Foliar Nitrate Reductase: A Marker for Assimilation of Atmospheric Nitrogen Oxides

摘要

Atmospheric deposition of nitrates to forest canopies has been implicated as predisposing trees to environmental stresses. A first step in the evaluation of this hypothesis is the determination of whether atmospheric nitrates are absorbed and metabolized by tree foliage. The enzyme nitrate reductase (NR) is an appropriate marker for nitrate metabolism because it is the rate-limiting step in the assimilation of nitrate into organic compounds and it is substrate-inducible. In laboratory studies, NR was not induced in red spruce foliage exposed to NO sub 3 sup -1 in acid mist, but NR activity increased dramatically in spruce seedlings exposed to NO sub 2 or HNO sub 3 vapor, suggesting that gaseous nitrogen oxides can be assimilated by spruce foliage. Nitrate reductase activity also can be measured in the field and may be a useful marker for trees that are impacted by nitrogen pollution, but extensive characterization of diurnal and seasonal variation in foliar NR activity is an important prerequisite. 24 refs. (ERA citation 13:037656)