 |
| Titel |
Diazotroph community succession during the VAHINE mesocosm experiment (New Caledonia lagoon) |
| VerfasserIn |
K. A. Turk-Kubo, I. E. Frank, M. E. Hogan, A. Desnues, S. Bonnet, J. P. Zehr |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 24 ; Nr. 12, no. 24 (2015-12-17), S.7435-7452 |
| Datensatznummer |
250118219
|
| Publikation (Nr.) |
 copernicus.org/bg-12-7435-2015.pdf |
|
|
|
|
|
| Zusammenfassung |
| 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 m3) mesocosms. This experiment provided a unique
opportunity to study the succession of different N2-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
Richelia associated with Rhizosolenia (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−1 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 (nifH) verified
that diazotrophs targeted in qPCR assays were collectively among the major
lineages in the lagoon and mesocosm samples, with the exception of
Crocosphaera-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 Braarudosphaera bigelowii symbiont unicellular group A
(UCYN-A) were present simultaneously in the lagoon, with the recently
described B. bigelowii/UCYN-A2 association present at higher
abundances than the B. bigelowii/UCYN-A1 association. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|