| Comparative study was carried out on the effects of critical environmental factors (temperature, irradiance) on the photosynthetic and respiratory rate between Spirulina platensis (S1) derived from the alkaline lake in Maousu Sandy Land in Inner Mongolia and two imported species Spirulina platensis (S2) and Spirulina maxima (S3). The results show: (1) The light compensation point and light saturation point of S1 S2 and S3 were in range of 12~27μmol/m2 s and 180~360μmol/m2 s, respectively, and they changed with the irradiance. (2) Both light compensation point and light saturation point of S1 were higher than those of S2 and 83, and S1 showed greater capability against high irradiance than S2 and S3.(3) The optimal temperature of the three strains were 25℃, 35℃ and 30℃, respectively, and they had temporal effect. (4) Respiratory rate rose as the temperature rising, and at about 40℃, it reached the peak. Under 25℃, the photosynthetic rate of S1 was the highest while its respiratory rate was the lowest, so S1 showed good adaptability to low temperature.(5) The photosynthetic rate of Spirulina varies with the irradiance. Higher irradiance led to a relatively wider optimal irradiance range, and larger adaptability to high irradiance. The temperature stress made the cells optimal irradiance range narrow and also made their sensitivity to irradiance .Study on the daily variation of photosynthesis in different weather in four seasons in a year was carried out, too. The results showed that the daily variation curves of S1, S2 and S3 were two-peak curves in high irradiance, and the higher the irradiance was, the earlier the first peak appeared. In the weather with low irradiance (for example, in cloudy day), the photosynthetic rate varied with the irradiance changing.
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