Induction of nitrate reductase activity by nitric acid vapor in California black oak (Quercus kelloggii), canyon live oak (Quercus chrysolepis), and ponderosa pine (Pinus ponderosa) seedlings

The induction of the enzyme nitrate reductase in needles may be a prerequisite for the assimilation of foliar-absorbed nitrogen oxide pollutants by red spruce (Picearubens Sarg.) trees. To test for induction of nitrate reductase, 1-year-old red spruce seedlings were exposed to NO2, HNO3 vapor, or acid mist containing nitrate, and the activity of nitrate reductase in needles was measured. One day after exposure to NO2 (75 nL•L−1) began, nitrate reductase activity was three times greater than that of unexposed control plants. One day after exposure ended, the nitrate reductase activity returned to the control level. Older red spruce seedlings that had been excavated from a spruce–fir stand exhibited a similar pattern of response, but the level of nitrate reductase activity was much lower than that of the 1-year-old seedlings. Nitric acid vapor (75 nL•L−1) also induced nitrate reductase in red spruce needles, and the pattern of response was similar to that with NO2, except that the nitrate reductase activity did not return to control levels until 2 days after exposure ended. Exposure of seedlings to acid mist containing nitrate (pH 3.5 and 5.0) did not result in a change in nitrate reductase activity. These results indicate that red spruce is capable of assimilating NO2 and HNO3 vapor and that hypotheses of forest decline based on foliar assimilation of pollutant nitrogen oxides are tenable.

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Seasonal variation in nitrate reductase activity in needles of high-elevation red spruce trees

Canadian Journal of Forest Research ◽

10.1139/x92-049 ◽

1992 ◽

Vol 22 (3) ◽

pp. 375-380 ◽

Cited By ~ 12

Author(s):

M.G. Tjoelker ◽

S.B. McLaughlin ◽

R.J. DiCosty ◽

S.E. Lindberg ◽

R.J. Norby

Keyword(s):

Nitrate Reductase ◽

Nitrate Reductase Activity ◽

Reductase Activity ◽

Nitrate Assimilation ◽

High Elevation ◽

Preliminary Evidence ◽

Air Pollutant ◽

Red Spruce ◽

Acid Vapor ◽

Assimilation Capacity

To assess seasonal and site variation in foliar nitrate reductase activity and its utility as a biochemical marker for the uptake of nitrogen oxide pollutants in high-elevation forests, we measured nitrate reductase activity in current-year needles of red spruce (Picearubens Sarg.) saplings at two high-elevation stands (1935 and 1720 m) in the Great Smoky Mountains, North Carolina. Measurements spanned two growing seasons between September 1987 and September 1988. Nitrate reductase activity peaked near 60 nmol•g−1•h−1 at both sites in September and October 1987 and August 1988 and declined 80% in November 1987 and 65% in September 1988. Although nitrate reductase activity was 30% greater in saplings at the higher site relative to the lower site in September and October 1987, activity dropped to approximately 10 nmol•g−1•h−1 at both sites in November 1987. No differences among sites were evident the following year. Comparing deposition of nitric acid vapor at a nearby site to nitrate reductase activity suggests that needle nitrate reductase activity is not an unequivocal marker for foliar uptake of nitrogen oxides during air pollutant episodes. The changes in soil nitrate levels in this system provide preliminary evidence that foliar nitrate assimilation may, in part, include nitrate taken up from the soil, as the highest activity occurred during periods of higher A-horizon nitrate concentrations in 1988. These measurements of nitrate reductase activity suggest that red spruce are capable of assimilating nitrate in foliage in the field and that the nitrate assimilation capacity varies throughout the year.

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