the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Dec 2022
An Experimental Investigation of Precipitation Utilization of plants in Arid Regions
Abstract. What is the water source for ecological restoration plants in arid region is still up to debate. To address this issue, we conducted an in-situ experiment in the Ulan Buh Desert of China. We selected Tamarisk, a common drought-salt-tolerance species in the desert for ecological restoration as our research subject, used a new designed lysimeter to monitor precipitation infiltration, a sap flow system to track reverse sap flow that occurred in shoot, branch, and stem during the precipitation event, and observed the precipitation redistribution process of the Tamarisk plot. The results showed that Tamarisk indeed directly absorb precipitation water, when precipitation occurs, the main stem, lateral branch, and shoot all show the signs of reversed sap flow, and the reversed sap flow accounted for 21.5 % of the annual sap flow in the shoot and branch, and 13.6 % in the stem. Precipitation event in desert was dominated by light precipitation events, which accounted for 81 % of the annual precipitation events. It was found that light precipitation can be directly absorbed by the Tamarisk leaves, especially in nighttime or cloudy days. Even when the precipitation is absent, it was found that desert plants can still absorb unsaturated atmospheric vapor, as reversed sap flow was observed when the atmospheric relative humidity reached 75 %. This study indicated that the effect of light precipitation on desert plants was significant and should not be overlooked in terms of managing the ecological and hydrological systems in arid regions.
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Interactive discussion
Status: closed
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RC1: 'Comment on hess-2022-392', Anonymous Referee #1, 05 Jan 2023
This study investigates the potential of leaf water uptake of Tamarisc in an arid region in China by i) evaluation of reverse sapflow measured in shoots, branches and stems; and ii) by weighting leaf mass before and after drying, prior and post precipitation events, and using the difference in weight as a proxy for leaf water uptake. The results are promising; the manuscript, however, lacks some structure and consistency.
Along with the annotations and comments I made throughout the manuscript, I want to point out some key aspects where improvement is needed.
- The authors consider two conditions under which water can be taken up by the leaves. These are i) uptake of water when relative humidity is greater than a certain threshold, and ii) uptake of water when precipitation occurs. These 2 processes are not mutually exclusive, given that i) during precipitation, the relative humidity normally is at high levels, and ii) during high relative humidity conditions without precipitation, droplets of water might still occur on leaves and mimick the presence of precipitation. This raises the question whether distinguishing these 2 conditions is meaningful in the first place. Like the authors, I agree that isolating the 2 conditions is good practice, but throughout the manuscript this distinguishment is not consistent and sometimes confusing (multiple terms describing similar things are used + the structure of the manuscripts does not always reflect this distinguishment). I would like to see clear results where leaf water uptake is occuring under the two conditions, which allows meaningful interpretation and comparison.
- The discussion part could benefit from some additions, I made some suggestions in the manuscript. Also,in the results section the authors already discuss, try to keep results and discussion separate. I have a feeling that key results should be highlighted more in the text and that headlines could be more specific. I would change the order of the presented results. In particular, I would put figure 7 and the corresponding section very early in the results, because it shows nicely a lot of key findings. I would consider to stick at either RH or VPD, or make it more clear why you need both.- I would like to read a more distinct paragraph on the potential mechanisms leading to leaf water uptake. I'm sure there is lots of research on the subject. You do have it in the manuscript, but it is short and not really describing the mechanisms or theory behind.
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AC1: 'Reply on RC1', Yiben Cheng, 31 Jan 2023
We thank Editor and an anonymous reviewer for their constructive comments. Based on your comments, we have made extensive modification on the original manuscript and restructured the paper to improve the consistency. Specifically, we have adjusted the research methods and discussion to avoid repetitive and unnecessary description. We have also made efforts to improve the writing.
We have revised the text to clearly state the aims of our research in the introduction. We assume that transpiration ceases during the precipitation event and the relative humidity (RH) of the air reaches 100%, a presumption that has been supported by many previous field experimental observations. The first step in our experiment was to demonstrate that Tamarisk leaves absorb atmospheric vapor under high RH conditions, and the experiment results demonstrated that Tamarisk leaves absorbed atmospheric vapor if the RH was greater than 75%. This suggests that the leaves certainly absorb atmospheric vapor during the precipitation period when RH is close to 100%. Second, we dried and weighed the leaves samples to calculate the amount of atmospheric vapor that was absorbed by the leaves. Third, we recorded the duration of precipitation, including light precipitation which was defined in the introduction. As we collected Tamarisk leaves for weighing before and after the artificial precipitation experiment and dried them afterward to calculate the moisture content of the leaves, then the percentage of precipitation absorbed by the leaves can be computed. Overall, our objective was to investigate the absorption of precipitation by Tamarisk, so we did not quantify the absorption of atmospheric vapor by Tamarisk leaves under non-precipitation conditions with high RH. The process of absorption of unsaturated atmospheric vapor by Tamarisk will be a subject of future investigations. We have moved Figure 7 and the associated results to the first paragraph of results. We decided to remove VPD as an indicator and we will analyze the results based entirely on RH.
We have added the fundamental process of atmospheric vapor absorption by leaves and the status of related research in the discussion section, please see section 4.1 with the following sentences: “How plants absorb atmospheric vapor is still an open question. At the plant scale, there are two pathways for the vegetation to uptake atmospheric vapor (Liu et al., 2021). First, atmospheric vapor condenses and infiltrates into the root soil layer for uptake. Second, plants uptake atmospheric vapor through the leaves. The isotopic tracer experiments have showed that δ18O in specially designed artificial precipitation event was found in the plant stems, suggesting that leaves can absorb the atmospheric vapor during precipitation events (Hill et al., 2021). At the leaf scale, there are three possible pathways for atmospheric vapor to enter the leaf (Zhang et al., 2019). First, when plant leaves breathe and the stomata is open, vapor can enter the leaves. Second, when precipitation event happens, atmospheric water pressure is below leaf water pressure, thus water enters the leaf through membrane, driven by the water pressure gradient. Third, there are some hydrophilic proteins on the cell surface and these protein channels can absorb water and transport the absorbed water into cells. How the three pathways work is not exactly clear at present (Zhuang et al., 2021).” All the issues that should be corrected in the revised version are listed in the supplement.
Thanks again to the anonymous reviewers for their careful and meticulous review.
-
AC1: 'Reply on RC1', Yiben Cheng, 31 Jan 2023
-
RC2: 'Comment on hess-2022-392', Anonymous Referee #2, 15 Feb 2023
The manuscript entitled “An Experimental Investigation of Precipitation Utilization of plants in Arid Regions” by Cheng et al. shows an interesting experimental approach to improve our understanding of how plants in arid environments survive. Furthermore, the manuscript shows a great effort in logistics and resource allocation for a research project in a remote area, features that must be praised in this review. Nonetheless, the manuscript has three significant issues that the authors should consider in the current manuscript.
Major Comments
1. As an experimental hydrologist, I understand the need to squeeze all the information and possible results from experiments, field campaigns, and databases. The effort put into the collection and analysis is not of minor importance. However, scientific productivity must be measured in terms of findings, new insights, novel results, or discoveries, and as scientists, we must restrain ourselves from duplicating our work. Also, all research groups must be committed to creating knowledge based on the scientific method. Therefore, using the same data set in different manuscripts must lead to or show additional findings. Nonetheless, the current manuscript has too many similarities with a new paper published by the same group of authors on 4 January 2023 in the journal Plants (Xin et al., 2023):
Xin, Z.; Feng, W.; Zhan, H.; Bai, X.; Yang, W.; Cheng, Y.; Wu, X. Atmospheric Vapor Impact on Desert Vegetation and Desert Ecohydrological System. Plants 2023, 12, 223. https://doi.org/10.3390/plants12020223
In Xin et al. (2023), the authors use the same experimental setup and data set as the current manuscript under review. Using the same experimental description is not wrong in science if the data sets collected lead to findings in different areas of knowledge. However, two aspects raise a concern about the quality of the manuscript submitted to HESS:
First, the conclusions of Xin et al. (2023) partly overlap with the manuscript under review with the same data set. Xin et al. (2023) stated in part of their conclusions that “… Tamarisk is an excellent drought and salinity tolerant plant, absorbing water vapor from the atmosphere under specific conditions to maintain survival. …” and also “… and part of the vapor is transported downwards in the form of reverse sap flow.”. These conclusions overlap with the main conclusions of the manuscript under review: line 550: “… Our results showed that Tamarisk leaves could absorb unsaturated water vapor and precipitation directly.”, and in line 559: “In summary, water absorption of Tamarisk leaves is very important for Tamarisk to survive in a harsh water-deficit desert environment”.
Secondly, there are a series of inconsistencies in the current manuscript that show how both experimental descriptions were copied without paraphrasing. For example, lines 146 to 157 of the current manuscript are textually the same as the section “3.1 Deep Soil Recharge Observation” of Xin et al. (2023). Also, this description doesn’t match Figure 2 of the current manuscript, where there is no diagram or design of a lysimeter but it is the same as Figure 3 of Xin et al. (2023). This aspect can also be found in the section “2.4.2 Calculation of leaf water absorption“(line 253), which is textually the same as section “3.2.3 Calculation of Leaf Water Absorption” of Xin et al. (2023).
2. The authors give for granted that Tamarisk plants use foliar water uptake as a strategy since the methodology defines thresholds for the process to occur (lines 215-216). But it is contradictory to assume that the process happens before showing the evidence or literature supporting this assumption. Also, the assumption that dew appears at 90% relative humidity without showing proof of specific air humidity and air temperature is risky. A high air relative humidity is not enough evidence to support the affirmation that dew forms on plant surfaces. Instead, dew formation should be evaluated in terms of cloud formation processes. I recommend the authors to change the data analysis towards a more physical base evaluation. The study of specific air humidity will provide enough information on the actual water mass to be deposited as dew and to support or reject the hypothesis that the water flow observed by the reverse sap flow corresponds to leaf water uptake. The authors can check Stull (1988, 2019):
Stull, R. B. 1988. An introduction to boundary layer meteorology, vol. 4, Springer Netherlands, Dordrecht, 1 edn., https://doi.org/10.1007/978-94-009-3027-8
Stull, R. B. 2017. Practical meteorology: an algebra based survey of atmospheric science, BC Campus, available at: http://www.eos.ubc.ca/books/Practical_Meteorology/
3. The authors consider the reverse sap flow as the only evidence of foliar water uptake by Tamarisk plants. However, they do not discuss other theories that may have a stronger foundation in plant physiology. The authors mention that stomata remain open at night as evidence of night transpiration. However, there is no evaluation of meteorological conditions that may trigger this process (e.g., forcing by wind). This evaluation is essential to understand if the species has an isohydric or anisohydric strategy for controlling the stomata, which can also influence the open/closing processes during precipitation or high humidity conditions. Therefore, some questions need to be answered before assuming the foliar water uptake to happen. For example:
Is the reverse sap flow likely an effect of stomatal closure or not?
Is there any evidence in terms of stomatal conductance measured on-site?
Is the specific humidity of the air large enough to supply the flux of water entering the plant tissue system?
Is the reverse sap flow consistent with the available water in the atmosphere?
How do the initial soil water conditions affect the reverse flow?
How extreme is the soil matric potential to force the plants to absorb water through the possible paths mentioned in the introduction?
Finally, I strongly encourage the authors to improve the data analysis of the manuscript by providing new elements of discussion or novelty to a data set already used with a similar research question, with similar conclusions, by the same research group, in a different journal, at the same time.
Citation: https://doi.org/10.5194/hess-2022-392-RC2
Interactive discussion
Status: closed
-
RC1: 'Comment on hess-2022-392', Anonymous Referee #1, 05 Jan 2023
This study investigates the potential of leaf water uptake of Tamarisc in an arid region in China by i) evaluation of reverse sapflow measured in shoots, branches and stems; and ii) by weighting leaf mass before and after drying, prior and post precipitation events, and using the difference in weight as a proxy for leaf water uptake. The results are promising; the manuscript, however, lacks some structure and consistency.
Along with the annotations and comments I made throughout the manuscript, I want to point out some key aspects where improvement is needed.
- The authors consider two conditions under which water can be taken up by the leaves. These are i) uptake of water when relative humidity is greater than a certain threshold, and ii) uptake of water when precipitation occurs. These 2 processes are not mutually exclusive, given that i) during precipitation, the relative humidity normally is at high levels, and ii) during high relative humidity conditions without precipitation, droplets of water might still occur on leaves and mimick the presence of precipitation. This raises the question whether distinguishing these 2 conditions is meaningful in the first place. Like the authors, I agree that isolating the 2 conditions is good practice, but throughout the manuscript this distinguishment is not consistent and sometimes confusing (multiple terms describing similar things are used + the structure of the manuscripts does not always reflect this distinguishment). I would like to see clear results where leaf water uptake is occuring under the two conditions, which allows meaningful interpretation and comparison.
- The discussion part could benefit from some additions, I made some suggestions in the manuscript. Also,in the results section the authors already discuss, try to keep results and discussion separate. I have a feeling that key results should be highlighted more in the text and that headlines could be more specific. I would change the order of the presented results. In particular, I would put figure 7 and the corresponding section very early in the results, because it shows nicely a lot of key findings. I would consider to stick at either RH or VPD, or make it more clear why you need both.- I would like to read a more distinct paragraph on the potential mechanisms leading to leaf water uptake. I'm sure there is lots of research on the subject. You do have it in the manuscript, but it is short and not really describing the mechanisms or theory behind.
-
AC1: 'Reply on RC1', Yiben Cheng, 31 Jan 2023
We thank Editor and an anonymous reviewer for their constructive comments. Based on your comments, we have made extensive modification on the original manuscript and restructured the paper to improve the consistency. Specifically, we have adjusted the research methods and discussion to avoid repetitive and unnecessary description. We have also made efforts to improve the writing.
We have revised the text to clearly state the aims of our research in the introduction. We assume that transpiration ceases during the precipitation event and the relative humidity (RH) of the air reaches 100%, a presumption that has been supported by many previous field experimental observations. The first step in our experiment was to demonstrate that Tamarisk leaves absorb atmospheric vapor under high RH conditions, and the experiment results demonstrated that Tamarisk leaves absorbed atmospheric vapor if the RH was greater than 75%. This suggests that the leaves certainly absorb atmospheric vapor during the precipitation period when RH is close to 100%. Second, we dried and weighed the leaves samples to calculate the amount of atmospheric vapor that was absorbed by the leaves. Third, we recorded the duration of precipitation, including light precipitation which was defined in the introduction. As we collected Tamarisk leaves for weighing before and after the artificial precipitation experiment and dried them afterward to calculate the moisture content of the leaves, then the percentage of precipitation absorbed by the leaves can be computed. Overall, our objective was to investigate the absorption of precipitation by Tamarisk, so we did not quantify the absorption of atmospheric vapor by Tamarisk leaves under non-precipitation conditions with high RH. The process of absorption of unsaturated atmospheric vapor by Tamarisk will be a subject of future investigations. We have moved Figure 7 and the associated results to the first paragraph of results. We decided to remove VPD as an indicator and we will analyze the results based entirely on RH.
We have added the fundamental process of atmospheric vapor absorption by leaves and the status of related research in the discussion section, please see section 4.1 with the following sentences: “How plants absorb atmospheric vapor is still an open question. At the plant scale, there are two pathways for the vegetation to uptake atmospheric vapor (Liu et al., 2021). First, atmospheric vapor condenses and infiltrates into the root soil layer for uptake. Second, plants uptake atmospheric vapor through the leaves. The isotopic tracer experiments have showed that δ18O in specially designed artificial precipitation event was found in the plant stems, suggesting that leaves can absorb the atmospheric vapor during precipitation events (Hill et al., 2021). At the leaf scale, there are three possible pathways for atmospheric vapor to enter the leaf (Zhang et al., 2019). First, when plant leaves breathe and the stomata is open, vapor can enter the leaves. Second, when precipitation event happens, atmospheric water pressure is below leaf water pressure, thus water enters the leaf through membrane, driven by the water pressure gradient. Third, there are some hydrophilic proteins on the cell surface and these protein channels can absorb water and transport the absorbed water into cells. How the three pathways work is not exactly clear at present (Zhuang et al., 2021).” All the issues that should be corrected in the revised version are listed in the supplement.
Thanks again to the anonymous reviewers for their careful and meticulous review.
-
AC1: 'Reply on RC1', Yiben Cheng, 31 Jan 2023
-
RC2: 'Comment on hess-2022-392', Anonymous Referee #2, 15 Feb 2023
The manuscript entitled “An Experimental Investigation of Precipitation Utilization of plants in Arid Regions” by Cheng et al. shows an interesting experimental approach to improve our understanding of how plants in arid environments survive. Furthermore, the manuscript shows a great effort in logistics and resource allocation for a research project in a remote area, features that must be praised in this review. Nonetheless, the manuscript has three significant issues that the authors should consider in the current manuscript.
Major Comments
1. As an experimental hydrologist, I understand the need to squeeze all the information and possible results from experiments, field campaigns, and databases. The effort put into the collection and analysis is not of minor importance. However, scientific productivity must be measured in terms of findings, new insights, novel results, or discoveries, and as scientists, we must restrain ourselves from duplicating our work. Also, all research groups must be committed to creating knowledge based on the scientific method. Therefore, using the same data set in different manuscripts must lead to or show additional findings. Nonetheless, the current manuscript has too many similarities with a new paper published by the same group of authors on 4 January 2023 in the journal Plants (Xin et al., 2023):
Xin, Z.; Feng, W.; Zhan, H.; Bai, X.; Yang, W.; Cheng, Y.; Wu, X. Atmospheric Vapor Impact on Desert Vegetation and Desert Ecohydrological System. Plants 2023, 12, 223. https://doi.org/10.3390/plants12020223
In Xin et al. (2023), the authors use the same experimental setup and data set as the current manuscript under review. Using the same experimental description is not wrong in science if the data sets collected lead to findings in different areas of knowledge. However, two aspects raise a concern about the quality of the manuscript submitted to HESS:
First, the conclusions of Xin et al. (2023) partly overlap with the manuscript under review with the same data set. Xin et al. (2023) stated in part of their conclusions that “… Tamarisk is an excellent drought and salinity tolerant plant, absorbing water vapor from the atmosphere under specific conditions to maintain survival. …” and also “… and part of the vapor is transported downwards in the form of reverse sap flow.”. These conclusions overlap with the main conclusions of the manuscript under review: line 550: “… Our results showed that Tamarisk leaves could absorb unsaturated water vapor and precipitation directly.”, and in line 559: “In summary, water absorption of Tamarisk leaves is very important for Tamarisk to survive in a harsh water-deficit desert environment”.
Secondly, there are a series of inconsistencies in the current manuscript that show how both experimental descriptions were copied without paraphrasing. For example, lines 146 to 157 of the current manuscript are textually the same as the section “3.1 Deep Soil Recharge Observation” of Xin et al. (2023). Also, this description doesn’t match Figure 2 of the current manuscript, where there is no diagram or design of a lysimeter but it is the same as Figure 3 of Xin et al. (2023). This aspect can also be found in the section “2.4.2 Calculation of leaf water absorption“(line 253), which is textually the same as section “3.2.3 Calculation of Leaf Water Absorption” of Xin et al. (2023).
2. The authors give for granted that Tamarisk plants use foliar water uptake as a strategy since the methodology defines thresholds for the process to occur (lines 215-216). But it is contradictory to assume that the process happens before showing the evidence or literature supporting this assumption. Also, the assumption that dew appears at 90% relative humidity without showing proof of specific air humidity and air temperature is risky. A high air relative humidity is not enough evidence to support the affirmation that dew forms on plant surfaces. Instead, dew formation should be evaluated in terms of cloud formation processes. I recommend the authors to change the data analysis towards a more physical base evaluation. The study of specific air humidity will provide enough information on the actual water mass to be deposited as dew and to support or reject the hypothesis that the water flow observed by the reverse sap flow corresponds to leaf water uptake. The authors can check Stull (1988, 2019):
Stull, R. B. 1988. An introduction to boundary layer meteorology, vol. 4, Springer Netherlands, Dordrecht, 1 edn., https://doi.org/10.1007/978-94-009-3027-8
Stull, R. B. 2017. Practical meteorology: an algebra based survey of atmospheric science, BC Campus, available at: http://www.eos.ubc.ca/books/Practical_Meteorology/
3. The authors consider the reverse sap flow as the only evidence of foliar water uptake by Tamarisk plants. However, they do not discuss other theories that may have a stronger foundation in plant physiology. The authors mention that stomata remain open at night as evidence of night transpiration. However, there is no evaluation of meteorological conditions that may trigger this process (e.g., forcing by wind). This evaluation is essential to understand if the species has an isohydric or anisohydric strategy for controlling the stomata, which can also influence the open/closing processes during precipitation or high humidity conditions. Therefore, some questions need to be answered before assuming the foliar water uptake to happen. For example:
Is the reverse sap flow likely an effect of stomatal closure or not?
Is there any evidence in terms of stomatal conductance measured on-site?
Is the specific humidity of the air large enough to supply the flux of water entering the plant tissue system?
Is the reverse sap flow consistent with the available water in the atmosphere?
How do the initial soil water conditions affect the reverse flow?
How extreme is the soil matric potential to force the plants to absorb water through the possible paths mentioned in the introduction?
Finally, I strongly encourage the authors to improve the data analysis of the manuscript by providing new elements of discussion or novelty to a data set already used with a similar research question, with similar conclusions, by the same research group, in a different journal, at the same time.
Citation: https://doi.org/10.5194/hess-2022-392-RC2
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