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Investigating ammonium toxicity in chrysanthemums
Abstract
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
Plant propagation|Agronomy|Botany
Recommended Citation
Thomas, David M, "Investigating ammonium toxicity in chrysanthemums" (2003). ETD collection for University of Nebraska-Lincoln. AAI3116612.
https://digitalcommons.unl.edu/dissertations/AAI3116612