Using Natural Isotope Variations of Nitrogen in Plants as an Early Indicator of Air Pollution Stress

Abstract

Model experiments (container experiments) were used to investigate whether natural variations of nitrogen constitute a suitable means for the early indication of harmful effects on plants and the level at which changes in nitrogen metabolism may occur. Wheat plants were exposed under near-ambient, controlled conditions (open-top chambers) to ozone for 2 or 6 weeks. The responses of the nitrogen metabolism in these plants were compared with non-exposed organisms at various biochemical levels. In the short-term experiment (2 weeks), wheat plants exhibited altered δ15N values under stress conditions right at the molecular level in the individual amino acids, whereas the biochemical N-fractions (structural protein (SP), soluble protein (LP) and non-protein nitrogen (NPN)) remained nearly unchanged. In the long-term experiment (6 weeks), the impact of ozone treatment and the combined effects of ozone and carbon dioxide on the wheat plants were examined. An increase in δ15N values was found as a reaction to ozone treatment in both the LP amino acids detected and in all biochemical N-fractions. Combined exposure to ozone and carbon dioxide was found to have a lesser impact at the level of the N-fractions and also at the molecular level of amino acids. The results show an example of how stable isotopes can be used as sensitive ecotoxicological indicators to provide early warning of environmental damage. © 1997 by John Wiley & Sons, Ltd.