Dear Authors,

Thank you for submitting your response to the referee's comments. As you can see, both referee 2 and 3 find your study of interest, but referees 1 and 3 raise large concerns regarding the utility of the optimization and the large biases evident in some important aspects of model performance. I agree with referee 1, in that the optimization appears to tell us little about what is 'wrong' with the model, and with referee 3, in that the large biases that persist post-optimization question whether the model/version used is really fit for purpose.

Although it would have been more satisfying to identify what mechanisms are inadequately described in the model (following suggestions of reviewer 1), I also feel that it is useful to highlight model failures, especially for commonly used models such as CLM, as these can guide future research on issues that may not be resolvable within a single study. I therefore recommend the authors submit a revised version taking into account the referees comments, but would advise the authors to use caution when presenting possible causes of the model-data mismatch, however, as the study provides no causal evidence. For example, statements such as: "This model bias arises, in part, from the lack of a short-term non-structural carbohydrate storage pool and progressive timing of within-plant transport", should be toned down to reflect that this is not a result but a proposed hypothesis in need of further testing. Other interpretations are also given as fact rather than interpretations: for example on line 744, the authors argue that model bias towards too much growth indicates that the allocation model is too simplistic, but this is just one interpretation out of many possible. The allocation could be simply wrong, not too simple. Or the coefficients could be inadequately parameterized. The manuscript should be checked thoroughly for for this.

I would also note that the authors response to the main concerns of referee 3, regarding bias, does not address the reviewers concern. The authors need to address the reviewers concerns or risk that the reviewer will recommend rejection. I would advise them to reconsider their response and better address the issue of bias in the manuscript.

Please check your manuscript thoroughly for typos, for example Lobolly on line 304.

I look forward to receiving your revised manuscript,
Trevor

Dear authors,

Both referees now agree that your revisions have addressed their previous concerns and significantly improved the manuscript. We are now happy to accept your manuscript for publication in Biogeosciences, subject to some minor technical corrections. Congratulations for a job well done!

Best wishes,
Trevor


Technical corrections:
line 102: separate 'are' and 'important'
lines 137-138: there appears to be a typo, a few words added on to the end of the sentence.
line 278: Table 1 does not indicate which parameters were taken directly from observations.
line 343: eliminate words 'at least'
line 523: eliminate 'All evidence indicates that'
line 550: insert 'of' between 'type' and 'nocturnal'
line 698: change 'suggested' to 'suggest'