Peer review of: Microbial diversity drives carbon use efficiency in a model soil (2020)

Reviewers' Comments:
 Reviewer #1:
 Remarks to the Author:
 Domeignoz-Horta et al. have successfully addressed my concerns. I have no further comments on
 the manuscript. Congratulations!
 Xin Jing
 4/27/2020
 
 
 
Reviewer #2: 
Remarks to the Author: 
The authors have addressed my main initial comments and I find the manuscript improved. 
However, I still have some relatively minor suggestions/comments: 
 
General: it seems that supplementary Figures are not referred to in the same order in which they 
are presented in supplementary information. 
L44: several papers have studied microbial growth and respiration at different soil moisture levels, 
though not all have explicitly reported CUE-soil moisture relations (e.g., Anderson and Domsch, 
1986; Göransson et al., 2013); I would not state that the impact of moisture changes on microbial 
metabolism is limited to two studies. 
L45: osmoregulation is performed via synthesis or accumulation of osmolytes, not via EPS, which 
have other functions (maintaining hydration and solute transport). 
L71: hypothesis 3 is rather vague and hard to falsify – could it be formulated in a more specific 
way, indicating an expected direction of change of CUE with varying environmental conditions? 
L86: suggested amendment “fungal:bacterial ratio” 
L87: connectivity relies on water-filled pores, so it can be higher within aggregates in dry 
conditions, but in wet conditions when large inter-aggregate pores are filled and water is moving I 
would argue that connectivity is highest among aggregates. 
L135: it is useful to remind about the hypothesis, but then I would suggest doing it in the previous 
paragraph, where there is already a sentence on diversity effects on CUE (L130). 
L142: I would include this threshold as a vertical line in Figure 2. 
L224: how about osmolytes? They would also be missed with a DNA-based method if the relation 
between biomass and DNA was assessed at a time when osmolytes where not produced. 
L253: but see more recent papers showing a different pattern (Soares and Rousk, 2019). 
L276: the last sentence of the conclusion is rather generic and does not point to the main message 
of the paper – I would remove it. 
L382: minor detail – use Greek symbol ‘mu’, not ‘u’ in micrometer 
L385: the MWD definition should be amended – remove the equal sign (this is not an equation), 
and place “i” as subscripts. 
L386: based on the formula above, “X” should have an overbar indicating averaging. 
L407: note that the logarithmic function is monotonically increasing, but does not saturate; the 
negative exponential function is monotonically decreasing, so not a good choice for data showing 
and increasing pattern. 
L408: are the break point calculated based on piecewise linear functions? 
L427: which “bacterial data” are referred to here? Diversity or CUE data, or both? 
 
References 
Anderson, T.H., Domsch, K.H., 1986. Carbon assimilation and microbial activity in soil. Z. 
Pflanzenernahrung Bodenkd. 149, 457–468. 
Göransson, H., Godbold, D.L., Jones, D.L., Rousk, J., 2013. Bacterial growth and respiration 
responses upon rewetting dry forest soils: Impact of drought-legacy. Soil Biol. Biochem. 57, 477–
486. https://doi.org/10.1016/j.soilbio2012.08.031 

Soares, M., Rousk, J., 2019. Microbial growth and carbon use efficiency in soil: Links to fungal-
bacterial dominance, SOC-quality and stoichiometry. Soil Biol. Biochem. 131, 195–205. 
https://doi.org/10.1016/j.soilbio.2019.01.010