Simulating Increased Permafrost Peatland Plant Productivity in Response to Belowground Fertilisation Using the JULES Land Surface Model

Round 1

Reviewer 1 Report

Interesting to read, really relevant and high significance of interest. Mostly formatting and minor methodological errors and text editing, See in more details below

Overall: Improvement and standardization of acronym is required,

Title: Arctic, always with a capital A

Introduction: Develop about species influence and species change link to a long-term northern migration of biome, Why is warmer in the Arctic develop about Arctic Amplification, Develop on N forms and speciation

Methods: L60: Add site coordinate and/or map of peat mire and Abisko research station, L61: specify type of permafrost, isolated, sporadic, discontinuous …L 75-76: add plant species common name in the text, L78: How N fertilizer was added and form, Line 104-109, eg of better used of acronym NPP and C, Active layer depth? 1^st paragraph after equation 4 ‘0°C’, L143-145: Arctic, L182: 1°C, develop of number of growing degrees day about 5°C, index of plant growth, Line 316-317: 2 gm-2 and 1 gm-2, L350: use same nomenclature for plant species E. hermaphroditum or Empetrum h … along the paper, L358-360: 1 gm-2 and 9 gm-2, L372: add reference, L373: 4.8°C

Discussion: develop on species change

Conclusion: Short and clear, L534: Arctic

Figure 1: formatting required, box legend fig1c, and remove 2014 on the graph

Figure 2: increase figure size and fonts

Figure 3: (gm-3)

Figure 5 : increase font size in box legend, and figure, can not see yellow and red trends in left figure

Figure 6: formatting required, text in the figure and at the bottom, why various colour, any variability SE and or statistical analysis for significant variation?  

Figure 8: selection of colour questionable, such as lite yellow on white

Figure 9: any variability SE and or statistical analysis for significant variation?  

Table 1: increase the space between line, root density … should be on the same line and ‘layer (gm-2)’, title on top of table

Table 2: title on top of table

Table 3: increase the space between line or

Table 4: formatting required, use same format than previous table, title on top of table

Table A1: Arctic and increase the space between line, font seems different between A1 and A2

Table A3: formatting required, use same format than previous table

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This is a well-written and interesting paper. The justification for the study is well articulated and the methods are clearly explained. The focus of the paper is both timely and of great relevance for understanding the nature of how arctic plants may respond to warming and permafrost thaw. The JULES simulation that successfully replicated past study results from a field experiment (Keuper et al. 2012) provides a robust foundation for future modeling scenarios. Because the present study build on the research design of a previous study I have no quibbles about the Results per se. Rather, I wish to see the Discussion expanded somewhat in light of my comments below:

My main critique of this paper, and others of similar structure, rests on the implicit assumption that these model projections provide useful information despite little consideration of other likely future changes in ecosystem dynamics. This is a contradiction of basic ecological principles. To rectify this shortcoming, papers presenting reasonable (but inherently reductionistic) modeling approaches to important ecological questions, needs to pay more homage and attention to addressing the caveats of “manipulating one variable while keeping everything else constant”.

The present version of the manuscript provides inadequate attention to the factors influencing N mineralization com=ntrolling N uptake at the thaw front, especially the temperature controls thereof versus the actual magnitude of N mineralization to support plant uptake demand. Moreover, thaw depth development is a time dependent process, which may not by synchronized with plant N demand. Not only are root suberization over the growing season slowing potential uptake capacity, but arctic plants species may be re-translocating nutrients back into storage tissues by the time a meaningful change in thaw depth has occurred. A bit more discussion of this issue would be helpful.

The paper makes no mention of role of organic N (especially free amino acids) which in acidic, arctic soils may be as important to plant nutrition as ammonium. It strikes me that the phenomenon of permafrost thaw could reveal much greater consequences for nitrogen cycling and NPP if a broader perspective on plant N nutrition would be considered – especially since the controls over protein turnover vs. N mineralization may be quite different. I realize that this modeling exercise was tied to the methods of Keuper et al. 2012, but the Discussion should at least pay lip service to this dimension of N cycling in the Arctic.

The authors provide insufficient treatment of plant species changes, especially graminoid responses to increased inorganic N availability. Moreover, in light of the extensive shrubbification of the Arctic, canopy overtopping of present PFT such as Rubus and Empetrum is likely to reduce the capacity of these species to respond to warming-induced changes in N availability – thus making projections of responses by 2100 a great deal more uncertain. The authors, to their credit, acknowledge the absence of this consideration in their paper, but a broader discussion is warranted.

I don’t fault the authors for not incorporating the issues that I have mentioned above, but I think simulation studies of the kind presented here need to provide a broader discussion of the thought-provoking, yet reductionistic, model outputs. We are all interested in understanding what the arctic system will be like by 2100. Consequently we cannot honestly present the responses of a single/few species to a single/few drivers without discussing a broader subset of the multitude of ecological interactions that could profoundly affect the magnitude and direction of the particular phenomena investigated in the present paper. Consequently, greater attention to these broader issues would both convince readers of the importance of the present study and provide a meaningful context to address additional questions in the future.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Dear colleagues. I studied your paper.

In general, I must say that it is well and carefully prepared and states a number of facts.
I have just a few small comments.
In the abstract, the novelty of your ideas could be emphasized more. I know the last sentence does it in part, but I think it could be done a little better.

The introduction is brief, but I don't think it matters - many papers unnecessarily copy older information without further binding. He would easily keep it in this form.

In the methodology, it might not be wrong to increase meteorological data, ie precipitation and temperature during the year, not just average values ...

On the contrary, the model and the result part are described very well and in detail. Although this problem is not purely my specialization, it was easy to navigate the data.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

The manuscript is devoted to solving an essential issue for the Arctic region related to the assessment of additional nitrogen released during permafrost thawing impact on plant productivity. In general, the manuscript can be accepted for publication in the journal after a minor revision.

Some specific comments:

L 78 and L 208: In which form was this slow-release nitrogen fertilizer applied (organic/mineral, nitrate/ammonium)? How was the nitrogen content and migration in the soil profile controlled during the experiment?

Table 1: Please provide data about the content of aboveground biomass of plants in g/m². Please specify the depth of the top layer in which the root content was evaluated. Have rhizomes been taken into account when assessing belowground biomass?

L 108: Please give examples of plant parts included in the DPM and RPM fractions.

All Latin names of species should be italicized (for instance, see L 268 and 622)

Please use the same type of terms spelling in the text (for example, there are three spellings: above ground / above-ground/ aboveground; below ground/ below-ground/ belowground; shallower rooting/ shallow rooting/ shallow-rooting, ect.)

Fig. 3, 6 and 7: Please correct the abscissa axis

I tend to think that the manuscript Conclusion may be reduced. Please edit the text of this chapter.

Please double-check the text because many spaces were missed.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I am very satisfied with the honest and constructive responses by the authors to my review.