Preliminary Study On Nitrogen-Fixing Bacteria From Rhizosphere Soil Of Betula Platyphylla And Larix Gmelinii In Arxan

In recent years,the biological nitrogen fixation in economic crops and nitrogen-fixing trees was pays more attention,but the biological nitrogen fixation in non nitrogen-fixing trees was little investigated.The aim was to study diversity of nitrogen-fixing bacteria isolated from Betula platyphylla and Larix gmelinii in Arxan.The traditional separation and cultivation of bacterial was applied,combined with 16S rDNA sequence analysis,the diversity of cultivable azotobacter community rhizospherein in different periods in Arxan.Determination of the growth characteristics of dominant nitrogen-fixing bacteria.The community structure of rhizosphere nitrogen-fixing bacteria in two non-nitrogen-fixing tree species of Larix gmelinii and Betula platyphylla was analyzed.The main results are as follows:1.The traditional separation and cultivation of bacterial was applied,combined with 16S rDNA sequence analysis and other methods,the diversity of cultivable azotobacter community of Betula platyphylla and Larix gmelinii rhizospherein in different periods in Arxan.The results show that:(1)A total of 97 bacterial strains were isolated and purified from Betula platyphylla rhizosphere soil,belonging to 19 genera.They were respectively,32 strains of Pseudomonas,2 strain of Serratia,1 strain of Enterobacter,1 strain of Acinetobacter,8 strains of Burkholderia,4 strains of Paraburkholderia,2 strain of Variovorax,1 strain of Alcaligenes,1 strain of Stenotrophomonas,7 strain of Paenibacillu,1 strain of Staphylococcus,3 strain of Bacillus,3 strain of Rhodococcus,6 strain of Arthrobacter,l strain of Mucilaginibacter,1 strain of Novosphingobium,10 strain of Rhizobium,1 strain of Caulobacter,12 strain of Phyllobacterium,among them,the dominant flora is Pseudomonas,and the sub-dominant flora is Phyllobacterium and Rhizobium.(2)A total of 112 bacterial strains were isolated and purified from Larix gmelinii rhizosphere soil,belonging to 14 genera.They were respectively,57 strains of Pseudomonas,10 strains of Burkholderia,6 strains of Rhizobium,10 strains of Phyllobacterium,9 strains of Arthrobacter,3 strains of Paenibacillus,3 strain of Serratia,1 strain of Erwinia,3 strains of Curtobacterium,1 strain of Bacillus,2 strain of Enterobacter,4 strain of Acinetobacter,1 strain of Caulobacter,2 strain of Rhodococcus,among them,the dominant flora is Pseudomonas,and the sub-dominant flora is Phyllobacterium,Burkholderia and Arthrobacter.2.The results show that clear seasonality appears in community composition of dominant nitrogen-fixing bacteria in the rhizosphere of birch and larch with higher values in summer and lower values in winter.However,the amplitude and shape of seasonality differ in different period of variation characteristics.3.The results of canonical correspondence analysis(CCA)for the relationship between the nitrogen-fixing bacteria in the rhizosphere of birch and larch and 6 environmental factors showed that the pH,available K,available P,available N,and organic matter were the main environmental factors affecting the distribution characteristics of the nitrogen-fixing bacteria community.