Thank you very much for evaluating our manuscript positively. Please find our response to your concerns in the attached file. We hope our reply and suggested revisions will satisfy your concerns.

Thank you very much for your kind evaluations of our manuscript.

First, I want to clarify our measurement of soil water content during the incubation period. Yes, we have periodically measured soil water content during the incubation, even in the drying stage under the DWC treatment for Day 1 to Day 8 and Day 18 to Day 25. For each drying stage, we conducted measurements of soil water content once to twice. The measurements were performed by weighing those soils. Based on these data, we confirmed that the mean soil water content during DWC incubation was equal to that during constant moisture incubation. Figure 3 (bottom panels) shows these data on soil water content. We have written some explanations for measuring soil water content at L129-L131, but this was somewhat unclear. In the revision, we will provide more explicit explanations for measuring soil water content during the incubation, as described above.

Additionally, under the constant water treatment, we surrounded the small vial with 20 mL of water within the incubation jar to prevent the soil from drying. Sorry for lacking this explanation. We will also add this explanation to the Materials and Methods.

We expect our explanations on measuring soil water content during the incubation will solve some of your primary concerns in our study. Then, we will respond to your other comments later.

Thank you for your suggestions. We additionally measured soil textures as particle size distributions, i.e., relative compositions of clay, silt, and sand-sized particles. Then, we found that the amounts of clay and sand-sized particles showed significant correlations with IF_CO2 after rewetting in 1st cycle (p < 0.05, r = -0.66 for clay and 0.71 for sand particles). However, those correlations between the particle contents and IF_CO2 were insignificant for IF_CO2 for a total of three cycles. Nevertheless, pyrophosphate-extractable Al (Alp) content showed significant correlations with IF_CO2 for all incubation stages (r = 0.84 to 0.74 with p < 0.05), as described in the manuscript (Figure 5 and L165-L171). This result supports our argument that pyrophosphate-extractable Al (Alp) content is likely the primarily important factor for the magnitude of CO₂ release increase by DWC. We will add these results and descriptions to the revised manuscript.

Regarding water retention, we consider the water-holding capacity (WHC) of soils. As presented in Table 2, we have measured WHC in addition to soil water content as soil properties used for the experiment. Whereas there was a significantly positive correlation between WHC and soil water content (r = 0.87, p<0.01; thus, soil water content at the soil sampling also reflected the ability of soil to hold the water and the usual water contents in the field), none of the soil water content at the soil sampling and the WHC showed a significant relation with IF_CO2 not only as a linear correlation but also as a nonlinear relation, which was examined visually (Table 4; please also see the figure in our reply to RC1). These facts from the obtained data support us in stating that the variations in IF_CO2 were significantly associated with soil metal-humus complexes and soil microbiology rather than different WHC among soils (Tables 4 and 5, Fig 5). We will refine our sentences for the results of exploring predictors of IF_CO2 in the manuscript (L165-L171), adding the positive correlation between the soil water content and WHC to the material and method section of the soil sampling (L80 to L88).

For the soil organic matter quality, we can consider the C/N ratio of K₂SO₄ extractable organic matter in addition to the C/N ratio of total organic matter. Their correlations with IF_CO2 were statistically insignificant, as presented in Tables 4 and 5. We will add this description to L165-L176. Whereas we currently have no data on POM, we are now conducting the measurement of POM, and the results will be presented in the revised manuscript. Moreover, given the similar IF_CO2 values between the forest and pasture soils of Kuju (Figure 4, less than 12% differences between them), possibly substantial differences in POM content between the forest and pasture grassland might be negligible in the currently investigated soils. We will add this discussion to the revised manuscript with the result of the POM contents of investigated soils.

We sincerely hope those explanations can also satisfy your concerns about insufficient soil information and evaluation for soil texture, soil moisture retention characteristics, and soil organic matter quality.

Much more information about mechanisms for CO₂ release increases under DWC:

Because our first primary purpose is to clarify the overall trend of DWC effect on soil CO₂ release under the comparison between DWC and constant moisture conditions, which have the same mean water content during the incubation, we less mentioned the proposed mechanism for CO₂ release increases under DWC in the introduction section. Roughly three mechanisms are proposed: (i) increase in available carbon source via the releases of cellular metabolites from microbial cells destroyed by rewetting after the strong drought, (ii) increase in available carbon source by the releases of carbon from macroaggregates destroyed by repeated DWC, and (iii) changes in the microbial communities in response to transient moisture conditions. Whereas the DWC-induced destructions of macroaggregates might be related to changes in association between mineral/metal and organic matters, we cannot find any literature which specifically mentioned the organo-Al complexes, which is the primary predictor for IF_CO2 in the present our study. We will add the brief description of currently proposed mechanisms for CO₂ release increase under DWC to the introduction section, especially after the paragraph to describe the current knowledge about the trend of DWC effects on soil CO₂ release in L39-L56.

Motivation for using 10 Japanese soils:

This was that these soils were variously affected by volcanic ash during their pedogenesis, and therefore include several Andisols, which are known to have a high SOM storage capacity, likely due to the protection of SOM from microbial decomposition by enrichment of reactive minerals and metals in these soils. Our previous study showed the significant increase in CO₂ release by DWC for two Japanese forest soils. Especially, a volcanic ash soil showed a substantially large increase. This was why we used those 10 Japanese soils differently affected by volcanic ash. Whereas we have presented those information in L52-L67, this might be not clear. We will thoroughly refine those sentences in the revised manuscript, to present clear description of our motivation using 10 Japanese soils.

Monitoring soil moisture content:

Please see our reply entitled as 'Reply on RC2 (particularly about the measurement of soil water content during the incubation)'.

CO₂ measurement during the incubation:

Sorry for confusing you. Our CO₂ measurement for constant moisture condition were conducted periodically during the 84-day incubation. Namely, in the incubations with the constant moisture condition, the CO₂ release rates were measured for Day 1 to Day 12, Day 13 to Day 28, Day 29 to Day 40, Day 41 to Day 56, Day 57 to Day 68, and Day 69 to Day 84, as shown in Figure 3. We will revise sentences in L128-L129 to describe the measurement of CO₂ release for the constant moisture conditions. Because we observed significant absorption of CO₂ by silica gels in preliminary experiments, we did not conduct the measurement of CO₂ release during the drying stages. Other previous studies also assumed the linear changes in CO₂ release rate during the drying. Furthermore, significant relationships between IF_CO2 and organo-Al complex was also observed in IF_CO2 after the rewetting in addition to the IFCO2 for total 1^st cycle and three cycles. Therefore, shortcomings from unmeasured CO₂ release during the drying periods should be minor as the uncertainty in our main findings in the present study. We will add those description for Discussion section.

Details:

L44 “…in comparison with the medium level of constant moisture content” is not clear, what is meant by medium level here?:

This means that the comparison was made with the medium level of constant moisture content which was equivalent to the mean water content during DWC incubation. We carefully revise this sentence for clear understanding.

L46 “Another 29 data were calculated…” sounds awkward and furthermore with this sentence you are not bringing any message: what was now the outcome of this comparison?:

This sentence emphasizes the lacking of actually measured data of CO2 release rate under DWCs which have the same mean water content during the incubation with that for constant moisture conditions. We carefully revise this sentence for clear understanding.

It is not clear really what is intended by “soil carbon content-specific CO2 release rate under continuous constant moisture conditions (qCO2_soc)” – requires further clarification:

The qCO2_soc should be an index for availability of carbon substrate to microbes under normal moisture conditions. High qCO2_soc suggests that substantial parts of carbon in soils are available for microbes, and lower values suggests low availability of carbon substrate. We will add this explanation.

Fig 2 would be useful to indicate the point in time what interval this ‘after rewetting in first cycle’ now precisely ended:

Thanks. We will add an arrow suggesting the end point of the rewetting stage to Fig. 2.

L94 to measure field capacity, likely also soil was allowed to leach out after its saturation? But that is not well described here.:

WHC was measured by the Hilgard method using capillary action of air-dried soils to soak the water (e.g., Ahn et al., 2008 Water Management). After the weighing saturated soils, we oven-dried soils and weighed those soils again, to obtain the amount of water soaked in soils. We will add description about measuring the WHC by the Hilgard method.

L194 “Especially, the importance of Alp for variations in IFCO2… “ this link between Alp content comes in too early and is best omitted from this start of the discussion section.:

Thanks. We will omit this from this start of the discussion section, then move to the end of third paragraph (L216-L223) in the Discussion section.

L196 Better not directly make a leap towards podzols, safer to just restrict the interpretation to volcanic soils.:

Thanks. We will remove the sentence related to podzols and restrict the interpretation to volcanic soils.

L234 the link to CH4 and N2O emission is best not made.:

Thanks. We will remove the sentence for the link to CH₄ and N₂O emission .

L238 A strange starting sentence ‘insight in the precise quantification’ needs to be revised:

Thanks. Our meaning is that “The present study provides significant insights into precisely quantifying the effects of DWCs on soil CO₂ release”. We will revise the sentence.