The Effect Of Several Main Physical And Chemical Factors On The Photosynthesis Of Botryococcus Braunii

The effects of temperature, light intensity, potential of hydrogen and salinity on photosynthesis of B. braunii UTEX 572 and B. braunii UTEX 2441, and the effects of C, N, P on photosynthesis of B. braunii UTEX 572, were studied by measuring net photosynthetic O₂ evolution. The effects of carbon concentration, pH and depth of medium on the CO₂ absorption ratio were thoroughly investigated in this work, and evidence for improvement of CO₂ utilization in mass culture of microalgae were provided. The main results are as follows:1. For B. braunii UTEX 572, the suitable light intensity range is 400—1600μmol.m^-2.s^-1 ,with the saturation light intensity 800μmol.m^-2.s^-1, the suitable temperature range is 25—35℃, with the optimal temperature about 30℃; the suitable pH range is 5.0—8.0, with the optimal pH about 7.0,the suitable salinity range is 0—0.2 mol/L, with the optimal salinity about 0.1mol/L. For B. braunii 2441 , the suitable light intensity range is 400—1600μmol.m^-2.s^-1 , with the saturation light intensity 400μmol.m^-2.s^-1; the suitable temperature range is 25—35℃, with the optimal temperature about 30℃; the suitable pH range is 5.0—8.0, with the optimal pH about 7.0; the net photosynthetic O₂ evolution decreased dramatically while the salinity increased a little. The photosynthetic characteristics of two B. braunii strains indicate the basic physiological and ecological characteristics: adapt to relative strong light intensity, relative high temperature, neutral to acid environment and lower salinity.2. Photosynthetic oxygen evolution of B. braunii UTEX 572 reachs it's maximum at C (NaHCO₃) 8mmol/L, N (KNO₃)100mg/L, P (K₂HPO₄) 40 mg/L, respectively.3. Some differences exist between two B. braunii strains in their response to the change of light intensity, temperature, pH and salinity, compared with B. braunii UTEX 2441, B. braunii UTEX 572 has higher saturation light intensity, adapt to higher temperature and much broader pH , its growth is promoted by mild increase of salinity , it indicates that B. braunii UTEX 572 has great potential for fast growth in cultivation. 4. Based on the effects of main physical and chemical factors on photosynthesis of B. braunii, the culture conditions of B. braunii UTEX 572 were modified as:C (NaHCO₃) 8mmol/L, N (KNO₃)100mg/L, P (K₂HPO₄) 40 mg/L, salinity 0.1mol./L, Under the condition of :Light intensity 100μmol.m^-2.s^-1, Temperature 30℃, pH 7.0.5. Under modified culture conditions, B. braunii UTEX 572 was cultivated with an imitation system of open circular pond, the alga grew fast with doubling time of 2.05day, it approached the shortest doubling time reported(2.00±0.02day).6. At solution depth of 10cm, 20cm, 40cm and 80cm, when carbon concentration increased from 4.76mmol/L to 95.24mmol/L, CO₂ absorption ratio increased about 12%, 10%, 12% and 11% respectively; At carbon concentration of 4.76mmol/L, 9.52 mmol/L and 95.24mmol/L, when solution depth increased from 10cm to 80cm, CO2 absorption ratio increased about 25%, 22% and 25% respectively; Both depth of solution and carbon concentration affected CO₂ absorption ratio. In the range of pH 7.0-10.6, pH affected CO₂ absorption ratio, and the degree of effectiveness was positively associated with the carbon concentration. Carbon concentration 9.52mmol/L was the turning point; below this point, pH had no significant effect on CO₂ absorption ratio; above this point, pH affected CO₂ absorption ratio significantly. The affect rate of these three factors is: depth of solution>carbon concentration >pH. CO₂ absorption ratio might be improved by increasing solution depth and keeping higher carbon concentration and higher pH. CO₂ may be saved by about 20% with appropriate technique to increase depth of solution from 14.5cm to 80cm at the site of CO₂ bubbling, and get remarkable commercial and ecological benefits.