1,617 research outputs found
Pea-barley intercrop N dynamics in farmers fields
Knowledge about crop performances in farmersâ fields provides a link between on-farm practice and re-search. Thereby scientists may improve their ability to understand and suggest solutions for the problems facing those who have the responsibility of making sound agricultural decisions.
Nitrogen (N) availability is known to be highly heterogeneous in terrestrial plant communities (Stevenson and van Kessel, 1997), a heterogeneity that in natural systems is often associated with variation in the distri-bution of plant species. In intercropping systems the relative proportion of component crops is influenced by the distribution of growth factors such as N in both time and space (Jensen, 1996). In pea-barley intercrops, an increase in the N supply promotes the growth of barley thereby decreasing the N accumulation of pea and giving rise to changes in the relative proportions of the intercropped components (Jensen, 1996). The pres-sure of weeds may, however, significantly change the dynamics in intercrops (Hauggaard-Nielsen et al., 2001). Data from farmersâ fields may provide direct, spatially explicit information for evaluating the poten-tials of improving the utilisation of field variability by intercrops
FARO server: Meta-analysis of gene expression by matching gene expression signatures to a compendium of public gene expression data
Virkningsmekanismer for neurotoksisk effekt af mangan og kombinationseffekt af mangan, chlorpyrifos og maneb
Bacterial viruses enable their host to acquire antibiotic resistance genes from neighbouring cells
Prophages are quiescent viruses located in the chromosomes of bacteria. In the human
pathogen, Staphylococcus aureus, prophages are omnipresent and are believed to be responsible
for the spread of some antibiotic resistance genes. Here we demonstrate that release of
phages from a subpopulation of S. aureus cells enables the intact, prophage-containing
population to acquire beneficial genes from competing, phage-susceptible strains present in
the same environment. Phage infection kills competitor cells and bits of their DNA are
occasionally captured in viral transducing particles. Return of such particles to the prophagecontaining
population can drive the transfer of genes encoding potentially useful traits such
as antibiotic resistance. This process, which can be viewed as âauto-transductionâ, allows
S. aureus to efficiently acquire antibiotic resistance both in vitro and in an in vivo virulence
model (wax moth larvae) and enables it to proliferate under strong antibiotic selection
pressure. Our results may help to explain the rapid exchange of antibiotic resistance genes
observed in S. aureus
Early and Middle Jurassic mires of Bornholm and the Fennoscandian Border Zone: a comparison of depositional environments and vegetation
Suitable climatic conditions for peat formation existed during EarlyâMiddle Jurassic times in the Fennoscandian Border Zone. Autochthonous peat and allochthonous organic matter were deposited from north Jylland, south-east through the Kattegat and Ăresund area, to SkĂĽne and Bornholm. The increase in coal seam abundance and thickness from north Jylland to Bornholm indicates that the most favourable peat-forming conditions were present towards the south-east. Peat formation and deposition of organic-rich muds in the Early Jurassic coastal mires were mainly controlled by a continuous rise of relative sea level governed by subsidence and an overall eustatic rise. Watertable rise repeatedly outpaced the rate of accumulation of organic matter and terminated peat formation by lacustrine or lagoonal flooding. Organic matter accumulated in open-water mires and in continuously waterlogged, anoxic and periodically marine-influenced mires. The latter conditions resulted in huminite-rich coals containing framboidal pyrite. The investigated Lower Jurassic seams correspond to peat and peaty mud deposits that ranged from 0.5â5.7 m in thickness, but were generally less than 3 m thick. It is estimated that on Bornholm, the mires existed on average for c. 1200 years in the HettangianâSinemurian and for c. 2300 years in the Late Pliensbachian; the Early Jurassic (HettangianâSinemurian) mires in the Ăresund area existed for c. 1850 years. Aalenian uplift of the RingkøbingâFyn High and major parts of the Danish Basin caused a significant change in the basin configuration and much reduced subsidence in the Fennoscandian Border Zone during the Middle Jurassic. This resulted in a more inland position for the Middle Jurassic mires which on occasion enabled peat accumulation to keep pace with, or temporarily outpace, watertable rise. Thus, peat formation was sometimes sustained for relatively long periods, and the mires may have existed for up to 7000 years in the Ăresund area, and up to 19 000 years on Bornholm. The combination of the inland position of the mires, a seasonal climate, and on occasion a peat surface above groundwater level caused temporary oxidation of the peat surfaces and formation of inertinite-rich coals. The spore and pollen assemblages from coal seams and interbedded siliciclastic deposits indicate that the dominant plant groups in both the Early and Middle Jurassic mires were ferns and gymnosperms. However, significant floral differences are evident. In the Lower Jurassic coals, the palynology testifies to a vegetation rich in cycadophytes and coniferophytes (Taxodiaceae family) whereas club mosses were of lesser importance. Conversely, in the Middle Jurassic coals, the palynology indicates an absence of cycadophytes, a minor proportion of coniferophytes (Taxodiaceae) and a significant proportion of club mosses. These variations are probably related to adaptation by different plants to varying environmental conditions, in particular of hydrological character
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