북서태평양에서의 질소고정자들의 분포, 다양성 및 생태학적 중요성

Abstract

The availability of nitrogen is important in regulating biological productivity in marine environment. Deepwater nitrate has long been considered the major source of new nitrogen supporting primary production in oligotrophic regions of the open oceans, but recent studies have shown that biological N2 fixation has a critical role in supporting oceanic new production. Distribution, diversity, and N2 fixing rates were investigated for the tropical marine environment, th ePhilippine Sea, the Kuroshio and the East China Sea to ascertain the importance of N2 fixation in the northwestern Pacifric Ocean. The results showed that colonical or solitary cyanobacterium Trichodesmium spp. were the dominant diazotrophs in the study area with heterocycous-forming cyanobacterial symbiont of diatoms. In the tropical and subtropical oligotrophic waters, small unicellular cyanobacteria Crocosphaera sp. showed high abundance. Also, heterotrophic dinoflagellate genera Ornithocercus and Histoneis often hosted clusters of cyanobacteria. Analysis of nifH gene indicated that Crocosphaera sp. is a dominant nitrogen fixer in tropical water. In addition, diverse nifH genes of heterotrophic bacteria was also found abundantly. In the tropical oligotrophic waters with very high abundance of N2 fixing cyanobacteria showed high primary production rates up to 504.6 mgCm-2d-1. Based on on-going analyses of the distribution, diverstiy and nitrogen fixing rates of nitrogen fixers in the northwestern Pacific Ocean are examined, and the role of these organisms in the ocean ecosystem is also examined.