Dear Jeffrey,

Your manuscript was evaluated by two referees, both suggesting major revisions but providing a constructive list of comments and suggestions to improve the manuscript. Based on your author comments, I would therefore encourage you to submit a revised version of your manuscript, for re-evaluation by the original reviewers.

With best regards
Steven Bouillon

Dear Jeffrey

Both reviewers have evaluated your revised manuscript, and I agree with them that you've greatly improved the manuscript and handled all suggestions very well, with a detailed point-by-point reply to the original comments.

You will note that Ref#2 still has a few minor suggestions/questions which I feel you should incorporate, the issue of the regression fit through 0 for Figure 2 was also raised again by Ref#1, in the sense that he/she recommended that you provide your arguments (and perhaps the the comparison of the outcome when forcing the intercept through zero or not) in the final manuscript, as this would be an obvious question for readers.

Two additional technical corrections:
-in Table 1, please use one decimal for the estimated contribution of C4 material (to be consistent with those for C3 material)
-in the ms, please specify (Methods and/or elsewhere) whether C:N ratios are presented on a molar or weight basis.

In case you have any questions, don't hesitate to contact me directly.

Best regards
Steven Bouillon