Abstract
Authors
YASUDA Yukio, WATANABE Tsutomu, OHTANI Yoshikazu, OKANO Michiaki, Nakayama KeiichiYear
1998Title
Seasonal variation of CO2 flux over a broadleaf deciduous forest.落葉広葉樹林上におけるCO2フラックスの季節変化
Journal
Journal of Japan Society of Hydrology & Water ResourcesVolume
11(6)Page
575-585DOI
Keywords
CO2 flux. Eddy correlation method, Closed-path measurement, Seasonal variation. Temperate deciduous forestCO2フラックス，渦相関法，Closed-path型測定，季節変化，落葉広葉樹林
URL
http://www.journalarchive.jst.go.jp/english/jnlabstract_en.php?cdjournal=jjshwr1988&cdvol=11&noissue=6&startpage=575Abstract
Long-term measurement of CO2 flux has been continued since April 1997 over a temperate deciduous forest. The flux is directly measured by the eddy correlation method using a closed-path CO2 analyzer.Seasonal variation of the CO2 flux was clearly correlated with that of the leaf area index. When the foliation began in Apri1, the CO2 flux changed its direction from upward to downward and increased rapidly as leaves grew. The downward CO2 flux reached its maximum in June when the leaf area index became maximum. The flux was then decreased gradually as leaves senesced, followed by rapid reduction during the leaf-fa11. The direction of flux finally turned upward at the middle of November. Day-by-day variations were also observed in the CO2 flux during the growing season, which were mainly caused by the variations of photosynthetic photon flux density.
The net annual carbon uptake was estimated by integrating flux data and interpolating missing data using the relations between measured fluxes and environmental factors. The net carbon flux was
森林のCO2吸収の実態を把握するため，落葉広葉樹林上においてCOフラックスを1997年４月から連続測定している．CO2分析器としてClosed-path型分析器を用い，渦相開法によってフラックスの直接測定を行っている．
CO2フラックスは明瞭な季節変化を示した．フラックスは春から秋まではﾄﾞ向きとなり，冬には上向きとなった．春，樹木が一斉に展葉すると，フラックスの向きが上向きから下向きに転じ，その後フラックスの大きさが急激に増加した．夏から秋のなかごろまで，下向きフラックスは徐々に減少し，秋の終わりには落葉とともに急激に減少した．また，日毎のフラックスの変化は，樹木の葉が茂りCO2吸収が盛んに行われているとき，光合成有効光量子束密度と高い相関がある．
大気と森林との間の年間炭素交換量を把握するため，欠測目のCO2フラックスを，怪聞はフラックスの光反応曲線から，夜間は気温とフラックスの関係から推定し，フラックスデータの袖間を行った．CO2フラックスの合計から得られた年間炭素交換量は