| Porphyra yezoensis belongs to Rhodophyta, Protofloridea, Bangiaceae. It has the highest value of nutrition among the algae which is Large-scale cultivated. The laver is also the world's highest output seaweed cultivation. At present, cultivation of laver in China develops so quickly that its output is larger than any other countries all over the world. However, the rate of progress in laver breeding can not meet the rapid development of laver cultivation industry, coupled with the more serious degradation of quality. Therefore, breeding new strains with good characteristics for the cultivation of laver is very crucial. photosynthetic efficiency is an important breeding target. It reflects the algae carbon assimilation, production of organic capabilities. Higher photosynthetic efficiency of algae might mean a higher rate of growth, thus it may shorten the growing season, increase economic efficiency. Therefore, choose new strain of Porphyra yezoensis which can maintain photosynthetic efficiency in different ecological conditions will help to improve the output of laver.In this study, photosynthetic efficiency of P. yezoensis thallus (including Y-h001, Y-9146, Y-h2001, Y-w0401, Wjs, Gm, Wqd) was tested under different light intensities,temperatures, and photosynthetic efficiency of another strains of P. yezoensis thallus(Y-w0401, Y-9970, Y-zkh, Y-h001, Wqd, Hy-1, Yh-1)were tested under different nitrogen and phosphorus concentration, salinity, pH and light quality by mini-PAM, the content of the photosynthetic pigments and the recover time after photoinhibiting were also measured in the this experiment.The results showes that:1:From 20μmol/m2 s to 1200μmol/m2 s, the efficiency decreased gradually with the light intensity increasing, however, the degree of decrease varied among strains of Porphyra yezoensis:the photosynthetic efficiency of Yjs when it suffered from the highest light intensity decreased by 27% comparing with the photosynthetic efficiency at the lowest light intensity, Yw by 33%, Gm by 53%, and Yqd by 50%; 2:Within the temperature range from5℃to 20℃, all the samples obtained the highest efficiency under the condition of 15—20℃,120μmol/m2s, and most of them reach the peak at the 15℃,except the Yh2 and Wjs which reach the peck at the 20℃;3:After the photoinhibiting(200μmol/m2s), the strains can recover in 30～60min,under the condition of 60μmol/m2s,12℃;4:This study found that the optimum growth nitrogen concentration of of P. yezoensis thallus was 1.0～1.5mg/L, the optimum P concentration of 0.05～0.15mg/L;5:Salinities from 20-30 is better for Porphyra yezoensis, in this range, the sample can keep a high grade of Fv/Fm;6:The fitting pH for Porphyra yezoensis is 8.0;7:The result varies when the sample was irradiated by different light quality. The sequence of photosynthetic efficiency among different light quality is white> green> red> blue;8:In this study, No direct relationship was found between the photosynthetic efficiency and the content of photosynthetic pigments (especially the phycobiliprotein). There may be one in which photosynthetic pigments threshold, when content of the photosynthetic pigment is smaller than the threshold value, the photosynthetic pigment content have a significant impact for the photosynthetic efficiency; when the content was higher than the threshold value, the photosynthetic pigment content will not be the decisive factor in photosynthetic efficiency.
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