Simulation of effects of atmospheric ethylene on tree leaf shedding

This study made a preliminary assessment of the possibility that ethylene contained in polluted atmospheres affects leaf shedding of trees. The effect of ethylene dosage (ppb x h) on leaf shedding at various temperatures was approximated by using a polynomial regression. The effect of ethylene dosage on shedding of tree leaves with various sensitivities to this hydrocarbon was simulated in connection with the relationship between ethylene concentrations (10-100 ppb), dosage periods (0-50 days) and temperature (10-30 degrees C). The simulated results indicated the possibility that, for the tree group having high sensitivity, the rate of leaf shedding due to a dosage of ethylene with a concentration as low as 20 ppb, which is commonly observed in urban atmospheres, increased with temperature. On the other hand, the same concentration scarcely influenced leaf shedding in the low sensitivity group even at a temperature as high as 30 degrees C. The results for the real atmosphere determined at the Tokyo metropolitan center indicated the possibility that, for trees having high sensitivity, the rate of leaf shedding increased with rises in both monthly ethylene concentrations and air temperatures and reached a maximum of 90% in July. But in December when the concentration again reached the same value as in July while the mean monthly air temperature was 9.3 degrees C, the rate was only 10%.