Allometries in Plants as Drivers of Forage Nutritive Value: A Review

Round 1

Reviewer 1 Report

Allometries in plants as drivers of forage nutritive value: A review

This review proposes a more functional approach allowing the expression of the causal link between plant biomass accumulation processes and the ontogenetic decline in the nutritive value of forages.

The manuscript is well written and represents a nice review regarding the related topic, leading to a very clear message, which is well supported by a plenty of already available data and well discussed. The proposed approach is also methodologically relevant for a better exploitation of some forage crops.

The manuscript reports interesting information.

Few specific comments and suggestions are listed thereafter

For a wider audience, climatic details of locations, where data (presented in figures) were originally collected, are useful.

Only in the caption of figure 5 it is reported the trial location i.e. “in Eastern Canada” Why?

My suggestion is to indicate “where” in all (or almost all) figure captions as it is reported in figure 5 caption. In this way, readers might immediately refer to countries and environments where related experiments were carried out.

At species level, the review is based on data collected on (relatively) few species such as tall fescue, alfalfa, timothy and sweet sorghum.

If the paper message could be generalized (i.e. it is valid for other forage crops/countries/contexts) then this possibility must be mentioned and stressed.

Additionally, what about (grass and legume) annual forage species other than sorghum? (more a question than a comment!). Authors might add a comment on it.

L 26 an ? (to be removed)

L 31 Allometry is already in title

L 78 The short-lived perennial legume sulla, under Mediterranean climate, might be at least mentioned as another example of legume species. See: Borreani et al. 2003. Quantifying morphological stage to predict the nutritive value in sulla (Hedysarum coronarium L.) Agronomy Journal, 95, 1608-1617.

L 190 the DNDFof , a space requested

L 231 timothy (Phleum pratense L), scientific name was already described so it is unnecessary

L 234 %Div in text vs  %ivD in y axis of fig. 5 . Please, standardize it.

L 242 fig. 5 caption, please, check and revise it ( ()­, regressionuntil, comma instead of “.”….)

L 402 wall ?

L 427 ()?

Author Response

Dear colleague,

Thank you very much for your favourable comments. We have tried to follow all your suggestions for improving our manuscript:

1- We have included the location with Long. and Lat. where each experiment had been realized in each corresponding legend of Figures. So we think readers could have an idea of the type of climatic conditions where data have been obtained.

2- We have add a comment in conclusion about the genericity of the framework we have developed and its capacity for being extrapolated to a wider range of forage species. We cannot do more and we identified the study of Genotype-Environment-Management interactions as a research perspective by using this framework as a tool for analysing this variation.

3- We have taken into account all your detail remarks in the text

Thank you for the time you spent for reading and reviewing our manuscript and for your positive appreciation.

Gilles LEMAIRE

Reviewer 2 Report

Referee Comments

December 2019

Agriculture

Allometries in plants as drivers of forage nutritive value: A review.

Lemaire & Belanger

The authors, both preeminent thinkers and leaders in forage plant dynamics and grassland ecology, present an important retrospective on herbage nutritive value and propose a novel means to link plant productivity with changes in composition. Data models herbage nutritive value in a mechanistic way, linking plant development and productivity with herbage chemical composition. In essence, the relationships outlined in this review provide a fine-tuning mechanism to understand more clearly the causal relationship of plant development and nutritive value. The approach proposed can provide insight into the responses of plants to complex genotype-management-environment interactions. Outcomes could lead to improved plant resources for use in variable weather and management situations.

Please consider making a major revision of the Abstract.   There are some awkward statements (pg 1, ln 8. “ . . . . has been for a very long time determined . . . “and very long sentences (pg 1, ln 10-14). Information defining the problem being addressed, the importance of developing a resolution of new approach and what was done to achieve the objectives is a bit difficult to extract from the Abstract as it is now written.

Suggest avoiding personal pronouns (e.g., Abstract pg 1, ln 24. “you”; also Introduction pg 1, ln 36. “their”).

Check for spelling (pg, ln 26. Should “an” be “and”?).

Pg 3, ln 110. The references cited note reference 14 twice – that is 14-14-16-17. Should this actually be shown as 14-15-16-17?

Pg 13, ln 397. The Reference number is missing in the Figure 10 legend Lemaire and Allirand [ ] ???

Pg 14, ln 427. Reference number not provided for Moulia et al ()???

Citation 43 does not appear to be used in the text – this referee may have missed it somewhere. Please check.

Please check format of Refences. In some instances the author names are presented as: Adams, A.B. and C.D. Ball; and in other instances the names appear as Adams, A.B. and Ball, C.D.  Some series are connected by “and” and some are not

e.g., Reference 13 – no “and”; Reference 9 includes “and”

Be consistent and compliant with journal format and style.

A question – the caption for Figure 12 states that the “core” of an alfalfa canopy has shaded and senescing leaves that display decreasing digestibility and have a low N concentration. Do not shaded leaves tend to have somewhat higher N concentrations as a mechanism to increase efficiency of light capture? It is likely that the leaves occurring in the core are older and that very well could be another complicating feature of the relationships under consideration. Perhaps the change is more directly related to senescing leaves that shading – just a thought.

The conclusions drawn from the theoretical models presented in the review are relevant and provide new insight into the relationship of forage plant development and nutritive value; however, the authors should consider revising the presentation for clarity. The sentences in the conclusion section are very long and have several ideas presented in each. Thus, the ideas become entangled are difficult to follow – the concepts presented are involved and complex (dynamics of growth, morphology, chemical composition) and a reader can become lost in the shifting ideas, foundational concepts and ensuing relationships presented in each statement. This referee believes a revision of the Conclusion section is warranted to highlight the creative approach the authors pursued to illustrate the relationships presented in the review.

Author Response

Dear colleague

Thank you very much for your positive and encouraging comments. As you suggested we have deeply improved the abstract by rewording some sentences. We have included all your remarks and corrections within the new version.

For your question about the two effect of shadding: (i) leaf N distribution following irradiance level from top to down within canopy; and (ii) leaf senescence... we have shown in Lemaire et al. 1991 that the effect (i) exists independently of the effect (ii) as this effect is reversible when the leaves at the base of canopy are put in full light after clipping neighbouring plants... So the two effects co-exist. I did not want to develop this aspect too much in this paper and readers can refer to the Lemaire et al. 1991 paper cited in the text.

Thank you very much for the time spent for reading and reviewing our manuscript.

Sincerely yours

Gilles LEMAIRE