the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Controls on leaf water hydrogen and oxygen isotopes: A local investigation across seasons and altitude
- 1State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
- 2National Observation and Research Station of Earth Critical Zone on the Loess Plateau of Shaanxi, Xi’an, 710061, China
- 3Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China
- 4State Key Laboratory of Hydraulics and Mountain River Engineering & College of Water Resource and Hydropower, Sichuan University, 610065, Chengdu, China
- 5Institute of Global Environmental Change, Xi’an Jiaotong University, Xi’an, 710054, China
- 6College of resources and environmental engineering, Ludong University, 264025, Yantai, China
- 1State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
- 2National Observation and Research Station of Earth Critical Zone on the Loess Plateau of Shaanxi, Xi’an, 710061, China
- 3Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China
- 4State Key Laboratory of Hydraulics and Mountain River Engineering & College of Water Resource and Hydropower, Sichuan University, 610065, Chengdu, China
- 5Institute of Global Environmental Change, Xi’an Jiaotong University, Xi’an, 710054, China
- 6College of resources and environmental engineering, Ludong University, 264025, Yantai, China
Abstract. The stable oxygen (δ18Oleaf) and hydrogen (δ2Hleaf) isotopes of leaf water act as a bridge that connects hydroclimate to plant-derived organic matter. However, it remains unclear whether the source water (i.e., twig water, soil water, and precipitation) or meteorological parameters (i.e., temperature, relative humidity, and precipitation) are the dominant controls on δ18Oleaf and δ2Hleaf. Here, we reported seasonal analysis of δ18Oleaf and δ2Hleaf together with isotopes from potential source waters and meteorological parameters along an elevation transect on the Chinese Loess Plateau. We found that δ2Hleaf values were more closely correlated with source water isotopes than δ18Oleaf values, whereas δ18Oleaf and δ2Hleaf values were similarly correlated with meteorological parameters. Dual-isotope analysis showed that the δ18Oleaf and δ2Hleaf values were closely correlated because of their similar altitudinal and seasonal responses, and so generated a well-defined isotope line relative to the local meteoric water line (LMWL). We also compared the measured δ18Oleaf and δ2Hleaf values with predicted values by the Craig-Gordon model, and found no significant differences between them. We demonstrate that the first-order control on δ18Oleaf and δ2Hleaf values was the source water, and the second-order control was the enrichment associated with biochemical and environmental factors.
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Jinzhao Liu et al.
Status: final response (author comments only)
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RC1: 'Comment on hess-2022-246', Anonymous Referee #1, 30 Jul 2022
I appreciate the Editor to give me a chance to review the paper.
The manuscript “Controls on leaf water hydrogen and oxygen isotopes: A local investigation across seasons and altitude” presents a dataset on analysis of δ18Oleaf and δ2Hleaf together with isotopes from potential source waters and meteorological parameters along an elevation transect on the Chinese Loess Plateau. The research topic is important and within the scope of the journal.
But it seems a bit simple and not systematic in the content. The manuscript at present lacks novel results or theory that would provide a significant advance in this field.
1) The main conclusion of this paper has been confirmed by previous studiesï¼ the first-order control on δ18O leaf and δ2Hleaf values was the source waterï¼and the second-order control was the enrichment associated with biochemical and environmental factorsï¼Cernusak et al., 2016; Barbour et al., 2017; Munksgaard et al., 2017). The experimental design and results of the paper are not innovative.
2) A large number of studies have shown that the enrichment associated with plant transpiration is an important factor affecting δ18Oleaf and δ2Hleaf values. However, the authors did not carry out research and discussion in this paper.
3)Plants and soils were sampled in May, July, and September 2020 (In the experimental design). Why only choose this three months? Is it persuasive?
4ï¼Besides, what is the specific sampling interval?
5) Why only one or two deciduous and coniferous trees were chosen in each plot?
6) There are large differences in population and altitude between sampling points 5-8(Fig.1). But there is no weather station here.
7) In 4.1ï¼these results argued with the recent global meta-analysis thatδ18Oleaf and δ2Hleaf values reflect climatic parameters (i.e., RH and temperature) differently. What are the reasons for the controversial conclusion?
8) It seems a bit simple in the conclusion. It needs a stronger ending for the conclusion. Besides, it is suggested to supplement the existing deficiencies and prospects.
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AC1: 'Reply on RC1', Jinzhao Liu, 05 Sep 2022
Comment:
I appreciate the Editor to give me a chance to review the paper.
The manuscript “Controls on leaf water hydrogen and oxygen isotopes: A local investigation across seasons and altitude” presents a dataset on analysis of δ18Oleaf and δ2Hleaf together with isotopes from potential source waters and meteorological parameters along an elevation transect on the Chinese Loess Plateau. The research topic is important and within the scope of the journal.
But it seems a bit simple and not systematic in the content. The manuscript at present lacks novel results or theory that would provide a significant advance in this field.
Response:
Thanks a lot for your comments. Our study have two significant novel points: 1) the previous studies have always emphasized on the combined δ18O and δ2Hvalues of leaf water (δ18Oleaf and δ2Hleaf), few considering the respective responses or variations of δ18Oleaf and δ2Hleaf. A recent global meta-analysis indicate that the respective δ18Oleaf and δ2Hleaf reflected differently, seen details in Cernusak et al. (2022; NP). However, our local-study supported that δ2Hleaf responds more closely to xylem water than δ18Oleaf, but both δ18Oleaf and δ2Hleaf responds comparatively to climatic factors (RH, T), challenging the global meta-analysis (Cernusak et al., 2022); 2) We proposed a framework that control the leaf water isotope line by using multivariate statistical methods (Hierarchical clustering, Craig-Cordon model, Structural equation model, HYSPLIT, etc)
Reference
Cernusak, L. A., Barbeta, A., Bush, R., Eichstaedt R., Ferrio, J., Flanagan, L., Gessler, A., Martín-Gómez, P., Hirl, R., Kahmen, A., Keitel., C., Lai, C., Munksgaard, N., Nelson, D., Ogée J., Roden, J., Schnyder, H., Voelker, S., Wang L., Stuart-Williams, H., Wingate, L., Yu, W., Zhao, L., Cuntz, M., 2022. Do 2H and 18O in leaf water reflect environmental drivers differently? New Phytologist, DOI: 10.1111/nph.18113.
Comment:
- The main conclusion of this paper has been confirmed by previous studiesï¼ the first-order control on δ18O leaf and δ2Hleaf values was the source waterï¼and the second-order control was the enrichment associated with biochemical and environmental factorsï¼Cernusak et al., 2016; Barbour et al., 2017; Munksgaard et al., 2017). The experimental design and results of the paper are not innovative.
Response:
Thanks. “The first-order control on δ18Oleaf and δ2Hleaf values was the source waterï¼and the second-order control was the enrichment associated with biochemical and environmental factorsï¼Cernusak et al., 2016; Barbour et al., 2017; Munksgaard et al., 2017)” is deed analyzed by previous studies, as discussed in Introduction section. Our studies analyzed the responses of respective (δ18Oleaf and δ2Hleaf) and both to source waters (xylem water, soil water, and precipitation) and to meteorological parameters (temperature, RH). As above stated, we have two significant novel points.
Comment:
2) A large number of studies have shown that the enrichment associated with plant transpiration is an important factor affecting δ18Oleaf and δ2Hleaf values. However, the authors did not carry out research and discussion in this paper.
Response:
Thanks. We have added more discussion on transpiration.
Comment:
3)Plants and soils were sampled in May, July, and September 2020 (In the experimental design). Why only choose this three months? Is it persuasive?
Response:
Thanks. The growing season lasts from late April to Early October on the Chinese Loess Plateau, so we selected the pre- (May), peak (July), and post-(September) growing season. Also, the precipitation δ18O and δ2H varies across months (Fig. 5a, b), which was caused by different moisture transport routes from HYSPLIT (Fig, 5c).
Additionally, we sampled at the same plots (ten plots) along an elevation transect from ~600 m to ~3600 m, the three repeated sampling is OK. If more, the sampling will be a burdensome work and the plants is not available for more repeated sampling.
Comment:
4ï¼Besides, what is the specific sampling interval?
Response:
Thanks. The sampling plots were arranged for ten plots from ~600 m to ~3600 m along an elevation transect, which was detailed in Fig, 1 and supplementary Table S1.
The sampling plots were randomly selected in the first campaign from the bottom to top of mountain, then repeated by the next two sampling campaigns.
Comment:
5) Why only one or two deciduous and coniferous trees were chosen in each plot?
Response:
Thanks. There was a significant vegetation zone along an elevation transect of Mt. Taibai (Fig.1 and M&M), so we selected the dominant species at each zones.
Comment:
6) There are large differences in population and altitude between sampling points 5-8(Fig.1). But there is no weather station here.
Response:
Thanks. The weather stations along an elevation transect was very hard to settle up, the available weather stations were presented in Fig.1. We thank to Shaanxi Meteorological Bureau for supporting meteorological data. It is possible that more weather stations will be settled up along this elevation transects in the future.
Comment:
7) In 4.1ï¼these results argued with the recent global meta-analysis thatδ18Oleaf and δ2Hleaf values reflect climatic parameters (i.e., RH and temperature) differently. What are the reasons for the controversial conclusion?
Response:
Thanks. It is really a good question, I think it is probably due to the scale difference, e.g., global vs. local. The reason needs to be further explored in the future.
Comment:
8) It seems a bit simple in the conclusion. It needs a stronger ending for the conclusion. Besides, it is suggested to supplement the existing deficiencies and prospects.
Response:
Thanks. We have strengthen the conclusion.
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AC1: 'Reply on RC1', Jinzhao Liu, 05 Sep 2022
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RC2: 'Comment on hess-2022-246', Anonymous Referee #2, 20 Aug 2022
Liu et al, based on field sampling of leaf water and measuring isotope composition (δ18O and δ2H) along an elevation transect on the Chinese Loess Plateau belt to illustrate controls on leaf water hydrogen and oxygen isotopes. The results point that the first-order control on δ18O and δ2H was the source water, and the second-order control was the enrichment associated with biochemical and environmental factors. Overall, this is an important and hard-working investigation for deepening the understanding of the control of leaf water isotopic composition in field conditions. However, the current analysis is mediocre, the scientific questions are poorly elaborated, and new discoveries are lacking. Secondly, the results show that source water is the main control of leaf water isotopes, which is contrary to the previous results which indicate that relative humidity is the main control of leaf water isotopes both under leaf and ecosystem scale. Therefore, there requires more evidence to support your conclusion. I recommend major revisions before considering publication in this journal.
Minor revision:
Line 148-150, “For the plants, one or two deciduous and coniferous trees were chosen in each plot, and several large leaves and suberized twigs were collected for each species.” Here should be describe in details.
Line 214-215, How was the ðð and ðð obtained? Here should be describe in details.
Line 264, predicted δ18O and δ2H values of leaf water were quiet simper, and need consider non stead state (NSS) under complex environment condition.
Line 456-459ï¼there need more deep-seated analysis but not common knowledge in this area.
Line 466-469, The conclusion is too simple and needs to be further explored.
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AC2: 'Reply on RC2', Jinzhao Liu, 05 Sep 2022
Comment:
Liu et al, based on field sampling of leaf water and measuring isotope composition (δ18O and δ2H) along an elevation transect on the Chinese Loess Plateau belt to illustrate controls on leaf water hydrogen and oxygen isotopes. The results point that the first-order control on δ18O and δ2H was the source water, and the second-order control was the enrichment associated with biochemical and environmental factors. Overall, this is an important and hard-working investigation for deepening the understanding of the control of leaf water isotopic composition in field conditions. However, the current analysis is mediocre, the scientific questions are poorly elaborated, and new discoveries are lacking. Secondly, the results show that source water is the main control of leaf water isotopes, which is contrary to the previous results which indicate that relative humidity is the main control of leaf water isotopes both under leaf and ecosystem scale. Therefore, there requires more evidence to support your conclusion. I recommend major revisions before considering publication in this journal.
Response:
Thanks a lot for your approvedness and suggestions. For the first question, we have two significant novel points: 1) the previous studies have always emphasized on the combined δ18O and δ2Hvalues of leaf water (δ18Oleaf and δ2Hleaf), few considering the respective responses or variations of δ18Oleaf and δ2Hleaf. A recent global meta-analysis indicate that the respective δ18Oleaf and δ2Hleaf reflected differently, seen details in Cernusak et al. (2022; NP). However, our local-study supported that δ2Hleaf responds more closely to xylem water than δ18Oleaf, but both δ18Oleaf and δ2Hleaf responds comparatively to climatic factors (RH, T), challenging the global meta-analysis (Cernusak et al., 2022); 2) We proposed a framework that control the leaf water isotope line by using multivariate statistical methods (Hierarchical clustering, Craig-Cordon model, Structural equation model, HYSPLIT, etc). The leaf water isotope line was generated by our analysis, which provides an important baseline for leaf-derived organic matter such as cellulose and leaf wax.
For the second question, our results were actually consistent with the previous conclusion. We proposed a hierarchical control on leaf water isotopes, as the following figure. The first-order control is source water, which is also affected by climate factors (e.g., T, RH). The climatic factors (e.g. RH) affect source water and directly affect leaf water isotopes. Without considering source water, the RH is the main control on leaf water isotopes.
Comment:
Minor revision:
Line 148-150, “For the plants, one or two deciduous and coniferous trees were chosen in each plot, and several large leaves and suberized twigs were collected for each species.” Here should be describe in details.
Response:
Thanks. We have added more details.
Comment:
Line 214-215, How was the ðð and ðð obtained? Here should be describe in details.
Response:
Thanks. We have added new citation, the kinetic fractionation equations for hydrogen and oxygen isotopes can be found in the reference.
Comment:
Line 264, predicted δ18O and δ2H values of leaf water were quiet simper, and need consider non stead state (NSS) under complex environment condition.
Response:
Thanks. It is a good question. We used the steady-state condition in this study because our sampling campaigns take place during the day when leaf water is generally near isotopic steady state because chloroplasts are mostly located near to the evaporative sites (Cernusak et al., 2016). The non-steady state effects on leaf water isotopes were expected at night because of low stomatal conductance (Cernusak et al., 2005; Cuntz et al., 2002; Cernusak et al., 2016).
Comment:
Line 456-459ï¼there need more deep-seated analysis but not common knowledge in this area.
Response:
Thanks. We have depleted it. This needs to be further explored in the future.
Comment:
Line 466-469, The conclusion is too simple and needs to be further explored.
Response:
Thanks. We have strengthen the conclusion.
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AC2: 'Reply on RC2', Jinzhao Liu, 05 Sep 2022
Jinzhao Liu et al.
Jinzhao Liu et al.
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