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41.
Extraction of PAH from Oh-horizon material after dispersion of air-dried samples in water resulted in a 80% higher yield of 20 PAH species compared to extraction of air-dried, freeze-dried or ground samples. Concurrently, the free surface area (BET method) of the organic matter increased. It was assumed that dispersion resulted in a disaggregation and/or stretching of organic aggregates, which makes interior aggregate regions available to the extractant that were pre-viously not accessible for the extractant due to diffusion barriers. 相似文献
42.
The influence of Mg- and Ca-deficiency on the micromorphology of epicuticular waxes and on the wettability of spruce needles The influence of Mg- and Ca-deficiency in nutrient solution on epicuticular waxes of needles of Norway spruce (Picea abies [L.] Karst.) was investigated in greenhouse experiments. Spruce clones were cultivated in sand and supplied with nutrient solution. For two vegetation periods, plants of the treatment groups -Mg, -Ca and -Mg/-Ca were provided with only 15 % of the respective mineral element of the control. At the end of the second vegetation period, the nutrient deficiency was documented by reduced Mg- and/or Ca-content of the needles and changes in chlorophyll fluorescence. No effect on micromorphology of epicuticular waxes and wettability of needles of any age was observed following deficient Mg and/or Ca supply. 相似文献
43.
Michael RichterUeli A. Hartwig Emmanuel FrossardJosef Nösberger Georg Cadisch 《Soil biology & biochemistry》2003,35(10):1325-1335
Plant response to increasing atmospheric CO2 partial pressure (pCO2) depends on several factors, one of which is mineral nitrogen availability facilitated by the mineralisation of organic N. Gross rates of N mineralisation were examined in grassland soils exposed to ambient (36 Pa) and elevated (60 Pa) atmospheric pCO2 for 7 years in the Swiss Free Air Carbon dioxide Enrichment experiment. It was hypothesized that increased below-ground translocation of photoassimilates at elevated pCO2 would lead to an increase in immobilisation of N due to an excess supply of energy to the roots and rhizosphere. Intact soil cores were sampled from Lolium perenne and Trifolium repens swards in May and September, 2000. The rates of gross N mineralisation (m) and NH4+ consumption (c) were determined using 15N isotopic dilution during a 51-h period of incubation. The rates of N immobilisation were estimated either as the difference between m and the net N mineralisation rate or as the amount of 15N released from the microbial biomass after chloroform fumigation. Soil samples from both swards showed that the rates of gross N mineralisation and NH4+ consumption did not change significantly under elevated pCO2. The lack of a significant effect of elevated pCO2 on organic N turnover was consistent with the similar size of the microbial biomass and similar immobilisation of applied 15N in the microbial N pool under ambient and elevated pCO2. Rates of m and c, and microbial 15N did not differ significantly between the two sward types although a weak (p<0.1) pCO2 by sward interaction occurred. A significantly larger amount of NO3− was recovered at the end of the incubation in soil taken from T. repens swards compared to that from L. perenne swards. Eleven percent of the added 15N were recovered in the roots in the cores sampled under L. perenne, while only 5% were recovered in roots of T. repens. These results demonstrate that roots remained a considerable sink despite the shoots being cut at ground level prior to incubation and suggest that the calculation of N immobilisation from gross and net rates of mineralisation in soils with a high root biomass does not reflect the actual immobilisation of N in the microbial biomass. The results of this study did not support the initial hypothesis and indicate that below-ground turnover of N, as well as N availability, measured in short-term experiments are not strongly affected by long-term exposure to elevated pCO2. It is suggested that differences in plant N demand, rather than major changes in soil N mineralisation/immobilisation, are the long-term driving factors for N dynamics in these grassland systems. 相似文献
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46.
Induction of tumors in mice by genomic hypomethylation 总被引:1,自引:0,他引:1
Gaudet F Hodgson JG Eden A Jackson-Grusby L Dausman J Gray JW Leonhardt H Jaenisch R 《Science (New York, N.Y.)》2003,300(5618):489-492
Genome-wide DNA hypomethylation occurs in many human cancers, but whether this epigenetic change is a cause or consequence of tumorigenesis has been unclear. To explore this phenomenon, we generated mice carrying a hypomorphic DNA methyltransferase 1 (Dnmt1) allele, which reduces Dnmt1 expression to 10% of wild-type levels and results in substantial genome-wide hypomethylation in all tissues. The mutant mice were runted at birth, and at 4 to 8 months of age they developed aggressive T cell lymphomas that displayed a high frequency of chromosome 15 trisomy. These results indicate that DNA hypomethylation plays a causal role in tumor formation, possibly by promoting chromosomal instability. 相似文献
47.
Drissner D Kunze G Callewaert N Gehrig P Tamasloukht M Boller T Felix G Amrhein N Bucher M 《Science (New York, N.Y.)》2007,318(5848):265-268
The arbuscular mycorrhizal (AM) symbiosis represents the most widely distributed mutualistic root symbiosis. We report that root extracts of mycorrhizal plants contain a lipophilic signal capable of inducing the phosphate transporter genes StPT3 and StPT4 of potato (Solanum tuberosum L.), genes that are specifically induced in roots colonized by AM fungi. The same signal caused rapid extracellular alkalinization in suspension-cultured tomato (Solanum lycopersicum L.) cells and induction of the mycorrhiza-specific phosphate transporter gene LePT4 in these cells. The active principle was characterized as the lysolipid lyso-phosphatidylcholine (LPC) via a combination of gene expression studies, alkalinization assays in cell cultures, and chromatographic and mass spectrometric analyses. Our results highlight the importance of lysophospholipids as signals in plants and in particular in the AM symbiosis. 相似文献
48.
Coleman JN Lotya M O'Neill A Bergin SD King PJ Khan U Young K Gaucher A De S Smith RJ Shvets IV Arora SK Stanton G Kim HY Lee K Kim GT Duesberg GS Hallam T Boland JJ Wang JJ Donegan JF Grunlan JC Moriarty G Shmeliov A Nicholls RJ Perkins JM Grieveson EM Theuwissen K McComb DW Nellist PD Nicolosi V 《Science (New York, N.Y.)》2011,331(6017):568-571
If they could be easily exfoliated, layered materials would become a diverse source of two-dimensional crystals whose properties would be useful in applications ranging from electronics to energy storage. We show that layered compounds such as MoS(2), WS(2), MoSe(2), MoTe(2), TaSe(2), NbSe(2), NiTe(2), BN, and Bi(2)Te(3) can be efficiently dispersed in common solvents and can be deposited as individual flakes or formed into films. Electron microscopy strongly suggests that the material is exfoliated into individual layers. By blending this material with suspensions of other nanomaterials or polymer solutions, we can prepare hybrid dispersions or composites, which can be cast into films. We show that WS(2) and MoS(2) effectively reinforce polymers, whereas WS(2)/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties. 相似文献
49.
Matter described by quantum chromodynamics (QCD), the theory of strong interactions, may undergo phase transitions when its temperature and the chemical potentials are varied. QCD at finite temperature is studied in the laboratory by colliding heavy ions at varying beam energies. We present a test of QCD in the nonperturbative domain through a comparison of thermodynamic fluctuations predicted in lattice computations with the experimental data of baryon number distributions in high-energy heavy ion collisions. This study provides evidence for thermalization in these collisions and allows us to find the crossover temperature between normal nuclear matter and a deconfined phase called the quark gluon plasma. This value allows us to set a scale for the phase diagram of QCD. 相似文献
50.
Johnson WL Kaltenboeck G Demetriou MD Schramm JP Liu X Samwer K Kim CP Hofmann DC 《Science (New York, N.Y.)》2011,332(6031):828-833
The development of metal alloys that form glasses at modest cooling rates has stimulated broad scientific and technological interest. However, intervening crystallization of the liquid in even the most robust bulk metallic glass-formers is orders of magnitude faster than in many common polymers and silicate glass-forming liquids. Crystallization limits experimental studies of the undercooled liquid and hampers efforts to plastically process metallic glasses. We have developed a method to rapidly and uniformly heat a metallic glass at rates of 10(6) kelvin per second to temperatures spanning the undercooled liquid region. Liquid properties are subsequently measured on millisecond time scales at previously inaccessible temperatures under near-adiabatic conditions. Rapid thermoplastic forming of the undercooled liquid into complex net shapes is implemented under rheological conditions typically used in molding of plastics. By operating in the millisecond regime, we are able to "beat" the intervening crystallization and successfully process even marginal glass-forming alloys with very limited stability against crystallization that are not processable by conventional heating. 相似文献