Effects of Above- and Below-Ground Interactions of Plants on Growth of Tree Seedlings in Low-Elevation Tropical Rainforests on Hainan Island, China
Round 1
Reviewer 1 Report
The paper has been improved based on the comments from the first review. This is my second review of this paper. My previous comments have been incorporated into the revised version, which is nice to see.
I have one lingering concern with the wording of the conclusions of the paper. I would warn the researchers to not over-step the bounds of the study and reach a lofty, unsupported conclusion.
I am speficially referring to the following lines, which appear at the end of the abstract: "Our study demonstrates that aboveground competition is more important than belowground competition in seedling community assembly of the lowland tropical rainforests."
The study compares the effect of aboveground vegetation removal vs. trenching. These are not equal in their magnitude of competition release and do not directly measure the magnitude of competition. Therefore, the authors must rephrase this sentence to compare the relative effects of aboveground vegetation removal vs. trenching on the above vs. belowground biomass production of tree seedlings.
Please re-phrase comparing the effects of understory plant canopy removal vs. trenching, removing the references to competition (which you have not directly measured). I started this in my first review and it should be taken very seriously now.
Author Response
Comments from reviewer # 1:
I am specifically referring to the following lines, which appear at the end of the abstract: "Our study demonstrates that aboveground competition is more important than belowground competition in seedling community assembly of the lowland tropical rainforests."
The study compares the effect of aboveground vegetation removal vs. trenching. These are not equal in their magnitude of competition release and do not directly measure the magnitude of competition. Therefore, the authors must rephrase this sentence to compare the relative effects of aboveground vegetation removal vs. trenching on the above vs. belowground biomass production of tree seedlings.
Please re-phrase comparing the effects of understory plant canopy removal vs. trenching, removing the references to competition (which you have not directly measured). I started this in my first review and it should be taken very seriously now.
Response: Thank you very much for your constructive suggestions. We have rephrased the sentence as "Our study demonstrates that aboveground vegetation removal had a stronger effect than trenching on the growth and assembly of tree seedlings in the lowland tropical rainforests." In addition, we have replaced the word “competition” with “plant interaction” in many places of the text including the title on basis of your concerns. However, the main theme of the study was on the above- and below ground treatments on plant interactions, which were competitive in many conditions, thus we still use the word competition in some sentences of the text. We ask your understanding on this aspect.
Author Response File: 
Author Response.docx
Reviewer 2 Report
I have reviewed the MS as a previous submission. Unfortunately, the new submission bears the same flaws which were not corrected.
General comments:
The Authors suggested quite a simple research plan but the results may be of interest for the journal's readership.
L. 148-151: It should be explained why the Authors use linear regression to analyze RGR vs. PAR while using Pearson correlation in RGR vs. root biomass. Why not using the same method of comparison?
L. 198-199: 'While their results show that the treatment of reducing underground competition significantly improve the growth rate' - it should be indicated if the cited authors used the same method of belowground competition reducing (trenching) or not. Any suggestion why the published results disagree with those of the Authors?
L. 228-231: The logic of the explanation is rather vague. Currently, it looks like: 'deciduous species shed their leaves during the dry season' + 'evergreen leaf allows plants to maintain a photosynthetically active canopy ' -> 'deciduous species grow rapidly'. How does the conclusion follow from the two suppositions?
Minor comments:
L. 16-18: The sentence has neither subject nor predicate.
L. 21: 'our deciduous species' - four?
L. 107: 'PAR (photosynthetically active radiation) of seedlings' - PAR cannot be 'of seedlings', the expression requires a reformulation.
L. 109-110: Incomplete sentence.
L. 139: 'The relative growth rate (RGR) of each seedling were' - wrong use of the plural.
L. 148: 'Linear regression were' - wrong use of the plural.
Table 1, Figure 1: The indications 'a' and 'b' should be explained in the captions.
L. 178: Figure 3: wrong number of the figure.
L. 183-184: 'the effect of belowground competition on seedling growth were not' - wrong use of the plural.
L. 199: 'treatment of reducing underground competition significantly improve' - improves.
Author Response
Comments from reviewer # 2:
Major comments:
- 148-151: It should be explained why the authors use linear regression to analyze RGR vs. PAR while using Pearson correlation in RGR vs. root biomass. Why not using the same method of comparison?
Response: Thanks for your checks. We have used the same method of comparison and tested the relationship of seedling RGR and root biomass also by linear regression according to your suggestion.
- 198-199: 'While their results show that the treatment of reducing underground competition significantly improve the growth rate' - it should be indicated if the cited authors used the same method of belowground competition reducing (trenching) or not. Any suggestion why the published results disagree with those of the Authors?
Response: We inserted the sentence “whose method of belowground competition reducing (trenching) is the same as ours.” in the new version of the manuscript. And we have analyzed the possible reasons for the inconsistent results. ” Their study just analyzed the effect of belowground competition on seedling growth in Panama. They didn’t compare the effects of aboveground and belowground competition on seedlings growth simultaneously. In their studied system, probabllly the underground resources such as water or nutrients were in shortage, resulting in a strong competition among the seedlings. However, in our studied area, understory vegetation was dense, which might pose a serious constraint on the growth of tree seedlings in terms of light availability. And the belowground resources such as water and nutrients were still ample enough for the utilization of all the competing seedlings of plants.
- 228-231: The logic of the explanation is rather vague. Currently, it looks like: 'deciduous species shed their leaves during the dry season' + 'evergreen leaf allows plants to maintain a photosynthetically active canopy ' -> 'deciduous species grow rapidly'. How does the conclusion follow from the two suppositions?
Response: We changed this sentence to “The difference in relative growth rate between deciduous and evergreen species may be related to leaf functional traits. Most studies to date have found that the greater RGR of deciduous species seems to be determined by their higher specific leaf area. The higher specific leaf area enhances the carbon capture efficiency of leaves. Consequently, deciduous species with higher specific leaf area grow rapidly.”
Minor comments:
- 16-18: The sentence has neither subject nor predicate.
- 21: 'our deciduous species' - four?
- 107: 'PAR (photosynthetically active radiation) of seedlings' - PAR cannot be 'of seedlings', the expression requires a reformulation.
- 109-110: Incomplete sentence.
- 139: 'The relative growth rate (RGR) of each seedling were' - wrong use of the plural.
- 148: 'Linear regression were' - wrong use of the plural.
Table 1, Figure 1: The indications 'a' and 'b' should be explained in the captions.
- 178: Figure 3: wrong number of the figure.
- 183-184: 'the effect of belowground competition on seedling growth were not' - wrong use of the plural.
- 199: 'treatment of reducing underground competition significantly improve' - improves.
Response: Thank you very much for your careful readings. We have modified all the minor mistakes according to your suggestion.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Review of Forests Lu et al – 2021 – Effects of aboveground and belowground competition on seedling growth of lowland tropical rainforests on Hainan Island.
Xinghui Lu et al present results from a seedling experiment conducted in the seasonal lowland tropical forests of Bawaling Hainan Island. They measured seedling relative growth rates for eight tropical tree seedlings (4 evergreen and 4 deciduous) grown in an experimental design where plots were either cleared for aboveground vegetation, trenched, or both.
I found the manuscript in descent shape. Some strengths of the paper are its simplicity and sound design which have the potential to help understand the relative effects of light vs water/ nutrient limitation on seedling growth rates in this seasonal forest. Several weaknesses exist in the paper; 1) the English language and grammar need clarification in many place (I have worked to point out where those are). 2) the logical links between “competition” above and belowground and the experiment need to be better explained (see my comments below). 3) the results should include a section for the effect of root biomass on seedling RGR (similar to the section already included about PAR effects on seedling RGR).
Major comments:
Point 1: English language and grammar: just proofread and watch for spelling mistakes. The grammar will improve with continued practice.
Point 2: you need to explain that you are using the seedling growth response to light as a metric for above ground competition (between seedlings and tree and between seedlings and themselves). This is because light is commonly considered the most limiting resource aboveground in the understory of tropical forests. This response metric does not necessarily measure the strength of completion per se but is an indicator of the release from competition in the vegetation removal plots. You need to clearly articulate this point in the abstract and early in the introduction. It appears on line 104, but I think it should appear earlier I the intro .
L24: no mention of light (photosynthetically active radiation) prior to this. You should include in your abstract a justification that the effect of light on RGR serves as a proxy for aboveground competition and that the effect of root trenching on RGR serves as proxy for belowground competition.
It also needs to be stipulated when you explain the results on L 159
L64-67: shade-intolerance and deciduousness are not perfectly correlated and do not always/ only indicate a pioneer strategy. Likewise, shade intolerance and evergreen status are not perfectly related and do not always
Point 3: you have evaluated the response of PAR in seedling heigh RGR (as your proxy for aboveground competition), but you have not fitted any regressions for root biomass. I suggest you include as section 3.4 on the relationships between root biomass and RGR between evergreen and deciduous species across the treatments. Even if the relationships are non significant, you need to show them so that you can complete the comparison between effects of PAR vs. root trenching (i.e. above vs. belowground). Right?
Line comments:
L20: and no vegetation removal or trenching (as the control)
L21: growth rates of seedlings
L21: ANOVA
L25: can you R and R+T treatments – 1) R and R+T treatments significantly increased…
L27 higher -> greater
L25: growth rate increased with more PAR
L28: “This study demonstrates that aboveground competition is more important than belowground competition”… This statement is not supported by the previous sentences in the abstract! How does it demonstrate this? Can you elaborate and be more specific?
L37: seedling mostly compete with mature trees and themselves for… point: seedling to seedling competition is important also.
L38: proverbially true?
L39 tropical forests
L40: resource factors -> resources
L42: strongly (spelling)
L42-44: this sentence does not make sense. Rewrite and clarify
L50 conduce to?? -> affect or result in
L50: much works -> either say “much work has” or say “many works have”
L58: are of great importance
L59: dry forests are. L60: wet tropical forests are
L88: need to explain how above and below competition relate to trenching and vegetation removal – see point 2 above
L:104: how many plots per treatment were done? 8?
L114: Field SCOUT quantum light meter
L116: sunny
L117 photosynthetically ACTIVE radiation (PAR) can use abbreviation here.
L119: this is repetitive from L115.
L120: root biomass
L130: nursery site? No mention of nursery site until now. Why was this done? Need to justify and explain more.
L149: species
Lines 159 and 172: you need to give the F statistics and degrees of freedom in addition to the p values.
Table 1: label the last column dry root biomass. Why do you give numbers in gX100 cm^-3? Why not just g cm^3?
Figure 1: why do you only have 2 x-axis labels for treatments when you have 4 treatments?
Figures 1 and 2. Change y-axis labels to “seedling height relative growth rate”
L170 was significantly increased -> increased significantly.
L175: seedling RGR increased in all treatments in response to PAR. Okay, but how does this demonstrate competition?
L177: Evergreen
L184: “had a greater effect” based on what evidence in the results?
L195: seedling carbon fixation.
L198-199. You need to give definitions for symmetric (i.e., between seedling and seedlings) and asymmetric (between seedlings and trees), here. right? always define terms like these when you use them in a discussion.
L205: depth in the stand? What is meant by this? This is unclear
L220: deciduous species shed their leaves… yes, okay, but the seedling usually don’t shed their leaves so… what the point here?
L226: I disagree, the effect of light on the RGR of deciduous vs. evergreen species looks the same to me, The increases when vegetation is removed are about the same. Yes, the growth rates are different among the two groups, but the response to light looks to be about equal. I strongly disagree with the conclusions here about the strength of competition. i.e., that “the growth of shade-intolerant, deciduous species is more significantly affected by the competition of contiguous trees” your results do not show this. If they do, you need to more clearly explain how you have come to that conclusion. (i.e., based on what evidence)
L232: intense light
L235 appear and dominate. Our results indicate??
L237: could play or likely play
L238: forest restoration? What?? Where does restoration come into play here. you go from talking about successional dynamics to restoration. This jump is haphazard and unclear.
L248: again you need more results from the belowground part of the study to support this claim.
L256: “provide important theoretical support to accelerate the future recovery or secondary forests” how so? What is the new theoretical support?
Reviewer 2 Report
Dear Authors,
Please find comments in the file attached.
Regards
Comments for author File: 
Comments.pdf
Reviewer 3 Report
The Authors suggested quite a simple experimental plan. Nevertheless, the manuscript (MS) may be of practical interest for the journal's readership as a short communication.
General comments:
L. 120: The data on the fine roots do not seem to be used anywhere in the analysis. What is the sense of the data?
L. 130-138: The experiment was set up rather long ago and lasted for only two years. Why not project it for a longer time?
L. 144: 'RGR = (ln(H1) - ln(H0))... - why the logarithmic form was used? The reference 'RGR were log transformed to improve normality' doesn't explain this because here the Authors log transform the heights.
L. 171-172: 'The seedling RGR 171 of deciduous species was significantly higher than that of evergreen species (P < 0.05).' Significantly higher in what treatment?
L. 181: In Table 2, is the P-value relate to the constant or the coefficient of the equation?
Minor comments:
L. 16: It is a standard that the Latin names are provided with the authors' names at the first appearance in the MS.
L. 22: 'One-way ANOV (?) were used to compare the RGR' - the RGR abbreviation should be defined at the first appearance.
L. 49: 'lignt' light?
L. 54: 'is less' - is less than what? less frequent?
L. 57: 'growth are great importance in determining the species present' - of great importance? presence?
L. 71: 'decidous monsoon rainforest were higher than the tropical lowland' - deciduous? than in?
L. 74: 'rain forest and tropical decidous monsoon rainforest' - deciduous? Rain forest or rainforest? The usage should be consistent throughout the MS.
L. 98: '(monthly precipitation > 100 m)' - needs correction
L. 149: 'specie' - s omitted?
L. 161: Table 1 must be improved. The notations 'a' and 'b' must be defined as their repeat in the Table.
L. 163-164: Figure 1 must be improved. The notations 'a' and 'b' must be defined in the caption. The vertical axis should be corrected to provide the visibility of 'b'.
L. 177: 'vergreen' - 'e' omitted?
L. 195: 'seedlingscarbon' - space omitted?
L. 219-220: 'may related to leaf phenology' - be related?
L. 230: 'strong effect species dynamics' - effect on?
L. 234: 'shde-tolerant' - 'a' omitted?
L. 237: 'chage' - change?
