Diazotroph community succession during the VAHINE mesocosm experiment (New Caledonia lagoon)
The VAHINE mesocosm experiment, conducted in the low-nutrient low-chlorophyll waters of the Noumea lagoon (coastal New Caledonia) was designed to trace the incorporation of nitrogen (N) fixed by diazotrophs into the food web, using large volume (50 m<sup>3</sup>) mesocosms. This experime...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2015-12-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/12/7435/2015/bg-12-7435-2015.pdf |
| _version_ | 1818526533949587456 |
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| author | K. A. Turk-Kubo I. E. Frank M. E. Hogan A. Desnues S. Bonnet J. P. Zehr |
| author_facet | K. A. Turk-Kubo I. E. Frank M. E. Hogan A. Desnues S. Bonnet J. P. Zehr |
| author_sort | K. A. Turk-Kubo |
| collection | DOAJ |
| description | The VAHINE mesocosm experiment, conducted in the low-nutrient low-chlorophyll
waters of the Noumea lagoon (coastal New Caledonia) was designed to trace the
incorporation of nitrogen (N) fixed by diazotrophs into the food web, using
large volume (50 m<sup>3</sup>) mesocosms. This experiment provided a unique
opportunity to study the succession of different N<sub>2</sub>-fixing
microorganisms (diazotrophs) and calculate in situ net growth and mortality
rates in response to fertilization with dissolved inorganic phosphate (DIP)
over a 23-day period, using quantitative polymerase chain reaction (qPCR)
assays targeting widely distributed marine diazotroph lineages. Inside the
mesocosms, the most abundant diazotroph was the heterocyst-forming
<i>Richelia</i> associated with <i>Rhizosolenia</i> (Het-1) in the first
half of the experiment, while unicellular cyanobacterial Group C (UCYN-C)
became abundant during the second half of the experiment. Decreasing DIP
concentrations following the fertilization event and increasing temperatures
were significantly correlated with increasing abundances of UCYN-C. Maximum
net growth rates for UCYN-C were calculated to range between
1.23 ± 0.07 and 2.16 ± 0.07 d<sup>−1</sup> in the mesocosms, which are
among the highest growth rates reported for diazotrophs. Outside the
mesocosms in the New Caledonia lagoon, UCYN-C abundances remained low,
despite increasing temperatures, suggesting that the microbial community
response to the DIP fertilization created conditions favorable for UCYN-C
growth inside the mesocosms. Diazotroph community composition analysis using
PCR targeting a component of the nitrogenase gene (<i>nifH</i>) verified
that diazotrophs targeted in qPCR assays were collectively among the major
lineages in the lagoon and mesocosm samples, with the exception of
<i>Crocosphaera</i>-like phylotypes, where sequence types not typically
seen in the oligotrophic ocean grew in the mesocosms. Maximum net growth and
mortality rates for nine diazotroph phylotypes throughout the 23-day
experiment were variable between mesocosms, and repeated fluctuations between
periods of net growth and mortality were commonly observed. The field
population of diazotrophs in the New Caledonian lagoon waters appeared to be
dominated by Het-1 over the course of the study period. However, results from
both qPCR and PCR analysis indicated a diverse field population of
diazotrophs was present in the lagoon at the time of sampling. Two ecotypes
of the <i>Braarudosphaera bigelowii</i> symbiont unicellular group A
(UCYN-A) were present simultaneously in the lagoon, with the recently
described <i>B. bigelowii</i>/UCYN-A2 association present at higher
abundances than the <i>B. bigelowii</i>/UCYN-A1 association. |
| first_indexed | 2024-12-11T06:24:17Z |
| format | Article |
| id | doaj.art-e2201a0a16c84eefb71232247913b734 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-11T06:24:17Z |
| publishDate | 2015-12-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-e2201a0a16c84eefb71232247913b7342022-12-22T01:17:43ZengCopernicus PublicationsBiogeosciences1726-41701726-41892015-12-0112247435745210.5194/bg-12-7435-2015Diazotroph community succession during the VAHINE mesocosm experiment (New Caledonia lagoon)K. A. Turk-Kubo0I. E. Frank1M. E. Hogan2A. Desnues3S. Bonnet4J. P. Zehr5Ocean Sciences Department, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USAOcean Sciences Department, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USAOcean Sciences Department, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USAMediterranean Institute of Oceanography (MIO) – IRD/CNRS/Aix-Marseille University, IRD Noumea, 101 Promenade R. Laroque, BPA5, 98848 Noumea Cedex, FranceMediterranean Institute of Oceanography (MIO) – IRD/CNRS/Aix-Marseille University, IRD Noumea, 101 Promenade R. Laroque, BPA5, 98848 Noumea Cedex, FranceOcean Sciences Department, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USAThe VAHINE mesocosm experiment, conducted in the low-nutrient low-chlorophyll waters of the Noumea lagoon (coastal New Caledonia) was designed to trace the incorporation of nitrogen (N) fixed by diazotrophs into the food web, using large volume (50 m<sup>3</sup>) mesocosms. This experiment provided a unique opportunity to study the succession of different N<sub>2</sub>-fixing microorganisms (diazotrophs) and calculate in situ net growth and mortality rates in response to fertilization with dissolved inorganic phosphate (DIP) over a 23-day period, using quantitative polymerase chain reaction (qPCR) assays targeting widely distributed marine diazotroph lineages. Inside the mesocosms, the most abundant diazotroph was the heterocyst-forming <i>Richelia</i> associated with <i>Rhizosolenia</i> (Het-1) in the first half of the experiment, while unicellular cyanobacterial Group C (UCYN-C) became abundant during the second half of the experiment. Decreasing DIP concentrations following the fertilization event and increasing temperatures were significantly correlated with increasing abundances of UCYN-C. Maximum net growth rates for UCYN-C were calculated to range between 1.23 ± 0.07 and 2.16 ± 0.07 d<sup>−1</sup> in the mesocosms, which are among the highest growth rates reported for diazotrophs. Outside the mesocosms in the New Caledonia lagoon, UCYN-C abundances remained low, despite increasing temperatures, suggesting that the microbial community response to the DIP fertilization created conditions favorable for UCYN-C growth inside the mesocosms. Diazotroph community composition analysis using PCR targeting a component of the nitrogenase gene (<i>nifH</i>) verified that diazotrophs targeted in qPCR assays were collectively among the major lineages in the lagoon and mesocosm samples, with the exception of <i>Crocosphaera</i>-like phylotypes, where sequence types not typically seen in the oligotrophic ocean grew in the mesocosms. Maximum net growth and mortality rates for nine diazotroph phylotypes throughout the 23-day experiment were variable between mesocosms, and repeated fluctuations between periods of net growth and mortality were commonly observed. The field population of diazotrophs in the New Caledonian lagoon waters appeared to be dominated by Het-1 over the course of the study period. However, results from both qPCR and PCR analysis indicated a diverse field population of diazotrophs was present in the lagoon at the time of sampling. Two ecotypes of the <i>Braarudosphaera bigelowii</i> symbiont unicellular group A (UCYN-A) were present simultaneously in the lagoon, with the recently described <i>B. bigelowii</i>/UCYN-A2 association present at higher abundances than the <i>B. bigelowii</i>/UCYN-A1 association.http://www.biogeosciences.net/12/7435/2015/bg-12-7435-2015.pdf |
| spellingShingle | K. A. Turk-Kubo I. E. Frank M. E. Hogan A. Desnues S. Bonnet J. P. Zehr Diazotroph community succession during the VAHINE mesocosm experiment (New Caledonia lagoon) Biogeosciences |
| title | Diazotroph community succession during the VAHINE mesocosm experiment (New Caledonia lagoon) |
| title_full | Diazotroph community succession during the VAHINE mesocosm experiment (New Caledonia lagoon) |
| title_fullStr | Diazotroph community succession during the VAHINE mesocosm experiment (New Caledonia lagoon) |
| title_full_unstemmed | Diazotroph community succession during the VAHINE mesocosm experiment (New Caledonia lagoon) |
| title_short | Diazotroph community succession during the VAHINE mesocosm experiment (New Caledonia lagoon) |
| title_sort | diazotroph community succession during the vahine mesocosm experiment new caledonia lagoon |
| url | http://www.biogeosciences.net/12/7435/2015/bg-12-7435-2015.pdf |
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