Plant genotype determines biomass response to flooding frequency in tidal wetlands

Reents, Svenja; Mueller, Peter; Tang, Hao; Jensen, Kai; Nolte, Stefanie

doi:https://doi.org/10.5194/bg-18-403-2021

Articles | Volume 18, issue 2

https://doi.org/10.5194/bg-18-403-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-18-403-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 2

Research article

|

18 Jan 2021

Research article |

| 18 Jan 2021

Plant genotype determines biomass response to flooding frequency in tidal wetlands

Svenja Reents, Peter Mueller, Hao Tang, Kai Jensen, and Stefanie Nolte

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Final revised paper (published on 18 Jan 2021)
Preprint (discussion started on 09 Jun 2020)

Interactive discussion

Status: closed

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

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RC1: 'Comments', Anonymous Referee #1, 24 Jun 2020
- AC1: 'Reply to reviewer comments', Svenja Reents, 07 Sep 2020
RC2: 'Comments', Anonymous Referee #2, 25 Jun 2020
- AC2: 'Reply to reviewer comments', Svenja Reents, 07 Sep 2020

Peer-review completion

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

ED: Reconsider after major revisions (08 Sep 2020) by Sara Vicca

AR by Svenja Reents on behalf of the Authors (09 Oct 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (11 Oct 2020) by Sara Vicca

RR by Anonymous Referee #2 (31 Oct 2020)

Suggestions for revision or reasons for rejection

This manuscript examines responses of different genotypes of the same species to changes in inundation, thereby addressing an understudied area of potential plant responses to SLR. The results focus on plant responses to different flooding frequencies, highlighting differences in biomass, leaf and shoot, and rhizome growth between low-marsh and high-marsh genotypes of E. athericus. The revised version of the paper addresses most of the concerns raised during the first round of review by situating this work within the context of other studies examining population-level or genotypic differences in species’ responses to global change factors, providing more information in the methods, and expanding the data presented in the results. The addition of these new data, however, raised some additional questions that should be addressed in a subsequent revision. I’ve noted these questions and some others below.

Hypotheses: consider expanding to include more than just the biomass response, as several variables deal with other growth responses (leaf and shoot length, rhizome length, etc.) and are subsequently discussed as important findings of the study.

Materials and methods: The revisions addressed most of the concerns raised previously, but more information on the field site from which plants were collected and how the experimental design relates to field-relevant conditions would be useful, as noted below for the different sections.

Section 2.1. Provide a brief description of the tides and elevation range of the site, the distribution of the genotypes along this gradient, and other environmental data (e.g., salinity), which would then allow the reader to understand how the experimental design corresponds to the field conditions.

Section 2.1, line 84: How did you quantify “similar size” of individual plants? Was it just initial shoot length and number as noted in the discussion? If so, this does not necessarily reflect potential differences in initial biomass. Are these variables correlated with biomass, and if so, are their allometric relationships to demonstrate this relationship? What about belowground biomass? It would be helpful to more explicitly note the measures taken to document initial plant variables, which when combined with the random assignment of plants to treatments, minimizes potential size-based bias. If these data are not available, then anecdotal visual assessments of biomass (no obvious outliers), when combined with the shoot and leaf length data and random assignment of plants to treatments, would help reduce concerns about initial size bias in the study.

Section 2.3.1. The inclusion of root:shoot is a nice addition, but it raises some new questions. For root:shoot, rhizomes were excluded, yet it appears that rhizomes were included in the belowground biomass values reported in Fig. 1. Based on an estimated calculation using the biomass values in the figure, the root:shoot values do not appear to be derived from the values reported for above- and below-ground biomass in Fig. 1. If rhizomes had been included as belowground biomass for the calculations of root:shoot, it appears that a different pattern for root:shoot would emerge, especially for the high flooding treatment. This raises the question of where and when rhizomes were incorporated into measures of biomass and how this affects interpretations of results. To clarify this confusion, explain what material is included in measures of above- and below-ground biomass in the methods, justify the removal of rhizomes from calculations of root:shoot (or include rhizomes in the calculations and refer to it as belowground:aboveground ratio instead), and consider the implications of not including rhizomes in the calculation of root:shoot. For example, rhizomes would contribute to vertical resilience by contributing to soil volume, a mechanism noted in the paper, and may be an important component when considering potential allocation responses by the genotypes.

Section 2.3.2. Provide additional information here about the differences in initial measures of plant growth, as noted above.
Results: Consider reorganizing the subsections so that all biomass measures are presented consecutively (Total biomass, above- and belowground biomass, root and rhizome biomass, ratio), followed by shoot and leaf length and number. The figures could be grouped similarly, rather than having the shoot and leaf data combined with the rhizome and root biomass.

Section 3.1. Include reference to Fig. 1 when presenting root:shoot results.

Section 3.2. Present these data in the order in which they are presented in figure 2 (or reorder the panels in figure 2).

Sections 3.2-3.3. The data for number of shoots and leaves and rhizome length are not shown anywhere, yet there are significant patterns of interest for leaves and rhizome length that are subsequently highlighted in the discussion. Add a table or figure to show the means for the different genotype x flooding combinations for these data so that all patterns are shown for variables with significant findings.

Discussion:

Lines 179-180. What is the significance of low-marsh genotypes maintaining aboveground biomass regardless of flooding treatment?

Lines 180-185. Move this to the results or methods as evidence that any initial differences in plant size were insignificant.

Update the discussion considering any changes in the presentation and interpretation of root:shoot data.

Some additional technical corrections are provided below:
Line 16: delete “a” prior to “higher aboveground biomass”
Line 41: add a space between “loss” and “(Chmura…”
Line 73: close the parentheses
Line 85: add “(described in 2.2)” after “flooding treatments”
Line 85: add “to facilitate drainage” at the end of the sentence.
Line 88: change “placed on each step” to “assigned to one of three flooding treatments” because steps are not explained until the next section.
Lines 143-145: cite Fig. 1
Line 151: “with increasing flooding”
Line 152: Section numbering is repeated. This should be Section 3.3.
Line 156: Should be Section 3.4.
Line 178: include citations
Line 179: delete “a” before “high aboveground biomass”
Line 206: “have” instead of “has”
References: check formatting; some title are capitalized throughout and others aren’t; scientific names are not italicized
Figures: consider adding panel labels (A, B, C, D) and adding the specific panel reference to the text when figures are referenced. Also, check captions that suggest asterisks indicate significance, but no asterisks are included on the graphs. For variables with main effects of flooding but no interactions, these differences can be shown on the graphs by adding letters or symbols denoting differences over the LM-HM pairs for each flooding treatment. Similarly, it would be useful to note variables with differences between genotypes (in the absence of interactive effects) somehow – perhaps by noting this in caption.

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ED: Publish subject to minor revisions (review by editor) (02 Nov 2020) by Sara Vicca

AR by Svenja Reents on behalf of the Authors (30 Nov 2020) Author's response Manuscript

ED: Publish subject to technical corrections (01 Dec 2020) by Sara Vicca

AR by Svenja Reents on behalf of the Authors (02 Dec 2020) Manuscript

Short summary

By conducting a flooding experiment with two genotypes of the salt-marsh grass Elymus athericus, we show considerable differences in biomass response to flooding within the same species. As biomass production plays a major role in sedimentation processes and thereby salt-marsh accretion, we emphasise the importance of taking intraspecific differences into account when evaluating ecosystem resilience to accelerated sea level rise.