共查询到20条相似文献,搜索用时 31 毫秒
1.
Earthworms emit nitrous oxide (N2O) and dinitrogen (N2). It has been hypothesized that the in situ conditions of the earthworm gut activates ingested soil denitrifiers during gut passage and leads to these in vivo emissions (M. A. Horn, A. Schramm, and H. L. Drake, Appl. Environ. Microbiol. 69:1662-1669, 2003). This hypothesis implies that the denitrifiers in the earthworm gut are not endemic to the gut but rather are regular members of the soil denitrifier population. To test this hypothesis, the denitrifier populations of gut and soil from three different sites were comparatively assessed by sequence analysis of nosZ, the gene for the terminal enzyme in denitrification, N2O reductase. A total of 182 and 180 nosZ sequences were retrieved from gut and soil, respectively; coverage of gene libraries was 79 to 100%. Many of the nosZ sequences were heretofore unknown, clustered with known soil-derived sequences, or were related to N2O reductases of the genera Bradyrhizobium, Brucella, Dechloromonas, Flavobacterium, Pseudomonas, Ralstonia, and Sinorhizobium. Although the numbers of estimators for genotype richness of sequence data from the gut were higher than those of soil, only one gut-derived nosZ sequence did not group phylogenetically with any of the soil-derived nosZ sequences. Thus, the phylogenies of nosZ from gut and soil were not dissimilar, indicating that gut denitrifiers are soil derived. 相似文献
2.
Peatlands cover more than 30% of the Finnish land area and impact N 2O fluxes. Denitrifiers release N 2O as an intermediate or end product. In situ N 2O emissions of a near pH neutral pristine fen soil in Finnish Lapland were marginal during gas chamber measurements. However, nitrate and ammonium fertilization significantly stimulated in situ N 2O emissions. Stimulation with nitrate was stronger than with ammonium. N 2O was produced and subsequently consumed in gas chambers. In unsupplemented anoxic microcosms, fen soil produced N 2O only when acetylene was added to block nitrous oxide reductase, suggesting complete denitrification. Nitrate and nitrite stimulated denitrification in fen soil, and maximal reaction velocities ( vmax) of nitrate or nitrite dependent denitrification where 18 and 52 nmol N 2O h -1 g DW
-1, respectively. N 2O was below 30% of total produced N gases in fen soil when concentrations of nitrate and nitrite were <500 μM. v max for N 2O consumption was up to 36 nmol N 2O h -1 g DW
-1. Denitrifier diversity was assessed by analyses of narG, nirK/nirS, and nosZ (encoding nitrate-, nitrite-, and nitrous oxide reductases, respectively) by barcoded amplicon pyrosequencing. Analyses of ~14,000 quality filtered sequences indicated up to 25 species-level operational taxonomic units (OTUs), and up to 359 OTUs at 97% sequence similarity, suggesting diverse denitrifiers. Phylogenetic analyses revealed clusters distantly related to publicly available sequences, suggesting hitherto unknown denitrifiers. Representatives of species-level OTUs were affiliated with sequences of unknown soil bacteria and Actinobacterial, Alpha-, Beta-, Gamma-, and Delta-Proteobacterial sequences. Comparison of the 4 gene markers at 97% similarity indicated a higher diversity of narG than for the other gene markers based on Shannon indices and observed number of OTUs. The collective data indicate (i) a high denitrification and N 2O consumption potential, and (ii) a highly diverse, nitrate limited denitrifier community associated with potential N 2O fluxes in a pH-neutral fen soil. 相似文献
4.
Analyses of the complete genomes of sequenced denitrifying bacteria revealed that approximately 1/3 have a truncated denitrification pathway, lacking the nosZ gene encoding the nitrous oxide reductase. We investigated whether the number of denitrifiers lacking the genetic ability to synthesize the nitrous oxide reductase in soils is important for the proportion of N 2O emitted by denitrification. Serial dilutions of the denitrifying strain Agrobacterium tumefaciens C58 lacking the nosZ gene were inoculated into three different soils to modify the proportion of denitrifiers having the nitrous oxide reductase genes. The potential denitrification and N 2O emissions increased when the size of inoculated C58 population in the soils was in the same range as the indigenous nosZ community. However, in two of the three soils, the increase in potential denitrification in inoculated microcosms compared with the noninoculated microcosms was higher than the increase in N 2O emissions. This suggests that the indigenous denitrifier community was capable of acting as a sink for the N 2O produced by A. tumefaciens. The relative amount of N 2O emitted also increased in two soils with the number of inoculated C58 cells, establishing a direct causal link between the denitrifier community composition and potential N 2O emissions by manipulating the proportion of denitrifiers having the nosZ gene. However, the number of denitrifiers which do not possess a nitrous oxide reductase might not be as important for N 2O emissions in soils having a high N 2O uptake capacity compared with those with lower. In conclusion, we provide a proof of principle that the inability of some denitrifiers to synthesize the nitrous oxide reductase can influence the nature of the denitrification end products, indicating that the extent of the reduction of N 2O to N 2 by the denitrifying community can have a genetic basis. 相似文献
5.
Denitrification is an important microbial process in soils and leads to the emission of nitrous oxide (N 2O). However, studies about the microbial community involved in denitrification processes in polluted paddy fields are scarce. Here, we studied two rice paddies which had been polluted for more than three decades by metal mining and smelter activities. Abundance and community composition were determined using real-time polymerase chain reaction (PCR) assay and denaturing gradient gel electrophoresis of nitrite reductase and nitrous oxide reductase gene amplicons ( nirK and nosZ), while denitrifying activities were assessed by measuring potential denitrifier enzyme activity. We found that the community structure of both nirK and nosZ containing denitrifiers shifted under pollution in the two rice paddies. All the retrieved nirK sequences did not group into either α- or β- proteobacteria, while most of the nosZ species were affiliated with α- proteobacteria. While the abundance of both nirK and nosZ was significantly reduced in the polluted soils at “Dexing” (with relatively higher Cu levels), these parameters did not change significantly at “Dabaoshan” (polluted with Cd, Pb, Cu, and Zn). Furthermore, total denitrifying activity and N 2O production and reduction rates also only decreased under pollution at “Dexing.” These findings suggest that nirK and nosZ containing denitrifier populations and their activities could be sensitive to considerable Cu pollution, which could potentially affect N 2O release from polluted paddy soils. 相似文献
6.
Cryoturbated peat circles (that is, bare surface soil mixed by frost action; pH 3–4) in the Russian discontinuous permafrost tundra are nitrate-rich ‘hotspots'' of nitrous oxide (N 2O) emissions in arctic ecosystems, whereas adjacent unturbated peat areas are not. N 2O was produced and subsequently consumed at pH 4 in unsupplemented anoxic microcosms with cryoturbated but not in those with unturbated peat soil. Nitrate, nitrite and acetylene stimulated net N 2O production of both soils in anoxic microcosms, indicating denitrification as the source of N 2O. Up to 500 and 10 μ nitrate stimulated denitrification in cryoturbated and unturbated peat soils, respectively. Apparent maximal reaction velocities of nitrite-dependent denitrification were 28 and 18 nmol N 2O g DW−1 h −1, for cryoturbated and unturbated peat soils, respectively. Barcoded amplicon pyrosequencing of narG, nirK/nirS and nosZ (encoding nitrate, nitrite and N 2O reductases, respectively) yielded ≈49 000 quality-filtered sequences with an average sequence length of 444 bp. Up to 19 species-level operational taxonomic units were detected per soil and gene, many of which were distantly related to cultured denitrifiers or environmental sequences. Denitrification-associated gene diversity in cryoturbated and in unturbated peat soils differed. Quantitative PCR (inhibition-corrected per DNA extract) revealed higher copy numbers of narG in cryoturbated than in unturbated peat soil. Copy numbers of nirS were up to 1000 × higher than those of nirK in both soils, and nirS nirK−1 copy number ratios in cryoturbated and unturbated peat soils differed. The collective data indicate that the contrasting N 2O emission patterns of cryoturbated and unturbated peat soils are associated with contrasting denitrifier communities. 相似文献
7.
Wetlands are sources of denitrification-derived nitrous oxide (N 2O). Thus, the denitrifier community of an N 2O-emitting fen (pH 4.7 to 5.2) was investigated. N 2O was produced and consumed to subatmospheric concentrations in unsupplemented anoxic soil microcosms. Total cell counts and most probable numbers of denitrifiers approximated 10 11 cells·g DW−1 (where DW is dry weight) and 10 8 cells·g DW−1, respectively, in both 0- to 10-cm and 30- to 40-cm depths. Despite this uniformity, depth-related maximum reaction rate ( vmax) values for denitrification in anoxic microcosms ranged from 1 to 24 and −19 to −105 nmol N 2O h −1· g DW−1, with maximal values occurring in the upper soil layers. Denitrification was enhanced by substrates that might be formed via fermentation in anoxic microzones of soil. N 2O approximated 40% of total nitrogenous gases produced at in situ pH, which was likewise the optimal pH for denitrification. Gene libraries of narG and nosZ (encoding nitrate reductase and nitrous oxide reductase, respectively) from fen soil DNA yielded 15 and 18 species-level operational taxonomic units, respectively, many of which displayed phylogenetic novelty and were not closely related to cultured organisms. Although statistical analyses of narG and nosZ sequences indicated that the upper 20 cm of soil contained the highest denitrifier diversity and species richness, terminal restriction fragment length polymorphism analyses of narG and nosZ revealed only minor differences in denitrifier community composition from a soil depth of 0 to 40 cm. The collective data indicate that the regional fen harbors novel, highly diverse, acid-tolerant denitrifier communities capable of complete denitrification and consumption of atmospheric N 2O at in situ pH.Nitrous oxide (N 2O) is a potent greenhouse gas with a global warming potential that is 300-fold higher than that of CO 2, and its concentration increased from 270 ppb in 1750 to 319 ppb in 2005 ( 17). N 2O can be produced in soils during denitrification, nitrification, the dissimilatory reduction of nitrate to nitrite and/or ammonium (hereafter referred to as dissimilatory nitrate reduction), or the chemical transformation of nitrite or hydroxylamine ( 5, 7, 49). The percentage of N 2O produced in any of these processes is variable, depending mainly on the redox potential, pH, and C/N ratio ( 49). In anoxic ecosystems such as waterlogged soils, most of the N 2O is considered to be denitrification derived ( 7, 9). Complete denitrification is the sequential reduction of nitrate to dinitrogen (N 2) via nitrite, nitric oxide (NO), and N 2O ( 75). The main product of denitrification varies with the organism and in situ conditions and is usually either N 2O or N 2 ( 68). N 2O can occur as a by-product during dissimilatory nitrate reduction when accumulated nitrite interacts with nitrate reductase to form N 2O ( 59). The production of N 2O by dissimilatory nitrate reducers is favored in environments with large amounts of readily available organic carbon ( 65). Thus, their contribution to nitrate-dependent production of N 2O in soils is likely insignificant compared to that of denitrifiers.The oxidoreductases involved in denitrification are termed dissimilatory nitrate reductase (Nar, encoded by narGHJI, or Nap, encoded by napEDABC), nitrite reductase (Nir, encoded by nirK and nirS), NO reductase (cNor and qNor, encoded by norBC and norB, respectively), and N 2O reductase (Nos, encoded by nosZ) ( 75). Nitrate reductase is also found in dissimilatory nitrate reducers ( 60). narG can therefore be used as a molecular marker to assess both denitrifiers and dissimilatory nitrate reducers, whereas nosZ is specific for the assessment of denitrifiers ( 25, 43, 48).Denitrification in soils is regulated by temperature, pH, substrate (i.e., carbon) availability, and water content ( 10, 24, 66). Although denitrification increases with increasing temperature, it can still occur at temperatures below 0°C ( 10, 24). Low temperatures appear to limit the activity of N 2O reductase more severely than other enzymes involved in denitrification and thus yield higher relative amounts of denitrification-derived N 2O ( 24). Although denitrification activity usually decreases under acidic conditions, the relative percentage of N 2O to total denitrification-derived nitrogenous gases increases with increasing acidity, a result attributed to the sensitivity of N 2O reductase to low pH ( 27, 70). However, denitrifier communities can be adapted to the in situ pH of the system ( 40, 58, 73).Wetlands are ecosystems in which denitrification is likely a dominant source of emitted N 2O ( 7, 44, 45). The identification and analysis of main drivers for N 2O production (i.e., the microbiota catalyzing N 2O production and consumption) is thus of major concern in such environments. Fens are specialized wetlands characterized by soil acidity ( 67). However, information on acid-tolerant denitrifier communities of such wetlands is scarce. It is hypothesized that fens harbor a diverse, hitherto unknown, denitrifier community that is adapted to in situ conditions and associated with N 2O fluxes (i.e., fen denitrifiers are acid tolerant and have a high affinity for nitrate and N 2O). Thus, the main objectives of the present study were to evaluate the capacities of denitrifier communities of an N 2O-emitting fen ( 20) to produce or consume N 2O and to determine if a novel and diverse denitrifier community was associated with these capacities. 相似文献
8.
Temperature responses of denitrifying microbes likely play a governing role in the production and consumption of N 2O. We investigated temperature effects on denitrifier communities and their potential to produce N 2O and N 2 by incubating grassland soils collected in multiple seasons at four temperatures with 15N-enriched NO 3 ? for ~24 h. We quantified [N 2O] concentration across time, estimated its production and reduction to N 2, and quantified relative abundance of genes responsible for N 2O production ( cnorB) and reduction ( nosZ). In all seasons, net N 2O production was positively linked to incubation temperature, with highest estimates of net and gross N 2O production in late spring soils. N 2O dynamics were tightly coupled to changes in denitrifier community structure, which occurred on both seasonal and incubation time scales. We observed increases in nosZ abundance with increasing incubation temperature after 24 h, and relatively larger increases in cnorB abundance from winter to late June. The difference between incubation and in situ temperature was a robust predictor of cnorB:nosZ. These data provide convincing evidence that short-term increases in temperature can induce remarkably rapid changes in community structure that increase the potential for reduction of N 2O to N 2, and that seasonal adaptation of denitrifying communities is linked to seasonal changes in potential N 2O production, with warmer seasons linked to large increases in N 2O production potential. This work helps explain observations of high spatial and temporal variation in N 2O effluxes, and highlights the importance of temperature as an influence on denitrification enzyme kinetics, denitrifier physiology and community adaptations, and associated N 2O efflux and reduction. 相似文献
9.
Nitrous oxide (N 2O) is a potent greenhouse gas and the predominant ozone depleting substance. The only enzyme known to reduce N 2O is the nitrous oxide reductase, encoded by the nosZ gene, which is present among bacteria and archaea capable of either complete denitrification or only N 2O reduction to di-nitrogen gas. To determine whether the occurrence of nosZ, being a proxy for the trait N 2O reduction, differed among taxonomic groups, preferred habitats or organisms having either NirK or NirS nitrite reductases encoded by the nirK and nirS genes, respectively, 652 microbial genomes across 18 phyla were compared. Furthermore, the association of different co-occurrence patterns with enzymes reducing nitric oxide to N 2O encoded by nor genes was examined. We observed that co-occurrence patterns of denitrification genes were not randomly distributed across taxa, as specific patterns were found to be more dominant or absent than expected within different taxonomic groups. The nosZ gene had a significantly higher frequency of co-occurrence with nirS than with nirK and the presence or absence of a nor gene largely explained this pattern, as nirS almost always co-occurred with nor. This suggests that nirS type denitrifiers are more likely to be capable of complete denitrification and thus contribute less to N 2O emissions than nirK type denitrifiers under favorable environmental conditions . Comparative phylogenetic analysis indicated a greater degree of shared evolutionary history between nosZ and nirS. However 30% of the organisms with nosZ did not possess either nir gene, with several of these also lacking nor, suggesting a potentially important role in N 2O reduction. Co-occurrence patterns were also non-randomly distributed amongst preferred habitat categories, with several habitats showing significant differences in the frequencies of nirS and nirK type denitrifiers. These results demonstrate that the denitrification pathway is highly modular, thus underpinning the importance of community structure for N 2O emissions. 相似文献
10.
Benthic invertebrates affect microbial processes and communities in freshwater sediment by enhancing sediment-water solute fluxes and by grazing on bacteria. Using microcosms, the effects of larvae of the widespread midge Chironomus plumosus on the efflux of denitrification products (N 2O and N 2 + N 2O) and the diversity and abundance of nitrate- and nitrous-oxide-reducing bacteria were investigated. Additionally, the diversity of actively nitrate- and nitrous-oxide-reducing bacteria was analyzed in the larval gut. The presence of larvae increased the total effluxes of N 2O and N 2 + N 2O up to 8.6- and 4.2-fold, respectively, which was mostly due to stimulation of sedimentary denitrification; incomplete denitrification in the guts accounted for up to 20% of the N 2O efflux. Phylotype richness of the nitrate reductase gene narG was significantly higher in sediment with than without larvae. In the gut, 47 narG phylotypes were found expressed, which may contribute to higher phylotype richness in colonized sediment. In contrast, phylotype richness of the nitrous oxide reductase gene nosZ was unaffected by the presence of larvae and very few nosZ phylotypes were expressed in the gut. Gene abundance of neither narG, nor nosZ was different in sediments with and without larvae. Hence, C. plumosus increases activity and diversity, but not overall abundance of nitrate-reducing bacteria, probably by providing additional ecological niches in its burrow and gut. 相似文献
11.
The present study investigated the abundance, richness, diversity, and community composition of denitrifiers (based on nirS and nosZ genes) in the stratified water columns and sediments in eutrophic Dianchi Lake and mesotrophic Erhai Lake using quantitative PCR assay and high-throughput sequencing analysis. Both nirS- and nosZ denitrifiers were detected in waters of these two lakes. Surface water showed higher nosZ gene density than bottom water, and Dianchi Lake waters had larger nirS gene abundance than Erhai Lake waters. The abundance of sediment nirS- and nosZ denitrifiers in Dianchi Lake was larger than that in Erhai Lake. nirS richness and diversity and nosZ richness tended to increase with increasing sediment layer depth in both lakes. The distinct structure difference of sediment nirS- and nosZ denitrifier communities was found between in Dianchi Lake and Erhai Lake. These two lakes also differed greatly in water denitrifier community structure. Moreover, phylogenetic analysis indicated the presence of several different groups of nirS- or nosZ denitrifiers in both lakes. The novel nirS denitrifiers were abundant in both Dianchi Lake and Erhai Lake, while most of the obtained nosZ sequences could be affiliated with known genera. 相似文献
12.
Rivers are important sources of N 2O emissions into the atmosphere. Nevertheless, N 2O production processes in rivers are not well identified. We measured concentrations and isotopic ratios of N 2O, NH 4 +, NO 2 ?, and NO 3 ? in surface water to identify the microbial processes of N 2O production along the Tama River in Japan. We also measured the functional gene abundance of nitrifiers and denitrifiers ( amoA-bacteria, nirK, nirS, nosZ clade I, nosZ clade II) together with concentrations of dissolved organic carbon (DOC) and fluorescence intensities of protein and humic components of dissolved organic matter (DOM) to support the elucidation of N 2O production processes. The observed nitrogen (δ 15N) and oxygen (δ 18O) of N 2O were within the expected isotopic range of N 2O produced by nitrate reduction, indicating that N 2O was dominantly produced by denitrification. The positive significant correlation between N 2O Net concentration and nirK gene abundance implied that nitrifiers and denitrifiers are contributors to N 2O production. Fluorescence intensities of protein and humic components of DOM and concentrations of DOC did not show significant correlations with N 2O concentrations, which suggests that DOC and abundance of DOM components do not control dissolved N 2O. Measurement of isotope ratios of N 2O and its substrates was found to be a useful tool to obtain evidence of denitrification as the main source of N 2O production along the Tama River. 相似文献
13.
Land‐use practices aiming at increasing agro‐ecosystem sustainability, e.g. no‐till systems and use of temporary grasslands, have been developed in cropping areas, but their environmental benefits could be counterbalanced by increased N 2O emissions produced, in particular during denitrification. Modelling denitrification in this context is thus of major importance. However, to what extent can changes in denitrification be predicted by representing the denitrifying community as a black box, i.e. without an adequate representation of the biological characteristics (abundance and composition) of this community, remains unclear. We analysed the effect of changes in land uses on denitrifiers for two different agricultural systems: (i) crop/grassland conversion and (ii) cessation/application of tillage. We surveyed potential denitrification (PD), the abundance and genetic structure of denitrifiers (nitrite reducers), and soil environmental conditions. N 2O emissions were also measured during periods of several days on control plots. Time‐integrated N 2O emissions and PD were well correlated among all control plots. Changes in PD were partly due to changes in denitrifier abundance but were not related to changes in the structure of the denitrifier community. Using multiple regression analysis, we showed that changes in PD were more related to changes in soil environmental conditions than in denitrifier abundance. Soil organic carbon explained 81% of the variance observed for PD at the crop/temporary grassland site, whereas soil organic carbon, water‐filled pore space and nitrate explained 92% of PD variance at the till/no‐till site, without any residual effect of denitrifier abundance. Soil environmental conditions influenced PD by modifying the specific activity of denitrifiers, and to a lesser extent by promoting a build‐up of denitrifiers. Our results show that an accurate simulation of carbon, oxygen and nitrate availability to denitrifiers is more important than an accurate simulation of denitrifier abundance and community structure to adequately understand and predict changes in PD in response to land‐use changes. 相似文献
14.
The in vivo production of nitrous oxide (N 2O) by earthworms is due to their gut microbiota, and it is hypothesized that the microenvironment of the gut activates ingested N 2O-producing soil bacteria. In situ measurement of N 2O and O 2 with microsensors demonstrated that the earthworm gut is anoxic and the site of N 2O production. The gut had a pH of 6.9 and an average water content of approximately 50%. The water content within the gut decreased from the anterior end to the posterior end. In contrast, the concentration of N 2O increased from the anterior end to the mid-gut region and then decreased along the posterior part of the gut. Compared to the soil in which worms lived and fed, the gut of the earthworm was highly enriched in total carbon, organic carbon, and total nitrogen and had a C/N ratio of 7 (compared to a C/N ratio of 12 in soil). The aqueous phase of gut contents contained up to 80 mM glucose and numerous compounds that were indicative of anaerobic metabolism, including up to 9 mM formate, 8 mM acetate, 3 mM lactate, and 2 mM succinate. Compared to the soil contents, nitrite and ammonium were enriched in the gut up to 10- and 100-fold, respectively. The production of N 2O by soil was induced when the gut environment was simulated in anoxic microcosms for 24 h (the approximate time for passage of soil through the earthworm). Anoxia, high osmolarity, nitrite, and nitrate were the dominant factors that stimulated the production of N 2O. Supplemental organic carbon had a very minimal stimulatory effect on the production of N 2O, and addition of buffer or ammonium had essentially no effect on the initial N 2O production rates. However, a combination of supplements yielded rates greater than that obtained mathematically for single supplements, suggesting that the maximum rates observed were due to synergistic effects of supplements. Collectively, these results indicate that the special microenvironment of the earthworm gut is ideally suited for N 2O-producing bacteria and support the hypothesis that the in situ conditions of the earthworm gut activate ingested N 2O-producing soil bacteria during gut passage. 相似文献
15.
Biogenic emissions of nitric and nitrous oxides have important impacts on the photochemistry and chemistry of the atmosphere. Although biogenic production appears to be the overwhelming source of N 2O, the magnitude of the biogenic emission of NO is very uncertain. In soils, possible sources of NO and N 2O include nitrification by autotrophic and heterotrophic nitrifiers, denitrification by nitrifiers and denitrifiers, nitrate respiration by fermenters, and chemodenitrification. The availability of oxygen determines to a large extent the relative activities of these various groups of organisms. To better understand this influence, we investigated the effect of the partial pressure of oxygen (pO 2) on the production of NO and N 2O by a wide variety of common soil nitrifying, denitrifying, and nitrate-respiring bacteria under laboratory conditions. The production of NO per cell was highest by autotrophic nitrifiers and was independent of pO 2 in the range tested (0.5 to 10%), whereas N 2O production was inversely proportional to pO 2. Nitrous oxide production was highest in the denitrifier Pseudomonas fluorescens, but only under anaerobic conditions. The molar ratio of NO/N 2O produced was usually greater than unity for nitrifiers and much less than unity for denitrifiers. Chemodenitrification was the major source of both the NO and N 2O produced by the nitrate respirer Serratia marcescens. Chemodenitrification was also a possible source of NO and N 2O in nitrifier cultures but only when high concentrations of nitrite had accumulated or were added to the medium. Although most of the denitrifiers produced NO and N 2O only under anaerobic conditions, chemostat cultures of Alcaligenes faecalis continued to emit these gases even when the cultures were sparged with air. Based upon these results, we predict that aerobic soils are primary sources of NO and that N 2O is produced only when there is sufficient soil moisture to provide the anaerobic microsites necessary for denitrification by either denitrifiers or nitrifiers. 相似文献
16.
We studied potential links between environmental factors, nitrous oxide (N 2O) accumulation, and genetic indicators of nitrite and N 2O reducing bacteria in 12 boreal lakes. Denitrifying bacteria were investigated by quantifying genes encoding nitrite and N 2O reductases ( nirS/ nirK and nosZ, respectively, including the two phylogenetically distinct clades nosZ
I and nosZ
II) in lake sediments. Summertime N 2O accumulation and hypolimnetic nitrate concentrations were positively correlated both at the inter-lake scale and within a depth transect of an individual lake (Lake Vanajavesi). The variability in the individual nirS, nirK, nosZ
I, and nosZ
II gene abundances was high (up to tenfold) among the lakes, which allowed us to study the expected links between the ecosystem’s nir-vs- nos gene inventories and N 2O accumulation. Inter-lake variation in N 2O accumulation was indeed connected to the relative abundance of nitrite versus N 2O reductase genes, i.e. the ( nirS+ nirK)/ nosZ
I gene ratio. In addition, the ratios of ( nirS+ nirK)/ nosZ
I at the inter-lake scale and ( nirS+ nirK)/ nosZ
I+II within Lake Vanajavesi correlated positively with nitrate availability. The results suggest that ambient nitrate concentration can be an important modulator of the N 2O accumulation in lake ecosystems, either directly by increasing the overall rate of denitrification or indirectly by controlling the balance of nitrite versus N 2O reductase carrying organisms. 相似文献
17.
Previous studies have documented the capacity of European earthworms belonging to the family Lumbricidae to emit the greenhouse gas nitrous oxide (N 2O), an activity attributed primarily to the activation of ingested soil denitrifiers. To extend the information base to earthworms in the Southern Hemisphere, four species of earthworms in New Zealand were examined for gut-associated denitrification. Lumbricus rubellus and Aporrectodea rosea (introduced species of Lumbricidae) emitted N 2O, whereas emission of N 2O by Octolasion cyaneum (an introduced species of Lumbricidae) and emission of N 2O by Octochaetus multiporus (a native species of Megascolecidae) were variable and negligible, respectively. Exposing earthworms to nitrite or nitrate and acetylene significantly increased the amount of N 2O emitted, implicating denitrification as the primary source of N 2O and indicating that earthworms emitted dinitrogen (N 2) in addition to N 2O. The alimentary canal displayed a high capacity to produce N 2O when it was supplemented with nitrite, and alimentary canal contents contained large amounts of carbohydrates and organic acids indicative of fermentation (e.g., succinate, acetate, and formate) that could serve as sources of reductant for denitrification. nosZ encodes a portion of the terminal oxidoreductase used in denitrification. The nosZ sequences detected in the alimentary canals of L. rubellus and O. multiporus were similar to those retrieved from soil and were distantly related to sequences of uncultured soil bacteria and genera common in soils (i.e., Bradyrhizobium, Azospirillum, Rhodopseudomonas, Rhodospirillum, Pseudomonas, Oligotropha, and Sinorhizobium). These findings (i) suggest that the capacity to emit N 2O and N 2 is a general trait of earthworms and not geographically restricted, (ii) indicate that species belonging to different earthworm families (i.e., Megascolecidae and Lumbricidae) may not have equal capacities to emit N 2O, and (iii) also corroborate previous findings that link this capacity to denitrification in the alimentary canal.Earthworms are dominant members of the soil fauna and affect the structure and fertility of soils ( 5, 20, 22, 23). Various species of European earthworms belonging to the family Lumbricidae (e.g., Aporrectodea caliginosa, Lumbricus rubellus, and Octolasion lacteum) emit dinitrogen (N 2) and the greenhouse gas nitrous oxide (N 2O), and their burrowing activities and feeding habits in combination with in situ conditions can influence the emission of nitrogenous gases from soils that they inhabit ( 1, 2, 13, 17, 25, 27, 39).The microbiology of the earthworm alimentary canal has been addressed in numerous studies ( 3, 4, 6, 9, 14, 16, 32). The alimentary canal of the earthworm is anoxic, in marked contrast to the aerated material that earthworms ingest ( 14, 39). Anoxia and other in situ conditions of the alimentary canal appear to stimulate soil microbes capable of surviving under anaerobic conditions during passage through the gut ( 3, 4). Soils are rich in denitrifying bacteria ( 37), and the capacity of European earthworms to emit nitrogenous gases has been attributed primarily to the in situ activity of ingested denitrifying bacteria that appear to be highly active under the anoxic conditions of the earthworm alimentary canal ( 12, 15, 17, 25, 39). However, it is not known if the capacity to emit nitrogenous gases is a general trait of earthworms independent of their taxonomic family or geographic location. The main objectives of this study were to examine the capacity of Southern Hemisphere earthworms in New Zealand to emit N 2O and to determine if this capacity was linked to denitrifying bacteria in the alimentary canal. 相似文献
18.
Nitrous oxide (N 2O) is an important greenhouse gas in the troposphere controlling ozone concentration in the stratosphere through nitric oxide production. In order to quantify bacteria capable of N 2O reduction, we developed a SYBR green quantitative real-time PCR assay targeting the nosZ gene encoding the catalytic subunit of the nitrous oxide reductase. Two independent sets of nosZ primers flanking the nosZ fragment previously used in diversity studies were designed and tested (K. Kloos, A. Mergel, C. Rösch, and H. Bothe, Aust. J. Plant Physiol. 28:991-998, 2001). The utility of these real-time PCR assays was demonstrated by quantifying the nosZ gene present in six different soils. Detection limits were between 10 1 and 10 2 target molecules per reaction for all assays. Sequence analysis of 128 cloned quantitative PCR products confirmed the specificity of the designed primers. The abundance of nosZ genes ranged from 10 5 to 10 7 target copies g −1 of dry soil, whereas genes for 16S rRNA were found at 10 8 to 10 9 target copies g −1 of dry soil. The abundance of narG and nirK genes was within the upper and lower limits of the 16S rRNA and nosZ gene copy numbers. The two sets of nosZ primers gave similar gene copy numbers for all tested soils. The maximum abundance of nosZ and nirK relative to 16S rRNA was 5 to 6%, confirming the low proportion of denitrifiers to total bacteria in soils. 相似文献
20.
Hotspots of N 2O emissions are generated from legume residues during decomposition. Arbuscular mycorrhizal fungi (AMF) from co-cultivated intercropped plants may proliferate into the microsites and interact with soil microbes to reduce N 2O emissions. Yet, the mechanisms by which or how mycorrhizal hyphae affect nitrifiers and denitrifiers in the legume residues remain ambiguous. Here, a split-microcosm experiment was conducted to assess hyphae of Rhizophagus aggregatus from neighbouring maize on overall N 2O emissions from stubbles of nodulated or non-nodulated soybean. Soil microbes from fields intercropped with maize/soybean amended with fertilizer nitrogen (SS-N1) or unamended (SS-N0) were added to the soybean chamber only. AMF hyphae consistently reduced N 2O emissions by 20.8%–61.5%. Generally, AMF hyphae promoted the abundance of N 2O-consuming ( nosZ-type) denitrifiers and altered their community composition. The effects were partly associated with increasing MBC and DOC. By contrast, AMF reduced the abundance of nirK-type denitrifiers in the nodulated SS-N0 treatment only and that of AOB in the non-nodulated SS-N1 treatment. Taken together, our results show that AMF reduced N 2O emissions from soybean stubbles, mainly through the promotion of N 2O-consuming denitrifiers. This holds promise for mitigating N 2O emissions by manipulating the efficacious AMF and their associated microbes in cereal/legume intercropping systems. 相似文献
|