ages taken from a single core sample collected off Walvis Bay, south-west Africa. Extractable humic acids were found to be by far the major form of organic carbon in both sediments, the near-surface younger sample containing predominantly high molecular weight (>100 000 molecular weight) humic acids and little fulvic acids whilst the deeper, older sample contained relatively less humic acid and relatively more fulvic acid of a range of molecular weights. A significant age difference was found between the >300 000 molecular weight and the <30 000 molecular weight fractions of the near-surface sample, the lower molecular weight fraction being older than the higher molecular weight fraction.The data suggest that in this rapidly accumulating, organic-rich sediment the first step en route from the planktonic matter to the humic complexes is direct and rapid incorporation of the biogenic material into high molecular weight humic acids. 相似文献
13.
《Deep Sea Research Part II: Topical Studies in Oceanography》2010,57(16):1486-1493
The ocean plays a major role in global biogeochemical carbon cycling; it holds an important reservoir of reduced organic carbon, mostly in the form of dissolved organic carbon (DOC), and processes about one-half of the total primary production of the planet. Dissolved molecules present between living and assimilable size extremes (∼1000 nm-1 nm), constitute the most abundant form of remnant biochemicals in the ocean, outweighing the total living biomass by a factor of roughly 200. Because DOC is the fundamental substrate for marine microorganisms, and is primarily composed by small refractory biopolymers, this prompted the idea that the ocean might function as a huge repository of recalcitrant carbon. The missing link that elucidates this paradox and explains how the rich and vast stock of DOC becomes available to bacteria was the discovery that DOC throughout the water column remains in reversible assembly/dispersion equilibrium forming porous microscopic gels (Chin et al., Nature 391, 568-572, 1998). This abiotic DOC-POM shunt yields a microgel pool containing ∼70 gigatons of carbon forming discrete patches of high nutrient concentration that can be readily colonized by microorganisms. The presence of this huge gel mass in seawater extending far into the dark ocean has ramifications that might well scale nonlinearly through the microbial loop to the World Ocean and global climate system and it is fundamentally changing how oceanographers think about processes linking the microbial loop and biological pump to the rest of the biosphere and the geosphere. Even if a small fraction of DOC remains self-assembled, marine scientists will have to revise the rationale of established aquatic paradigms ranging from trace metal chelation, size–reactivity relationships, the microbial loop, the biological pump, colloid pumping, and humification. A ubiquitous, reversible DOC assembly/dispersion process implies a dynamic “patchiness” spanning from the molecular to the micron scale, where the assignment of static bulk features including dimension, concentration, functionalities and vertical fluxes can be open to question. This brief revision illustrates two case studies that show how simple methods and principles of polymer networks theory can be used to advance the understanding of one of the most intriguing and significant processes taking place in the ocean. Namely, the kinetics and thermodynamics of: (a) Ca-driven DOC self-assembly, and (b) hydrophobic bond-driven self assembly of DOC by amphiphilic exopolymers released by marine bacteria. 相似文献
14.
《Deep Sea Research Part II: Topical Studies in Oceanography》2010,57(16):1519-1536
This paper synthesizes recent findings regarding microbial distributions and processes in the bathypelagic ocean (depth >1000 m). Abundance, production and respiration of prokaryotes reflect supplies of particulate and dissolved organic matter to the bathypelagic zone. Better resolution of carbon fluxes mediated by deep microbes requires further testing on the validity of conversion factors. Archaea, especially marine Crenarchaeota Group I, are abundant in deep waters where they can fix dissolved inorganic carbon. Viruses appear to be important in the microbial loop in deep waters, displaying remarkably high virus to prokaryote abundance ratios in some oceanic regions. Sequencing of 18S rRNA genes revealed a tremendous diversity of small-sized protists in bathypelagic waters. Abundances of heterotrophic nanoflagellates (HNF) and ciliates decrease with depth more steeply than prokaryotes; nonetheless, data indicated that HNF consumed half of prokaryote production in the bathypelagic zone. Aggregates are important habitats for deep-water microbes, which produce more extracellular enzymes (on a per-cell basis) than surface communities. The theory of marine gel formation provides a framework to unravel complex interactions between microbes and organic polymers. Recent data on the effects of hydrostatic pressure on microbial activities indicate that bathypelagic microbial activity is generally higher under in situ pressure conditions than at atmospheric pressures. High-throughput sequencing of 16S rRNA genes revealed a remarkable diversity of Bacteria in the bathypelagic ocean. Metagenomics and comparative genomics of piezophiles reveal not only the high diversity of deep sea microbes but also specific functional attributes of these piezophilic microbes, interpreted as an adaptation to the deep water environment. Taken together, the data compiled on bathypelagic microbes indicate that, despite high-pressure and low-temperature conditions, microbes in the bathypelagic ocean dynamically interact with complex mixtures of organic matter, responding to changes in the ocean’s biogeochemical state. 相似文献
15.
Seasonal monitoring was carried out to investigate the influence of extracellular enzymatic activity (EEA) on metal speciation and organic matter cycling in the rhizosediment of Spartina maritima . Heavy metal speciation was achieved by the Tessier scheme, and showed a similar pattern of variation of the organic-bound fraction, indicating a decomposition process in progress. Both humic acid and organic matter showed the same seasonal pattern. The basal respiration of the rhizosediments also presented a similar seasonal pattern, indicating a microbial degradation of organic matter. The high organic-bound fraction found in the summer gradually decreased towards the winter. This decrease was found to be related to the increase of activity of peroxidase, β- N -acetylglucosaminidase and protease. Also the activity of sulphatase was found to be related to the depletion on the exchangeable fraction, probably due to sulphide formation and consequent mobilization. The results show an interaction between several microbial activities, affecting metal speciation. 相似文献
16.
Microbial oceanography is undergoing a dramatic revolution thanks to the rapid development of novel techniques that allow
the examination of microbial diversity and functions via molecular methods, including genomic and metagenomic analyses. During
the past decade, studies have revealed previously unknown and surprisingly diverse bacterial communities in marine waters.
These studies have radically changed our understanding of spatiotemporal patterns in marine bacterial community composition
and the distribution of specific genes. However, our knowledge of the role of individual bacterial subgroups in oceanic food
webs and biogeochemical cycles remains limited. To embed the internal dynamics of bacterial communities into marine biogeochemistry
models, the characteristic parameters of individual bacterial subgroups (i.e., growth, mortality, and utilization of dissolved
organic matter) must be determined. Here, we survey the approaches used to assess variation in and factors controlling bacterial
communities in marine environments, emphasizing the importance of quantitative studies that examine growth and grazing parameters
of bacterial subgroups. 相似文献
17.
Extracellular peptide hydrolysis rates were measured in seawater and sediment from Flax Pond salt marsh using peptide analogs (LYA-peptides) as substrates. This technique allows the direct measurement of specific hydrolysis products and thus provides insights into enzymatic hydrolysis pathways. In sediments, hydrolysis rate constants of LYA-peptides varied seasonally and with depth. Highest activity was found in spring and summer, and most cores exhibited a subsurface maximum. Calculations using the concentrations of chemically-measured peptides suggested that extracellular hydrolysis of peptides is faster than the rate of free amino acids uptake. However, not all peptides may be available for enzymatic hydrolysis. In both seawater and sediment, extracellular hydrolysis of peptides of up to 8 amino acids yielded smaller peptides and free amino acids. Hydrolysis rates depended on size of the peptide substrate, although a clear relationship with number of amino acid constituents was not evident. Peptides containing >2 amino acids were hydrolyzed 10–400 times faster than dipeptides or the fluorogenic substrate Leucine-MCA. Thus, dipeptidases are either uncommon in nature, or hydrolysis is carried out by nonspecific hydrolases that with a low affinity for dipeptides. This is also suggested by the presence of a lag time before dipeptide hydrolysis begins, and the absence of dipeptide hydrolysis in 0.2-μm-filtered. One implication of this finding is that measurements of hydrolysis rates using substrates like Leu-MCA may not accurately predict the magnitude of hydrolysis rates of macromolecules in the marine environment. Even though dipeptide hydrolysis is slow compared to that of larger peptides, LYA-dipeptides are preferentially produced from the hydrolysis of larger substrates. LYA-dipeptides do not penetrate cell membranes of microorganisms because of their size, but natural dipeptides are smaller and can be transported across the cell membrane. Since dipeptides do not appear to accumulate in natural waters, they must be rapidly removed by microorganisms. 相似文献
18.
The biogeochemistry of organic matter in a macrotidal estuary, the Loire, France, has been studied for two years during different seasons. Both particulate matter and sediment have been sampled in the riverine zone, in the maximum turbidity zone and in the ocean near the river mouth. Two techniques have been used: carbon isotopic ratio determination and analysis of lipid-marker signatures in the n-alkane, n-alkene and fatty acid series. For the period corresponding to the output of the maximum turbidity zone in the ocean, the complete change of organic matter, continental in nature in the inner estuary, pure marine in the outer estuary is well illustrated by the decrease of δ13C values and of carbon preference index of n-alkanes. Input sources of organic matter by continental plants, plankton and micro-organisms are discussed from biogeochemical-marker analyses data along with the processes of accumulation of particles and their evolution with the season. Some criteria for evidencing the nature of various organic-matter pools are assessed and compared in different chemical-marker series as follows: high molecular weight n-alkanes and fatty acids, perylene for continental imprints, polyunsaturated 18-, 20- and 22-carbon fatty acids, n-C17, n-alkenes and squalene for algae imprints, branched iso and anteiso fatty acids, Δ11-C18:1 for microbial imprints. 相似文献
19.
海洋蓝碳是海洋碳汇研究的重要领域,厘清不同蓝碳生境中沉积物有机碳组分格局是当前研究的热点之一。为更好地理解此问题,现以近海厚壳贻贝养殖区这一特殊蓝碳生境为对象,解析沉积物中的碳氮组分格局;进一步通过关联沉积物微生物群落、结合卡尔文循环和还原三羧酸循环的关键基因相对丰度分析,评估厚壳贻贝养殖区沉积物的固碳潜力。结果表明,相较于非养殖区,厚壳贻贝养殖区沉积物惰性碳的累积较大,氮组分主要以氨氮形式存在;同时养殖区高微生物量碳和微生物量氮指示了其沉积物中碳周转较快,碳氮组分特征差异明显。沉积物微生物高通量测序结果显示养殖区沉积物微生物主要以Gamma变形菌纲和Delta变形菌纲为主,且微生物类群与颗粒有机碳、惰性碳等碳组分存在明显的相关性。与惰性碳存在明显正相关关系的硫微螺菌科(Thiomicrospiraceae)丰度在养殖区沉积物中显著高于非养殖区沉积物。贻贝养殖区沉积物包含cbbL在内的6种关键功能基因,固碳潜力明显。研究结果将为进一步探究蓝碳生境的有机碳来源和微生物固碳效率提供基础依据。 相似文献
20.
Enzymatic activity in the rhizosphere of Spartina maritima: potential contribution for phytoremediation of metals 总被引：2，自引：0，他引：2
Extracellular enzymatic activity (EEA) of five enzymes (peroxidase, phenol oxidase, beta-glucosidase, beta-N-acetylglucosaminidase and acid phosphatase) was analysed in sediments colonised by Spartina maritima in two salt marshes (Rosário and Pancas) of the Tagus estuary (Portugal) with different characteristics such as sediment parameters and metal contaminant levels. Our aim was a better understanding of the influence of the halophyte on microbial activity in the rhizosphere under different site conditions, and its potential consequences for metal cycling and phytoremediation in salt marshes. Acid phosphatase and beta-N-acetylglucosaminidase presented significantly higher EEA in Rosário than in Pancas, whereas the opposite occurred for peroxidase. This was mainly attributed to differences in organic matter between the two sites. A positive correlation between root biomass and EEA of hydrolases (beta-glucosidase, beta-N-acetylglucosaminidase and acid phosphatase) was found, indicating a possible influence of the halophyte in sediment microbial function. This would potentially affect metal cycling in the rhizosphere through microbial reactions. 相似文献