Similarities in response of maize genotypes to water logging and ammonium toxicity1

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Abstract
Plant growth, total nitrogen (N), and free ammonia (NH3) in tissue of different maize genotypes were compared in the presence of either nitrate (NO3)‐or ammonium (NH4)‐forms of ? at two oxygen (O2) levels in solution culture. Shoot and root growth was significantly less with ??4 than with NO3 under low O2 conditions; however, NH4 toxicity was significantly reduced by supplying maize plants with additional O2 in the solution culture, and root and shoot growth of NH4‐supplied plants were not significantly different than that of NO3‐treated plants. On the other hand, maize genotypes differed significantly in their response to ? forms and O2. The genotype, Saracura, selected for tolerance to water logging, had the highest tolerance to ??4 based on plant growth under low O2 pressure and the concentration of free NH4 in tissues. This research suggests there may be a common mechanism or an interaction with the mechanism for tolerance to NH4 and water logging.