PARENT SESSION
Poster Session 39: Late Breaking and Newsworthy Posters
Friday, August 12, 8:30 AM - 10:30 AM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Leaf luxes of NO and NO₂ in four herbaceous plant species: The role of ascorbic acid.

Teklemariam, Thomas ^*,1, Sparks, Jed¹, ¹ Ecology and Evolutionary Biology, Ithaca, NY, USA

ABSTRACT- Nitrogen oxides (NO_x = NO + NO₂) are a common group of nitrogen containing trace gases that interact significantly with plant canopies and play a critical role in atmospheric chemistry including the formation of ozone, smog and nitric acid. The controls over leaf-atmosphere exchange of NO_x (NO_x = NO + NO₂) have been characterized for a few plant species and important drivers have been identified including stomatal conductance, the partial pressure gradient from the interior and exterior of the leaf, and, most recently the level of ultraviolet radiation. However, our ability to predict leaf fluxes has been hampered by a dearth of information describing the reactions occurring between NO_x and internal constituents of the leaf (referred as the mesophyllic resistance). In this study, we investigated NOx uptake in four plant species and specifically tested the hypothesis that ascorbic acid within the intercellular space may be a significant control over mesophyllic resistance. Measurements were made using a dynamic leaf chamber at ambient mixing ratios typical of urban atmospheres. Measured NO and NO₂ leaf fluxes were lower than the potential flux calculated assuming stomatal conductance as the sole driver (i.e., no mesophyllic resistance). The ratios of leaf intercellular to ambient concentrations (C_i/C_a) for NO across partial pressures and plant species was usually > 0.99 and the leaf uptake rates of NO were negligible within the ranges examined. In contrast, leaf uptake for NO₂ was much greater and C_i/C_a) were often as low as 0.75. For both gases, C_i/C_a) ratios > 1 were observed at low ambient mixing ratios indicating emission from leaves. Across the species, plants with higher leaf nitrogen contents showed higher NO₂ emission rates and plants with higher leaf-ascorbate concentrations had higher leaf NO₂ uptake rates. These results suggest that in addition to the known effects of stomatal conductance and incident UV radiation, leaf nitrogen content and the capacity for the scavenging of NO_x by ascorbic acid may explain the variation in the ability of plants to absorb atmospheric nitrogen oxides.

Key words: nitric oxide, nitrogen dioxide, conductance, ascorbic acid