Significant Synergy Effects of Biochar Combined with Topdressing Silicon on Cd Reduction and Yield Increase of Rice in Cd-Contaminated Paddy Soil

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript entitled (Significant synergy effects of biochar combined with topdressing silicon on Cd reduction and yield increase of rice in Cd-contaminated paddy soil) explained that the application of either biochar (BC) or silicon (Si) can effectively reduce Cd concentrations in various parts of the rice plant (roots, stems, and milled rice). Also, the combination of biochar and Si (TBC+JSi) shows synergistic effects in reducing Cd concentrations in milled rice to levels below the safety value standard. This is a significant finding with potential practical applications in mitigating Cd contamination in rice. While the manuscript provides valuable insights into the combined application of biochar (BC) with topdressing silicon (Si) in reducing cadmium (Cd) concentration in milled rice, improving rice yield, and enhancing soil fertility, there are a few questions:
1- The manuscript contains grammatical errors and awkward phrasing in some sentences. Proofreading for language and style is recommended to enhance clarity and readability.
2- In the statistical part, which statistical test was employed to assess and compare the mean data?
3- Some information, such as the concentrations of Cd in different rice tissues, is repeated in different part of the text. This repetition can be minimized to avoid redundancy.
4- The increase in Cd concentrations in leaves after the application of BC and Si may raise concerns. The manuscript should provide a more in-depth analysis or discussion on the potential implications of this increase, as it seems counterintuitive to the overall goal of reducing Cd contamination.
5- Based on the information provided in the Supplementary, given that a certain amount of cadmium accumulates in the leaves, and according to the division reported concerning the direct effects of cadmium on the reduction of photosynthesis, and considering that no difference was observed in leave Cd partitioning ratio, what interpretation do the authors provide? Are these aspects related?
6- The discussion refers to findings from previous studies (e.g., Wang et al.) without providing specific details. It would be beneficial to include full references for readers to access the original studies and gain a more comprehensive understanding of the background and context.
7- It is mentioned in the discussion that the behavior of Cd in the soil-plant system is complex and that the deep mechanisms need further study. This part acknowledges the complexity of Cd behavior in the soil-plant system but doesn't delve deeply into the specific complexities or potential confounding factors.
8- In the discussion of the manuscript, the inclusion of these articles will help increase the depth of the content.
• Zeng, P., Zhou, H., Deng, P., Gu, J. and Liao, B., 2023. Effects of topdressing silicon fertilizer at key stages on uptake and accumulation of arsenic in rice. Environmental Science and Pollution Research, 30(11), pp.31309-31319.
• Berahim, Z., Omar, M.H., Zakaria, N.I., Ismail, M.R., Rosle, R., Roslin, N.A. and Che’Ya, N.N., 2021. Silicon improves yield performance by enhancement in physiological responses, crop imagery, and leaf and culm sheath morphology in new rice line, PadiU Putra. BioMed research international, 2021.

 

 

Comments on the Quality of English Language

I have no idea

Author Response

Response to Reviewer 1 Comments (Agronomy-2867596)

1. Summary
Thank you very much for taking the time to review our manuscript. The assessments and suggestions given by you are very helpful for us to revise and improve the manuscript. Please find the detailed point-by-point responses below and the corrections highlighted in red track changes in the re-submitted files. If there are some need to be revised, please do not hesitate to point it. Thank you again!
2. Questions for General Evaluation	Reviewer’s Evaluation	Response and Revisions
Does the introduction provide sufficient background and include all relevant references?	Can be improved	Thanks for your recognition and evaluation of this manuscript. The manuscript does needs further improvement before it would be published.
Are all the cited references relevant to the research?	Yes	Thank you！
Is the research design appropriate?	Can be improved	Thanks. Your suggestion is an important guiding for our research.
Are the methods adequately described?	Yes	Thank you！
Are the results clearly presented?	Can be improved	Thanks. The results had been further improved.
Are the conclusions supported by the results?	Can be improved	Thanks. The conclusions had been improved.

 

3. Point-by-point response to Comments and Suggestions for Authors

COMMENT: The manuscript entitled (Significant synergy effects of biochar combined with topdressing silicon on Cd reduction and yield increase of rice in Cd-contaminated paddy soil) explained that the application of either biochar (BC) or silicon (Si) can effectively reduce Cd concentrations in various parts of the rice plant (roots, stems, and milled rice). Also, the combination of biochar and Si (TBC+JSi) shows synergistic effects in reducing Cd concentrations in milled rice to levels below the safety value standard. This is a significant finding with potential practical applications in mitigating Cd contamination in rice. While the manuscript provides valuable insights into the combined application of biochar (BC) with topdressing silicon (Si) in reducing cadmium (Cd) concentration in milled rice, improving rice yield, and enhancing soil fertility, there are a few questions.

RESPONSE: Thanks for your recognition and evaluation of this manuscript. The questions are very valuable for improving the manuscript. Thank you again!

 

COMMENT:  1- The manuscript contains grammatical errors and awkward phrasing in some sentences. Proofreading for language and style is recommended to enhance clarity and readability

RESPONSE: Thanks for your suggestion. The grammar and language of the manuscript have been proofread and revised thoroughly.

 

COMMENT:  2- In the statistical part, which statistical test was employed to assess and compare the mean data?

RESPONSE: Good question! It The method of statistical test was listed from line 166 to 168 in original manuscript. But there was a written mistake. Now it had been revised as one-way ANOVA followed by Duncan's test (p＜0.05) were performed to analyze the experimental data with SPSS 26.0 software..

 

COMMENT: 3- Some information, such as the concentrations of Cd in different rice tissues, is repeated in different part of the text. This repetition can be minimized to avoid redundancy.

RESPONSE: 3: Excellent suggestion. The repeated information such as the concentrations of Cd in different rice tissues was deleted.

 

COMMENT: 4- The increase in Cd concentrations in leaves after the application of BC and Si may raise concerns. The manuscript should provide a more in-depth analysis or discussion on the potential implications of this increase, as it seems counterintuitive to the overall goal of reducing Cd contamination.

RESPONSE: 4: Good question and suggestion! In this paper, Cd concentrations in leaves after the application of BC and Si was raised significantly. The reason might be related to the effects of BC and Si on the growth and development of rice plants under Cd-polluted soil. Previous studies have showed that the application of BC and Si could alleviate the toxic effects of Cd on leaves (plants) and increase the Cd tolerance of leaves (plants), thus enhancing the retention capacity of Cd in leaves through immobilizing Cd in inert forms [1]. In addition, the application of BC and Si could decrease the bioavailability of Cd in soil and the total Cd absorbed by plants, but increase the partitioning ration in leaves, and reduce the transport of Cd to edible grain [2-3]. So, it doesn’t counterintuitive to the overall goal of reducing Cd contamination.

 

• Pan, B.; Liu, B.; Cai, K.; Wang, W.; Tian, J.; Lv, W.; Cai, Y. Effects of silicon staged application on photosynthetic characteristics and matter accumulation in Cd-contaminated rice. Ecologica. Sinica. 2022, 42(14): 5934-5944.
• Bian, R.; Chen, D.; Liu, X.; Cui, L.; Li, L.; Pan, G.; Xie, D.; Zheng, J.; Zhang, X.; Zheng, J.; Chang, A. Biochar soil amendment as a solution to prevent Cd-tainted rice from China: Results from a cross-site field experiment. Eng. 2013, 58, 378-383
• El-Naggar, A.; Chang, S.; Cai, Y.; Lee, Y.; Wang, J.; Wang, S.; Ryu, C.; Rinklebe, J.; Ok, Y. Mechanistic insights into the (im)mobilization of arsenic, cadmium, lead, and zinc in a multi-contaminated soil treated with different biochars. Int. 2021, 156, 106638

 

 

COMMENT: 5- Based on the information provided in the Supplementary, given that a certain amount of cadmium accumulates in the leaves, and according to the division reported concerning the direct effects of cadmium on the reduction of photosynthesis, and considering that no difference was observed in leave Cd partitioning ratio, what interpretation do the authors provide? Are these aspects related?

RESPONSE: Good question! We agree with the review’s point that the photosynthesis of plants could be declined by Cd stress because of its toxic effect on leaves. But this toxic effect could be alleviated and the resistance of rice to Cd could be improved by the application of BC and Si [1,3]. Some physiological responses such as scavenging of ROS induced by Cd stress, Cd sequestration in leaves, chlorophyll synthesis, and so on could be motivated by the application of BC and Si [2-6]. Thus, the net photosynthetic rate could be improved and the photosynthetic function of rice could be extended, which would improve yield performance under Cd stress.

 

• Pan, B.; Liu, B.; Cai, K.; Wang, W.; Tian, J.; Lv, W.; Cai, Y. Effects of silicon staged application on photosynthetic characteristics and matter accumulation in Cd-contaminated rice. Ecologica. Sinica. 2022, 42(14): 5934-5944.
• Berahim, Z.; Omar, M.; Zakaria, N.; Ismail, M.; Rosle, R.; Roslin, N.; Che’Ya, N. Silicon improves yield performance by enhancement in physiological responses, crop imagery, and leaf and culm sheath morphology in new rice line, PadiU Putra. BioMed research international. Biomed Res. Int. 2021,2021, 6679787
• Farooq, M.; Detterbeck, A.; Clemens, S.; Dietz, K. Silicon-induced reversibility of cadmium toxicity in rice, Exp. Bot. 2016, 67, 3573–3585.
• Houben, D.; Evrard, L.; Sonnet, P. Beneficial effects of biochar application to contaminated soil on the bioavailability of Cd, Pb and Zn and the biomass production of rapeseed (Brassica napus). Biomass bioenergy. 2013, 57, 196-204
• Islam, M.; Zhu, J.; Xiao, L.; Khan, Z; Saqib, H; Gao, M.; Song, Z. Enhancing rice quality and productivity: Multifunctional biochar for arsenic, cadmium, and bacterial control in paddy soil. 2023, 342,140157
• Wang, Y.; Zhang, K.; Lu, L.; Xiao, X.; Chen, B. Novel insights into effects of silicon-rich biochar (Sichar) amendment on cad-mium uptake, translocation and accumulation in rice plants. Pollut. 2020, 265, 114772.

 

 

COMMENT: 6- The discussion refers to findings from previous studies (e.g., Wang et al.) without providing specific details. It would be beneficial to include full references for readers to access the original studies and gain a more comprehensive understanding of the background and context.

RESPONSE: 6: Thanks for your suggestion. The findings from previous studies (e.g., Wang et al.) had been revised and supplemented in discussion (line 334-338, red fonts).

 

COMMENT: 7- It is mentioned in the discussion that the behavior of Cd in the soil-plant system is complex and that the deep mechanisms need further study. This part acknowledges the complexity of Cd behavior in the soil-plant system but doesn't delve deeply into the specific complexities or potential confounding factors.

RESPONSE: Thank you for your comments! This paper mainly focused on the combined effect of BC with topdressing Si on the Cd uptake and rice yield, but rarely exhibited on the underlying mechanisms behind. In fact, the mechanisms involved in the Cd behavior in the soil-plant system is rather complicated, which might be clear elaborated step by step in multiple trials. The experiments conducted in this study have not involved in the underlying mechanisms much more, so the specific complexities or potential confounding factors have not been discussed deeply.

 

COMMENT: 8- In the discussion of the manuscript, the inclusion of these articles will help increase the depth of the content.

• Zeng, P., Zhou, H., Deng, P., Gu, J. and Liao, B., 2023. Effects of topdressing silicon fertilizer at key stages on uptake and accumulation of arsenic in rice. Environmental Science and Pollution Research, 30(11), pp.31309-31319.
• Berahim, Z., Omar, M.H., Zakaria, N.I., Ismail, M.R., Rosle, R., Roslin, N.A. and Che’Ya, N.N., 2021. Silicon improves yield performance by enhancement in physiological responses, crop imagery, and leaf and culm sheath morphology in new rice line, PadiU Putra. BioMed research international, 2021.

RESPONSE:8: Thank you for your suggestion! These references are helpful for further discussing the underling mechanism of the results. Thank you again!

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Author Response

Response to Reviewer 2 Comments (Agronomy-2867596)

1. Summary
Thank you very much for taking a lot of time to review our manuscript and give us many excellent suggestions. The constructive assessments and suggestions given by you are very helpful for us to revise and improve the manuscript. Please find the detailed point-by-point responses below and the corrections highlighted in red track changes in the re-submitted files. If there are some need to be revised, please do not hesitate to point it. Thank you again!
2. Questions for General Evaluation	Reviewer’s Evaluation	Response and Revisions
Does the introduction provide sufficient background and include all relevant references?	Can be improved	Thanks for your recognition and evaluation of this manuscript. The manuscript does needs further improvement before it would be published.
Are all the cited references relevant to the research?	Yes	Thank you！
Is the research design appropriate?	Yes	Thank you！
Are the methods adequately described?
Are the results clearly presented?	Can be improved	Thanks. The results had been further improved.
Are the conclusions supported by the results?	Can be improved	Thanks. The conclusions had been improved.

 

3. Point-by-point response to Comments and Suggestions for Authors

COMMENTS: The topic of this manuscript is timely and relevant for the journal. The text is generally well written, but the scientific background of the topic is poor.

RESPONSES: Thanks for your affirmation and the valuable comments and suggestions. The scientific background of the topic had been supplemented.  

COMMENTS: Abstract:

1. The abstract does not provide specific details about the methodology used in the study, such as the experimental design, sample size, or statistical analyses conducted. Including this information would give readers a better understanding of the study's validity and reliability.
2. The abstract mentions the effects of biochar and silicon on Cd concentrations in rice tissues and soil but does not specify the exact results or findings. Providing quantitative data or key results in the abstract would make it more informative and impactful.
3. The abstract states that the application of biochar and silicon increased soil nutrients and rice yield but does not mention the specific nutrients or the extent of the yield increase. Including this information would enhance the clarity and completeness of the abstract.
4. The abstract could benefit from a concise statement about the implications of the study findings for agriculture or environmental remediation. Including a brief discussion on the practical significance of the results would make the abstract more comprehensive.

RESPONSES:

1. Thanks for your comments! Considering that the submission system limits words numbers in the abstract (300 words), the methodology used in the study, such as the experimental design, sample size, or statistical analyses conducted, was not provided in details in the Abstract, because which were all fully given in the Materials and Methods.
2. We agreed with the review that the key results supported by quantitative data would enhance the clarity and completeness of the abstract. Data of Cd concentrations in rice tissues and soil had been supplemented.
3. Thanks! Data of the nutrients and yield increase had been added.
4. Thanks for your advice. A concise statement had been rewritten.

COMMENT: Introduction:

1. The introduction does not provide a clear and concise statement of the research objectives or hypotheses. Including a specific research question or aim at the beginning of the introduction would help orient readers to the study's purpose.
2. The introduction lacks a comprehensive review of relevant literature on the topic of biochar, silicon, and cadmium contamination in paddy soils. Incorporating more background information and citing key studies in the field would strengthen the introduction and provide context for the current research.
3. The introduction does not clearly establish the significance of the study or explain why the topic is important for agronomy or environmental science. Including a brief discussion on the relevance of the research to addressing current challenges or advancing knowledge in the field would enhance the introduction.
4. The introduction could benefit from a more structured approach, such as outlining the key sections or topics that will be covered in the paper. Providing a roadmap of the content to follow would improve the flow and organization of the introduction.

RESPONSE:

1. Thanks for your suggestion! The research objectives have been rewritten.
2. We agree with the review that citing key relevant literatures could strengthen the background information of the introduction, and which have been improved in revised manuscript.
3. The purpose and significance of the study have been further clarified.
4. Great suggestion for constructing paragraph! Some topics have been outlined in paragraph.

 

COMMENT: Material and Methods:

1. The Materials and Methods section lacks specific details about the sources of biochar and silicon used in the study. Providing information on the characteristics, origins, and preparation methods of these materials would enhance the reproducibility and transparency of the study.
2. The section does not include a detailed description of the experimental setup, including the number of replicates, controls used, and randomization procedures. Providing this information would help readers understand the robustness of the experimental design and the validity of the results.
3. The Materials and Methods section does not specify the methods used for data analysis, statistical tests performed, or criteria for significance. Including details on the statistical analyses conducted would clarify how the results were interpreted and evaluated.
4. The section lacks information on the specific instruments or equipment used for measuring Cd concentrations in soil and plant samples. Including details on the analytical methods, calibration procedures, and detection limits would improve the transparency and reliability of the results.
5. The Materials and Methods section does not provide information on how potential confounding factors or sources of variability were controlled during the experiments. Including details on measures taken to minimize bias or external influences would strengthen the study's methodology.

RESPONSE:

1. Thanks for your suggestion! The detailed information of the application of biochar and silicon had been rewritten in Material and Method.
2. Thanks! The detailed description of the experimental setup had been supplemented and revised.
3. Thank you! There were written mistakes in original manuscript. Now the method used for data analysis had been corrected.
4. The methods used for measuring Cd concentrations in soil and plant samples had been supplemented.
5. Good suggestion! In the process of conducting the experiment, other operations were basically the same except for the difference between the treatments.

 

COMMENT: Results and Discussion:

1. In the Results section, there is a reference to Figure 2, but the specific details of Figure 2 are not provided in the text. It would be helpful to include a brief description of the figure or refer to the correct figure.

Response: Thank you for your comments and suggestion! Figure 2 had been rewritten in detail in revised manuscript.

 

2. In the Discussion section, there is a statement about the reduction of Cd concentration in milled rice being less than the safety value standard of 0.20 mg·kg-1. However, the specific safety standard reference for Cd concentration in milled rice is not cited. Providing the source for this safety standard would strengthen the argument.

Response: Good suggestion! The source for this safety standard had been cited and supplemented in revised manuscript.

 

3. The discussion mentions the significant reduction of Cd concentration in milled rice by the TBC+JSi treatment but does not provide specific quantitative data or statistical analysis to support this claim. Including the exact percentage reduction or statistical significance would enhance the credibility of the statement.

Response: Thanks for your suggestion! The discussion mentions the significant reduction of Cd concentration in milled rice had been rewritten and corrected in the revised manuscript. The specific quantitative data had been supplemented.

 

4. The discussion could benefit from a more detailed explanation of the mechanisms through which biochar and topdressing silicon interact to reduce Cd uptake in rice plants. Providing additional information on the specific pathways or processes involved would enrich the discussion.

Response: Good suggestion! Some information involved in the mechanisms through which biochar and topdressing silicon interact to reduce Cd uptake in rice plants had been corrected and rewritten.

 

5. The Results section mentions interactions between biochar and topdressing silicon but does not elaborate on the nature of these interactions or provide a detailed analysis of the combined effects. Including a more in-depth discussion of the synergistic effects of the two treatments would enhance the interpretation of the results.

Response: Good suggestion! The detailed analysis of the combined effects had been provided in discussion in revised manuscript.

 

6. The figures and tables in the manuscript lack detailed captions or titles that clearly explain the content and significance of the data presented. Including informative titles or captions would help readers understand the key findings and interpretations without having to refer back to the text.

Response: Good suggestion! The detailed captions or titles had been improved, and figures had been redrawn.

 

7. Some figures or tables may be referenced in the text without providing a direct link or explanation of their relevance to the discussion. It would be beneficial to ensure that each figure or table is properly integrated into the text with clear references and explanations of their importance.

Response: Good suggestion! Some figures or tables referenced in the text had been explained clearly. If there are some, please do not hesitate to point out. Thank you again!

 

8. The figures and tables could benefit from more descriptive labels and legends to clarify the variables, units of measurement, and statistical significance indicated in the data. Improving the clarity of labels and legends would enhance the interpretability of the figures and tables.

Response: Good suggestion! Some figures had been repainted, and the clarity of labels and legends for figures and tables had been improved in revised manuscript.

 

9. In some cases, the figures or tables may contain errors in data presentation, such as inconsistent formatting, missing values, or unclear data points. Conducting a thorough review of the figures and tables to ensure accuracy and consistency in data representation would improve the overall quality of the visual aids.

Response: Thanks for your suggestion! All figures and table had been checked, some of which had been corrected in revised manuscript.

 

COMMENT: General questions:

1. What specific concentrations of biochar and topdressing silicon were used in the pot and field trials?

Response: Thanks! This information had been revised in manuscript. In 2.2 Experimental Design, lines 116 and 121 (original manuscript for review), the concentration of biochar and topdressing silicon applied in pot experiment were 100 g BC/pot (calculated as 20 g BC/kg soil) and 2.44 g Si/pot (calculated as 488 mg Si/kg soil), respectively. In line 131 to 132 (original manuscript for review), the dosage of biochar and silicon fertilizer in field experiment is 15 t·hm^-2 and 0.15 t·hm^-2 respectively.

 

2. How was the biochar prepared and applied in the study?

Response: Good question! The biochar used in this study was bought from the producer of Liaoning Jinhefu Agricultural Development Co., Ltd (China), which was pyrolyzed from rice straw at 600 ℃. (Line 102-103 in original manuscript)

 

3. What was the duration of the pot trial, and how frequently were the treatments applied?

Response: Thanks! The pot experiment was conducted from August 16^th to November 28^th, 2020.

 

4.How was the Cd concentration in rice plants measured in the study?

Response: Thank you for your question. The method of the Cd concentration in rice plants and soil measured in the study was forgotten to be marked. Now, it has been revised.

 

5.What were the soil characteristics of the Cd-contaminated paddy soil used in the field trials?

Response: Thank you for your question. In this study, the soil used in pot trials was sampled and collected from the field. So, the characteristics of the Cd-contaminated paddy soil used in the field trials was the same with the pot trials. Now this has been explained in manuscript.

 

6. Were there any interactions observed between biochar and topdressing silicon in terms of Cd reduction and yield increase?

Response: It is an interesting question. Yes, there was a significant synergistic interaction between biochar and topdressing silicon on the Cd reduction of milled and on the increase of rice yield. The concentration of Cd in milled rice treated by TBC+JSi was decreased by 22.7 and 10.52%, respectively, when compare to that by biochar and silicon alone, while the yield of TBC+JSi was increased by 9.59 and 9.74%, respectively.

 

7. What were the mechanisms proposed for the reduction of Cd uptake in rice plants by biochar and topdressing silicon?

Response: Good question! According to the results of this study and previous literatures, the mechanism proposed for the reduction of Cd uptake in rice plants by biochar and topdressing silicon might be speculated as following: (1) soil Cd bioavailability was declined through immobilization, adsorption, precipitation by biochar and silicon, thus decreasing Cd uptake by rice; (2) Biochar and silicon could enhance the detoxification of Cd including cell wall adsorption, cytoplasmic chelation, and vacuolar sequestration, thus reducing the transfer of Cd from root to stem, and to leaves and grains; (3) The combined use of biochar and topdressing Si synergistically promotes rice growth in Cd-contaminated environments, and more Cd were fixed in leaves. But the behavior of Cd in soil-plant system is very complex, the underling mechanisms needs to be further deeply studied.

 

8.Were there any adverse effects observed on rice growth or soil health due to the application of biochar and topdressing silicon?

Response: Good question! One of the adverse effects observed on rice might the increase of Cd concentration in leaves. The leaves accumulated a certain amount of Cd might cause potential harm to soil (if straw turnover) or to livestock (if used as forage). Therefore, the straw should be collected and centrally processed, which is a challenge in practical production. In addition, more cadmium was still remained in the soil, which yet exist potential risks to environments.

 

9. How did the treatments affect the nutrient content of the soil and rice plants?

Response: Excellent question! According to the results of this study and previous research, the nutrient content of the soil and rice plants affected by the treatments might through the following ways:

Biochar contains a certain amount of nutrients, which will be released when it is applied to soil. And it was also able to effectively improve the physicochemical properties of the soil due to its characters such as large specific surface area and well-developed pore structure, thus increasing soil nutrients contents. These nutrients could be absorbed by roots absorb, and then transported it to the overground, so the nutrient contents in rice was increased [1].

The addition of Si could affect the physicochemical and biochemical properties of paddy soils. As an alkaline substance, the hydrolysis of potassium silicate (K₂SiO₃⋅5H₂O) in soil system was stronger, and further promoted the activation of alkali nutrient elements (including Alkali-N, Olsen-P and Avail-K) [2]. Accordingly, the nutrients absorbed by rice plant also increased.

The combined application of BC with topdressing Si had a significant superposition effect on the soil nutrient contents, the reason might be that BC could provide a living environment and nutrients for microorganisms, while nutrients provided by K₂SiO₃ could be adsorbed by BC, and then the formation of oxygen-containing functional groups on the surface of BC was promoted and soil pH was increased yet. Finally soil fertility and plant nutrients were all improved [3].

[1] Hossain, M.; Bahar, M.; Sarkar, B.; Donne, S.; OK, Y.; Palansooriya, K.; Kirkham. M.; Chowdhury. S.; Bolan, N. Biochar and its importance on nutrient dynamics in soil and plant. Biochar. 2020,4, 379–420. https://doi.org/10.1007/s42773-020-00065-z

[2] Chandrakala, C.; Voleti, S.; Bandeppa, S.; Kumar, N.; Latha, P. Silicate Solubilization and Plant Growth Promoting Potential of Rhizobium Sp. Isolated from Rice Rhizosphere. Silicon. 2019, 11, 2895-2906. https://doi.org/10.1007/s12633-019-0079-2

[3] Sattar, A.; Sher, A.; Abourehab, M.; Ijaz, M.; Nawaz, M.; Ul-Allah, S.; Abbas, T.; Shah, A.; Imam, M.; Abdelsalam, N.; Hasan, M.; Abbas, A.; Javaid, M. Application of silicon and biochar alleviates the adversities of arsenic stress in maize by triggering the morpho-physiological and antioxidant defense mechanisms. Front. Environ. Sci. 2022,11, 979049. https://doi.org/10.3389/fenvs.2022.979049

 

10. What are the implications of these findings for sustainable agriculture practices in Cd-contaminated areas?

Response: Thank you for your question. The results of this study implied that the combined application of biochar with topdressing silicon might be considered as an effective agronomic method to decrease Cd in milled rice in Cd-contaminated paddy soil, which would guarantee the food safety.

 

11. How did the application of biochar and topdressing silicon influence the Cd concentration in milled rice?

Response: Good question! In this study, the Cd concentrations in milled rice tread by biochar or by silicon could be reduced, but had no difference with CK. However, the combined application of biochar with silicon decreased the Cd concentration in milled rice significantly, which was reduced by 34.62%, 22.73% and 10.53%, respectively, when compared to CK, TBC and JSi. In the results of manuscript, the influence of treatments on milled-rice concentrations was revised and improved.

 

12. What were the specific effects of biochar combined with topdressing silicon on rice yield components in Cd-contaminated paddy soil?

Response: Good question! In this study, rice yield components such as effective panicle per pot, spikelet numbers per panicle, seed setting and 1000-grain weight were increased significantly by the combined application of biochar with topdressing silicon when compared to CK, but there was no difference between the combined treatment and individual application.

 

13. How did the concentrations of organic matter, total nitrogen, and total phosphorus change with the application of biochar and silicon?

Response: In this study, the concentrations of organic matter, total nitrogen, and total phosphorus were all increased significantly either by the application of biochar or by topdressing silicon when compared with CK, as well as by the combined application of biochar with topdressing Si. However, the interactions were observed between biochar and topdressing silicon in terms of total nitrogen and total phosphorus.

 

14. What were the Pearson correlation matrix results for Cd concentrations and soil nutrients in soil and plants?

Response: In this study, the concentration of available Cd was negatively correlated with the contents of Olsen P and available K, while total Cd concentration in soil was positively correlated with soil nutrients. The reason might be that the increase of soil nutrients after the application of biochar and silicon leaded to the increase of the total Cd retained in soil but the decrease of the available Cd, so there was a significant positive correlation between soil total Cd and soil nutrients.

In this study, the Cd concentrations of roots, stems and milled rice were negatively correlated with soil nutrients, while leaf Cd were positively correlated with soil nutrients and plant nutrients. The reason might be that the growth of rice plant was improved by the application of biochar and silicon, and the sequestration of Cd by leaves was enhanced.

 

15. How did the application of biochar enhance the retention and sequestration of Cd in the study?

Response: Biochar retained Cd in the soil significantly, thanks to its ionic and covalent bonds on the inner sphere surfaces and functional groups [1], decreasing its uptake by rice

[1] Lv, G.; Yang, T.; Chen, Y.; Hou, H.; Liu, X.; Li, J.; Wei, L.; Li, J. Biochar-based fertilizer enhanced Cd immobilization and soil quality in soil-rice system. Ecol. Eng. 2021, 171, 106396. https://doi.org/10.1016/j.ecoleng.2021.106396

 

16. What were the key findings regarding the effects of biochar and silicon on Cd sequestration by leaves?

Response: This is a good question. The key findings regarding the effects of biochar and silicon on Cd sequestration by leaves was that the Cd concentration in leaves was raised by the application of biochar and topdressing silicon, and the transfer coefficient of Cd from leaves to milled rice was declined. This implied that the Cd immobilization in leaves was enhanced by the application of biochar and silicon, and which could be reinforced more effective by the combined application of biochar and silicon.

 

17. How did the application of biochar and silicon affect the total and available Cd concentrations in soil at rice maturity?

Response: In this study, at rice maturity, the concentrations of total Cd in soil treated by the application of biochar and silicon were higher than that of CK, while those of available Cd was lower than CK. This implied that more Cd was remained in soil as the inert forms after the application of biochar and silicon, which would decrease the transfer of Cd from soil to rice plant. The reason might relate to the changes of soil properties affected by biochar and silicon, immobilizing more Cd in soil. 

 

18. What statistical analyses were performed on the experimental data in the study?

Response: Thanks for your question. It was a written mistake in original manuscript. It had been corrected as that means of the treatments were compared using one-way ANOVA followed by Duncan's test (p＜0.05) with SPSS 26.0 software.

 

19. How did the application of biochar and silicon influence Cd concentrations in different parts of the rice plant?

Response: Good question! In this study, the application of biochar and silicon could decrease Cd uptake by rice plant. Most of Cd absorbed by rice plant was distributed in roots (Figure S1), which would be declined by the application of biochar and silicon, especially by the topdressing silicon. Correspondingly, the Cd concentrations in root were reduced significantly by topdressing silicon and the combined application of biochar with silicon, and which in stem and milled rice also were cut down, while that in leaves was increased yet because of the increase in the transfer coefficient of Cd from stem to leaf (Table 1).

 

20. What were the differences in Cd concentrations in roots, stems, leaves, and milled rice between treatments?

Response: Excellent question! In this study, the Cd concentrations in root, stems, leaves and milled rice showed a trend of roots ˃ stems ˃ leaves ˃ milled rice in Cd-polluted paddy soil, while after the application of biochar and topdressing which displayed a trend of roots ˃ leaves ˃ stems ˃ milled rice. This result had been observed in our early research [1], the reason might be related with the variety used in trials.

[1] Zhang, S.; Cai, K.; Wang, W.; Huang, F.; Cai, Y. Regulation of silicon application on cadmiun accumulation and translocation in rice (Oryza sativa.L) grown under high concentration cadmium-polluted soil. Research of Environmental Sciences, 2016, 29(7): 1032-1040.

 

21. How did the application of silicon at the jointing stage impact Cd concentrations in roots compared to biochar treatment?

Response: An interesting question! The application of silicon at jointing stage could decrease Cd concentrations in roots much more than biochar. The reason might be that the capacity of rice to accumulate silicon could be activated and enhanced by silicon application [1], which could improve rice root resistance under cd stress [2]. Moreover, silicon application could reduce Cd concentration in iron plaque of root [3], which would reduce Cd uptake by root.

[1] Gong, D.; Zhang, X.; Yao, J.; Dai, G.; Yu, G.; Zhu, Q.; Gao, Q.; Zheng, W.; Synergistic effects of bast fiber seedling film and nano-silicon fertilizer to increase the lodging resistance and yield of rice. Sci Rep. 2021, 11, 12788. https://doi.org/10.1038/s41598-021-92342-5

[2] Pang, Z.; Shen, S.; Ma, Q.; Wang, Y.; Peng, H.; Liang, Y. Extracellular silicon (Si) nanocoating induced by cationic polymers enhances heavy metal resistance in both Si-accumulating and non-Si-accumulating plants. Environ. Technol. Innov. 2024, 33. https://doi.org/10.1016/j.eti.2023.103500

[3] Pan, BG, Cai YX, Liu BQ, Cai KZ, Lv WW, Tian JH, Wang W. Abatement of Cd in rice grain and toxic risks to human health by the split application of silicon at transplanting and jointing period. J. Environ. Manage. 2022, 302: 114039.

 

22. What was the significance of the reduction in Cd concentration in milled rice by the TBC+JSi treatment?

Response: Good question! Cadmium (Cd), a toxic and carcinogenic metalloid, has received wide attention because it can produce serious threats to human health. Milled rice (white rice) is the main source of Cd in Chinese diet, and 55% of Cd intake by the Chinese population is from rice. Therefore, rice security is significantly linked to human health, and effective measures should be applied to decrease Cd content in milled rice. The reduction in Cd concentration in milled rice could render the milled rice edible and reduce health harm of human. The application of biochar combined with topdressing silicon is an effective, eco-friendly, and exercisable measure in production to control Cd in milled rice.

 

23. How did the concentration of Cd in roots compare to other tissues in the rice plant?

Response: Good question! The concentration of Cd in roots was the highest in the whole rice tissues, followed by stems and leaves, and finally grains, more than half of Cd absorbed by rice plants was distributed in root.

 

24. What were the concentrations of soil total Cd at rice maturity for the different treatments?

Response: In this study, at rice maturity soil total Cd for the treatments of CK, TBC, JSi and TBC+JSi were 2.37 mg/kg, 3.14 mg/kg, 3.13 mg/kg and 3.17 mg/kg, respectively. After the application of biochar and silicon, more Cd was remained in soil, and the transfer from soil to rice plant was reduced.

 

25. How did the application of biochar and silicon affect the concentrations of soil total Cd compared to the control group?

Response: In this study, the concentrations of soil total Cd after the application of biochar and silicon were increased significantly when compared to CK.

 

Questions from 26 to 39 are the same as questions from 12 to 25.

Questions from 40 to 50 are the same as questions from 1 to 11.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Editor-in-Chief in Agronomy Journal

This manuscript is acceptable after fixing the structural defects

Comments on the Quality of English Language

To some extent, the English language problems have been fixed