Diversity Of Bacteria And Frankia In Rhizosphere Soil And Root Nodules Of Hippophae Rhamnoides

Non-legumes form nodules with Frankia for efficient symbiotic nitrogen fixation,and enhance the resistance of Hippophae rhamnoides to drought,cold,salt and other abiotic stresses.Comparative analysis of bacterial diversity differences in roots and nodules of Hippophae rhamnoides helps to reveal the mechanism of plant-microbial interaction.Comparative analysis of the diversity difference of Frankia in roots and nodules of Hippophae rhamnoides is helpful to reveal the symbiosis mechanism.The main research results of this paper are as follows:（1）pH and soluble potassium（AK）were important factors affecting the bacterial community construction in the rhizosphere soil of Hippophae rhamnoidesThe richness and diversity of bacterial communities in the rhizosphere soils of Hippophae rhamnoides collected from Liaoning and Shanxi’were higher than those from Shaanxi.Actinobacteria and Proteobacteria were the dominant phyla,and the abundance of Chloroflexi,Acidobacteria,Gemmatimonadetes,Firmicutes and Bacteroidetes were significantly different among the three groups.The dominant bacteria genera in sampling sites of Liaoning were Acinetobacter,Pseudomonas and Variibacter.And Bacillus,Streptomyces,Paenibacillus,Nocardioides were dominant genera in Shaanxi’sites.RB41 and Roseiflexus were dominant genera in Shaanxi sites.The diversity of bacterial community in the rhizosphere soil of Hippophae rhamnoides was affected by the physical and chemical properties of the soil,and pH and AK were important factors for the construction of bacterial community in the rhizosphere soil of Hippophae rhamnoides.（2）Frankia is the dominant bacteria distributed in the middle cortex of the root nodules of Hippophae rhamnoidesThe nodule structure from inside to outside is:stele,cortex.The latter is divided into 3 parts:inner cortex,cortex middle,outer cortex.The results of paraffin section and ultrathin section showed that Frankia mainly grew and developed in the parenchyma cells in the middle of the cortex and filled the nodule cells with mycelium or expanded vesicles.Nodules of Hippophae rhamnoides with Frankia as the advantage bacteria within the bacterial diversity,in addition to colonization of Pseudomonas,Nocardia,Streptomyces,which may play a promoting role in the initial nodules formation.（3）Frankia of cluster 3 were selected to form symbiotic nodules of Hippophae rhamnoidesIn the rhizosphere soil of Hippophae rhamnoides,there were abundant clusters of Frankia,including clster 1a,clster 1b,clster 3 and clster 4.Cluster 3 accounted for 76%-80%in the rhizosphere soil,while only Frankia of cluster 3(EAN1_pec,FMc3 and FMc5)was distributed in the nodules,indicating that the high abundance of cluster 3 was uniform in the rhizosphere soil and nodules.（4）Isolation and salt tolerance of FrankiaSections,gradient dilution coating and liquid culture were used to isolate Frankia from nodules,but none of them were successfully isolated.Literature investigation combined with the sequencing results of Frankia in the nodules,the failure may be mainly due to the inappropriate carbon source types.The two Frankia model strains,CpI1 and CcI3,had certain tolerance to salt stress,with the maximum tolerance concentration of 4%,but the number of vesicles increased and mycelial destruction occurred in the bacteria to some extent.