Belowground and Aboveground Responses to Mixed Metal Contamination in Native Central European Trees in Relation to the Species-Specific Autecology
, Rainer Schulin 2, Patrick Schleppi 1 and Pierre Vollenweider 1
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript reports the results of a long term experiment with tree species and it is well written with important sets of data. It is an imprtnat ocntribution to studies on phytoremediation with native species and trees.
I have just to mention that the recent literature usually calls the "heavy metals" as "potentially toxic elements".
There are few places where the inclusion of many numbers in the text makes the reading extremely difficult. I have also identified problems in some tables and figures.
The comments are below.
Line 78 to 80 - I think the plant species names should be accompanied by the botanical authority at first mention. They are however at L542 and following
Table 1 - I do not understand the attribution of letters for significance to the different values. For instance, in the row related to P, the order of letters is not understandable. It should be a, ab, b and b in my opinion. Also for Zn it should be a, c, b, d. Compare also Figure 1. If you give "a" to the lowest number, then it should be consistent throughout the whole manuscript. In Table 1, "a" is given to the lower values, whereas in the figures "a" or "A" goes to the higher values.
L138 Table 3 is cited before Table 2
L158 and following - maybe it would be better to have the TF vallues in a table rather than in the text.
L167 - the use of colour in Figure 2 (and 3) is such that the figure is not understandable without the colours. Maybe using different point shape for each species could help.
L293-298 please rephrase
L307 - in what sense "as a metal element"?
Figure 8: see "A: P, K, B: Ca, Mg, C: S, Fe, D: C, N" - the use of letters and element symbols separated by commas makes this a little confusing
Author Response
The manuscript reports the results of a long term experiment with tree species and it is well written with important sets of data. It is an important contribution to studies on phytoremediation with native species and trees.
I have just to mention that the recent literature usually calls the "heavy metals" as "potentially toxic elements".
Answer: There were four instances where we used the term “heavy metal” or “heavy metals”: twice in the abstract, once at the start of the introduction, and in the keywords. We replaced it with “toxic metal” or “toxic metals” in the first instance in the abstract, the introduction and the keywords, and with “metals” in the second instance in the abstract.
There are few places where the inclusion of many numbers in the text makes the reading extremely difficult. I have also identified problems in some tables and figures.
The comments are below.
Line 78 to 80 - I think the plant species names should be accompanied by the botanical authority at first mention. They are however at L542 and following.
Answer: Botanical authority is now inserted line 80-82.
Table 1 - I do not understand the attribution of letters for significance to the different values. For instance, in the row related to P, the order of letters is not understandable. It should be a, ab, b and b in my opinion. Also for Zn it should be a, c, b, d. Compare also Figure 1. If you give "a" to the lowest number, then it should be consistent throughout the whole manuscript. In Table 1, "a" is given to the lower values, whereas in the figures "a" or "A" goes to the higher values.
Answer: Letters in the rows of Table 1 are given from the left to the right in ascending order of the alphabet, i.e. starting with “a”, then “b” for the next value that is significantly different from previous “a” values, then “c” for the next value significantly different from the previous “a” and “b” values, and so on. Combinations of letters are given where values are significantly different from some but not from all other values with a common letter. The only instance where this happened in Table 1 was for P. So, we added “c” to the last value on the right as well as to the second “a” value to indicate that it was not significantly different from the second “a” value, while it was significantly from the first “a” value. Letters indicating significance are given individually for each table and figure. This is a common standard.
L138 Table 3 is cited before Table 2
Answer: The numbering corresponds to the order in the text, disregarding the captions for Figure 1.
L158 and following - maybe it would be better to have the TF values in a table rather than in the text.
Answer: Including an additional table of TF values in the text would take up unnecessary space; in our view, a reference to Fig. S1 is sufficient.
L167 - the use of colour in Figure 2 (and 3) is such that the figure is not understandable without the colours. Maybe using different point shape for each species could help.
Answer: Probably the reviewer means the PCA Figs. 2 and 5. Today readers look at the Figs. in colour online. We shouldn’t distinguish between the species using different symbols as well. The colour is sufficient. We already use different symbols to distinguish the MC treatments from the controls. If we then also use different symbols for the species, it will only become even more confusing.
L293-298 please rephrase
Answer: “in roots for a few” has been moved, it is now correct (Line 296-300).
Line 161-166 also needed a rephrasing.
L307 - in what sense "as a metal element"?
Answer: It has been rephrased (line 311-316).
Figure 8: see "A: P, K, B: Ca, Mg, C: S, Fe, D: C, N" - the use of letters and element symbols separated by commas makes this a little confusing
Answer: Changed to boxed A, B, C, D, E in the figure caption and in L304. (The characters were needed for the submission of the figures). It is sufficient to refer to Fig. 8. Readers will immediately see which part of the figure relates to which nutrient.
Thank you for your comments.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear authors,
Thank you for providing this article.
This article has a distinctly ecological focus and examines the ability of various plant species to phytoremediate soil contaminated with heavy metals. The authors used a number of agrochemical, biometric, and microscopic methods.
Recommendations for improving the article:
1. Key words should be listed alphabetically.
2. The citations in the article do not comply with MDPI guidelines.
3. Am I correct in assuming that only two trees were planted in each experimental plot and that all the parameters studied were analyzed only from these two trees? In my opinion, this is completely insufficient. To obtain results based on reliable statistics, at least three plants, and preferably five, are needed.
4. The methodological section states that certain plant species were planted in the experimental plots as cuttings, while others were planted as seedlings. Is this difference in the vegetative development of the seedlings appropriate for further comparison? I believe all plant species should have been the same age when planted.
5. The Methodological Section of the article lacks references to the methods used; a separate section on statistical data processing is needed.
6. In my opinion, the results would look more appealing as box blots, which show the spread of the data. The images provided by the authors aren't entirely clear what exactly they represent—is this an average value? So where are the errors or deviations?
7. To systematize all the results obtained, I recommend the authors add a diagram, for clarity, combining all the results obtained on different tree species.
8. More references for 2025-2026 should be added to the References section to increase the relevance of the article.
The article may be published in the journal "Plants" after revision.
Respectfully yours, reviewer.
April 2, 2026
Author Response
Dear authors,
Thank you for providing this article.
This article has a distinctly ecological focus and examines the ability of various planduring the layoutt species to phytoremediate soil contaminated with heavy metals. The authors used a number of agrochemical, biometric, and microscopic methods.
Recommendations for improving the article:
1. Key words should be listed alphabetically.
Answer: It has been changed.
The citations in the article do not comply with MDPI guidelines.
Answer: The references were written using EndNote for MDPI guidelines. A correction already has been done in the layout.
- Am I correct in assuming that only two trees were planted in each experimental plot and that all the parameters studied were analyzed only from these two trees? In my opinion, this is completely insufficient. To obtain results based on reliable statistics, at least three plants, and preferably five, are needed.
Answer: As written in the methods section, there were 2 trees of each species per plot. With 10 plots each for the control and the metal contamination treatment this gave 280 trees in total. The mean values of the 2 trees per species in each plot (inserted in line 614-616) were taken for statistical analyses, with the plot as a statistical unit with 10 repetitions.
The methodological section states that certain plant species were planted in the experimental plots as cuttings, while others were planted as seedlings. Is this difference in the vegetative development of the seedlings appropriate for further comparison? I believe all plant species should have been the same age when planted.
Answer: Yes, this is due to the different propagation strategies used in practice for the tree species in question, based on their differing biological characteristics. Propagation by cuttings is not possible for Fagus and Picea. By using these propagation methods, we were able to ensure that the initial weight of the various tree species was similar. We inserted a statement emphasizing this fact on L 552-554.
The Methodological Section of the article lacks references to the methods used; a separate section on statistical data processing is needed.
Answer: We think references are given where needed. Statistics are also clearly described. In our opinion, the description of the methods is sufficient to allow for a replication of the whole experiment.
In my opinion, the results would look more appealing as box blots, which show the spread of the data. The images provided by the authors aren't entirely clear what exactly they represent—is this an average value? So where are the errors or deviations?
Answer: We believe that whether to use dot plots or boxplots is a matter of personal preference. Also, we do not understand the problem of the reviewer with the meaning of the points and the vertical bars. In the caption we explained that the points represent mean values of 10 replicate plots, and the error bars give standard errors (mean values ± SE, n = 10 plots).
To systematize all the results obtained, I recommend the authors add a diagram, for clarity, combining all the results obtained on different tree species.
Answer: Data analysis is summarised in Table 2 and in the conclusions.
More references for 2025-2026 should be added to the References section to increase the relevance of the article.
Answer: We now did another check of the literature for more recent work on the topic of the paper but did not find additional relevant publications, except the new reference {Lovynska, 2025}, with metal concentrations in forest trees near ancient smelters, which is now inserted Line 382 [40].
Thank you for your comments.
