Ethylene evolution and ammonium accumulation by tomato plants with various nitrogen forms and regimes of acidity. Part I

Abstract

Ammonium nutrition of plants in soil or solution culture leads to development of a strongly acidic regime in the medium. Foliar evolution of ethylene and accumulation of ammonium are stimulated by ammonium nutrition. This stimulation may be due in part to the acidification of media by ammonium nutrition. To determine the effects of medium pH on ethylene evolution and ammonium accumulation by plants, tomato (Lycopersicon esculentum Mill. ‘Heinz 1350’ and neglecta‐1) were grown with nitrate, ammonium, or urea nutrition and with various pH regimes in solution culture. Ammonium nutrition decreased medium pH to 3.5 and increased ethylene evolution and ammonium accumulation by plants. Urea nutrition at pH 3.5 also increased ammonium accumulation and ethylene evolution by plants. Nitrate nutrition at pH 3.5 slightly increased ammonium accumulation but had no effect on ethylene evolution. Media supplied with different ratios of nitrate to ammonium relieved toxic effect of ammonium relative to 100% ammonium nutrition. The symptoms of ammonium toxicity were observed on the plants with high ethylene evolution. High ethylene evolution occurred on the plants with relative high ammonium accumulation regardless of nitrogen forms and pH regimes. The results indicate that toxic symptoms and increased ethylene evolution are directly related to high ammonium accumulation and that low pH may cause ammonium accumulation in plants.

Notes

Present address: Department of Soil Science, North Carolina State University, Raleigh, NC 27695–7619.