Variety and Site Drive Salix Mixture Effects on Soil Organic Matter Chemistry and Soil Carbon Accumulation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors investigated the effects of willow variety and mixture, and site on the soil C stocks, SOM chemical composition and thermal stability. This study emphasize the significance of site-specific context and variety or species identity in shaping soil C accumulation in willow plantations. This study can provide a scientific basis for ecological protection to help policymakers design better policies.  I suggest publication with some modifications.

Abstract: Please clarify the research method further

Line234: papaer ?

Line237: what is the CO 2 respiration?

Please compared the present study with previous research further in the discussion section.

Author Response

Comments 1: [Abstract: Please clarify the research method further]

Response 1: [A more detailed description of the Py-FIMS methods have been added to the abstract “Using pyrolysis-field ionization mass spectrometry (Py-FIMS), a method of stepwise thermal degradation in ultrahigh vacuum combined with soft ionization in high electric field, followed by mass-spectrometric separation and detection of molecular ions, we analysed SOM in the top 10 cm of soil from two 7-year-old experimental sites in Germany and Sweden. Monocultures and mixtures of two willow varieties (Salix spp.) belonging to different species were grown at the experimental plots.” (starting at line 16).]

Comments 2: [Line234: papaer?]

Response 2: [The sentence has been modified as suggested (line 247)]

Comments 3: [Line237: what is the CO 2 respiration?]

Response 3: [We interpreted this comment to relate to the definition of CO2 respiration. We have replaced "CO2 respiration" with "soil respiration" and added further clarification: “Soil respiration was defined as CO2 release from soil caused by respiration and was measured at 4-week intervals (8 times) during the growing season (April to October) for the year 2021 at the Uppsala site as a proxy for decomposition.” (starting at line 168).]

Comments 4: [Please compare the present study with previous research further in the discussion section.]

Response 4: [The discussion has been expanded to include further reasoning around the SOM chemical composition between sites in relation to soil C accumulation: “Additionally, more recalcitrant compounds such as lipids and lignin dimers were more abundant at the Rostock site, possibly contributing to SOM formation [86,87].” (starting at line 486). Furthermore, we now also relate our findings to a recent study (Dufour et al., 2024), which found differences in SOM chemical composition between willow varieties: “A fertilization experiment in central Sweden, using mid-infrared spectroscopy and pyrolysis-gas chromatography-mass spectrometry (GC/MS) for their analysis, also observed a different SOM chemical composition between willow varieties ‘Loden’ and ‘Tora’ [90].” (line 511) and SOM chemical diversity: “Enhanced SOM chemical diversity under ‘Loden’ compared to ‘Tora’ has also been reported in a recent study [90].” (line 516).]

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

I am pleased to read and review your manuscript titled "Variety and site drive Salix mixture effects on soil organic matter chemistry and soil carbon accumulation", which is dealing with investigation of the effects of willow  variety and mixture as well as on the soil C stocks, SOM chemical composition and thermal stability.

This study is a good example of experimental work and further comprehensive analysis of soil organic matter and carbon accumulation.

The experimental design of the work as well as laboratoty analyses are well-described, the choos of respective laboratory techniques is understandable.

Some of my remarks are below:
- Please provide the map (may be an insert map would be good) of experimental sites (Rostock, Germany (54°02’ N 12°05′ E) and Uppsala, Sweden (59°49’ N 17°39′ E).

- It will be also great if you could show the readers how these sites look like - so please give some real photos of experimental sites. 

- Please consider merging "Results" and "Discussion' into one chapter, in the present form of the manuscript the "Discussion" part is rather short. I believe that paper would benefit from incorporating discussion into respective results of the study.

- Please also consider widening "Conclusions" chapter. You have more results of your study to be declared as conclusions as it is in present form. 

Overall, I believe that paper "Variety and site drive Salix mixture effects on soil organic mat- 2 ter chemistry and soil carbon accumulation" is worth to be published in Forests journal after respective corrections and minor revision.

I would be pleased to read your paper in a revised form one more time and give some comments.

Comments on the Quality of English Language

none

Author Response

Comments 1: [Please provide the map (may be an insert map would be good) of experimental sites (Rostock, Germany (54°02’ N 12°05′ E) and Uppsala, Sweden (59°49’ N 17°39′ E).]

Response 1: [The TreeDivNet website (https://treedivnet.ugent.be/experiments/ECOLINKSalix.html) provides more information on the experimental sites, including their locations and appearances. The link has been included in the methods section (line 121).]

Comments 2: [It will be also great if you could show the readers how these sites look like - so please give some real photos of experimental sites.]

Response 2: [See previous point.]

Comments 3: [Please consider merging "Results" and "Discussion' into one chapter, in the present form of the manuscript the "Discussion" part is rather short. I believe that paper would benefit from incorporating discussion into respective results of the study.]

Response 3: [We would prefer not to merge the results and discussion sections of the paper as we would like to keep the results presentation and interpretation strictly separate from each other.]

Comments 4: [Please also consider widening "Conclusions" chapter. You have more results of your study to be declared as conclusions as it is in present form.]

Response 4: [The conclusions have been expanded to include results on willow variety effects on soil C accumulation and thermal stability: “Willow variety ‘Loden’ showed higher soil C accumulation rates compared to ‘Tora’ at the Rostock site, while both varieties had similar rates at the Uppsala site. SOM under ‘Tora’ showed generally higher thermal stability than under ‘Loden’ at the Rostock site, while the opposite was true at the Uppsala site.” (starting at line 564). A suggestion for future research has also been added: “Further research should investigate the environmental factors influencing the effects of tree species on soil chemistry.” (starting at line 576).]

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript is well prepared but I missing some information.

1: Supplementary materials are missing.

2. I recommend putting at least one MS spectra.

3. What molecular ions (m/z) were used in each compound class? I recommend to put into the table 2.

Author Response

Comments 1: [Supplementary materials are missing.]

Response 1: [The supplementary material should be available now.]

Comments 2: [I recommend putting at least one MS spectra.]

Response 2: [Two Py-FIMS spectra are now included in the supplementary material (Figures S2 & S3).]

Comments 3: [What molecular ions (m/z) were used in each compound class? I recommend to put into the table 2.]

Response 3: [Marker signals included in each compound class are now presented in a table in the supplementary materials (Table S8).]