Variation in Water Uptake Dynamics of Dominant Wood Plants of Pinus taiwanensis Hayata Communities Based on Stable Isotopes

Round 1

Reviewer 1 Report

This is an interesting study and the authors have collected a good dataset.

 

Abstract

No comments

 

Introduction

No comments

 

Materials and Methods

No comments.

 

Results

No comments.

 

Discussion

I suggest citing the two recent studies below. These studies found there were monthly dynamic changes of juniper water use driven by precipitation and soil moisture. I think these recent citations will improve the paper.

 

-        Abdallah, M.A.B., Durfee, N., Mata-González, R., Ochoa, C.G., & Noller, J.S. (2020). Water use and soil moisture relationships on western juniper trees at different growth stages. Water, 12, 1596; doi:10.3390/w12061596.

 

-        Mata-González, R., Abdallah, M.A.B, & Ochoa, C.G. (2021). Water use by mature and sapling western juniper (Juniperus occidentalis) trees. Rangeland Ecology & Management, 74, 110-113.

 

Conclusions

It will be great if the authors consider trying to add some language that might broaden the implications of their work to a wider audience.

 

 

 

 

 

 

 

 

 

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript examined the water uptake of woody plants of Pinus taiwanensis communities in a subtropical mountain using stable hydrogen and oxygen isotopes. I think that this study presents interesting datasets on the water use of the three plant species. However, there seem many issues to be addressed in the current version of the manuscript. 

 

First, the explanations about the methods, the data analysis and interpretation would need to be performed more carefully. For example, please describe in Materials and Methods how much water in soil or the xylem was collected from the branches and how the isotopic measurement was conducted (H-device or an equilibrium device was used?). 

 

Second, it is unclear why the niche segregation in water use among the three plant species was argued in Discussion (L389), even though there was no significant difference in the d2H value among them (L300). Please explain which findings support the statement about niche partitioning. Besides, it seems that the definition of soil depth is arbitrarily modified in the text (e.g., 40-80cm  deep, 0-40cm upper, 0-20 cm surface soil , 20-40cm middle in Abstract). Please define the depth in Materials and Methods and use them consistently throughout the text. 

 

Finally, I am not convinced by the argument that the plants use surface water in August(L341). Because there are litter differences in d2H values of soil water (ca. 10 permil) along the depth, possibly due to the heavy rain, it should be difficult to assign the water source depth only by the d2H values of soil water. In addition, the standard error or deviation of the 2H values of stem water should be presented in Fig. 6. I suppose the variations in the d2H values of stem water for each plant species were taken into account for the IsoSource estimation (Fig.7). However, it does not seem that differences in the depth of soil water source among the plant species or months were statistically tested. 

 

Minor comment:

L 13: Plant community should be determined not only by competition but also by many other factors (resource limitation etc.)

L L89: This study does not seem to evaluate the climate change effects on forest health.

L121: Spell out the genus names. 

L130: I don’t think that voucher ID needs to be presented in Table. 

L148: Please explain what is the max and min water holding capacity.

L241: This figure is difficult to read. Please modify.

L256: The SWC data show no clear seasonal changes in soil moisture. This seems not to support the argument in Discussion (L349). 

L386: Statistical support should be needed to conclude the existence of the flexible shift in water sources during the season.

 

Author Response

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Reviewer 3 Report

Review_Forests_1816689:

Authors of this paper

The authors of the article investigated the seasonal water uptake pattern of typical species of a subtropical woody plant community during the meteorologically differing months of a year. They found that the water uptake of the three characteristic woody plant species from the 5 depth layers of the soil varies with the soil moisture content and the distribution of precipitation. They also found that the three co-existing species took up water from the same soil layer, which will later result in competition in the case of water shortages caused by climate change.

The article is logically structured and edited. The literature review is thorough and the objectives of the work are clearly stated. The characterization of the test site is sufficiently detailed. The language of the article is reasonably good. The most valuable thing is that the stable hydrogen and oxygen isotope testing methodology was used to determine the water uptake pattern of the selected woody plants.

Major comment:

To what extent can the study year with 777 mm more rainfall be considered average weather for the water absorption pattern of the three woody plants in years with other weather conditions?

Minor comments:

Line 119-120: How was it determined that the permanent sampling sites of 10 x 10 m represent a suitable minimum area?

Line 136: An explanation of the DBH abbreviation is missing.

Line 144-145: The determination methods’ descriptions of soil particle-size and the maximum and minimum water holding capacity values ​​reported in Table 2 are missing.

Line 168-171: The formula for calculating the soil water content determined by the oven-drying method is well known, so it is unnecessary to specify it.

Line 220-230: It is not consistent to give the precipitation average of 65 years once, and then present the precipitation average of 56 years in Figure 2. Anyway, 30-year averages are used in meteorology.

Line 248-261: Changes in the moisture content of the soil layers and plant water uptake could be interpreted much better using the soil's available moisture storage. So, it's just a simple description now.

Line 281-282: It is not clear what the actual meaning of the soil moisture evaporation line in Figure 5?

 

 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

I appreciate the authors’ effort to revise the ms according to the reviewers' comments. I think that this ms has been much improved but still has issues to be addressed. 

 

Fig. 6 shows that the d2H values of soil water 10-20cm and 60-80cm in November were similar. In addition, the d2H values of the tree waters were similar among the three species (the difference in d2H value is close to the SE of d2H values of soil water). These results indicate that it should be difficult to distinguish the contribution of the two water sources to the plants and that the three plant species might be similarly dependent on the surface soil water (0-20cm). However,  Figure 7 shows that the contribution of deep soil water to R. dilatatum is much greater than that of surface water, which is the main conclusion of this manuscript. I think that this discrepancy stems from the summing up the contributions of water source depth (40-60 and 60-80cm) as deep soil in Fig. 7. Please calculate the water contribution of each soil depth to plants and then make a discussion about the relative importance of soil depth to water in plants. I think this re-calculation would modify the conclusion of the present study. 

 

Regarding the analytical method of d2H values, please describe the procedure in more detail (e.g., temperature of the furnace and how much water was packed into silver cups, and how the measured values were calibrated against international standards).

Author Response

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Author Response File: Author Response.docx