Riverine influence on nitrogen fixation in the upwelling region off Vietnam, South China Sea

Voß, Maren; Bombar, Deniz; Loick, Natalie; Dippner, Joachim W.

doi:10.1029/2005gl025569

Cited by 90 publications

(111 citation statements)

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“…Previously, it was estimated that N 2 fixation provides up to 10% of the total carbon production in the SCS (Voss et al, 2006;Loick et al, 2007). The highest potential for N 2 fixation was suggested to occur during the summer monsoon with no contribution during spring intermonsoon .…”

Section: Discussionmentioning

confidence: 99%

“…The central gyre is permanently stratified and oligotrophic, and N limitation of phytoplankton growth has been reported (Wu et al, 2003), suggesting that the environment is favorable for nitrogen (N 2 ) fixation. Rate measurements suggest that production based on N 2 fixation contributes approximately 10% of total production, with the highest rates measured during the monsoon seasons in winter and summer and the lowest rates during intermonsoon (Voss et al, 2006). Bloom-forming filamentous N 2 -fixing cyanobacterium Trichodesmium spp.…”

Section: Introductionmentioning

confidence: 99%

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Diversity and abundance of diazotrophic microorganisms in the South China Sea during intermonsoon

et al. 2008

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The spatial heterogeneity of diversity and abundance of diazotrophs were investigated off the Vietnamese coast in the South China Sea (SCS). The study area extended from the Mekong River plume to the shelf region and beyond to stations extending to 1700 m depth. The SCS diazotroph community, based on nifH gene diversity, had components closely related to sequences from open ocean, estuarine, saltmarsh and microbial mat communities. Rarefaction analysis suggested that by using a 97% similarity operational taxonomic unit definition, the majority of nifH sequence diversity in the samples was covered by the 384 nifH clones obtained. The majority of the nifH sequences recovered fell into two clusters: one comprised of Trichodesmium sequences and the other an a-proteobacterial group. Unicellular cyanobacterial groups A and B, and symbiotic filamentous cyanobacterial diazotrophs were detected sporadically. Trichodesmium was by far the most abundant diazotroph, with up to 6 Â 10 5 nifH gene copies per liter. Quantitative PCR probe-primer sets were designed and used to quantify two proteobacterial groups, revealing abundances up to 10 3 -10 4 nifH gene copies per liter, with the highest abundances in the photic zone. Major components of the clone library were also revealed by a nifH microarray and multidimensional scaling (MDS) analysis. MDS showed that samples from the 410 lm size fraction from 0-to 5-m depths clustered separately from the rest of the samples, primarily due to the abundance of Trichodesmium sequences. The SCS diazotroph community has a relatively low diversity and is a mixture of both estuarine and oceanic fingerprints.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Diversity and abundance of diazotrophic microorganisms in the South China Sea during intermonsoon

et al. 2008

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“…This figure is higher than is found in other parts of the SCS (Grosse et al 2010). Furthermore, nitrogen fixation rates measured in the upwelling region off Vietnam showed an approximately 10-fold increase during the monsoon season compared with the inter monsoon season (Voss et al 2006). Factors mentioned above have increased the heterogeneity of the distribution of diazotrophs in this area.…”

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confidence: 60%

Phylogenetic diversity and spatio-temporal distribution of nitrogenase genes (nifH) in the northern South China Sea

Kong¹,

Jing²,

Kataoka³

et al. 2011

Aquat. Microb. Ecol.

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We examined the phylogenetic diversity and abundance of diazotrophs along a transect from the Pearl River plume to oceanic waters in the northern South China Sea by constructing a clone library and using the quantitative polymerase chain reaction (qPCR). All the diazotrophic phylogenetic groups recovered, including heterotrophic proteobacteria, phototrophic cyanobacteria and Cluster III diazotrophs, and showed distinct spatio-temporal variation along the transect. At the oceanic sampling stations, gammaproteobacteria formed the dominant diazotrophic group, with cyanobacterial diazotrophs accounting for only a relatively small proportion; at the station influenced by the Pearl River plume all the diazotrophs were non-cyanobacterial, making this station distinct from the other stations. Multidimensional analysis demonstrated that salinity was the key environmental factor determining the spatio-temporal variations of diazotrophic communities along the transect. Trichodesmium spp. were the most abundant among the cyanobacterial diazotrophs and were potentially the most important nitrogen fixers at all the oceanic stations. The absence of cyanobacterial diazotrophs in winter, and at the station influenced by the plume, could be due to the relatively high nutrient conditions in these waters. KEY WORDS: Diazotrophs · nifH gene · Phylogenetic diversity · qPCR · South China Sea Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 65: 15-27, 2011 16 copy numbers of nifH genes in genomic DNA, thus enabling the study of the environmental diazotrophic community (Zehr & McReynolds 1989).A wide range of diazotrophs have been discovered in aquatic ecosystems, all of which occur in the domains Bacteria and Archaea (Chien & Zinder 1994, Zehr et al. 2003. Proteobacteria and Cyanobacteria are the 2 main groups of diazotrophic bacteria inhabiting the upper marine ecosystems. Among them, Cyanobacteria are well-studied and the filamentous cyanobacterium Trichodesmium spp. is reported to be abundant in oligotrophic tropical and subtropical oceans (Carpenter & Romans 1991, Capone et al. 1997. Oceanic symbiotic Cyanobacteria, such as Richelia sp., occur as endosymbionts in some genera of diatoms, such as Rhizosolenia, Hemiaulus and Chaetoceros, and are also important nitrogen fixers (Carpenter et al. 1999, Foster & Zehr 2006. More recently, unicellular diazotrophic cyanobacteria, named group A (UCYN-A), group B (UCYN-B) and group C (UCYN-C), have been discovered on the basis of molecular techniques (Zehr et al. 2001, Langlois et al. 2005, Foster et al. 2007, and their contribution to total nitrogen fixation was estimated to be equal to, or even greater than, that of Trichodesmium spp. (Falcón et al. 2004, Goebel et al. 2007.Although most cyanobacterial diazotrophic groups can be detected simultaneously in the marine environment (Church et al. 2005a, Foster et al. 2007, Fong et al. 2008, different diazotrophic groups have shown different patterns of distribution in the ocean (Rieman...

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“…Later it was also shown that in the SCS, N 2 fixation occurs at very high and ecologically significant rates in surface waters affected by Mekong River outflow (Voss et al 2006) ( Table 2). By combining approaches to study hydrography and nutrient setting in the Mekong River plume, we can now provide a clearer picture of how environmental factors determine phytoplankton species selection and lead to enhanced N 2 fixation.…”

Section: Discussionmentioning

confidence: 95%

Distribution of diazotrophic microorganisms and nifH gene expression in the Mekong River plume during intermonsoon

Bombar¹,

Moisander²,

Dippner³

et al. 2011

Mar. Ecol. Prog. Ser.

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N 2 fixation by marine pelagic prokaryotes plays a critical role in supplying new N to the ocean, and there is growing evidence that oceanic N 2 fixation is generally enhanced in tropical river plumes, where N 2 fixers (diazotrophs) benefit from riverine phosphorus and/or iron. Here we used nifH gene quantitative polymerase chain reaction (QPCR) and reverse transcription (RT) QPCR to investigate the horizontal distribution and activity of 9 diazotroph phylotypes in the Mekong River plume, South China Sea (SCS), in April 2007 (intermonsoon, lowest annual discharge). The nifH gene diversity was investigated by cloning and sequencing. Hydrodynamic modeling of the surface water advection revealed that the same water masses were sampled during the entire study, and helped to elucidate the physical forcing on diazotroph abundances and distributions. According to our estimates of nifH abundances and expression, the high N 2 fixation rates detected in the Mekong plume can primarily be attributed to Trichodesmium spp. and the symbiotic diatom-diazotroph associations (DDAs) Rhizosolenia -Richelia and Hemiaulus -Richelia. NifH phylotypes from unicellular cyanobacterial groups B and C and a gammaproteobacterial group (24774A11) were exclusively detected and expressed at oceanic stations. Clone libraries of nifH were dominated by Trichodesmium spp. but also included proteobacterial-and cluster III-like nifH sequences, including new lineages, possibly representing other active diazotrophs in the Mekong plume and SCS offshore waters. This study extends the known distribution of quantitatively important oceanic diazotrophs, and shows that the Mekong River plume hosts a diverse diazotroph community, of which particularly Trichodesmium spp. and DDAs fix N 2 at high rates.KEY WORDS: Nitrogen fixation · Phytoplankton ecology · Trichodesmium · Diatoms · Symbiosis · South China Sea · River discharge Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 424: 39-52, 2011, Foster & Zehr 2006. Further, by analyzing the diversity and distribution of the nifH gene (encoding the iron-containing subunit of nitrogenase enzyme), previously unrecognized unicellular microbes were discovered in the marine environment (Zehr & McReynolds 1989, Zehr et al. 1998. Many subsequent studies have focused on unicellular cyanobacterial diazotrophs, and results suggest that they as well contribute substantially to oceanic N 2 fixation , Montoya et al. 2004, Church et al. 2005a.Although N 2 fixation is recognized as a key component of the oceanic nitrogen cycle, it remains challenging to reliably integrate diazotroph inputs over large spatial scales. In order to improve these estimates, it is necessary to better understand how environmental factors control the distributions of various diazotroph species. Diazotroph communities appear to differ between surface waters of the open ocean, deeper waters, and the coastal ocean, reflecting different selective pressures acting on diazotrophs in these environments (Z...

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Riverine influence on nitrogen fixation in the upwelling region off Vietnam, South China Sea

Cited by 90 publications

References 20 publications

Diversity and abundance of diazotrophic microorganisms in the South China Sea during intermonsoon

Diversity and abundance of diazotrophic microorganisms in the South China Sea during intermonsoon

Phylogenetic diversity and spatio-temporal distribution of nitrogenase genes (nifH) in the northern South China Sea

Distribution of diazotrophic microorganisms and nifH gene expression in the Mekong River plume during intermonsoon

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Riverine influence on nitrogen fixation in the upwelling region off Vietnam, South China Sea

Cited by 90 publications

References 20 publications

Diversity and abundance of diazotrophic microorganisms in the South China Sea during intermonsoon

Diversity and abundance of diazotrophic microorganisms in the South China Sea during intermonsoon

Phylogenetic diversity and spatio-temporal ­distribution of nitrogenase genes (nifH) in the northern South China Sea

Distribution of diazotrophic microorganisms and nifH gene expression in the Mekong River plume during intermonsoon

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Phylogenetic diversity and spatio-temporal distribution of nitrogenase genes (nifH) in the northern South China Sea