報告書番号

U95016

タイトル（和文）

樹木の生長等におよぼす高濃度炭酸ガスの影響評価研究の現状

タイトル（英文）

CURRENT STUDIES TO ASSESS EFFECTS OF ENRICHED ATMOSPHERIC CARBON-DIOXIDE TREE ON GROWTH

概要 （図表や脚注は「報告書全文」に掲載しております）

現状大気濃度の２倍程度のＣＯ２に樹木を暴露した場合、短期的には、光合成が促進され成長が増加するが、暴露の長期化にともなって、光合成産物の過剰蓄積や順化等により成長の促進程度は低下することが報告されている。しかし、樹木におよぼす１年以上にわたる高濃度ＣＯ２の影響を調べた研究は少なく、かつ、高濃度ＣＯ２に対する樹木の反応は、樹種や樹齢などの内的要因や気象条件や土壌条件などの外的要因により左右されることも報告されている。以上のことから、大気中ＣＯ２濃度上昇の樹木への影響を評価・予測するためには、（１）高濃度ＣＯ２に対する順化、（２）ＣＯ２濃度と他の環境要因との複合影響、などについて定量的なデータの蓄積が必要である。そのためには、屋外、または実環境を再現した条件下で、２年以上の長期暴露実験を行う必要がある。

概要 （英文）

ATMOSPHERIC CARBON DIOXIDE (CO2) ENRICHMENT WILL HAVE VARIOUS EFFECTS ON TREES. THIS PAPER REPORTS THE CURRENT STUDIES CONCERNING THESE EFFECTS BASED ON THE LITERATURE. (1)SHORT-TERM EXPOSURE PHOTOSYNTHESIS OF TREES IS STIMULATED BY EXPOSURE TO ENRICHED ATMOSPHERIC CO2. IN MANY EXPERIMENTS WITH 1-YEAR EXPOSURE, THE TREE GROWTHINCREASED WITH CO2 EXPOSURE AT DOUBLE NORMAL CONCENTRATIONS (ABOUT 700PPM)DUE TO SIMULATION OF PHOTOSYNTHESIS. (2)LONG-TERM EXPOSURE IT HAS BEEN REPORTED THAT THE INCREASING RATIO OF TREE GROWTH OBSERVED AS THE SHORT-TERM RESPONSE FELL WITH PROLONGED EXPOSURE.THE CAUSES ARE AS FOLLOS: (1)INHIBITION OF CO2-ASSIMILATION-ENZYME ACTIVITY WITH ACCUMULATIONOF STARCH IN THE CELL, (2)REDUCTION OF CO2 ABSORPTION WITH FALLING STOMATAL DENSITY, (3)CHANGES IN LIGHT STATUS IN CROWN, (4)ACCLIMATION TO ENRICHED CO2. BUT THERE ARE FEW REPORTS THAT EVALUATE THE EFFECTS OF LONG-TERM EXPOSURE (OVER2-YEARS). (3)ENVIRONMENTAL CONDITION THE GROWTH RESPONSES TO HIGHER CO2 CONCENTRATIONS VARY WITH ENVIRONMENTAL FACTORS, TREE SPECIES, AND AGE. THE INTERACTIONS OF THESE RESPONSES HAVE NOT BEENCLARIFIED QUANTITATIVELY. (4)MODEL ESTIMATION SEVERAL TREE-GROWTH MODELS HAVE BEEN USED TO ESTIMATE THE EFFECTS OF ENRICHED CO2 ON FORESTS. THE RESULTS SUGGEST THAT THE GROWTH OF FORESTS WOULD BE STIMULATED BY INCREASING CO2 CONCENTRATIONS. BUT THE COMPLEX EFFECTS OF ENRICHED CO2 AND ENVIRONMENTAL FACTORS AND INDIRECT IMPACTS HAVE NOT BEEN INVESTIGATEDSUFFICIENTLY. (5)FUTURE INVESTIGATION IT IS NECESSARY TO OBTAIN THE FOLLOWING DATA TO ESTIMATE THE LONG-TERM EFFECTS OF INCREASING ATMOSPHERIC CO2 CONCENTRATION ON TREES: (1)QUANTITATIVE DATA ON THEACCLIMATION RESPONSE, (2)COMPLEX EFFECTS OF ENRICHED CO2 AND OTHER ENVIRONMENTAL FACTORS, AND (3)CHARACTERISTIC RESPONSES OF TREE SPECIES.

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