the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Oct 2022
Responses of elemental content and macromolecule of the coccolithophore Emiliania huxleyi to reduced phosphorus availability and ocean acidification depend on light intensity
Yong Zhang
Shuai Ma
Hanbing Chen
Jiabing Li
Zhengke Li
Kui Xu
Ruiping Huang
Hong Zhang
Yonghe Han
Abstract. Global climate change leads to simultaneous changes in multiple environmental drivers in the marine realm. Although physiological characterization of coccolithophores have been studied under climate change, there is limited knowledge on the biochemical responses of this biogeochemically important phytoplankton group to changing multiple environmental drivers. Here we investigate the interactive effects of reduced phosphorus availability (4 to 0.4 μmol L–1), elevated pCO2 concentrations (426 to 946 μatm) and increasing light intensity (40 to 300 μmol photons m–2 s–1) on elemental content and macromolecules of the cosmopolitan coccolithophore Emiliania huxleyi. Reduced phosphorus availability reduces particulate organic nitrogen and protein contents under low light intensity, but not under high light intensity. Reduced phosphorus availability and ocean acidification act synergistically to increase particulate organic carbon (POC) and carbohydrate contents under high light intensity but not under low light intensity. Reduced phosphorus availability, ocean acidification and increasing light intensity act synergistically to increase the allocation of POC to carbohydrates. Under future ocean acidification and increasing light intensity, enhanced carbon fixation could increase carbon storage in the phosphorus-limited regions of the oceans where E. huxleyi dominates the phytoplankton assemblages. In each light intensity, elemental carbon to phosphorus (C : P) and nitrogen to phosphorus (N : P) ratios decrease with increasing growth rate. These results suggest that coccolithophores could reallocate chemical elements and energy to synthesize macromolecules efficiently, which allows them to regulate its elemental content and growth rate to acclimate to changing environmental conditions.
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Journal article(s) based on this preprint
Yong Zhang et al.
Interactive discussion
Status: closed
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CC1: 'Comment on egusphere-2022-947', Peng Jin, 07 Nov 2022
The manuscript reported a practical finding that responses of elemental content and macromolecule of the Emiliania huxleyito reduced phosphorus availability and ocean acidification depend on light intensity. The results of the study showed that under future ocean acidification and increasing light intensity conditions, enhanced carbon fixation could increase carbon storage in the phosphorus-limited regions of the oceans where E. huxleyi dominates the phytoplankton assemblages. This research could provide vital information for evaluating carbon cycle in marine ecosystems under global change.
The paper is well structured, the data are presented well, and the figures are well organized. However, some parts of the manuscript need further explanation and to be improved before acceptance for publication.
Line 60-61, 63-64: Please specify the light levels for “low light” and “high light”. Particulate organic nitrogen and protein contents at a cellular basis or on a total scale?
Line 62: I was wondering if it is more appropriate to use the term of “elevated pCO2” rather than “ocean acidification”, which has not been introduced in the text before. In fact, the authors used the terms of elevated pCO2 and ocean acidification (used in a broad sense to include effects of both elevated dissolved CO2 and the resulting decrease in pH) in the text, which is confusing. So, I would suggest the authors to select one term and use it consistently throughout the whole manuscript.
Line 140-141: Under reduced phosphorus availability, increasing light intensity and ocean acidification conditions. Should be cellular POC content? Please check this issue throughout the whole manuscript.
Line 143: Cellular PIC content?
Line 283-287 The method described in the paper is very similar to the phenol-sulfuric acid method for the determination of polysaccharides. Is the carbohydrate assay the same as the polysaccharide assay?
Line158-214 The description of At LL intensity (Part 1) is too tedious and complicated, please simplify. Just explain the reasons for selecting the light intensity, phosphate concentration, acidification conditions and the approximate experimental steps. Or put the picture of the experimental method in the supplement to the manuscript, after all, there are only three figures in the manuscript.
Line 290-292 The percentages of carbon and nitrogen contributed by carbohydrate and protein were an important element of this study. Please provide more details of this method.
Fig 2 and 3, if the purpose of the authors is to compare the different responses between the light level 40 and 300μmol photons m–2s–1, it would be better to merge Fig 1a and 1b.
Line 330-333: The p-values (0.48 and 0.68) indicated that the differences are not statistically significant. Also see this issue at Lines 365, 407, 413-414, 430 etc.
Line 337: See my comment above
Line 338-340: As the author concluded that there was significant interaction between CO2 and P (acted synergistically), it would be better to present the results of three-way ANOVA analysis in the text to support this statement. This issue occurred at Lines 360-362, and Lines 415-417 (included but not limited, please check throughout the whole manuscript).
Line 385-388: Please rephrase the wordings here.
Line 484-487: Please rephrase the wordings here.
Line 520-521: I cannot see any “regulation mechanisms” that were proposed in the present study.
Q8. Line 524 ‘Therefore, the reduced phosphorus availability dominantly reduces the RNA content (Fig. S5)’. Was the algal cell RNA content also measured in this study? The method for this determination was not described in the M&M section, at least.
Line 545: ‘(Rokitta et al., 2016; Zhang et al., 2020; Wang et al., 2022) (Fig. S6)’?
Line 555 ‘…..and small subunit ribosomal protein S3E, S5E, SAE (PR-S3E, PR-S5E, RP-SAE) in E. huxleyi (Fig. S7)’. Please provide references for this statement.
Line 574: The authors found that more POC were allocated to carbohydrates but not to protein under high light intensity, reduced phosphorus availability and ocean acidification. This is a quite interesting finding. So, what is the possible reason for this? Could you please explain?
Citation: https://doi.org/10.5194/egusphere-2022-947-CC1 -
AC1: 'Reply on CC1', Yong Zhang, 05 Jan 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-947/egusphere-2022-947-AC1-supplement.zip
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AC1: 'Reply on CC1', Yong Zhang, 05 Jan 2023
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RC1: 'Comment on egusphere-2022-947', Anonymous Referee #1, 25 Nov 2022
Dr Zhang and colleagues evaluate the interactive effect of changes on multiple environmental drivers (namely phosphorous concentration, pCO2 and light intensity) on the elemental and macromolecule content of the model coccolithophore species Emiliania huxleyi. Authors identify that multiple stressors interact on the physiological response of E. huxleyi and that underlying mechanisms are complex. For example, authors identify that reduced phosphorus availability results in a reduction of both particulate organic nitrogen and protein contents under low light intensity, but not under high light intensity. Interestingly, reduced phosphorus concentration in combination with ocean acidification result in an increase in both POC and carbohydrate contents only under high light conditions. A large body of evidence indicate that coccolithophores are sensitive to projected changes in oceanic conditions driven by ongoing human-induced climate change, such as ocean acidification and changes in nutrient supply, mixed layer depth and light intensity. Given their abundance and fundamental role in the biological and carbonate counter pumps, changes in coccolithophore performance will most likely have impacts in the oceanic carbon cycle and marine ecosystems. Therefore, there is an urgent need of studies such as the one presented here to evaluate how multiple environmental drivers affect key marine organism in order to predict how ongoing environmental change will impact marine ecosystems. The paper is clearly written, the figures are appropriate and the findings interesting and useful for the scientific community. Therefore, I recommend acceptance of this manuscript after the comments listed below have been addressed.
Lines 84-85. The sentence “These ocean changes expose phytoplankton cells within the UML to multiple drivers,” is vague. Do authors mean that environmental changes in the UML will expose phytoplankton cells to physiological stress? Please clarify.
Line 109. Authors could dedicate a sentence or two to the importance/relevance of multi-stressor experiments highlighting that numerous environmental factors will simultaneously change in the future ocean and therefore, this kind of experiments are needed to evaluate the response of different organisms to ongoing environmental change.
Line 149. The specialized reader would appreciate an SEM picture of the coccosphere and or coccoliths either in the main text or as supplementary material.
Line 151. could authors mention the date when this strain was isolated?
Line 510 Coccolithophores play a complex role in the carbon cycle through production and export of organic carbon to depth but also through the carbonate counter pump (releasing CO2 during the calcification process). Authors should clarify this in the text.
Line 530. Could authors explain (or speculate) about the metabolic process behind the relationship between low light intensity and nitrate uptake reduction?
Citation: https://doi.org/10.5194/egusphere-2022-947-RC1 -
AC2: 'Reply on RC1', Yong Zhang, 05 Jan 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-947/egusphere-2022-947-AC2-supplement.zip
-
AC1: 'Reply on CC1', Yong Zhang, 05 Jan 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-947/egusphere-2022-947-AC1-supplement.zip
-
AC2: 'Reply on RC1', Yong Zhang, 05 Jan 2023
-
RC2: 'Comment on egusphere-2022-947', Anonymous Referee #2, 21 Dec 2022
December 21, 2022
Reviewer’s comments for
Ms. Ref No.: egusphere-2022-947
Title: Responses of elemental content and macromolecule of the coccolithophore Emiliania huxleyi to reduced phosphorus availability and ocean acidification depend on light intensity
Authors: Yong Zhang et al.
Submitted to: Biogeosciences
General comments
The authors show interesting experimental data on the responses of an important coccolithophore to changing three environmental drivers. Culture experiments are carefully designed and conducted. Results are complex and result descriptions can be more accomplished but acceptable. I found some concern in the present manuscript. The following comments should be considered before this paper being considered for publishing in Biogeosciences.
Major comments
- I consider that a message from the present title (the importance of light condition on the coccolithophore responses) does not link with the conclusion of this paper (reallocation of material and energy to acclimate to climate change).
- Results section. In cases of the difference between treatments being not statistically significant, one case is described as increase or decrease (e.g. line 331), another case is described as not significantly different (e.g. line 351). What is the threshold for authors to change the descriptions? I consider that this may lead readers to the direction of authors’ thought.
Furthermore, the authors show statistical information on interactions in three-way ANOVAs in Table S1, but these information are lacking in the text. - Figures 3a and 3b, and L615-617. If the growth rate hypothesis is working here, all data lay on a line as shown in Figure 3C. Different P storage contents, as shown below, between LL and HL may cause the separation of the regression line among light conditions. Similar discussion may be required to interpret the results for POP contents (not organic actually I think).
Specific comments
- To confirm carbonate chemistry in some case, salinity data are needed.
- Is the low DIP 0.43 umol/L an upper end of DIP conc in coastal waters? I do not consider this as a general case in coastal waters.
- Authors’ selection on total boron formulation also may be important.
- I understand the procedures remove PIC, so the measurements represent POC. On the other hand, for nitrogen and phosphorus inorganic forms are not removed from the filter samples, so these are not PON and POP but total particulate N and P. This may be critical to understand the variations in cellular contents of N and P. In particular, P storages occur in inorganic forms, and environmental drivers can alter the P storage capacity of the cells.
- I found no descriptions on protein-N:PON ratios.
- Results for POC:PON ratios are shown in Table S1 and Figure S4, but why are these not described in the text?
- The main cultures are conducted in 2 days, but authors conducted three pre-experimental cultures, resulting at least 8 generations acclimations. Therefore cells have enough time periods to change growth rate against the low phosphate conditions.
- POC:PON is not discussed in Results and Discussion sections, so this discussion is sudden and not readily acceptable for readers.
- L625-629. This discussion on carbon cycle is not match with this paragraph. A new paragraph should be made for this discussion.
- Figures and Tables. For this kind of experiments, data should be shown as a mean and standard error.
- Figures 1 and 2. I understand that statistical analyses are performed including two different light conditions (e.g. Figure 1a and b). I consider that two light conditions should be shown in a graph. Two columns can be shown for each treatment (e.g. HP+LC).
- Figure S4. The label of treatments for right edge in each panel should be “LP+HC” but not “LP+LC”.
- Figure S6. I do not understand the meanings for the authors showing these graphs.
- Figure S7. No descriptions on methodology for the gene analyses are found in the text.
Citation: https://doi.org/10.5194/egusphere-2022-947-RC2 -
AC3: 'Reply on RC2', Yong Zhang, 05 Jan 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-947/egusphere-2022-947-AC3-supplement.zip
Interactive discussion
Status: closed
-
CC1: 'Comment on egusphere-2022-947', Peng Jin, 07 Nov 2022
The manuscript reported a practical finding that responses of elemental content and macromolecule of the Emiliania huxleyito reduced phosphorus availability and ocean acidification depend on light intensity. The results of the study showed that under future ocean acidification and increasing light intensity conditions, enhanced carbon fixation could increase carbon storage in the phosphorus-limited regions of the oceans where E. huxleyi dominates the phytoplankton assemblages. This research could provide vital information for evaluating carbon cycle in marine ecosystems under global change.
The paper is well structured, the data are presented well, and the figures are well organized. However, some parts of the manuscript need further explanation and to be improved before acceptance for publication.
Line 60-61, 63-64: Please specify the light levels for “low light” and “high light”. Particulate organic nitrogen and protein contents at a cellular basis or on a total scale?
Line 62: I was wondering if it is more appropriate to use the term of “elevated pCO2” rather than “ocean acidification”, which has not been introduced in the text before. In fact, the authors used the terms of elevated pCO2 and ocean acidification (used in a broad sense to include effects of both elevated dissolved CO2 and the resulting decrease in pH) in the text, which is confusing. So, I would suggest the authors to select one term and use it consistently throughout the whole manuscript.
Line 140-141: Under reduced phosphorus availability, increasing light intensity and ocean acidification conditions. Should be cellular POC content? Please check this issue throughout the whole manuscript.
Line 143: Cellular PIC content?
Line 283-287 The method described in the paper is very similar to the phenol-sulfuric acid method for the determination of polysaccharides. Is the carbohydrate assay the same as the polysaccharide assay?
Line158-214 The description of At LL intensity (Part 1) is too tedious and complicated, please simplify. Just explain the reasons for selecting the light intensity, phosphate concentration, acidification conditions and the approximate experimental steps. Or put the picture of the experimental method in the supplement to the manuscript, after all, there are only three figures in the manuscript.
Line 290-292 The percentages of carbon and nitrogen contributed by carbohydrate and protein were an important element of this study. Please provide more details of this method.
Fig 2 and 3, if the purpose of the authors is to compare the different responses between the light level 40 and 300μmol photons m–2s–1, it would be better to merge Fig 1a and 1b.
Line 330-333: The p-values (0.48 and 0.68) indicated that the differences are not statistically significant. Also see this issue at Lines 365, 407, 413-414, 430 etc.
Line 337: See my comment above
Line 338-340: As the author concluded that there was significant interaction between CO2 and P (acted synergistically), it would be better to present the results of three-way ANOVA analysis in the text to support this statement. This issue occurred at Lines 360-362, and Lines 415-417 (included but not limited, please check throughout the whole manuscript).
Line 385-388: Please rephrase the wordings here.
Line 484-487: Please rephrase the wordings here.
Line 520-521: I cannot see any “regulation mechanisms” that were proposed in the present study.
Q8. Line 524 ‘Therefore, the reduced phosphorus availability dominantly reduces the RNA content (Fig. S5)’. Was the algal cell RNA content also measured in this study? The method for this determination was not described in the M&M section, at least.
Line 545: ‘(Rokitta et al., 2016; Zhang et al., 2020; Wang et al., 2022) (Fig. S6)’?
Line 555 ‘…..and small subunit ribosomal protein S3E, S5E, SAE (PR-S3E, PR-S5E, RP-SAE) in E. huxleyi (Fig. S7)’. Please provide references for this statement.
Line 574: The authors found that more POC were allocated to carbohydrates but not to protein under high light intensity, reduced phosphorus availability and ocean acidification. This is a quite interesting finding. So, what is the possible reason for this? Could you please explain?
Citation: https://doi.org/10.5194/egusphere-2022-947-CC1 -
AC1: 'Reply on CC1', Yong Zhang, 05 Jan 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-947/egusphere-2022-947-AC1-supplement.zip
-
AC1: 'Reply on CC1', Yong Zhang, 05 Jan 2023
-
RC1: 'Comment on egusphere-2022-947', Anonymous Referee #1, 25 Nov 2022
Dr Zhang and colleagues evaluate the interactive effect of changes on multiple environmental drivers (namely phosphorous concentration, pCO2 and light intensity) on the elemental and macromolecule content of the model coccolithophore species Emiliania huxleyi. Authors identify that multiple stressors interact on the physiological response of E. huxleyi and that underlying mechanisms are complex. For example, authors identify that reduced phosphorus availability results in a reduction of both particulate organic nitrogen and protein contents under low light intensity, but not under high light intensity. Interestingly, reduced phosphorus concentration in combination with ocean acidification result in an increase in both POC and carbohydrate contents only under high light conditions. A large body of evidence indicate that coccolithophores are sensitive to projected changes in oceanic conditions driven by ongoing human-induced climate change, such as ocean acidification and changes in nutrient supply, mixed layer depth and light intensity. Given their abundance and fundamental role in the biological and carbonate counter pumps, changes in coccolithophore performance will most likely have impacts in the oceanic carbon cycle and marine ecosystems. Therefore, there is an urgent need of studies such as the one presented here to evaluate how multiple environmental drivers affect key marine organism in order to predict how ongoing environmental change will impact marine ecosystems. The paper is clearly written, the figures are appropriate and the findings interesting and useful for the scientific community. Therefore, I recommend acceptance of this manuscript after the comments listed below have been addressed.
Lines 84-85. The sentence “These ocean changes expose phytoplankton cells within the UML to multiple drivers,” is vague. Do authors mean that environmental changes in the UML will expose phytoplankton cells to physiological stress? Please clarify.
Line 109. Authors could dedicate a sentence or two to the importance/relevance of multi-stressor experiments highlighting that numerous environmental factors will simultaneously change in the future ocean and therefore, this kind of experiments are needed to evaluate the response of different organisms to ongoing environmental change.
Line 149. The specialized reader would appreciate an SEM picture of the coccosphere and or coccoliths either in the main text or as supplementary material.
Line 151. could authors mention the date when this strain was isolated?
Line 510 Coccolithophores play a complex role in the carbon cycle through production and export of organic carbon to depth but also through the carbonate counter pump (releasing CO2 during the calcification process). Authors should clarify this in the text.
Line 530. Could authors explain (or speculate) about the metabolic process behind the relationship between low light intensity and nitrate uptake reduction?
Citation: https://doi.org/10.5194/egusphere-2022-947-RC1 -
AC2: 'Reply on RC1', Yong Zhang, 05 Jan 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-947/egusphere-2022-947-AC2-supplement.zip
-
AC1: 'Reply on CC1', Yong Zhang, 05 Jan 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-947/egusphere-2022-947-AC1-supplement.zip
-
AC2: 'Reply on RC1', Yong Zhang, 05 Jan 2023
-
RC2: 'Comment on egusphere-2022-947', Anonymous Referee #2, 21 Dec 2022
December 21, 2022
Reviewer’s comments for
Ms. Ref No.: egusphere-2022-947
Title: Responses of elemental content and macromolecule of the coccolithophore Emiliania huxleyi to reduced phosphorus availability and ocean acidification depend on light intensity
Authors: Yong Zhang et al.
Submitted to: Biogeosciences
General comments
The authors show interesting experimental data on the responses of an important coccolithophore to changing three environmental drivers. Culture experiments are carefully designed and conducted. Results are complex and result descriptions can be more accomplished but acceptable. I found some concern in the present manuscript. The following comments should be considered before this paper being considered for publishing in Biogeosciences.
Major comments
- I consider that a message from the present title (the importance of light condition on the coccolithophore responses) does not link with the conclusion of this paper (reallocation of material and energy to acclimate to climate change).
- Results section. In cases of the difference between treatments being not statistically significant, one case is described as increase or decrease (e.g. line 331), another case is described as not significantly different (e.g. line 351). What is the threshold for authors to change the descriptions? I consider that this may lead readers to the direction of authors’ thought.
Furthermore, the authors show statistical information on interactions in three-way ANOVAs in Table S1, but these information are lacking in the text. - Figures 3a and 3b, and L615-617. If the growth rate hypothesis is working here, all data lay on a line as shown in Figure 3C. Different P storage contents, as shown below, between LL and HL may cause the separation of the regression line among light conditions. Similar discussion may be required to interpret the results for POP contents (not organic actually I think).
Specific comments
- To confirm carbonate chemistry in some case, salinity data are needed.
- Is the low DIP 0.43 umol/L an upper end of DIP conc in coastal waters? I do not consider this as a general case in coastal waters.
- Authors’ selection on total boron formulation also may be important.
- I understand the procedures remove PIC, so the measurements represent POC. On the other hand, for nitrogen and phosphorus inorganic forms are not removed from the filter samples, so these are not PON and POP but total particulate N and P. This may be critical to understand the variations in cellular contents of N and P. In particular, P storages occur in inorganic forms, and environmental drivers can alter the P storage capacity of the cells.
- I found no descriptions on protein-N:PON ratios.
- Results for POC:PON ratios are shown in Table S1 and Figure S4, but why are these not described in the text?
- The main cultures are conducted in 2 days, but authors conducted three pre-experimental cultures, resulting at least 8 generations acclimations. Therefore cells have enough time periods to change growth rate against the low phosphate conditions.
- POC:PON is not discussed in Results and Discussion sections, so this discussion is sudden and not readily acceptable for readers.
- L625-629. This discussion on carbon cycle is not match with this paragraph. A new paragraph should be made for this discussion.
- Figures and Tables. For this kind of experiments, data should be shown as a mean and standard error.
- Figures 1 and 2. I understand that statistical analyses are performed including two different light conditions (e.g. Figure 1a and b). I consider that two light conditions should be shown in a graph. Two columns can be shown for each treatment (e.g. HP+LC).
- Figure S4. The label of treatments for right edge in each panel should be “LP+HC” but not “LP+LC”.
- Figure S6. I do not understand the meanings for the authors showing these graphs.
- Figure S7. No descriptions on methodology for the gene analyses are found in the text.
Citation: https://doi.org/10.5194/egusphere-2022-947-RC2 -
AC3: 'Reply on RC2', Yong Zhang, 05 Jan 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-947/egusphere-2022-947-AC3-supplement.zip
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Yong Zhang et al.
Yong Zhang et al.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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