報告書番号

U03065

タイトル（和文）

ホンダワラ類藻場生産力モデルの開発 --ヤツマタモクの光合成特性の解明--

タイトル（英文）

Development of a mathematical modeling for productivity estimation of Sargassum bed. 1.Photosynthetic properties of Sargassum patens (Fucales, Phaeophyta)

概要 （図表や脚注は「報告書全文」に掲載しております）

ホンダワラ類海藻の遷移系列上の途中段階に位置し，分布域が広いヤツマタモクの光・温度・窒素濃度－光合成特性を明らかにした。1)光飽和時の光合成速度は0.5～1.0 gO2 m-2 h-1で，初夏から夏に高く，秋から冬に低くなる明瞭な季節性が見られた。補償光量（呼吸速度に見合う光合成速度が得られる光量）は5.1～6.8 マイクロmol photons m-2 s-1であり，ノコギリモクに比べて大きく，ヤツマタモクがより浅所に生育するとともに，遷移過程でノコギリモクに負ける一因と考えられた。2)光合成最適温度は28℃であり，7℃での光合成速度は最適温度での速度の35%，33℃での速度が67%であった。3)低窒素濃度への応答は個体による差が大きく，光合成速度が1/2に低下するのに早いものでも4週間を要し，遅いものでは約8週間経過した後も40%程度の低下にとどまった。

概要 （英文）

Through a numerical simulation model analysis, which incorporates the available seaweed information, it may be possible to develop a better understanding of the complex seaweed ecosystem. Clarification of seaweed photosynthesis and respiration is important in the production analysis within the ecosystem. Sargassum patens is widely distributed species on rocky shores in Japan except Hokkaido, Photosynthetic rate and respiration rate of S. patens were measured with an oxygen electrode method. 1) Light saturated photosynthetic rate were maximal in early summer (1.0 gO2 m-2 h-1) and minimal in autumn-winter (0.5 gO2 m-2 h-1). Compensation irradiance of S. patens (5.1 - 6.8 micro mol photons m-2 s-1) was higher than values of Sargassum macrocarpum and Ecklonia cava that grow in deeper than S. patens.2) A computed optimum temperature for photosynthesis of S. patens was 28℃. Photosynthetic rate in 7℃ and 33℃ were 35% and 67% of the rate in the optimum temperature, respectively. This result was similar to temperature-photosynthesis relationship of S. horneri that is another widely distributed Sargassum species in Japan.3) S. patens showed decreased photosynthesis activity correlated with culture period in lower DIN (dissolved inorganic nitrogen: sum of nitrate, nitrite, and ammonia) condition. Response to lower DIN showed big variation by the individual. The photosynthetic rate with faster response became half in four weeks, but the rate with slower response became 60% in eight weeks. The response of S. patens was slower than the response of E. cava that is distributed in Pacific coast of central Japan that is higher DIN concentration than Sea of Japan.

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