Regulation of inorganic carbon acquisition in a red tide alga (<i>Skeletonema costatum</i>): the importance of phosphorus availability

Gao, Guang; Xia, Jianrong; Yu, Jinlan; Fan, Jiale; Zeng, Xiaopeng

doi:https://doi.org/10.5194/bg-15-4871-2018

Articles | Volume 15, issue 16

https://doi.org/10.5194/bg-15-4871-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-15-4871-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 15, issue 16

Research article

|

17 Aug 2018

Research article |

| 17 Aug 2018

Regulation of inorganic carbon acquisition in a red tide alga (Skeletonema costatum): the importance of phosphorus availability

Guang Gao, Jianrong Xia, Jinlan Yu, Jiale Fan, and Xiaopeng Zeng

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Final revised paper (published on 17 Aug 2018)
Supplement to the final revised paper
Preprint (discussion started on 29 Nov 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of Gao et al. "Regulation of inorganic acquisition in a red tide alga (Skeltonema costatum): the importance of phosphorus availability', Chris Hunt, 14 Feb 2018
- AC1: 'Response to RC1', Jianrong Xia, 21 Mar 2018
RC2: 'Review of BG-2018-475', Anonymous Referee #2, 14 Mar 2018
- AC2: 'Response to RC2', Jianrong Xia, 21 Mar 2018

Peer-review completion

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

ED: Reconsider after major revisions (28 Mar 2018) by Clare Woulds

AR by Jianrong Xia on behalf of the Authors (29 Mar 2018)

ED: Referee Nomination & Report Request started (25 Apr 2018) by Clare Woulds

RR by Chris Hunt (15 May 2018)

RR by Douglas Campbell (18 Jun 2018)

Suggestions for revision or reasons for rejection

The authors grew the model diatom Skeletonema costatum in seawater media at pH 8.2 at 5 [PO4-].
They shifted samples to pH8.2 (no change) or to pH 8.7 and measured the photosynthetic responses to a matrix of imposed [PO4-] and [CO2].
They do not state (although they have the data) the [DIC] under their treatments, and I question their protocol for lowering [CO2] which depends on blocking equilibration between the culture suspension and the headspace, if any.

I offer suggestions for major (although easy) redesign of the figures that might help convey the findings.
best regards, Doug Campbell

Figure 1:
This figure should be an X-Y plot of photosynthesis (A) or respiration (B) vs. umol Phosphate l-1. Each graph should have 2 series, a low carbon dioxide and a high carbon dioxide.

Do not erect unnecessary levels of coding; 'AC'? 'LC'?? Why? Just give the CO2 concentrations.

Fig. 2 should be panel C of Figure 1, same comments as above.

rETR umol e- m-2 s-1 is not a meaningful unit for a suspension of cells. Think about what is being measured and how.
Same comment regarding XY plot as Figure 1

Fig. 4 same comment

Fig. 5, OK, now we switch the rules and plot photosynthesis vs. DIC, with series for [PO4-].

Fig. 6, same comment as Fig. 1. Do not put a quantitative data series as a categorical axes. 0.05 to 10 umol PO4- l-1 are not different categories, they are arbitrary measurement points along a (potentially) continuous axes of PO4-.
Use a log scale if necessary.

Fig. 7, same comment.

Materials & Methods:
Lines 101-103
This is an odd, incomplete way of expressing the applied DIC treatment.
What was the [DIC] under the two treatments?
A shift from bubbling with ambient air (outdoor? indoor?) pH 8.2 to ph 8.2 (no change) or pH 8.7 (increase) would lead to increased dissolution of head space CO2 into water at pH 8.7, with a conconmitant increase in [DIC] if the cell suspension is allowed to equilibrate with a headspace.
If not headspace is provided the suspension will be in [CO2] deficit as pH equilibration drives [DIC] to [HCO3-], lowering [CO2].
Then, any exposure to gas with ambient CO2 will lead to uptake.

Line 140: the rETR units are algebraically correct, but are not meaningful in the sense of a cell suspension.

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ED: Publish subject to minor revisions (review by editor) (10 Jul 2018) by Clare Woulds

AR by Jianrong Xia on behalf of the Authors (18 Jul 2018) Author's response Manuscript

ED: Publish as is (07 Aug 2018) by Clare Woulds

AR by Jianrong Xia on behalf of the Authors (08 Aug 2018) Manuscript

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Short summary

Diatoms commonly dominate algal blooms. However, little is known regarding how diatoms overcome CO₂ limitation and maintain growth during blooms. Our results show that enrichment of phosphorus enhances diatoms’ photosynthetic pigment, photosynthetic rate, and the capacity for inorganic carbon acquisition. This study indicates the essential role of phosphorus in coping with CO₂ limitation for diatoms and sheds light on how bloom-forming algae cope with carbon limitation during blooms.