The study addresses an interesting and additional angle in vegetation modelling - NSC dynamics across different organs. As such, the study could make a worthwhile contribution to readers of EGUsphere, I believe. 

That being said, the modelling exercise shows several logical flaws and conceptual inconsistencies, at least in my eyes. While I understand that a model 'validation' based on observations is an imporrant procedure to show that the model can reproduce reality to some degree, the main findings, i.e. the modelled  NSCs showed good agreement in seasonality with the observed NSCs at four sites, are a matter of model parameterization and not a proof of model precision.  Being an ecophysiologist, not a modeller, I may be wrong, but it appears to be logic that a model constrained by field data will produce simulations that fall within the range of that data.

Even more important, I believe that the central piece of the study, the model validation, is a red herring and does not provide show that this augmented model produces more realistic simulations than simpler ones. In particular, it would be really interesting to see whether the model can achieve what the authors claim in the discussion, i.e. "the model has a high potential to simulate various biotic effects on terrestrial ecosystems". Several studies during the last decade or so (e.g., Stich et al. 2008 GCB, Wu et al. 2018 J Climate, Hartmann et al. 2022 ARPB)  have shown that large-scale vegetation models have substantial difficulties in simulating stress responses to drought and heat, and cannot reproduce impacts of biotic disturbances on vegetation dynamics. If, as the authors clain, this model has a high potential to do just that, it would be great if their study could show it. This would then really be a substantial contribution to modelling science.

I also found that authors appear to confound NSC with carbon storage, which are not interchangeable terms. Some NSC, in particular starch, play a role in carbon storage, whereas other NSC, like soluble sugars, are primary metabolites of immediate use. They are needed in physiological functions and are thus not really storage that is put aside for later use. Maybe this confusion also led to the somewhat uncommon allocation scheme shown in Fig. 2. Whether my confusion about the carbon flow from trunk to leaves to roots shown in that figure comes from the lack of a thorough explanation in the text of figure caption, I cannot say, but I am concerned that this is a documentation of the authors' misunderstanding of C allocation in real plants.

Please find more comments in the attached annotated pdf document.

Comments to the Authors

First of all, I really enjoyed to read the manuscript and found it very interesting!!

The authors developed a new non-structural carbohydrate (NSC) module and incorporated it into a spatially explicit individual-based dynamic global vegetation model SEIB-DVGM. In recent years, the magnitude and frequency of extreme weather events have been increasing. Further increases in magnitude and frequency are also predicted. To accurately understand or predict tree responses to extreme weather events, an understanding of NSC dynamics is essential. Therefore, I believe that this study contributes significantly to understandings and future projections of forest dynamics under significant climate change.

This study certainly has merit, though I’ve got some concerns list below. The main issue in my mind is lack of explanation of the simulation scheme. Specifically, with regard to the comparison with observational NSC dynamics, is the age and/or tree size of the simulated forests same or similar with the observations? Also, it was unclear to me how the coefficients of NSCmax (a and b) were determined for the global-scale validation.

If the authors could consider above, I believe that it would improve the readability of this manuscript, and I would strongly encourage them to provide the consideration in a revised version of this manuscript.

Specific Comments:

Introduction

Line 42: What do the” spatial and temporal drivers” describe?

Line 80-95: The authors explain the indirect impacts first, but it seems easier to understand if the direct impacts are explained first.

Line 118-120: It would be easier to understand if it were stated after line 110, which describes the advantages of individual-based SEIB-DGVM.

Line 126-129: To demonstrate the superiority of the enhanced model (SEIB-DVGM-NSC), I think a comparison of the enhanced model with the original model (SEIB-DGVM) in discussion section would be of more interest to the readers. For example, regarding the comparison with the observation of NSC dynamics, is there a significant increase in similarity in the enhanced model over the original model that only considers the stock to the trunk? how much difference is observed when Fig5 is drawn in the original model compared to FIg5 in the enhanced model?

Model

Line 158-160: It would be better to have an explanation of the process of carbon stocking in the trunk in the original model.

Line 257-258: I did not understand how the authors determined the coefficients in Table 2. Please add a little explanation.

Line 260-262: What happens if the total carbon stock is insufficient?

Line 292-294: With regard to the comparison with observations of NSC dynamics, is the age and/or tree size of the simulated forests same or similar with the observations? This point may be important since it is mentioned in this manuscript that tree size is important for carbon allocation.

Line 405-406: Why decide from January percentage of NSC and biomass?

Line 411-413: It is unclear to me how the coefficients of NSCmax (a and b) were determined for the global-scale validation.

Results

Discussion

To demonstrate the superiority of the enhanced model (SEIB-DVGM-NSC), I think a comparison of the enhanced model with the original model (SEIB-DGVM) in discussion section would be of more interest to the readers. For example, regarding the comparison with the observation of NSC dynamics, is there a significant increase in similarity in the enhanced model over the original model that only considers the stock to the trunk? how much difference is observed when Fig5 is drawn in the original model compared to FIg5 in the enhanced model?

Line 620-622: The sentence is not clear. What did the authors want to say?

Line 626-627 :The sentence is not clear. What did the authors want to say?