the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Biocrust-linked changes in soil aggregate stability along a climatic gradient in the Chilean Coastal Range
- 1University of Tübingen, Department of Geosciences, Soil Science and Geomorphology, Rümelinstr. 19–23, 72070 Tübingen, Germany
- 2Technical University of Munich, Soil Science, Emil-Ramann-Str. 2, 85354 Freising, Germany
- 3GFZ German Research Centre for Geosciences, Section 5.3 Geomicrobiology, Telegrafenberg, 14473 Potsdam, Germany
- 4Department of Geosciences and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark
- 5Universidad de Atacama, Centro Regional de Investigación y Desarrollo Sustentable de Atacama (CRIDESAT), Copayapu 485, Copiapó, Chile
- 6Universidad de Chile, Facultad de Ciencias Agronómicas, Av. Santa Rosa #11315, La Pintana, 8820808 Santiago, Chile
- 7University of Potsdam, Institute of Geosciences, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany
- 1University of Tübingen, Department of Geosciences, Soil Science and Geomorphology, Rümelinstr. 19–23, 72070 Tübingen, Germany
- 2Technical University of Munich, Soil Science, Emil-Ramann-Str. 2, 85354 Freising, Germany
- 3GFZ German Research Centre for Geosciences, Section 5.3 Geomicrobiology, Telegrafenberg, 14473 Potsdam, Germany
- 4Department of Geosciences and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark
- 5Universidad de Atacama, Centro Regional de Investigación y Desarrollo Sustentable de Atacama (CRIDESAT), Copayapu 485, Copiapó, Chile
- 6Universidad de Chile, Facultad de Ciencias Agronómicas, Av. Santa Rosa #11315, La Pintana, 8820808 Santiago, Chile
- 7University of Potsdam, Institute of Geosciences, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany
Abstract. Biological soil crusts (biocrusts) composed of cyanobacteria, bacteria, algae, fungi, lichens, and bryophytes stabilize the soil surface. This effect has mainly been studied in arid climates, where biocrusts constitute the main biological agent to stabilize and connect soil aggregates. Besides, biocrusts are an integral part of the soil surface under mediterranean and humid climate conditions, mainly covering open spaces in forests and on denudated lands. They often develop after vegetation disturbances, when their ability to compete with vascular plants increases, acting as pioneer communities and affecting the stability of soil aggregates. To better understand how biocrusts mediate changes in soil aggregate stability under different climate conditions, we analyzed soil aggregate samples taken under biocrust communities from four national parks in Chile along a large climatic gradient ranging from (north to south) arid (Pan de Azúcar), semi-arid (Santa Gracia), mediterranean (La Campana) to humid (Nahuelbuta). Biocrust communities showed a stabilizing effect on the soil aggregates in dry fractions for the three northern and the wet aggregates for the southernmost sites. Here, permanent vascular plants and higher contents of organic carbon and nitrogen in the soil control aggregate stability more than biocrusts, which are in intense competition to higher plant communities. Moreover, we found an increase in stability for edge aggregate size classes (< 2.0 mm and 9.5–30.0 mm). The geometric mean diameter of the soil aggregates showed a clear effect due to the climatic gradient, indicating that the aggregate stability presents a log-normal instead of a normal distribution, with a trend of low change between aggregate size fractions. Based on our results, we assume that biocrusts affect the soil structure in all climates. Their role for aggregate stability is masked under humid conditions by higher vegetation and organic matter contents in the topsoil.
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Nicolás Riveras-Muñoz et al.
Status: final response (author comments only)
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RC1: 'Comment on soil-2021-141', Anonymous Referee #1, 11 Mar 2022
The study by Riveras-Muñoz et al. describes dry and wet aggregate stability along a climatic gradient in Chile and evaluates the effect of biocrusts on this stability. Dealing with these two factors, climatic gradient and biocrusts, the paper is multidisciplinary and should be of broad international interest.
However, I have some comments that I would like the authors to consider when revising their manuscript. These are:
General comments
- Given that in the present study aggregate stability was analyzed and discussed with regard to (i) the effect of climate and further (ii) the biological influence, all sections including the introduction and abstract as well as hypotheses should not start with BSC but should follow this order: aggregate stability in general, effects of climate, effects of BSC.
- Also, a strict order within sentences or paragraphs will improve readability of the text. This applies for the order of factors (climate/BSC), treatments (BSC-, BSC+) and sites (north to south).
- Some sentences are very complicated in structure and content. Hence, I suggest to split these sentences for better reading and understanding.
Specific comments
Line 31 and 271: what are “edge aggregate size classes”? please explain
Line 55 ff: please, consider the fact that the occurrence of lichens is not restricted to more humid locations but that many lichens were also found in PA (e.g., Jung et al. 2019: DOI: 10.1111/gbi.12368; Jung et al., 2020: doi.org/10.1016/j.isci.2020.101647)
Line 59: please consider: available water for lichen growth can also mainly be provided by fog and dew (e.g., Jung et al, 2019: DOI: 10.1002/mbo3.894)
Line 67: please explain: what do you mean by “small scale”? Elbert et al. 2012 (DOI: 10.1038/NGEO1486) pointed out that globally cryptogamic covers take up 3.9 Pg C per year.
Line 89: do you mean “soil structure-forming processes DUE TO biocrusts”?
Line 94: not only cyanobacteria but also green-algae are well known to produce extrapolymeric substances which can glue soil particles together (e.g. Lewin 1956: doi.org/10.1139/m56-079); please add
Line 98: what do you mean by “which physically traps aggregates and soil particles“? Please explain
Line 99: please clarify: because of what are soil aggregate stabilization processes dynamic and occur on different time and space scales?
Line 107: what do you mean by “external soil factors”, please explain
Line 108: why only “in the short term”? please explain
line 133: what do you mean by “on the soil surface”? please specify
line 136: do not confine any of this hypothesis but discuss later in the discussion
line 169: it does not become clear how biocrusts were collected exactly – please explain;
please show pictures of the biocrusts sampled at each site (plot picture)
line 177: for the time being: please refer to other researcher’s work on algae and cyanobacteria in BSCs of these locations (e.g., Baumann et al., 2018: doi.org/10.1016/j.soilbio.2018.09.035; Samolov et al., 2020: doi:10.3390/microorganisms8071047)
line 183: please describe exactly how and up to which depth biocrusts were removed (e.g., were the rhizoids of the mosses cut at the soil surface?); what did the BSC look like in PA and what exactly was sampled?
Line 190: Total C and N of what were analyzed? Please describe more precisely
Line 195ff: please explain: what do you mean by “…and corrected by coarse fragments content”?
Line 197 f: insert “difference” before “mean” and “geometric”; please spent some more sentences to explain what results of these indices will mean
Line 204: insert “fraction” after “2-30 mm aggregate”
Line 205: insert “differences” before “geometric”
Line 206: explain what “exp” means
Line 209 and 212: insert abbreviation in brackets
Line 214f: is “weight” correct or should it be “mass”?
Line 253f: start paragraph with “Dry sieving showed…..”
Tables: please insert in the captions that significant factors for response variables are given in the appendix
Fig 1: improve Fig. by noting BSC+ and BSC- also on left hand site of Fig.
Line 319-328: These paragraphs are repetitive and should be removed from here
Line 340: what is does mean: “with a more stable condition”? please explain
Line 341: which “different category”? please explain
Line 370 f: what do you mean by this sentence? Please reword
Line 375 f: “In this sense…..”: the deduction of this idea is not clear, please explain
Line 403: what do you mean by “an indicator of values outside the study range”?, please explain
Line 404 f: split this sentence into two
Line 416 f: for this statement it is very important to know how biocrusts looked like and were sampled and what exactly was included for bulk density, especially for samples in PA; please see grit porosity as outlined in Jung et al. 2019 and 2020
Line 426: what do you mean by “no differences is made between….”? Please explain
Line 429: bryophytes have no hyphae but rhizoids – please add
Line 437: please repeat text of hypothesis
Line 442 ff: please split sentence
Line 444 ff: please reword sentence and repeat hypotheses
Line 449: what other factors do you mean? Please speculate
Line 454: please repeat text of hypothesis
Line 455: please reword the sentence to show its importance
Technical corrections
Line 116: close bracket before “with”
Line 186: please insert name of reference
Line 198: use lower case g for “geometric”
Line 359: insert “a” before “property”
Line 378 f and 421 f: do not spell out total carbon and nitrogen again but use abbreviations
Line 390: insert “out” after “points”
Line 452: replace “,” by “and” before “sand”
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AC1: 'Reply on RC1', Nicolás Riveras Muñoz, 16 Mar 2022
Dear reviewer,
Thank you very much for taking the time to revise this preprint and for giving this positive evaluation with constructive comments. We were very pleased to see that our manuscript is an interesting topic for you, and we appreciate your valuable suggestions for improving our manuscript. We will consider your comments and respond in detail soon.
Best regards,
Nicolás Riveras-Muñoz
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AC2: 'Comment on soil-2021-141', Nicolás Riveras Muñoz, 05 Apr 2022
Dear reviewer,
we appreciate the time spent and the very enriching feedback to improve the document. We are going to apply the proposed structure and to follow the suggested sequence. In some parts of the discussion, it is not fully applicable because the factors climate, BSC and topography are interrelated. However, the suggested order was incorporated as a reference and large parts of the manuscript will be restructured. We will also shorten long sentences (a Chilean/German speciality:-) for better reading and understanding with the help of a native speaker.
We also thank the reviewer for the very helpful and detailed specific comments. We are going to change the text accordingly and give answers to your questions.Best regards,
Nicolás Riveras-Muñoz
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RC2: 'Comment on soil-2021-141', Anonymous Referee #2, 17 May 2022
The importance of biocrust on soil aggregrate stability is underexplored. The research covers a large climate gradient transect of ecological relevance.
There are some issues with the paper which warrant comments or improvements from the full author team. The fact that only Ct is measured is somewhat of mistake. It is clear that in the southern site NA most of C will be organic C and in PA iit be inorganic C (carbonate) which will have differing effect on the aggregate structure, stability and formation. The other issue is whether or not we are observing the effect of pure lichen biocrust (PA) versus a moss containing or dominating biocrust (SG, LC and NA) on aggregates. It is not 100% clear from the paper what the relevance is of the selected aggregate size, it feels somewhat random. Are all these macro-aggregates if so this should be stated. It is concerning that the aggregate size which show increased stability are the largest and smallest size bins selected, a leftover effect ? Also to sme extend visible in Fig 1 where 30 mm and 2.0 mm size fractions look complete different from all others, even without considering the biocrust effect.
The paper decribes in minute detail difference between fractions and sometimes looses the bigger picture. The visualisation of the data is minimal, most data is tabulated. With only one Figure. In all tables and the figure it is not clear what differences are actually significant in the four sites between treatment (biocrust) and for the various size fractions. Errors on the means (standard deviation or standard error ?) are generally larger making it even more difficult to see what is of real significance and what is not. The lack of visualisation make the paper unappealing for the reader to look at.
The conclusion reads extremely long a full page. Most is (semi)-discussion and should go there.
I think it good to go back to some of the original work relevant to this study but this leads to reference of papers from 1950, 1929 and ultimately 1883. This is not fully balanced by lots of recent papers on the topic last 5 years.
Overall the paper has not fully reached its potential, the paper can be streamleined by focus on the key issues and fsignificant findings rather than spending a lot of time and effeort on detailed differences which are not necessarily always significant I guess.
Appendix A already give a good guidance what is of interest. Basically the 4 sites are nearly always significantly different for each parameter, not supprising based on the selecting of the sites with this large climate gradient. Biocrust has no effect on coarser fractions (e.g. sand), C and C/N which could be organic C vs inorganic C reflection between sites. Largest and smallest aggregate size fraction, adn R <2. What maybe wortwile is to look at the site * biocrust interaction what it tells about the aggregate stability /biocrust issue
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AC3: 'Reply on RC2', Nicolás Riveras Muñoz, 17 Jun 2022
Dear reviewer,
We were delighted to see that our manuscript is an interesting topic for you, and we thank you so much for your valuable suggestions for improving our manuscript. We appreciate the time you took to review this preprint and for giving this evaluation with constructive comments.
Regarding the measurement of total carbon, we agree with your view about the origin of the carbon along the climatic gradient. Nevertheless, based in the experimental setup, the observations about biocrust effect in the content of carbon still valuable. In this sense, the discussion of those results is not balanced, giving little importance to the biocrust effect. To respond to this, we gave less emphasis to the climatic influences and more to biocrusts and the interaction of both factors.
Concerning the pure lichen biocrust (PA) versus a moss-containing or dominating biocrust (SG, LC, and NA), our study approach biocrusts from the point of view of their functionality along different biomes and not their taxonomy, where they may have different compositions, not even 100% covered in our study (we did not analyze archaea, fungi, bacteria, cyanobacteria, algae, etc.).
Aggregate sizes are arbitrary and partially cover the range of macroaggregates. The main contributors to macroaggregate formation are plant roots, mycorrhizae, and earthworms, relevant in terms of biocrusts. In this case, the more one subdivides, the more in detail one observes changes in aggregate stability, which is usually evaluated through indexes. So, the exact value of the divisions does not matter as long as they are done homogeneously. On the other hand, the increase in the number of aggregates at the smallest size is indeed due to a leftover effect due to the experimental setup.
All the tables have been replaced for figures, including mean, standard error/standard deviation, and letter-based display for significant differences. More recent references have been added to the topics that require it.
Best regards,
Nicolás Riveras-Muñoz
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AC3: 'Reply on RC2', Nicolás Riveras Muñoz, 17 Jun 2022
Nicolás Riveras-Muñoz et al.
Nicolás Riveras-Muñoz et al.
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