Effects of Fires on Microbial and Metazoan Communities in Peatlands

Round 1

Reviewer 1 Report (Previous Reviewer 1)

The proposed manuscript aims to study the impact of fire on peatland organisms, however in my opinion the written objectives were only partially fulfilled. The importance of the studied groups of organisms (heterotrophic bacteria, flagellates, testate amoebae, ciliates and nematodes) is not well explained, neither in the introduction nor discussion. Bacteria are the main decomposers which can contribute to greenhouse gases emission but what significance have other studied groups for the environment?

One of the major drawbacks of the research is the sample collection methodology and lack of taxonomical classification. Even more important is that it is unclear what samples were analyzed. There is information about sampling in the edge zone and central zone. Furthermore, for 2018 and 2019 there is only one sample in the results while you state that samples were taken once a month. Clarify.

The methodology description, discussion and conclusions need to be improved, they are too general. Some of the discussion seems inappropriate, for example, an increase of bacteria after 8 months is related to the observed change of temperature and C:N:P ratio rather than the availability of nutrients which were also abundant directly after the fire.

Author Response

I wish to kindly thank you for the reviews. I have taken into consideration all remarks and suggestions from the reviewers and editorial comments.

• In the chapter Introduction subchapters were introduced as suggested. We added information on the role of studied group of organisms: “These studies have mainly concerned bacteria or fungi in forest or peatland ecosystems, while there is nearly a complete lack of studies on protozoa (testate amoebae and ciliates) and nematodes and their responses to peatland fires. In peatland ecosystems bacteria are the main decomposers which can contribute to greenhouse gases emission. Testate amoebae, ciliates and nematodes are significant consumers of algae, bacteria, and flagellates, and they participate in the decomposition of organic matter and the cycling of nutrients [12]. Knowledge of fires on microbial and metazoan communities and trophic relationships is…” – l. 46-51
• In the chapter Methods was added mor information on sample methodology: l. 110 “From April to November at each site the following were analysed according…”, l. 118-126 “Microbial communities (bacteria, flagellates, ciliates and testate amoebae) and nematodes were analysed for four years – once a month from April to November before the fire (2018-2019) and subsequently 2, 4, 8 and 12 months after the fire. Samples were taken from two study sites: the edge zone of the bog and the central zone. In each month (April-November), from each site three samples of surface water were taken with a plexiglass corer (length 1.0 m, Ø50 mm). The size of each sample (the amount collected by the corer) was 400-500 ml. For each group of micro- and macro- organisms in each of the study months, three replicate samples were mixed together and the integrated sample was treated as representative for the site.:, l. 136 “…..microscope at 600 × magnification.”
• As suggested, we added information on taxonomical classification: Taxonomic identification of investigated group of organisms was based on works Porter and Feig [25], Caron [26], Foissner et al. [29], Clarke [30].
• As suggested, in discussion section we added information on relation between C:N:P: l. 350-356 “Then after eight months there was a sudden increase in the abundance of bacteria, which was probably linked to changes of tmperature and C:N:P ratio. Similar observations were reported by Barreino and Diaz-Raviña [21]. Widden and Parkinson [34] found that bacteria diversity were closely related to the N:P and C:P ratios. These results suggest that bacteria communities may be limited by the imbalances of C, N, and especially P in afforested ecosystems, which provides evidence of linkages between bacteria, plants and soil.” We corrected conclusion: l. 450-460 „In conclusions, the fire modified the physical and chemical parameters in water of the peat bog, increasing temperture, pH, water mineralization, and concentrations of biogenic compounds, organic matter and decreasing of oxygen concentrations. Our study show that fire significantly influences on moisture regime of peatlands and vegetation changes to typically drier habitats. The fire distinctly modified the qualitative and quantitative structure and the functioning of microbial food webs, and thus influences on carbon cycling. This was reflected in a increase in the abundance of ciliates and decrease in the species number and abundance of testate amoebae. The functioning of food webs after fires is still very little known, but it is important for an understanding of the functioning of peatlands, which due to global climate change are increasingly susceptible to fires.

 

Reviewer 2 Report (Previous Reviewer 3)

This paper studied "Effects of fires on microbial communities and food webs in peat lands", which is an interesting and meaningful work. This research is systematic and its data is detailed. Before this work will be published, the following issues need be further revised.

 

(1) About the title. Food webs should be a big concept, which should include all kinds of creatures. However, the authors only looked at microbial communities and nematodes. Explain whether the microbial communities and nematodes can be used to illustrate the true meaning of the food web in the peat land. If not, it is recommended to modify the title.

 

(2) Lines 84, Why use only heterotrophic bacteria, flagellates, testate amoebae and ciliates but not other bacteria to represent microbial communities in peat lands？

Author Response

- As suggested we corrected title on: Effects of fires on microbial and metazoan communities in peatlands

- L. 84 we added information: These studies have mainly concerned bacteria or fungi in forest or peatland ecosystems, while there is nearly a complete lack of studies on protozoa (testate amoebae and ciliates) and nematodes and their responses to peatland fires. In peatland ecosystems bacteria are the main decomposers which can contribute to greenhouse gases emission. Testate amoebae, ciliates and nematodes are significant consumers of algae, bacteria, and flagellates, and they participate in the decomposition of organic matter and the cycling of nutrients [12]. L45-51 and we analysed total abundance of bacteria, not only heterotrophic – we rejected this sentence.

Reviewer 3 Report (New Reviewer)

I found article “Effects of fires on microbial communities and food webs in peatlands” as very interesting and important to publish. However, I have some comments which I make in the points below.

 

·         Figure 1 is very ascetic. It seems to me that showing the location of the research area against the background of the orthophotomap / any other background will improve the reader's perception. Here, apart from the general shape and location of the cut, nothing can be seen in the background of the contour of Poland. I think that this figure should be enriched for better reception by the reader.

·         In the vicinity of line number 250, a vertical black line appears on the left - to be deleted

·         Figure 6 - here all markings written in color and italics are illegible - indistinguishable for the discerning reader

·         The article analyzes the example of a god from eastern Poland. I think that enriching it with examples from other parts of Poland (or even mentioning them) would enrich the introduction presented in the article. A good example is Biebrza, which was also on fire. Biebrza is also a good example for comparison due to a different fact - there was no drainage there and its fragments were unchanged by humans - you can read and decide if you want to include this in the following:

DOI 10.7717/peerj.13418.

DOI 10.1051/kmae/2021036.

 

I am not a native English speaker, it is difficult for me to evaluate the quality of the English language in general. The authors should read the text of the manuscript very carefully once again.

Author Response

- As suggested we corrected fig. 1 on ortophotomap type.

- We rejected black line in l. 250

- We corrected Fig. 6 to better reader.

- We cited the literaturę as suggested:

Grygoruk, Ł.; Szałkiewicz, E.; Grodzka-Łukaszewska, M.; Mirosław Świątek, M.; Oglęcki, P.; Pusłowska-Tyszewska, D.; Sinicyn, G.; Okruszko, T. Revealing the influence of hyporheic water exchange on the composition and abundance of bottom-dwelling macroinvertebrates in a temperate lowland river. Knowledge and Management of Aquatic Ecosystems 2001, 37, 9; https://doi.org/10.1051/kmae/2021036. – l. 426 and corrected English

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

 

Manuscript ID: ijerph-1869239 by Mieczan et al., entitled “Effects of fires on microbial communities and small Metazoa in peatland ecosystems" aim to investigate the relationship between physical and chemical factors, microbial communities, and food webs before and after peat bog fire.

 

General comments:

Firstly the title should be modified into “…aquatic ecosystems”. Water samples and soil samples highly differ in microbial communities and their functionality, with aquatic communities having less impact on the carbon cycle and greenhouse gas emissions.

It seems that the proposed manuscript was constructed so to reveal the implications of peat bog fire, concerning global warming and the possible increased risk of future peat bog fires. However, in my opinion, understanding the functioning of these habitats, need deeper insight using novel technologies i.e. next-generation sequencing. To fulfil the given (by you) research objectives, taxonomical/functional analyzes/discussions must be done. The structure was analyzed only for testate amoebae and ciliates. For other groups, only abundance was tested.

Furthermore, the applied methodology with the sedimentation procedure is not optimal, it may be sufficient for bigger organisms such as testate amoebae or ciliates but only a fraction of bacteria and fungi are in the pellet. See for example https://doi.org/10.1039/D0SM02115F Sedimentation time and level may be highly dependent on the concentration of different compounds in the water, thus introducing bias to the results.

 

In my opinion, the applied monitoring of bacteria, heterotrophic flagellates, ciliates, testate amoebae and nematodes is not explained well. Bacteria and fungi are the main decomposers of organic matter so relevant research is justified but why in your work there is more emphasis on other groups? The reasons must be explained/justified because in the present form the reader may not know why research on aquatic flagellates, ciliates, testate amoebae and nematodes may be important for the functioning of peat bog. Add relevant information in the introduction and discussion, highlighting taxa which may somehow contribute to the structure and functioning of microbial food webs of peat bog. Very interesting would be research/discussion on certain groups with specific metabolic activity for example methanotrophic/methanogenic bacteria.

The studied peat bog seems to have a small area and be in proximity to the industrial area. There is some information about agriculture and tourism infrastructure but it may be discussed more, because for a small research area it may have a very high impact.

Furthermore, you wrote that  “Analyses of hydrological (surface water level) and physicochemical parameters were carried out in the years 2018-2021 – once a month from April to November before the fire (2018-2019) and subsequently 2, 4, 8 and 12 months after the fire, which took place in April of 2020. Samples were collected from two study sites: the edge zone of the bog and the central zone.” What data are presented in the manuscript for 2018 and 2019 (table 1), and for which month? Based on the temperature I presume the measurement for 2018 and 2019 was done either in April or November. Are the data for average measurement? Average from the edge zone of the bog and the central zone? Mark collection points on the map. Also, a map may not be schematic. If possible add pictures of how peat bog looks before and after a fire.

Besides references to other papers about applied techniques, I prefer a short description in the proposed manuscript of how the samples were processed to obtain the presented results (not searching in references), often researchers modify their procedures.

The conclusions should be corrected. They are rather general and obvious. Highlight the key significant conclusions. For example, Peat bog water did not recover dominant amoebae from fire, while ciliates did partially.

Consider moving Figures 2, 4, and 8 to the supplementary file.

 

Specific remarks

Line 46-50 Why there is a lack of protozoa research? How amoebae and ciliates contribute to “Knowledge of these effects and of trophic relationships is extremely important in predicting the response of biocoenoses to the increasingly dynamic phenomena resulting from global climate change.” (also pointed out in general remarks)

Line 158 Clarify. First, you wrote that the average water level before the fire was 20 cm, then you show in Table 1 that the level in studied timepoints was 7 cm. The water level depends on the month when the measurement was conducted. Data refers to which month(s)? I am not entirely convinced if the water level is due to the fire leading to higher evaporation or rather dry years and human activity in the vicinity of the peat bog.

Line 178 Add separator between before fire and after fire timepoints

Line 180 Make figures the same size, otherwise, it seems sloppy

Line 239 Figure 5, add full names because the reader does not know what are three-letter abbreviations

Line 258-260 overestimated statement, the following sentence is relevant, although for me it seems that there is some correlation with 3-4 taxa.

Line 323 pH can highly impact the enzymatic activity of enzymes thus metabolic activity of organisms adapted to acidic pH of peat bog

lines 342-345 “large amount of organic matter and nutrients  from dead microorganisms” is rather not the key factor as there were abundant directly after the fire. Bacteria divide very fast but they need appropriate C:N:P stoichiometry for the metabolic activity as well as temperature, for which shifts was observed 8 months after the fire

Line 348 I a little doubt that predator pressure could have a such strong impact

Line 365 how would soil moisture increase when there was a high decrease in water level?

Reviewer 2 Report

• This article studied the impacts of fires on microbial communities in peatland ecosystems. The writing is clear. The discussion can be elaborated to discuss the practical implication of this work. It is recommend for minor revision.
• Relevant questions:
• In term of potential mitigation, what efforts can be made and what would be the life-cycle costs. One LCA reference is recommended: Engineering interface between bioenergy recovery and biogas desulfurization: Sustainability interplays of biochar application

Reviewer 3 Report

This paper studied "Effects of fires on microbial communities and small Metazoa in peatland ecosystems", which is an interesting and meaningful work. This research is systematic and its data is detailed. Before this work will be published, the following issues need be further revised.

 

1. In the abstract section, the author mentions that “The increase in the frequency of peatland fires is due to both global climate change and deliberate human activity.” Obviously both fire and climate warming can cause an increase in temperature, so the physicochemical factor of temperature should also be important.In the article, although the factor of temperature was also discussed. But in the summary section (lines 440-450), the factor of temperature increase was not mentioned, which is not suitable. And the temperature factor should be mentioned in the summary section and  a summary of how temperature works should be presented.

 

2. This article lacks a detailed discussion about extending the findings of the study into a context of greater significance, such as the relationship of this work with climate change or global ecology etc.. This should be elaborated so that the reader can learn and understand the findings and purpose of this work in a more meaningful and more valuable context.