Temporal and Spatial Variations in CO2 Concentration within a Japanese Cedar Forest on a Slope Land

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スギ人工林内において二酸化炭素濃度を継続測定した。林冠上，林冠上部，林冠下部，林床近くの計4点に測定個所を設けた。大気湿度および光強度，気温，風速，風向を併せて測定した。これまでに報告されているような林内での二酸化炭素濃度の階層化は明瞭ではなかった。しかしながら，垂直方向の風速が弱いときには，林床近くの二酸化炭素濃度が他の3点よりも60ppm以上高くなることがあった。4点ともに夏季の晴天日には，夜間は二酸化炭素濃度が安定しており，日の出後に濃度が下がり始め，やがて安定し，日の入り前に再び上昇するという日変化をした。二酸化炭素濃度はスギの樹冠光合成速度の影響を強く受けていた。光強度が強いほど日中の二酸化炭素濃度の低下量が大きかったが，光強度が600μmol・m-2・sec-1以上になると低下量が安定した。この関係はスギの光―樹冠光合成曲線に類似していた。北西から風が吹くと二酸化炭素濃度が急激に上昇することがあり，高濃度の二酸化炭素を含む都市部の空気の移流が示唆された。Atmospheric carbon dioxide concentrations within a Japanese cedar (Cryptomeria japonica D. Don) manmade forest on a slope land were continuously measured at four sampling points, above the canopy, in the upper canopy, in the lower canopy and near the forest floor. Air humidity, light intensity, air temperature, wind velocity and wind direction were measured simultaneously. The stratification of CO2 concentrations, which has been reported by earlier researchers within the flat forests, was generally not clear. However, when the vertical wind speed was low, the CO2 concentrations near the forest floor were more than 60 ppm higher than those at the other measurement points. During fine weather in summer, the CO2 concentrations at all measurement points were stable during the nighttime and dropped after daybreak to a stable level during the middle of the day, followed by an increase up to the nighttime level before sunset. The CO2 concentration was strongly affected by the crown photosynthetic rates of Japanese cedar. The decrease of CO2 concentrations in daytime from the nighttime level extended as the light intensity increased. However, if the light intensity exceeded 600μmol・m-2・sec-1, the decrease of CO2 concentrations from the nighttime level was constant. This relationship between light intensity and daytime CO2 concentrations decrease was similar to that between the light intensity and the crown photosynthetic rate of Japanese cedar. When the wind blew from the northwest, the CO2 concentrations at all heights rose and dropped in short time. This might indicate the influence of CO2 enriched air inflow from the urban area.
東京大学大学院農学生命科学研究科附属演習林,The Tokyo University Forests,東京大学大学院農学生命科学研究科森林科学専攻,東京大学農学部附属演習林千葉演習林,日本大学生物資源科学部森林資源科学科,Department of Forest Science, Graduate School of Agricultural and Life Sciences, The University of Tokyo,University Forest in Chiba, Faculty of の論文

Temporal and Spatial Variations in CO2 Concentration within a Japanese Cedar Forest on a Slope Land

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