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ROLE OF LEAF SURFACE WATER IN THE BI-DIRECTIONAL AMMONIA EXCHANGE BETWEEN THE ATMOSPHERE AND TERRESTRIAL BIOSPHERE
WU, Y., J. T. WALKER, JR. K, C. PETERS-LIDARD, D. B. SCHWEDE, R. L. DENNIS, AND W. ROBARGE. ROLE OF LEAF SURFACE WATER IN THE BI-DIRECTIONAL AMMONIA EXCHANGE BETWEEN THE ATMOSPHERE AND TERRESTRIAL BIOSPHERE. In Proceedings, Agricultural Air Quality: State of the Sciences, Potomac, MD, June 05 - 08, 2006. Ecological Society of America, Ithaca, NY, 1-9, (2006).
Improve the understanding of the interaction of the atmosphere and the underlying surface and EPA's ability to simulate that interaction.
A field experiment was conducted to study the ammonia exchange between plants and the atmosphere in a soybean field in Duplin County, North Carolina during the summer of 2002. Measurements indicate that the net canopy-scale ammonia exchange is bi-directional and has a significant diurnal cycle. In general, ammonia concentrations peak a few hours after sunrise. Deposition occurs in the evening and early morning hours while emission occurs in the late morning and early afternoon. To investigate the mechanisms that control the exchange process, a new model is developed based on the Multi-Layer BioChemical deposition (MLBC) model (Wu et al., 2003) with additional parameterizations for the leaf ammonia compensation point (Wu et al., 2006) and leaf surface water effects. The MLBC model considers biochemical processes such as photosynthesis, respiration, and membrane passive transport through the cuticle. The leaf surface water thickness is based on a simple water budget equation. Model results suggest that while accurate prediction of the stomatal compensation point is critical, leaf surface water also plays an important role in the net canopy-scale ammonia flux.