Nickel Effects on Growth and Phytolith Yield of Grasses in Contaminated Soils

Round 1

Reviewer 1 Report

11. Introduction. Page 2, lines 47-48. Different elements have different toxicity levels. Please indicate for which element the indicated toxicity levels apply. A reference to a specialized study is not suitable for fundamental quantities. It is better to refer to monographs of famous authors.

  2. Page 2, line 56. Genera - Megathyrsus, species - Megathyrsus maximus.

  3.  Materials and methods. line 81. Write the specific method and device on which it was determined available Ni concentration in soils.

 4  4.  line 98. It is better to replace the term “The factors” with “variant”

  5. Table 1. There is no data for nickel in soils - everywhere the concentration is 0.0. When using normal methods for determining nickel, such values should not exist. What methods were used to determine the nickel content in soils? What are the units of measurement?

      6. Measurements and Analytical Determinations.

Line 25-126. The methodology of the extraction of phytoliths from the shoot should be described in detail, rather than referring to work with a comparative analysis of methods!

How was the mass control calculated after the phytoliths were isolated?

What was the weight of phytoliths for determining nickel in them?

  7. Soil characterization and experimental design.

Explain why the soils were limed before adding nickel, if it is known that liming reduces the mobility of heavy metals in soils?

In the form of what compounds was nickel introduced into the soils?

  8. 9 page line 254. Figures 2 a, b do not reflect plants growth, as indicated in the text. Provide a table or diagram of plant growth, biomass and yield, please.

Author Response

Responses to the reviewer 1 - Correction in light blue

1) Introduction. Page 2, lines 47-48. Different elements have different toxicity levels. Please indicate for which element the indicated toxicity levels apply. A reference to a specialized study is not suitable for fundamental quantities. It is better to refer to monographs of famous authors.

Response: Ni was indicated as an element and was changed to a reference for a review on Ni.

2) Page 2, line 56. Genera - Megathyrsus, species - Megathyrsus maximus.

Response: Corrected in text.

3) Materials and methods. line 81. Write the specific method and device on which it was determined available Ni concentration in soils.

Response: Corrected in text.

4) line 98. It is better to replace the term “The factors” with “variant”

Response: Corrected in text. I believe that the best option would be to indicate that the treatments were the combination of the two grasses and the concentrations of Ni added and the control (without Ni).

5) Table 1. There is no data for nickel in soils - everywhere the concentration is 0.0. When using normal methods for determining nickel, such values should not exist. What methods were used to determine the nickel content in soils? What are the units of measurement?

Response: The analysis was carried out before implementing the experiments. The extraction method was USEPA 3052, which determines the total concentration of any element in the soil, only values below 0.1 mg/kg of Ni were detected. Practically, the soil used in the experiments has practically no value.

6) Measurements and Analytical Determinations.

6.1) Line 25-126. The methodology of the extraction of phytoliths from the shoot should be described in detail, rather than referring to work with a comparative analysis of methods!

6.2) How was the mass control calculated after the phytoliths were isolated?

6.3) What was the weight of phytoliths for determining nickel in them?

Response: Corrected in text.

7) Soil characterization and experimental design.

7.1) Explain why the soils were limed before adding nickel, if it is known that liming reduces the mobility of heavy metals in soils?

Response: Liming and basic fertilization were necessary to provide conditions for the growth of grasses. Correcting soil acidity by increasing base saturation to 45%, adequate for grass growth, but not sufficient to reduce Ni availability in the soil.

7.2) In the form of what compounds was nickel introduced into the soils?

Response: The addition of Ni to the soils was in the form of nickel chloride as a pure reagent for analysis.

8) 9 page line 254. Figures 2 a, b do not reflect plants growth, as indicated in the text. Provide a table or diagram of plant growth, biomass and yield, please.

Response: Suggestion accepted. Table 2 was added with the data estimated with the equations to facilitate the interpretation of the results obtained.

Reviewer 2 Report

This manuscript describes the results of a study carried out in green house conditions in order to assess the Ni effects on the growth and phytolith yield of grasses in two soils artificially contaminated. The authors are attempting to address a very studied area - soil contamination and the behaviour of different plant species under contamination stress. The topic fits the scope of the journal and the results  and the results are of certain interest.The methods used for investigation are quite simple. This manuscript describes the results of rather simple pot experiments but with high yield of data. However, there are some shortcomings in the manuscript. Minor revisions care needed before it could be published in Soil Systems

Some suggestions for the improvement of the manuscript can be found below:

·         Table 1 - in my opinion is impossible to have zero value for nickel content in soil (even if there are no contamination);

·         Line 108 – please change pot instead of plot  because Plot means the basic units of a field research project—the specific-sized areas in which each treatment is applied and pot is used for Pot experiments, as a complement to field measurements, allow the investigation of plants under controlled conditions

·         Line 123 - Please, provide the recovery rate (comparing with assigned value of CRM) for Ni

·         Line 125 – please check the expression used using

·         Figure 1, and 3 – please check the equation  and explain what does it mean **, this is confusing

·         Figure 1 – please insert in section 2.2. the description of method used for assessment of Ni availability in soil (extraction method mentioned in caption of the figure).

Author Response

Responses to the reviewer 2 - Correction in green

1) Table 1 - in my opinion is impossible to have zero value for nickel content in soil (even if there are no contamination);

Response: I agree with the note made by another reviewer. The analysis was carried out before implementing the experiments. The extraction method was USEPA 3052, which determines the total concentration of any element in the soil, only values below 0.1 mg/kg of Ni were detected. Practically, the soil used in the experiments has practically no value.

2) Line 108 – please change pot instead of plot because Plot means the basic units of a field research project—the specific-sized areas in which each treatment is applied and pot is used for Pot experiments, as a complement to field measurements, allow the investigation of plants under controlled conditions

Response: Corrected in the text.

3) Line 123 - Please, provide the recovery rate (comparing with assigned value of CRM) for Ni

Response: Corrected in the text.

4) Line 125 – please check the expression used using

Response: Corrected in the text.

5) Figure 1, and 3 – please check the equation and explain what it means **, this is confusing

Response: Corrected in the text.

6) Figure 1 – please insert in section 2.2. the description of method used for assessment of Ni availability in soil (extraction method mentioned in caption of the figure).

Response: The Ni extraction method using the Mehlich-1 extractor was mentioned when soil sampling was carried out, after the reaction of Ni doses added to the soil.

Reviewer 3 Report

This study investigated how soil characteristics and Ni concentration affected yield and phytolith of two different grasses. Overall, it is a straightforward study with some scientific merit. The experiment was well-designed and the manuscript was well written.  I only I have some minor comments regarding the materials and methods:

Line 80-81: I believe USEPA 3052 method measures total Ni, not available Ni. Based on your result, you actually used Mehlich 1 method for available Ni.

Line 82-88: what is the final pH after liming?

Line 85: please also define CTC

Line 87-88: “ts. Liming requirements with dolomitic limestone (380 g kg-1 of CaO, 125 g kg-1 of MgO, and 90% total neutralizing power).” It is not a complete sentence. Please revise.

Line 97: need to describe the size of the pot and the amount of soil per pot

very minor revision required

Author Response

Responses to the reviewer 3 - Correction in dark blue

1) Linha 80-81: Acredito que o método USEPA 3052 mede o Ni total, não o Ni disponível. Com base no seu resultado, você realmente usou o método Mehlich 1 para o Ni disponível.

Response: The initial analysis of the soils was carried out using USEPA 3052, which determines total Ni for the purpose of verifying the existing concentration of Ni. Mehlich-1 was carried out to evaluate the availability of Ni after the application of Ni to soils and the response of grasses in the production of dry matter and phytoliths.

2) Line 82-88: what is the final pH after liming?

Response: Liming was necessary to provide conditions for the growth of grasses. Correcting soil acidity by increasing base saturation to 45%, was adequate for grass growth, but it was not enough to raise the soil pH, only to provide Ca and Mg for the grasses.

3) Line 87-88: “ts. Liming requirements with dolomitic limestone (380 g kg-1 of CaO, 125 g kg-1 of MgO, and 90% total neutralizing power).” It is not a complete sentence. Please revise.

Response: Corrected in the text.

4) Line 97: need to describe the size of the pot and the amount of soil per pot

Response: Corrected in the text.

Reviewer 4 Report

The work deals with a very interesting topic. Due to the continuous emission of heavy metals into the environment, the topic of phytoremediation, although discussed quite often, is still relevant. Especially when it concerns an element that, on the one hand, is essential for plants and is a microelement, and on the other hand, its excess may turn out to be toxic to them. In cultivation conditions, such a situation requires development of recommendations for appropriate dosage depending on the type of soil and plant species. However, in the case of contaminated soils, the appropriate selection of species depending on the type of soil allows for efficient phytoremediation and even phytoextraction.

In my opinion, although the work is short, it raises important issues related to the topic, focuses on the observed results and explains them well in the discussion.

Despite this, I suggest correcting a few minor errors:

Abstract:

-        lines 25 - 28 - the authors provide the doses used: 20, 40 - 120 mg kg-1, and then refer to the concentration of 30 mg kg-1, after which caused toxicity. Please explain this.

Materiał and methods:

-        please indicate in the methodology whether the soil was thoroughly mixed after adding nickel chloride.

Results:

-        the doses of Ni used were 20, 40 and 120 mg kg-1, and the authors refer to the safe level of this element in the amount of 30 mg kg-1, but there is no specific indication of the doses used. Although I admit it was very well illustrated in the charts .

-        too few references to the doses used, which were already toxic and still reflected the demand

-        drawings 2 and 3 - the footer should contain the titles of the drawings: a, b, c and d.

Discussion:

-        well written, but I would suggest introducing annotations from the latest available publications from 2021 - 2023.

References:

Please arrange the list according to editorial requirements, the observed omissions that require correction are certainly:

-        line 367 – remove the year after giving the authors of the publication, the year is given after the name of the journal

-        likewise poems: 375; 380, 382, 384, 396, 398 and 406.

In my opinion, after following the above suggestions, the work can be published in Soil Systems.

Author Response

Responses to the reviewer 4 - Correction in Purple

1)   lines 25 - 28 - the authors provide the doses used: 20, 40 - 120 mg kg-1, and then refer to the concentration of 30 mg kg-1, after which caused toxicity. Please explain this.

Response: The concentration of 30 mg/kg was the applied concentration that provided the maximum dry mass production of the grasses evaluated, being considered the concentration with a micronutrient effect and after this concentration there was a toxic effect with the increase in the applied concentrations.

2) Materiał and methods: please indicate in the methodology whether the soil was thoroughly mixed after adding nickel chloride.

Response: Corrected in the text.

3) Results:

3.1) the doses of Ni used were 20, 40 and 120 mg kg-1, and the authors refer to the safe level of this element in the amount of 30 mg kg-1, but there is no specific indication of the doses used. Although I admit it was very well illustrated in the charts.

Response: The concentration of 30 mg/kg of Ni was an average of the maximum concentrations obtained for each grass and soil and was already justified in question 1.

3.2) too few references to the doses used, which were already toxic and still reflected the demand

Response: There are no recommendations for applying Ni to the soil. It was used as a reference for choosing the Ni concentrations to be applied to Brazilian environmental legislation.

3.3) drawings 2 and 3 - the footer should contain the titles of the drawings: a, b, c and d.

Response: Corrected in the text.

4) Discussion: well written, but I would suggest introducing annotations from the latest available publications from 2021 - 2023.

Response:  The references are to some basic texts and scientific articles that must be cited.

5) References: Please arrange the list according to editorial requirements, the observed omissions that require correction are certainly:

-        line 367 – remove the year after giving the authors of the publication, the year is given after the name of the journal

-        likewise poems: 375; 380, 382, 384, 396, 398 and 406.

Response: Corrected in the text.