Peer review of: Blind spots in global soil biodiversity and ecosystem function research (2021)


RR2
Reviewers' Comments:
 Reviewer #1:
 Remarks to the Author:
 The authors have done a good job in addressing some of the comments I
 brought up in the previous version, but my main concern still remains and I still
 feel that the paper adds very little scientific progress to what is currently
 known. While the text and the presentation of the results are clearer in the
 current version, I still find it highly descriptive, with too much text (I cannot see
 a clear separation between sections 2.1 and 2.2, and between 2.3 and 2.4).
 Surely, the key messages can be delivered in 2-3 pages and 2-3 figures.
 In my previous report, I suggested to perform more in-depth analyses of the
 data extracted from the literature. The authors argue that this is beyond the
 scope of the ms, but, in my opinion, this decreases its value. I am “only” seeing
 a great effort in collating study records and the description of what is known or
 not known using a vote-counting system which does not grant such lengthy
 paper. I cannot see why the authors could not have used statistical tools such
 as meta-analysis to draw some meaningful conclusions on the available
 literature: e.g. Can we quantitative link more collembolans to more soil
 respiration? Are drylands losing more carbon than forest due to soil biodiversity
 differences? Are the predictive factors we are measuring now (soil, organisms
 and environmental variables) informative enough and can we trust the
 knowledge already gathered? Which ecosystems across the globe are
 maintaining multi-functionality and which ones are under risk of losing it? Again,
 I apologise for being so critical but as a potential reader, I would have expected
 a more meaningful outcome from such a high impact journal.
 The cited similar work by Decäens (2010) actually contains these kind of
 analyses I am suggesting. The figures in this paper included analyses of species
 richness, latitudinal gradients, ecological relationships, etc., in addition to
 knowledge deficit (also in terms of number of papers dealing with the topic).
 Sorry to be so critical and please do not get me wrong, I do see enough merits
 in this study to be published in a high impact journal but perhaps on a more
 specific ecology journal?
 My overall conclusion after reading the re-submitted version still remains and
 although this is an interesting study that could attract many potential readers, it
 requires quantitative analyses of the available data to provide a more
 illuminating message.

 In addition, some other comments have not been satisfactorily addressed:
 From their responses, I got the confirmation that despite the claim in the
 abstract that > 17,000 sampling sites were included, only a much smaller
 number (45 studies) have been used in the spatial analyses. It is also confirmed
 that in the case of some maps, less than 3 studies were used (see my previous
 comments about Fig. S2). Therefore, the abstract promises much more than the
 rest of the text delivers.
 The response to my criticism on the lack of standardized protocols when
 compiling the data from the different studies has been addressed as a
 recommendation for future research but not by indicating how this issue has
 been tackled in this paper.
 Other specific comments:
 L57: “T”o contribute?
 L60: Soil biodiversity or specific taxa?
 L61: The number of studies used for the spatial analyses should be indicated
 here.
 L74 (and throughout the text): Oligochaeta include groups that belong to
 macro- and meso-fauna. I think the authors are referring to earthworms.
 L221-242: These two paragraphs appear to be misplaced in this section because
 they refer to biogeographical aspects and repeat the same statement derived
 from the previous section, i.e. biases towards temperate regions.
 L149: What do you mean with “organism biomass”? total soil fauna biomass?
 Specific taxa biomass? How were these data analysed, e.g. if you have studies
 dealing with a specific group and others dealing with several groups of soil
 organisms?
 L155-158: How many records did you collect for the missing groups mentioned
 in the methods (e.g. termites, earthworms, etc.)?
 L172: Fig. 2e should be accompanied by a column chart showing the
 distribution of biomass data per taxonomic group (equivalent to Fig. 2b).
 L190: Please complete this sentence and indicate which other soil functions
 have been included in the remaining studies.
 L192 and 196: They both repeat the same information.
 L255: pH > 7.33 and silt content < 19% are extreme ranges?
 L268: I do not understand the point you are trying to make here... How did you
 estimate the “50.6% of the global climate”?
 L271: Sorry, I am not able to grasp the meaning of this graph. According to the
 legend, it should represent “ecological blind spots”, that is knowledge gaps in

 the ecological relationships between soil biodiversity and their environment.
 However, the graph shows, side by side, how well represented soil biodiversity
 and soil functions are.
 L277: A symbol missing here (mean annual temperature)?
 L310-311: Really? According to the methods and the supplementary material,
 only three properties (organic carbon content, sand content and pH) were used
 in the analyses.
 L309-340: Are all these paragraphs and Fig. 3 not describing biogeographical
 biases (section 2.1)?
 L329: I like this graph which is very much along my suggestion of producing
 some statistically sound results. In the legend of this figure, do you mean “The
 extent to which mean soil biodiversity and ecosystem functions are....”? Please
 also indicate the meaning of the square slices.
 L358-367: I think this paragraph should be integrated in the next section.
 L979: Table 3 is based on 7 studies only?
 Reviewer #2:
 Remarks to the Author:
 I had a careful reading of the manuscript “Blind spots in global soil biodiversity
 and ecosystem function research” from Gerra et al., and was fully satisfied to
 see that they take into account all the comments I made on the first version of
 their work. The few and minor concerns I had on the initial version have all
 been corrected, or the authors provided convincing arguments to justify their
 position. I therefore have no more comments to add on the new version. I want
 to acknowledge the authors for the time they have spent in carrying out this
 outstanding synthesis, and for the efforts they produced at improving their
 manuscript.