Verlag des Forschungszentrums Jülich
JUEL-3568
Eickriede, Antje
Aufnahme und Einbau 15N-markierter Stickoxide durch krautige und holzige Pflanzen
127 S., 1998
Sunflowers (Helianthus annuus L.), mays (Zea mays L.) and poplar (Populus tremula x P. alba) were exposed to ambient concentrations of nitrogen oxides. By using 15N enriched nitrogen oxides (15NO2 and 15NO, summarised as 15NOx) the uptake and incorporation of 15NOx in dependance of the exposition concentration, nitrogen nutrition (nitrate or ammonium as sole N source), and harvesting time were examined. Moreover, the influence of nitrogen oxide exposition on the distribution pattern of 15NOx nitrogen within the plants and on the amino acid content of plant leaves was investigated.
The amount of nitrogen taken up as 15NOx nitrogen was very small compared with the total nitrogen uptake of the plants. In 15NO2 exposed plants less than 1 % of the total nitrogen derived from 15NO2 uptake, in 15NO exposed plants less than 0,1 %. After exposure the highest concentrations of 15N tracer were located in the leaves, followed by stems and roots. High 15N enrichments were found in the alcohol soluble amino acids indicating a very rapid assimilation of atmospheric nitrogen oxide. Therefore, the activity of the enzyme systems involved in the assimilation of 15NOx nitrogen by plants was not a limiting factor. More than 80% of 15NOx nitrogen was fixed in the organic nitrogen fraction (proteins, glucosamines, lipids) of the leaves. Apparently, leaves are not only the main site of uptake, but also of storage of the 15NOx nitrogen. According to these results the distribution patterns of 15NO nitrogen within the plant and between nitrogen fractions are comparable to those of nitrogen dioxide. Therefore, the assimilation pathway of both oxides is probably the same.
With a delayed harvesting point, sunflowers and poplars show an decreasing 15N enrichment in the soluble amino acids of their leaves. Therefore, it may be suggested that 15NO2 nitrogen from the atmosphere is incorporated into the alcohol insoluble nitrogen fractions with time.
Exposing sunflowers and poplars to 15NOx influences the amino acid content of the leaves significantly. In the leaves of sunflower the content of glutamic acid are significantly higher, while the alanin content was significantly lower compared to the non-exposed plants. The later the plants are harvested the more the amino acid content of the leaves increases. Under the same conditions the leaves of poplar plants contain significantly lower asparagine, glutamic acid, and arginin concentrations as compared to non-exposed plants, but no influence of the harvest point was found.
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