| Budget Amount *help |
¥2,400,000 (Direct Cost: ¥2,400,000)
Fiscal Year 2006: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2005: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
Tropical rainforests are estimated to be a major source of isoprene to the atmosphere. By association, the vegetation of subtropical areas can be a potential source of isoprene to the atmosphere. However, there is scant data on isoprene emission from tropical tree species in subtropic regions. Although several modeling studies to estimate isoprene emission in Asia area have been made, limited information on the direct measurement of isoprene emission from tropical trees growing in subtropics is available. Thus, this study surveyed isoprene emission from 42 indigenous and exotic tropical trees in subtropic Okinawa, Japan. Of the 42 trees studied, 4 emitted isoprene at a rate in excess of 20 μg g^<-1>h^<-1>, and 28 showed the rates of 1 to 10 μg g^<-1>h^<-1>.The remainder emitted less than 1 μg g^<-1>.The majority of trees in this study may therefore fall within the lower emitting species. However, species in Moraceae that is indigenous in Okinawa emitted isoprene at relatively higher ra
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tes with an average of 14.2 μg g^<-1>h^<-1>. The highest emission rate of 107.1 μg g^<-1>h^<-1> for Ficus virgata yielded the area basis rate of 47.4 nmol m^<-2>s^<-1>, which is almost equivalent to the rate of high emitting species. Furthermore, a linear relationship between light intensity and isoprene emission was noted with Ficus virgata up to 1700 μmol m^<-2>S^<-1>. These findings may show the potential importance of subtropical areas as sources of isoprene to the atmosphere.
Several environmental factors have been reported to regulate the isoprene emission from plant leaves. Among the factors, light and temperature have been well studied as to their effect on isoprene emission. Besides these two factors, humidity is another part of environmental factor to affect the plant physiology. However, no attempt in laboratory scale has been made to elucidate the effect of humidity on isoprene emission. Thus this also studied the effect of humidity on isoprene emission from leaves of a tropical tree Ficus virgata for the first time. Under high humidity, a sharp rise in the emission rate was seen with the lapse of irradiance at 500 and 1000 μmol M^<-2> S^<-1>, respectively. However, this is not the case for low humidity. A lack of sharp rise was noted under low humidity. Furthermore, the steady state emission rate increased with high humidity without any changes in the leaf temperature. The present study therefore suggested that humidity is an important environment factor to control the isoprene flux from tropical plant, and should be taken into consideration for future estimation of isoprene flux from tropical forest. Less
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