This manuscript comprehensively employs multiple techniques (stable isotopes, PIB method, water age model, geological drilling, and ERT) with the aim of revealing the interaction mechanism of "rock-root-water" in the karst critical zone. The research question holds significant scientific value, and the experimental design is generally reasonable. The obtained data effectively support the main conclusion that "rock fractures are the core for regulating water supply and transpiration water age in the root zone". However, the manuscript needs further improvement in terms of logical fluency, terminological accuracy, and the depth of explanation for some core concepts.

1. The statements of the two scientific hypotheses in the abstract and introduction are slightly different. It is recommended to ensure that the statements of the two scientific hypotheses are completely consistent throughout the entire text (abstract, introduction, and discussion).
2. L47: The core indicator "transpiration water age" was directly used, but it was not defined and its ecological hydrological significance was not explained in the introduction. Before introducing the research question, define "transpiration water age" in 1-2 sentences and point out: "Understanding transpiration water age is crucial for revealing whether plants utilize current precipitation or stored 'old water' to cope with environmental changes, and it is the key to analyzing the temporal dimension of plant water use."
3. L99-101: The statement of Hypothesis (i) is slightly long and the expression "exploring water sources" is ambiguous. It is recommended to refine and strengthen it: make the hypothesis more direct and testable.
4. L232: Why is "root zone water storage" equated to "rock fissure water" to calculate the recharge rate β? This deviates from the traditional application of the PIB method in soil-dominated systems. Suggestion: Add a theoretical argument at the beginning of Section 2.4 or in the methods section.
5. Some paragraphs read like "data recitation" and fail to highlight the main contradictions. In Section 3.2 of the original text: "The δ²H of deep-rooted and shallow-rooted tree xylem water ranged from -65.9‰ to -57.6‰ and δ¹⁸O from -8.5‰ to -6.8‰ in the rainy season; in the dry season, they were -59.7‰ to -52.9‰ and -7.3‰ to -5.7‰ respectively."
6. The results section contains too much explanatory content. For example, in Section 3.3, "Overall, the hydrological connectivity of deep-rooted trees in the rainy season was lower than that of shallow-rooted trees, while the opposite was true in the dry season, which may be related to the depth of the plant roots and the water utilization strategies." It is recommended to strictly distinguish between "results" and "discussion". The results section should objectively state the discovered data and phenomena, while moving all explanations, comparisons, and mechanism analyses to the discussion section. This will make the manuscript structure clearer and the argument more powerful.
7. Lack of clear statistical information. It is recommended to specify the statistical test methods: indicate in the methods section or figure captions what statistical tests were used (e.g., one-way ANOVA with Tukey's HSD post hoc test).
8. L385: What does "hydrological disconnection" mean?
9. L454-472: The author's speculation and description of root depth in this paragraph are too rough and the logic is confusing. It is suggested to further clarify the context and present a clearer expression.
10. L522-529: "However, within the context of climate change—particularly in regions with limited water storage capacity like karst areas—this "old water" sustains transpiration during dry seasons, thereby creating a critical survival window for plants to await subsequent precipitation recharge." The discussion about "old water" and the vulnerability of the ecosystem needs to be balanced.
11. At the end of the discussion, there is no strong review and confirmation of whether the two scientific hypotheses have been verified. It is suggested to add a summary paragraph: In Section 4.3, it is clearly stated: "The results of this study fully support the two scientific hypotheses initially proposed. ... " 。 This jointly proves that the interaction between rock fissures and root depth is a regulatory factor for the water utilization of karst plants...
12. L557-560: The manuscript mentions that the study area is dominated by rocks (with a soil thickness of approximately 40 cm). I do not recommend that the author stratify such a shallow soil. Instead, the soil sampling description should be adjusted to an integrated single-layer approach, represented as soil or overlying soil. This is because when quantifying plant water sources through the Bayesian mixing model, excessive division of water sources would weaken the importance of rock fissure water emphasized in the manuscript.
13. Make sure that the text in the charts (especially the axis labels and legends) is of appropriate size and legible in the PDF version. For instance, can the axes and images in Figure 9 be presented more clearly through other inversion software?