Vertical partitioning of phosphate uptake among picoplankton groups in the low Pi Mediterranean Sea

Talarmin, A.; Van Wambeke, F.; Lebaron, P.; Moutin, T.

doi:https://doi.org/10.5194/bg-12-1237-2015

Articles | Volume 12, issue 4

https://doi.org/10.5194/bg-12-1237-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-12-1237-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 12, issue 4

Research article

|

26 Feb 2015

Research article |

| 26 Feb 2015

Vertical partitioning of phosphate uptake among picoplankton groups in the low Pi Mediterranean Sea

A. Talarmin, F. Van Wambeke, P. Lebaron, and T. Moutin

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Final revised paper (published on 26 Feb 2015)
Supplement to the final revised paper
Preprint (discussion started on 13 Oct 2014)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC C6445: 'Review comment', Anonymous Referee #1, 04 Nov 2014
- AC C7824: 'bg-2014-464_Reply to Referee 1', Agathe Talarmin, 05 Jan 2015
RC C6541: 'review Talarmin et al.', Anonymous Referee #2, 08 Nov 2014
- AC C7858: 'bg-2014-464_Reply to Referee 2', Agathe Talarmin, 06 Jan 2015
RC C6562: 'Comments on bg-2014-464', Anonymous Referee #3, 09 Nov 2014
- AC C7834: 'bg-2014-464_Reply to Referee 3', Agathe Talarmin, 05 Jan 2015

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Agathe Talarmin on behalf of the Authors (06 Jan 2015) Author's response

ED: Referee Nomination & Report Request started (17 Jan 2015) by Koji Suzuki

RR by Anonymous Referee #1 (20 Jan 2015)

RR by Anonymous Referee #2 (27 Jan 2015)

Suggestions for revision or reasons for rejection

The manuscript is much improved. However, there are remaining minor issues in the new text, listed below in order of appearance, that will need to be addressed prior to publication considerations. There also seems that text may be missing (p17).

P5, ln 22. Insert “were” between ‘Pi’ and ‘higher’

P8, ln 20. Were the blank values subtracted from the counts?

P11, ln 15. Change ‘Table 2’ to ‘Table 1’

P12, ln 9. Syn abundance - 7700 is less than 14000, so something is incorrect in this statement.

P14, ln5-7. This sentence is difficult to understand. Does it mean that, at Station C, K+Sn were the same for all sorted groups?

P14, ln 16. What is meant with “discrepancies’ between turnover time and SRP concentrations? What relationship was expected?

P15, ln 3. These rates are quite high compared to these other studies, even when considering bulk rates measured previously in the Mediterranean (e.g. Flaten et al. 2005: ~1nmol L-1 h-1).

P15, ln 6. You present 4 possible reasons for the high per cell P uptake rates observed in Proc in this study compared to the Sargasso Sea (~ 16x higher). However, it seems to me that these points address Proc rates compared to community rates. Is that what was meant? I also have questions with the different points.

Point i), although it is now realized that Proc group has great genetic variability, is there reason to believe that the Proc community in the Med is hugely different from that in other oligotrophic oceans?

Point ii) the proportion of Proc to the cyanobacterial community should not affect per cell rates, but bulk rates. Also, Pi (which here equates to orthophosphate) does not readily undergo redox changes, so 'oxidation of Pi' is probably not what you intended.

Point iii) this would require that if 100% of Proc is live in the Mediterranean then >90% will be dead in the Sargasso Sea (15/16). Point iv) is valid but again requires that >90% of the label is lost. Is there such a large discrepancy between sorted rates compared to bulk rates from the cited studies?

P15, ln 16. If the missing fraction doesn’t contribute much to the bulk P-uptake, then even with higher per cell uptake they will not make up for the missing portion, as the comparison is between bulk and sorted cells, and bulk>sum of sorted groups.

P16, ln 3. “Our data suggests that microbial communities have the potential to take up Pi faster when Pi turnover is short.” I am not sure what is meant here. Maybe the inverse (faster rates makes shorter turnover)? However, turnover time is a function of biomass, available P-pool size and community (or group) uptake rate. Your data from the top 50 m shows rates to increase with increasing SRP concentration, which is what would be expected where the Pi pool often is below concentrations where Vmax can be reached. So it may well be that at higher SRP concentrations the highest rates are achieved and the turnover times get shorter as a result.

P17, ln 22. Is there missing text here? “..in stained samples: such..”

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ED: Publish subject to minor revisions (Editor review) (28 Jan 2015) by Koji Suzuki

AR by Agathe Talarmin on behalf of the Authors (02 Feb 2015) Author's response Manuscript

ED: Publish subject to technical corrections (04 Feb 2015) by Koji Suzuki

AR by Agathe Talarmin on behalf of the Authors (05 Feb 2015) Manuscript

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Short summary

Along a transect in the warm nutrient-depleted Mediterranean Sea, we found that microorganisms shared phosphate resources by using different uptake strategies. Heterotrophic prokaryotes dominated phosphate uptake in the upper layers while cyanobacteria dominated uptake fluxes around the deep chlorophyll maximum depth. Synechococcus seemed well equipped to respond to pulses of phosphate, whereas Prochlorococcus and heterotrophs were more adapted to very low concentrations.