the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Mar 2025
Comparative analysis of nutrient concentrations in generalist and specialist tree species on clay and sandy soils in the Central Amazon
Abstract. Tropical forest soils generally have low nutrient availability. Some species exhibit specialized behavior, occurring exclusively in a single soil type, while others are generalists, thriving across different soils and water table depths. This study assessed the influence of topographic variation on leaf and trunk macronutrient and carbon amounts of tree species occurring only in one topographic position and species occurring across topographic positions and their relationship with soil macronutrient and carbon stocks. We selected nine species occurring in different topographic positions: three plateau specialists, three valley specialists, and three generalists (with four replicates each, totalling 35 individuals), where leaf and trunk samples were collected from each individual, and soil samples for carbon and nutrient analysis and quantification. Leaf and trunk nutrient concentrations varied across specialist and generalist functional groups, with valley specialists showing the highest concentrations of leaf and trunk nutrients and carbon. Nutrient concentrations within generalists remained consistent across topographic positions, underscoring their adaptive strategy to sustain productivity across environments. The concentrations of certain trunk nutrients of plateau and valley specialists and generalists mirrored those found in leaves, albeit at lower relative concentrations. Trunk carbon concentrations did not vary significantly compared to leaves, suggesting that other biological or environmental factors influenced tree nutritional status. We found evidence of variations in plant carbon and nutrient concentrations between generalist and specialist species inhabiting plateau and valley habitats in Central Amazonia, and a weak correlation between the stocks of some soil nutrients and leaf and trunk nutrient amounts.
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Status: open (until 16 May 2025)
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RC1: 'Comment on egusphere-2025-391', Anonymous Referee #1, 02 Apr 2025
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I thank the authors for their detailed and relevant look into nutrient cycling in tropical forest and appreciate the hard work that has undoubtedly been done to achieve the results presented. However, I have many remarks throughout the text on phrasing, word choice, nuance, and more importantly, on the quality of the scientific analysis, discussion, and the data analyses. Nonetheless, I believe the expected changes/clarifications are feasible, which is why I would reconsider the manuscript after major revisions. Please find my general remarks below; for the detailed and textual remarks, I refer to the attached annotated pdf (please do not mind what is written on the first page - I noted those comments more clearly in the 'major general comments' below). The reason for providing the annotated pdf is that there were many textual issues that would simply take too much time to write in this reviewer comment.
Major general comments:
- The title does not represent the core of the study: at first, it seemed the study was about the difference between specifically sand- or clay soils, whereas the focus was actually on topography.
- Did you use pith-to-bark samples for basic wood density? You always mentioned the diameter of the wood samples you collected, but not their length (thus also not if they were pith-to-bark cores). Additionally, these samples are usually collected with 2 replicates per stem, to account for asymmetry in the stem's shape. Note that you can correct for not using pith-to-bark sensu https://bsapubs.onlinelibrary.wiley.com/doi/full/10.3732/ajb.0900243).
- Additionally, please explicitly mention how you treated the bark - was it included in measurements or not? This is also relevant for the wood nutrient analyses.
- The methodology of submerging the cores in water for 20 days has certain limitations: you probably over-estimate the fresh volume, so mention that one can also use conversion factors sensu https://bsapubs.onlinelibrary.wiley.com/doi/full/10.1002/ajb2.1175.
- Add more info in the methods section. The authors often refer to a protocol used by the lab, but the reader would have to see which steps were taken in the sample preparation, extraction methods, which machines were used to analyze the contents, ....
- The statistical analyses were carried out or discussed (or both) to a limited extent. The paragraph in the M&M section discusses the check of normality, but not of homoscedasticity. Additionally, and more importantly, the authors mention ANOVA as the method to test "whether leaf and trunk nutrient- and C concentrations differ between the generalist and specialist species," or Kruskal-Wallis in case the normality assumption was violated. The authors need to acknowledge that they have a categorical variable 'tree functional type' with 3 levels: valley spec., plateau spec., and generalist. ANOVA can only tell you if at least 1 of these levels differs significantly from the others, not if which levels differ from each other. For the latter comparison, you would need a suitable post-hoc test. Nonetheless, e.g. Fig. 4 shows the 3 factor levels with specific indications of significance marked as '*', which would have to mean post-hoc testing has been conducted. If this is the case, please mention in the M&M section. Additionally, Fig. 3 reports t-test results, while the method was not mentioned in the M&M, nor the assumptions to be evaluated. Finally, Fig. 6 shows Spearman correlations with p-values. Which statistical test was carried out? And why was a non-patametrical correlation coefficient used?
- Further, for now, the discussion of the results is quite limited and a bit 'shallow'. I believe the results are valuable, but require better understanding and more consistent and robust analysis. It is, e.g., important to acknowledge that you are not looking into soil nutrient availability, only to total nutrient stocks. Hence, is it surprising you don't find strong correlations with tissue nutrient contents?
- I'm still a bit unclear to what the actual impactful result is you found. As mentioned before, the discussion contains many general statements that are not necessarily informative. Following is an example from the abstract: "Trunk carbon concentrations did not vary significantly compared to leaves, suggesting that other biological or environmental factors influenced tree nutritional status." --> What do we learn from this? Is it maybe simply to be expected that wood vs. foliar carbon contents vary to a different extent? How is this linked to the 'tree nutritional status'?
- Additionally, in the discussion, always start with your results, and then put them in a context using literature.
Additional comments were written on the attached document, close to the corresponding sentence in the MS. Please also formulate a reply to these comments/questions in case of resubmission.
Minor general comments:
- Use 'wood' instead of 'trunk' or 'trunk woody material'
- Use 'content' instead of 'concentration' for mass-based measures (µg /g etc)
- Add a soil properties description table to the site description or results.
- The colors in Figures 3, 4, 5 are not particularly meaningful
- Make a clear distinction in terminology between plant functional types, often defined in the context of pioneer trees vs. shade-tolerants etc. Just to avoid confusion.
- Make sure to use abbreviations in full only at first mention: e.g., 'carbon (C)' --> Later only 'C'
- Fig. 3: plot means with diamond shapes, make y-axis labels bigger and simpler: 'Soil C (g C kg-1)', make sure to add the specific element after 'g' as in this example, why are they called 'average' concentrations? (similar remarks for Fig. 4 and 5)
- Fig. 6: what is the shaded area?
- Fig. 7: improve names: "Ca_Soil_Mg.ha" --> "Soil_Ca", put units in caption + What is the logic behind the colors?
- Why do you note down doi links for a few references only?
- Fig. S1: use different colors for different tree categories (--> how spatially separated are the classes actually?) + add classification what you define as valley and what as plateau. + relative height is relative to what?
- Fig. S2: I count 13 trees for valley specialists
- Fig. S3: Give info only for relevant species
- Generally: what do the confidence intervals indicate? How were they constructed?
- Is there no suppl. fig. 6?
- see comments in attached file for Suppl. Fig. 7 & 8.
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