Variation in Leaf Functional and Plant Defense Traits of Introduced Eucalyptus Species across Environmental Gradients in Their New Range in Southern China

Round 1

Reviewer 1 Report

1.    The age of trees has a significant effect on functional leaf traits and secondary metabolites. If the age of the trees was taken into consideration for selecting the stands of three Eucalyptus species.

 

2.    The use of the term populations is a little confusing as the trees were occurring in plantations at different locations, it is suggested to use the term stands of trees rather than populations.

 

3.    If it is possible to include photographs of the three species in the study area under material and methods.  

 

4.    There is no information on the general soil characteristics of the study area, it would be interesting to add some information on the soil type.

 

 

5.    The plant defence traits could have been related to changing climatic conditions. 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer, 

Thank you for your feedback on our manuscript. Please find our response to your comments below:

1. The age of trees has a significant effect on functional leaf traits and secondary metabolites. If the age of the trees was taken into consideration for selecting the stands of three Eucalyptusspecies.

Response: This is a good point. When sampling in the field, we selected mature trees that were several years old. This is now clarified in the manuscript.

Lines in revised manuscript: 181-182

 

2. The use of the term populations is a little confusing as the trees were occurring in plantations at different locations, it is suggested to use the term stands of trees rather than populations.

Response: We often sampled naturalized trees on roadsides or hillsides, so many of the trees were not in plantations (they had natural sprouted, see Table 1 for details of trees sampled). That is why we used the term ‘population’. However, some of the individuals sampled were planted (also indicated in Table 1). Therefore, we agree that tree stand is probably a better term to use to avoid confusion. As such, we have changed ‘populations’ to ‘tree stands’ throughout the manuscript.

Lines in revised manuscript: 158, 163, 167, 174, 178, 179, 195.

 

3. If it is possible to include photographs of the three species in the study area under material and methods.  

Response: Thank you for the suggestion, photographs of each species, parts (a), (b) and (c) have been added to Figure 1 with the map of the study area as part (d).

Changes to revised manuscript: Figure 1 and caption (lines 173-176)

 

 

4. There is no information on the general soil characteristics of the study area, it would be interesting to add some information on the soil type.

Response: Thank you for this comment. We have added details of the soil type to Table 1. The soil data was obtained from the China Resources Environment Science and Data Center on the Spatial Distribution of Soil Types, available at https://www.resdc.cn/ (now indicated in the manuscript).

Changes in revised manuscript: Table 1 and caption (lines 199-200)

 

5. The plant defence traits could have been related to changing climatic conditions. 

Response: We agree and have revised the Discussion to discuss how variations in plant defense traits could be related to changes in climate. For example, we found that phenolic compounds of all Eucalyptus species increased with elevation and now point out that this could be related to changes in climate, as well as harsher environmental conditions. Also, we did find that phenolics increased with MAP in both E. saligna and E. grandis (Supplementary Fig. S6). This is also pointed out in the Discussion and further highlights the influence of climatic variables on plant defense traits in these two species.

Lines in revised manuscript: 471, 478- 479

 

Comments from Reviewer 1 in the pdf:

Line 4: ‘in southern China’

Response: We have added ‘in southern China’ to the end of the title of the manuscript.

Lines in revised manuscript: 4

 

Line 17: ‘stands’

Response: We have changed ‘populations’ to ‘stands’ here.

Lines in revised manuscript: 17

 

Line 25: ‘the tree populations’

Response: We have changed ‘populations’ to ‘the tree populations’ here.

Lines in revised manuscript: 25

 

Line 27: ‘small’

Response: We have changed ‘marginal’ to ‘small’ here.

Lines in revised manuscript: 27

 

Line 28: ‘range’

Response: We have changed ‘population’ to range’ here.

Lines in revised manuscript: 28

 

Line 142: add ‘Eucalyptus’

Response: We have added ‘Eucalyptus’ here.

Lines in revised manuscript: 141

 

Line 157: ‘stands’

Response: We have changed ‘populations’ to ‘stands’ here.

Lines in revised manuscript: 156

 

Line 159: ‘tree stands’

Response: We have changed ‘populations’ to ‘tree stands’ here.

Lines in revised manuscript: 158

 

Line 162: ‘reproducing trees’

Response: We have changed ‘populations’ to ‘reproducing trees’ here.

Lines in revised manuscript: 161

 

Line 164: ‘tree stands’

Response: We have changed ‘populations’ to ‘tree stands’ here.

Lines in revised manuscript: 163

 

Line 168: ‘tree stands’

Response: We have changed ‘populations’ to ‘tree stands’ here.

Lines in revised manuscript: 167

 

Line 172: ‘Location of tree stands’

Response: We have changed ‘Location of populations’ to ‘Locations of tree stands’ here.

Lines in revised manuscript: 173-174

 

Line 176-177: ‘populations’ highlighted

Response: We have changed all highlighted ‘populations’ to ‘tree stands’ here

Lines in revised manuscript: 178-179

 

Line 192: Table 1: ‘Tree stands’

Response: We have changed ‘Populations’ to ‘Tree stands’ here.

Lines in revised manuscript: 195

 

Line 216: ‘phosphorus’

Response: We have changed ‘phosphorous’ to ‘phosphorus’ here.

Lines in revised manuscript: 220

 

Line 255: ‘all functional’

Response: We have changed ‘all traits’ to ‘all functional traits’ here.

Lines in revised manuscript: 259

 

Line 282: ‘were’

Response: We have changed ‘was’ to ‘were’ here.

Lines in revised manuscript: 282

 

 

Author Response File: Author Response.docx

Reviewer 2 Report

Liu et al looked at the phenological changes in three introduced Eucalyptus species in Southern China. The researchers examined leaf physical characteristics, nitrogen and phosphorus content, and phenolic compounds in different populations of each species. They found that functional traits such as leaf size and thickness decreased at lower latitudes, particularly in E. grandis. Leaf phosphorus was lower at higher latitudes and altitude in E. grandis, while leaf nitrogen and phosphorus decreased with altitude in E. robusta. These findings suggest both species allocate resources conservatively, with E. grandis having enhanced chemical defenses at higher elevations. Moreover, marginal populations of E. grandis had higher SLA, indicating population expansion at the edge of the species' geographic distribution. The study concludes that it is important to consider interspecific trait differences across wide geographic areas when studying the spread of invasive species in new ranges.

This manuscript is well organized and written with detailed methods and adequate results. The authors made hypotheses before conducting research and inspected the hypotheses with their findings. I would recommend its acceptance for publication if several minor issues listed below can be addressed:

1. In table 2 and 3, the authors should explain what “t” and “T” are in the table captions.

2. In line 226, a reference may be added for the phenolic compounds' measurement method.

3. "MAT" has 2 distinct meanings: maximum annual temperature (for example in line 343) and mean annual temperature (for example in line 354), the authors should solve this ununiformness problem throughout the manuscript.

4. In Abstract (line 29) the authors pointed out the importance of considering interspecific trait differences, while in Introduction (line 62) and Conclusion part (line 537) it seems the intraspecific variation/differences is the focus. The authors should clarify which one is the subject.

Author Response

Dear Reviewer,

Thank you for your comments on our manuscript. Please see our response to your comments below:

Liu et al looked at the phenological changes in three introduced Eucalyptus species in Southern China. The researchers examined leaf physical characteristics, nitrogen and phosphorus content, and phenolic compounds in different populations of each species. They found that functional traits such as leaf size and thickness decreased at lower latitudes, particularly in E. grandis. Leaf phosphorus was lower at higher latitudes and altitude in E. grandis, while leaf nitrogen and phosphorus decreased with altitude in E. robusta. These findings suggest both species allocate resources conservatively, with E. grandis having enhanced chemical defenses at higher elevations. Moreover, marginal populations of E. grandis had higher SLA, indicating population expansion at the edge of the species' geographic distribution. The study concludes that it is important to consider interspecific trait differences across wide geographic areas when studying the spread of invasive species in new ranges.

This manuscript is well organized and written with detailed methods and adequate results. The authors made hypotheses before conducting research and inspected the hypotheses with their findings. I would recommend its acceptance for publication if several minor issues listed below can be addressed:

Response: Thank you for your positive feedback on our manuscript. We have gone through your comments and revised the manuscript. Please see below for our detailed responses to each comment.

 

1. In table 2 and 3, the authors should explain what “t” and “T” are in the table captions.

Response: The t value in the tables is the test statistic for the mixed effects models. In the outputs from the R package lmer, the P value (significance) is for the t test (Kuznetsova et al. 2017). We have clarified the t value in the manuscript. We checked our tables again and could not see a “T” value in the tables in our version.

 Lines in revised manuscript: 280, 371

 Reference

Kuznetsova A, Brockhoff PB, Christensen RH (2017) lmerTest package: tests in linear mixed effects models. Journal of statistical software 82:1-26.

 

2. In line 226, a reference may be added for the phenolic compounds' measurement method.

Response: Thank you for this comment. We have added the reference Singleton and Rossi (1965) for the method used to measure phenolic compounds.

 Lines in revised manuscript: 230

Reference

Singleton VL, Rossi JA (1965). Colorimetry of total phenolics with phosphomolybdic-phosphotungstic acid reagents. American journal of Enology and Viticulture 16(3):144-58.

 

3. "MAT" has 2 distinct meanings: maximum annual temperature (for example in line 343) and mean annual temperature (for example in line 354), the authors should solve this ununiformness problem throughout the manuscript.

Response: We apologise for the confusion. We used mean annual temperature (MAT) and mean annual precipitation (MAP) in our study. We have checked these terms throughout the manuscript and they are now uniform in the text.

Lines in revised manuscript: 197, 343

 

4. In Abstract (line 29) the authors pointed out the importance of considering interspecific trait differences, while in Introduction (line 62) and Conclusion part (line 537) it seems the intraspecific variation/differences is the focus. The authors should clarify which one is the subject.

Response: We apologise for the confusion here. Our study investigated functional trait differences at the population-level of three species and as such it gave us the opportunity to explore both interspecific and intraspecific trait differences. Since few studies on introduced tree species have focused on the population-level (i.e., intraspecific differences), we emphasised the importance of this in the Introduction and Conclusion. However, we did find some notable differences between the species, particularly for SLA between E. grandis and E. robusta, with the northern populations of E. robusta displaying a more conservative growth strategy and some populations of E. grandis having higher SLA and indicating range expansion at the edge of this species distribution. Yet, these differences across species were revealed by studying intraspecific differences. As such, we have changed the Abstract, to say that it is important to consider ‘intraspecific differences’ to be consistent with the focus of the rest of the manuscript.

Lines in revised manuscript: 29

 

 

Author Response File: Author Response.docx