The Hydration-Dependent Dynamics of Greenhouse Gas Fluxes of Epiphytic Lichens in the Permafrost-Affected Region

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I have thoroughly reviewed the manuscript "The hydration-dependent dynamics of greenhouse gas fluxes of epiphytic lichens in the permafrost-affected region" and find it to be a valuable contribution to the field of greenhouse gas fluxes and climate studies. The authors have addressed an important and under-researched topic - the production of methane in oxygen-rich environments, in particular by epiphytic lichens. Their results provide critical insights into methane fluxes in boreal ecosystems, with important implications for our understanding of global methane budgets under climate change.

The methodology is sound, particularly the incubation approach used to measure CH₄ production, and the link between methane production and CO₂ photoassimilation is compelling. The authors provide clear evidence that thallus water content plays a regulatory role in CH₄ production, which is consistent with the current literature. This research is both timely and relevant, especially given the increasing focus on the role of non-traditional methane sources in permafrost regions.

In my opinion, the manuscript is well-written, scientifically sound, and presents its findings in a clear and concise manner. I am confident that this study will serve as an excellent foundation for future research on methane fluxes in high-latitude ecosystems and beyond.

Author Response

Comments 1: I have thoroughly reviewed the manuscript "The hydration-dependent dynamics of greenhouse gas fluxes of epiphytic lichens in the permafrost-affected region" and find it to be a valuable contribution to the field of greenhouse gas fluxes and climate studies. The authors have addressed an important and under-researched topic - the production of methane in oxygen-rich environments, in particular by epiphytic lichens. Their results provide critical insights into methane fluxes in boreal ecosystems, with important implications for our understanding of global methane budgets under climate change.

The methodology is sound, particularly the incubation approach used to measure CH₄ production, and the link between methane production and CO₂ photoassimilation is compelling. The authors provide clear evidence that thallus water content plays a regulatory role in CH₄ production, which is consistent with the current literature. This research is both timely and relevant, especially given the increasing focus on the role of non-traditional methane sources in permafrost regions.

In my opinion, the manuscript is well-written, scientifically sound, and presents its findings in a clear and concise manner. I am confident that this study will serve as an excellent foundation for future research on methane fluxes in high-latitude ecosystems and beyond.

Response 1: We appreciate Reviewer 1's careful reading of our manuscript and the positive feedback on our work.

Reviewer 2 Report

Comments and Suggestions for Authors

This paper investigated the diversity of epiphytic lichen (EL) in a permafrost-affected region, their potential of CO2 and CH4 emissions and the effects of moisture content through field observation and lab incubation. I agree that the topic is very interesting and important in the contact of climate change and the vulnerable permafrost area. I hope the author can make major revisions.

For the lab incubation, the authors investigated the lichen diversity in field by observing two different heights (0.5 m and 1.3 m) and organs (branches and stems). For the incubation experiments, where did those lichen samples collect?  In Figure 6, why there were six points for each position of Bryoria while more than six points for Evernia? From different height? And seems there were significant differences within the same color dots?  Did I miss something? Suggest to change ’C-CO2, C-CH4’ to ‘CO2-C, CH4-C’

I don’t know how and why the authors choose incubation temperature (18℃). “The average yearly temperature in this area is -9.5 °C, with mean monthly temperatures varying from -36 °C in January to 16 °C in July”(line 101-103). So is 18°C applied to the real situation? Or because you sampled during  June 18-23, 2024, you decided 18°C? Then is it applied to other seasons? The CH4 fluxes you measured only showed the upper end of the range in this area?

Also for the moisture content/hydration condition, the authors highlight the oxic CH4 production, but hydration to 100% 200% even 400%, is it still oxic environment?

The authors only collected gases under illumination, what about dark condition? Since you set up the light condition as a 18 hour cycle, why didn’t you measure the gases in dark?

No measurement of the TC and TN for the ELs？

I would suggest to use a table/Figure to show the values of 13CO2 and 13CH4 though you showed the points in Figure 10. Does the 13C data can give more information of the source? Any comparison with the literature? You didn’t explore  13CH4 enough.

In the Table 1 and 2, what is the factor of ‘day of the incubation’? Three days? So during the three days, the fluxes varied a lot? Not sure it is meaning for to use P<0.1as significance.

The authors used PCA to show negative correlation between CO2 and CH4, I would think correlation analysis is better based on only four parameters (CO2, CH4, 13CO2, and 13CH4), or the authors need to give the correlation table of PCA in the text or supplementary materials.

There are 10 figures in the manuscript. Check if there is a limits for the number of figures and tables.

Author Response

Comments 1: This paper investigated the diversity of epiphytic lichen (EL) in a permafrost-affected region, their potential of CO2 and CH4 emissions and the effects of moisture content through field observation and lab incubation. I agree that the topic is very interesting and important in the contact of climate change and the vulnerable permafrost area. I hope the author can make major revisions.

Response 1: We appreciate Reviewer 2's thorough reading of our work and thankful for the constructive comments which will be effective in improving the manuscript.

 

Comments 2: For the lab incubation, the authors investigated the lichen diversity in field by observing two different heights (0.5 m and 1.3 m) and organs (branches and stems). For the incubation experiments, where did those lichen samples collect? 

Response 2: Since the EL richness and projecting cover were maximal at larch branches compared to larch stems, therefore all EL samples used for the incubations were collected from branches. We mention it in subsection 2.5.1. (see L289-290 in old version).

 

Comments 3: In Figure 6, why there were six points for each position of Bryoria while more than six points for Evernia? From different height? And seems there were significant differences within the same color dots?  Did I miss something?

Response 3: The different point number is due to the different replication number. The number of replications is determined by the amount of EL material collected. Big differences within the same color dots are due to the high variation in the GHG fluxes by the ELs. We assessed only significance between the GHG fluxes due to the different EL exposures on branches, EL water contents, and EL species as we mentioned at L311-312 (see subsection 2.6.).

 

Comments 4: Suggest to change ’C-CO2, C-CH4’ to ‘CO2-C, CH4-C’

Response 4: We used the standard writing of’C-CO2, C-CH4’ , so we did not change it.

 

Comments 5: I don’t know how and why the authors choose incubation temperature (18℃). “The average yearly temperature in this area is -9.5 °C, with mean monthly temperatures varying from -36 °C in January to 16 °C in July”(line 101-103). So is 18°C applied to the real situation? Or because you sampled during  June 18-23, 2024, you decided 18°C? Then is it applied to other seasons?

Response 5: First, we used an air temperature of 18 °C because we are evaluating the potential GHG fluxes from the ELs. Next, we have to compare the GHG fluxes produced by ELs inhabiting Middle Siberia's non-permafrost and permafrost regions as part of our research project. For that, we incubated the ELs from the permafrost and non-permafrost areas in similar conditions (e.g., at 18 °C). In addition, an average monthly summer air temperatures up to 20 °C is usually characterises thermal conditions in the study area.

Prokushkin A. S., Geis T. N., Kolosov R. A., Korets M. A., Panov A. V., Polosukhina D. A., Prokushkina M. P., Titov S. V., Tokareva I. V., Sidenko N. V, Shamonina Yu. V., Prokushkin S. G. Lateral carbon flux in the cryolithozone of central Siberia // Sibirskij Lesnoj Zurnal (Sib. J. For. Sci.). 2024. N. 3. P. 67–82 (in Russian with English abstract and references).

 

Comments 6: The CH4 fluxes you measured only showed the upper end of the range in this area?

Response 6: we changed the sentence by adding the range of the CH4 fluxes to the sentence. so, the sentence now is as follows: “During the 2-hour incubation under the illumination, both species, regardless of branch exposure, emitted CH4 with the median values of ca. 0.6 ng CH4-C g-1 h-1; though the range of the CH4 fluxes was within the values from -0.15 to 1.8 ng CH4-C g-1 h-1 (Figure 6).”

 

Comments 7: Also for the moisture content/hydration condition, the authors highlight the oxic CH4 production, but hydration to 100% 200% even 400%, is it still oxic environment?

Response 7: The ELs always were in an aerobic environment. EL thallus can be still in oxic conditions even if the thallus water content is higher than 400%. We included Figure S4 in the Supplementary to help clarify that.

 

Comments 8: The authors only collected gases under illumination, what about dark condition? Since you set up the light condition as a 18 hour cycle, why didn’t you measure the gases in dark?

Response 8: Since we attempted to link the GHG fluxes by ELs with light conditions in this study—as suggested by several studies that demonstrated the connection between the light-dependent physiological processes and CH4 emission by the components of lichens—we did not measure the ELs GHG fluxes in dark conditions (e.g., Bižić et al. 2020). Our research is only just getting started; in the future, we hope to extend it to the photoperiod's dark phase and investigate the effects of additional factors on the GHG fluxes produced by the ELs.

 

Comments 9: No measurement of the TC and TN for the ELs？

Response 9: Although TC and TN measurements were not done for this study, they are planned for the future.

 

Comments 10: I would suggest to use a table/Figure to show the values of 13CO2 and 13CH4 though you showed the points in Figure 10. Does the 13C data can give more information of the source? Any comparison with the literature? You didn’t explore  13CH4 enough.

Response 10: We analyzed 13C in gases; therefore, we used keeling plots because they are used for gases. Data on the source of 13C are used in organic matter, which accumulates in the soil for a long time. Since methane can both be emitted (for unknown reason) and be consumed by methanotroths concurrently in aerobic conditions, we are unable to determine the source of the 13CH4.  We, however, provided the keeling plot for 13CH4 (Figure S5 in Supplementary) and added the results on 13CH4 into the results section (“The air sampled in the flasks after the 2-h incubation of ELs was depleted in 13C (from -57‰ to -70‰) in CH4 (Figure S5). That supports the dominated process of CH4 emission during the 2-h ELs incubation under the illumination (Figure 6 and 8).”). Also, we provided a discussion of that results as follows “Regarding δ ¹³CH₄ values in the air sampled from the flasks following the 2-h incubation in this study, since CH₄ can both be emitted (for still the unknown reason) and be consumed by methanotroths simultaneously in aerobic conditions, we are unable to identify the source of the ¹³C in CH₄. We cannot appropriately compare the δ¹³CH₄ with the other EL studies due to the absence of the latter either. Only a preliminary comparison between our δ¹³CH4 data and the ¹³CH₄ studies in the EL's constituent organisms could be made. As an example, δ¹³CH₄ in Cyanobacteria species ranged from -36‰ to -49‰ [76]. In contrast, Figure S5 shows that the range of δ¹³CH₄ in the air sampled in the flasks following the 2-hour EL incubation was -57‰ to -70‰ in our study. Thus, more research on that is required.”.

76. Klintzsch, T.; Geisinger, H.; Wieland, A.; Langer, G.; Nehrke, G.; Bizic, M.; Greule, M.; Lenhart, K.; Borsch C.; Schroll, M.; Keppler, F. Stable carbon isotope signature of methane released from phytoplankton. Geophysical Research Letters 2023, 50, e2023GL103317.

 

Comments 11: In the Table 1 and 2, what is the factor of ‘day of the incubation’? Three days? So during the three days, the fluxes varied a lot? Not sure it is meaning for to use P<0.1as significance.

Response 11: Only one case (CH4 fluxes; see Table 2) shows that factor "Day of incubation" has a significant impact on GHG fluxes; however, other combinations of factors (e.g., "Day of the incubation: Exposure of ELs" and "Day of the incubation: EL species: Exposure of ELs" in Table 1) exist. Nevertheless, the CH4 and CO2 samples were taken simultaneously at the same flask before and after the 2-hour incubation, so we opted to aggregate all 3-day data.

 

Comments 12: The authors used PCA to show negative correlation between CO2 and CH4, I would think correlation analysis is better based on only four parameters (CO2, CH4, 13CO2, and 13CH4), or the authors need to give the correlation table of PCA in the text or supplementary materials.

Response 12: PCA, in our opinion, effectively displays our results, so we chose to retain it. We added the table of the contributions of variables and individuals of PCs to the supplementary file (see Table S2).

 

Comments 13: There are 10 figures in the manuscript. Check if there is a limits for the number of figures and tables.

Response 13: The Instructions for Authors contained no restrictions on the quantity of figures or tables.

Reviewer 3 Report

Comments and Suggestions for Authors

The topic of this article is in line with the scope of “Forests” and is highly relevant to the ongoing phenomenon of climate change and the increasing knowledge about methane dynamics in vulnerable ecosystems, particularly high-latitude ecosystems. The article has been presented quite well and systematically, but there are a few points of improvement that need to be considered:

1. Introduction

The introduction already covers the basic reasons for conducting this research. Some of these points need to be strengthened to be more comprehensive and clear in showing the scientific contribution, the relevance of this research on a wider scale, and what benefits are obtained by achieving the objectives of this research.

Line 59-62: Add a citation.

L. 68: Authors should clarify the specific gaps that they want to fill through their current research. Likewise, any novelty or advantages in this research need to be stated in the Introduction section, for example, the advantages of the method in incubation experiments can be added by authors at the end of the Introduction; Is there any difference with the method in the article in reference number [18].

2. Materials and Methods

L.94-105: Add citation using the recent reference. Reference number [28] was published in 1979, and may no longer be relevant to the climate conditions of the study area.

L.183: In lichen sampling methods, it should be stated whether there is an attempt to control for other environmental variability, such as wind, rainfall, or temperature.

L.279: If available, please provide additional information about the sensitivity and accuracy of the tool, to demonstrate the reliability of the data generated.

L.280: Authors should include the formula since the flux data from the incubation experiments are the main result of this study, and make sure that the formula was created directly by Matvienko. If not, include a citation from the reference when the formula was first used/created.

L.295: There needs to be an explanation of the justification for using artificial rainwater; and what the chemical composition of the water is.

3. Results-Discussion

L.395-407: Although the authors have presented the results of ANOVA and PCA, the explanation of the factors that influence CO2 and CH4 fluxes is still lacking in detail. The authors should explain in the discussion section about the varying results. A deeper disclosure of the biological mechanisms or environmental characteristics that cause these differences would strengthen the results.

L. 400: Principal component analysis (PCA) has not been explained in the Method section.

L.670-681: At the end of the discussion, it is best to include the limitations of this research, for example, there are uncontrollable environmental factors that can affect the results and suggestions for what needs to be done for further research.

4. Conclusions

Conclusions must be rewritten so that the research objectives in L. 87-91 can be answered clearly. In the conclusion, a statement can also be added regarding the influence of ecological conditions and long-term implications for climate change modeling.

Comments on the Quality of English Language

Some sentences still feel complex and need to be simplified to make them easier to understand, for example in L. 68-71, 73-76, etc.

Author Response

Comments 1: The topic of this article is in line with the scope of “Forests” and is highly relevant to the ongoing phenomenon of climate change and the increasing knowledge about methane dynamics in vulnerable ecosystems, particularly high-latitude ecosystems. The article has been presented quite well and systematically, but there are a few points of improvement that need to be considered:

1. Introduction

The introduction already covers the basic reasons for conducting this research. Some of these points need to be strengthened to be more comprehensive and clear in showing the scientific contribution, the relevance of this research on a wider scale, and what benefits are obtained by achieving the objectives of this research.

Response 1: We appreciate Reviewer 3's thorough reading of our work and thankful for the constructive comments which will be effective in improving the Introduction.

 

Comments 2: Line 59-62: Add a citation.

Response 2: We added [Lenhart et al. 2016].

 

Comments 3: L. 68: Authors should clarify the specific gaps that they want to fill through their current research. Likewise, any novelty or advantages in this research need to be stated in the Introduction section, for example, the advantages of the method in incubation experiments can be added by authors at the end of the Introduction; Is there any difference with the method in the article in reference number [18].

Response 3: Incubation method is a standard method. Therefore, we cannot say in the introduction about its novelty. The advantages and novelty of our research are  indicated in the following paragraph: “The C cycle and temperature-dependent processes in high latitudes that contribute to climate change have been the subject of much research conducted in the last few decades [19–21]. Nevertheless, not much is known about the ELs, a significant segment of the cryptogamic cover community, and their contribution to maintaining the C balance of these ecosystems, particularly in Siberia. However, GHG emissions by ELs may have the potential to influence overall assessments of ecosystem GHG fluxes, thereby affecting our understanding of current processes and future projections. We discovered that ELs were producing CH₄ in the non-permafrost Siberian birch forest in our earlier study [18]. Consequently, we hypothesize about the possible GHG emissions—particularly the production of CH₄—by the ELs in the permafrost area of the Middle Siberia. The ELs CH₄ production could occur in the oxic conditions; therefore, it results from the non-methanogenic processes, unlike the methanogenesis, which is restricted by the non-oxic conditions and represented by the methanogenic bacteria (e.g., Archaea) [22–23]. Boreal forests can be quite abundant in the ELs [24–25]. Hence, the ELs can contribute to the C balance of the climate change affected ecosystems of high latitudes due to the ELs GHG emissions.”.

 

Comments 4: 2. Materials and Methods

L.94-105: Add citation using the recent reference. Reference number [28] was published in 1979, and may no longer be relevant to the climate conditions of the study area.

Response 4: Thank you for the suggestion. We added a more recent reference for this situation: Prokushkin, A. .; Geis,T.N.; Kolosov, R.A.; Korets, M.A.; Panov, A.V.; Polosukhina, D.A.; Prokushkina, M.P.; Titov, S.V.; Tokareva, I.V.; Sidenko, N.V.; Shamonina, Yu.V.; Prokushkin, S.G. Lateral carbon flux in the cryolithozone of central Siberia. Sibirskij Lesnoj Zurnal (Sib. J. For. Sci.) 2024, 3, 67–82 (in Russian). Also, we updated the climate information in the text as follows “As it was assessed for the period of 1928-2023, the mean monthly temperatures vary from -35.7 °C in January to 16.7 °C in July. The area receives 363 mm of precipitation annually on average for the years 1928-2023, of which 30–40% falls as snow (an average of 40–50 cm) [28].”

 

Comments 5: L.183: In lichen sampling methods, it should be stated whether there is an attempt to control for other environmental variability, such as wind, rainfall, or temperature.

Response 5: Thank you for the comment. We clarified the sentence at L. 183 regarding the weather conditions during the sampling of the ELs. Now, it is as follows “Lichens were collected on windless sunny days of similar air temperature conditions (19-23 °C) during the daytime for future incubation experiments in order to investigate GHG gas fluxes (CO2 and CH4). Besides, as the overall light conditions varied, we took EL samples at each branch exposure (northern, eastern, southern, and western).”

 

Comments 6: L.279: If available, please provide additional information about the sensitivity and accuracy of the tool, to demonstrate the reliability of the data generated.

Response 6: Thank you for the suggestion. We added additional information about the technical characteristics of the device: “Picarro 2201-i has several modes for measuring CO2 and CH4; we used the mode that allows for simultaneous measurement of two gases. Picarro's technology allows for simultaneous measurement of δ13C in two gases, making it unique. In the CO2/CH4 mode, δ13C measurements are performed every few seconds, resulting in a higher measurement rate than the gas exchange rate in the cell. δ13C measurements in the combined mode have high reproducibility, exceeding 0.16‰ for CO2 and 1.15‰ for CH4.”.

 

Comments 7: L.280: Authors should include the formula since the flux data from the incubation experiments are the main result of this study, and make sure that the formula was created directly by Matvienko. If not, include a citation from the reference when the formula was first used/created.

Response 7: Thank you for the suggestion, the formula for GHG fluxes calculation was added to the subsection 2.5.

 

Comments 8: L.295: There needs to be an explanation of the justification for using artificial rainwater; and what the chemical composition of the water is.

Response 8: Thank you for the comment. We added the justification for using artificial rainwater in the text and changed several sentences as follows: “In the laboratory, air-dried EL samples were separated from the substrate (bark, mosses, etc.). Then, due to the possible osmotic stress caused by distilled water [17,35], we used the artificial rainwater of the following composition (8.8 mg l⁻¹ K2CO3, 4.6 mg l⁻¹ Na2CO3, 5.0 mg l⁻¹ CaCO3, 4.4 mg l⁻¹ FeSO47H2O, 0.6 mg l-1 MnSO4H2O, pH adjusted to 7). Therefore, ELs were sprinkled by the artificial rainwater in order to reach the 200% EL thallus water content.”

17. Lenhart, K.; Weber, B.; Elbert,W.; Steinkamp, J.; Clough, T.; Crutzen, P.; Pöschl, U.; Keppler, F. Nitrous oxide and methane emissions from cryptogamic covers. Glob. Chang. Biol. 2015, 21 (10), 3889–3900.
18. Johansson, O., Olofsson, J., Giesler, R., & Palmqvist, K. (2011). Lichen responses to nitrogen and phosphorus additions can be explained by the different symbiont responses. New Phytologist, 191(3), 795-805.

 

Comments 9: 3. Results-Discussion

L.395-407: Although the authors have presented the results of ANOVA and PCA, the explanation of the factors that influence CO2 and CH4 fluxes is still lacking in detail. The authors should explain in the discussion section about the varying results. A deeper disclosure of the biological mechanisms or environmental characteristics that cause these differences would strengthen the results.

Response 9: We rewrote the paragraph according to the Reviewer 3’ suggestions as follows “Our study shows that, unlike the CH₄ fluxes, CO₂ fluxes vary depending on the type of EL, its thallus water content, and the exposure of the branch to which it is attached. For example, south- and west-exposed Bryoria simplicior demonstrated the mixed dynamics of CO₂ fluxes during 2-hour incubation under illumination, though north- or east-exposed Bryoria simplicior predominantly showed photoassimilation of CO₂ (Figure 6). As showed PCA (Figure 7), such variation can be associated with the variation in the PAR and ALT regarding the branch exposure in this particular species. On the contrary, Evernia mesomorpha showed no significant differences regarding the branch exposure and mostly emitted CO₂ during 2-hour incubation under the illumination. Interesting that Bryoria simplicior and Evernia mesomorpha inhabiting the branches of northern and eastern exposure showed contrasting results regarding CO₂ fluxes, i.e., Bryoria simplicior mostly showed CO₂ photoassimilation, though Evernia mesomorpha demonstrated CO₂ emission under the illumination (Figure 6). These specific responses of various EL species toward the different factors broaden the uncertainty in the GHG fluxes by the EL communities of different compositions, which complicates the assessment of the EL contribution to the C cycle of forest ecosystems.”.

 

Comments 10: L. 400: Principal component analysis (PCA) has not been explained in the Method section.

Response 10: Thank you for the comment. We added the following sentence in the subsection 2.6.: “Principal component analysis (PCA) was employed for the analysis of GHG fluxes by the ELs colonized the larch branches of various exposures depending on the thallus water content and EL species and was visualized using R-package “factoextra”.”.

 

Comments 11: L.670-681: At the end of the discussion, it is best to include the limitations of this research, for example, there are uncontrollable environmental factors that can affect the results and suggestions for what needs to be done for further research.

Response 11: Thank you for the suggestion. We added the following part “Furthermore, because of the potential links to light-dependent physiological processes in the photobiont of an EL, our analysis is restricted to the measurements of GHG fluxes under illumination conditions. Therefore, in an effort to understand the mechanisms underlying the oxic CH4 emissions, next step will be the investigation of the dark-related processes that led to GHG fluxes by ELs.”.

 

Comments 12: 4. Conclusions

Conclusions must be rewritten so that the research objectives in L. 87-91 can be answered clearly. In the conclusion, a statement can also be added regarding the influence of ecological conditions and long-term implications for climate change modeling.

Response 12: We rewrote to conclusions according to the request of the Reviewer 3 as follows: “Here, we expand current knowledge on non-methanogenesis CH₄ emissions in oxic conditions by including some ELs inhabiting permafrost areas. In our study, using incubation experiments with illumination, we found that permafrost ELs primarily emit GHGs like CO₂ and CH₄. Using the most common epiphytic species in the study region, Bryoria simplicior and Evernia mesomorpha, which reside on larch with the projecting cover up to 70% at larch branches depending on the EL species, it has been shown that the GHG fluxes from the surface of these lichens are highly species-specific. Overall, among studied EL species, CH₄ fluxes varied from -0.15 to 1.8 ng CH₄-C g^-1 h^-1 and CO₂ fluxes varied from -31 to 59.3 μg CO₂-C g^-1 h^-1. Moreover, the lichen-inhabited branch's exposure and the water content of the EL thallus determine the magnitude and direction of CO₂ and CH₄ fluxes. It can be preliminary said that due to EL lower C emission rates in the permafrost zone, their contribution to permafrost area GHG emissions is expected to be less than those in the non-permafrost zone of Siberia. Therefore, it is crucial to investigate the impact of ecological and environmental conditions fluctuations on the various EL species caused by ongoing climate changes, taking into account the revealed differences in GHG fluxes by the EL of permafrost and non-permafrost habitats. New data on the EL GHG fluxes, along with the related parameters like branch or stem exposure, EL thallus water content, etc., are suggested then being incorporated into the models on a long-term basis.”

 

Comments 13: Comments on the Quality of English Language

Some sentences still feel complex and need to be simplified to make them easier to understand, for example in L. 68-71, 73-76, etc.

Response 13: Thank you for the suggestion. We simplify some sentences that sound complex. For example, we changed the sentence at L68-71 (“During the last decades, much research concentrates on the C cycle and temperature-dependent processes in high latitudes that cause climate change [19–21], while little is known about the contribution of ELs—a big group of the cryptogamic covers—to the C balance of such ecosystems, particularly in Siberia.”) to the following: “The C cycle and temperature-dependent processes in high latitudes that contribute to climate change have been the subject of much research conducted in the last few decades [19–21]. Nevertheless, not much is known about the ELs, a significant segment of the cryptogamic cover community, and their contribution to maintaining the C balance of these ecosystems, particularly in Siberia.”.

We changed the sentence at L73-76 (“As we found the CH4 production by ELs in the non-permafrost Siberian birch forest in our previous study [18], we, therefore, hypothesize on the potential GHG emissions by the ELs in the permafrost area of the Middle Siberia, especially CH4 production.”) to the following “We discovered that ELs were producing CH4 in the non-permafrost Siberian birch forest in our earlier study [18]. Consequently, we hypothesize about the possible GHG emissions—particularly the production of CH4—by the ELs in the permafrost area of the Middle Siberia.”.