Roles of Arbuscular Mycorrhizal Fungi on Plant Growth and Performance: Importance in Biotic and Abiotic Stressed Regulation

Round 1

Reviewer 1 Report

The subject of the proposed review: "importance of arbuscular mycorrhizal fungi on plant growth and performance in stressed environments" is particularly attractive and interesting. Problem, the content of the text does not agree with the title.

 

Section 1. Introduction

Citation 1 should be replaced with a more specific and recent citation on the importance of arbuscular mycorrhizae for crop plants. I have also found citations that deserve to be replaced by citations from work more in line with the objective of authors (1, 11, 12, 14, 114 for example).

 

Section 2

Mainly generalities on the roles of arbuscular mycorrhizae. You forget the purpose of your review: stressed environments. To put the question another way: how the arbuscular mycorrhization of a plant contributes to improving its environmental fitness.

L94 to L125: it is not clear whether the work you are reporting concerns stressed environments.

Zn is a dose-dependent toxic microelement. For this element, an improvement of its absorption thanks to the mycorrhization can lead to toxicity; this has already been mentioned.

The role of Se in the physiology of plant-arbuscular mycorrhizal interactions is poorly documented. This paragraph should either be developed further or withdrawn.

 

Sub-section 3.1 off topic. You describe the roles of arbuscular mycorrhizae in drought tolerance but not how this function is different from a plant that is not exposed to water stress.

 

Latin names of species should be cited with authorities the first time they are cited; why only mention Linnaeus?

 

Sub-section 3.4

We do not see the contribution of symbiosis in the treatment of stress.

 

Sub-section 3.5

In heavy metal tolerance, you only mention polluted soils. Why haven't you treated soils that are naturally rich in metals like some mining soils.

For the record, As is not a heavy metal, but a metalloid.

You do not mention the mechanisms put in place by the symbiosis to adapt to high concentrations of potentially toxic elements. It is however supposed to be the subject of your review

 

Section 5

Soil aggregation. You are not reporting anything that would allow us to understand a possible contribution of arbuscular mycorrhizal symbiosis to the formation of microaggregates in the soil.

 

Section 7

The conclusion needs to be completely rewritten to truly capture the major points of the role of arbuscular mycorrhizal symbiosis in stress adaptation.

Author Response

Response to the reviewer: 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

 

This is a nice review, very comprehensive, showing deep knowledge on the literature. It sometimes however, trys to cover too much ground, making some bits of it too dense. Additionally, some paragraphs feel like a concatenation of facts, rather than a well structured text. Please find here my comments and suggestions which I hope will help improve this manuscript.

Abstract

Please revise the language in this section.

Introduction

L35 Arbuscular mycorrhizal fungi (AMF) […]

L35-37 The sentence has some redundancie, as agricultural crops are agricultural plants, etc. are agricultural plants.

L43 Phosphorus

L49-52 “AMF improve soil nutrients and water access to […]” The information in this sentence was already fully stated a few sentences above.

L53-57 The declared scope of this review seems to be too wide and extensive. The title suggests a more narrow and practical approach, centered in stressed environments, aim expressed explicitly at the end of the abstract.

Contribution of AM fungi to plant nutrition and growth

This section reads less as a text than as a concatenation of facts. In my opinion it is often too specific.

L60-64 While it demonstrates a good grasp on the relevant literature, I believe this list of studied plants is unnecessarily long/arbitrary. Please consider structuring it with something like “The effects of AMF on the performance and nutrition of agricultural plants have been widely studied, and demonstrated for many relevant crops (e.g. common names….citations), fruit trees (e.g. common names….citations) etc.

L72-75 These two sentences seem to be out of place, shouldn’t they be in the drought stress section?

L84-88 This is a good example of how the section could be improved by adding structure (and reducing details). I don´t see the need to mention all of the “species” used in the study. The main message is that AMF effect can be dependent on a particular combination of host and symbiont. This message is also explicit in L104. Consider creating groups of studies, where you first deliver the main message (e.g., micronutrient uptake, host-symbiont combinations, etc) and then mention a few examples. You should only go into specific details of the study if those are relevant for your message or deviate from the standard.

L130 & L134 Here again, I believe that you´re trying to cover too much ground. The mention to gene expression seems to me out of context with the rest of the section, and mycorrhizal networks and community level interactions driven by AMF are here vaguely mentioned and clearly beyond the scope declared in your title and abstract.

 

Role of AM fungi in alleviation of abiotic stresses in plants

The introduction to this section carries relevant messages, i.e. 1. different stresses will alter AMF community composition, which will have a feedback effect on plant communities. 2. AMF help plants cope with abiotic stressors, some of them of potential importance in climate change scenarios. The first point is more of a community ecology nature, and hence less related to this ms, but still valid. The second is at the heart of your message and should be made clear as such. In this short text, several short sentences repeat the same information, adding bits of new data in “baby steps”. I recommend you to stick to the messages you want to deliver, and condensate the text in a few elaborated phrases around them, keeping it clear and to the point.

L156 “By enhancing plant performance in poor and stressed environments, mycorrhiza improves host plant adaptation to new climates.” Do you mean a changing climate? Otherwise I disagree: AMF would help the plant cope with environmental stressors, but an adaptation to a new climate sounds like a niche widening or colonization of new environments, which would be far fetched to assume just from the previous statements.

AMF and plant drought tolerance

I like the beginning of this section, particularly the delimitation of drought mitigation and drought tolerance. Later in the section however, they seem to get blurred. I suggest re-ordering it making clear which mechanisms and examples belong to mitigation, and which to tolerance. In some cases, extended explanations on the plant physiology make the text heavier, and could be simplified.

L202 I believe this bridge sentence is not needed, as each section has its own explanatory under title. You could keep the citation for the next section.

 AMF and plant flooding tolerance

The examples provided seem to explain how AMF perform in wetlands, rather than how they may benefit plants during flooding. Please consider carefully if “flooding tolerance” is discussed here. For instance, the table refers to rice, where flooding is not a stress, but its natural environment.

L215 217 AMF distribution is dependent on AMF identity? That sounds like a circular argument, please consider rephrasing.

AMF and plant tolerance to extreme temperatures

L228 The authors from [104]? And what is the connection of this information with the benefit of mycorrhization?

When you make a connection to climate change, you should specify what you mean (tolerance to a wider range of temperatures and moderate temperature extremes). The effects on N uptake and potential denitrification are related to climate change indeed, but not to AMF and plant temperature tolerance (and hence don´t belong here).

AMF and plant tolerance to salinity

Generally speaking this section is ok. Bits as in L253-257 are again way too specific, I see no need to list all enzymes tested AND the effect sizes of the treatments. One can instead formulate sentences as “AMF had positive effect in the activities of various enzymes related to the mitigation of salt stress” or something in these lines.

AMF and plant tolerance to heavy metals

It seems to me like at some point this section switches from tolerance to heavy metal stress to nutrient acquisition of biologically essential heavy metals (e.g. Fe or Zn). If this is the case, please state it clearly.

Role of AM fungi in alleviation of biotic stresses in plants

I like this section, which also is better structured as the previous ones.

Influence of AMF on soil aggregation

The section is well written, and I agree on the great importance of soil aggregation and the role of AMF in it. However, in the cope of “Plant Growth and Performance in Stressed  Environments”, I see no connection between the rest of the manuscript and this section. Unless a clear point is made relating soil aggregation and stress tolerance, I believe this section should be removed.

Interaction between AM fungi and other beneficial soil microorganisms

This section is extensive, and in my opinion would benefit from grouping the information in smaller subsections by organism (e.g. 6.1 Frankia, 6.2 PGPR, etc).

Conclusion

Nice!

Supplementary figure

Please revise the language.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

The review on AMF by the authors is a good overview on the ability to improve plant growth under various stress conditions. The cited literature is quite impressive and gives a good overview on the different aspects of AMF plant interaction.

The structure of the paper is reasonable, but I would put chapter 5 at the beginning of the paper, because this chapter contains more general information about AFM.

Chapter 3 is very detailed and partly a bit confusing. It is also not always clear what is meant. For example, the relation between N₂O and AFM is not clear to me without reading the original paper. In this chapter all Latin names are not written in italics. What is meant with the following sentence: “However, these  authors  have  demonstrated  that  a  temperature  above  30°C  affects  growth  and development of maize plants?

Lines 297 to 304 should go to chapter 2 for nutrition.

The tables give a very nice overview on the research done on the different topics on AFM and abiotic stress.

In the chapter on biotic stress and AFM, should also be discussed the priming effect of AFM. (see https://onlinelibrary.wiley.com/doi/abs/10.1002/9781119312994.apr0680) as a good review on it.

The conclusion should be more detailed, where more research is needed and where AFM should be applied

Author Response

Please see attachments 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

acceptable

Reviewer 2 Report

I consider that the manuscript has now significantly improved, congratulations on a well done job.