Marine Nitrogen-Fixing Organisms and Their Contribution to the N and C Requirement for Marine Biological Production
海洋固氮生物多样性及其对海洋生产力的氮、碳贡献

Nitrogen-fixing marine microorganisms and their symbiotic associations can convert the most abundant, but inert form of nitrogen into biologically available substrate and therefore, they play an important role in the introduction of N into the biosphere. This process has important significance especially in natural and oligotrophic ecosystems. This paper reviews the research development on biological nitrogen-fixation, and offers a comprehensive understanding of the nitrogen-fixation role, which nitrogen-fixers play in marine biogeochemical cycling and biological production. It summarizes the N 2-fixing contribution to C and N requirement for marine ecosystems, which include mangrove forest, coral reefs, coastal waters, estuaries, detrital sediment and microbial mats, and marine grass beds such as Syringodium, Spartina alterniflora, Diplanthera wrightii, and Thalassia testudini communities. The review of the resources, ecological distribution, community structure and function of marine N 2-fixing organisms shows that there is a strong direct relationship between photosynthesis (sinks of atmospheric CO 2) and biological N 2-fixation (uptake of new nitrogen) in every ecosystem described above. In conclusion, the research progresses have been made on the discovery of diversity of N 2-fixing organisms and their symbiotic associations. N 2-fixers include cyanobacteria Trichodesmium, Oscillatoria, Pelagothrix, Katagnymene, Synechococcus, Microcysits, Synechocystis, Calothrix, Richelia intracellularis, Lyngbya confervoides, Microcoleus chthonoplastes, Scytonema, Rivularia, Dichothrix, Tolypothrix, Hyella, Mastigocoleus, Phormidium, Gloeocapsa, Nodularia, Plectonema,Scopulonema, Aphanizomenon, Chamaesiphon, Anabaena,and Nostoc, heterotrophic N 2-fixing bacteria including members of the genera Klebstella, Vibrio, Clostridium, Desulfovibrio,and Pseudomonas, photosynthetic bacteria like Chromatium, and Beggiatoa as well as their symbiotic association such as Richelia intracellularis -Rhizosolenia; Richelia intracellulatis-Climacodium, Hemiaulus-Cyanobacteria, Sponge-Cyanobacteria and Syringodium isoetifolium-Cyanobacteria.