Ethylenediurea (EDU) effects on Japanese larch: an one growing season experiment with simulated regenerating communities and a four growing season application to individual saplings.

Japanese larch ( (Lamb.) Carr.) and its hybrid are economically important coniferous trees widely grown in the Northern Hemisphere. Ground-level ozone (O) concentrations have increased since the pre-industrial era, and research projects showed that Japanese larch is susceptible to elevated O exposures. Therefore, methodologies are needed to (1) protect Japanese larch against O damage and (2) conduct biomonitoring of O in Japanese larch forests and, thus, monitor O risks to Japanese larch. For the first time, this study evaluates whether the synthetic chemical ethylenediurea (EDU) can protect Japanese larch against O damage, in two independent experiments. In the first experiment, seedling communities, simulating natural regeneration, were treated with EDU (0, 100, 200, and 400 mg L) and exposed to either ambient or elevated O in a growing season. In the second experiment, individually-grown saplings were treated with EDU (0, 200 and 400 mg L) and exposed to ambient O in two growing seasons and to elevated O in the succeeding two growing seasons. The two experiments revealed that EDU concentrations of 200-400 mg L could protect Japanese larch seedling communities and individual saplings against O-induced inhibition of growth and productivity. However, EDU concentrations ≤ 200 mg L did offer only partial protection when seedling communities were coping with higher level of O-induced stress, and only 400 mg EDU L fully protected communities under higher stress. Therefore, we conclude that among the concentrations tested the concentration offering maximum protection to Japanese larch plants under high competition and O-induced stress is that of 400 mg EDU L. The results of this study can provide a valuable resource of information for applied forestry in an O-polluted world.