報告書番号

V05004

タイトル（和文）

シラカンバ、ダケカンバ、ブナ、アカマツ、スギにおよぼすO3とCO2の単独および複合影響

タイトル（英文）

Effects of elevated O3 and/or CO2 on Japanese white birch, Japanese mountain birch, Siebold's beech, Japanese red pine and Japanese cedar seedlings

概要 （図表や脚注は「報告書全文」に掲載しております）

5樹種の苗木に，2段階のO3濃度（外気1.0倍／1.5倍）と2段階のCO2濃度（外気／1.5倍）を組み合わせて処理した。その結果、5樹種の生長は高濃度O3処理によって抑制され、原因は純光合成速度低下による生長の基となる光合成産物量減少であることが明らかとなった。一方、高濃度CO2処理によって5樹種の生長は増加し、この原因は純光合成速度増加による光合成産物量増加であることが明らかとなった。また、シラカンバとスギでは，高濃度CO2処理によって高濃度O3処理による生長抑制が緩和された。両樹種では高濃度CO2によって気孔の開度が低下し，他の3樹種では気孔開度にも有意な変化はなかった。したがって、複合影響の樹種間差異には高濃度CO2に対する気孔反応が関与し，シラカンバとスギではCO2濃度上昇による気孔開度の低下が葉内へのO3吸収を減少させた結果，O3処理による生長抑制が緩和されたものと考えられた。

概要 （英文）

Japanese white birch, Japanese mountain birch, Siebold’s beech, Japanese red pine and Japanese cedar were exposed to O3 and/or CO2 over two growing seasons (from 12 July to 31 October in 2002 and from 26 March to 31 October in 2003) in open-top chambers at Gunma, Japan. Ten open-top chambers were used to deliver five treatments: charcoal-filtered air (CFA), ambient air (1.0x ambient O3), elevated O3 (1.5x ambient O3), elevated CO2 (1.5x ambient CO2 plus 1.0x ambient O3), or elevated O3 + CO2 (1.5x ambient O3 plus 1.5x ambient CO2). At ambient CO2 concentration, white birch and mountain birch seedlings developed white flecks on the foliage and this was followed by premature senescence in elevated O3 treatment. Red pine needles showed yellowing in elevated O3 treatment. O3 exposure accelerated defoliation of white birch, mountain birch, beech and pine. These effects were reflected in an accelerated decline in foliar chlorophyll concentrations in white birch, mountain birch, beech and pine exposed to O3. Leaf net photosynthetic rate [A] determined at 380 ppm CO2 decreased linearly with increasing O3 in all tree species. The decline in photosynthesis induced by O3 was associated with reduced foliar concentrations of non-structural carbohydrates. Growth was decreased by O3 treatment for all studied species by the end of 2nd season. In elevated CO2 treatment (at ambient O3 concentrations), foliar nitrogen content in white birch, mountain birch, pine and cedar decreased compared with equivalent trees maintained in ambient air treatment. Moreover, foliar chlorophyll concentration was decreased by exposure to elevated CO2 in all tree species. Nevertheless, elevated CO2 resulted in an increase in A when comparisons were made at growth CO2 concentrations for all studied species. The stimulation in photosynthesis induced by elevated CO2 was reflected in increased foliar concentrations of non-structural carbohydrates (mainly starch). In addition, in beech, the number of leaves produced in second flushes increased in elevated CO2. Growth was stimulated for all tree species in the elevated CO2 treatment (at ambient O3 concentrations) in comparison with their counterparts maintained throughout in ambient air by the end of 2nd season. Interactions were in evidence in white birch and cedar, with elevated CO2 generally affording protection against the adverse effects of O3 on growth-related parameters. The protection afforded by elevated CO2 was consistent with the response of stomatal conductance [Gs] at the growth CO2 concentration ‐ Gs declining further in elevated CO2 + O3 treated white birch and cedar compared with mountain birch, beech and pine. Findings suggested responses to the combination of elevated O3 + CO2 were species-specific and governed, at least to some extent, by differences in the extent of stomatal closure induced by elevated CO2 (i.e. the absorbed dose of O3).

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