赤潮時における鞭毛藻類の光-光合成曲線

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  • アカシオジ ニ オケル ベンモウソウルイ ノ ヒカリ コウゴウセイ キョクセン
  • Characteristics of Light-photosynthesis Curve of Flagellates in Red Tide

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Characteristics of light-photosynthesis curve of flagellates causing red tide was examined. Our experimental organisms were Prorocentrum micans, Olisthodiscus sp., Gymnodinium sp. (called tentatively as G. type '65) and Prorocentrum sp. whose cell concentration and chlorophyll-a content were more than 7.6×10³ cells ml⁻¹ and 30 μg l⁻¹ respectively. It was characteristic of their light-photosynthesis curves that maximum photosynthesis ranged widely from 1.4 to 14.2 mg C・mg chl-a⁻¹・ hr⁻¹ and photo-inhibition of photosynthesis at high light intensity of about 100 klux was not recognized. Meanwhile, cultured Olisthodiscus sp. decreased maximum photosynthesis as its population developed from the logarithmic phase to the stationary phase. Photo-inhibition was recognized at 40 klux in the logarithmic phase, but was not recognized even at 100 klux in the stationary phase. Another experiment was conducted with cultured Olisthodiscus sp. in early stationary phase, which was diluted with filtrated culture media to the cell concentrations of 10 and 50 percent. The result showed that maximum photosynthesis increased and photo-inhibition became more clearly in the proportion to the degree of dilution. The effect of the length of dark treatment on photosynthesis was examined with cultured Olisthodiscus sp. Photo-inhibition was recognized after dark treatment of less than 7 hours, but not after dark treatment of more than 12 hours. In the view of the above, it is thought that the fluctuations of photosynthesis in red tide are dependent on the species of consisting organisms and on the population phase within the species. It seems that the disappearance of photo-inhibition is related to the shading effect of each cell in high concentration and to the length of dark treatment.

長崎県下大村湾および長崎湾で発生した鞭毛藻類を原因とする4赤潮の光-光合成曲線を求めた結果,その特徴は次の諸点にあることがわかった。(1)飽和光下における光合成速度は,1.4～14.2mg C・mg chl.-a⁻¹・hr⁻¹の広い範囲にあり,それは赤潮を構成する種および個体群の生長過程と関連するようである。特に,対象となる個体群が活発に増殖をおこなっている群であるか否かによって異なる。(2)天然の赤潮では強光下における光合成阻害がみられなかった。これは高密度による自己しゃへいおよび昼夜のリズムのうち夜間の存在と関連があるらしいことが推測された。

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