FONT SIZE:
ミズゴケ類の光合成に及ぼす温度, pH, 塩濃度の効果
原口, 昭
Permalink : http://hdl.handle.net/2115/59062
JaLCDOI : 10.14943/lowtemsci.73.31
Abstract
ミズゴケ類は, 一般に周極域の寒冷で, 貧栄養な酸性土壌の泥炭地で優占するが, この総説では,ミズゴケ類の主な分布環境とは異なる, 高温環境, 高いpH 環境, 高塩分環境でのミズゴケ類の光合成活性に関する計測結果を総合して述べる. pH に対する光合成, 呼吸活性の応答に関しては,pH＝3.8-9.8の範囲で８種について計測した. 総光合成速度, 暗呼吸速度について, それぞれ１種のみがpH に対する有意な応答を示し, 他では有意な応答は認められなかった. ミズゴケ類の主な生育環境とは異なる塩基性の環境でも生理的な光合成活性は高い値を保っていると言える. 温度依存性に関しては5-40℃の範囲で５種について計測した. 全種について30-35℃で総光合成速度が最大値を示したが, ２種についてのみ温度に対する有意な応答が認められた. 低温環境に分布の中心を有するミズゴケ類は, 必ずしも低温環境で高い光合成活性を示すとは限らず, 40℃までの範囲では比較的高温の環境でも高い生理活性を示すことがわかった. 塩濃度依存性については２種間の比較を行ったが, 0-500mM の塩化ナトリウム溶液中への9-12日間の浸漬の結果, １種でのみ塩濃度の上昇に伴う総光合成速度の低下と暗呼吸速度の有意な増加が認められたが, ２種ともに300mM 以上の高い塩濃度環境でも光合成活性を維持していた. このように, ミズゴケ種は, 優占する生育環境とは異なる特殊環境においても生理的に高い耐性を有していると考えられる.
Sphagnum spp. dominate in peat-forming mires in the circumpolar zone with acidic, low-temperature, and oligotrophic environments. However, some Sphagnum spp. colonize mires in coastal and volcanic areas with high pH (6.0-7.0) and high salt concentrations resulting from sea water and volcanic ash, and high-temperature mires (＞40℃ in the hot season). This review discusses the responses of photosynthesis and respiration of Sphagnum spp.under extreme conditions of pH,temperature,and salinity. The pH-dependence of photosynthesis in eight Sphagnum spp.was analyzed in the range of pH 3.8 to pH 9.8. The gross photosynthetic rate of most Sphagnum spp.did not show a significant response to pH. The dark respiration rate of Sphagnum spp.increased with increasing pH. The temperature dependence of photosynthesis of five Sphagnum spp.was evaluated in the range of 5℃ to 40℃. The optimal temperature range of gross photosynthesis was 30-35℃. Dark respiration of Sphagnum spp. increased with increasing temperature. Photosynthesis of Sphagnum spp.was evaluated in the salinity range of 0 to 500 mM NaCl. The gross photosynthetic and dark respiration rates of two Sphagnum spp. showed positive values at ＞300 mM NaCl. The dark respiration rate of these two Sphagnum spp. increased with increasing salinity. Thus,Sphagnum spp.show physiological tolerance to extreme environments that differ from their normal growth habitats.
Sphagnum spp. dominate in peat-forming mires in the circumpolar zone with acidic, low-temperature, and oligotrophic environments. However, some Sphagnum spp. colonize mires in coastal and volcanic areas with high pH (6.0-7.0) and high salt concentrations resulting from sea water and volcanic ash, and high-temperature mires (＞40℃ in the hot season). This review discusses the responses of photosynthesis and respiration of Sphagnum spp.under extreme conditions of pH,temperature,and salinity. The pH-dependence of photosynthesis in eight Sphagnum spp.was analyzed in the range of pH 3.8 to pH 9.8. The gross photosynthetic rate of most Sphagnum spp.did not show a significant response to pH. The dark respiration rate of Sphagnum spp.increased with increasing pH. The temperature dependence of photosynthesis of five Sphagnum spp.was evaluated in the range of 5℃ to 40℃. The optimal temperature range of gross photosynthesis was 30-35℃. Dark respiration of Sphagnum spp. increased with increasing temperature. Photosynthesis of Sphagnum spp.was evaluated in the salinity range of 0 to 500 mM NaCl. The gross photosynthetic and dark respiration rates of two Sphagnum spp. showed positive values at ＞300 mM NaCl. The dark respiration rate of these two Sphagnum spp. increased with increasing salinity. Thus,Sphagnum spp.show physiological tolerance to extreme environments that differ from their normal growth habitats.
FULL TEXT:PDF