Recovery of 15N Labelled Urea as Affected by Fixation of Ammonium by Clay Minerals     

Huating Dou  Diedrich Steffens 《植物养料与土壤学杂志》1995,158(4):351-354

A greenhouse experiment was conducted with Lolium perenne to determine whether ammonium (NH₄⁺-N) fixation by clay minerals can increase the recovery of nitrogen following application of ¹⁵N labelled urea. A silty loam subsoil, B_t horizon from an Alfisol derived from loess, pH (CaCl₂) 7.9, was chosen for the experiment. The NH₄⁺-N fixation capacity was altered by varying the distribution of potassium (K) in the upper and lower soil layer. In the K₀ treatment (control), the upper soil layer fertilized with urea was not supplied with K, whereas the lower soil layer was fertilized with 300 mg K kg^?1 soil. In the K₁^?, K₂^? and K₃ treatment the upper soil was supplied with 100-, 200- and 300 mg K kg^?1 soil, respectively. The soil in the lower layer of the K₃ treatment was not supplied with K. The recovery of ¹⁵N from applied urea (¹⁵N uptake of Lolium perenne plus residual soil ¹⁵N_t) was 86.1% in the K₀ treatment and 75.2%, 69.1% and 69.6% in K_1-, K_2- and K₃ treatments, respectively, showing that ¹⁵N losses were smallest in the K₀ treatment. Two weeks after applying ¹⁵N labelled urea the amounts of nonexchangeable ¹⁵NH₄⁺-N in the upper soil layer were significantly higher in the K₀ treatment than in the treatments with K application. Apparently, NH₄⁺-N fixation by clay minerals can reduce NH₃ volatilization after urea fertilization, if the amount of exchangeable K is low.  相似文献   

Snowfall-driven growth in East Antarctic ice sheet mitigates recent sea-level rise   总被引：1，自引：0，他引：1  

Davis CH  Li Y  McConnell JR  Frey MM  Hanna E 《Science (New York, N.Y.)》2005,308(5730):1898-1901

Satellite radar altimetry measurements indicate that the East Antarctic ice-sheet interior north of 81.6 degrees S increased in mass by 45 +/- 7 billion metric tons per year from 1992 to 2003. Comparisons with contemporaneous meteorological model snowfall estimates suggest that the gain in mass was associated with increased precipitation. A gain of this magnitude is enough to slow sea-level rise by 0.12 +/- 0.02 millimeters per year.  相似文献   

Experimental repetitive quantum error correction     

Schindler P  Barreiro JT  Monz T  Nebendahl V  Nigg D  Chwalla M  Hennrich M  Blatt R 《Science (New York, N.Y.)》2011,332(6033):1059-1061

The computational potential of a quantum processor can only be unleashed if errors during a quantum computation can be controlled and corrected for. Quantum error correction works if imperfections of quantum gate operations and measurements are below a certain threshold and corrections can be applied repeatedly. We implement multiple quantum error correction cycles for phase-flip errors on qubits encoded with trapped ions. Errors are corrected by a quantum-feedback algorithm using high-fidelity gate operations and a reset technique for the auxiliary qubits. Up to three consecutive correction cycles are realized, and the behavior of the algorithm for different noise environments is analyzed.  相似文献   

Cell biology. Cytonemes show their colors     

Affolter M  Basler K 《Science (New York, N.Y.)》2011,332(6027):312-313

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Axonal neuregulin-1 regulates myelin sheath thickness     

Michailov GV  Sereda MW  Brinkmann BG  Fischer TM  Haug B  Birchmeier C  Role L  Lai C  Schwab MH  Nave KA 《Science (New York, N.Y.)》2004,304(5671):700-703

In the nervous system of vertebrates, myelination is essential for rapid and accurate impulse conduction. Myelin thickness depends on axon fiber size. We use mutant and transgenic mouse lines to show that axonal Neuregulin-1 (Nrg1) signals information about axon size to Schwann cells. Reduced Nrg1 expression causes hypomyelination and reduced nerve conduction velocity. Neuronal overexpression of Nrg1 induces hypermyelination and demonstrates that Nrg1 type III is the responsible isoform. We suggest a model by which myelin-forming Schwann cells integrate axonal Nrg1 signals as a biochemical measure of axon size.  相似文献   

N-linked glycosylation in Campylobacter jejuni and its functional transfer into E. coli     

Wacker M  Linton D  Hitchen PG  Nita-Lazar M  Haslam SM  North SJ  Panico M  Morris HR  Dell A  Wren BW  Aebi M 《Science (New York, N.Y.)》2002,298(5599):1790-1793

N-linked protein glycosylation is the most abundant posttranslation modification of secretory proteins in eukaryotes. A wide range of functions are attributed to glycan structures covalently linked to asparagine residues within the asparagine-X-serine/threonine consensus sequence (Asn-Xaa-Ser/Thr). We found an N-linked glycosylation system in the bacterium Campylobacter jejuni and demonstrate that a functional N-linked glycosylation pathway could be transferred into Escherichia coli. Although the bacterial N-glycan differs structurally from its eukaryotic counterparts, the cloning of a universal N-linked glycosylation cassette in E. coli opens up the possibility of engineering permutations of recombinant glycan structures for research and industrial applications.  相似文献   

E protein silencing by the leukemogenic AML1-ETO fusion protein     

Zhang J  Kalkum M  Yamamura S  Chait BT  Roeder RG 《Science (New York, N.Y.)》2004,305(5688):1286-1289

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Mbeki and AIDS in Africa     

Markus MB  Fincham JE 《Science (New York, N.Y.)》2000,288(5474):2131d

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Germination, genetics, and growth of an ancient date seed     

Sallon S  Solowey E  Cohen Y  Korchinsky R  Egli M  Woodhatch I  Simchoni O  Kislev M 《Science (New York, N.Y.)》2008,320(5882):1464

An ancient date seed (Phoenix dactylifera L.) excavated from Masada and radiocarbon-dated to the first century Common Era was germinated. Climatic conditions at the Dead Sea may have contributed to the longevity of this oldest, directly dated, viable seed. Growth and development of the seedling over 26 months was compatible with normal date seedlings propagated from modern seeds. Preliminary molecular characterization demonstrated high levels of genetic variation in comparison to modern, elite date cultivars currently growing in Israel. As a representative of an extinct date palm population, this seedling can provide insights into the historic date culture of the Dead Sea region. It also has importance for seed banking and conservation and may be of relevance to modern date palm cultivation.  相似文献   

Phylogeny of the SARS coronavirus     

Eickmann M  Becker S  Klenk HD  Doerr HW  Stadler K  Censini S  Guidotti S  Masignani V  Scarselli M  Mora M  Donati C  Han JH  Song HC  Abrignani S  Covacci A  Rappuoli R 《Science (New York, N.Y.)》2003,302(5650):1504-1505

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