| Soil saline-alkalifying is becoming more and more severe because of the unsuitable irrigation, excess using of fertilizers and vegetation destroying. People have paid more attention on the soil improvement and remediation, including engineering, chemical and biological techniques. The engineering and chemical strategies are effective, but they are usually unefficient with high cost. Nowadays, the bio-remediation is mainly focused on the culture of alkaline-resistant plants and it appeared that the improvement has been work slowly for either the traditional or the genic method.Songnen alkaline-saline plain was selected as research objective at present paper based on the view of ecological engineering and for the purpose of eco-remediation of alkaline-saline land. The physi-chemical properties and the microbe communities were investigated. Appraise the original cyanobacterias was conducted. Two species of nitrogen-fixing cyanobacteria belonging to two genera Nostoc commune and Anabaena azotica Ley tolerate of different concentrations of Na2CO3 in BG110 medium. Some experiments were carried on to investigate the effects of the sum of inoculation and the ratio of water in the soil towards the remediation of saline-alkaline soil which based on nitrogen-fixing cyanobacteria Nostoc commune and Anabaena azotica Ley. The effects of the Anabaena azotica Ley on the growth of Leymus chinensis were investigated by inoculation of the strains to laboratorial basin experiments. Ecological adaptability and repairing effect of Anabaena azotica Ley were studied in field experiments.Three blocks of 100×100m2, which represents different saline-alkalifying extent of heavy, medium and common alkaline-saline land were choosed for the present study. The results showed that different physic-chemical characteristics and microbe structure in three types of soil. Light saline soil belongs to non-alkalinity sodium soils, middling saline soil and heavy saline soil belong to alkalinity sodium soil. Soil salinization related to soil physicochemical properties and microbial communities. The soil saline alkaline degree became larger amount of bacterium, fungi, actinomycetes and algae gradually decreased. The difference of microbial quantity reaches extremely significant level or significant level.Twenty out of 200 isolates of cyanobacteria mainly from saline soils of Songnen Plain of China were successfully grown on BG11 N-free medium. However, at 5 % NaCl only 6 of the isolates exhibited a high rate of nitrogenase activity. The experiment of appraising the original cyanobacterias shows that there are ten kinds of cyanobacterias in the three typical areas. There are four kinds in medium alkaline-saline and three kinds in the other two kinds. We can conclude that medium alkaline-saline is more proper for the growth of cyanobacterias.Two species of nitrogen-fixing cyanobacteria belonging to two genera Nostoc commune and Anabaena azotica Ley tolerate of different concentrations of Na2CO3 (from 0.2×10-4g/ml to 1.8×10-4g/ml) in BG110 medium. The variation in the chlorophyll (Chl) a content, extracellular saccharide , amino acid and nitrogenase activity are measured respectively. It is found that both of nitrogen-fixing cyanobacteria can thrive under Na2CO3 salt stress. When the concentration of Na2CO3 increase, the chlorophyll (Chl) a content,extracellular saccharide,amino acid and nitrogenase activity increase first and then decrease. With the increase of time of incubation, the change curve of chlorophyll (Chl) a content of Nostoc commune and Anabaena azotica Ley is similar to the growth curve of microorganism, extracellular saccharide and amino acid increase in a synchronism with chlorophyll (Chl) a, the maximum of nitrogenase activity appears at 21 days for Anabaena azotica Ley and appears at 28 days for Nostoc commune. Compare Anabaena azotica Ley with Nostoc commune, the former possesses better resistance to salt and higher nitrogen-fixing ability.In the experiments which carried on in flowerpots we find that when the ratio of water in the soil is 30%, the cyanobacteria can grow normally, when the ratio is 50%, they can grow much better; when the sum of inoculation is 0.03mg dry cyanobacterias/cm2, it is more proper for Anabaena azotica Ley to be planted in common alkaline-saline land, when the sum is 0.18 mg dry cyanobacterias/cm2,it is better to plant Nostoc commune in the medium alkaline-saline land. We measure cation and antion, pH value, the ratio of conducter,the total sum of dissolved salt, the exchange-able Na+, TOC at every periods (ten days is a period) and measure BAB and nitrogenase activity at the last period. The results showed that the inoculation of nitrogen-fixing cyanobacteria can increase the organic matter by 530.01% in the soil effectively, decreasing soil pH, increasing soil nitrogen content by 269.12% and decreasing soil exchangeable sodium by 86.28%. But when the depth was up to 9cm, the function is becoming weaker. Taking the typical plant of Leymus chinensis as target research objective, the effects of inoculation of Anabaena azotica Ley into laboratorial potted plant were investigated by measuring the heights of Leymus chinensis at different periods. After inoculation, the heights of Leymus chinensis were 30% higher than that of controlled and the function were lasted in the whole experimental periods. The nitrogenase of rhizomes was also determined and results implied the changes of nitrogenase might be owing to inoculation of Anabaena azotica Ley. This might be one reason resulting in the growth of Leymus chinensis. Strains of alkaline-saline resistant cyanobacteria can not only adapt to alkaline-saline soil environment, but also can improve the content of nitrogen.The experiment results onsite have shown that the Anabaena azotica Ley have a good ecological adaptability with temperature, light and alkalinity, but also accumulate soil organic matter, transform inorganic salts, fixation of atmospheric nitrogen, decrease soil pH and increase soil nitrogen content 106.99%.The results showed that nitrogen fixing cyanobacteria can improve the soil quality, simultaneouly promote plant growth. Thus, the cyanobacteria were important and effective in ecological restoration of saline soils.
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