| The saline and alkaline Songnen grassland is poorly nutritious and plant litter is an important nutrient source.Cellulose-degrading bacteria are of great significance to the nutrient cycling in saline-alkaline grassland ecosystems.In this paper,we studied the effects of salinization stress on the degradation characteristics and plant growth promoting properties of cellulose-degrading bacteria,as well as their resistance and recovery characteristics.The results of the study are as follows:1.The strains DS-19,DS-28,Sn-9,and DS-30 grew well under in 9,5,8 and10%NaCl conditions respectively.The results showed that the lag time increased and the growth rate were initially suppressed,but eventually they could adapt to the environment with the increase of the pH and salt content,2.The results revealed the strain DS-30 had the highest CMC enzyme activity,reached 8.19×10-2 IU/mL in the neutral and NaCl-free environments.With the increase of salinity,the CMC enzyme activity of all strains decreased.Among them,DS-19 was the least and DS-30 was the most affected by pH.The xylanase activity of strain DS-30 was also higher in each experimental gradient than the other three strains,particularly in the control group,reaching 0.63 IU/mL.With the increase of salinity,the xylanase activity of the four strains decreased.3.The results of plant growth-promoting characteristics of strains under different saline-alkali environments showed that the four strains had nitrogen-fixing ability.The nitrogenase activity in neutral and NaCl-free medium was DS-30>DS-28>DS-19>Sn-9,and the nitrogenase activity of the strain decreased and the order of activity changed with the increase of salinity.Four strains could produce IAA,and the IAA yields of the four strains decreased with increasing salinity;among them,the strain Sn-9 produced the highest IAA yield at pH 7?10.676?g/mL?.Strains DS-28,DS-30 can produce iron carriers,but the ability to produce iron carriers is weak.Except the strain DS-28,other three strains have the ability to dissolve phosphorus.Sn-9 was greatly affected by saline-alkaline stress,and no dissolved phosphorus was detected in the medium of pH 10?150 mM NaCl?.Only the strain DS-30 had an ACC deaminase activity of 1.209?mol·mg-1·h-1 detected at pH 7.4.The growth-promoting results of experimental strains on Leymus chinensis showed that the height,root length,leaf width,wet weight and dry weight of Leymus chinensis treated with strain DS-19 were higher than in the control group and other treatments in the neutral mountain soil.In the neutral mountainous soil with 150 mM NaCl added,the plant height,root length,leaf width,wet weight,and dry weight of Leymus chinensis treated with strain Sn-9 were higher than in the control and other treatment groups.In saline-sodic soil,the plant height,leaf width,wet weight,dry weight of Leymus chinensis treated with strain DS-19 were higher than those in the control and other treatment groups?P<0.05?.The growth status of Leymus chinensis in neutral mountain soil,neutral mountain soil with 150 mM NaCl showed that with the increase of soil salinity,all the growth indexes of Leymus chinensis showed a downward trend.The effect of salinization on plants was obvious,but compared with the control group,the four experimental strains had a promoting effect on plant height,root length,dry weight,and wet weight in three different soils.In summary,the four strains could improve the growth of Leymus chinensis in the saline-alkaline environment and helped the Leymus chinensis adapt to the saline-alkaline environment.5.The four strains and their mixtures could degrade the leaves of Leymus chinensis in the neutral mountain soil and saline-sodic soil under pot conditions.The degradation rates of DS-30 and Sn-9 in the two soils were significantly higher than the other two strains,and the degradation of Leymus chinensis by these two strains were the least affected by the soil alkalinity.It is of great significance to study the resistance and adaptation of microorganisms to the saline-alkali environment for the improvement of Songnen grassland and better understanding of how microorganisms control soil biochemistry. |
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