Long-Term Nitrogen Addition Decreases Soil Carbon Mineralization in an N-Rich Primary Tropical Forest
, Jiangming Mo 1,2, Fanglong Su 1 and Zongqing Pang 1Round 1
Reviewer 1 Report
line 21, not sure if there's a mistake with the spacing between mineralization and results. line 23 I think its is "through" not though. line 117: Can you please cite some literature with some of the present N deposits on which you based your own experiment. Line 129: Can you provide citation to some of the protocols you used to analyze for pH and nitrates if possible.Author Response
Line 21, not sure if there's a mistake with the spacing between mineralization and results. Line 23 I think it is "through" not though. line 117: Can you please cite some literature with some of the present N deposits on which you based your own experiment. Line 129: Can you provide citation to some of the protocols you used to analyze for pH and nitrates if possible.
Response: Thanks for these comments. We have done as suggested.
(1) The spacing was deleted (Line 21 in the revised manuscript).
(2) "through" is correct (Line 35).
(3) We added the literature with some of the present N deposits (Lines 151-155).
(4) We have added the protocols as suggested (Lines 184-204)
Reviewer 2 Report
Dear authors,
- The most important findings of the research is lacking in the abstract.
- All the equipment used should be appropriately explained in the materials and methods section.
- The content of the paper mainly focuses on the long-term N deposition effect of soil C mineralization rate. However, little is discussed on how the different N rates added over the long-term affect rate of C mineralization, CO2 fluxes, commutative CO2 fluxes and other parameters.
- For details please, follow the tracked comments in the manuscript.
Comments for author File: 
Comments.pdf
Author Response
Comments and Suggestions for Authors
The most important findings of the research is lacking in the abstract.
Response: Thanks. We have added some key findings. Please see lines 25-35 in the revised manuscript.
All the equipment used should be appropriately explained in the materials and methods section.
Response: Thanks. We have done as suggested. Please see lines 184-207.
The content of the paper mainly focuses on the long-term N deposition effect of soil C mineralization rate. However, little is discussed on how the different N rates added over the long-term affect rate of C mineralization, CO2 fluxes, commutative CO2 fluxes and other parameters.
Response: Thanks. We have added the information on the different N rates in the Discussion and Conclusion. (1) L231-234: “…long-term N additions significantly decreased soil C mineralization rates and cumulative CO2 emissions over the incubation period, with the lowest values in the High-N treatments (Fig 1a-b)”. (2) Lines 581-588: “…and there were significant negative relationships between N treatment rates and soil pH,” and “There were significantly positive relationships between microbial biomass and soil pH (Table 2).” (3) Lines 666-671: “It is noteworthy that the inhibiting effect increased with elevated N addition, indicating higher soil C storage may happen with higher N addition as shown in Table 1.”
For details please, follow the tracked comments in the manuscript.
Response: Thanks. We have done as suggested. Please see the revised manuscript.
Reviewer 3 Report
After reading the document, I consider it an enriching work to understand the effect of increased N deposition on carbon mineralization. However, I think that it is a work although well designed. It sounds like the extra data to previous works that tell a partial story lacks depth and generates a more short communication type than a primary research article.
Some particular comments are:
L15 Please change cycling by dynamic: shaping soil carbon dynamic and storage.
L55-56 Please contrast the heterotrophic soil respiration with total soil respiration and net primary productivity to better understand the magnitude of the first in the C cycle in the tropical forest.
L56-57 Please explain the mechanisms of excess of N over C mineralization to link with the hypothesis.
Table 1. The letter of statistical differences are loss in MBC/MBN and MMQ
Author Response
Comments and Suggestions for Authors
After reading the document, I consider it an enriching work to understand the effect of increased N deposition on carbon mineralization. However, I think that it is a work although well designed. It sounds like the extra data to previous works that tell a partial story lacks depth and generates a more short communication type than a primary research article.
Response: Thanks for this comment. In this study we aimed to explore how and to what extend continuing N deposition affects soil C mineralization process at a longer time scale (e.g., > 10 years), which is an open question because the previous studies mainly focused on short-term N addition (e.g. <5 years) or one-time N addition. Understanding on N accumulation effect is urgent for predicting soil C stability and sequestration with the globalization of N deposition. We select the top soils because they are more sensitive to the environmental changes than the deeper soils based on our long-term monitoring. Although short communication type seems good, the story of our manuscript depends on long-term field monitoring and measurement, so we prefer to publish it as a primary research article.
Some particular comments are:
L15 Please change cycling by dynamic: shaping soil carbon dynamic and storage.
Response: Thanks. Done as suggested.
L55-56 Please contrast the heterotrophic soil respiration with total soil respiration and net primary productivity to better understand the magnitude of the first in the C cycle in the tropical forest.
Response: Thanks. We have added as follows: “Studies in subtropical successional forests showed that the contribution of heterotrophic soil respiration to total soil respiration reached 64% (Huang et al., 2016), indicating that microbial-driven soil heterotrophic respiration is a critical CO2 flux to the atmosphere in tropical ecosystems...” (Lines 80-84).
L56-57 Please explain the mechanisms of excess of N over C mineralization to link with the hypothesis.
Response: Thanks. We have added the new information. (1) Lines84-87: Many studies showed that high N inputs decreased soil respiration, where lower soil pH suggested to be a key driver because of negative priming effects. (2) L110-115: We hypothesize that long-term N additions decrease soil C mineralization in this N-rich forest, considering N-addition-induced soil acidification and alteration in microbial community composition in the studied site (Lu et al., 2014; Wang et al., 2018; Tian et al., 2019) and global negative effects of nitrogen deposition on soil microbes (Zhang et al., 2018).
Table 1. The letter of statistical differences are loss in MBC/MBN and MMQ
Response: Thanks. There were no statistical differences between the treatments. We have added the letters in Table 1.
In addition, we have carefully check out manuscript with the help of our English-speaking colleague.
Round 2
Reviewer 2 Report
Dear authors,
The paper has been sufficiently improved. Yet, the abbreviations (MBC, MBN, DOC... etc) need to be spelled out as the table by itself should be explanatory under the table 2.
With best
Comments for author File: Comments.pdf
Author Response
The paper has been sufficiently improved. Yet, the abbreviations (MBC, MBN, DOC... etc) need to be spelled out as the table by itself should be explanatory under the table 2.
Respnse: Thanks. We have changed as suggested. Please see the revised Table 2, and the notes: "(2) MBC, microbial biomass carbon; MBN, microbial biomass nitrogen; DOC, dissolved organic carbon; C-min, C mineralization rate; MNQ, microbial metabolic quotient; pH, soil pH value."
