Variations in diurnal and seasonal net ecosystem carbon dioxide exchange in a semiarid sandy grassland ecosystem in China's Horqin Sandy Land

Niu, Yayi; Li, Yuqiang; Yun, Hanbo; Wang, Xuyang; Gong, Xiangwen; Duan, Yulong; Liu, Jing

doi:https://doi.org/10.5194/bg-17-6309-2020

Articles | Volume 17, issue 24

https://doi.org/10.5194/bg-17-6309-2020

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

https://doi.org/10.5194/bg-17-6309-2020

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

Articles | Volume 17, issue 24

Research article

|

15 Dec 2020

Research article |

| 15 Dec 2020

Variations in diurnal and seasonal net ecosystem carbon dioxide exchange in a semiarid sandy grassland ecosystem in China's Horqin Sandy Land

Yayi Niu, Yuqiang Li, Hanbo Yun, Xuyang Wang, Xiangwen Gong, Yulong Duan, and Jing Liu

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Preprint (discussion started on 21 Apr 2020)
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Interactive discussion

Status: closed

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

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RC1: 'Review', Anonymous Referee #1, 04 Jun 2020
- AC1: 'Reponse Reviewer 1', Yuqiang Li, 04 Jul 2020
RC2: 'Horquin Sanday Land grassland carbon exchange review', Anonymous Referee #2, 10 Jun 2020
- AC2: 'Reponse Reviewer 2', Yuqiang Li, 04 Jul 2020

Peer-review completion

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

ED: Reconsider after major revisions (21 Jul 2020) by Trevor Keenan

AR by Yuqiang Li on behalf of the Authors (07 Aug 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (24 Aug 2020) by Trevor Keenan

RR by Anonymous Referee #3 (08 Sep 2020)

Suggestions for revision or reasons for rejection

I reviewed this manuscript for the first time. I realized it has been improved a lot after taking the reviewers’ comments in the first round. But I think some further improvements remain required before being publishable. See my advices.

1. L19-21,”Sandy grasslands are sensitive to climate change, yet the magnitudes, patterns, and environmental controls of their CO2 flows are poorly understood”, the expression is not backed up by the current literature. Generally, there are lots of studies of carbon fluxes over sandy grasslands worldwide, but for some specific regions, the expression may hold.
2. L136, ‘CO2 dynamics’ -> ‘CO2 fluxes’
3. L98, ‘quantified the temporal variation’, you actually quantified the CO2 fluxes over different timescales.
4. L183-187, the description of precision and accuracy are very confusing, μmol/m2/s is the unit of flux, but here the authors are evaluating the raw measurements of IRGA; also, the precision and accuracy should be on the raw measurement of 0.1 s timescale for a given 10 Hz EC. It is strange to discuss the topic for raw measurement but on the timescale (30min) for the averaged flux.
5. L165, the measurement sections were messed up. You could describe meteorological measurements soon after the experimental site, then describe EC measurement and flux calculation, quality control etc. That way, the method section may flow better.
6. L219, the EC system you used is an open path one, I am not aware of any requirement of lag correction. You need to detail it.
7. L225, avoid using not so necessary description: you do not need to remove data during power failure as no data can be stored as the data logger is also dead then, right?
8. L226, it is more intuitive if you use umol/m2/s as the unit of carbon flux.
9. L229-231, The definition of daytime or nighttime NEE seems not useful and breaks the flow of the paragraph. As I reviewed it progressively, this sentence can be moved to the following paragraph for data gap filling.
10. L249-251, you may use a graph with Rn-G as x-axis and H+LE as y-axis to show the energy closure, which can be part of the supplementary information.
11. Fig.3-5, the y-axis can be named as ‘CO2 fluxes’
12. L355, The discussion needs further improvement. For 4.1, a more accurate subsection title is required. This subsection is very long, but the information is very divergent. So is the second part of the discussion. The authors may re-write the discussion. The authors can consider what to discuss before writing, e.g., you can have a subsection with a title like ‘comparison with other arid grassland ecosystem’, in which you can discuss if your finding is different from others and what new knowledge you can bring. Also, this is a data driven research, a possible limitation of the study can give the readers some knowledge to how much degree the conclusion is subject to some uncertainty, e.g., data quality or data treatment. I suggest the authors articulate the discussion in a clearer way rather than lay them out like a twin of the result section.

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RR by Anonymous Referee #1 (13 Sep 2020)

ED: Reconsider after major revisions (23 Sep 2020) by Trevor Keenan

AR by Yuqiang Li on behalf of the Authors (26 Oct 2020) Author's response Manuscript

ED: Publish as is (03 Nov 2020) by Trevor Keenan

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Short summary

We report the results from continuous year-round CO₂ observations from a sandy grassland in the Horqin Sandy Land using the eddy covariance technique. To quantify the diurnal, seasonal, and annual variation in net ecosystem CO₂ exchange, gross primary productivity, and ecosystem respiration and to identify the different scales of environmental factors and the underlying mechanisms, we also explored how the annual precipitation affects the net ecosystem CO₂ exchange and its components.