| Effects of different factors (including medium concentration; nitrogen and phosphorus source; nitrogen, phosphorus and silicon concentration; temperature; light intensity; nitrogen, phosphorus and silicon starvation time) on the chlorophyll fluorescence parameters, cell density, dry weight, chlorophyll content, total lipid content and fatty acid composition of benthic diatom Cylindrotheca sp. were studied in this experiment. The results indicated that:1. Different medium concentration had significant effects on the chlorophyll fluorescence parameters of Cylindrotheca sp.. In f/4 and f/2 treatments, the maximal photochemical efficiency (F/Fm) and photochemical quenching (qP) were significantly lower than those in other treatments, but non-photochemical quenching (NPQ) was significantly higher. In the later experiment, the maximum efficiency of photosynthesis (Pm), the initial slope (a) and half-saturation light intensity (Ik) in f/4 and f/2 treatments were significantly lowest. The cell density, dry weight and chlorophyll content were in f/4 and f/2 treatments were lower than those in other treatments, while the higher total lipid content was recorded in these two treatments, which indicated that the low concentration of medium was conducive to the accumulation of total lipid, high concentration of medium in favor of growth and reproduction of Cylindrotheca sp.. The content of saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA) were higher in the low concentration of medium, while the increase of concentration of medium was in favor of the accumulation of polyunsaturated fatty acid (PUFA).2. When nitrogen sources were studied, the highest values of F/Fm were observed in urea treatment from the 1 st day to the 4th day and in sodium nitrate treatment from the 7th day to the 9th day, respectively. For the parameters Pm and qP, the highest values were recorded in sodium nitrate treatment from 3rd day to 9th day and the lowest values were recorded in urea treatment during the entire experimental period. The highest values of a were detected in sodium nitrate treatment from the 1st day to the 7th day, while those of Ik were recorded in sodium nitrate treatment from the 4th day to the 9th day. The final cell density and dry weight in sodium nitrate treatment were all higher than those in other treatments. As to the chlorophyll content, the lowest values were showed in ammonium chloride treatment while the higher values were reached in sodium nitrate and urea treatments, but there were no significant difference among the two treatments. When phosphorus sources were studied, the highest values of F/Fm were observed in sodium dihydrogen phosphate treatment while the lowest values in disodium adenosine triphosphate treatment from the 5th day to the 9th day. The parameters qP and a were found significantly higher under sodium dihydrogen phosphate treatment than those in other treatments from the 3rd day to the 9th day. As to parameters Pm and Ik, the highest and lowest values were recorded in sodium dihydrogen phosphate and disodium adenosine triphosphate treatments, respectively from the 6th day to the 9th day. The final cell density, dry weight and chlorophyll content under sodium dihydrogen phosphate treatment were significantly higher than those observed in other two treatments. The highest value of total lipid content was found in urea treatment, phosphorus sources had no significant effect on the total lipid content. The accumulation of SFA was higher in sodium nitrate and urea treatment, the higher content of PUFA was found in ammonium chloride treatment. The higher contents of SFA and PUFA were recorded when sodium dihydrogen phosphate as a phosphorus source3. Nitrogen concentrations had significant effects on the chlorophyll fluorescence parameters. The value of F/Fm in 0 and 0.11mmol/L treatments decreased mostly, but the larger value of F/Fm were recorded in 0.44 and 0.88mmol/L treatments. The values of qP and Pm in 1.76mmol/L treatments decreased mostly. In the late culture, the higher values of a were recorded in 0.44 and 0.88 mmol/L treatments, the higher values of Ik were recorded in 0 and 0.11mmol/L treatments. The higher cell densities were recorded in 0.44 and 0.88mmol/L treatments. The values of cell density and dry weight in 0 mmol/L were both lowest. Chlorophyll concentration increased with increasing nitrogen concentration. The highest total lipid content in 0.11 mmol/L treatment was recorded, then with the increasing nitrogen concentration increased. The contents of C 16:1, SFA and MUFA decreased with the increase of nitrogen concentration, the contents of C20:4, C20:5 and PUFA increased gradually with the increase of nitrogen concentration.4. In the late culture, different phosphorus concentrations had significant effects on the chlorophyll fluorescence parameters, F/Fm in 36.7 and 73.4μmol/L treatments had higher values, qP was higher in 73.4μmol/L treatment, NPQ was significantly higher in 0 and 4.58μmol/L treatments. The values of Pm、a and Ik were also higher in 73.4μmol/L treatment in the late culture. At the end of the experiment, the largest cell density was recorded in 73.4μmol/L treatment, the larger dry weight was founded in 9.18～73.4μmol/L treatments, the maximum chlorophyll concentration was recorded in 36.7μmol/L treatment. The larger total lipid content of 31.8% and 31.4% were recorded in 9.18 and 18.35μmol/L treatment, respectively. In 36.7μmol/L treatment, the contents of C16:0, C16:1, SFA and MUFA content were lower, but that of C20:4, C20:5 and PUFA were higher.5. The fluorescence parameters were significantly influenced by silicon concentration. The values of F/Fm in 0～14.7μmol/L decreased mostly, while that in 117.6μmol/L treatment decreased less. In the late culture, the values of Pm, a and Ik in 7.35 and 14.7μmol/L treatments were both lower. The cell density was significantly influenced by silicon concentration. The highest value of 8.18×106 cells·mL-1 was recorded in 117.6μmol/L treatment. The lower values of dry weight and chlorophyll content were in 0-14.7μmol/L treatments, while higher values in 117.6μmol/L treatment. The total lipid content decreased gradually with increasing silicon concentration. The contents of C16：0、C16:1、SFA and MUFA decreased with increasing silicon concentrations, While C20:4, C20:5 and PUFA contents increased with increasing silicon concentration.6. The fluorescence parameters were significantly influenced by temperature. In the 35℃ treatment, F/Fm decreased from 0.68 to 0.2. The values of qP、Pm and Ik were higher in 10℃ treatment, but lower in 35℃ treatment. The temperature had a significant influence on the cell density, under the condition less than 10℃ or higher than 35℃, the algal cell can not grow. The values of dry weight and chlorophyll content increased first and then decreased along with the increase of temperature, the maximum values were both recorded in the 25℃ treatment. The total lipid content increased firstly and then decreased with increasing temperature, reaching the higher values in 20℃ and 25℃ treatment, but there was no significant difference between this two treatments. The contents of C 14:0 and C16:1 decreased with a rise in temperature, the contents of C20:4 and C20:5 increased first and then decreased with increasing temperature, and both reached the highest value in the 25℃ treatment. The highest content of PUFA was recorded in the 25℃ treatment.7. The light intensity had significant effects on the chlorophyll fluorescence parameters, the value of F/Fm decreased with the increasing light intensity. The largest value of Pm was recorded in 20μmol·m-2·s-1 from the 4th to the end of the experiment. The values of Ik in 20 and 50 μmol·m-2·s-1 treatments increased with increasing culture time, while decreased with increasing culture time in 90-μmol·m-2·s-1 treatments. The lowest and highest values of cell density were found in 20 and 210μmol·m-2·s-1 treatments, respectively. The largest values of dry weight and chlorophyll content were recorded in 210 and 50μmol·m-2·s-1, respectively. The total lipid content decreased with the increase of light intensity. The contents of C14:0, C20:4, C20:5 and PUFA decreased gradually with the increasing light intensity; the contents of C 16:0 and C16:1 increased at first and then decreased with the increase of light intensity, and reached the maximum values in 130 and 170μmol·m-2·s-1, respectively. The contents of SFA and MUFA increased with the increasing light intensity.8. With the increase of nitrogen, phosphorus and silicon starvation time, the chlorophyll fluorescence parameters were significantly affected, and the values of F/Fm, qP, Pm and Ik all decreased significantly. Under three elements separately starvation conditions, the cell density and dry weight increased greatly with the starvation time. Under nitrogen and silicon separately starvation conditions, the chlorophyll concentration increased first and then decreased with the starvation time; the chlorophyll concentration increased with the starvation time under phosphorus starvation condition. The total lipid content increased gradually with the increasing nitrogen starvation time; the largest value of total lipid content was recorded at 4th day under phosphorus and silicon starvation conditions. Under nitrogen starvation conditions, the contents of C16:0, C16:1, SFA and MUFA increased gradually with increasing starvation time. Under phosphate starvation conditions, the contents of C16:0 and SFA increased with the increase of phosphate starvation time. Under silicon starvation conditions, the contents of C16:1, C18:1, C20:5, MUFA and PUFA all increased with the increase of silicon starvation time.The effects of various growth conditions on the growth and propagation speed, total lipid accumulation and fatty acid composition of Cylindrotheca sp. were studied according to the changes of chlorophyll fluorescence parameters, growth and physiological and biochemical parameters, to provide the theoretical basis for the large-density cultivation and the development of bio diesel oil and the extract of polyunsaturated fatty acids of the Cylindrotheca sp.. |
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