PROCEEDINGS: Index of Abstracts
INTERNAL UPTAKE AND ASSIMILATION OF GASEOUS NITRIC
ACID BY WESTERN FOREST TREE SPECIES
1-USDA Forest Service, Northeastern Forest Experiment
Station, Newtown Square, PA 19073. 2-Institute of Botany, Polish
Academy of Sciences, Krakow, Poland. 3-USDA Forest Service, Pacific
Southwest Research Station, Riverside, CA. 4-Canadian Forest Service,
Maritimes Region, Fredericton, New Brunswick, Canada.
A nitric acid gas analysis system was designed, tested, and calibrated
to measure nitric acid deposition to forest tree species. Two modified
Monitor Labs 8440 NO, NOx, NO2 analyzers were used in parallel to
measure the nitric acid deposited onto leaf surfaces of ponderosa
pine (Pinus ponderosa) and California black oak (Quercus kelloggii)
seedlings. Measurements were made during 24 hr exposures in which
plants were kept in dark, temperature controlled growth chambers.
The broadleaf oaks had much higher rates of deposition than pines
on a leaf area basis: 4.7 nmoles HNO3 m-2 s-1 for oaks, and 0.6
nmoles HNO3 m-2 s-1 for pines. There was good agreement in HNO3
deposition calculated from the nitric acid gas analysis system and
that measured by nitrate analysis of leaf washings.
Alternate light with dark period experiments (48 hr fumigation)
showed that nitric acid deposition was about 2X greater than fumigation
under darkness calculated by gas analysis and 15N labeling methods.
Nitrate reductase activity was used as an indicator of internal
uptake and assimilation of HNO3 into the leaf foliage.
The enzyme activity increased in the alternate light/dark fumigated
plants 10X greater than the unfumigated control. Preliminary experiments
on the epicuticular waxes showed increases in the proportion of
free fatty acids and alkyl esters, while estolide fractions decreased.
These results indicate that nitric acid vapor may decrease the cuticular
resistance to the nitric acid uptake into the leaf.
This HNO3 analysis system is a significant advancement into nitric
acid research and has the potential to measure the physiological
response of plants to nitric acid exposures.