Effects of Different Remediation Treatments and Rice Intercropping on the Integrated Quality of Paddy Soils Mildly Contaminated by Cadmium and Copper

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript provides a evaluation of the effects of various remediation treatments, in conjunction with rice intercropping, on paddy soils mildly contaminated by cadmium (Cd) and copper (Cu). The study is well-constructed and offers valuable insights into the remediation of heavy metal-contaminated paddy soils. Below are a few comments and suggestions for improvement.

Major Comments:

In this study, two rice cultivars were utilized: the highly cadmium-tolerant hybrid rice variety Teyou 671 and the low cadmium-tolerant conventional rice variety Baixiang 139. I am curious about the mechanisms that enable Teyou 671 to be cadmium-tolerant, whereas Baixiang 139 is not. Are there any existing studies on these two varieties regarding their abilities in Cd uptake, transportation, and detoxification? Since rice was used for intercropping in this study, it's essential to discuss the mechanisms of cadmium toxicity, detoxification, and tolerance in plants.

While the study concentrates on the effects of remediation treatments on soil quality, it does not address the potential impact on rice production and grain quality. For effective remediation treatments, is there an increased accumulation of heavy metals such as cadmium and copper in the rice plants, particularly in the grains? This could potentially pose a threat to food security and human health.

The effects of remediation treatments on soil quality are reported based on data from a single growing season. Have the long-term effects been considered, particularly whether the most effective remediation treatments remain consistent and stable over two or more consecutive growing seasons?

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions.

Comments 1: In this study, two rice cultivars were utilized: the highly cadmium-tolerant hybrid rice variety Teyou 671 and the low cadmium-tolerant conventional rice variety Baixiang 139. I am curious about the mechanisms that enable Teyou 671 to be cadmium-tolerant, whereas Baixiang 139 is not. Are there any existing studies on these two varieties regarding their abilities in Cd uptake, transportation, and detoxification? Since rice was used for intercropping in this study, it's essential to discuss the mechanisms of cadmium toxicity, detoxification, and tolerance in plants.

Response 1: The ability of rice to absorb, transport and accumulate Cd is directly related to its Cd tolerance, and the level of Cd tolerance is also reflected in the adaptability to Cd pollution. In order to screen rice varieties with distinct Cd tolerance，we did some research in the early stage.

The following are the published articles in the laboratory :

1. ZHU S N. Physiological response of rice intercropping systems with different cadmium tolerance to cadmium pollution[D]. Fuzhou: Fujian Agriculture and Forestry University, 2020.
2. WEN H H, ZHENG X Y, XIAO Q T, et al. Physiological response of cadmium-contaminated rice to Pseudomonas TCd-1 microbial repair[J]. Acta Ecologica Sinica, 2022, 42(5):1924−1933.
3. HONG Y, LIN J L, ZHONG X M, et al. Screening of Oryza sativa varieties with different cadmium tolerances[J]. Journal of Fujian Agriculture and Forestry University ( Natural Science Edition), 2022, 51(06):730-736.

 

Comments 2: While the study concentrates on the effects of remediation treatments on soil quality, it does not address the potential impact on rice production and grain quality. For effective remediation treatments, is there an increased accumulation of heavy metals such as cadmium and copper in the rice plants, particularly in the grains? This could potentially pose a threat to food security and human health.

Response 2: We found that different remediation treatments significantly inhibited the migration of heavy metals such As Cd, Cu, As and Pb to aboveground parts, especially to the grain. However, the grain data was included in unpublished study and therefore not presented in this study. It was used to elucidate effects and mechanisms of in-situ remediation technology on grain heavy metals accumulation under contaminated conditions.

 

Comments 3: The effects of remediation treatments on soil quality are reported based on data from a single growing season. Have the long-term effects been considered, particularly whether the most effective remediation treatments remain consistent and stable over two or more consecutive growing seasons?

Response 3: Thanks for your suggestions, the evaluation of multiple seasons can be carried out in further research. In this study, the data of mature period has certain persuasion. Whether the change of heavy metals content in soil will be transferred to grains has always been a concern. Compared with the jointing, heading and other stages, the soil quality at maturity stage can be related to the content of heavy metals in grains, which provides a basis for explaining soil remediation and food security.

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript describes a research project with the potential to significantly impact rice production in China. The authors investigated the application of various remediation treatments with rice to enhance soil quality and rice production. They tested two types of rice-high Cd tolerant and low Cd tolerant rice-as plant materials. The research, which is both comprehensive and extensive, produced many high-quality results supported by statistical analysis. These findings will significantly contribute to our understanding of soil quality improvement for increased rice production in China.

 

As a reviewer, I have no major complaints about the concept of the paper, the methodology, and the manner of presenting the results. The only suggestion to the authors would be to state the analytical methods by which they obtained the parameters of the chemical analysis of rice (lines 120-127 and lines 140-150)

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions.

Comments: As a reviewer, I have no major complaints about the concept of the paper, the methodology, and the manner of presenting the results. The only suggestion to the authors would be to state the analytical methods by which they obtained the parameters of the chemical analysis of rice (lines 120-127 and lines 140-150)

Response: The analytical methods of parameters have been described in detail in section 2.3 chemical analysis.

The collected soil samples were air-dried and ground with an agate mortar, sieved through a 0.149 mm mesh, then stored in sealed polyethylene bags, and finally digested with an acid mixture of HClO4 and HNO3. The contents of Cd, Pb, Cr, Ni, Cu, and Zn in the soils were determined by inductively coupled plasma mass spectrometry (ICP-MS, NexION 300X) (Lin et al. 2019; Fernández et al. 2021), while the contents of Hg and As were investigated by hydride generation-atomic fluorescence spectrometry (HG-AFS, AFS-9230) (Jia 2021). Furthermore, the available Cd, Cu, Cr, Zn, Ni and Pb in the soil samples were determined by ICP-MS (NexION 300X), and the available Hg and As were determined by HG-AFS (AFS-9230).

The soil pH, cation exchange capacity (CEC), organic matter (OM), total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available phosphorus (AP) and available potassium (AK) were measured as previously described by Zha (2017) and Bao (2000). The activities of soil catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO), acid phosphatase (ACP), urease (URE), sucrase (SUC), cellu-lase (CUE) and protease (PRO) were analyzed following the methods of Guan (1986). Soil microbial biomass carbon (MBC) was determined by the chloroform fumiga-tion-potassium sulfate extraction method (Gong et al. 2021). (lines 180-196)

Reviewer 3 Report

Comments and Suggestions for Authors The manuscript presents a study on the effects of various remediation measures combined with rice intercropping on the quality of soils mildly contaminated with cadmium and copper. The research is scientifically sound, the experimental design is reasonable, and the data are comprehensive, contributing significantly to understanding and improving soil remediation. The paper provides valuable insights into soil heavy metal pollution remediation and safe rice production, offering positive contributions to agricultural sustainability and food security.   Areas for Improvement: 1. The description of the experimental site is brief; more background information on the site, such as climate conditions and soil types, should be provided to help readers better understand the experimental environment. 2. While the experimental methods are described in detail, certain sections, such as soil sampling and processing methods, need further clarification to ensure the reproducibility of the study. 3. In the discussion section, the authors should further explore the potential mechanisms of the different remediation measures and how they interact to affect soil quality and rice growth. 4. The interpretation of data is adequate, but the presentation of data in some figures could be more intuitive, such as by adding more figures or adjusting the layout of existing ones. Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions.

Comments 1: The description of the experimental site is brief; more background information on the site, such as climate conditions and soil types, should be provided to help readers better understand the experimental environment.

Response 1: The site belongs to the mid-subtropical monsoon climate, with average annual temperature of 20°C and average annual rainfall of 1645.3 mm. The preceding crop in the experimental paddy field was tobacco. (lines 119-122)

 

Comments 2: While the experimental methods are described in detail, certain sections, such as soil sampling and processing methods, need further clarification to ensure the reproducibility of the study.

Response 2: Part of the soil samples were immediately packed in plastic bags and stored in a refrigerator at 4°C for determination of soil enzyme activity and microbial biomass carbon. Another samples were air-dried at room temperature, removing stones, roots and other foreign materials. The soil was crushed into 10 mesh and 100 mesh samples for the determination of soil physical and chemical properties and heavy metal content. (lines 173-178)

 

Comments 3: In the discussion section, the authors should further explore the potential mechanisms of the different remediation measures and how they interact to affect soil quality and rice growth.

Response 3: In section 4.3, we have discussed the potential mechanism by which in-situ remediation techniques affect the quality of paddy soils. The addition of BC obviously changes the quality of paddy soil through complexation, precipitation, adsorption, oxidation and reduction processes after the addition of BC in the field. This could be verified by the significant degradation of soil available Cd and Cu under the different planting modes. Pseudomonas TCd-1 has a strong Cd tolerance and accumulation ability, can promote plant growth-promoting rhizosphere bacterial activity and plays an essential role in protecting plants from HM toxicity. Lime can not only affect the adsorption, precipitation and complexation of HMs in soil by changing the soil pH and CEC, but also increase rice yield and reduce the content of HMs in various organs of rice. Foliar spraying of SE regulated plant HMs accumulation by decreasing HMs bioavaila-bility, which could be associated with a variety of HMs that produce antagonistic effects that reduce plant susceptibility to HMs absorption. (lines 522-529, lines 540-542 and lines 562-565)

 

Comments 4: The interpretation of data is adequate, but the presentation of data in some figures could be more intuitive, such as by adding more figures or adjusting the layout of existing ones.

Response 4: Thank you for pointing this out. Several tables contain the detailed data, which can illustrate exhaustive information in the context. If they were converted to figures, we are afraid it is not conducive to effective reading.