ANALYSES OF ENZYME-ACTIVITIES AND OTHER METABOLIC CRITERIA AFTER 5 YEARS OF FUMIGATION

Enzymatic activity (peroxidase, glutamate dehydrogenase, glutamine synthetase), foliage buffering capacity, soluble protein and nitrogen content were measured in current and previous year needles from young spruce (Picea abies) and fir (Abies alba). The trees were exposed to low levels of SO2 and/or O3 and simulated acidic precipitation (pH 4.0) in open-top chambers from 1983 through 1988. Needle samples were taken during March 1988 at the end of the five-year fumigation period. Exposure to SO2 substantially increased sulphur content in both needle age classes of spruce and fir, and concomitantly reduced the foliage buffering capacity index (BCI), whereas the combined fumigation with SO2 and O3 had no effect on BCI. Peroxidase activity was markedly higher in year-old needles compared to current-year needles. However, trees from the SO2 and SO2 + O3 treatments exhibited statistically significant stimulated peroxidase activities. Similarly, changes in the activities of the nitrogen-metabolizing enzymes indicated an altered cellular function of the trees after the long-term pollution stress. Levels of activity of both glutamate dehydrogenase and glutamine synthetase were increased by exposure to SO2, especially in spruce. Although glutamate dehydrogenase in spruce was affected by all treatments, such changes in activity were found in fir only with the SO2 treatment. The highest activity of glutamine synthetase, however, occurred in the older needles of trees exposed to SO2 + O3. Total nitrogen concentration was either unaffected by the pollutant treatments or decreased in spruce compared to the controls. No statistically significant changes due to the fumigation were found in soluble protein concentrations. Results indicated that chronic exposure to air pollutants lead to alterations in metabolic processes in conifer needles, detectable either by changes in typical stress indicating values or by increases in ammonium assimilation capacity.