Reviews and syntheses: on the roles trees play in building  and plumbing the critical zone

Brantley, Susan L.; Eissenstat, David M.; Marshall, Jill A.; Godsey, Sarah E.; Balogh-Brunstad, Zsuzsanna; Karwan, Diana L.; Papuga, Shirley A.; Roering, Joshua; Dawson, Todd E.; Evaristo, Jaivime; Chadwick, Oliver; McDonnell, Jeffrey J.; Weathers, Kathleen C.

doi:https://doi.org/10.5194/bg-14-5115-2017

Articles | Volume 14, issue 22

https://doi.org/10.5194/bg-14-5115-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-14-5115-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 14, issue 22

Reviews and syntheses

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17 Nov 2017

Reviews and syntheses | Highlight paper |

| 17 Nov 2017

Reviews and syntheses: on the roles trees play in building and plumbing the critical zone

Susan L. Brantley, David M. Eissenstat, Jill A. Marshall, Sarah E. Godsey, Zsuzsanna Balogh-Brunstad, Diana L. Karwan, Shirley A. Papuga, Joshua Roering, Todd E. Dawson, Jaivime Evaristo, Oliver Chadwick, Jeffrey J. McDonnell, and Kathleen C. Weathers

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Final revised paper (published on 17 Nov 2017)
Preprint (discussion started on 03 Mar 2017)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of manuscript bg-2017-61: On the roles trees play in building and plumbing the Critical Zone', L. L. Taylor, 10 Apr 2017
RC2: 'Review of Brantley et al', Anonymous Referee #2, 14 Apr 2017
SC1: 'Comments from P. Zion Klos and Southern Sierra CZO', P. Zion Klos, 27 Apr 2017
AC1: 'Final author comments on behalf of all co-authors', Jennifer Williams, 24 May 2017

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (05 Jun 2017) by Sönke Zaehle

AR by Jennifer Williams on behalf of the Authors (05 Jul 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Jul 2017) by Sönke Zaehle

RR by L. L. Taylor (14 Aug 2017)

RR by Anonymous Referee #3 (16 Aug 2017)

Suggestions for revision or reasons for rejection

This review deals with how trees shape the structure and function of the critical zone (CZ). More specifically, it examines the role of tree roots in ‘building and plumbing’ the CZ, through several biophysical processes associated with tree functioning: mechanical stability and water and nutrient acquisition. The paper starts with a conceptual summary of plant-fungi interactions, tree root form and function and CZ architectural dynamics. But the core of the manuscript is the 9 hypotheses on how trees build and plumb the CZ. Overall, the authors have managed to link existing interdisciplinary knowledge on the CZ to highlight knowledge gaps and set the foundations for future CZ research.

Although I agree with comments from previous reviews pointing to the lack of more explicit guidelines for future work, I am aware that the paper is already lengthy and that the field is too interdisciplinary to provide more specific ways forward for the 9 hypotheses posed here. This manuscript provides a first roadmap to develop more specific approaches, that may need to be dealt with in papers more individually focused on ‘plumbing’ or ‘building’ processes, for example.

Nevertheless, I do think that sections 4 and 5 could still be improved. Section 4, on synthesis and challenges is short and does not build on the hypotheses presented earlier in the manuscript. For example, could the authors prepare a graphic summary of the hypotheses in a figure that could be used to structure this last section? Maybe showing areas of overlap or interaction between ‘building’ and ‘plumbing’? Illustrating whether fungi play a role or not?

Specific comments

The abstract ends quite abruptly after listing the 9 hypotheses, without any closing sentence. This also relates to the insufficient treatment of the synthesis and future work sections in the paper.

Figure 1. I wonder whether this figure is necessary to support the text, because some of the information may seem quite obvious (e.g. forest-atmosphere exchange of water and energy) or somehow already shown in Fig. 2 (e.g. erosion).

P. 2, L. 17. I think there is a major leap here between CZ research in broad terms and the focus on trees. To me, the major biotic influence on CZ is through vegetation, and this includes not only forests, but also shrublands and grassland, for example. Are there any papers on the broader role of vegetation on CZ that could be cited here? I am not asking for a long sentence, but, being a review paper, and before moving on to trees, maybe the authors should acknowledge any previous work on the vegetation-CZ relationship.

P. 2, L. 23. The transpiration estimates from isotopic measurements in the Jasechko paper may be biased too high according to several papers published thereafter. The number presented by the authors could be adjusted to reflect more realistic estimates gathered from various methods: Schlesinger, W.H. & Jasechko, S. (2014) Transpiration in the global water cycle. Agricultural and Forest Meteorology, 189–190, 115–117.

P. 14, L. 15. When you refer to ‘some depth’ could you be more precise?

P. 16, L. 4. Instead of ‘tree age and size’, I would say that that tree density is affected more by competition, in line with the preceding statement on self-thinning.

P. 23, L. 19. The reference by Nippert and Knapp is on grassland species, and in fact the paragraph seems to be focused on ‘plants’ in general, not on trees. This can be a bit confusing, given the focus of the paper on trees only. I suggest that you provide a more clear link to tree functioning in this paragraph.

P. 23, L. 25. I think that the authors should express more clearly that the two water worlds hypothesis is a controversial one, obscured by several methodological issues. I suggest that they look at a couple of recently published papers which deal with the TWW hypothesis from the ecophysiological and hydrological perspectives:

Berry, Z.C., Evaristo, J., Moore, G., Poca, M., Steppe, K., Verrot, L., Asbjornsen, H., Borma, L.S., Bretfeld, M., Hervé-Fernández, P., Seyfried, M., Schwendenmann, L., Sinacore, K., De Wispelaere, L. & McDonnell, J. (2017) The two water worlds hypothesis: Addressing multiple working hypotheses and proposing a way forward. Ecohydrology .10.1002/eco.1843

Sprenger, M., Leistert, H., Gimbel, K. & Weiler, M. (2016) Illuminating hydrological processes at the soil-vegetation-atmosphere interface with water stable isotopes. Reviews of Geophysics, 54, 2015RG000515.

P. 25, L. 8-9. There is another study, published before Meinzer et al. 2016, which provides a more comprehensive compilation of predawn water potentials globallIy. In fact, this study could be cited earlier (P. 24,L. 20-21) to support the statement that the concept of a universal ‘wilting point’ might not be appropriate.
Martínez-Vilalta, J., Poyatos, R., Aguadé, D., Retana, J. & Mencuccini, M. (2014) A new look at water transport regulation in plants. New Phytologist, 204, 105–115.

P. 30, L. 4-6. What about other global databases and networks? Could they be used to advance CZ research?
For instance: fine root database http://roots.ornl.gov/, soil moisture networks, https://ismn.geo.tuwien.ac.at/, sap flow database, http://sapfluxnet.creaf.cat

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ED: Publish subject to minor revisions (Editor review) (21 Aug 2017) by Sönke Zaehle

AR by Jennifer Williams on behalf of the Authors (19 Sep 2017) Author's response Manuscript

ED: Publish as is (22 Sep 2017) by Sönke Zaehle

Short summary

This review represents the outcome from an invigorating workshop discussion that involved tree physiologists, geomorphologists, ecologists, geochemists, and hydrologists and developed nine hypotheses that could be tested. We argue these hypotheses point to the essence of issues we must explore if we are to understand how the natural system of the earth surface evolves, and how humans will affect its evolution. This paper will create discussion and interest both before and after publication.