3,554 research outputs found
IFN-alpha-stimulated genes and Epstein-Barr virus gene expression distinguish WHO type II and III nasopharyngeal carcinomas.
No full textEpstein-Barr-Virus-Encoded LMP2A Induces Primary Epithelial Cell Migration and Invasion: Possible Role in Nasopharyngeal Carcinoma Metastasis.
No full textGermination in declining and common herbaceous plant populations co‐occurring in an acid peaty heathland
No full textAntennaria dioica, Arnica montana, Filago minima, Galium saxatile, Nardus stricta and Viola canina are herbaceous plant species in The Netherlands which are declining and even locally extinct. The germination biology of freshly collected seeds of these species was studied in relation to constant and alternating temperatures and was compared with that of some common co‐occurring plant species. It is concluded that germination responses with respect to temperatures are unlikely to account for their declining situation
Responses of plants to Al, Mn and Fe, with particular reference to Succisa pratensis moench
No full textGermination in populations of Solanum-Dulcamara L. from contrasting habitats
No full textSolanum dulcamara L. grows in widely contrasting habitats, from waterlogged and shaded to relatively dry and fully exposed sites. Representative seed samples from a number of populations were collected. Germination was studied under a variety of experimental conditions in order to determine whether populations from different habitats were genetically differentiated. Under the conditions employed in these experiments it was concluded that populations probably did not differ genetically in their germination responses
CHARACTERIZATION OF THE TYPE AND EXTENT OF NUTRIENT LIMITATION IN GRASSLAND VEGETATION USING A BIOASSAY WITH INTACT SODS
No full textAn important methodological problem in plant ecology concerns the way in which the type and extent of nutrient limitation in terrestrial communities should be assessed. Conclusions on nutrient limitation have been founded mainly on soil extractions, fertiliser trials and tissue nutrient concentrations. In order to avoid some of the problems associated with these methods, we employed a special technique using intact sods which rooted both in the intact soil and in a nutrient solution, from which N, P and K were omitted stepwise. The method was applied to hay-field communities which differed in their history of fertiliser application. Four fields were compared which were not fertilised for 2, 6, 19 or 45 years, while hay making continued. This was done to restore former species-rich grassland communities. We tested the hypothesis that the increase in species diversity in these grasslands was attended by an increase in the number of limiting nutrients.We observed clear shifts in the type and extent of nutrient limitation. Fields which were recently fertilised were characterised by nitrogen and potassium limitation, while phosphorus limitation increased in importance towards the later stages of succession. In the last field (45 years unfertilised) N, P and K equally limited production at the community level. These conclusions differed from those-drawn from a fertiliser trial in these same four fields, which failed to detect phosphorus limitation.It is concluded that the use of this method provides a valuable extra source of information while studying relationships between nutrient limitation and species diversity in grassland communities.</p
Effect of ionic Al in culture solutions on the growth of Arnica montana L. and Deschampsia flexuosa (L.) Trin
No full textThe distribution ofArnica montana L., a hemicryptophytic plant of acid peaty heathlands on nutrientpoor humic podzols has declined in the Netherlands since 1950. The decline is significantly correlated with the 95-percentile of the SO2 concentration in the air over the winter period of 1978/1979. The resulting acid rain could have caused increased levels of ionic Al in low-buffered soils as ‘Haar’ and ‘Veld’ (humic) podzols. Ionic Al is generally considered to be an important growth-limiting factor in many acid soils which are often leached causing additionally low levels of Ca and Mg. The toxic effect of Al3+ on seedlings growth of Arnica and on the Al-tolerant, calcifugous grassDeschampsia flexuosa (L.) Trin. was investigated. Seedlings of both species were grown on complete nutrient solutions situated in a heated greenhouse. Various concentrations of Al3+ at high acidity (pH 3.8) were used. Relatively high and low levels of Ca and/or Mg were factorially combined. It appeared that Arnica and Deschampsia are Al tolerant, the former being somewhat less so. At relatively low concentrations (e.g. 5 mg l−1) of ionic Al, growth of shoot and roots of both species were stimulated. Tolerance to Al3+ is possibly due to an internal Al-chelating mechanism. The Ca and Mg supply did show an influence on growth (yield), but both divalent ions did not affect the magnitude of Al toxicity. These results may indicate that it is not likely that the decline of the regional distribution and abundance of Arnica since 1950 is regulated by ionic Al in the rooting zon
CHARACTERIZATION OF THE TYPE AND EXTENT OF NUTRIENT LIMITATION IN GRASSLAND VEGETATION USING A BIOASSAY WITH INTACT SODS
No full textAn important methodological problem in plant ecology concerns the way in which the type and extent of nutrient limitation in terrestrial communities should be assessed. Conclusions on nutrient limitation have been founded mainly on soil extractions, fertiliser trials and tissue nutrient concentrations. In order to avoid some of the problems associated with these methods, we employed a special technique using intact sods which rooted both in the intact soil and in a nutrient solution, from which N, P and K were omitted stepwise. The method was applied to hay-field communities which differed in their history of fertiliser application. Four fields were compared which were not fertilised for 2, 6, 19 or 45 years, while hay making continued. This was done to restore former species-rich grassland communities. We tested the hypothesis that the increase in species diversity in these grasslands was attended by an increase in the number of limiting nutrients. We observed clear shifts in the type and extent of nutrient limitation. Fields which were recently fertilised were characterised by nitrogen and potassium limitation, while phosphorus limitation increased in importance towards the later stages of succession. In the last field (45 years unfertilised) N, P and K equally limited production at the community level. These conclusions differed from those-drawn from a fertiliser trial in these same four fields, which failed to detect phosphorus limitation. It is concluded that the use of this method provides a valuable extra source of information while studying relationships between nutrient limitation and species diversity in grassland communities
An experimental comparison of aluminium and manganese susceptibility in Antennaria dioica, Arnica montana, Viola canina, Filago minima and Deschampsia flexuosa
No full textAntennaria dioica, Arnica montana, Viola canina and Filago minima are declining in The Netherlands and are even locally extinct. This process of decline has been associated with an increased rate of acidification of soils and an increased availability of aluminium and manganese to plants up to potentially phytotoxic levels. This paper examines whether, and to what extent, aluminium and manganese are important environmental variables in determining the decline in plant species. Susceptibility to ionic aluminium and manganese was studied in three experiments under controlled conditions. Young plants were grown on a complete nutrient solution containing variable concentrations of aluminium, manganese or aluminium plus manganese (pH 3·8). Responses (dry weights after 5 weeks of growth) were compared to those of Deschampsia flexuosa , known to be aluminium and manganese resistan
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