Dear Prof. Jiang,

Thank you for submitting your manuscript to BG for consideration. The responses to comments are reasonable, and I would like to see a revised version. However, I still have some minor concernsyou’re your reference.

Minor concerns
(1) As for non-carbonate soil on the basis of CO2 measurement. Please provide the detection limit. Moreover, it has to be specified about the amount of soil, the HCl added, and the volume of headspace”. The readers will otherwise has no ideas of what the authors want to say. For example, if one injects 1 mL pure CO2 into a 2ml-bottle, the CO2 concentration can reach 50%. However, if this 1-ml CO2 is injected into a vast tank (1 million cubic meters), the concentration is virtually zero. Therefore, pls do provide the detailed information of your CO2 measurement.
(2) The authors assume that sulfate content in surface soils might account for the negative correlation between soil pH and inorganic carbon concentration. Pls add few sentences for discussion.
(3) Please add one or two sentences why HNO3 is somehow justified for pBHC determination. The widely used protocol does not necessarily the correct one.
(4) Figure 1 legend. Please specify whether the same/similar figure has been used in other papers, and mention it properly in figure legend to avoid confusion for readers.
(5) Figure 1 legend. The authors apparently would like to use these 52 sites as indicator of a 3600-km long transect. How representative it is. The author may add few sentences to explain why the regions with green shading can be represented by these 52 sites. For example, in the remote western region, there is no sampling site but with green shading.
(6) Figure 1 legend. The authors state that from east to west, there is a gradient of increasing temperature and decreasing precipitation. This statement needs to be supported with solid evidence. Please make two column with color gradients showing the change of temperature and precipitation respectively.
(7) Figure 2 legend. It is still confusing. The authors state that “Effects of acid addition (16 mmol H+ kg−1 soil) (approximately the average cumulative amount of acid deposited over 10 years) on soil pH in the carbonate containing soils (squares) and the non-carbonate containing soils (circles)”. This statement has no point. What does soil pH in y-axis mean? Soil pH in y-axis is an absolute value. The authors added 16mmol acids per kilo soil, and very likely could have resulted in CHANGE of soil pH. Only through the inset, can one see the effect of acid addition on soil pH. But what information does your main figure 2 represent, except for the inset?
Yours sincerely
Zhongjun Jia

Dear Prof. Jiang,
Thank you for submitting the revised manuscript. Most comments have been adequately addressed, and I still have some minor concerns before publication.
Minor concerns
(1) As for the detection limit of CO2 measurement. First of all, please simply provide the information about the instrument you used for CO2 measurement (such as brand name of the instrument). Secondly, please clearly state the detection limit of this instrument ( one may not understand what does “0.1 mm of released CO2” mean). Finally, please clearly state the HEADSAPCE VOLUME of the vial in which 10 gram soil was placed for acidification. Furthermore, CO2 of any origin (calcium carbonate or urea) can be used for generating standard curve. This is not the key point.
(2) L140. Rephrased as ”Soil pHBC was measured by titration using HNO3 because the nitrate anion is widely thought to interacts with soil materials to a much less extent than other known acid anions.
(3) L146. Pls provide the instrument information for pH measurement.
(4) L212. Please give the absolute concentration like ppm rather than simply saying detection limit.
(5) Figure S1. It is certainly not accepted that part of China map is overlapped with MAP and temperature inset. The entire territory of China needs to be displayed.
(6) Figure 1 legend is still confusing. First of all, there is filled square and empty square. Pls specify what does this meant. I guess the empty square means soil pH for natural control soil, while the filled square means pH values of soils after 16 mmol acid amendment. Then the dashed line represents the means of pH values of soil treated with 16 mmoL acid? If so, the figure legend can be rephrased as “Acidification of grassland soils upon acid addition (16 mmol H+ kg-1 soil added) to carbonate containing soils (squares) and the non-carbonate containing soils (circles) collected from the 3600 km-long transect. The empty symbol denotes background soil pH as control, while the filled symbol represents soil pH value after acidification. Mean changes in pH values for both carbonate-containing and non-carbonate containing soils are shown in the inset. The solid line and dashed line represent the mean pH values of controls and acid-treated soils across the transect, respectively.”

Yours sincerely
Zhongjun Jia

Dear Prof. Jiang

Thank you for submitting your revised ms to BG.

Before publication, I would like to have your attention:
(1) There are some islands in Southern Sea that are missing in the map of China. pls be careful about this point in your figure S1. In addition, I do feel the MAT and MAP can be placed within Figure S1 as inset. But please make your own decision
(2) It seems for me that your Table 2 is too fancy to be published. You may get rid of the color and use some lines within the table.

Yours Sincerely

Zhongjun Jia