| The saline-sodic soils in the Songnen grassland is poorly nutritious.Plant litter,in which cellulose is the most abundant component,is the main source of organic matter,and its decomposition by cellulolytic bacteria ensures the recycling of nutrients in saline-sodic grassland ecosystems.In this paper,we studied the cellulolytic bacteria which isolated from different saline-sodic soils and evaluated its functional traits.The isolates from Leymus chinensis?pH 9.00?grassland,weeds grassland?pH 10.01?and saline-alkaline patches?pH10.48?were identified.The results of the study are as follows.1.Isolation of cellulolytic microbes from different saline-sodic soilsThe cellulolytic strains were isolated,purified and identified on CMC-Na agar plate.Twenty-two cellulolytic bacteria were isolated from collected three soil samples.15 strains were peculiar in Leymus chinensis grassland soil,5 strains come from weeds grassland soil and 2 strains which were peculiar in saline-alkaline patches.The cellulolytic bacteria were analyzed and identified by morphological,biochemical properties and 16S rDNA gene fragment sequences.The same strain was removed,and 19 strains were remained.The results showed that the Streptomyces were clearly dominated cellulolytic microbial communities.Streptomyces deccanensis were isolated from the Leymus chinensis soil and weeds soil simultaneously.Streptomyces massasporeus exsisted in all three kinds of grassland soil.At the same time,by analyzing the abundance of cellulose-degrading bacteria in different salinized soils,it was concluded that Streptomyces strains were the dominant cellulose degrading bacteria in the saline-sodic soils of Songnen grassland.2.Salty effects on cellulolytic characteristics of isolatesThe cellulolytic isolated were cultivatied in different salt concentration,and the cellulase activities were determined.The results showed that,the strains still had the ability to produce cellulase activities under salt stress.With the increase of salinity,the CMC enzyme activities of all strains decreased.Additionally,the cellulolytic activities of the strains were studied under different salt concentration substrates.The results showed that cellulase from cellulolytic bacteria still had cellulase activity in studied salt conditions.3.Nitrogenase and plant growth-promoting traits of cellulolytic bacteriaThe nitrogenase activities of isolates were determined by acetylene reduction method.Results show that all isolates could produce nitrogenase.The nitrogenase activity of Streptomyce sp.DSS-12 was the highest,and the activity was 10.01 nmoL·ml·h-1.The plant growth-promoting characteristics of isolates were determined.IAA production by the isolates were determined.The results showed that all strains could produce IAA?range from 1.20 to 19.48mg/L?.The effect of salt concentration on IAA production activities of the strains was studied.The results showed that the strains could still produce IAA in different salt concentration,and the IAA yields of the most strains decreased with increasing salinity.The traits of siderophore production were tested qualitatively through CAS assay method.Most of isolates strains had the ability of siderophore production.Streptomyce sp.DSS-04 and Pseudomonas sp.DS-13 had strongly abilities of siderophore production.Most of isolates had phosphate solubilizing abilities.4.Evaluation of Leymus chinensis growth promotion by the isolatesStreptomyce sp.DSS-04 and Pseudomonas sp.DS-13 were selected to study the growth promoting effect on Leymus chinensis.Pot experiment showed that both strains had the growth promoting effect to Leymus chinensis.Plants treated with isolated Pseudomonas was higher compared to the control in enhancing plant height.Plants treated with isolated Streptomyce was heavier compared to the control in plant weight.Mix group of both strains were also have the growth promoting effects to Leymus chinensis in comparison with the control.But the mixed groups were have no obvious plant growth promoting effects than the single strain group. |
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