Temperature Effects on the Shoot and Root Growth, Development, and Biomass Accumulation of Corn (Zea mays L.)

Round 1

Reviewer 1 Report

This manuscript reports on the effects of different day-night temperature regimes (increasing temperatures, all with 8 C between max and min daily temps) on vegetative growth and root-shoot partitioning in maize. It is interesting data, if somewhat constrained by the use of uniform day/night temperature regimes and by having plants grow for only 28 days in chambers.

Note: pasting the review resulted in all "l." (line) and "ll." being rendered as "1":

1. 17 – it would be helpful to provide some idea of what “developmental traits” were measured

 

1. 19 – meaning of “exemplified” in this context unclear

 

1. 26-28 – this is a real stretch – field-grown plants do not behave the same as chamber-grown plants with consistent daily temperature regimes.

 

1. 61-62 –a sentence beginning with “Research indicates…” needs a citation at the end

 

1. 77-78 – statements such as “modern agricultural research has often ignored plant roots…” may sound good to someone but are specious (including the fact that “research” doesn’t “ignore” anything – people do that.) There has been a lot of research on plant roots, and there is good reason why many studies do not include roots.

 

1. 116 – “all” should be “each”

 

1. 124-136 – methodological differences among studies do not make the useless in terms of describing how plants respond to temperature. Would it be possible to at least give some cardinal temperatures here that have been reported?

 

1. 192 – is the “stem” mentioned here (and on l. 204) the actual stem, or the pseudostem made up (mostly) of leaf sheaths?

 

1. 283 – please remove redundancies such as “…examples”…are “exemplified” here and throughout.

 

1. 284 – what are “more extensive” leaves?

 

1. 288 – is “as temperatures rise” supposed to be “as temperatures rise above 30/22”?

 

Figure 3 D-F – suggest shifting horizontal scale to make displayed numbers correspond with temperature means: 16, 21, 26, 31, 36

 

1. 303-305 – in fact, the increases in height “appear” to be accelerating, not linear; a test of the regression model would settle this and allow the “appeared” to be eliminated. It certainly wasn’t linear at higher temperatures.

 

1. 307-308 – meaning of “…may be more sensitive to supraoptimal temperatures than sub-optimal levels…” is confusing – if it’s temperatures and not levels, say that.

 

1. 322 – suggest using something like “leaf appearance rate” rather than “development,” since there are other leaf development parameters.

 

1. 326-328 – this is confusing – Equation 2 is a linear equation, and the lines in Fig. 3E are not linear. The discussion that follows is not clear, and the question of whether leaves at high temperature were physiologically damaged is not addressed. The Topt and Tmax calculations are estimates based on (imperfectly fit) functions and is it not clear that differences here compared to those form other reports are meaningfully different.

 

Table 3 – the first column is labeled “Parameter, unit” but I see no units. The acronyms need to be spelled out in the table caption, as they are in Table 2. Failing that, the reader should be pointed to Table 2 to see them. Suggest using the same number of significant digits for all R^2 values. Why is Tmin labeled as “estimated?” and Topt and Tmax aren’t? Tmin is well outside the range of temperatures used, but so in Tmax, in some cases.

 

1. 361 – this certainly seems stronger than a “suggestion”. It is not made clear whether roots were at the same temperatures as the chamber air in these experiments, but was the effect o high temperatures on root length a direct temperature effect or one brought about by leaf damage and lack of photosynthate?

 

1. 377 – the phrase “classical expo-linear growth” has gotten a bit tired by now.

 

Figure 7 – it would be helpful to keep the same vertical axis on the right (each runs from 0 to 1) as on the left; it’s confusing that the 28 DAS proportions seem high, when in fact only the axis is expanded.

 

1. 470-471 – eliminate “; thus, shoot development” to end up with “…was LN, which had s Tmin…”

 

1. 481-486 – the M(modified) GGD model described by Angel et al is an empirical model based on field observations. It incorporates temperatures that vary over time as development progresses. It also includes effects of water insufficiency at high temperatures, which is art of the reason it uses Tmax of 30 C, when we know that maize photosynthesizes faster at 32 or 33 C than at 30 C, as long as it is well-watered. And, although it uses 10 C as a base temperature, it is not accurate to designate that as a Tmin – it serves as a base for daily high temperatures, but the growth on a day with the minimum T at 5 C and the maximum at 10 C is (reasonably) assumed to be zero, even though there could be some low-temperature damage. As such, this system cannot be directly compared to one developed under constant temperatures in growth chambers.

 

1. 508 – is the contention then that these are the first cardinal temperatures reported for root development? If so, this should say that, not that there aren’t any (reported).

 

1. 512 and following – here in the Discussion we suddenly find a new figure (8) that seems useful, but whose placement is rather odd. The paragraph beginning on l. 537 has more of the same, but apparently no figure. Then, at line 555, there appears a complex figure that also is labeled as Figure 8, that seems to be some sort of extraction from earlier figures, and a table (4) with regression parameters, cited along with Figure 8 (it must be the second Figure 8?) This all needs to be incorporated better into the manuscript, or, if it belongs in the supplemental materials, be placed there.

 

As a general comment, while this manuscript is relatively straightforward, it remains the fact that the data are derived form pants grown under fixed temperature regimes in chambers. We cannot expect such plants to grow the same as field-grown plants, although the authors might have compared some literature values of early dry matter accumulation in field-grown plants (likely much lower in field-grown plants). The current data is useful in a comparative sense but attempting to apply it to field-grown plants, as the authors suggest in the abstract, will be difficult.

Author Response

This manuscript reports on the effects of different day-night temperature regimes (increasing temperatures, all with 8 C between max and min daily temps) on vegetative growth and root-shoot partitioning in maize. It is interesting data, if somewhat constrained by the use of uniform day/night temperature regimes and by having plants grow for only 28 days in chambers.

We appreciate the suggestions and comments. We did incorporate those suggestions in the revision submitted.

Note: pasting the review resulted in all "l." (line) and "ll." being rendered as "1":

1. 17 – it would be helpful to provide some idea of what “developmental traits” were measured

Thanks. We added those parameters in the abstract.

1. 19 – meaning of “exemplified” in this context unclear

Modified to make it clear. The word exemplified is changed to as shown in the figure.

26-28 – this is a real stretch – field-grown plants do not behave the same as chamber-grown plants with consistent daily temperature regimes.

We absolutely agree with the reviewer. Plants grown under low-light environments behave differently than field-grown plants.

However, these are sunlit plant growth chambers and the plants are grown under natural sunlight levels. We have incorporated many of the functions derived from the experiments conducted into crop models that were validated and used for the field and policy arena. Here, in the abstract, we could not add references, in the other places in the manuscript, we added those references.

.   61-62 –a sentence beginning with “Research indicates…” needs a citation at the end

 A citation is added as suggested.

1. 77-78 – statements such as “modern agricultural research has often ignored plant roots…” may sound good to someone but are specious (including the fact that “research” doesn’t “ignore” anything – people do that.) There has been a lot of research on plant roots, and there is good reason why many studies do not include roots.

Modified to make those statements more appropriate. Thanks for the suggestions.

1. 116 – “all” should be “each”

 Changed as suggested.

1. 124-136 – methodological differences among studies do not make the useless in terms of describing how plants respond to temperature. Would it be possible to at least give some cardinal temperatures here that have been reported?

In this section we are not stating that methodological differences make the data useless. We are just pointing out that the cardinal temperatures provided by Sanchez et al. are a conglomerate of multiple studies and out study differs by estimating cardinal temperatures all within the same experiment. We do believe that our study provides superior comparison however. Comparisons to cardinal temperatures provided in Sanchez et al. review are provided in the results and discussion.

1. 192 – is the “stem” mentioned here (and on l. 204) the actual stem, or the pseudostem made up (mostly) of leaf sheaths?

The plant height was measured as defined in the methods. Without dissecting, it will be difficult to see the real stem.

Added clarity to the document that leaves were removed from the stem at the leaf collar to better define what we considered the stem.

 283 – please remove redundancies such as “…examples”…are “exemplified” here and throughout.

Modified as suggested.

1. 284 – what are “more extensive” leaves?

Deleted the phrase and add a greater number of leaves

1. 288 – is “as temperatures rise” supposed to be “as temperatures rise above 30/22”?

Thanks, and modified as suggested.

Figure 3 D-F – suggest shifting horizontal scale to make displayed numbers correspond with temperature means: 16, 21, 26, 31, 36

Thanks. We changed all the figures from 15 to 40 °C with 5 °C increments levels. The average temperatures were 16.9, 21.79, 26.12, 30.53, and 35.59 °C. respectively and they are not exactly equally spaced among them.

 303-305 – in fact, the increases in height “appear” to be accelerating, not linear; a test of the regression model would settle this and allow the “appeared” to be eliminated. It certainly wasn’t linear at higher temperatures.

Thanks. We modified to make those changes more appropriate. 

307-308 – meaning of “…may be more sensitive to supraoptimal temperatures than sub-optimal levels…” is confusing – if it’s temperatures and not levels, say that.

 Thanks, and modified as suggested.

1. 322 – suggest using something like “leaf appearance rate” rather than “development,” since there are other leaf development parameters.

Thanks, and modified as suggested.

1. 326-328 – this is confusing – Equation 2 is a linear equation, and the lines in Fig. 3E are not linear. The discussion that follows is not clear, and the question of whether leaves at high temperature were physiologically damaged is not addressed. The Topt and Tmax calculations are estimates based on (imperfectly fit) functions and is it not clear that differences here compared to those form other reports are meaningfully different.

Thanks and the sentences were modified for clarity. 

Table 3 – the first column is labeled “Parameter, unit” but I see no units. The acronyms need to be spelled out in the table caption, as they are in Table 2. Failing that, the reader should be pointed to Table 2 to see them. Suggest using the same number of significant digits for all R^2 values. Why is Tmin labeled as “estimated?” and Topt and Tmax aren’t? Tmin is well outside the range of temperatures used, but so in Tmax, in some cases.

The unit is deleted, and abbreviations are added to the Table caption. We see no need to add units for the parameters as the other columns only present cardinal temperatures for that respective growth and developmental parameters.

 361 – this certainly seems stronger than a “suggestion”. It is not made clear whether roots were at the same temperatures as the chamber air in these experiments, but was the effect o high temperatures on root length a direct temperature effect or one brought about by leaf damage and lack of photosynthate?

We did not monitor root zone soil temperatures in this experiment. Based on previous studies, root cardinal temperatures were slightly lower than the short growth parameters. Photosynthesis is less responsive to temperature than growth and development based on our previous studies.

 377 – the phrase “classical expo-linear growth” has gotten a bit tired by now.

Thanks, deleted classical.

Figure 7 – it would be helpful to keep the same vertical axis on the right (each runs from 0 to 1) as on the left; it’s confusing that the 28 DAS proportions seem high, when in fact only the axis is expanded.

Thanks, and changes the graph Y-axis scales to be equal.

470-471 – eliminate “; thus, shoot development” to end up with “…was LN, which had s Tmin…”

Modified as suggested.

1. 481-486 – the M(modified) GGD model described by Angel et al is an empirical model based on field observations. It incorporates temperatures that vary over time as development progresses. It also includes effects of water insufficiency at high temperatures, which is art of the reason it uses Tmax of 30 C, when we know that maize photosynthesizes faster at 32 or 33 C than at 30 C, as long as it is well-watered. And, although it uses 10 C as a base temperature, it is not accurate to designate that as a Tmin – it serves as a base for daily high temperatures, but the growth on a day with the minimum T at 5 C and the maximum at 10 C is (reasonably) assumed to be zero, even though there could be some low-temperature damage. As such, this system cannot be directly compared to one developed under constant temperatures in growth chambers.

In this section, we are not attempting to invalidate the GDD model, we are just comparing the results we found in our study to how the GDD model works. Similar methodologies to ours have been used and are stated in the methods section.

1. 508 – is the contention then that these are the first cardinal temperatures reported for root development? If so, this should say that, not that there aren’t any (reported).

Thanks. We modified to as suggested.

1. 512 and following – here in the Discussion we suddenly find a new figure (8) that seems useful, but whose placement is rather odd. The paragraph beginning on l. 537 has more of the same, but apparently no figure. Then, at line 555, there appears a complex figure that also is labeled as Figure 8, that seems to be some sort of extraction from earlier figures, and a table (4) with regression parameters, cited along with Figure 8 (it must be the second Figure 8?) This all needs to be incorporated better into the manuscript, or, if it belongs in the supplemental materials, be placed there.

The process for grouping parameters into categories and calculating the curves in figure 8 is outlined in the methods section, 2.5.3. We added an extra statement to line 255 to clarify. We completely revised the section referring to figure 9 and table 4. We have added a note in the discussion to refer to the methods section to add clarity to the document. The figure numbers were miss numbered and that has been corrected.  

 As a general comment, while this manuscript is relatively straightforward, it remains the fact that the data are derived form pants grown under fixed temperature regimes in chambers. We cannot expect such plants to grow the same as field-grown plants, although the authors might have compared some literature values of early dry matter accumulation in field-grown plants (likely much lower in field-grown plants). The current data is useful in a comparative sense but attempting to apply it to field-grown plants, as the authors suggest in the abstract, will be difficult.

We agree with the reviewer's comments on plants grown under low light environments. Those plants will not behave similarly to the field-grown plants. That is why these sunlit chambers were designed to generate data that could be used to develop models for field applications. We cited some those modeling papers and the validation efforts in the article. There is no easy way to develop models for field applications. We have only a few facilities like ours in the world that are being used to generate data and develop models for field applications. We respectfully disagree with the statement that data could not create models for field applications.

We thank you for a though and careful review and critique and the manuscript has been improved by your suggestions for clarity of presentation.

Thanks again.

 With regards,

KR Reddy
William L. Giles Distinguished Professor
Mississippi State University
Mississippi State, MS 39762, USA

 

Reviewer 2 Report

The manuscript „Temperature effects on the shoot and root growth, development, and biomass accumulation of corn (Zea mays L.)” by Walne and Reddy presents interesting results on the temperature influence on corn’s early vegetative growth and development. The experiments were conducted with valid methodologies and data handling was appropriate. The findings are clearly reported in the text and a valid discussion section in perspective to the results and literature has been presented. In my opinion it is very valuable work.

There are a few things that need to be improved, namely:

1. Second part of Table 2 in my opinion is not described – the meaning of letters should be clearly indicated in the Table description.
2. Line 413 – additional word ‘Dry’ is written at the beginning of the sentence
3. Line 542 – next to the Celsius degrees is additional symbol ‘.
4. References - please check that the references are written in accordance with the journal's requirements

Author Response

Response to the reviewer's comments:

We appreciate your critical review and suggestions.

1. Second part of Table 2 in my opinion is not described – the meaning of letters should be clearly indicated in the Table description.

Thank you. Additional explanations are added to the Table foot.

 2. Line 413 – additional word ‘Dry’ is written at the beginning of the sentence

Thanks and the extra word 'Dry" was deleted in the revision.

3. Line 542 – next to the Celsius degrees is an additional symbol ‘.

Thanks again, the additional symbol was deleted in the revision.

4. References - please check that the references are written in accordance with the journal's requirements

All references are made according to the journal style.

We appreciate the comments and suggestions in improving the presentation.