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| Titel |
Production, partitioning and stoichiometry of organic matter under variable nutrient supply during mesocosm experiments in the tropical Pacific and Atlantic Ocean |
| VerfasserIn |
J. M. S. Franz, H. Hauss, U. Sommer, T. Dittmar, U. Riebesell |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 11 ; Nr. 9, no. 11 (2012-11-20), S.4629-4643 |
| Datensatznummer |
250007401
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| Publikation (Nr.) |
 copernicus.org/bg-9-4629-2012.pdf |
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| Zusammenfassung |
| Oxygen-deficient waters in the ocean, generally referred to as oxygen
minimum zones (OMZ), are expected to expand as a consequence of global
climate change. Poor oxygenation is promoting microbial loss of inorganic
nitrogen (N) and increasing release of sediment-bound phosphate (P) into the
water column. These intermediate water masses, nutrient-loaded but with an N
deficit relative to the canonical N:P Redfield ratio of 16:1, are
transported via coastal upwelling into the euphotic zone. To test the impact
of nutrient supply and nutrient stoichiometry on production, partitioning
and elemental composition of dissolved (DOC, DON, DOP) and particulate (POC,
PON, POP) organic matter, three nutrient enrichment experiments were
conducted with natural microbial communities in shipboard mesocosms, during
research cruises in the tropical waters of the southeast Pacific and the
northeast Atlantic. Maximum accumulation of POC and PON was observed under
high N supply conditions, indicating that primary production was controlled
by N availability. The stoichiometry of microbial biomass was unaffected by
nutrient N:P supply during exponential growth under nutrient saturation,
while it was highly variable under conditions of nutrient limitation and
closely correlated to the N:P supply ratio, although PON:POP of accumulated
biomass generally exceeded the supply ratio. Microbial N:P composition was
constrained by a general lower limit of 5:1. Channelling of assimilated P
into DOP appears to be the mechanism responsible for the consistent offset
of cellular stoichiometry relative to inorganic nutrient supply and nutrient
drawdown, as DOP build-up was observed to intensify under decreasing N:P
supply. Low nutrient N:P conditions in coastal upwelling areas overlying
O2-deficient waters seem to represent a net source for DOP, which may
stimulate growth of diazotrophic phytoplankton. These results demonstrate
that microbial nutrient assimilation and partitioning of organic matter
between the particulate and the dissolved phase are controlled by the N:P
ratio of upwelled nutrients, implying substantial consequences for nutrient
cycling and organic matter pools in the course of decreasing nutrient N:P
stoichiometry. |
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