Tradeoff between the Conservation of Soil C Stocks and Vegetation Productivity in Temperate Grasslands

Round 1

Reviewer 1 Report

I accept the authors' answers and recommend that the article be published in this form. However, one thing is problematic. Nutrient input by animals. It would be appropriate to omit this only if there was the same animal load. In such a case, this factor could be "ignored".

Author Response

Dear Reviewer 1,

We thank you for accepting our answers and recommending in this form the publication of the paper. As we agree with your comment on the taking into account of nutrient inputs by animal we have calculated, for grazed fields, N inputs by grazing animals according IPCC guidelines Tier 2 (IPCC 2006, Chapter 10.5.2). This N excreted by livestock (kg N ha^-1) has been added in table 1 under mineral and organic fertilization. The figure 5 has been also modified by including this N inputs by animals in the total N supply. The relationships between N supply, SOC and either ANPP or root C:ABG C ratio are slightly affected but remain significant.

Best regards,

Servane Lemauviel-Lavenant

Reviewer 2 Report

The manuscript "Tradeoff between C stocks conservation and vegetation productivity in temperate grasslands", addresses an interesting research topic. The authors used community traits to unravel the mechanisms behind soil C storage from the vegetation perspective. Thus, to explain soil C storage the authors combined C input (productivity) and output indicators, the last indirectly explained by community leaf traits, which are in fact related to the degradability of the organic matter (for instance, leaf dry matter content). This approach provided interesting results that may provide some guidelines to manage grassland ecosystems.

However, my main concern is the statement of the hypothesis 2 (Hyp2): “easy measurable leaf traits are strong indicators for primary productivity and conservation of C stocks”. In my opinion this hypothesis is unspecific and needs to be reformulated. It is well known that leaf traits are indicators of some ecosystem services, including productivity. The word “strong” is too unspecific. In my opinion what the authors aimed to identify is the best functional traits to describe the given ecosystem services:  productivity and soil C storage. Please rephrase this hypothesis and following conclusions.

Please see specific comments in the attached document.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer 2,

We warmly thank you for this fine review of our paper and for your help in improving it by proposing precise changes. We modified the formulation of hypothesis 2 and made the suggested changes throughout the manuscript. These changes are detailed in the explanations below.

Best regards,

Servane Lemauviel-Lavenant

General comments

“However, my main concern is the statement of the hypothesis 2 (Hyp2): “easy measurable leaf traits are strong indicators for primary productivity and conservation of C stocks”. In my opinion this hypothesis is unspecific and needs to be reformulated. It is well known that leaf traits are indicators of some ecosystem services, including productivity. The word “strong” is too unspecific. In my opinion what the authors aimed to identify is the best functional traits to describe the given ecosystem services:  productivity and soil C storage. Please rephrase this hypothesis and following conclusions. »

Indeed, we were looking for the functional trait which would be the more accurate to describe both ecosystem services (i.e. Forage productivity and Soil C storage). We have reformulated the hypothesis 2: “we postulated (Hyp2) that among the easy measurable leaf traits, one trait could be identified as the best descriptor for both primary productivity and conservation of C stocks and thus constitute a relevant indicator for the study of the relationships between these two services.” and also the conclusions “Our data support also the second hypothesis (Hyp2), as among leaf traits, LDMC_cwm, closely related to both primary productivity and the conservation of C stocks, appears particularly relevant for analyzing the relationship between these two services.”

Specific comments :

-Line 20: “Conservative syndrome” has been replaced by “conservative strategy”

-Line 21: “Our results hypothesize” has been replaced by “Our results show”

-Line 31: “including” has been added in the sentence “but they also deliver a number of ecosystem services (ES) [2], including regulation of air and soil quality”

-Line 33: The sentence has been rephrased “Indeed, grasslands have a high potential to mitigate climate change through C sequestration [5]”

Line 34-38 : The sentences “According to the IPCC [6], CO2 is the Greenhouse Gas that have contributed the most to global warming through radiative forcing, with an estimated contribution of 80%. There are two ways to reduce the concentration of CO2 in the atmosphere; one is the reduction of emissions, and the other the increase in transfers and storage of C in terrestrial or marine compartments, where it is stabilized as organic matter.” Have been removed

Line 44: The sentence has been rephrased and is now: “Soil carbon sequestration in is regulated by…”

Line 51: “for soil C storage” has been replaced by “to store soil C”

Line 52: “the activation of soil respiration” has been replaced by “an increase of soil respiration”

Line 93: The sentence “conflicting relations between provisioning services and regulating services” has been précised: “Literature describes conflicting relations between provisioning services such as the provision of nutritional biomass and regulating services such as C sequestration”

Line 96: The hypothesis 2 has been reformulated “we postulated (Hyp2) that among the easy measurable leaf traits, one trait could be identified as the best descriptor for both primary productivity and conservation of C stocks and thus constitute a relevant indicator for the study of the relationships between these two services.”

Line 322: The sentence has been précised “Literature has often reported trade-offs between livestock production and regulating services such as air or water quality or C sequestration”

Line 330: “that” has been added, “the” removed and “was stored” added.

Line 332: We have précised the SOC threshold of 2%: “Overall, SOC content ranged between 2.9 and 6.8 % (of the soil dry mass), which is largely above the threshold of 2% which is often considered as the threshold (2 %) under which a serious decline in soil quality may occurs [49].”

Line 336: “comparable and” has been removed to rephrase the sentence.

Line 350: The sentence has been rephrased “The relationship between of above-ground C pool with and SOC stock suggests…”

Line 353: “distributions” has been corrected.

Line 381 : We agree that the sentence was not clear neither than the link with Hypothesis 2. We have reformulated the sentence to clarify our point: “The low HWC proportion observed in the less productive old fields characterized by high LDMC_cwm may indicate that high C stocks result from slow degradation of plant residues”

Line 384: “to” has been replaced by “with”.

Line 390: “our” has been added.

Line 435: We agree that the last sentence of the conclusion was confusing, it implied C inputs to soil whereas we meant the conservation of soil C stocks. We changed the wording of the sentence: “Management practices act on the productivity of vegetation and therefore on C inputs as well as on the characteristics of plant communities including the quality of organic matter and therefore the C exports. Accordingly, grassland management plays a key role in mitigating atmospheric carbon dioxide though “best” management practices, being adopted to a compromise between forage production and conservation of soil C stocks.”

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

I read the manuscript "Tradeoff between C stocks conservation and vegetation productivity in temperate grasslands", which describes a study on the relationship between vegetation production and soil C stocks in temperate grassland sites of various productivity levels.

In my opinion, the manuscript is well structured, relatively well written and although not novel, it does report interesting results from a scientific point of view.

Regarding the contents of the manuscript, I have mainly one general comment regarding the analysis of plant functional traits and their effect on productivity and C stocks, followed by a list of specific comments.

General comments:

In my opinion, the analysis of plant functional traits to investigate the relationship between the conservation of C stocks and grassland productivity is very interesting, since the effect of community plant functional traits on soil biochemical processes is complex and therefore remains ambiguous. However, I found that the authors did not give it enough emphasis in the context of climate change, which is a key factor in determining management practices in grasslands. The authors found that plant functional traits, particularly LDMC affects C stocks and grassland productivity. What are the implications of these findings? Why are they important and valuable for the scientific community? What are the implications of these findings on management practices in grasslands? Several studies suggest a strong shift in vegetation composition in grasslands under climate change, and consequently a shift in community functioning and productivity. Therefore I would invite the authors to consider with greater attention the role of plant functional traits, based on their results and literature, in soil C storage and productivity and the possible implications of their findings on management practices and productivity under climate change.

- Specific comments:

• Line 10: Delete the "s" at the end of "grasslands" in "grasslands management"
• Line 21: Replace "hypothesis" by "hypothesize"
• Line: Remove "s" at the end of " global changes"
• Line 36: Edit "C input is mainly due to CO₂ fixation by plants. and C output...": "C input mainly originates/results from CO₂ fixation by plants and C output is the result of the release of CO₂ into the atmosphere..."
• Lines 44-45: By "short duration grasslands", do you mean "short-term grasslands"?, "grasslands with short rotation"?
• Line 53: Add "By" or "Through" before "modeling C cycling..."
• Line 61: Add "-" between "community" and "level": "community-level leaf traits..."
• Line 67": Add "-" between "fast" and "growing": "(fast-growing) species..."
• Line 69: Add "-" between "slow" and "growing" "slow-growing species"
• Line 82: Substitute "of an experimental farm..." by "from an experimental farm..."
• Line 86: Remove "case"
• Line 87: Add "s" at the end of "exist" as follows: "What relationship exists..."
• Line 95: Remove "an" in "and an daily temperature..."
• Line 100: "Briefly" instead of "Breifly"
• Line 100: Add "s" at the end of "field": "fields 1 to 3"
• Line 101: Same as the previous comment: "fields 4 to 7"
• Line 102: Repetitive. Remove "and 1995 in field 4 to 7"
• Line 102: Add "s" at the end of "field" in "The 7 grassland field..."
• Line 107: Add "s" at the end of "field" in "field 1 and 5 were..."
• Line 189: Remove "so as"
• Line 243: Remove "was"
• Line 245: Add "the" before "latter"
• Line 255: Replace "took part to..." by "took part in..."
• Line 326: Remove "s" at the  end of "others"
• Line 338: Add "the" before "latter"
• Line 339: Remove "s" at the end of "suggests"
• Line 367: Restructure sentence. For example: "Among the community weighted mean traits, LDMC_CWM appeared to be the most relevant trait..."
• Lines 368-370: Restructure sentence "Measured traits...as reported also by literature". For example: The negative  correlation between SLA_CWM and LNC_CWM,and LDMC_CWM and LC:N_CWM has been reported in other studies..."

Suggested papers to check:

Figures

• Figure 4: C is missing in SOC and ) is missing in "HWC (%". Also, please move the position of R-square value = 0.6) to be easily viewed.

Author Response

#Reviewer 1

I read the manuscript "Tradeoff between C stocks conservation and vegetation productivity in temperate grasslands", which describes a study on the relationship between vegetation production and soil C stocks in temperate grassland sites of various productivity levels. In my opinion, the manuscript is well structured, relatively well written and although not novel, it does report interesting results from a scientific point of view. Regarding the contents of the manuscript, I have mainly one general comment regarding the analysis of plant functional traits and their effect on productivity and C stocks, followed by a list of specific comments.

General comments:

In my opinion, the analysis of plant functional traits to investigate the relationship between the conservation of C stocks and grassland productivity is very interesting, since the effect of community plant functional traits on soil biochemical processes is complex and therefore remains ambiguous. However, I found that the authors did not give it enough emphasis in the context of climate change, which is a key factor in determining management practices in grasslands.

Author’s response: We agree with the reviewer on the lack of contextualization of this paper in the global change. We have improved the introduction to place the study in the context of global warming and the need to decrease the concentration of CO₂ in the atmosphere. The link between the functioning of grasslands, which is influenced by many factors including global change, and the C storage appears as an important key to improve mitigation of global changes. We have also revised the discussion to point that LDMC as other leaf traits are involved both in the response and in the effect on global change.

The authors found that plant functional traits, particularly LDMC affects C stocks and grassland productivity.  What are the implications of these findings? Why are they important and valuable for the scientific community? What are the implications of these findings on management practices in grasslands? Several studies suggest a strong shift in vegetation composition in grasslands under climate change, and consequently a shift in community functioning and productivity. Therefore I would invite the authors to consider with greater attention the role of plant functional traits, based on their results and literature, in soil C storage and productivity and the possible implications of their findings on management practices and productivity under climate change.

Author’s response: We agree, we did not underline implication and potential recommendations as C storage depends on more than management. However, to improve the section we have added a table corresponding to the correlation matrix of C pools in the results section and we have discussed this point. It shows that SOC stocks are stronger linked to annual above-ground C (ABG C; negatively) than with Root C (positively). A leaf trait such as LDMC, which was the trait with the stronger link with both services, appears then as relevant to analyze the relationship between them. Our paper shows that intensive management led to a plant community with exploitative syndrome having high productivity, and reduced soil C stocks. We have completed the conclusion with “Grassland management plays a key role in mitigating the increase in atmospheric carbon dioxide, since management practices may be adopted to find a compromise between forage production and C inputs to soil.”

Specific comments:

• Line 10: Delete the "s" at the end of "grasslands" in "grasslands management"

Done

• Line 21: Replace "hypothesis" by "hypothesize"

Done

• Line: Remove "s" at the end of " global changes"

Done

• Line 36: Edit "C input is mainly due to CO₂fixation by plants. and C output...": "C input mainly originates/results from CO₂ fixation by plants and C output is the result of the release of CO₂ into the atmosphere..."

It has been corrected, thanks!

• Lines 44-45: By "short duration grasslands", do you mean "short-term grasslands"?, "grasslands with short rotation"?

Indeed, we meant short term grasslands, “duration” has been replaced by “term”.

• Line 53: Add "By" or "Through" before "modeling C cycling..."

We have added “By”.

• Line 61: Add "-" between "community" and "level": "community-level leaf traits..."

Done

• Line 67": Add "-" between "fast" and "growing": "(fast-growing) species..."

Done

• Line 69: Add "-" between "slow" and "growing" "slow-growing species"

Done

• Line 82: Substitute "of an experimental farm..." by "from an experimental farm..."

Done

• Line 86: Remove "case"

It has been removed.

• Line 87: Add "s" at the end of "exist" as follows: "What relationship exists..."

We have modified this sentence to follow comments of reviewer 3.

• Line 95: Remove "an" in "and an daily temperature..."

Done

• Line 100: "Briefly" instead of "Breifly"

Done

• Line 100: Add "s" at the end of "field": "fields 1 to 3"

Done

• Line 101: Same as the previous comment: "fields 4 to 7"

Done

• Line 102: Repetitive. Remove "and 1995 in field 4 to 7"

The sentence was not clear enough, it has been modified : “while fields 4 to 7 were croplands cultivated with corn before their conversion to grasslands respectively in 1991, 1995, 2008 and 1995”.

• Line 102: Add "s" at the end of "field" in "The 7 grassland field..."

Done

• Line 107: Add "s" at the end of "field" in "field 1 and 5 were..."

Done

• Line 189: Remove "so as"

Done

• Line 243: Remove "was"

Done

• Line 245: Add "the" before "latter"

Done

• Line 255: Replace "took part to..." by "took part in..."

Done

• Line 326: Remove "s" at the  end of "others"

Done

• Line 338: Add "the" before "latter"

Done

• Line 339: Remove "s" at the end of "suggests"

Done

• Line 367: Restructure sentence. For example: "Among the community weighted mean traits, LDMC_CWMappeared to be the most relevant trait..."

Done

• Lines 368-370: Restructure sentence "Measured traits...as reported also by literature". For example: The negative correlation between SLA_CWMand LNC_CWM, and LDMC_CWM and LC:N_CWM  has been reported in other studies..."

The sentence has been reformulated as suggested.

• Figure 4: C is missing in SOC and ) is missing in "HWC (%". Also, please move the position of R-square value = 0.6) to be easily viewed.

Thank you for this remark, the problem came from a change of form on the file. It is now pasted as an image to avoid these problems.

Reviewer 2 Report

I rate the article very highly. It is written clearly. It brings significant results in the field of ecosystem services. I have only a few comments on it, which are indicated in the attached text. They concern the addition of a methodology for refining procedures.

Comments for author File: Comments.pdf

Author Response

#Reviewer 2

I rate the article very highly. It is written clearly. It brings significant results in the field of ecosystem services. I have only a few comments on it, which are indicated in the attached text. They concern the addition of a methodology for refining procedures.

• Line 96: Was it the same on all seven surfaces? If so, it should be emphasized.

Yes, the soil was the same (eutric cambisol) for the seven grassland fields, it is now specified more clearly.

• Line 107: which category of animals grazed?

Only cows grazed grasslands here, it is now specified in the previous sentence.

As suggested by reviewer 2, all “yr” have been replaced by “year in the text.

• Table 2:I think that if the animals were grazed, they left nutrients there. So the stands were also fertilized with organic fertilizers. It would be appropriate to take this into account.

We have only specified in the table the fertilization that has been provided, but obviously we are aware that the presence of animals implies inputs via urine and faeces.

• Line 117: I think it would be more appropriate to use the term "Dominance". Abundance expresses the number rather than the percentage.

“Abundance” has been replaced by “relative cover” which corresponds to what we have evaluated.

• Table 3: I think this table, basically the results, belongs rather to the results section. Also with a comment.

Table 3 has been moved to the results section

• Line 147: in what phenosis was the stands mowed ?, according to which the date of grazing was determined?, in how many repetitions were samples taken from the area? 10 ?. as indicated in lines 108 to 111?

Author’s response: The dates of mowing were determined by both production (to reach enough hay) and phenosis, before flowering to avoid a decrease in forage quality. It was decided by the managers of the experimental farm which had managed the grasslands as they did before. We have completed the text with: “The dates of mowing and grazing period were decided by the experimental farm taking into account both production (to reach enough hay or forage) and phenology (to avoid a decrease in forage quality)”.

 Indeed 10 replicates were sampled in each grassland field at each harvest. “ten replicates” was added in the text.

• Line 149: veľmi malá plocha, najmä pre zisťovanie nadzemnej hmoty v prípade kosených porastov. Pre lúčne porasty by malo byť od 10 do 25 metrov štvorcových, pre pasienky od 5 do 20 metrov štvorcových (very small area, especially for detecting above-ground mass in the case of mowed stands. For meadows it should be from 10 to 25 square meters, for pastures from 5 to 20 square meters)

Author’s response: We agree that the areas were small but were repeated ten times per grassland field and per harvest. The small size allowed a meticulous cut 5cm above the ground and above all a meticulous harvest of the shoot compartment of the first 5 centimeters above the ground. Looking at figure 1 (ANPP) or figure 2 (C amounts obtained from C contents and biomasses) you will see that standard errors obtained for the productivity were not too big.

• Line 197: from an analytical point of view, the comparison of production with such different management systems is debatable. In this phase and the evaluation built in this way, I see space rather only in the documentation level.

Author’s response: We agree that the productions of mowed and grazed grasslands are complicated to compare, however it was our choice to integrate into this study usual ways of managing grasslands in Normandy. The objective was to use a panel of fields to obtain a gradient of productivity and SOC_stock. In addition, the functional traits are good indicators of productivity and their use helps to confirm our results.

Reviewer 3 Report

Review of

Tradeoff between C stocks conservation and vegetation productivity in temperate grasslandsCaroline Kohler, Annette Morvan-Bertrand, Jean-Bernard Cliquet, Katja Klumpp and Servane Lemauviel-Lavenant

I can not discover a clear line of arguments, leading from clear cut hypotheses, via results that serve to test those hypotheses, to a critical discussion that allows to support or dismiss those hypotheses.

At the present state, the MS leaves me clueless. I see a large amount of redundancies and carefully formulated, long sentences, where I expect well sorted, dry data to suffice. This makes the text very hard to read.

I was also very surprised, that it is never mentioned that the ecosystem where most C is extracted (via harvest) and least C goes to the soil (via roots) has the lowest SOC stock, while the ecosystem where least C is extracted and most C goes to the soil has the highest SOC stock. At least this is what Fig. 2 seems to suggest.

Instead, the authors discuss (l. 370 ff) ≫ The positive relationship observed between LDMC_CWM (leaf dry matter content, reviewer) and SOC_stock again supported the hypothesis of a strong effect of plant tissue quality on SOC stocks.≪. They conclude (l. 389 ff) ≫ In this study, among the plant community functional traits used, LDMC_CWM appeared as the best predictor of both ES and their relationships. ≪

Maybe it would be a good idea to go back to the bare bones: Reduce the message to one single sentence and then add only what is necessary to explain that one sentence.

Author Response

#Reviewer 3

I can not discover a clear line of arguments, leading from clear cut hypotheses, via results that serve to test those hypotheses, to a critical discussion that allows to support or dismiss those hypotheses. At the present state, the MS leaves me clueless. I see a large amount of redundancies and carefully formulated, long sentences, where I expect well sorted, dry data to suffice. This makes the text very hard to read.

Author’s response: We have modified the end of the introduction to clarify our aims and we have reformulated our research questions by enouncing our hypotheses. These hypotheses are those which are discussed in the discussion section.

I was also very surprised, that it is never mentioned that the ecosystem where most C is extracted (via harvest) and least C goes to the soil (via roots) has the lowest SOC stock, while the ecosystem where least C is extracted and most C goes to the soil has the highest SOC stock. At least this is what Fig. 2 seems to suggest. Instead, the authors discuss (l. 370 ff) “The positive relationship observed between LDMCCWM (leaf dry matter content, reviewer) and SOC_stock again supported the hypothesis of a strong effect of plant tissue quality on SOC stocks” They conclude (l. 389 ff) “In this study, among the plant community functional traits used, LDMCCWM appeared as the best predictor of both ES and their relationships”. Maybe it would be a good idea to go back to the bare bones: Reduce the message to one single sentence and then add only what is necessary to explain that one sentence.

Author’s response: To answer to reviewer about the relationship between root C and SOC stock, we have added a table corresponding to the correlation matrix of C pools in the results section. It shows that SOC stocks are stronger linked to annual above-ground biomass C (ABG C; negatively) than to Root C (positively). We have then discussed this point in the discussion section and we hope that this will clarify the message. Then the messages of this paper is that 1) There is a tradeoff between the two ecosystem services (conservation of C stocks and grassland productivity) and thus management leading to increase productivity may decrease the conservation of soil C stocks, 2) LDMC, a leaf trait appears as a relevant trait, it may constitute an interesting indicator of both services and can be useful to understand the relationship between primary productivity and Soil C stocks and thus.

Round 2

Reviewer 3 Report

None. Comments to the Editor only. Please compare below.

I reject the submission of the revised MS.

The text provided here (agronomy-789745-peer-review-v2.pdf)

is identical with the previous version.

I do not wish to further participate in the review process.

Kind regards, Matthias Volk

ps: The ratings in 'Recommendations for Editors' for 'Report 2' were already filled in when I opened the website.