Spatial variations in terrestrial net ecosystem productivity and its local indicators

Cui, Erqian; Bian, Chenyu; Luo, Yiqi; Niu, Shuli; Wang, Yingping; Xia, Jianyang

doi:https://doi.org/10.5194/bg-17-6237-2020

Articles | Volume 17, issue 23

https://doi.org/10.5194/bg-17-6237-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-17-6237-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 23

Research article

|

09 Dec 2020

Research article |

| 09 Dec 2020

Spatial variations in terrestrial net ecosystem productivity and its local indicators

Erqian Cui, Chenyu Bian, Yiqi Luo, Shuli Niu, Yingping Wang, and Jianyang Xia

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Final revised paper (published on 09 Dec 2020)
Supplement to the final revised paper
Preprint (discussion started on 28 Feb 2020)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Comments on "Spatially asynchronous changes in strength and stability of terrestrial net ecosystem productivity"', Xiangzhong Luo, 23 Mar 2020
- AC2: 'Response to comments from reviewer #1', Jianyang Xia, 09 May 2020
- AC3: 'Response to comments from reviewer #1', Jianyang Xia, 09 May 2020
RC2: 'Spatially asynchronous changes in strength and stability of terrestrial net ecosystem productivity', Anonymous Referee #2, 23 Mar 2020
- AC1: 'Response to comments from reviewer #2', Jianyang Xia, 09 May 2020
AC1: 'Response to comments from reviewer #2', Jianyang Xia, 09 May 2020
AC2: 'Response to comments from reviewer #1', Jianyang Xia, 09 May 2020

Peer-review completion

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

ED: Reconsider after major revisions (10 May 2020) by Sönke Zaehle

AR by Jianyang Xia on behalf of the Authors (12 Jun 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Jul 2020) by Sönke Zaehle

RR by Anonymous Referee #1 (21 Jul 2020)

Suggestions for revision or reasons for rejection

Review of “Spatial variations in terrestrial net ecosystem productivity and its local indicators”

I appreciate the responses from Cui et al. and happy to see that most of my comments have been properly addressed. The study provides a new perspective to look into the spatial variation in NEP by transforming the component of NEP into logarithmic form. I have a major comment and two technical comments left.

1. The manuscript proposed to study the relationship between ln(U/R) and NEP. Since we know that NEP = U – R and ln(U/R) = ln(U) – ln(R), therefore it is expected to see a strong r2 between ln(U/R) and NEP (Figure 1-3). I am more curious about why some ecosystems (i.e. boreal ecosystems in Figure 2) seems to defy such correlation, and why the slope of this correlation (i.e. beta) changes spatially? Further discussions on these would be appreciated.

For latter, the variation in beta is suggested to be related to IAV_NEP, which is regarded as an indicator of the carbon sink stability. Wouldn’t IAV_NEP normalized by mean NEP make more sense here? I would be curious to see if there is a relationship between normalized IAV_NEP and beta, as sites with larger NEP seem more likely to have larger beta.

2. Figure 3a presents the correlation between annual mean NEP and ln(U/R) across sites. I think there is a need to clarify the calculation of ln(U/R) here as this indicator changes year-to-year for each site (did you use the mean ln(U/R) of each site?).

3. It would be helpful to give more details on Equation (6). I could not understand how to decompose ln(U/R) into the two components from what is presented here, but the method seems critical to Figure 4. Is equation (6) a multivariate linear function?

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RR by Sönke Zaehle (21 Aug 2020)

Suggestions for revision or reasons for rejection

Editorial Review.

My apologies for the delay in the review process. Having failed to find a reviewer in time, I provide a review myself. Line numbers refer to the manuscript with track changes.

The authors have generally done a good job at responding to the previous reviewer comments (but see the other review). I briefly summarise some remaining issues.

Major points

As has been raised before, I think some discussion is necessary as to whether it is not to be expected that there is such a correlation as U and R are derived from NEP.

Please provide a derivation of Eq 4. This does not logically follow from Eq. 1

Minor points

L41 rephrase to “large-scale estimates from an atmospheric inversion product”

L44: linearily related to ln (X) is equivalent to logarithmically related to X?

L45: beta has not been defined (the slope of what?). Explain “well indicated”

L49: gridded products of what?

L77: unclear what “the compiled” refers to here

L82: Isn’t this a contradiction? If they are strongly correlated in space, then how would they determine the spatial variation in NEP?

L107: here and in the following: the total NET uptake. Also this isn’t entirely correct because as you note later also the strength of the source/sink within each period can vary.

L110: I don’t understand the use of the word “innovatively attributed” here. Please clarify

L146: Add “to infer thenet CO2 exchanges between land, ocean and atmosphere at large scales

L165ff: Is this correct? Are the effects of land cover changes not implicitly included by the use of satelite derived fAPAR?

L168: Please provide correct link to the data portal

L190: A quantitative definition of CUP and CRP is missing here.

L254: Verified is the wrong word here

L272: use “across-site variation” instead to spatial change?

L283: The use of “mostly” is inappropriate here, because CUP/CRP explains less than 60% of the variance.

L317: But what if most of this crop IAV is related to changes in the local crop from year to year and are therefore not representative of regional scale cropland IAV?

L325/L326: These statements need to be adjusted to reflect that the difference in explanatory power is “only” 58 to 42%.

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ED: Publish subject to minor revisions (review by editor) (21 Aug 2020) by Sönke Zaehle

AR by Jianyang Xia on behalf of the Authors (03 Sep 2020) Author's response Manuscript

ED: Publish subject to technical corrections (18 Oct 2020) by Sönke Zaehle

AR by Jianyang Xia on behalf of the Authors (22 Oct 2020) Author's response Manuscript

Post-review adjustments

AA: Author's adjustment | EA: Editor approval

AA by Jianyang Xia on behalf of the Authors (30 Nov 2020) Author's adjustment Manuscript

EA: Adjustments approved (30 Nov 2020) by Sönke Zaehle

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Short summary

Mean annual net ecosystem productivity (NEP) is related to the magnitude of the carbon sink of a specific ecosystem, while its inter-annual variation (IAV_NEP) characterizes the stability of such a carbon sink. Thus, a better understanding of the co-varying NEP and IAV_NEP is critical for locating the major and stable carbon sinks on land. Based on daily NEP observations from eddy-covariance sites, we found local indicators for the spatially varying NEP and IAV_NEP, respectively.