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Investigating ammonium toxicity in chrysanthemums

David M Thomas, University of Nebraska - Lincoln


Ammonium is a ubiquitous intermediate in plant metabolism, an excess can be toxic to many plant species. Symptoms are; leaf yellowing, stunted growth, damaged roots, and death. Symptoms have been attributed to ammonium-induced disorders such as pH regulation, effects of free ammonia, mineral deficiencies, carbohydrate limitations, lack of NO3− as an osmoticum, and reduced water uptake. Researchers know that NH4 + toxicity exists, but do not fully understand its cause. The purpose of this research was to answer three questions. First, does the presence of NH4+ cause toxicity? Second, does microelement form make a difference in nutrient uptake? Third, does pH alone or in combination with N form and microelement form affect nutrient uptake and thus NH 4+ toxicity? ^ Hydroponics solutions were used supplying 200 ppm N; 100% NO3 and 25:75 NH4+:NO3. Chrysanthemum × morifolium cv. Bright Golden Anne, NH4+ sensitive, was the test plant. Microelements were supplied as chelates or ionic salts. All nutrients were supplied at equal concentrations. ^ The first series of experiments determined hourly and daily pH fluctuations of the solutions and the timing of solution changes; pH was measured hourly over the first 24 hours and 4 times a day for 14 days thereafter. Nitrate solutions showed a pH increase within 5 hours. In the 25:75 treatments, pH decreased in the ionic salts solution while the chelate solution was stable. Over 5–7 days the pH declined in all solutions suggesting a need to refresh the solutions. ^ In the second series of experiments leaf tissue and nutrient solution analysis were used to determine if a toxicity or deficiency occurred. Leaf yellowing and stunted roots occurred in both ionic salts treatment. Spring analysis revealed Fe deficiency and Zn toxicity. No detrimental effects of NH4+ were seen in plants grown in the NH4 +:NO3 treatment with chelated microelements. Iron must be present as a chelate or it may not be available. Fall analysis revealed N deficiency, Zn and B toxicity. These factors make it difficult to determine the exact cause of visual symptoms. ^

Subject Area

Agriculture, Agronomy|Biology, Botany|Agriculture, Plant Culture

Recommended Citation

Thomas, David M, "Investigating ammonium toxicity in chrysanthemums" (2003). ETD collection for University of Nebraska - Lincoln. AAI3116612.