EFFECT OF PHOSPHORUS AND TEMPERATURE ON THE GROWTH AND NITROGENASE ACTIVITY IN Azolla-Anabaena ASSOCIATION

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The effects of light and O_2 on the nitrogenase activity in the Azolla-Anabaena association were studied using 2 species of Azolla, A. imbricata and A. japonica, grown in a growth chamber under artificial light. Acetylene reduction activity (ARA) was strongly enhanced by a high light intensity up to 4,200 lx. Under the dark condition, ARA was much lower than under the light condition though not suppressed completely. Different responses of ARA to O_2 concentration in the atmosphere were obtained in the light and in the dark. The activity was maximum at about 4% P_<O_2> in the light. In the dark, however, the activity increased as the O_2 concentration increased up to 40% P_<O_2>. To study the P requirement, A. imbricata plants were grown in a batch culture at 25℃ with a culture solution containing P levels ranging from 0.1 to 20 ppm. The experiments were carried out under the illumination of 5,000 lx (16 h light-8 h dark). The growth was not stimulated by increasing P levels, but the nitrogenase activity and N content were found to be increased. The enhancement of the Mg uptake was attributed to this increase. To examine the tolerance to high temperature, the culture was carried out at 32. The growth rate, nitrogenase activity, and N content were lower than at 25 and the latter two did not recover by high P supply.
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