The Increase in the Karstification–Photosynthesis Coupled Carbon Sink and Its Implication for Carbon Neutrality

Round 1

Reviewer 1 Report

Comments on the MS agronomy-1884760: The increase in the karstification-photosynthesis coupled carbon sink and its implication for carbon neutrality, submitted by Yanyou Wu and Yansheng Wu

 

The review covers an interesting topic that is relevant for Agronomy. In my opinion, there are some points that should be clarified before final acceptance.

 

1- First, I have to mention that I am a plant physiologist, my main expertise is photosynthesis with a background (B.Sc.) in agronomy. So for me and for most of the readers of Agronomy, more details concerning the karstification process and the carbon biogeochemical cycle are needed to clarify a possible confusion arising from two apparently contradictory affirmations, 1) The dissolution of carbonate rocks has a profound effect on carbon sinks on short time scales (li.69-70) and 2) From the geological process of carbonate dissolution on land to marine sedimentation, karst geological action does not produce net carbon sinks (li.77-78), or “Karst geological action by itself is a 0-carbon sink process (li. 72, 358)”. I understand the importance of time scale. Globally, vegetation (dead and alive) is an important C sink, but a single non-woody plant is just a transient sink. In that case, the term biosequestration seems more appropriate.

 

2- Another important aspect to improve in this review is the references to previous works concerning the coupling between karstification and photosynthesis. The references supporting the karstification-photosynthesis coupling (36, 42, and 43) are from the author(s) of this review, and there no references to other authors that have previously shown such coupling (for examples):

Sun  et al. 2021 Dynamics in riverine inorganic and organic carbon based on carbonate weathering coupled with aquatic photosynthesis in a karst catchment, Southwest China Water Research 189(19):116658 DOI: 10.1016/j.watres.2020.116658

Rui Yanget al.  (2020) Temporal variations in riverine hydrochemistry and estimation of the carbon sink produced by coupled carbonate weathering with aquatic photosynthesis on land: an example from the Xijiang River, a large subtropical karst-dominated river in China.  Environmental Science and Pollution Research volume 27, p. 13142–13154

Cao et al. 2018 Global significance of the carbon cycle in the karst dynamic system: evidence from geological and ecological processes. China Geology Volume 1, Issue 1, March 2018, Pages 17-27

3- The title announces “The increase in the karstification-photosynthesis coupled carbon sink” but this review presents the nature and the importance of this coupling. I may have missed some points, but I did not see clearly in the text that the importance of this coupling (in tern of C flux) is increasing.

4-I found that Figure 2 is not well connected to the text and therefore is not very helping. On the contrary, I spent too much time trying to understand it, but it adds little or not all to figure 1. If k + ki is the karstification of carbonate rocks, ki cannot be the amount of root-originated HCO3- used by plants (rather originating from carbonate rocks?). Also, the variable s is not defined.

5- Line 217 :  Please explain in few word the bidirectional isotope tracer culture technology. Also, what kind of “metabolic regulation technology” do you refer? (li. 209-210).

6- In Table 1, the units for Karst carbon sink intensity are tCO₂ km^-2 y^-1, and the same units are used for the Carbon sink fluxes in Table 2. It is important to be more consistent.

7- Also in Table 1, the “Average dis-solution rate” and the Karst carbon sink intensity are exactly the same thing, the latter is obtained by multiplying the former by a factor of 4.64.  

8- Li. 254: the expression “amount of dissolution” seems incorrect. Rather the rate…

9- Li, 167: 4 3

9- The conclusion is inefficiently written. The sentences seem to be disconnected, so the text is not fluid.  The factors, driver and pivot of the karstification-photosynthesis coupling are respectively bicarbonate ions, bicarbonate uses by plants and carbonic anhydrase. What is the difference between a factor, a driver and a pivot? Also, the conclusion does not support the title, i.e. the “increase in the karstification-photosynthesis coupled carbon sink”.

 

Author Response

Questions: (1)

1- First, I have to mention that I am a plant physiologist, my main expertise is photosynthesis with a background (B.Sc.) in agronomy. So for me and for most of the readers of Agronomy, more details concerning the karstification process and the carbon biogeochemical cycle are needed to clarify a possible confusion arising from two apparently contradictory affirmations, 1) The dissolution of carbonate rocks has a profound effect on carbon sinks on short time scales (li.69-70) and 2) From the geological process of carbonate dissolution on land to marine sedimentation, karst geological action does not produce net carbon sinks (li.77-78), or “Karst geological action by itself is a 0-carbon sink process (li. 72, 358)”. I understand the importance of time scale. Globally, vegetation (dead and alive) is an important C sink, but a single non-woody plant is just a transient sink. In that case, the term biosequestration seems more appropriate.

Reply:

Thanks for your good comments.Your understanding is very worthy of appreciation.

From geological time scale, dissolution and deposition of carbonate rocks are balanced. Therefore, karst geological action by itself is a 0-carbon sink geological process.

We revised as following:

Karstification by itself is a 0-carbon sink geological process due to the balance of dissolution and deposition of carbonate rocks on a billion-year long time scale (Line 78-79).

Karst geological action by itself is a 0-carbon sink process on a billion-year long time scale. (Line 390-391).

The short time scale here refers to the time scale generally concerned by human society.

We added in the review as following (Line 71-77):

From short time scale, the development and utilization of fossil fuels released a large amount of carbon dioxide in advance due to human activities, especially the industrial revolution, which breaks the balance between the sequestration of carbon dioxide and the release of carbon dioxide, and conversely affect carbonate rocks dissolution. Meanwhile, the lag in plant development and evolution led to the insufficient photosynthetic carbon sequestration. Therefore, the effect of carbonate rocks dissolution on carbon sinks is more profound on short time scale.

 

Questions: (2)

2- Another important aspect to improve in this review is the references to previous works concerning the coupling between karstification and photosynthesis. The references supporting the karstification-photosynthesis coupling (36, 42, and 43) are from the author(s) of this review, and there no references to other authors that have previously shown such coupling (for examples):

Sun  et al. 2021 Dynamics in riverine inorganic and organic carbon based on carbonate weathering coupled with aquatic photosynthesis in a karst catchment, Southwest China Water Research 189(19):116658 DOI: 10.1016/j.watres.2020.116658

Rui Yanget al.  (2020) Temporal variations in riverine hydrochemistry and estimation of the carbon sink produced by coupled carbonate weathering with aquatic photosynthesis on land: an example from the Xijiang River, a large subtropical karst-dominated river in China.  Environmental Science and Pollution Research volume 27, p. 13142–13154

Cao et al. 2018 Global significance of the carbon cycle in the karst dynamic system: evidence from geological and ecological processes. China Geology Volume 1, Issue 1, March 2018, Pages 17-27

Reply:

Thanks for your good comments. We added these references in our manuscript.

44.  He S., Yu S., Pu J., Yuan Y., Zhang C. Dynamics in riverine inorganic and organic carbon based on carbonate weathering coupled with aquatic photosynthesis in a karst catchment, Southwest China. Water Res 2021, 189, 116658.
45.  Yang R., Sun H., Chen B., Yang M., Zeng Q., Zeng C., HuangJ.,Luo H.,Lin D. Temporal variations in riverine hydrochemistry and estimation of the carbon sink produced by coupled carbonate weathering with aquatic photosynthesis on land: an example from the Xijiang River, a large subtropical karst-dominated river in China. Environ Sci Pollut R 2020, 27, 13142-13154.
46.  Cao J.H., Wu X., Huang F., Hu B., Groves C., Yang H., Zhang C.L. Global significance of the carbon cycle in the karst dynamic system: evidence from geological and ecological processes. China Geol2018,1, 17-27.

 

Questions: (3)

3- The title announces “The increase in the karstification-photosynthesis coupled carbon sink” but this review presents the nature and the importance of this coupling. I may have missed some points, but I did not see clearly in the text that the importance of this coupling (in tern of C flux) is increasing.

Reply:

Thanks for your good comments.The total photosynthesis of plants includes assimilation of carbon dioxide from the atmosphere and bicarbonate from the soil. Assuming that the plant uses 10% of bicarbonate (originated from karst carbon sink) (Figure 2), its total photosynthetic capacity is 110% that of the plants that only assimilate carbon dioxide from the atmosphere. In this way, the photosynthetic area will be 1.1 times that of the plants that only assimilate carbon dioxide from the atmosphere, and in the second year, its assimilation area will be 1.1 * 1.1 times that of the plants that only assimilate carbon dioxide from the atmospher. According to this calculation: The carbon sink capacity of a 10-year woody plant with a karstification-photosynthesis coupling of 10% is 1.6 times that with a karstification-photosynthesis coupling of 5% (1.10¹⁰/1.05¹⁰),

 

We  revised as following

In fact, karstification that is not coupled with photosynthesis has limited carbon sink capacity, but if karstification has a high coupling with photosynthesis, its carbon sink capacity is extremely huge. Theoretically, the carbon sink capacity of a 8-year woody plant with karstification-photosynthesis coupling of 10% will be twice that without karstification-photosynthesis coupling. The carbon sink capacity of a 10-year woody plant with a karstification-photosynthesis coupling of 10% is 1.6 times that with a karstification-photosynthesis coupling of 5% (1.10¹⁰/1.05¹⁰), thus the karst carbon sink capacity is twice that of the latter.(Line 381-388)

 

Questions: (4)

4-I found that Figure 2 is not well connected to the text and therefore is not very helping. On the contrary, I spent too much time trying to understand it, but it adds little or not all to figure 1. If k + ki is the karstification of carbonate rocks, ki cannot be the amount of root-originated HCO₃^- used by plants (rather originating from carbonate rocks?). Also, the variable s is not defined.

Reply:

Thanks for your good comments. The understanding of Figure 2 needs to be linked to Figure 1 and Figure 3. Figure 1 illustrated karstification-photosynthesis coupling processes and their role in the water-carbon balance in nature. While figure 3 illustrated carbonic anhydrase is pivotal in karstification-photosynthesis coupling on cycle of water–carbon. Carbonic anhydrase is highly spatiotemporally heterogeneous and sensitive to the environment and is dubbed the karstification "mortise", catalyzing the biogeochemical cycle of water–carbon and even other elements, regulating the migration and transformation of substances between different interfaces, and maintaining the biodiversity and stability of the system. k+ki is the apparent karst carbon sink of carbonate rock, which includes the apparent karst basic carbon sink k and intermediate carbon sink ki from karstification-photosynthesis coupling. Carbonic anhydrase can not only rapidly catalyze the CO₂ hydration reaction, improve the conversion rate between CO₂ and H⁺ and HCO₃^- but also catalyze the dissolution and deposition of carbonate rocks, ki represents the part of carbonate rock dissolved and converted bicarbonate that is used by plants. And s is the carbon sink of soil.(Line 200 )

 

Questions: (5)

5- Line 217 :  Please explain in few word the bidirectional isotope tracer culture technology. Also, what kind of “metabolic regulation technology” do you refer? (li. 209-210).

Reply:

Thanks for your good comments. We had changed as following(Line 216-228):

Therefore, to solve the problem of signal interference during inorganic carbon conversion and isotope exchange, we successfully developed a bidirectional isotope tracer culture technology. Bidirectional  isotope tracer culture technology is to simultaneously label and culture two identical plants with two kinds of bicarbonates at different stable carbon isotope ratios (the difference more than10‰), respectively, eliminate signal interference in the process of inorganic carbon transformation and isotope exchange by using parallel isotope difference signals, and finally analyze and quantify the utilization information of different inorganic carbon sources. Now, bidirectional isotope tracer culture technology has become a promising technique for analyzing and quantifying the utilization of different inorganic carbon sources. Using this technique, combined with metabolic regulation technology (such as applying specific inhibitors), bicarbonate and CO₂ utilization by plants were quantified [35,37-39,41-42].

 

Questions: (6)

6- In Table 1, the units for Karst carbon sink intensity are tCO₂ km^-2 y^-1, and the same units are used for the Carbon sink fluxes in Table 2. It is important to be more consistent.

Reply:

Thanks for your good comments. Table 1 shows the rate of dissolution measured by the carbonate-rock-tablet test method for different land use types, while Table 2 shows carbon sink fluxes measured by the solute load method from several different karst catchments. Although the carbon sink flux units are the same, the research objects (land types and karst catchments) and experimental methods are different.

 

Questions: (7)

7- Also in Table 1, the “Average dissolution rate” and the Karst carbon sink intensity are exactly the same thing, the latter is obtained by multiplying the former by a factor of 4.64.  

Reply:

Thanks for your good comments. Keeping the units of Karst carbon sink intensity and Carbon sink fluxes consistent.

The average dissolution rate calculation formula is as follows [64]:

E = ( W1－W2) × 10³ × 360 /( T × S),

E is the “Average dissolution rate” ( mg cm^-2y^-1 ); W1 is the initial weight of the specimen (g); W2 drying weight (g) for the specimen after retrieval; ( W1 -W2 ) for the specimen weight difference during burial time ( g ) ; T is the number of days of burial (d); S is the specimen surface area ( approx. 28.91 cm² )

The karst carbon sink intensity calculation formula is as follows:

F = E × R × 2M1 /M2 × 10

F is the “Karst carbon sink intensity” ( tCO₂ km^-2y^-1 ) ; E is the “Average dissolution rate” ( mg cm^-2·y^-1 );  The purity of carbonate rock R for rock test sheet is 0. 97; M1 is CO2 with a molecular weight of 44; M2 is CaMg(CO3)2 with a molecular weight of 184. So, F=0.97 ×2 ×44/188 ×10=4.64 × E

Questions: (8)

8- Li. 254: the expression “amount of dissolution” seems incorrect. Rather the rate…

Reply:

Thanks for your kindly reminding, we have revised the comments as the follows:

“ As seen from Table 1, the rate of dissolution varies depending on land use, different types of vegetation or the same vegetation type for different observations.” (line 273-274)

Table 1. Dissolution of different land use types (Line 267)

 

Questions: (9)

9- Li, 167: 4 3

Reply:

Thanks for your good comments. We deleted this line. Other subheadings had be changed accordingly. (Line 177)

 

Questions: (10)

10- The conclusion is inefficiently written. The sentences seem to be disconnected, so the text is not fluid.  The factors, driver and pivot of the karstification-photosynthesis coupling are respectively bicarbonate ions, bicarbonate uses by plants and carbonic anhydrase. What is the difference between a factor, a driver and a pivot? Also, the conclusion does not support the title, i.e. the “increase in the karstification-photosynthesis coupled carbon sink”.

Reply:

Thanks for your good comments. We had changed as following (Line 390-409):

Karst geological action by itself is a 0-carbon sink process on a billion-year long time scale. Uncoupled karstification limits photosynthetic carbon sequestration by plants. Karstification-photosynthesis coupling driven by bicarbonate utilization of plants and pivoted by carbonic anhydrase, can promote inorganic carbon assimilation in plants and the dissolution of carbonate rocks, thereby stabilizing and increasing the capacity of karst carbon sinks and photosynthetic carbon sinks. Karstification-photosynthesis coupling determines the carbon sink of karst ecosystems. Full use of the adaptation strategies of karst-adaptable plants with high karstification-photosynthesis coupling can maximize carbon sequestration and the enhancement effect of plants in karst areas. Finally, a carbon sequestration system encompassing ecological restoration, rocky desertification control and sustainable use of plant resources can be developed.

Author Response File: Author Response.docx

Reviewer 2 Report

This is an overall solid review which thoroughly addresses a subject which tends to be most addressed in one particular field in a manner that is comprehensible to other fields.  Figure 1 in particular is very well-done.  I do have a few comments for overall readability:

 

Line 30: "an increase rate of 50%" - this is an increase, not a rate

Line 48: "the edge of Australia" - please be more specific

Lines 50-52: not quantifiable statements, please clarify without descriptions like "the most beautiful".

Line 85: Is there an alternate term that could be used for "double-space structure"?  This is not a common term and almost all usage of it seems to go back to a single paper, which in context makes the usage of this term confusing to a reader.

Section 2.1 is entitled "karst drought" but never explains to the reader what this actually is; it can be inferred from context but saying it directly would help.

Lines 220-226 discuss share of carbon fixation from presumably karst-derived bicarbonate and give carbon fixation rates, but what are these rates when growing without karst?

Author Response

Questions: (1)

Line 30: "an increase rate of 50%" - this is an increase, not a rate

Reply: Thanks for your kindly reminding, we have revised the comments as the follows (Line 28-30):

Since the Industrial Revolution, atmospheric carbon dioxide (CO₂) concentrations have increased from 280 ppm before the Industrial Revolution to 421 ppm today, an increase of 50% [1].

 

Questions: (2)

Line 48: "the edge of Australia" - please be more specific

Reply: Thanks for your good comments, we have revised the corresponding parts in the manuscript according to your kindly suggestions. The global distribution of karst is mainly concentrated in low latitudes, and a map shows the karst distribution in Australia is concentrated in the southern region by Hartmann, “The new global lithological map database GLiM: A representation of rock properties at the Earth surface, Geochem. Geophys. Geosyst., 2012, 13, Q12004, doi:10.1029/2012GC004370.”, so we rewrite it as follows：

“The global karst distribution area is nearly 22 million km², accounting for approximately 15% of the planet’s land area, and the population living on karst areas is approximately one billion and is mainly concentrated in low latitudes, including Southwest China, Southeast Asia, Central Asia, the Mediterranean, the east coast of North America, the Caribbean, the west coast of South America and the south of Australia.”(Line44-48).

 

Questions: (3)

Lines 50-52: not quantifiable statements, please clarify without descriptions like "the most beautiful".

Reply: Thanks for your kindly reminding, we have revised the comments as the follows:

“Karst in Southwest China is known for its larger continuous distribution area and for being the complete development type, the beautiful landscape and the fragile ecological environment” (Line 50-52)

 

Questions: (4)

Line 85: Is there an alternate term that could be used for "double-space structure"?  This is not a common term and almost all usage of it seems to go back to a single paper, which in context makes the usage of this term confusing to a reader.

Reply: Thanks for your kindly reminding, we have rewrite it as follows (Line 91-93):

“Long-term strong karstification has caused the hydrogeological structure in karst areas to be a special spatial structure on the surface and underground.”

 

Questions: (5)

Section 2.1 is entitled "karst drought" but never explains to the reader what this actually is; it can be inferred from context but saying it directly would help.

Reply: Thanks for your good comments. we have rewrite it as follows（Line 89- 93）

Drought is mostly caused by low precipitation, while karst drought are mainly caused by special geological environments, because the average annual rainfall in the karst region of Southwest China is sufficient, up to 1000~1800 mm[17].

 

Questions: (6)

Lines 220-226 discuss share of carbon fixation from presumably karst-derived bicarbonate and give carbon fixation rates, but what are these rates when growing without karst?

Reply: Thanks for your kindly reminding. We did ignore this detail and needed to explain it accordingly. Bicarbonate is used to simulate karst environments, and in non-karst cases, bicarbonate is not added in medium. Specifically, when growing in non-karst environments, the the share of karst-derived bicarbonate utilization of plants is 0.

Reviewer 3 Report

The article is about the karstification strategies. The authors reviewed the current strategies and noted that uncoupled karstification with photosynthesis limit the capability of CO2 sequestration. They described the dissolution  depending on the lands used. It is an interesting review summarizing the carbon sink capability of karstification. The review would have benefit to describe quantitatively the mass balance and the quantity of CO2 sequestrated. It recommended to consolidate the analysis.

Please find below possible improvements:   

1- section 1 introduction: The sentence is not correct "280 ppm before the Industrial Revolution to 421 ppm today, an increase rate of 50%" 280 ppm is not a rate but a concentration

2- line 234 , PEG can be detrimental for microorganisms. Authors should explain the role of PEG in this experiment and if the toxicity of PEG has been checked. 

3- Table 1 , Authors should discuss whether the CO2 sink intensity described in the table 1 can have an effect on the global CO2 concentration in the atmosphere. In other words, can these sinks 1) stop the increase of CO2 or 2) decrease the CO2 concentration in the atmosphere ?   

4 - figure 1 should specify where the carbon sink is happening

5 - Table 1 , authors should explain the difference between "Average dissolution rate" and " Karst carbon sink intensity". The reader understands that the carbon sequestration is the rate of precipitate calcium carbonate minus the dissolution rate.

6- figure 3 is very instructive , could the flux be described in the text or in another table?

7- section 6 is interesting, especially the end sentence, with the carbon sink capability over 10 year. Still it is not clear for the reader where / how it was calculated that coupling of 10% is 1.6 times than 5%? Can it be quantify ?

8- Authors should discuss , at least briefly about the capability of karstification to balance global emission of CO2 due to industries

  

Author Response

Questions: (1)

1- section 1 introduction: The sentence is not correct "280 ppm before the Industrial Revolution to 421 ppm today, an increase rate of 50%" 280 ppm is not a rate but a concentration

Reply: Thanks for your kindly reminding. We have rewrite it as follows (L (Line 28-30).

“Since the Industrial Revolution, atmospheric carbon dioxide (CO₂) concentrations have increased from 280 ppm before the Industrial Revolution to 421 ppm today, an increase of 50% [1].”

 

Questions: (2)

2- line 234 , PEG can be detrimental for microorganisms. Authors should explain the role of PEG in this experiment and if the toxicity of PEG has been checked.

Reply:

Thanks for your good comments. As a widely used chemical reagent, PEG 6000 have a high osmotic pressure after dissolution, and are often used as drought simulation reagents in plant physiological studies. The harm of PEG 6000 to microorganisms depends on the concentration used. In the concentration range used in these related experiments, the harm of PEG 6000 to microorganisms is slight.（Line 251-261）

 

Questions: (3)

3- Table 1 , Authors should discuss whether the CO₂ sink intensity described in the table 1 can have an effect on the global CO₂ concentration in the atmosphere. In other words, can these sinks 1) stop the increase of CO₂ or 2) decrease the CO₂ concentration in the atmosphere ?

Reply:

Thanks for your good comments. The data in Table 1 illustrate that CO₂ sink intensity are related to land use types, plant distributions and species. We have rewrite it as follows( line 271-282)

Dissolving 1 mol of carbonate rock can consume 1 mol of CO₂ from the atmosphere, contributing to the decline of atmospheric CO₂ concentration. Therefore, the rate of carbonate rock dissolution can reflect the karst carbon sink intensity. As seen from Table 1, the rate of dissolution varies depending on land use, different types of vegetation or the same vegetation type for different observations. Karst carbon sink intensities range from 0.65 tCO₂ km^-2y^-1 to 557.26 tCO₂ km^-2y^-1, with an average value of 98.60 tCO₂ km^-2y^-1 and a median of 28.81 tCO₂ km^-2y^-1, which is only 2% of the average carbon sink capacity of karst forests (1447.05 tCO₂ km^-2y^-1) [71].

 

Questions: (4)

4 - figure 1 should specify where the carbon sink is happening

Reply:

Thanks for your good comments. We pointed out carbon source and carbon sink process in the note of Figure 1.

Figure 1. Karstification-photosynthesis coupling processes and their role in the water-carbon balance in nature. Carbonate rocks (lithosphere) are dissolved under the action of water (hydrosphere) and carbon dioxide (atmosphere) to form Ca²⁺ and bicarbonate (biosphere)(carbon sink process). Ca²⁺ combines with bicarbonate to precipitate calcium carbonate (CaCO₃) into the lithosphere(carbon source process). Plants split bicarbonate and water to release oxygen and carbon dioxide, then assimilate carbon dioxide to form carbohydrates (CH₂O) (biosphere)(carbon sink process). Finally, organisms utilize oxygen to decompose carbohydrates into carbon dioxide that enters the atmosphere and water that enters the hydrosphere (carbon source process).

Questions: (5)

5 - Table 1 , authors should explain the difference between "Average dissolution rate" and " Karst carbon sink intensity". The reader understands that the carbon sequestration is the rate of precipitate calcium carbonate minus the dissolution rate.

Reply:

Thanks for your good comments. Dissolving 1 mol of carbonate rock can consume 1 mol of CO₂ from the atmosphere, contributing to the decline of atmospheric CO₂ concentration. Therefore, the rate of carbonate rock dissolution can reflect the karst carbon sink intensity..Here, carbon sequestration is equivalent to karst carbon sink intensity.(Line 271-273)

 

Questions: (6)

6- figure 3 is very instructive , could the flux be described in the text or in another table?

Reply: Thanks for your kindly reminding. We have rewrite it as follows(Line 315-323):

Characterized by its continuous distribution, abundance, specificity, and efficient and rapid catalysis of the unique mutual conversion reaction between CO₂ and HCO₃^- in karst ecosystems, carbonic anhydrase is the only key biological enzyme that can closely couple karstification with photosynthesis, that is, inorganic and organic carbon between carbonate rocks-soil-vegetation-atmosphere. On the one hand, CA catalyzes the dissolution of carbonate rocks and the deposition of calcium carbonate to regulate karstification at the rock-soil interface; On the other hand, CA catalyzes the reversible conversion between carbon dioxide and bicarbonate in the soil solution and plants to regulate photosynthesis and respiration of plants (Figure 3).

 

Questions: (7)

7- section 6 is interesting, especially the end sentence, with the carbon sink capability over 10 year. Still it is not clear for the reader where / how it was calculated that coupling of 10% is 1.6 times than 5%? Can it be quantify ?

Reply:

Thanks for your good comments.

The total photosynthesis of plants includes assimilation of carbon dioxide from the atmosphere and bicarbonate from the soil. Assuming that the plant uses 10% of bicarbonate, its total photosynthetic capacity is 110% that of the plants that only assimilate carbon dioxide from the atmosphere. In this way, the photosynthetic area will be 1.1 times that of the plants that only assimilate carbon dioxide from the atmosphere, and in the second year, its assimilation area will be 1.1 * 1.1 times that of the plants that only assimilate carbon dioxide from the atmospher. According to this calculation: The carbon sink capacity of a 10-year woody plant with a karstification-photosynthesis coupling of 10% is 1.6 times that with a karstification-photosynthesis coupling of 5% (1.10¹⁰/1.05¹⁰) (Line 383-388)

 

Questions: (8)

8- Authors should discuss , at least briefly about the capability of karstification to balance global emission of CO₂ due to industries

Reply:

Thanks for your good comments. Carbon sink capacity is equivalent to the capability of karstification to balance global emission of CO₂ due to industries. Therefore, we rewrite it as follows (Line 381-385):

In fact, karstification that is not coupled with photosynthesis has limited carbon sink capacity, but if karstification has a high coupling with photosynthesis, its carbon sink capacity is extremely huge. Theoretically, the carbon sink capacity of a 8-year woody plant with karstification-photosynthesis coupling of 10% will be twice  that without karstification-photosynthesis coupling. The carbon sink capacity of a 10-year woody plant with a karstification-photosynthesis coupling of 10% is 1.6 times that with a karstification-photosynthesis coupling of 5% (1.10¹⁰/1.05¹⁰), thus the karst carbon sink capacity is twice that of the latter.