Identifying Plant Functional Traits of Weeds in Fields Planted with Glyphosate-Tolerant Maize for Preferable Weed Management Practices

Round 1

Reviewer 1 Report

This is a well-writen manusctipt that has pottential to be published. This study assessed plants functional traits in order to have general information regarding weed community to guide weed management in some South African maize fields.

However, I have some suggestions and considerations that can contribute with some topics discussed within the manuscript.

In general, information about the importance of the seed bank for the formation of the weed community must be included. Furthermore, some distinctions regarding weed tolerance and resistance should also be considered and reviewed in the text.

Some specific comments:

L38-40 - In general, for weeds, phytossociological assessments are often used to this end.

As stated by the authors, plant functional traits have been widely used in ecological studies rathen than weed sciences.

So that a sentence should be included in that sense (stating the differences between this PFT and phytossociological aproach).

L71-75 - It is essential to make it clear here which region this is referring to, since the behavior of weeds and also the composition of the weed community is directly related to several factors, including management history, climate, crop-management practices adopted, among others.

L99-100 - How far are these areas from each other? This information is essential, since depending on soil and climate conditions, a group of species may stand out compared to the others.

L100-101 - This is also directly related to the management-history of a specific area (not only in the previous 3 or 5 years, but rather, considering longer periods), as it directly influences the appearance of the species related to the region's seed bank.

L112 - Some missconception here.

Tolerance is a charactistic intrisic to some species regarding specific herbicide molecules.

Authors are probably refering to weed resistence.

Also about weed resistence, I suggest the follow review (Vila-Aiub (2019) - Plants (Basel). 8(11): 469). In general, weed resistence is believed to appears from 2 forms: 1- selection from different genotypes (where some of them are naturally resistant); or 2- selection pressure forces mutation procces that might result (as mutation proces are not guided) on a benefic characteristic that allows biotype to survive to that herbicide.

This should be addressed throughout introduction.

Figure 3 - The meanings of the acronyms must be inserted in the description of the Figure.

Figure 4 - I suggest that the authors reconsider the terms "pre-planting" and "post-planting" to refer to the moments "before and after" the application of herbicides. This is necessary since there are two ways of applying herbicides (post-emergence and pre-emergence - which can even be carried out pre-planting or post-planting), therefore, this can cause confusion.

Why not just use "before and after" herbicide application?

L176-179 - Indicate which Figure or Table this passage is referring to.

L206-208 - Possibly greater seed dispersal. In any case, the seed bank should be disregarded under no circumstances. Therefore, this must be mentioned, essentially.

L235-239 - But how long these chemical management have been adopted?

In fact, repetitive chemical control (speccialy those using herbicides whitin the same mechanism of action) can contribute to the selection of a specific weed community. However, we should not exclude the management-history of a specific area (before herbicides) as it for sure contributed to the seed bank enrichness.

L246-247 - Repetitive use of same chemical management compostition (machanisms of action - see comment above)

L247-250 - There are several studies that state this (speccialy in the weed sciences research field). Please insert more references to support this sentence.

L263-264 - Need more references to base this sentence.

L274-276 - This passage needs to be reevaluated and used sparingly.

What about perennial weeds that are highly relevant in infested areas, such as Cyperus rotundus and Cynodon dactylon?

Because they propagate vegetatively, they are difficult to control, and improper management of these species (especially mechanical control) can cause their spread throughout the planting area.

Such information must be considered.

L276-278 - What about weed species that accelerate their reproductive period as a result of stress or unsuitable conditions for growth? This must be considered.

L278-287 - Soil seed bank should also be considered here, as well as the  historic of the studied area.

My point is: for sure repetitive crop cultivation and same chemical control utilization can act as weed community selection. However, what about all the species that were there before crop cultivation?

L290 - Please insert the reference or table to which this passage is refering to.

L295-296 - Please indicate specifically which group you refer to and the table in which this result can be found.

L296 - Be careful with that statement.

Are the authors referring specifically to a specific cultivated area? This varies according to several factors, including soil and climate conditions, appropriate management, type of planting adopted, history of the area, etc.

L304-305 - Indicate the table or figure to which this passage refers to. Same comment throughout the discussion topic.

L307-308 - Reference is missing for this sentence.

L328-331 - If you are referring to weed resistance, then you are referring to resistant populations. This means that within the same area, it is possible to find resistant and susceptible specimens, but which still belong to the same species. In other words, if this is possible within the same species, considering the family, in this case, seems to me to be a comparison somewhat distant from the reality of observing or finding resistant populations.

At the very least, this should be considered and mentioned.

The article mentioned in the previous comment (and other related articles) will possibly clarify some questions regarding this subject.

L339-342 - First mention in the text must be made with the complete genus. Please check it.

L341-342 - This sentence needs several references to support the statement.

L342 - 1- If there was adequate herbicide application (correct weed development stage, indicated herbicide, spraying carried out appropriately with recommended dose, etc) and the species still survived, then there is possibly a case of resistance (in this case, the accessions must be collected for further studies to confirm the case of resistance).

2- If the authors did not have control over all the specimens evaluated (which I believe was the case), it is extremely vague to mention that the species have traits that make them adapted to persist after the application of a herbicide. Possibly, what happened was that the specimens died and other seedlings emerged from the soil seed bank.

3- If all specimens persisted after the application of herbicides: either all species are tolerant to the herbicides applied, or the application was extremely ineffective.

I also emphasize that there is an area in weed science dedicated solely to studies in this sense. This literature must be visited.

L413-414 - This sentence should be better described and explored.

L416-417 - This should be reviewed as weed tolerance is weed-herbicide-specific.

L422-427 - Soil seed bank.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper presents interesting information on functional traits in weeds. However, the chosen functional traits often overlap and span across practically all weeds (e.g. both prostate and erect growing, both c3 and c4 photosynthetic pathway), some are not defined (what are the specialised storage organs of Chenopodium caritanum?), and some important traits for weed survival after crop plating and herbicide application (the tested factors) such as discontinuous germination, late emergence, seed longevity in the soil, short life span, depth of the root system, high genetic diversity….are not included while presence of spines is included. Weedy traits were initially defined by H.G. Baker (Baker, H. G. 1965. Characteristics and mode of origin of weeds. In H. G. Baker and G. L. Stebbins [eds.], The genetics of colonizing species, 147–172. Academic Press, New York, New York, USA.) and his work is not mentioned. Therefore the functional groups are not very coherent and their analysis does not provide new information. Species were counted before ploughing and herbicide application (dates?, what herbicides where applied, where herbicides with residual activity applied?, are all the species on the label of the herbicides applied?). What are the crop rotations? Moreover, the discussion presents only very general statements with little agronomic background. In the discussion it is mentioned that five species have traits tolerant to herbicides….annual life form, C4 photosynthesis and specified flowering season. This description would include many weed species! The conclusion basically states that weeds have weedy traits and although the information is meant to help producers, I do not see how knowing that there are more annuals after herbicide application and more perennials before herbicide application (perennials often emerge before annuals and many are controlled by plowing) can be useful. The authors should rethink the discussion.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have changed the manuscript accordingly.

The only issue is that the meanings of the acronyms MV, MJN, T and BM must be indicated in the figure legends (Figures 3 and 5). This can be easily changed for the final version of this manuscript.

Author Response

The acronyms are indicated in the figure legend on Figures 3 and 5. 

Author Response File: Author Response.pdf