Investigating the Performance of Red and Far-Red SIF for Monitoring GPP of Alpine Meadow Ecosystems

Round 1

Reviewer 1 Report

The manuscript explored the variation of SIF-GPP relationships of alpine meadow ecosystems using tower-based SIF data in different bands, environmental factors and GPP data. The current studies related to alpine meadow ecosystems lack. Therefore, this manuscript can improve the understanding of SIF performance in monitoring different ecosystems. Overall, the topic is interesting to broad audience. However, there are some shortcomings and unclearness in the current analysis. The authors need to fully resolve these before the next stage.

Major comments:

1) The authors need to amplify the novelty of the manuscript. Some of this can be achieved through improvements in technical writing. However, the ‘standard’ mode of comparing SIF with NDVI and EVI is so routine in the literature. I’m not sure we’re learning much here. Recent work has highlighted that NIRv is a better reflectance based proxy for productivity versus traditional VIs. You can find the calculation in the following references:

Badgley, Grayson, Christopher B. Field, and Joseph A. Berry. "Canopy near-infrared reflectance and terrestrial photosynthesis." Science advances 3, no. 3 (2017): e1602244.

Wang, Songhan, Yongguang Zhang, Weimin Ju, Bo Qiu, and Zhaoying Zhang.

"Tracking the seasonal and inter-annual variations of global gross primary production during last four decades using satellite near-infrared reflectance data." Science of the Total Environment 755 (2021): 142569.

Minor comments:

Please check the grammar and tense through the manuscript.

Line 53-103: Too much space is devoted to the effects of different bands and different

vegetation types on the SIF-GPP relationship. In fact, the manuscript also compares the effects of different environmental factors on the SIF-GPP relationship. However, the introduction presents little information about the influence of different environmental factors on SIF-GPP and does not explain the current knowledge gap.

Line 239: y=kx+b? But the table 1 linear model not have b.

Fig.4 SIFRed/GPP is less susceptible to PAR, TA and VPD than SIFFar-Red /GPP. Could you explain why?

Discussion: It is interesting to study the SIF-GPP relationship using tower observation data. However, you need to understand that the observation range of the flux tower is small, so the conclusions you get may not be generalizable. This needs to be stated in the discussion. You can refer to this reference below:

Qiu R , Han G , X Ma, et al. A Comparison of OCO-2 SIF, MODIS GPP, and

GOSIF Data from Gross Primary Production (GPP) Estimation and Seasonal Cycles in North America[J]. Remote Sensing, 2020, 12(2):258.

 

 

 

Author Response

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Reviewer 2 Report

This is an interesting study，which focuses on the reasons why red SIF shows more potential than far-red SIF for monitoring GPP in an alpine meadow ecosystem. There are still some issues should be addressed.

1.      In the abstract, the existing problems and the significance of the research need to be added.

2.      The key point of this study was the advantages of SIF_Red, but the introduction mainly introduced SIF_Far-red. Therefore, a review of the research progresses of SIF_Red should be added in the introduction.

3.      Line 154, 157 and 190. When we describe a device, we should use the following format. Manufacture, city, state acronym, country.

4.      Figure 2 was not clear and needed to be redrawn.

5.      Line 275-278, “In terms of the red and far- red band, SIF and GPP relationship apparently depends more on PAR than on Ta and VPD, which indicates that the illumination conditions are a major environmental factor influencing the relationship of SIF–GPP.” How did you get this conclusion?

6.      Line 332, “while SIF emission in the red band is mainly performed by PS I”, and Line 333, “theoretically, the SIF in the red contributed mostly by PS II”. Is SIF in the red contributed by PS I or PS II?

7.      Line 384-385, “However, during a period of vigorous vegetation growth, the SIF in the red band is inevitably affected by the reabsorption effect, resulting in the saturation of SIF_Red values.”. This phenomenon can not be seen from this study.

8.      Line 406-410, ” In alpine meadow ecosystems…. This indicates that SIF_Red is more sensitive and responsive to changes in the environment than SIF_Far-red, and these responses are more consistent with those of GPP.” How did you get this conclusion?

9.      Section 4.1 and 4.2 seemed to explain the same thing.

10.  As we all know, the environmental factors affected the SIF-GPP relationship. In the discussion, In the discussion, the effect of environmental factors upon the SIF-GPP relationship is less, and it should be thoroughly discussed.

11.   The limitations of this study and what could be done in future studies should also be described in Discussion.

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Reviewer 3 Report

The paper “Investigating the Performance of Red and Far-Red SIF for Monitoring GPP of Alpine Meadow Ecosystems” access the relationship between Red or Far-Red SIF with GPP. The data were obtained in western China during 2019-2020 from tower observation with 30 min and daily integration. The authors also evaluate the influence of photosynthetically active radiation, air temperature and vapor pressure deficit on SIF/GPP rate.

 

Methodology

It is necessary to include an item with the description of models (linear and non linear) employed to evaluate the relationship between SIF and GPP as well also incorporate the statistics measures used to evaluate model performance.

Results

Some statistics were calculated but not were analyzed in the text. (e.g. RMSE calculated in Table 1 and R2 and RMSE from figs 5 and 6

Minor comments are highlighted in the draft.

Comments for author File: Comments.pdf

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Reviewer 4 Report

Dear Authors,

Thanks for comprehensive analysis of GPP relationship with SIF (red and far-red) in alpine meadows and varying conditions (environmental factors) during 2 years of observation.

Please find here below minor suggestions from review:

L214 full text for SZA should be provided when used for the first time in the paper;

L331-332 check formulation "while SIF emission in the red band is mainly performed by PS I. Therefore, theoretically, the SIF in the red contributed mostly by PS II ..."

 

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Reviewer 5 Report

Minor English grammar and sentence structure edits would improve the quality of the manuscript.

I found the weakest section of the manuscript was the statistical discussion of findings in the Results.  The statistics presented in the Figures needs to be conveyed and discussed in the text of the Results.

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Reviewer 6 Report

  1. The authors should improve the introduction and add more recent publications in order to compare them with this study, please clarify the aims and novelty of this study.

2. The authors should improve the conclusion and add the main results obtained in this research. 

 

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Round 2

Reviewer 2 Report

The suggestions I mentioned have all been carefully revised. I think the manuscript can be accepted.