the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
An Experimental Investigation of Precipitation Utilization of plants in Arid Regions
- 1School of soil and water conservation, Beijing Forestry University, Beijing, China, 100083
- 2Xilingol Vocational College, Xilingol, China, 026000
- 3Department of Geology and Geophysics, Texas A&M University, College Station, Texas, USA, 77843
- 4The Sand Forestry Experimental Centre, Chinese Academy of Forestry, Dengkou, Inner Mongolia, China, 015200
- 5Low-coverage sand control company, Hohhot, Inner Mongolia, China, 010000
- 1School of soil and water conservation, Beijing Forestry University, Beijing, China, 100083
- 2Xilingol Vocational College, Xilingol, China, 026000
- 3Department of Geology and Geophysics, Texas A&M University, College Station, Texas, USA, 77843
- 4The Sand Forestry Experimental Centre, Chinese Academy of Forestry, Dengkou, Inner Mongolia, China, 015200
- 5Low-coverage sand control company, Hohhot, Inner Mongolia, China, 010000
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.
Yiben Cheng et al.
Status: open (extended)
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RC1: 'Comment on hess-2022-392', Anonymous Referee #1, 05 Jan 2023
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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
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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.
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AC1: 'Reply on RC1', Yiben Cheng, 31 Jan 2023
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Yiben Cheng et al.
Yiben Cheng et al.
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