For all the examined fresh soils taken from four different vegetations, degradation rates of ethylene (C
2H
4) under aerobic conditions showed logarithmic increases with the increase in atmospheric C
2H
4 concentration up to approximately 100 ppm. The degradation rates of the same soils air-dried were generally one-tenth lower than those of the fresh soils. At the atmospheric concentration of 30 ppmC
2H
4,the rates of the fresh soils of the Fagus crenata, Cryptomeria japonica and Thujopsis dolabrata forests and the paddy field examined were 150,130,60 and 5 nl/g d.w./day, respectively. Highly regular correlations were observed between theC
2H
4 degradation rates of the fresh soils and the amount of both the organic carbon and nitrogen in the soils. The rates determined under soil moisture ranging from 50 to 100% were approximately two times higher than those under the range from 150 to 200%. The decrease in atmospheric C
2H
4 concentration close to the soil surface was examined in the Cryptomeria japonica plantation by placing the vessel close to the soil surface. The decrease rates increased almost linearly with the increase of atmosphericC
2H
4 concentrations. The rate determined under atomosphericC
2H
4 concentrations of 10 ppm was 1.2×10
3 nl/cm
2 soil surface/hr.
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