Mixed-Species Stands Improve the Coordination between Leaf and Fine Root Traits in a Common Garden Experiment

Round 1

Reviewer 1 Report

The manuscript  titled “A significant mixture effect exists in the coordination between leaf and fine root traits in a 9-year common garden experiment” examines the coordination between leaf and fine root traits. The study offers deep understanding of whole-plant ecological strategies and reveals how community composition and diversity contribute to defining  ecosystems functioning.

The study succeeds in interpretation of variations in leaf and root traits among different tree species at different species richness. Overall, this research is potentially full of interest, as it addresses the relevant topic. Moreover, there is still a lack of examples of this type of research. I believe that the study is drafted in a clear and intelligible fashion; the text is well organized.

I have suggestions

1. Interspecific trait coordination needs to be presented and correlated well in the result and discussion section. These  trait variation should also be tested in contrasting soil conditions as well.

2. The performance of different tree species in plots have been poorly discussed in the manuscript.

Wish you luck

Quality of English is fine

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper from Li and colleagues analyses the leaf and fine root coordination along a species richness gradient, based on an experiment settled in subtropical China.

There is a great debate about the coordination between leaf and fine root functioning (see for example also Carmona et al., 2021), and this paper can help to add a new piece to this research topic. In general, the paper is clear and well-written, and the rationale is adequately supported by the analysis.

I have only some doubts regarding the potential interaction effect that different species types could have (see L229-232). What about if species types (i.e. root distribution, leaf habit, mycorrhizal type) have an interaction effect? A two-way ANOVA can allow comparison only within single species types. I would suggest at least to support with some evidence that there are no significant effects coming from interaction of multiple species types. For example, I would try multiple linear models. Maybe it will come out nothing significant, but at least it could be a good supporting material.  

Moreover, in all the text (also in the title and abstract) Authors refer to “coordination”. However, they would be more specific because the term is too generic. A coordination can be “big with big”, but also “big with small”. Maybe the term “convergence” is more clear?

In all the text Authors refer to “absorptive roots and transport roots”. I would suggest using the terms “fibrous and pioneer roots” (see Polverigiani et al. 2011). More importantly, it is not clear why Authors have done this distinction (as explained at L214-215) but then traits were measured considering all the fraction < 2mm (L219-222). Maybe there is an error in the text? It seems later that there are two matrices related to absorptive and transport root traits (L233-234 but also Figure 2 and 3)

Minor comments:

L2, title: I would suggest revising the term “mixture effects” in the title since it is a bit confusing. For example, “mixed species stands…” or “Increasing species richness...”

L17: I would define the types or at least use “species types defined according to root distribution, etc..”

L115: correct” rptake”

L130: the effect of species “richness” should be more described according to existent literature.

L131: here and in all the text correct “economic” with “economics”.

L193, Table 1: please list the species in some order!

L216: which scanner. It is essential that the scanner used for fine roots is one with transparent unit to avoid shade effects.

L232-234: it is not clear from this sentence how many RDA were run?

L236: which kind of correlation coefficient was used?

L239-240: this sentence is not methodological. Remove from here, and if relevant use in intro or discussion.

L267 (and 288), Figure 2 and 3: There are two columns with SRA in the figure. Is one for “DIA”? See also next point.

L269: where is “DIA” in the figure?

L270: please add also “ARP” in the abbreviations list.

 L290: I would repeat the same caption of figure 2 to explain variable abbreviations.

L414: delete “exists”.

L417-419: this is true, However there are also “management constraints” that can lead to functional convergence between aboveground and belowground root traits (see for example Dalle Fratte et al., 2022).

L426: correct “useing”.

L494-500: this sentence seems more appropriate for the abstract rather than for a conclusion.

L501: correct “fine root traits”.

Finally, I would suggest increasing the figure resolution.

References:

·         Carmona, C. P., Bueno, C. G., Toussaint, A., Träger, S., Díaz, S., Moora, M., ... & Tamme, R. (2021). Fine-root traits in the global spectrum of plant form and function. Nature, 597(7878), 683-687.

·         Dalle Fratte, M., Montagnoli, A., Anelli, S., Armiraglio, S., Beatrice, P., Ceriani, A., ... & Cerabolini, B. E. L. (2022). Mulching in lowland hay meadows drives an adaptive convergence of above-and below-ground traits reducing plasticity and improving biomass: A possible tool for enhancing phytoremediation. Frontiers in Plant Science, 13, 1062911.

·         Polverigiani, S., McCormack, M. L., Mueller, C. W., and Eissenstat, D. M. (2011). Growth and physiology of olive pioneer and fibrous roots exposed to soil moisture deficits. Tree Physiol. 31, 1228–1237. doi: 10.1093/treephys/tpr110.

Nothing to say about the English style.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

General notes:

In an afforestation experiment, the authors investigated how the number of tree species and binary plant property categories such as root depth/shallowness, mycorrhizal AM/ECM type, leaf evergreen/deciduous nature influence some leaf and root properties and each other. The authors' literature review and research methods are adequate, and the results obtained are good. I consider it important to communicate it after appropriate corrections. However, the manuscript needs thorough correction. Minor clarifications and additions are necessary in the material and method chapter, in the figures and tables. The Discussion chapter requires thorough revision, because there are many parts in it that belong to the Results and Introduction sections. There is faulty causality, little real discussion, and a lack of deeper understanding. The conclusion chapter was misinterpreted and a summary was written instead, so it needs to be completely revised. In several places, the cause-and-effect relationships are incorrect, there is little real discussion, and a deeper understanding is lacking.

Some used technical terms and abbreviations need to be corrected. In the manuscript the term of species type used is misunderstood. These are plant traits, artificially constructed binary trait categories, not plant species types. Instead of species richness, it is better to use the number of species, instead of root distribution (which includes several properties), it is more correct to use root depth, or the shallow/deep root category, or the deciduous/evergreen nature. The use of abbreviations should be simplified and standardized. If the abbreviations SRL and SRA are used for both root types, then only RN and RP should be ARN and TRN, the distinction between ARP and TRP is confusingly unnecessary. If RD is included in the introduction, then it should also be used instead of DIA. The explanation of the abbreviation ARP is missing (line 271). Abbreviation (RP) from line 92 is missing.

Nothing is written about the identification of the type of mycorrhiza. Mycorrhizality is only one possibility that does not always develop. If roots were examined, was mycorrhizal identification performed? This is important, because one of the examination aspects of the grouping of the species was precisely this.

I consider it unnecessary to mention 9 years in the title. After correction of the discussion chapter, the abstract should be modified, taking into account the general comments.

Lines 96-101. The sentence is too long and not completely understandable.

Line 106. Unnecessary, too general, should be deleted, perhaps the previous sentence as well.

Lines 117-119. It helps predict the properties of underground organs that cannot be seen.

Line 127. Not SRA?

Line 193. The table needs to be rearranged: column 1 is the species name, in alphabetical order; Column 2 is the abbreviation, followed by the family (this is for information purposes only). After that, the order remains, but the 3rd column is called "root", the 4th column is called "leaf" and the last one is "mycorrhiza". Abbreviate the categories of the table to one or two letters. Use root depth instead of root distribution. Furthermore, I would introduce the following abbreviations here: RD= root depth, LH= leaf habit, MT= mycorrhiza type. These are already shown in the first figure.

Line 195. It is not clear how the 672 individuals come out. The description of data collection should be clarified and simplified to make it easier to understand. This chapter should describe how the mycorrhizal type was determined.

Line 209. Table 2 contains repeated data (columns 2, 3, 4). These should be taken out and added in text to the figure explanation.

Line 247. The first row of figures is so faint that the columns of deep-rooted species are not visible. What do the letters A to R in the figures mean? The figure explanations must be interpretable independently, not additions to the previous figure.

Line 254. Insert at the beginning: the categories of the examined property, followed by their listing.

Lines 267 and 288: See what is written on line 247.

Line 289. The figure explanations must be interpretable independently, not additions to the previous figure.

Line 299. Move to a new line or paragraph.

Lines 305-306. The type of the figure is not good, because the species numbers are discrete values, you cannot connect them with a line (there is no 1.5 species). The explanation is also not adequate. Explanations of both figures (4.A and 4.B) are provided so that the figures can be interpreted independently. It is difficult to separate the blue-light blue-purple colors in Figure 4.A. Choose colors that are easier to separate or use markers.

Line 315. It should be worded more nuanced, because the figure also shows that this is only approximately true.

Line 317. Inaccurate statement.

Line 327. You should start on a new line.

Lines 334-336. No! You can only argue about increasing of number of species, because there is no evidence that previously acquired morphological and physiological characteristics are lost.

Lines 336-338. No! A higher number of species means more species living together, but it does not mean that they share different water and nutrient sources. In fact, quite the opposite.

Lines 338-340. It is already mentioned in the introduction or belongs there.

Lines 340-343. It should be correlated with your own results.

Lines 345-349. Mixed cause and effect. Water is more abundant in deep soil, which requires a longer (deeper) root system to reach it. More water gives the opportunity to grow larger leaves (LA), more evaporation, which cools the plant in high temperature conditions. A larger LA allows photosynthetic chloroplasts to arrange a larger surface, so they don't have to rely on a larger SLA, because they can evaporate more.

Lines 349-351. => No! A higher dry matter content of the leaf does not mean a greater allocation to the roots!

Lines 351-352. Of course! And ??

Lines 353-355. => I doubt it! Trees that develop a deeper root system often have a functionally separate root system, the deeper one mainly absorbs water, the one in the topsoil mainly absorbs nutrients.

Lines 356-360. This is a result, not a discussion, and it is already mentioned in the introduction, it belongs there.

Lines 360-365. The results should be explained in comparison with the literature.

Lines 366-369. Trees cannot do this, only their microorganisms.

Lines 369-372. That's not an explanation. Both types of mycorrhizae are symbiosis and can help supply the plant with nutrients.

Lines 372-374. The connection is not clear.

Lines 376-377. You have to compare your own results with the literature.

Lines 379-386. It is mentioned in the introduction, it is not necessary here.

Lines 388-394.=> This is not a discussion either.

Based on this guidance, the rest of the discussion chapter should be revised.

From 489: On the conclusion chapter, see general notes. The figures in the supplementary material are nice, but their legends are incomplete.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have improved the article a lot, so I will only suggest a few minor improvements.

Q3

„Our findings provide insights into the effects of species richness and trait categories on leaf-root trait coordination. Specifically, trait categories generally had a significant impact on leaf and absorptive fine root traits, while species richness significantly influenced most of the trait parameters of the leaf, absorptive, and transport fine root. Additionally, trait categories

played a crucial role in the coordination between leaf and fine root traits, and this coordination

increased with increasing species richness in deep-rooted, evergreen, and ECM species.”

The categories have no effect! The attribute categories were created by humans. Plant properties are the plant's responses to ecological factors. This needs to be corrected in several places in the article.

Q6

Species richness" is used widely in the papers of the BEF-China experiment to represent the species richness of plots”

I accept it, but this is an international paper, so if you want to use it that way, put an explanatory sentence at the beginning of the article on what you mean by Species richness, so that non-Chinese readers can understand it as well.

Q22: It is acceptable, but then it must be written that it is shown in Table 1.

Q26: Lines 305-306.

I understand that you want to show trends, but this figure is not mathematically correct, so replace it. The trend can be represented in another way.

Q43: Lines 376-377. “Leaves are directly exposed to light and are sensitive to the external environment. Therefore, leaf functional traits directly reflect the response of plants to changes in environmental factors (Niinemets et al.,2015).

The leaves are exposed to rapid changes in climatic factors, not only to light but not to all external environmental factors. There is only an answer to influencing factors. This is an interaction: if there is no response, then there is no influencing factor.

’Therefore, leaf functional traits directly reflect the response of plants to changes in environmental factors.”

Despite the literature reference, this statement is incorrect.

Q43-45. Regarding roots, there is a contradiction in the answers to questions Q43 and Q45.

„In contrast, transport roots are less susceptible to changes in the soil”

and

“The phenotypic plasticity of transport root is generally

higher than that of absorptive root”

Author Response

Please see the attachment.

Author Response File: Author Response.pdf