Molecular Soil Biology 2024, Vol.15, No.2, 46-58 http://bioscipublisher.com/index.php/msb 56 10 Concluding Remarks The research on screening and functional verification of pine rhizosphere nitrogen-fixing bacteria has yielded several significant findings. A total of 23 Azotobacter strains were isolated from the rhizosphere of Pinus massoniana Lamb, all exhibiting nitrogenase activity, with strains N4 and N9 showing particularly high activity levels. Additionally, six phosphorus-solubilizing strains and five potassium-solubilizing strains were identified, with notable strains including P3, P1, and K6. The study also highlighted the presence of diverse nitrogen-fixing bacteria such as Enterobacter, Burkholderia, Rhizobium, and others. Furthermore, the research identified Burkholderia tropica as a novel nitrogen-fixing species, expanding the known diversity within the genus Burkholderia. Other studies corroborated the presence of nitrogen-fixing bacteria in various plant rhizospheres, including those of sugarcane, maize, and desert plants, emphasizing the widespread occurrence and potential of these bacteria in different ecological settings. This research significantly contributes to the field of rhizosphere microbiology by expanding the understanding of the diversity and functionality of nitrogen-fixing bacteria in the pine rhizosphere. The identification of multiple strains with high nitrogenase activity underscores the potential of these bacteria to enhance soil fertility and plant growth, offering a sustainable alternative to chemical fertilizers. The discovery of Burkholderia tropica as a novel species further enriches the taxonomic and functional knowledge of nitrogen-fixing bacteria. Additionally, the study's findings on the co-occurrence of nitrogen-fixing and other plant growth-promoting traits, such as phosphorus and potassium solubilization, highlight the multifaceted roles these bacteria play in promoting plant health and productivity. Future research should focus on the in-depth characterization of the isolated strains, including their genetic and metabolic profiles, to better understand the mechanisms underlying their nitrogen-fixing and plant growth-promoting activities. Field trials should be conducted to evaluate the efficacy of these bacteria under natural conditions and to assess their potential as biofertilizers in various agricultural systems. Additionally, exploring the interactions between these bacteria and other soil microorganisms could provide insights into the complex dynamics of the rhizosphere microbiome. Practical applications should aim at developing microbial consortia that combine multiple beneficial traits, such as nitrogen fixation, phosphorus solubilization, and biocontrol, to create robust and effective biofertilizers. These efforts could lead to more sustainable agricultural practices, reducing the reliance on chemical inputs and enhancing soil health and crop productivity. Acknowledgments The authors extends sincere thanks to two anonymous peer reviewers for their feedback on the manuscript. Conflict of Interest Disclosure The authors affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest. References Aasfar A., Bargaz A., Yaakoubi K., Hilali A., Bennis I., Zeroual Y., and Kadmiri I., 2021, Nitrogen fixing azotobacter species as potential soil biological enhancers for crop nutrition and yield stability, Frontiers in Microbiology, 12: 628379. https://doi.org/10.3389/fmicb.2021.628379 Arfarita N., Muhibuddin A., and Imai T., 2019, Exploration of indigenous free nitrogen-fixing bacteria from rhizosphere of Vigna radiata for agricultural land treatment, Journal of Degraded and Mining Lands Management, 6(2): 1617-1623. https://doi.org/10.15243/JDMLM.2019.062.1617 Arsita R., Karim H., Hala Y., Iriany N., and Jumadi O., 2020, Isolation and identification of nitrogen-fixing bacteria in the corn rhizosphere (Zea mays L.) originating from Jeneponto Regency, South Sulawesi, IOP Conference Series: Earth and Environmental Science, 484: 012051. https://doi.org/10.1088/1755-1315/484/1/012051 Beneduzi A., Costa P., Parma M., Melo I., Bodanese-Zanettini M., and Passaglia L., 2010, Paenibacillus riograndensis sp. nov., a nitrogen-fixing species isolated from the rhizosphere of Triticum aestivum, International Journal of Systematic and Evolutionary Microbiology, 60(Pt 1) 128-133. https://doi.org/10.1099/ijs.0.011973-0
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