[Recruitment ability of Microcystis aeruginosa under low light-low temperature combination]

The responses of growth and PS II activities in Microcystis aeruginosa (FACHB 905) have been studied under a condition of low light-temperature combination use orthogonal experiment method. The contents and proportions of chlorophyll and carotenoid were determined by colorimetry, the PS II activities were assayed with a Water-PAM, and also, the photosynthesis recovery of M. aeruginosa was verified via reculture under a normal condition. The results showed that recruitment of M. aeruginosa should not be triggered since it could hardly grow under the temperature of 9 degrees C. Under 12 degrees C, the growth was greatly affected by the light intensity. 12 degrees C & 100 lx combination was considered to be the threshold value to induce recruitment of Microcystis due to the physiological responses in growth and photosynthetic system. The growth of alga was obviously inhibited in all samples. However, the biomass under 15 degrees C & 100 lx combination was the largest, which reached about 0.88 mg/L, and it was about 2-17 times compared to the other samples, respectively. We also found FACHB 905 could persist longer under low light intensity (100 lx) than a relative higher intensity (500 lx) under 15 degrees C, since the chlorophyll content, electron transfer rate and yield were relative higher in combination. Reculture of M. aeruginosa was conducted after a 20 d study, samples under the temperatures of 9 degrees C & 12 degrees C recovered soon in growth characters and PS II activities during 5 days. Meanwhile, all the samples of FACHB 905 reached a rather stable growing status, with a fluorescence quantum yield about 0.55-0.6, like other normal cultured samples finally. The present results should be important to determine the tolerance threshold and even to reveal the probable mechanisms in overwintering and recruitment of M. aeruginosa from lake sediments.