Rhizospheric soil metabarcoding analysis of Alnus nepalensis from Darjeeling hills reveals the abundance of nitrogen-fixing symbiotic microbes

Actinorhizal plants are employed as successional plants for ecological restoration mainly due to their nitrogen-fixing ability. Alnus nepalensis or Nepali alder of Darjeeling hills is one of the potential plants used for agroforestry and known for its symbiotic association with an actinobacterium, Frankia. In this study, we performed a comparative16S rRNA amplicon analysis among six soil samples of Alnus rhizosphere and Non-rhizosphere of different altitudes of Darjeeling hills. Bioinformatics analyses were performed through the MG-RAST web server. Results revealed a set of 32 core bacterial genera among both rhizosphere and non-rhizosphere. Interestingly, Alnus rhizospheric soil samples were more populated with nitrogen-fixing taxa than non-rhizospheric or bulk soil. Nitrogen-fixing bacteria like Frankia and Cyanobacteria may play an important synergistic role in the proper growth and developmental stages of these plants. They are crucial for increasing the nitrogen amount of the soil through nitrogen fixation and gradually help in increasing the soil fertility and thus help in the proper progression of Alnus through the seral stages of succession. Nonrhizospheric soil samples were having a distinct population of other soil bacteria like Streptomyces, Rubrobacter, and Xanthomonas with higher Alpha diversity (54.14) than Alnus rhizospheric soil (42.18). This result was also validated by the rare fraction curve, which indicated more biodiversity in Non-rhizospheric soil rather than Alnus rhizosphere.