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排序方式: 共有222条查询结果,搜索用时 93 毫秒
101.
Parducci L Jørgensen T Tollefsrud MM Elverland E Alm T Fontana SL Bennett KD Haile J Matetovici I Suyama Y Edwards ME Andersen K Rasmussen M Boessenkool S Coissac E Brochmann C Taberlet P Houmark-Nielsen M Larsen NK Orlando L Gilbert MT Kjær KH Alsos IG Willerslev E 《Science (New York, N.Y.)》2012,335(6072):1083-1086
It is commonly believed that trees were absent in Scandinavia during the last glaciation and first recolonized the Scandinavian Peninsula with the retreat of its ice sheet some 9000 years ago. Here, we show the presence of a rare mitochondrial DNA haplotype of spruce that appears unique to Scandinavia and with its highest frequency to the west-an area believed to sustain ice-free refugia during most of the last ice age. We further show the survival of DNA from this haplotype in lake sediments and pollen of Tr?ndelag in central Norway dating back ~10,300 years and chloroplast DNA of pine and spruce in lake sediments adjacent to the ice-free And?ya refugium in northwestern Norway as early as ~22,000 and 17,700 years ago, respectively. Our findings imply that conifer trees survived in ice-free refugia of Scandinavia during the last glaciation, challenging current views on survival and spread of trees as a response to climate changes. 相似文献
102.
Ma Sonia Rodríguez-Cruz Jacob Bælum Sebastian R. Sørensen Thomas Aspray Carsten S. Jacobsen Gary D. Bending 《Soil biology & biochemistry》2010,42(1):32-39
Mecoprop-p [(R)-2-(4-chloro-2-methylphenoxy) propanoic acid) is widely used in agriculture and poses an environmental concern because of its susceptibility to leach from soil to water. We investigated the effect of soil depth on mecoprop-p biodegradation and its relationship with the number and diversity of tfdA related genes, which are the most widely known genes involved in degradation of the phenoxyalkanoic acid group of herbicides by bacteria. Mecoprop-p half-life (DT50) was approximately 12 days in soil sampled from <30 cm depth, and increased progressively with soil depth, reaching over 84 days at 70-80 cm. In sub-soil there was a lag period of between 23 and 34 days prior to a phase of rapid degradation. No lag phase occurred in top-soil samples prior to the onset of degradation. The maximum degradation rate was the same in top-soil and sub-soil samples. Although diverse tfdAα and tfdA genes were present prior to mecoprop-p degradation, real time PCR revealed that degradation was associated with proliferation of tfdA genes. The number of tfdA genes and the most probable number of mecoprop-p degrading organisms in soil prior to mecoprop-p addition were below the limit of quantification and detection respectively. Melting curves from the real time PCR analysis showed that prior to mecoprop-p degradation both class I and class III tfdA genes were present in top- and sub-soil samples. However at all soil depths only tfdA class III genes proliferated during degradation. Denaturing gradient gel electrophoresis confirmed that class III tfdA genes were associated with mecoprop-p degradation. Degradation was not associated with the induction of novel tfdA genes in top- or sub-soil samples, and there were no apparent differences in tfdA gene diversity with soil depth prior to or following degradation. 相似文献
103.
Maria S Holtze Flemming EkelundLasse D Rasmussen Carsten S JacobsenKaare Johnsen 《Soil biology & biochemistry》2003,35(9):1175-1181
We investigated whether the prey-predator dynamics of bacteria and protozoa were affected by inorganic mercury at concentrations of 0, 3.5 and 15 mg Hg(II) kg soil−1. The amount of bioavailable Hg was estimated using a biosensor-assay based on the mer-lux gene fusion. The numbers of bacterial CFUs on the general medium 1/100 tryptic soy agar (TSA) were significantly decreased when the soil had been amended with Hg. In contrast, no effect was seen on the number of CFUs on the Pseudomonas-specific medium Gould's S1 agar. Protozoan numbers estimated by the most probable number (MPN) method with 1/100 TSB as growth medium were also negatively affected by Hg. The different fractions of protozoa were affected to different degrees suggesting that amoebae were less sensitive than slow-growing flagellates, which again were less sensitive than the fast-growing flagellates. In contrast, Hg did not induce any detectable changes in the diversity of flagellate morphotypes. In the treatment with 15 mg Hg kg−1 a transiently increased number of bacteria was seen at day 6 probably concomitant with a decrease in the numbers of protozoa. This might indicate that Hg affected the prey-predator dynamics in communities of culturable bacteria and protozoa in soil. Furthermore, we showed that the number of Pseudomonas spp. was not affected by Hg whereas the number of bacteria growing on a general medium was. 相似文献
104.
Niels Strange Carsten Rahbek Jacob K. Jepsen Mette P. Lund 《Biological conservation》2006,128(4):455-466
The current study focuses on the influence of geopolitical coordination of conservation strategies on cost and efficiency in terms of species representation when selecting network of protected areas. Conservation policies in the EU are implemented at many different administrative levels: from the European Union and national levels, to regional or/county levels within member countries. This arise the question what size of efficiency gains could be achieved if planning of conservation priorities could be coordinated between geopolitical units. Using data for the nationwide distribution of 763 species, representing all Danish species within eight taxa, we compared illustrative costs for the addition of new areas to the existing conservation network in order to ensure full coverage of all species. We found that the cost of independent regional planning is 20-fold higher than an inter-regional and nationally co-ordinated strategy. We also found that substituting land prices for a simple land-area measure in our analyses increased the expected conservation costs differential significantly, without increasing coverage of species representations. We suggest that in economic and biodiversity terms it can largely be a win-win situation to set a common goal, to develop priority-strategies, and to coordinate actions at higher rather than lower levels of administration. 相似文献
105.
Christian Bugge Henriksen Jesper Rasmussen Carsten Sgaard 《Soil & Tillage Research》2006,85(1-2):27-37
In the original ridge tillage system as practiced in the US Corn Belt, ridges are formed during the growing season. Several studies have documented that this can reduce leaching of nutrients and improve fertilizer efficiency. This study was conducted to determine whether ridges formed in autumn can be used as an alternative to ploughing to reduce N leaching during autumn and winter, and thereby increase growth and N uptake of a subsequent unfertilized crop. A factorial field experiment with tillage and residues as factors was conducted during 1998–2000. Tillage treatments were autumn ridging and ploughing. Residue treatments were stubble, stubble + straw and stubble + liquid manure in order to create a gradient of C/N ratios. From the time of harvest until planting of a subsequent barley crop (Hordeum vulgare L.), inorganic N was determined 11 times in 1998–1999 and 10 times in 1999–2000 in the 0–10, 10–30, 30–60 and 60–90 cm soil layers. Growth and N uptake of barley was quantified nine times in both 1999 and 2000. Barley grain and straw yields were determined. Ridging resulted in lower levels of inorganic N in the 30–90 cm soil layer in November and a significantly higher level of inorganic N in the 0–30 cm soil layer in late April, indicating reduced leaching and increased N availability for the subsequent crop. Ridging significantly increased growth, yield and N uptake of barley whereas incorporation of straw generally reduced growth, yield and N uptake. It is concluded that ridging in autumn has a N conserving effect, and it is suggested that the potential of ridging in autumn as an alternative to ploughing is further investigated in detailed studies of solute movement, N immobilization/mineralization and crop performance. 相似文献
106.
João Barateiro Diogo Tiago Natal-da-Luz José Paulo Sousa Christian Vogt Carsten Nowak 《Journal of Soils and Sediments》2007,7(6):388-392
Background, Aims, and Scope The springtail Folsomia candida is a commonly used model species in ecotoxicological soil testing. The species reproduces parthenogenetically and, thus,
laboratories use different clonal lineages. In this study, we investigated if genetic divergence between F. candida strains impacts the reaction to chemical stress and may thus affect the outcome of toxicity tests.
Methods In two exposure assays (life-cycle reproduction test and avoidance behaviour test), three laboratory strains of F. candida from Portugal (PTG), Spain (SPN) and Denmark (DNK) were exposed to different concentrations of the reference chemical phenmedipham.
Genetic divergence among strains was estimated based on mitochondrial COI sequence data.
Results No significant differences between tolerance towards phenmedipham exposure were observed in a reproduction test. In contrast,
one strain (SPN) showed a decreased susceptibility to phenmedipham compared to the other strains (PTG and DNK) in the avoidance
assay.
Discussion A phylogenetic tree based on mitochondrial COI sequences revealed clear genetic differentiation between both ‘reaction types’.
Thus, we found a potential lineage dependent stress reaction in avoidance behaviour towards the pesticide.
Conclusions Our findings have implications for the comparability of test results among laboratories. Reproduction tests seem to be more
robust towards interclonal genetic differentiation than avoidance tests.
Recommendations and Perspectives We recommend the use of molecular tools for simple and cost effective genetic characterization of F. candida strains used in chemical avoidance tests. Closer investigations concerning the relation between genetic relatedness and chemical
response will provide a more detailed and comprehensive picture on the role of intraspecific genetic differentiation in stress
tolerance.
ESS-Submission Editor: Prof. Dr. Henner Hollert (henner.hollert@bio5.rwth-aachen.de) 相似文献
107.
In order to gain insight into the community structure and the biodegradative potential of bacteria residing in a BTEX-contaminated field site, with benzene as main pollutant, an investigation strategy with a variety of cultivation-independent and -dependent approaches was undertaken. Based on 16S ribosomal DNA sequence analysis, sampling stations in the center of the pollution plume were found to be dominated by a bacterial consortium affiliated with various members of the class of Proteobacteria and Firmicutes, including different sporulating and non-sporulating sulfate-reducing bacteria and members of the genus Geobacter. Non-polluted samples retrieved from outside the plume revealed several phylotypes which were also observed in the centre of the plume. Bacterial sequences retrieved from the fringe of the plume were dominated by several genera of beta Proteobacteria subclass which were not associated with other phylotypes obtained in this study. All sampling stations were tested positive for catechol 2,3-dioxygenase genes, indicating the presence of microorganisms with the genetic potential degrading aromatic compounds via the meta-cleavage pathway. The groundwater system at the down-gradient edge of the plume was characterized, in contrast to all other sampling stations in the center and outside the plume, by high numbers of cultivable bacteria and cultivable aerobic benzene and toluene degraders. These findings are also in accordance with the investigations based on fluorescent in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes, suggesting the presence of an actively benzene degrading bacterial community of beta Proteobacteria at the fringe of the pollution plume. 相似文献
108.
Bioavailability of triazine herbicides in a sandy soil profile 总被引:1,自引:0,他引:1
Carsten S. Jacobsen Nir Shapir Lene O. Jensen Einar H. Jensen Réne K. Juhler Jens C. Streibig Ralphi T. Mandelbaum Arne Helweg 《Biology and Fertility of Soils》2001,33(6):501-506
The bioavailability of atrazine was evaluated in a Danish soil profile (Drengsted) using a combination of soil sorption, transport and mineralisation methods as well as inoculation using Pseudomonas ADP. Sorption of atrazine decreased markedly with depth as indicated by Kd values of 5.2 l kg-1 for the upper soil and 0.1 l kg-1 for the subsoils. The transport of atrazine was evaluated using soil TLC plates and the resulting Rf values were 0.1 for the upper soil and 0.9 for the subsoil. Only a relatively small amount of atrazine leached through undisturbed soil columns taken from the upper 60 cm. Inoculating with Pseudomonas strain ADP (1᎒6 CFU g-1 dry weight soil) revealed that the degradation of 0.01 ppm atrazine was fully completed (80% mineralisation) within 10 days in the subsoil, while it reached less than 15% in the upper soil. Over a period of 500 days, a total mineralisation of 37% of added atrazine in the upper soil was found (2 mg kg-1 incubated at 20° C). However, in the subsurface soil where 0.02 mg kg-1 of atrazine was incubated at 10°C, the degradation was slower, only reaching about 12%. Terbuthylazine mineralisation was found to be temperature-dependent and low (less than 5%) in the upper soil and very much lower in the subsoil. Desethylterbuthylazine was the most frequently found metabolite. Finally, Pseudomonas strain ADP inoculated into soils from different depths increased the mineralisation of terbuthylazine dramatically. Modelling using a "two-compartment model" indicated that desorption of terbuthylazine is the limiting step for its mineralisation. 相似文献
109.
Yanjun Xie Callum A. S. Hill Zefang Xiao Carsten Mai Holger Militz 《Wood Science and Technology》2011,45(1):49-61
The dynamic water vapour sorption properties of Scots pine (Pinus sylvestris L.) wood samples were studied to investigate the modifying effects of glutaraldehyde. Pine sapwood was treated with solutions
of glutaraldehyde and a catalyst (magnesium chloride) to obtain weight per cent gains of 0.5, 8.6, 15.5, and 21.0%, respectively.
The sorption behaviour of untreated and treated wood was measured using a Dynamic Vapour Sorption apparatus. The results showed
considerable reduction in equilibrium moisture content of wood and the corresponding equilibrium time at each target relative
humidity (RH) due to glutaraldehyde treatment. The moisture adsorption and desorption rates of modified and unmodified wood
were generally faster in the low RH range (up to approximate 20%) than in the high range. Modification primarily reduced the
adsorption and desorption rates over the high RH range of 20–95%. Glutaraldehyde modification resulted in a reduction in sorption
hysteresis due to the loss of elasticity of cell walls. 相似文献
110.
Jiang W Yun D Saleh L Barr EW Xing G Hoffart LM Maslak MA Krebs C Bollinger JM 《Science (New York, N.Y.)》2007,316(5828):1188-1191
In a conventional class I ribonucleotide reductase (RNR), a diiron(II/II) cofactor in the R2 subunit reacts with oxygen to produce a diiron(III/IV) intermediate, which generates a stable tyrosyl radical (Y*). The Y* reversibly oxidizes a cysteine residue in the R1 subunit to a cysteinyl radical (C*), which abstracts the 3'-hydrogen of the substrate to initiate its reduction. The RNR from Chlamydia trachomatis lacks the Y*, and it had been proposed that the diiron(III/IV) complex in R2 directly generates the C* in R1. By enzyme activity measurements and spectroscopic methods, we show that this RNR actually uses a previously unknown stable manganese(IV)/iron(III) cofactor for radical initiation. 相似文献