Nitrogen and Phosphorus Fertilization Reshapes the Abundance and Structure of Ammonia Oxidizers on a Leymus chinensis Steppe in Northern China

Round 1

Reviewer 1 Report

This manuscript describes some superficial and shallow results and discussion. Moreover, the hypothesis isn’t clear, then there was no hypothesis-targeted result analysis and manuscript writing. The manuscript level and rigor are not as good as the average level of undergraduate thesis. It can be said that the whole manuscript does not have any statistical analysis, the authors only used excel to do the analysis. Unclear soil sampling time, the experiment was established in 2013 (almost ten years ago), however no any information about the sampling date. Sorry for no detail comments on your manuscript. I suggest that maybe you should submit your manuscript to local journals.

Author Response

Thanks for your comments which help us improve the manuscript though some opinions we don't agree with. The manuscript has been revised to further clarify scientific hypothesis, we addressed two questions: (1) do N and P fertilization reshape the AOA and AOB abundance and structure of Leymus chinensis steppe? (2) How does fertilization reshape the ammonia-oxidizer abundance and structure of L. chinensis steppe? and strengthen the result analysis.

For the question about soil sampling time, the content of “section 2.3. Soil sampling, …… the assembled PVC pipe was installed and maintained in the field for 30 days of cultivation, from July 10 to August 9“, which could determine the soil sampling time was August 9. In order to clarify soil sampling time, the message of “Soil samples were collected on August 9” has been added in the manuscript.

For the question about statistic, we used the ANOVA model of SPSS v19 to examine the effects of N and P fertilization on the relative abundance of AOA and AOB based on amoA gene copies, and correlation bivariate models were applied to obtain Pearson relationship coefficients among AOA, AOB and soil characteristics, Excel software was used for graphing only. There is large soil heterogeneity in the L. chinensis steppe, our manuscript removed the complex analysis process on AOA /AOB community, which we did not guarantee its reliability, only the core content was retained, and the content have already answered the scientific hypothesis.

All in all, we thank for your comments and the manuscript has been improved substantially and hope the revised edition is qualified enough to the journal.

Reviewer 2 Report

The manuscript entitled “Nitrogen and phosphorus fertilization reshape the abundance 2 and structure of ammonia oxidizers on a Leymus chinensis 3 steppe in northern China” presents very important study.

The impact of N and P fertilization and soil properties on the number and community structure of ammonia oxidizing bacteria (AOB) and archaea ammonia oxidizing (AOA) in the Leymus chinensis steppe was analyzed

Manuscript is very extensive and written comprehensivel.

In my opinion, small corrections should be made

 

1.     The abstract needs to be corrected. The abstract should be 200 words, and you have 248.

2.     In the materials and methods section:

Please provide the area of plots where experiments were carried out in six variants, each in four replications.

It is an international journal. Please give a proper name of the soil according to FAO- WRB 2015 or soil taxonomy 2014.

 

3.     In the results and analysis section

Graph 1 includes figures A, B, C. The inscription is not explained in the description of the drawing.

There are no relevant references in the text under 3.1. Figure 1 is generally given. However, reference should be made to the results shown in Figure 1.A, 1.B or 1.C.

Author Response

Thanks for your positive comments on our manuscript.

The abstract was simplified and word count less than 200 words maximum now.

The contents of plots area and the soil type in the US system have been added in the manuscript.

We have revised the relevant references in the text of figure 2, and made the references consistent with the figure 2A, 2B and 2C.

Reviewer 3 Report

The study is important to characterize the contribution of ammonia-oxidizing archea AOA and ammonia-oxidizing bacteria AOB in Leymus chinensis steppe as affected by N and P fertilization. Overall, the paper is good.

Some more detailed description of methods is needed:

What extractant used for soil nitrate and ammonium and total N and total P determination?

How was measured the resin-derived anions, and what was the role to use it? Possibly to collect the leach out nitrate from the soil core, but how to calculate net N mineralization rates considering the resin trapped nitrate?

What type of correlation was used in the data analyses (e.g. Pearson’s or Spearman’s)?

Author Response

Thanks for your positive comments on our manuscript. The extractant used for soil nitrate and ammonium determination is 2 mol·L KCl solution, for TN and TP determination was concentrated H₂SO₄, which have revised in our manuscript.  

The function of resin is to collect the leach out nitrate from the soil core, The resin trapped nitrate was extracted by 1.5 mol·L H₂SO₄ solution and determined by dual-wavelength ultraviolet spectrophotometry. Both net soil nitrification and N mineralization calculation considering the resin trapped nitrate, Net soil nitrification was calculated by subtracting initial NO₃^--N from final NO₃^--N in soil and in anion exchange resin (AER), and net soil mineralization was calculated as (final NO₃^--N in soil + NO₃^--N in AER + final NH₄⁺-N in soil) - (initial NO₃^--N + initial NH₄⁺-N) , which have revised in our manuscript.

Pearson’s correlation was used in the data analyses, which have revised in our manuscript.

Reviewer 4 Report

The manuscript with the title “Nitrogen and phosphorus fertilization reshape the abundance and structure of ammonia oxidizers on a Leymus chinensis steppe in northern China”, investigates how AOA and AOB differences in their responses to N and P fertilization as well as soil characteristics, in a typical steppe from Saibei County – China.

Material and Method

I recommend authors to find a way for a visual representation of their experiment layout. Either as flow-chart or something to facilitate the reader to understand better.

Results

Figure 2. please used in figure caption and legend the same word either “oxidising” or “oxidizing”

Author Response

Thanks for your comments and suggestions on our manuscript. We added a new figure to show experiment layout and anion exchange resin sketch, which could facilitate the reader to understand our manuscript. We unified “oxidising” to “oxidizing” in figure caption and legend of both Figure 2 and Figure 5, which have revised in our manuscript.