High doses of ethylene diurea (EDU) are not toxic to willow and act as nitrogen fertilizer

Ethylene diurea (EDU) is synthetic chemical which protects plants against damage caused by ground level O-3 and is used experimentally as a biomonitoring tool at doses usually ranging from 200 to 400 mg L-1 a.i. Although several studies have investigated the protective action of EDU, this mechanism remains unclear. Important uncertainties in EDU action are whether EDU acts as a source of nitrogen (N) to plants and whether high doses are phytotoxic. In order to answer these questions, we conducted an open-field experiment where potted willow (Salix sachalinensis Fr. Schm) plants were exposed to ambient O-3 conditions and treated with 0, 800 or 1600 mg L-1 EDU as a soil drench, every nine days, for about 2.5 months. We examined approximately 50 response variables. Based on N content in different plant organs, we found that (a) all EDU was transferred to the leaves and (b) high doses of EDU increased the leaf N content. However, EDU did not affect the C content and distribution within the plant body. Still, even at the highest dose, EDU was not toxic to this fast-growing species (however such a high dose should not be applied in uncontrolled environments); and there was no EDU persistence in the soil, as indicated by soil N content. Notably, our soil was free from organic matter and N-poor. Key message: EDU per se does not cause toxicity to willow plants when applied as drench to a soil with no organic matter, rather, high EDU doses may act as nitrogen fertilizer in a nitrogen-poor soil. (C) 2016 Elsevier B.V. All rights reserved.