| Contamination of land had caused serious pollution to marine environment in recent year, negative impacts on marine ecosystem caused by effluence aquaculture also was concerned by more and more people. It was believed that it is one of best ways to culture macroalgae to reduce the accumulation of nutrients in culture system and decrease the negative impacts on marine ecosystem. In this thesis, a primary study on ecology of Sargassum thunbergii was conducted. Based on anniversary investigation on the growth, components and natural habitat of Sargassum thunbergii in Xiaoshidao, Weihai, the development of Sargassum thunbergii zygotes, effects of adhesive substrate on the growth and adhesive rate of germlings and influences of temperature and light intensity on the growth of germlings and organization were studied. Then studies on effects of environmental factors (temperature, salinity and light intensity) and nutrient factors (concentration of N, P and N/P) on the uptake of nutrients were conducted further.The main results were summarized as followings:1 A preliminary anniversary investigation was conducted on Sargassum thunbergii in Xiaoshidao, Weihai. The growth, and chemical constituents (C, N, P, pigment and carbohydrate) of Sargassum thunbergii were investigated and measured at lower water every month, meanwhile water temperature, salinity, pH and N, P concentration in the water of near by Sargassum thunbergii were also determined at the same time. The results showed that the content of NO3- in the water changed significantly with seasons, it was low in summer and early autumn, while high in winter and early spring. Compare to NO3- , the content of NH4+ was low and less changed with seasons. The content of total inorganic N showed the same trends as NO3- in the water. The content of total inorganic P fluctuated sharply with month, which was low at February to July, while high in autumn and winter. The growth of Sargassum thunbergii showed significant change with seasons. Their growth rate was high at April and May, and the greatest in the length at June and July. Lateral branches appeared at April, and the greatest in the length at July, however, disappeared at August. Receptacles appeared at May and matured at later July. Carbohydrate content in the algae was among 25.6-33.0%, which showed less change with season. N content in the algae fluctuated significantly with season, which showed the same trend as NO3- in the water, low in summer and autumn, and high in winter and spring. P content in the algae also showed significant change with season, which was high from November to April, and low from May to October. Pigment showed significant change with season, and its content was higher in autumn and winter than in spring and summer. The content of carbohydrate was high from April to July, while lower at August and September.2 The reproduction, the adhesion and growth of germlings of Sargassum thunbergii were investigated in this study. The growth and development of Sargassum thunbergii during the reproductive period at Xiaoshidao, Weihai, including the forming of receptacles and reproductive nest, the forming of sperms and eggs, fecundation, the process of adhesion and growth of germlings. Meanwhile, a two-factorial experiment was designed to evaluate the effects of temperature and light intensity on the growth of germlings, then growth and the adhesive rate of germlings in smooth plastic film and coarse bolting cloth were also compared. The results showed the effects of light intensity,temperature and their interaction on the growth of germlings were significant (P<0.05). In this study, Sargassum thunbergii grew the best in the combination of temperature of 20-25℃and light intensity of 80-100μE·m-2·s-1. There was no significant difference in the growth of germlings between plastic film and bolting cloth, however, adhesive ratio of germlings on the bolting cloth was significantly high than on plastic film(P<0.01).3 A two-factorial experiment was designed to investigate the effects of temperatures and light intensity on the rates of growth and body composition of Sargassum thunbergii. The result shows that temperature, light intensity and their interactions have significant effects on the growth of Sargassum thunbergii (P<0.01). The suitable temperature range was estimated at 15-20℃. With the increase of temperatures, light intensity needed by the algae increased. The growth of Sargassum thunbergii was inhibited at 10 and 15℃, however, increased with the increase of light intensity at 20 and 25℃. Temperature and light intensity have significant effects on content of chlorophyll-a and fucoxanthin in algae (P<0.01), and light intensity had more effect on content of chlorophyll-a and fucoxanthin than temperature. Both chlorophyll-a and fucoxanthin decreased with the increase of light intensity, however, increased with the increase of temperature. The content of carbohydrate significantly effected by light intensity (P<0.01), but no difference was found among different temperatures (P>0.05). The content of carbohydrate increased with the increase of light intensity. There were significant difference in the content of protein were found among different light intensity (P<0.01). The content of protein decreased with the increase of light intensity. The effect of temperature on the content of protein was also significant (P<0.05), and content of protein in Sargassum thunbergii was high at 10 and 15℃, and then decreased with the increase of temperature.4 The effects of temperature, salinity and light intensity on the uptake of nitrogen and phosphorus by Sargassum thunbergii were studied under laboratory conditions. Significant differences of nitrogen and phosphorus uptake rates at different temperatures or salinities were observed, and there was significant interaction between temperature and salinity (P<0.01). The uptake rates of nitrogen were reached as high as 11.26μmol·g dw-1·h-1 and 11.01μmol·g dw-1·h-1 at favorable salinity of 20 and temperature of 25℃, salinity of 30 and temperature of 30℃, respectively; while in the temperature of 15-30℃, the uptake rate of phosphorus was higher at salinity of 40 than any other salinities, which reached up to 1.50μmol·gdw-1·h-1. There were significant differences of nitrogen and phosphorus uptake rates at different temperatures or light intensities (P<0.01). The temperature and light intensity have significant interactive effects on nitrogen or phosphorus uptake (P<0.01). The nitrogen uptake rates were higher at 15℃and 140-180μE·m-2·s-1, 20-25℃and 60-100μE·m-2·s-1, which all reached up to 9.60μmol·g dw-1. The uptake rate of phosphorus reached 1.30μmol·g dw-1·h-1 at temperature of 25℃and light intensity of 60μE·m-2·s-1·h-1.5 The effects of nutrient factors on the uptake of N and P by Sargassum thunbergii were studied under laboratory conditions. The uptake rate of N and P by seaweed increased with enhancing of concentrations of N and P in the solution, and the saturation phenomenon in the uptake of N and P did not occurred. Concentrations of N and P have significant influences on N and P uptake by seaweed (P<0.01). The highest N uptake rate was 2.48μmol·g-1·h-1, which occurred at 200μmol·L-1 N in the solution, while the greatest P uptake rate was 0.11μmol·g-1·h-1, which occurred at 13.33μmol·L-1 P in the solution. The ratio of N to P and concentration of N in the solution have significant effects on the N and P uptake rate by seaweed (P<0.01), and significant interactive effects were found between them (P<0.01). The highest N uptake rate occur at 200μmol·L-1 N in the solution and 5:1 of N to P, while the highest P uptake rate occur at 80μmol·L-1 N and 5:1 of N to P. The inhibition between NH4+-N and NO3--N did not occurred in this study. The uptake rates of two chemical forms of N were proportional to their amount in the solution. The lowest uptake rate of total N occur at 10: 1 of NH4+-N to NO3--N, and there is no significant difference among other treatments. The uptake rate of total P is the highest at 10: 1 of NH4+-N to NO3--N, then decrease with the decrease of the ratio of NH4+-N to NO3--N in the solution.
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