淡水赤潮プランクトンPeridinium bipes fo.occultatumの増殖に及ぼす照度,温度,pHおよび窒素栄養塩の影響

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The alga causing a fresh water red tide in the Ananai-gawa Dam-controlled Lake was identified to be Peridinium bipes fo. occulutatum. The effects of light intensity, temperature, pH, and nitrogen on the growth of this alga was examined. The growth yield was greatest at a light intensity of 10, 000lx, a temperature of 20°C and a pH of 7.3-8.0. The growth rate was highest at a light intensity of 10, 000 lx and was not affected so much at temperatures from 10 to 25°C or a pH range of 6.0-8.7 as tested. The alga can use NO2--, NO3--, NH4+-, and urea-N under their low concentrations as a sole source of nitrogen and cannot use three amino acids (glycine, alanine, and glutamic acid) effectively. The half-saturation constant for nitrogen was 50-65μgN/l and specific growth rate was saturated at 0.5-1.3mgN/l, but a higher concentration of nitrogen (5mgN/l) was needed for reaching maximum cell yield. The minimum cell quota of nitrogen was calculated to be 0.32ng N/cell. Under the saturated condition of nitrogen, the maximum specific growth rate was 0.17-0.21 d-1. Among freshwater phytoplankton this alga was found to have a rather higher Ks value of nitrogen for growth and to have a smaller growth rate.
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