期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2009
卷号：106
期号：16
页码：6513-6518
DOI：10.1073/pnas.0810871106
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Several lines of evidence indicate that microorganisms in the meso- and bathypelagic ocean are metabolically active and respiring carbon. In addition, growing evidence suggests that archaea are fixing inorganic carbon in this environment. However, direct quantification of the contribution from deep ocean carbon sources to community production in the dark ocean remains a challenge. In this study, carbon flow through the microbial community at 2 depths in the mesopelagic zone of the North Pacific Subtropical Gyre was examined by exploiting the unique radiocarbon signatures ({Delta}14C) of the 3 major carbon sources in this environment. The radiocarbon content of nucleic acids, a biomarker for viable cells, isolated from size-fractionated particles (0.2-0.5 {micro}m and >0.5 {micro}m) showed the direct incorporation of carbon delivered by rapidly sinking particles. Most significantly, at the 2 mesopelagic depths examined (670 m and 915 m), carbon derived from in situ autotrophic fixation supported a significant fraction of the free-living microbial community (0.2-0.5 {micro}m size fraction), but the contribution of chemoautotrophy varied markedly between the 2 depths. Results further showed that utilization of the ocean's largest reduced carbon reservoir, 14C-depleted, dissolved organic carbon, was negligible in this environment. This isotopic portrait of carbon assimilation by the in situ, free-living microbial community, integrated over >50,000 L of seawater, implies that recent, photosynthetic carbon is not always the major carbon source supporting microbial community production in the mesopelagic realm.
