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Peer-Review Record

Effect of Post-Drought Rehydration on Winter Wheat Fluorescence and Photosynthetic Indices under Different Levels of Nitrogen Application

Water 2023, 15(2), 305; https://doi.org/10.3390/w15020305

by Daoxi Li¹, Huan Liu¹, Shikai Gao^1,*, Shah Jahan Leghari², Haosen Hou¹ and Yanbin Li¹

Reviewer 1:

Ya-Nan Zhao

Reviewer 2: Anonymous

Water 2023, 15(2), 305; https://doi.org/10.3390/w15020305

Submission received: 30 November 2022 / Revised: 28 December 2022 / Accepted: 5 January 2023 / Published: 11 January 2023

(This article belongs to the Special Issue Effects of Drought on Agriculture Water Resources and Crop Productivity)

Round 1

Reviewer 1 Report

The effects of two soil water regulation treatments on winter wheat fluorescence and photosynthetic indices under three N fertilizer levels were studied. It is valuable for wheat production. The following questions should be improved before the manuscript is accepted.

1 Some formats need to be adjusted, please check the whole paper. Many of the units in Table 1, 3, and 4 have the wrong superscript format; The format of “×” in line 82 maybe wrong; Why is the text format in line 95-96 different from others? Check references 1, 19, 26, 30, 33, 46. Here are some examples, not the only ones in the whole article.

2 “water nitrogen” in line 322. water and nitrogen?

3 line 87: It is best to supplement the name of brown soil according to FAO or Chinese soil taxonomy.

4 Some of the statements are unprofessional. The Farina in Table 1 appears to be “Silt”; In the whole manuscript, “growth” seems to be more appropriate than “fertility” when it refers to wheat growth stages.

5 Here are some of the fertility periods used by the authors: elongation and heading stages, tassel stage (Abstract); seedling stage, overwintering stage,greening stage, nodulation, heading and flowering stage, filling and maturity stage (lines 97-110); regreening stage, jointing stage, heading and flowering stage, milking repening stage (Table 2). These stage names should be professional and consistent throughout the paper.

6 The significance analysis in the figure 2-4 and table 4 is not appropriate; at the least, the significance analysis should be kept at the same time, but not all days after rehydration.

7 The structure of this manuscript is that Results are written separately from the Discussion, so much of the discussion in the analysis should be placed in the Discussion section.

8 line100: “50% of N fertilizer was applied at the bottom……”. at the bottom? before sowing？

9 line 125: there is something wrong with this sentence.

10 In this study, two water managements were set up under three nitrogen application levels. The difference between the two water managements was that lower limit of irrigation (60% FWHC) were different at jointing stage or flowering stage; All the others are 75%FWHC. Does the drought in “post-drought rehydration” in this study refer to 60% FWHC? Generally, soil moisture content should be maintained at what level is appropriate?

11 Which irrigation method is better for the same N fertilizer? 60%FWHC at jointing or flowering stage? What are the possible mechanisms? The author should conclude and discuss the reasons.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Review for Water journal: Effect of post-drought rehydration on winter wheat fluorescence and photosynthetic indices under different levels of nitrogen application.

Comments: Interesting work that includes the recovery after water stress that in most works with drought is not explored, using physiological parameters, which helps in understanding the processes involved in drought tolerance. The dry and nitrogen interaction also explores the combined effects of the factors.

Abstract: Line 9.

1) Line 13: I would not consider 125 kgN/ha low. My suggestion would be to classify as high (125 kg) and very high 250 ks).

Key words: Line 27/28.

2) Line 27/28: Keywords: Winter wheat; nitrogen application level; rewatering after drought; fluores- 27 cence parameters; photosynthetic index

Comments: I understand that keywords that are already in the title should not be included as keywords that should already appear in a search.

Winter wheat is already in the title, Nitrogen application is also already in the title; fluorescence is already in the title; photosynthetic indices is already in the title.

I suggest including sensor, SPAD, Mini Pan, water stress, photosynthesizer.

Introductions: Line 30.

3) Line 31/32: Wheat is one of the major food crops in China, accounting for more than 20% of the country's food crop cultivation área.

Comment: If possible, enter total production in tons.

4) Line 32/33: As the population grows and the economy develops, the amount of water available for agriculture decreases each year.

Comment: If possible, quantify this reduction.

5) Line 36/39: Studies have shown that crops suffering from drought stress can quickly recover their growth after rehydration, producing compensatory effect or even a super-compensatory effect, which can minimize the negative effects caused by drought in the early stage to a certain extent

Comment: Include the bibliographic citation of those studies.

6) Line 43/44: Chlorophyll fluorescence parameters can better reflect the photosystem performance of plants

Comment: Explain here that part of the energy goes to the photosynthetic process in photosystem 2, part is lost in the form of heat and a part returns as fluorescence, which can be measured, and correlates with the level of stress felt by the plant and therefore can be used as an evaluation tool.

7) Line 52/54: In period, irrigation at flowering stage maximizes the number of grains on the maize ears and significantly increase the photosynthetic rate of maize at the spatulation stage [11].

Comment: Insert comment: In addition to irrigation, the use of drought tolerant genotypes may be another option.

8) Line 70:. End the introduction with hypotheses and objectives.

Material and Methods: Line 71.

9) Line 90: Wold be possible to include a figure with water retention curve for the soil/wheat in order to find field water holding rate capacity and the level of stress?

10) Line 97: The experimental wheat variety is “Zhongmai 1062”, sown on September 30, 2020, and harvested 97 on June 1, 2021.

Comment: If possible, insert the genetic origin as well as the crossing that gave rise to the material.

11) Line 98: The sowing rate was 150.0 kg/hm2

Comment: Transform into plants per square meter because the materials have different seed sizes.

12) Line 100: 50% at the beginning of nodulation

Comment: Include the phenological phase (Zadoch scale).

13) Line 102: I suggest Zadoks scale.

14) Line 104/106: The lower limit of irrigation was 60% of field water holding capacity at the nodulation and heading and flowering stage, and 75% of field water holding rate during greening and filling and maturity.

Comments: I suggest supplementing here with the water retention curve for wheat in this soil to get an idea of the stress level.

15) Line 109/110: All agronomic measures were the same except for water and fertilizer control.

Comments: What does “same” mean?

16) Line 115/116: The main stems of wheat at the edge of the non-measurement pits were randomly selected and labeled in three holes for each treatment.

Comment: Not clear to me.

Results: 144

17) Line 146/147: Chlorophyll content is an important indicator of plant growth status. When chlorophyll content is high, the leaves can use more light energy, absorb and convert more CO2 for photosynthesis [16].

Comment: This statement should be used in the discussion part.

18) Line 148/150: There is a significant positive correlation between the relative chlorophyll content (SPAD) and chlo- 148 rophyll content of plant leaves, that is, the SPAD can be measured instead of the traditional meas- 149 urement of chlorophyll values [17-18].

Comment: This statement should be used in the discussion part.

19) Line 175: Figure 2. Changes in leaf SPAD of winter wheat under different treatments

Comment: Title of the figure should be self-explanatory to facilitate the reader's understanding.

20) Line 158: From the above results, SPAD peaked at the 5th d after rehydration and showed a small decline after 158 5 th d.

Comment: The adjective small does not characterize the effect found well. Better quantify.

21) Line 159: the reasons for this are the chlorophyllase activity in flag leaves did not fully recover at the 2nd d after rehydration due to the effects of the previous drought, and the chlorophyllase activity in flag leaves SPAD peaked at the 5th d after rehydration.

Comment: This statement should be used in the discussion.

22) Line 164/166: Because the drought at the jointing stage increased the resistance of winter wheat, which made the soil water more effectively after rehydration at the tassel stage and increased the compensation benefit of rehydration.

Comment: This statement should be used in the discussion.

23) Line 167/170: N is a necessary element for chlorophyll synthesis in- 167 creased the resistance of winter wheat under high-N conditions, while more N was benefit to chlo- 168 rophyll synthesis after rehydration. Therefore, physiological activity needs a recovery process when 169 winter wheat is rehydrated under drought, which is fully recovered in 5 th d in usual. Rehydration 170 treatment at the heading stage is better to improve N fertilizer utilization, chlorophyll formation 171 and promote photosynthesis in winter wheat under drought and moderate N at the nodulation 172 stage.

Comment: This statement should be used in the discussion.

24) Line 203: Figure 3. Changes in leaf Fv/Fm of winter wheat under different treatments

Comment: Title of the figure should be self-explanatory to facilitate the reader's understanding.

25) Line 182/183: Fv/Fm is the maximum photochemical quantum yield of chlorophyll PSII reaction center, which reflects the efficiency of light energy conversion in PSII reaction.

Comment: This statement should be used in the discussion.

26) Line 190/191: The Fv/Fm 190 value reached the maximum at the 5 th d after rehydration and gradually decreasing after 5 th d.

Comment: It is not possible to say that it decreased after the fifth day because the next evaluation was on the ninth day, no measurements were taken on the 6th, 7th and 8th.

Line 194/195: N can enhance the resistance and improve the physiological function of crops under drought conditions, increasing the ability of crops to absorb water.