Effect of Soil pH on the Uptake of Essential Elements by Tea Plant and Subsequent Impact on Growth and Leaf Quality

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors present extensive material in the manuscript on the issue of the relationship between soil pH and elemental uptake by tee trees. The following comments:
In Figure 1 it is difficult to determine the location in relation to the country, the map should include a larger area of the country with the location point of the field experiment marked.
In Section 2.1, the authors did not specify at what depth the samples were taken, at what depth the first roots appeared, and what volume of soil was taken for analysis, and from what genetic level of soil, whether it was the top humus layer of Ap or deeper levels, if so how did the data analysis take into account the effect of different soil levels with different physical, chemical and biological properties on the results of soil and tea leaf analysis.
Section 2.3 does not specify what elements were studied in the soil and in the plant.
In line 135 “the contents of N, Mn, C, P, Sr, Mg and Ba” the authors list the elements that were analyzed, why were these elements chosen? In the introduction, the authors did not mention which elements are particularly important for the quality of tea leaves. Why is there aluminum in the list of labeled elements and no iron, which is one of the more important elements found in high concentrations in very acidic environments.

Author Response

Comments and Suggestions for Authors

The authors present extensive material in the manuscript on the issue of the relationship between soil pH and elemental uptake by tee trees. The following comments:
In Figure 1 it is difficult to determine the location in relation to the country, the map should include a larger area of the country with the location point of the field experiment marked.

A: Thanks to the reviewers. The authors have added a map of China and a detailed distribution of the experimental sites (Figure S1).

In Section 2.1, the authors did not specify at what depth the samples were taken, at what depth the first roots appeared, and what volume of soil was taken for analysis, and from what genetic level of soil, whether it was the top humus layer of Ap or deeper levels, if so how did the data analysis take into account the effect of different soil levels with different physical, chemical and biological properties on the results of soil and tea leaf analysis.

A: Thanks to the reviewers. Tea tree is a fibrous root system and during the authors' study, they mainly collected the rhizosphere soil, i.e. the soil attached to the root system of tea tree. The authors have revised Material and method appropriately to make the description more detailed. "The sampling method of rhizosphere soil of tea tree was to remove the dead leaves and branches on the soil surface, shovel the soil layer by layer until 45-50 cm deep, dig out the tea tree, shake off the soil on the root system of the tea tree, and the soil that was still attached to the root system of the tea tree was the rhizosphere soil. The soil sampled at each sampling point was about 100 g."

Section 2.3 does not specify what elements were studied in the soil and in the plant.

A: Thanks to the reviewer.The authors used ICP-MS for the determination of multielemental content in soil and tea leaves. The method allowed for a large number of determinations of the content of different elements in soil and plants, which on the one hand made it possible to evaluate which elements were present in the soil or plant, and on the other hand to analyze whether there were differences in these elements. Therefore, the section started with a multi-element determination of soil and plants, and then further analyzed the elements with major differences through the data obtained.

In line 135 “the contents of N, Mn, C, P, Sr, Mg and Ba” the authors list the elements that were analyzed, why were these elements chosen? In the introduction, the authors did not mention which elements are particularly important for the quality of tea leaves. Why is there aluminum in the list of labeled elements and no iron, which is one of the more important elements found in high concentrations in very acidic environments.

A: Thank you to the reviewer. The authors did not express themselves clearly here. The authors converted the enrichment coefficients based on the measured soil and plant element contents, and then found that soil pH had the greatest effect on the enrichment coefficients of seven elements (N, Mn, C, P, Sr, Mg, and Ba) through simulation curves and TOPSIS analysis. Based on this, the authors used soil pots to plant tea tree seedlings and adjusted soil pH to verify whether changes in pH significantly affected the enrichment coefficients of these seven elements and whether they affected the physiological functions of tea trees? The authors revised the relevant expressions in Materials and Methods.

Second, the authors determined soil and tea tree leaf elements, including iron. The authors reflected this in the annexed table. Acidic conditions increased the ionic concentrations of iron and aluminum. In the analysis, the authors focused on whether the enrichment of elements by tea tree leaves changed significantly after the change of soil pH, so as to screen out the key elements whose enrichment could be significantly affected by soil pH. It was found that there was no significant change in Fe enrichment by tea tree leaves after the change in soil pH, while there was a significant change in Al enrichment. Therefore, Fe was excluded from the subsequent analysis.

Reviewer 2 Report

Comments and Suggestions for Authors

Although the authors attempted to address a very important subject in the manuscript, the quality of presentation and experimental design was very poor. Many questions arose throughout the manuscript, which I have appended below. The manuscript needs a new experimental design and drastic corrections. In its present form, I recommend rejection of the manuscript for publication as it will lead to incorrect conclusions.

1. The title of the article should be changed for wider readership. A suggested title is “Effect of Soil pH on the Uptake of Essential Elements by Tea Plant and Subsequent Impact on Growth and Leaf Quality.”

2. The word “tree” is not suitable here; “tea tree” should be replaced by “tea plant” throughout the manuscript.

3. Please discuss how ‘rhizosphere soil’ is different from ‘subsoil’ from the element uptake perspective of tea plants.

4. Experimental details are missing in the sample collection section. Separate section 2.1 into two separate sections. The first section should contain the details of the sampling site, weather data, and date of sample collection, including latitude and longitude data for every site (latitude and longitude data may be provided in a supporting information file). A new section under section 2 must include the method of soil sample collection. As the whole study is based on soil data, every possible detail should be included in this section. Also, include photographs of soil sample collection for better understanding. To what depth was the sample collected?

5. Section 2.4: Experimental details of quality parameters should be included thoroughly. Just referring to earlier literature makes it difficult to understand. It may also be given as supporting information. The sample collection method from tea seedlings is missing. What is the amount of green leaf sample generated from a 23 cm height, 0.25 cm diameter seedling? Was it enough to get a representative sample for proper analysis? Include all these details in the section.

6. Why were three seedlings planted in a single pot? This will adversely affect the growth of seedlings, and data generated from it will be misleading.

7. Line 20-21: What is a “soil cultivation experiment”? This should refer to the cultivation of tea, not soil. Please rewrite for better clarity.

8. Line 30-32, 203-205: Soil is not a carrier; it’s a source of elements for tea plants. I suggest rewriting this.

9. Line 30-32: “...different parts of the plant and utilized to provide for plant growth and…” – remove “to provide” from this sentence.

10. The quality contents such as polyphenols, caffeine, theanine, etc., are very low compared to much available literature on tea. Provide justification.

Comments on the Quality of English Language

Extensive editing of English language required

Author Response

Comments and Suggestions for Authors

Although the authors attempted to address a very important subject in the manuscript, the quality of presentation and experimental design was very poor. Many questions arose throughout the manuscript, which I have appended below. The manuscript needs a new experimental design and drastic corrections. In its present form, I recommend rejection of the manuscript for publication as it will lead to incorrect conclusions.

A: Thank you very much for the reviewer's suggestion. The authors are very sorry for not expressing themselves clearly. Firstly, the authors collected soil from 30 tea plantations and their corresponding tea tree leaves for multi-elemental determination by ICP-MS to obtain the possible elements and their contents in the samples. Then, the enrichment coefficients of the tea tree leaves for the elements were converted based on the measured elements to obtain the elements with enrichment coefficients greater than 1. Then, the simulation curve analysis was used to obtain the change of elemental enrichment coefficients by tea tree leaves after the change of soil pH. Finally, TOPSIS analysis was used to obtain the key elements that soil pH  significantly affected the enrichment of tea tree leaves. Through the above design and analysis, it was found that soil pH could significantly affect the enrichment of seven elements by tea tree leaves and lead to changes in the growth and quality of tea trees.

Based on this, the authors used soil pots to plant tea tree seedlings and regulate soil pH, on the one hand, to verify whether the enrichment of seven elements by tea tree leaves changed significantly after the change of soil pH, and on the other hand, to analyze whether this change would affect the growth and quality of tea trees.

Thank you again to the reviewers for their advice, and I apologize for any distress caused by the lack of clarity in the authors' presentation.

1. The title of the article should be changed for wider readership. A suggested title is “Effect of Soil pH on the Uptake of Essential Elements by Tea Plant and Subsequent Impact on Growth and Leaf Quality.”

A: Thanks to the reviewing experts for their suggestions. Based on the expert's suggestions, the authors have revised the title.

2. The word “tree” is not suitable here; “tea tree” should be replaced by “tea plant” throughout the manuscript.

A: Thanks to the reviewing experts. The authors have revised the entire text in accordance with the experts' suggestions.

3. Please discuss how ‘rhizosphere soil’ is different from ‘subsoil’ from the element uptake perspective of tea plants.

A: Thanks to the reviewing experts. The authors have made appropriate additions to the introduction. I hope it meets the requirements.

4. Experimental details are missing in the sample collection section. Separate section 2.1 into two separate sections. The first section should contain the details of the sampling site, weather data, and date of sample collection, including latitude and longitude data for every site (latitude and longitude data may be provided in a supporting information file). A new section under section 2 must include the method of soil sample collection. As the whole study is based on soil data, every possible detail should be included in this section. Also, include photographs of soil sample collection for better understanding. To what depth was the sample collected?

A: Thank you to the reviewer. The authors have divided 2.1 into two parts and listed the sampling information in detail. Also, the information about each sampling site was placed in Figure S1 of the Supplementary Material. Hopefully, it will meet the requirements. Thanks to the reviewers for their suggestions.

5. Section 2.4: Experimental details of quality parameters should be included thoroughly. Just referring to earlier literature makes it difficult to understand. It may also be given as supporting information. The sample collection method from tea seedlings is missing. What is the amount of green leaf sample generated from a 23 cm height, 0.25 cm diameter seedling? Was it enough to get a representative sample for proper analysis? Include all these details in the section.

A: Many thanks to the reviewers for their suggestions. This part was not clearly expressed by the authors.

The authors have made additions in Materials and Methods. Methods of extraction and determination of elements in soil and tea tree leaves have been described by the authors in Materials and Methods 2.3. Therefore, the determination of the elements in the soil and tea tree leaves in the potting experiments was carried out with reference to the method of 2.3. Plant height, leaf area, chlorophyll content and photosynthesis rate of tea trees were measured directly in vivo. One bud and two leaves of tea tree seedlings were collected to determine the quality indexes of the leaves, each replicate was about 15 g, which was enough for testing. The authors have provided additional information in Materials and Methods.

6. Why were three seedlings planted in a single pot? This will adversely affect the growth of seedlings, and data generated from it will be misleading.

A: Thanks to the reviewers for their suggestions. Since the experimental treatment was conducted for only 60 days, it was feasible to plant three tea tree seedlings per pot. Usually, when potting tea seedlings for 1 year or more, we could choose to plant 1 plant per pot, while for short time treatment, we should increase the number of plants appropriately. The authors found in long-term experiments with tea tree seedlings in soil pots that if 3 seedlings were potted, they needed to be transplanted after more than 180 days of planting. And potting 3 tea tree seedlings for a short period of time should not have any effect on the growth of the seedlings. Many thanks to the reviewers for their suggestions.

7. Line 20-21: What is a “soil cultivation experiment”? This should refer to the cultivation of tea, not soil. Please rewrite for better clarity.

A: Thanks to the reviewing experts. Based on the experts' comments, the authors have revised the relevant statements.

8. Line 30-32, 203-205: Soil is not a carrier; it’s a source of elements for tea plants. I suggest rewriting this.

A: Thanks to the reviewing experts. Based on the experts' comments, the authors have revised the relevant statements.

9. Line 30-32: “...different parts of the plant and utilized to provide for plant growth and…” – remove “to provide” from this sentence.

A: Thanks to the reviewing experts. Based on the expert's suggestions, the authors have made appropriate revisions.

10. The quality contents such as polyphenols, caffeine, theanine, etc., are very low compared to much available literature on tea. Provide justification.

A: Thanks to the reviewing experts. I am very sorry, this is the author's mistake. The unit here should be mg/g. The authors deeply apologize. Meanwhile, I would like to thank the reviewers for their serious and careful review. Thank you very much.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript may be accepted in the present form. 

Comments on the Quality of English Language

Moderate editing of the English language required