the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
30 Aug 2021
30 Aug 2021
Differential response of plant water consumption to rainwater uptake for dominant tree species in the semiarid Loess Plateau
- 1State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F University, Yangling, 712100, China
- 2State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences, Ministry of Water Resources, Yangling, 712100, China
- 1State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F University, Yangling, 712100, China
- 2State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences, Ministry of Water Resources, Yangling, 712100, China
Abstract. Whether uptake of rainwater can increase plant water consumption in response to rainfall pulses requires investigation to evaluate the plant adaptability, especially in water limited regions where rainwater is the only replenishable soil water source. In this study, the water sources from rainwater and three soil layers, predawn (Ψpd), midday (Ψm) and gradient (Ψpd−Ψm) of leaf water potential, and water consumption in response to rainfall pulses were analyzed for two dominant tree species, Hippophae rhamnoides and Populus davidiana, in pure and mixed plantations during the growing period (June–September). In pure plantations, the relative response of daily normalized sap flow (SFR) was significantly affected by rainwater uptake proportion (RUP) and Ψpd−Ψm for H. rhamnoides, and was only significantly influenced by Ψpd−Ψm for P. davidiana (P < 0.05). Meanwhile, the large Ψpd−Ψm was consistent with high SFR for H. rhamnoides, and the small Ψpd−Ψm was consistent with the low SFR for P. davidiana, in response to rainfall pulses. Therefore, H. rhamnoides and P. davidiana exhibited sensitive and insensitive responses to rainfall pulses, respectively. Furthermore, mixed afforestation significantly enhanced RUP, SFR, and reduced the water source proportion from the deep soil layer (100–200 cm) for both species (P < 0.05). The SFR was significantly influenced by RUP and Ψpd−Ψm for both species in the mixed plantation. Lower Ψm and higher Ψpd were adopted by H. rhamnoides and P. davidiana in mixed plantation, respectively, to enlarge Ψpd−Ψm, enhance rainwater uptake, and decrease water source competition from the deep soil layer. These results indicate that mixed afforestation enhanced the influence of rainwater uptake to water consumption after rainfall pulse, regardless of sensitivity to rainfall pulses. This study provides insights into suitable plantation species selection and management considering the link between rainwater uptake and consumption in water limited regions.
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Yakun Tang et al.
Status: final response (author comments only)
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CC1: 'Comment on hess-2021-351', Jiaping Pang, 07 Sep 2021
Tis manuscript analyzed water consumption in response to rainfall pulses of two dominant tree species in water limited region, the result showed that mixed afforestation enhanced the influence of rainwater uptake to water consumption after rainfall pulse, regardless of sensitivity to rainfall pulses.
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RC1: 'Comment on hess-2021-351', Anonymous Referee #1, 19 Sep 2021
The manuscript entitled "Differential response of plant water consumption to rainwater uptake for dominant tree species in the semiarid Loess Plateau" provide a reasonable contribution to clarify the response of plant water consumption to rainwater uptake and water potential in water-limited region. The manuscript suggested that there were different response of plant water consumption to rainwater uptake and leaf water potential gradient of two species in pure and mixed forest types. The topic of this manuscript is interesting and the results are clear. However, it needs some clarifications to robust the findings, there are also some instances where the term seems inappropriately use and some results should be added to support the relative sentences.
Main Comments:
1) Do you have any information about runoff generation of the studied plantation sites? Any runoff after rainfall pulse may influence the result of your manuscript since the contribution of precipitation to plant water uptake is central to your study, although precipitation amount was not the direct independent factor during the data analysis. Considering the potential runoff may strengthen and validity your result.
2) Potential/Reference Evapotranspiration is a key parameter indicator that reflect atmospheric evaporative demand, and also support some part of you conclusion. Please clarify why the Reference evapotranspiration (ET0) was used in the study - there are some other indicators also reflect the evaporative demand.
3) Throughout the manuscript, there are some instances where the term seems inappropriately use (e.g. only). I would suggest going through the entire paper and refining the language to more accurately reflect the result.
4) This manuscript should be looked over by a language editing service and/or a native English speaker - there are some awkward phrasings.
Minor Comments:
1) Lines 22 “only” is too arbitrary
2) Lines 30-32 “Regardless of sensitivity to rainfall pulses” ? this short sentence should be rewritten.
3) Lines 54-57 The “water uptake” should also be clearly described.
4) Lines 69-71 the author should be clarified this sentence for pure or coexisting species? Because the similar meaning and sentence can be observed at Lines 57-60.
5) Lines 131-132 Please clarify why the Reference evapotranspiration (ET0) was used in the study, as a large number of indicators can reflect atmospheric evaporative demand.
6) Lines 213-214 This sentence is nonsense and should be deleted.
7) Line 306 There are 7 Figures in the paper and the Tables 1-4 are the statistical analysis. These Tables are unnecessary list in the paper and its better remove to Supplementary file to concise the manuscript.
8) Lines 313, 338, 342 Averaged (± SD) or Averaged (Mean ± SD) ? Check it
9) Line 362 CV or CVs ? Clarify.
10) Line 366 Increased or enlarged Ψpd−Ψm ? the expression should be consistent through the text.
11) Line 415 Is “synchronization” correct in this sentence ? It’s not correct, you should check it.
12) Lines 478-480 Table S3 does not indicated the relationship between rainfall amount and water source proportion from deep soil layer. You should added the relative result to support the sentence.
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CC2: 'Comment on hess-2021-351', Ying Zhao, 09 Oct 2021
The authors provide a compelling case demonstrating the differential response of plant water consumption to rainwater uptake for dominant tree species (Hippophae rhamnoides and Populus davidiana) in the semiarid Loess Plateau. I appreciated that the study used multiple indicators such as plant physiology (leaf water potential) and root morphology, sap flow and rainwater uptake proportion to comprehensively address this topic. This study suggested that H. rhamnoides and P. davidiana exhibited sensitive and insensitive response to rainfall pulses, respectively, which provides insights into suitable plantation species selection. While, I have three small questions that I don’t understand, could you please answer them if it’s convenient?
(1) line 189-190 I haven't figured out the relationship between Eqs 4 and 5. What does PAP mean?
(2) line 190 This study calculated RUP using D and 18O, respectively. Are the results of these two stable isotopes consistent?
(3) The study calculated the use of precipitation by plants after five rainfall events. I guess the use of precipitation by plants depends not only on the magnitude of the rainfall, but also on the antecedent soil water condition. How do you consider the potential impact that differences in antecedent soil water conditions may have on the results? -
RC2: 'Comment on hess-2021-351', Anonymous Referee #2, 13 Dec 2021
The paper entitled “Different responses of plant water consumption to rainwater uptake for dominant tree species in the semiarid Loess Plateau” investigates the response of Hippophae rhamnoides and Populus davidiana, in both pure and mixed plantations, to rain pulses. The topic is well within the scope of the journal. However, I have several concerns that need to be addressed before the manuscript can be accepted for publication (see my comments below). In general, I think the manuscript would benefit from some language editing as there are numerous language and grammar issues. Hence, my recommendation in that the authors conduct a major revision and resubmit the manuscript.
Main comments:
- Personally, I find the terms ‘rainwater uptake’ and ‘water consumption’ (both central to this manuscript) rather ambiguous. I would recommend using ‘transpiration’ instead of ‘water consumption. On the other hand, the term rainwater uptake can be confusing, as it seems to suggest that these trees take up water directly from rainfall. Some trees can indeed take up rainwater through their leaves, but this is not the case for the species included in this study. In my opinion, it would be better to refer instead to the ‘uptake of recently recharged soil water’ or similar (uptake of soil water that has been recharged from a recent rainfall event).
- It would be very helpful if the authors could provide some additional information on the two studied tree species. The authors write (L.82-84): ‘Hippophae rhamnoides and Populus davidiana are typical dominant tree species, with high survival rate and drought tolerance, and occupy nearly 30% of the plantation area in this region (Liu et al., 2017; Tang et al., 2019)’. Could you give some species-specific information on e.g. their phenology or root system? How do the species differ, and are there any reasons to believe that they might respond differently to rain pulses in terms of transpiration and water source partitioning? Do you have any hypotheses? In addition, I would suggest the authors check the scientific names of the species. According to the World Flora Online, Hippophae rhamnoidesis not an accepted name but a synonym of Elaeagnus rhamnoides (L.) A.Nelson.
- The authors have done extensive field and lab work, which is extremely valuable. However, I find the material and method section a bit hard to follow given not only the number of measurements but also the use of multiple approaches to address the same question (for example RUP – rainwater uptake proportion - vs MixSIR, or MIXSir with 7 soil depth intervals vs. MIXSir with 3 soil layers). This affects as well the interpretation of the results. Therefore, I would suggest the authors clarify the different steps in the methodology better, whether the chosen approaches are complementary, and how.
- Where are the plantations where you conducted the measurements located? It would be good if you could provide a map to illustrate this. Also, what is the slope? Are there any terraces or other soil and water conservation measures? Are soil properties and land-use history similar across all nine plots included in the study? Do you have any information on the physical characteristics of the soils?
- The authors selected 5 distinct rainfall events of varying magnitude (ranging from 3.4 mm to 35.2 mm) to study the response of the tree species (in both pure and mixed stands) and how this varies according to the magnitude of the event. As stated in L. 168-169, ‘These rainfall events were selected with an interpulse period longer than 7 days to eliminate the potential influence of the previous rainfall event.’. However, I have serious doubts about this approach and the validity of the results from this specific analysis (e.g., L. 478-482: ‘The increasing rainfall amount significantly decreased water source proportion from deep soil layer (P<0.05) for H. 480 rhamnoides and P. davidiana in the mixed plantation (Table S3), with the corresponding values decreasing from 43.13 ± 13.74% and 47.07 ± 5.39% (both after 3.4 mm), respectively, to 21.54 ± 8.9% (after 35.2 mm) and 28.66 ± 12.26% (after 24 mm) (Fig 4)’). Unfortunately, the selected rainfall events not only differ in magnitude, but also in terms of antecedent conditions. For example, the 3.5 mm event (DOY 194) is the lowest rainfall event but also that following the most prolonged dry period (>30 days dry period from DOY 157 to 194). It is evident that when topsoil moisture content is low following a dry period, plants will tap into deeper, more reliable water sources. This is not so much related to a single rainfall event and its magnitude, but mostly to the antecedent conditions (prolonged dry period).
- I would strongly recommend that the authors include a plot of the local meteoric water line (LMWL). This should be relatively straightforward as they have analyzed the 19 collected rainfall samples for both δ18O and δH. On top of the LMWL I would then plot the signatures of the soil water at different depths. This would provide additional insights into the data and ease data interpretation (and can also be used to double-check that rainfall samples have not undergone evaporation). For instance, the rainfall signatures in Figure S5 could be visualized and interpreted much better in a dual-isotope plot.
Minor comments:
- In the study site description (section 2.1), it would be good if the authors could include a graph with the mean monthly rainfall throughout the year to get an overview of the rainfall seasonality in the study area. Right now, only the mean +- SD annual rainfall is provided, but there is no information on rainfall seasonality.
- When Describing the soil texture (L.105) please indicate it is the texture you refer to and add the correct source (USDA). Besides the soil texture, kindly provide the soil class.
- L.131: Explain what VPD stands for after equation 1 and give its units (as you have done for the other variable sin equation 1).
- L.145: What does the abbreviation TDPs mean?
- L.189, Formula 4: what is PAP?
- L.208-209: Kindly provide a reference that supports this assumption (‘no fractionation was considered during water source uptake by plant roots’)
- Figure 1: it would be helpful if the X axes could start earlier (about 20 days if possible) to be able to see if the first two rainfall events that are shown in panel a) are following a dry period or not.
- Figure 2: It would be good to show the precipitation bars in this plot too.
- L.321: in figure S5, kindly add the date of rainfall events. Moreover, the dD signature of rainwater for the 3.4 and 7.9 mm events is very enriched. Could it be that there has been some evaporation of the sample going on? In any case, as I mentioned earlier, it would be really good if the authors could provide a plot of the LMWL.
- L.395-396: have you measured the depth of the groundwater level?
- Figure 7: this is a very good overview, really clear!
Yakun Tang et al.
Yakun Tang et al.
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