Thank you for your submission to Biogeosciences. Your MS has received three reviews from highly qualified reviewers in this field, all of whom thought that this is a valuable dataset worth publishing, but offered numerous substantive comments to improve the paper. Thus, I will be happy to consider a revised submission that substantively addresses these reviewer comments. Based on the responses to reviewers 1 and 2, it looks like there is a sound plan for addressing the reviewers’ critical comments.

Unfortunately, I discovered too late that the comments from the third reviewer do not show up in the Biogeosciences system, so I have pasted them below. Please also consider these comments, which are generally consistent with those of reviewers 1 and 2, when revising your manuscript.

Please clearly describe how the text was revised according to the reviewer comments when submitting your revised manuscript. Thank you for your efforts, and for your support of Biogeosciences.

Sincerely,
Mike Weintraub
Associate Editor
Biogeosciences

This manuscript presents results of an incubation experiment conducted in mineral soils from one well-drained forest site. The authors use a factorial temperature and moisture treatment and measure the CO2 and CH4 produced over the 100-day incubation. While frequently moisture treatments explore the effects of anaerobic conditions on soils, this study instead chose to focus on the effects of drought and reducing moisture on CO2 and CH4 production. The authors found higher rates of CO2 production at 20°C than 4°C and lower rates of CO2 production with the drought treatment at both temperatures. CO2 production was larger than CH4 production by a factor of 106. There were interesting and surprising correlations between CO2 production and soil nitrogen content. The main point of this paper, and I think that it’s an important one, is that many upland forest soils in the boreal region that have permafrost will dry, and the majority of C will be emitted as CO2, but the magnitude of C emission will decrease under drought conditions (imposed by freely draining and no water inputs) by ~ 50-70%. Overall, I enjoyed reading this paper! It was nicely written although vague in a few parts.

My main criticism is that I think that the authors over-emphasize the results of the daily emissions and that the authors should further explore (or report) the results of the controls of the cumulative C emissions. I’m curious as to whether the relationships with soil C/N and %N observed in daily emissions still hold on cumulative emissions. The comparison between these soil parameters (i.e. ones that probably don’t change much throughout the course of the incubation, including temperature) and the cumulative fluxes is perhaps more appropriate. Perhaps modelers find the controls on daily fluxes interesting and these are likely quite useful in regards to the relationship between moisture and C production (i.e. changes on a daily basis), but I think that the controls on cumulative fluxes are quite interesting and could be further explored. For example, how do the results of soil properties vs. emissions compare to those of Schädel et al. (2014) and Schädel et al. (2016)? How do the moisture results compare to those of Wickland et al. (2008)? I do think that the time series of fluxes could be moved to the supplemental materials if the cumulative fluxes are explored in greater detail. I think this paper could be shortened a little bit although I didn’t find the length of the paper onerous. Along these lines, I think that the results summarized above from the cumulative emissions should be included in the abstract.

Specific comments
22: Daily CO2 fluxes?
26: positive or negative correlation?
27: daily CH4 flux?
28: cumulative production as CO2…as CH4.
29: Not really sure how the comparison as to the relative controls of T and moisture are evaluated.
50: see also updates in Hugelius et al. (2014)
63: Under some conditions (Olefeldt et al 2013): vague and confusing. Please clarify.
67: “substantial variabilities between studies” WHY?
72: Yes, this is an important question, but given that this isn’t measured in this study, perhaps this sentence should be omitted or re-written.
101: When did sampling occur?
112: Specify at the time of sampling
140: How frequently was moisture adjusted? Requires a bit more explanation. Were instantaneous moisture values used in analysis?
211: Please remember to complete DOI
215: Not sure what this value for soil dry mass indicates
216: Standard deviation for %C and %N is nearly 100%. Check values.
229: add units
231: add units
233: positively correlated
241: positively correlated
245-246: 106
253-254: So what variables were significant in predicting cumulative C emissions?
262: First mention of vegetation stress, remove, not clear how it’s related.
270. Add “.”
271: Specify soil type in which these measurements were made (results not surprising for a forest soil)
272: What about results from Wickland et al. (2008). Study found threshold for moisture importance
305-307: again, see Wickland et al. (2008)
322-324: cool!
344-345: Specify that the results in Treat et al. (2015) were for anaerobic incubations and were thus likely to be much smaller.
347-348: See also Lee et al. (2012)
364-365: See also Schadel et al. (2014). Also, I thought this section was a bit vague, probably could be shortened slightly.
383-384: “specific weaknesses”: vague
384: See also lag effects found in Treat et al. (2015)
393: “taking them out of depth” rephrase. Also could use this argument for the section on CH4 production.

Fig.1 : Edit figure to be color-blind friendly.
Fig. 2,3: When did watering / moisture adjustment occur? Consider indicating with arrows and specifying in text.
Fig. 4: Switch top and bottom panels as CO2 is always discussed before CH4. Also edit colors and patterns to be color-blind friendly.

Nice work! – Claire Treat

References

Hugelius, G., et al. (2014), Estimated stocks of circumpolar permafrost carbon with quantified uncertainty ranges and identified data gaps, Biogeosciences, 11(23), 6573-6593, doi:10.5194/bg-11-6573-2014.

Lee, H., E. A. G. Schuur, K. S. Inglett, M. Lavoie, and J. P. Chanton (2012), The rate of permafrost carbon release under aerobic and anaerobic conditions and its potential effects on climate, Global Change Biology, 18(2), 515-527, doi:10.1111/j.1365-2486.2011.02519.x.

Schädel, C., E. A. G. Schuur, R. Bracho, B. Elberling, C. Knoblauch, H. Lee, Y. Luo, G. R. Shaver, and M. R. Turetsky (2014), Circumpolar assessment of permafrost C quality and its vulnerability over time using long-term incubation data, Global Change Biology, 20(2), 641-652, doi:10.1111/gcb.12417.

Schädel, C., M.K.F. Bader, E. A.G. Schuur, R. Bracho, P. Capek, S. De Baets, K. Diakova, J. Ernakovich, C. Estop-Aragones, D. E. Graham, I. P. Hartley, C. M. Iversen, E.S. Kane, C. Knoblauch, M. Lupascu, S. Natali, R.J. Norby, J.A. O’Donnell, T. Roy Chowdhury, H. Santruckova, G. Shaver, V.L. Sloan, C.C. Treat, M.R. Turetsky, M. Waldrop, K.P. Wickland. Potential carbon emissions dominated by carbon dioxide from thawed permafrost soils, in press, Nature Climate Change.

Wickland, K. P., and J. C. Neff (2008), Decomposition of soil organic matter from boreal black spruce forest: environmental and chemical controls, Biogeochemistry, 87(1), 29-47.

You will be pleased to hear that your manuscript has been accepted for publication in Biogeosciences. Based on your responses to the reviews and my own review of your revised manuscript, I have concluded that this manuscript is now ready for publication. Thank you for your hard work and patience. Your efforts to improve this paper have paid off, and the current version manuscript is much improved from the original submission. Thank you for your efforts, and for your support of Biogeosciences.

Sincerely,
Mike Weintraub
Associate Editor
Biogeosciences