Abstract:The NaCl-induced inhibition of nitrogen-fixing activity of blue-green algae Anabaena 7120 was removed to a certain degree by the introduction of appropriate KNO3 into the culture medium.When the preincubation of algae cells was done in dark before experiment for 24 hours or in the presence of photosynthetic inhibitors,such as DNP or CCCP, the benefical effect of KNO3 on the nitrogen-fixing activity of Anabaena treated with NaCl stress weakened or disappeared.In the addition of O2 together with H2 the mitigative effect of KNO3on nitrogen-fixing activity of Anabaena was reinforced under NaCl stress.But a marked inaction in nitrogen-fixing activity of Anabaena occurred under NaCl stress when O2was introduced into the test system alone.When algae cells treated with NaCl stress were incubated in the aerobic condition(in air)the benefical action of KNO3 was higher than that in anaerobic condition(in Ar).The KNO3supported nitrogen-fixing activity of Anabaena was more evident under NaCl stress in the prensence of the exogenous sucrose or CO2.The migatative effect of KNO3 on nitrogen-fixing activity of Anabaena was accelerated under NaCl stress in the addition of N2 together with CO2, while it was depressed by adding N2 alone.