Bacterial degradation activity in the eastern tropical South Pacific oxygen minimum zone
<p>Oxygen minimum zones (OMZs) show distinct biogeochemical processes that relate to microorganisms being able to thrive under low or even absent oxygen. Microbial degradation of organic matter is expected to be reduced in OMZs, although quantitative evidence is low. Here, we present heterotro...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-01-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/17/215/2020/bg-17-215-2020.pdf |
| _version_ | 1818981269062549504 |
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| author | M. Maßmig J. Lüdke G. Krahmann A. Engel |
| author_facet | M. Maßmig J. Lüdke G. Krahmann A. Engel |
| author_sort | M. Maßmig |
| collection | DOAJ |
| description | <p>Oxygen minimum zones (OMZs) show distinct biogeochemical processes
that relate to microorganisms being able to thrive under low or even absent
oxygen. Microbial degradation of organic matter is expected to be reduced in
OMZs, although quantitative evidence is low. Here, we present heterotrophic
bacterial production (<span class="inline-formula"><sup>3</sup>H</span> leucine incorporation), extracellular enzyme
rates (leucine aminopeptidase/<span class="inline-formula"><i>β</i></span>-glucosidase) and bacterial cell abundance
for various in situ oxygen concentrations in the water column, including the upper
and lower oxycline, of the eastern tropical South Pacific off Peru.
Bacterial heterotrophic activity in the suboxic core of the OMZ (at in situ <span class="inline-formula">≤</span> 5 <span class="inline-formula">µ</span>mol <span class="inline-formula">O<sub>2</sub></span> kg<span class="inline-formula"><sup>−1</sup></span>) ranged from 0.3 to 281 <span class="inline-formula">µ</span>mol C m<span class="inline-formula"><sup>−3</sup></span> d<span class="inline-formula"><sup>−1</sup></span> and was not significantly lower than in waters of 5–60 <span class="inline-formula">µ</span>mol <span class="inline-formula">O<sub>2</sub></span> kg<span class="inline-formula"><sup>−1</sup></span>. Moreover, bacterial abundance in the OMZ and leucine
aminopeptidase activity were significantly higher in suboxic waters compared
to waters of 5–60 <span class="inline-formula">µ</span>mol <span class="inline-formula">O<sub>2</sub></span> kg<span class="inline-formula"><sup>−1</sup></span>, suggesting no impairment of
bacterial organic-matter degradation in the core of the OMZ. Nevertheless,
high cell-specific bacterial production was observed in samples from
oxyclines, and cell-specific extracellular enzyme rates were especially high
at the lower oxycline, corroborating earlier findings of highly active and
distinct micro-aerobic bacterial communities. To assess the impact of
bacterial degradation of dissolved organic matter (DOM) for oxygen loss in
the Peruvian OMZ, we compared diapycnal fluxes of oxygen and dissolved
organic carbon (DOC) and their microbial uptake within the upper 60 m of the
water column. Our data indicate low bacterial growth efficiencies of
1 %–21 % at the upper oxycline, resulting in a high bacterial oxygen demand
that can explain up to 33 % of the observed average oxygen loss over
depth. Our study therewith shows that microbial degradation of DOM has a
considerable share in sustaining the OMZ off Peru.</p> |
| first_indexed | 2024-12-20T17:28:38Z |
| format | Article |
| id | doaj.art-3be01bbff6ab4f409a19f4744375ecf4 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-20T17:28:38Z |
| publishDate | 2020-01-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-3be01bbff6ab4f409a19f4744375ecf42022-12-21T19:31:27ZengCopernicus PublicationsBiogeosciences1726-41701726-41892020-01-011721523010.5194/bg-17-215-2020Bacterial degradation activity in the eastern tropical South Pacific oxygen minimum zoneM. MaßmigJ. LüdkeG. KrahmannA. Engel<p>Oxygen minimum zones (OMZs) show distinct biogeochemical processes that relate to microorganisms being able to thrive under low or even absent oxygen. Microbial degradation of organic matter is expected to be reduced in OMZs, although quantitative evidence is low. Here, we present heterotrophic bacterial production (<span class="inline-formula"><sup>3</sup>H</span> leucine incorporation), extracellular enzyme rates (leucine aminopeptidase/<span class="inline-formula"><i>β</i></span>-glucosidase) and bacterial cell abundance for various in situ oxygen concentrations in the water column, including the upper and lower oxycline, of the eastern tropical South Pacific off Peru. Bacterial heterotrophic activity in the suboxic core of the OMZ (at in situ <span class="inline-formula">≤</span> 5 <span class="inline-formula">µ</span>mol <span class="inline-formula">O<sub>2</sub></span> kg<span class="inline-formula"><sup>−1</sup></span>) ranged from 0.3 to 281 <span class="inline-formula">µ</span>mol C m<span class="inline-formula"><sup>−3</sup></span> d<span class="inline-formula"><sup>−1</sup></span> and was not significantly lower than in waters of 5–60 <span class="inline-formula">µ</span>mol <span class="inline-formula">O<sub>2</sub></span> kg<span class="inline-formula"><sup>−1</sup></span>. Moreover, bacterial abundance in the OMZ and leucine aminopeptidase activity were significantly higher in suboxic waters compared to waters of 5–60 <span class="inline-formula">µ</span>mol <span class="inline-formula">O<sub>2</sub></span> kg<span class="inline-formula"><sup>−1</sup></span>, suggesting no impairment of bacterial organic-matter degradation in the core of the OMZ. Nevertheless, high cell-specific bacterial production was observed in samples from oxyclines, and cell-specific extracellular enzyme rates were especially high at the lower oxycline, corroborating earlier findings of highly active and distinct micro-aerobic bacterial communities. To assess the impact of bacterial degradation of dissolved organic matter (DOM) for oxygen loss in the Peruvian OMZ, we compared diapycnal fluxes of oxygen and dissolved organic carbon (DOC) and their microbial uptake within the upper 60 m of the water column. Our data indicate low bacterial growth efficiencies of 1 %–21 % at the upper oxycline, resulting in a high bacterial oxygen demand that can explain up to 33 % of the observed average oxygen loss over depth. Our study therewith shows that microbial degradation of DOM has a considerable share in sustaining the OMZ off Peru.</p>https://www.biogeosciences.net/17/215/2020/bg-17-215-2020.pdf |
| spellingShingle | M. Maßmig J. Lüdke G. Krahmann A. Engel Bacterial degradation activity in the eastern tropical South Pacific oxygen minimum zone Biogeosciences |
| title | Bacterial degradation activity in the eastern tropical South Pacific oxygen minimum zone |
| title_full | Bacterial degradation activity in the eastern tropical South Pacific oxygen minimum zone |
| title_fullStr | Bacterial degradation activity in the eastern tropical South Pacific oxygen minimum zone |
| title_full_unstemmed | Bacterial degradation activity in the eastern tropical South Pacific oxygen minimum zone |
| title_short | Bacterial degradation activity in the eastern tropical South Pacific oxygen minimum zone |
| title_sort | bacterial degradation activity in the eastern tropical south pacific oxygen minimum zone |
| url | https://www.biogeosciences.net/17/215/2020/bg-17-215-2020.pdf |
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