NitrateUptakebyTerrestrialandAquaticPlants Richard A. Larson, Marina Montez-Ellis, Karen Marley, and Gerald K. Sims University of Illinois at Urbana-Champaign Abstract Fertilizer-derived nitrate has been the subject of scrutiny among environmental scientists and regulatory agencies concerned about the ecological and public health effects of elevated nitrate levels in surface water, groundwater, and drinking water. An approach that has not received much attention is to remove or convert excess nitrate from at or near the point of application using plants. In this project, we demonstrated the kinetics of nitrate uptake from water and soil by plants of potential management value. Special attention was paid to potential cover crop species that might be planted in the autumn after fertilizer application, and plowed under or killed in the spring to act as “green manure.” In addition, we examined the activity of the key enzyme, nitrate reductase, in a variety of aquatic and terrestrial plants. Switchgrass (Panicum virgatum) and hornwort (Ceratophyllum demersum) appeared to be the most promising nitrate-removing species in preliminary studies. Introduction Nitrogen fertilization is an established practice in production agriculture for the maintenance of high yields in crops such as corn and soybeans. Nitrate is a highly soluble species, and is readily transported from the point of application, as surface runoff as well as leachate to subsurface waters. In central Illinois nitrate N losses at the field and watershed scales range from 15-40 kg N/hectare/year. High nitrate levels in groundwarer and drinking water have been linked to health disorders such as methemoglobinemia, gastric cancer, goiters, and birth malformations. In addition, some researchers have suggested that increases in midwestern N fertilizer application has led to the development of “dead zones” caused by overgrowth and dieoff of algae in the Gulf of Mexico. Suggestions that growers use lower nitrogen application levels, however, have been resisted by both farmers and industry. Literature Review Nitrate transformations. Nitrogen exists in several forms of importance to agriculture. The forms are interconverted in soil, water, and air in the geochemical nitrogen cycle. Atmospheric nitrogen, N2, is taken up or “fixed” by a few kinds of microorganisms, whose + enzymes convert it to ammonium, NH4 . Plants then convert ammonium to organic N, initially in the form of amino acids, which are eventually largely converted to proteins. In aerobic soil, ammonium is also nitrified, that is, oxidatively converted to nitrite (NO2�) and nitrate (NO3�) by _________________________________ Address: Department of Natural Resources and Environmental Sciences, Urbana, IL 61801. Address correspondence to Richard Larson.