Responses of Marine Diatom–Dinoflagellate Interspecific Competition to Different Phosphorus Sources

Round 1

Reviewer 1 Report

The manuscript presents very interesting data on the studies of competition between dinoflagellates and diatoms. The study was designed very well  and conclusions are supported by results. Due to extending harmful algal blooms the topic of MS is very actual. Authors gave comprehensive discussion with wide literature. It is rare case, when initially the paper written very well and don't require improvement. I think that paper can be published after checking of spelling and English grammar. 

 

Author Response

Responses to Reviewer #1’ comments

 

The manuscript presents very interesting data on the studies of competition between dinoflagellates and diatoms. The study was designed very well and conclusions are supported by results. Due to extending harmful algal blooms the topic of MS is very actual. Authors gave comprehensive discussion with wide literature. It is rare case, when initially the paper written very well and don't require improvement. I think that paper can be published after checking of spelling and English grammar.

Response: Thank you very much for your affirmation of our research, and we have checked the spelling and English grammar in this revised version.

Author Response File: Author Response.pdf

Reviewer 2 Report

Excellent paper that can be improved with some suggestions

Comments for author File: Comments.pdf

Author Response

Responses to Reviewer #2’ comments.

INTRODUCTION

1. Line 50: “Include concepts from Smayda and Reynolds, 2001, Community assembly in marine phytoplankton: application of recent models to harmful dinoflagellate blooms.”

Response: Thank you for this helpful suggestion. We have added this reference in the introduction. Please see the red reference number ([8]) in the first paragraph of introduction section.

2. Line 76: “I think it is important to include information about: A model of phytoplankton growth on multiple nutrients based on the Michaelis-Menten-Monod uptake, Droop’s growth and Liebig’s law.”

Response: Thank you for this important suggestion. Numerous studies have used the Lotka–Volterra model (Uchida et al., 1999) to simulate the growth interaction between two species in bi-algal cultures (Wang et al., 2006; Tameishi et al., 2009; Qiu et al., 2011; Wang et al., 2012; Wang et al., 2020). Therefore, we selected the classical interspecific competition model (Lotka–Volterra model) in this study. Considering the complex marine environmental conditions, in the future, we will try to apply this submodel to interspecific competition study and compare it with the classical model. In addition, we have added the description of interspecific competition model in the introduction and related discussion.

Please see the red part in the last paragraph of introduction section. The detailed description is as follows: and we use the classic interspecific competition model (Lotka–Volterra model) to estimate interspecific competition parameters [36].

Please see the red part in the discussion section: the first paragraph of Section 4.1. “Interspecific competition mechanism under P-sufficient condition”. The detailed description is as follows: Besides, other researchers also proposed and analyzed a model of phytoplankton dynamics which includes Michaelis-Menten-Monod uptake of nutrients, Droop's growth and the Liebig's law of the minimum [46]. Considering the complex marine environmental conditions, we will try to apply this submodel to interspecific competition study in the future and compare it with the classical model.

The relevant references:

Uchida, T.; Toda, S.; Matsuyama, Y.; Yamaguchi, M.; Kotani, Y.; Honjo, T. Interactions between the red tide dinoflagellates Heterocapsa circularisquama and Gymnodinium mikimotoi in laboratory culture. J. Exp. Mar. Biol. Ecol. 1999, 241(2), 285–299.

Wang, Y.; Yu, Z.M.; Song, X.X.; Zhang, S.D. Interactions between the bloom-forming dinoflagellates Prorocentrum donghaiense and Alexandrium tamarense in laboratory cultures. J. Sea Res. 2006, 56(1), 17–26.

Tameishi, M.; Yamasaki, Y.; Nagasoe, S.; Shimasaki, Y.; Oshima, Y.; Honjo, T. Allelopathic effects of the dinophyte Prorocentrum minimum on the growth of the bacillariophyte Skeletonema costatum. Harmful Algae 2009, 8, 421–429.

Qiu, Y.C.; Yamasaki, Y.; Shimasaki, Y.; Gunjikake, H.; Matsubara, T.; Nagasoe, S.; Etoh, T.; Matsui, S.; Honjo, T.; Oshima, Y. Growth interactions between the raphidophyte Chattonella antiqua and the dinoflagellate Akashiwo sanguinea. Harmful Algae 2011, 11, 81-87.

Wang, F.; Ge, W.; Chai, C.; Wang, J.Y.; Zhao, X.F. Effects of nutritional condition on the competitive parameters of Prorocentrum donghaiense and Skeletonema costatum. Chin. J. Appl. Ecol. 2012, 23(5), 1393–1399. (In Chinese with English abstract)

Wang, R.; Xue, Q.N.; Wang, J.T.; Tan, L.J. Competitive interactions between two allelopathic algal species: Heterosigma akashiwo and Phaeodactylum tricornutum. Mar. Biol. Res. 2020, 16(1), 1–12.

MATERIALS AND METHOD

1. Line 93: “It is a low intensity, which is related in nature to the depth of compensation. It can limit the growth of phytoplankton adapted to high saturation indices. Justify this low irradiance.”

Response: Thank you for this important comment. In order to clarify the mechanism between the succession of diatom–dinoflagellate blooms in the ECS in spring and summer, we checked the relevant literature and the photosynthetic characteristics of algae, and found that the light intensity was low when dinoflagellate blooms occurred in the East China Sea (Wang et al., 2008). Wang et al. (2008) also reported that P. donghaiense and K. mikimotoi have the ability to maintain growth under these conditions. Thus, we have added relevant descriptions in section 2.1. “Algae and culture conditions”. The detailed description is as follows: At the same time, we measured the effective quantum yield (F_q'/F_m', represent the photosynthetic physiological state) of algae using a pulse amplitude modulated fluorometer (PHYTO-PAM-ED, Walz, Effeltrich, Germany) before each subsequent experiment. The F_q'/F_m' values of S. costatum, P. donghaiense, and K. mikimotoi with a light intensity of 40 μmol m^-2s^-1 were 0.60 ± 0.02, 0.54 ± 0.04, and 0.54 ± 0.03, respectively, and there was no significant difference from the data measured under high light of 125 μmol m^-2s^-1 (P < 0.05). We assured the F_q'/F_m' values of algae were above 0.5 to ensure the vitality of algae was normal.

The relevant reference:

Wang, A.J.; Wang, X.L.; Han, X.R.; Li, Y.B.; Zhu, C.J. Effects of solar radiation on the growth and succession of harmful algae in the East China Sea in spring. Mar. Environ. Sci. 2008, 27(2), 144-148. (In Chinese with English abstract)

2. Line 94: “It is important to mention characteristics of the light source. Fluorescent or incandescent. Available wavelengths?”

Response: Thank you for these helpful suggestions. We have added a detailed description of the light source in 2.1. Algae and culture conditions section. The detailed description is as follows: S. costatum, P. donghaiense, and K. mikimotoi were maintained at 20 ℃ under 40 μmol m^-2s^-1 of cool-white fluorescent illumination (400-700 nm) with a light:dark cycle of 12:12h.

3. Line 106: “Similar to the Yangtze River Estuary has a low DIP concentration of 1.1-0.3 μM. Eutroficated?”

Response: Thank you for the careful reading on the details. The Yangtze River Estuary is a typical eutrophic sea area, but diatom blooms consume a large amount of phosphorus every spring, resulting in a very low phosphorus concentration in this area, while the nitrogen content is still high (Li et al., 2009; Zhao, 2010; Zhang et al., 2012).

The relevant references:

Li, J.; Glibert, P.M.; Zhou, M.J.; Lu, S.H.; Lu, D.D. Relationships between nitrogen and phosphorus forms and ratios and the development of dinoflagellate blooms in the East China Sea. Mar. Ecol. Prog. Ser. 2009, 383 (14), 11–26.

Zhao, D.Z. Occurrence Regularity of Marine Red Tide Disaster in Typical Areas in China, 1st ed.; Marine Press: Beijing, China, 2010.

Zhang, X.; Shi, X.Y.; Zhang, C.S.; Han, X.R. Nutrient characteristics in red-tide algal succession in Changjiang Estuary and adjacent sea areas. Mar. Environ. Sci. 2012, 31(6), 817-820. (In Chinese with English abstract)

4. Line 121: “Sorokin,Yu.I. (1999) Radioisotopic Methods in Hydrobiology. Springer, Heidelberg. 326 pp. In this type of work it is important to consider the assimilation.”

Response: Thank you for this important suggestion. It is indeed a better method to measure the nutrient content based on the radioisotopic method. Thanks for pointing out the direction for my future research.

 

RESULTS

1. Section 3.1(Figure 1): “The difference between figure A and B is not clear. Sc in bi-algal culture vs Pd in bi-algal culture (fig.1.2.3). I suggest homogenizing the units on the "y" axes (0 a 100, 0 a14). They can use post break on the axis (Fig 1,2,3).”

Response: Thank you for this helpful suggestion. We have revised these figures according to your suggestion.

2. Section 3.2(Figure 2): “The difference in scale of the Y-axis does not allow to observe differences in graphs.”

Response: Thank you for this helpful suggestion. We have revised these figures according to your suggestion.

3. Line 245: “The drastic drop in C figures does not appear to be a response to nutrients alone. What other possibilities can you discuss?”

Response: Thank you for this important comment. We analyzed this phenomenon in the discussion section. Please see the red part in discussion “the third paragraph of section 4.2. Interspecific competition mechanism under P deficient conditions”. The detailed description is as follows: Another possible reason for this discrepancy is the allelopathy between the two algae under P-deficient conditions. The allelopathy of some algal species is also enhanced under low nutrient conditions [67–70]. Li et al. [71] established that allelopathic compounds (or toxins) were the main antialgal mechanism of K. mikimotoi. Moreover, K. mikimotoi could produce lipophilic toxins, a characteristic volatile compound (cubenol), a reactive oxygen species with hemolytic and cytotoxic activity, and could cause cell burst in other plankton [71]. By contrast, P. donghaiense is a non-toxic dinoflagellate and does not release known phytotoxins [72]. In addition, this phenomenon also occurs in interspecific competition among other algae, for example, the results reported by Ji et al. [73] suggested that P. micans inhibited the growth of S. costatum and K. mikimotoi by the release of allelochemical(s). Wang et al. [74] found that A. minutum growth was inhibited when grown in S. costatum filtrate, but the filtrate of A. minutum exerted no allelopathic activity on S. costatum. Accordingly, further studies are required to clarify these aspects.

4. Section 3.4(Figure 4): “I suggest homogenizing the units on the "y" axes (0 a 100, 0 a14) They can use post break on the axis (Fig 1,2,3)”

Response: Thank you for this helpful suggestion. We have revised this figure according to your suggestion.

 

DISCUSSION

1. Line 314: “Tubay, J., Ito, H., Uehara, T. et al. The paradox of enrichment in phytoplankton by induced competitive interactions. Sci Rep, 3, 2835(2013). https://doi.org/10.1038/srep02835. This article may be useful for the discussion of the topic.”

Response: Thank you for this helpful suggestion. We have carefully read this document, and the conclusions on interspecific competition are very meaningful. We have added discussion related to this article. Please see the red part in the discussion of the third paragraph of 4.1. “Interspecific competition mechanism under P-sufficient condition”. The detailed description is as follows: Furthermore, the biodiversity loss of phytoplankton due to the outbreak of large-scale blooms, the interspecific competition between the bloom-forming species will lead to the simplification of species, affecting the stability of the marine ecosystem [55]. Hence, further investigations are needed to explore the underlying effects of the “diatom–dinoflagellate–diatom” bloom succession on marine biodiversity.

2. Line 320: “What are the survival strategies? Are there physiological adjustments? How is the model of nutrient assimilation in the three species?”

Response: Thank you for this helpful suggestion. The survival strategy in this study mainly refers to the growth of algae, which is characterized by the standing quantity of algae cell density, nutrient absorption and utilization (Bi et al., 2021). There are also some physiological indicators such as changes in alkaline phosphatase, please see the AP changes in the results (3.5. Changes in AP activity). We also presented some results on the absorption and utilization of P by these three algae. The relevant water quality changes please see in the results (3.4. Changes in DIP, DOP, and TP) and the relevant contents in the discussion section (Please see the red part in the discussion of the second paragraph of 4.1. “Interspecific competition mechanism under P-sufficient condition.”). The detailed description is as follows: One possible reason for this discrepancy is that despite the higher DIP absorption rate by S. costatum relative to that of P. donghaiense and K. mikimotoi (0.55×10^-3, 0.24×10^-3, and 0.30×10^-3 μM·cells^-1·h^-1, respectively, Fig. 4), when DIP was low in the late stage of the experiment, S. costatum cell density decreased significantly and its competitive advantage was reversed by dinoflagellates. In comparison to diatoms, dinoflagellates have higher AP affinity (this feature can indicate the ability of algae to hydrolyze DOP) to the DOP substrate and can express more AP [14,28], thus improving the utilization rate of DOP [31]. In the present research, the AP activities in the P. donghaiense and K. mikimotoi mono-algal cultures were significantly higher than those in the S. costatum mono- and bi-algal cultures whether under P-sufficient or P-deficient conditions (P < 0.05, Fig. 6). Therefore, P. donghaiense or K. mikimotoi has a stronger ability to hydrolyze DOP with AP relative to S. costatum.

The relevant reference:

Bi, R.; Cao. Z.; Ismar-Rebitz, S.M.H.; Sommer, U.; Zhang, H.L.; Ding, Y.; Zhao, M.X. Responses of marine diatom-dinoflagellate competition to multiple environmental drivers: Abundance, elemental, and biochemical aspects. Front. Microbiol. 2021, 12, 731786.

3. Line 328: “It is important to include the size of the organisms and their area to volume ratio. Assimilation capacity according to sizes scr strategies.”

Response: Thanks for your constructive comment. We have added the relevant analysis to test possible relationships between surface/volume of each microalga and the results of interspecific competition. Please see the red part in the discussion section of the third paragraph of 4.1. “Interspecific competition mechanism under P-sufficient condition”. The detailed description is as follows: Additionally, the higher growth rate of P. donghaiense may be affected by the surface/volume ratio of cell. Many studies revealed that small algae cells usually have high material transport efficiency and fast absorption rate of nutrients due to their higher surface/volume ratio and smaller diffusion boundary layer thickness, thus it tended to achieve a higher specific growth rate and maximum cell density [53,54]. Huang et al. [33] obtained that the cell volume ratio of K. mikimotoi and P. donghaiense was approximately 2, we also measured the volume of two kinds of algae are 1422 and 721 μm³, respectively (Unpublished data). The cell size of P. donghaiense was smaller and its specific surface area was higher, indicating P. donghaiense could propagate and absorb phosphorus nutrients more quickly.

4. Line 344: “What is the light saturation index of these species. 40 μmol m^-2s^-1 may be limiting factor.”

Response: Thanks for your constructive comment. In this study, the light saturation index of these algae was not measured, but we found that there was no significant difference of the photosynthetic physiological parameters (F_q'/F_m') of these algae between low light (40 μmol m^-2s^-1) and high light (125 μmol m^-2s^-1), indicating that this light intensity could not become a limiting factor for the growth of algae. In addition, the light intensity is also low due to the impact of plum rain when the HABs outbreak in the East China Sea in spring and summer, we set up this light intensity in the experiments. The detailed description please see the red part in section “2.1. Algae and culture conditions”.

5. Line 374: “Include reference.”

Response: Thank you for the careful reading on the details. We have added the reference number.

6. Line 377: “I think it should be discussed with what is proposed by strategies scr Smayda and Reynoldsed.”

Response: Thanks for your constructive comment. We have added relevant discussions based on this document. Please see the red part in the discussion section of the first paragraph of 4.2. “Interspecific competition mechanism under P deficient conditions”. The detailed description is as follows: Finally, in the face of the complex environment of the sea area during HAB, HAB community assembly and dynamics reflect two basic selection features—life-form and species-specific selection, which commonly held life-form properties override phylogenetic properties in bloom-species selection [8]. Some studies reported that three primary adaptive strategies consistent with C-S-R strategies recognized among freshwater phytoplankton species characterize the component dinoflagellate species [60-62], and it has also been successfully applied in the succession of marine HAB species [8].

Author Response File: Author Response.pdf

Reviewer 3 Report

Overall, the topic is interesting but is a very common research. I found some of the description of the paper to be not that detailed, while the description and explanation of some of the important points were missing or lacking. Review comments must be addressed first to accept this manuscript for publication. Also, the novel point in this study should be emphasized. Why is this study important and how is this research different from other previously reported ones. 

Major Comments:

1) Please strongly justify (in the introduction, discussion and conclusion) the NOVELTY of this study. How different is it from previous studies done using the same method from other microalgal species. Also, may I request the author(s) to provide a brief survey of previous studies done bialgal cultural experiments using S. costatum, P. donghaiense and K. mikimotoi and include this in the introduction and discussion part of the manuscript.

2) Several phytoplankton species interact through competition for nutrients and light, and smaller microalgal species are considered advantageous in the competition due to surface/volume considerations. Did the author(s) consider the advantages and disadvantages of the surface/volume of each microalgae in the growth experiment (both for P sufficient and P deficient experiment as well as the mono- and bi-algal cultural experiment) for S. costatum, P. donghaiense or K. mikimotoi? I suggest that the authors should include this in the discussion part of the manuscript.

3) The relative initial cell densities of S. costatum, P. donghaiense and K. mikimotoi are critical in determining the outcome of competition in co-culture experiment. The initial cell densities in each in co-cultures experiment are almost similar to each other, which meant that the small- sized species might lose the spatial advantages in the in- terspecific competition. The author(s) should also address this concern in the results and discussion part of the manuscript. 

4) Cell contact and allelopathy have been considered as important factors affecting growth interactions between microalgae in a bi-algal cultural experiment. Many microalgal species are known to be inhibited by allelopathic effects from other microalgae. Did the author checked the presence or absence of allelopathic substances in the culture experiments (especially in P deficicient) of S. costatum, P. donghaiense and K. mikimotoi ? The author(s) should include this in the results and discussion part of the manuscript. 

 

Author Response

Responses to Reviewer #3’ comments.

General comment:

Overall, the topic is interesting but is a very common research. I found some of the description of the paper to be not that detailed, while the description and explanation of some of the important points were missing or lacking. Review comments must be addressed first to accept this manuscript for publication. Also, the novel point in this study should be emphasized. Why is this study important and how is this research different from other previously reported ones.

Response: We deeply appreciate your helpful suggestions, which are important for improving the quality of this paper. Combined with our subsequent investigation and summary of relevant literature, we further summarized the innovation points of this study. The main innovation points as follow: in view of the fact that DIP and DOP coexist in the ocean, the results of inter-specific competition experiment conducted with a single P source as phytoplankton nutrient may be different from the real results. In comparison to diatoms, dinoflagellates have higher AP affinity to the DOP substrate and can express more AP, thus improving the utilization rate of DOP, which may lead to dinoflagellates have competitive advantages against diatoms in interspecific competition. However, up to date, no further research has been done in this regard. We hypothesized that DIP and DOP, as coexisting P sources, play a key role in the interspecific competition of algae, may have different results from single P sources. These findings can also provide strong evidence for revealing the succession of diatoms and dinoflagellates blooms in the ECS.

 

The main changes and responses are listed as follows:

Major Comments:

1) Please strongly justify (in the introduction, discussion and conclusion) the NOVELTY of this study. How different is it from previous studies done using the same method from other microalgal species. Also, may I request the author(s) to provide a brief survey of previous studies done bialgal cultural experiments using S. costatum, P. donghaiense and K. mikimotoi and include this in the introduction and discussion part of the manuscript.

Response: Thank you for these helpful suggestions. We have added the novelty of this study in the introduction, discussion and conclusion sections. The detailed description is as follows:

Introduction section- In view of the fact that DIP and DOP coexist in the ocean [12], the results of interspecific competition experiment conducted with a single P source as phytoplankton nutrient may be different from the real results. This is because different algae have different abilities and mechanisms to utilize DIP or DOP [27,28], which may lead to differences in the results of interspecific competition. However, so far, no further research has been done in this regard. We hypothesized that DIP and DOP, as coexisting P sources, play a key role in the interspecific competition of algae, and may have different results from single P sources. In this study, in order to clarify the mechanism between the succession of diatom–dinoflagellate blooms in the ECS in spring and summer, we set up experiments with conditions as close as possible to the marine environment (such as approximately 20 °C water temperature, coexistence of DIP and DOP, and low light intensity when dinoflagellate blooms occurred in May and June, P. donghaiense, and K. mikimotoi have the ability to maintain growth under these conditions [35]).

Discussion section- However, prior works that conducted experiments with only DIP or DOP may have different interspecific competition results from those that under sea environment conditions when blooms occurred. Therefore, to simulate the succession of bloom-forming species in the ECS in spring and summer, we set the different P concentrations with two P sources in this study. To our knowledge, this is the first report about marine diatom–dinoflagellate interspecific competition to different phosphorus sources with both DIP and DOP.

Conclusion section- Our findings are different from the outcomes of the competition between diatoms and dinoflagellates of previous studies under P-sufficient conditions, especially when DIP and DOP coexist.

In addition, we have briefly introduced the research progress of interspecific competition among S. costatum, P. donghaiense and K. mikimotoi, please see the red part in the third paragraph of introduction for specific modifications. The detailed description is as follows: For the main bloom-forming species S. costatum, P. donghaiense, and K. mikimotoi, some researchers reported S. costatum has strong competitiveness against P. donghaiense under DIP-rich conditions, and others gained the opposite competition results appeared under DIP-deficient conditions in the laboratory experiments [24,29,30] and mesocosm experiments [25,31]; besides, S. costatum also has strong competitiveness against K. mikimotoi under DIP-rich conditions regardless of the N:P ratio [32]. Some studies also showed that the interspecific competition between P. donghaiense and K. mikimotoi had their own advantages at different initial concentrations under DIP-rich conditions [33,34]. In addition, Ou et al. [18] found that S. costatum outcompeted P. donghaiense irrespective of the DIP or DOP substrate.

 

2) Several phytoplankton species interact through competition for nutrients and light, and smaller microalgal species are considered advantageous in the competition due to surface/volume considerations. Did the author(s) consider the advantages and disadvantages of the surface/volume of each microalgae in the growth experiment (both for P sufficient and P deficient experiment as well as the mono- and bi-algal cultural experiment) for S. costatum, P. donghaiense and K. mikimotoi? I suggest that the authors should include this in the discussion part of the manuscript.

Response: Thank you for these helpful suggestions. We have added the relevant analysis to test possible relationships between surface/volume ratio of each species and results of interspecific competition. Please see the red part in the discussion section of the third paragraph of 4.1. “Interspecific competition mechanism under P-sufficient condition”. The detailed description is as follows: Additionally, the higher growth rate of P. donghaiense may be affected by the surface/volume ratio of cell. Many studies revealed that small algae cells usually have high material transport efficiency and fast absorption rate of nutrients due to their higher surface/volume ratio and smaller diffusion boundary layer thickness, thus it tended to achieve a higher specific growth rate and maximum cell density [53,54]. Huang (2009) [33] obtained that the cell volume ratio of K. mikimotoi and P. donghaiense was approximately 2, we also measured the volume of two kinds of algae are 1422 and 721 μm³, respectively (Unpublished data). The cell size of P. donghaiense was smaller and its specific surface area was higher, indicating P. donghaiense could propagate and absorb phosphorus nutrients more quickly.

 

3) The relative initial cell densities of S. costatum, P. donghaiense and K. mikimotoi are critical in determining the outcome of competition in co-culture experiment. The initial cell densities in each in co-cultures experiment are almost similar to each other, which meant that the small- sized species might lose the spatial advantages in the interspecific competition. The author(s) should also address this concern in the results and discussion part of the manuscript.

Response: Thank you for this important suggestion. Some previous studies have also set different initial concentrations in interspecific competition, and the results also show that they will have a greater impact on competition results (Wang et al., 2006; Wang and Tang, 2008; Huang et al., 2009). On the other hand, Wang et al. (2013) found that S. costatum dominates P. donghaiense under high-nutrient conditions, and the interaction was independent of the initial cell densities. Therefore, in this study we have set the same initial cell densities in the bi-algal cultures. In future experiments, we will also try to carry out the effects of different initial cell densities on interspecific competition, especially under low phosphorus conditions.

The relevant references:

Wang, Y.; Yu, Z.M.; Song, X.X.; Zhang, S.D. Interactions between the bloom-forming dinoflagellates Prorocentrum donghaiense and Alexandrium tamarense in laboratory cultures. J. Sea Res. 2006, 56(1), 17–26.

Wang, Y.; Tang, X.X. Interactions between Prorocentrum donghaiense Lu and Scrippsiella trochoidea (Stein) Loeblich III under laboratory culture.Harmful Algae. 2008, 7, 65–75.

Huang, K.X.; Xie, Y.H.; Lu, S.H. The interspecific competition between Karenia mikimotoi and Prorocentrum donghaiense in co-cultural systems. Ecological Science. 2009, 28(2), 118–122. (In Chinese with English abstract)

Wang, J.T.; Zhang, Y.W.; Li, H.; Cao, J. Competitive interaction between diatom Skeletonema costatum and dinoflagellate Prorocentrum donghaiense in laboratory culture. J. Plankton Res. 2013, 35(2), 367–378.

 

4) Cell contact and allelopathy have been considered as important factors affecting growth interactions between microalgae in a bi-algal cultural experiment. Many microalgal species are known to be inhibited by allelopathic effects from other microalgae. Did the author checked the presence or absence of allelopathic substances in the culture experiments (especially in P deficicient) of S. costatum, P. donghaiense and K. mikimotoi? The author(s) should include this in the results and discussion part of the manuscript.

Response: Thank you for this important suggestion. Many studies have shown that allelopathy plays a very important role in interspecific competition (Ji et al., 2011; Wang et al., 2017, 2020). It is a pity that in this study, we focused on the impact of different phosphorus sources on the interspecific competition of algae, and did not set up experiments on allelopathy. Our future research will focus on the experiment of allelopathy on interspecific competition. In addition, we strengthened the discussion in this regard during the discussion, please see the red part in discussion section of the second and third paragraph of 4.2. “Interspecific competition mechanism under P deficient conditions”. The detailed description is as follows:

Second paragraph- The previous studies documented that the autoallelopathy of S. costatum plays an important role in the competition and succession between S. costatum and P. donghaiense, especially under P-deficient conditions [24,65]. However, as far as we know, the allelopathic effect of P. donghaiense or K. mikimotoi filtrate on the growth of S. costatum remains unclear. Given strong evidence of the autoinhibitory effect in S. costatum, the role of the allelopathic effect of P. donghaiense or K. mikimotoi in their competitions should be studied further.

Third paragraph- Another possible reason for this discrepancy is the allelopathy between the two algae under P-deficient conditions. The allelopathy of some algal species is enhanced under low nutrient conditions [67–70]. Li et al. [71] established that allelopathic compounds (or toxins) were the main antialgal mechanism of K. mikimotoi. Moreover, K. mikimotoi could produce lipophilic toxins, a characteristic volatile compound (cubenol), a reactive oxygen species with hemolytic and cytotoxic activity, and could cause cell burst in other plankton [71]. By contrast, P. donghaiense is a non-toxic dinoflagellate and does not release known phytotoxins [72]. In addition, this phenomenon also occurs in interspecific competition among other algae, for example, the results reported by Ji et al. [73] suggested that P. micans inhibited the growth of S. costatum and K. mikimotoi by the release of allelochemical(s). Wang et al. [74] found that A. minutum growth was inhibited when grown in S. costatum filtrate, but the filtrate of A. minutum exerted no allelopathic activity on S. costatum. Accordingly, further studies are required to clarify these aspects.

The relevant references:

Ji, X.Q.; Han, X.T.; Zheng, L.; Yang, B.J.; Yu, Z.M.; Zou, J.Z. Allelopathic interactions between Prorocentrum micans and Skeletonema costatum or Karenia mikimotoi in laboratory cultures. Chinese Journal of Oceanology and Limnology. 2011, 29(4), 840–848.

Wang, R.; Wang, J.T.; Xue, Q.N.; Sha, X.Y.; Tan, l.j.; Xin Guo, X. Allelopathic interactions between Skeletonema costatum and Alexandrium minutum. Chemistry and Ecology. 2017, 33(6), 485–498.

Wang, R.; Xue, Q.N.; Wang, J.T.; Tan, L.J. Competitive interactions between two allelopathic algal species: Heterosigma akashiwo and Phaeodactylum tricornutum. Mar. Biol. Res. 2020, 16(1), 1–12.

Author Response File: Author Response.pdf