Advances Research in the Floating Aquatic Fern Azolla: Taxonomy, Symbiotic Nitrogen Fixation, and Diversified Utilization

Azolla spp. is a unique floating aquatic fern that forms an obligate nitrogen-fixing symbiosis with the cyanobacterium Nostoc azollae, and has found extensive applications in green agricultural development and ecological and environmental governance. Through efficient nitrogen and carbon fixation, rapid biomass accumulation and bioactive metabolite synthesis, it significantly enhances its ecological adaptability and resource utilization value. Azolla is widely distributed in tropical, subtropical and temperate regions. Its obligate symbiosis with cyanobacteria is supported by specialized leaf cavities, and achieves efficient nitrogen fixation via carbon-nitrogen coupling. Relevant genomic and multi-omics resources have been initially established. Azolla has unique advantages in nutritional composition, functional metabolism and environmental adaptability, and has formed diversified application modes such as feed protein, paddy green manure, pollution remediation and biomass energy. This paper systematically reviews the taxonomic evolution, biological characteristics, molecular mechanism of symbiotic nitrogen fixation and diversified applications of Azolla, and proposes that future research should focus on directions including functional gene mining, germplasm innovation, anti-nutritional factor removal and large-scale production of high-value products.