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Title :亜熱帯沖縄産樹木からのイソプレンガス放出の環境特性と調節メカニズムの解明
Title alternative :Study on the isoprene emission of tropical trees in Okinawa island
Authors :屋, 宏典
Authors alternative :Oku, Hirosuke
Issue Date :May-2007
Abstract :平成17年度~平成18年度科学研究費補助金(基盤研究(C))研究成果報告書
研究概要:熱帯雨林は大気圏へのイソプレンガスの主要な供給源とされている。同様に亜熱帯域に生育する熱帯樹木も重要なイソプレン供給源であることが推測されるが、亜熱帯域の樹木のイソプレン放出能を直接的に測定した研究は少ない。本研究は亜熱帯沖縄に自生或いは外来の熱帯樹木42種のイソプレン放出能を計測するととともに光、温度等の環境因子に対するイソプレン放出の応答特性を明らかにすることを目的とした。計測した42種の中、4種の放出速度は20μg/g/hr以上であり、28種は1-10μg/g/hr、残りは1μg/g/hr以下であった。従って、本研究で計測した樹木類の大半は低放出群に分類されると判断された。しかしながら、沖縄在来のクワ科植物の放出速度は比較的高く、平均放出速度は14.2μg/g/hrと見積もられた。とりわけハマイヌビワ(Ficus virgata)の放出速度107.1μg/g/hrは葉面積換算では47.4nmol/m^2/sに相当し、高放出群に分類されると判断された。さらに、ハマイヌビワからのイソプレン放出は光強度1700μmol/m^2/sまで直線的に増加し、温帯植物において観察される600μmol/m^2/s近傍での光飽和現象は観察されなかった。これらの結果は熱帯同様亜熱帯域の植物も大気圏への重要なイソプレン供給源となることを示唆した。次いで、光、温度に次ぐ環境因子として、湿度のイソプレン放出速度への影響について検討した。高湿度環境下においては、光照射は急激なイソプレン放出速度の上昇を引き起こすが、低湿度条件下ではこのような現象は観察されなかった。さらに、定常状態のイソプレン放出速度も湿度依存的に増加した。これらの結果は光、温度のみならず湿度もイソプレン放出を規定する因子であることを示唆しており、今後の熱帯・亜熱帯植物のイソプレン放出予測式に取り入れる必要があることを指摘している。
要約(欧文):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 rates 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.
Type Local :研究報告書
Publisher :屋宏典
URI :http://hdl.handle.net/20.500.12000/13648
Appears in Collections:Research Report (COMB)

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