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Volume 41 Issue 4
Aug.  2020
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Chaoyang Yan, Yiming Zhang, Yanzhen Zhang, Zhiqi Zhang, Xianyu Huang. Habitat Influence on the Molecular, Carbon and Hydrogen Isotope Compositions of Leaf Wax n-Alkanes in a Subalpine Basin, Central China. Journal of Earth Science, 2020, 31(4): 845-852. doi: 10.1007/s12583-020-1322-x
Citation: Chaoyang Yan, Yiming Zhang, Yanzhen Zhang, Zhiqi Zhang, Xianyu Huang. Habitat Influence on the Molecular, Carbon and Hydrogen Isotope Compositions of Leaf Wax n-Alkanes in a Subalpine Basin, Central China. Journal of Earth Science, 2020, 31(4): 845-852. doi: 10.1007/s12583-020-1322-x

Habitat Influence on the Molecular, Carbon and Hydrogen Isotope Compositions of Leaf Wax n-Alkanes in a Subalpine Basin, Central China

doi: 10.1007/s12583-020-1322-x
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  • Epidermal leaf waxes of terrestrial higher plants have been widely utilized for the reconstructions of paleoenvironment and paleoclimate in peat deposits. In this study, specimens of four plant species growing in both peatland and non-peatland habitats were retrieved to compare their molecular, carbon (δ13C) and hydrogen (δ2H) isotopic compositions of leaf wax n-alkanes from a closed subalpine basin in Central China. Three of the four species show quite higher total concentrations of n-alkanes in the relatively dry non-peatland setting than in the peatland. In addition, the δ2H values of long-chain n-alkanes are generally less depleted in the peatland and are comparable among different plant species, which is interpreted as the influence of inundation condition and the possible limited supply of photosynthetic products. This study reveals different patterns of plant wax molecular and isotopic compositions between peatland and the surrounding non-peatland conditions, and confirms the paleoenvironmental potential of leaf wax ratios on the peat sequences.
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Habitat Influence on the Molecular, Carbon and Hydrogen Isotope Compositions of Leaf Wax n-Alkanes in a Subalpine Basin, Central China

doi: 10.1007/s12583-020-1322-x

Abstract: Epidermal leaf waxes of terrestrial higher plants have been widely utilized for the reconstructions of paleoenvironment and paleoclimate in peat deposits. In this study, specimens of four plant species growing in both peatland and non-peatland habitats were retrieved to compare their molecular, carbon (δ13C) and hydrogen (δ2H) isotopic compositions of leaf wax n-alkanes from a closed subalpine basin in Central China. Three of the four species show quite higher total concentrations of n-alkanes in the relatively dry non-peatland setting than in the peatland. In addition, the δ2H values of long-chain n-alkanes are generally less depleted in the peatland and are comparable among different plant species, which is interpreted as the influence of inundation condition and the possible limited supply of photosynthetic products. This study reveals different patterns of plant wax molecular and isotopic compositions between peatland and the surrounding non-peatland conditions, and confirms the paleoenvironmental potential of leaf wax ratios on the peat sequences.

Chaoyang Yan, Yiming Zhang, Yanzhen Zhang, Zhiqi Zhang, Xianyu Huang. Habitat Influence on the Molecular, Carbon and Hydrogen Isotope Compositions of Leaf Wax n-Alkanes in a Subalpine Basin, Central China. Journal of Earth Science, 2020, 31(4): 845-852. doi: 10.1007/s12583-020-1322-x
Citation: Chaoyang Yan, Yiming Zhang, Yanzhen Zhang, Zhiqi Zhang, Xianyu Huang. Habitat Influence on the Molecular, Carbon and Hydrogen Isotope Compositions of Leaf Wax n-Alkanes in a Subalpine Basin, Central China. Journal of Earth Science, 2020, 31(4): 845-852. doi: 10.1007/s12583-020-1322-x
  • Leaves of higher terrestrial plants are covered with a wax layer, which can prevent water loss (Eglinton and Halmiton, 1967). Leaf waxes consist of long-chain (>21 carbons) n-alkanes, n-alkanoic acids, and alcohols (Eglinton and Halmiton, 1967). As they are relatively resistant to degradation and easy to be extracted and purified from sediments, n-alkanes, in particular, have been widely utilized to reconstruct paleoenvironment and paleoclimate (Diefendorf and Freimuth, 2017; Bush and McInerney, 2013; Sachse et al., 2012). A robust interpretation of paleo information requires a thorough understanding of how environmental factors affect the molecular, carbon, and hydrogen isotope compositions of leaf wax n-alkanes in living plants.

    With the merits of containing abundant organic matter (typically >30%) in immature conditions, peat deposits have been widely investigated for lipid-based paleoenvironmental reconstructions (Naafs et al., 2019; Huang and Xie, 2016; Chambers et al., 2012). Among the lipid classes, leaf wax n-alkanes have attracted the most attention. Plenty of studies reveal the distinct distribution patterns between peat mosses and vascular peat-forming plants (e.g., Zhao et al., 2018; Nichols et al., 2006; Pancost et al., 2002; Nott et al., 2000). In addition, the carbon isotope compositions of leaf wax n-alkanes (δ13Calk) in peat-forming plants have the potential to track paleohydrological changes and biogeochemical processes (e.g., Inglis et al., 2019; Huang et al., 2018a, 2014; Nichols et al., 2014, 2009; Zheng et al., 2014; Yamamoto et al., 2010a, b). Furthermore, the hydrogen isotope compositions of leaf wax n-alkanes (δ2Halk) in peat-forming plants have been confirmed to have the potential to track paleohydrological conditions (e.g., Huang and Meyers, 2019; Huang et al., 2018b; Wang et al., 2016; Seki et al., 2011; Nichols et al., 2010).

    Lipid studies on peat deposits almost rely on the assumption that lipids preserved in peat deposits are mainly contributed by in-situ peat-forming plants (Pancost et al., 2002; Farrimond and Flanagan, 1996). Thus, it is realistic to utilize peat lipids to reflect the changes of peat-forming plants and peatland water levels, and to reconstruct the associated paleoclimate changes. Such an assumption is surely supported by the quite high organic matter content in peats relative to mineral soils and typical lacustrine sediments. However, knowledge of the lipid differences between peat-forming plants and plants growing in non-peatland habitats is still to be enriched, particularly in settings with fluctuations between lacustrine and peat deposits (e.g., Dahu swamp in southern China; Zheng et al., 2009; Zhou et al., 2005).

    Over the past years, our group has investigated the molecular, carbon, and hydrogen isotopic compositions of leaf wax n-alkanes in plants growing in the Dajiuhu Basin, a subalpine basin in Central China (see Zhao et al., 2018 for a synthesis). These studies show that leaf wax n-alkanes in plants vary distinctly with plant life forms (Zhao et al., 2018). In this study, we compare the molecular, carbon, and hydrogen isotopic compositions of leaf wax n-alkanes in the same species growing in different habitats (peatland vs. non-peatland). The objective is to reveal how habitats affect the leaf wax n-alkane compositions of higher plants growing in quite similar climatic context.

  • Dajiuhu (1 700 m above sea level, 31°28′N, 110°00′E) is a subtropical subalpine basin (Zhao et al., 1999), with a total area of 16 km2, in the Shennongjia Forestry District, Hubei Province, Central China (Xu et al., 2019; Wang et al., 2018; Huang et al., 2017). Climate is dominated by the East Asian Monsoon, with a mean annual rainfall of 1 560 mm and a mean annual temperature of 7.2 ℃. The dominant peat-forming plants are graminoids, Sphagnum palustre, and some forb species (Zhao et al., 2018; Luo et al., 2015; Li et al., 2007). Besides, shrubs and trees are the predominant plants in the dry land surrounding the peatland and grow smaller in the peatlands (Li et al., 2007).

    During a field campaign trip in August 2017, leaf samples of representative plants were collected in this basin (Fig. 1). Among these plants, four species (Quercus aliena, Geranium pretense, Malus hupehensis, and Crataegus wilsonii) were found in both peatland and non-peatland conditions. Here the non-peatland condition refers to the relatively dry habitat, developed with mineral soil, surrounding the peatland. Except G. pretense (forb), the other three species belong to trees growing in non-peatland and dwarfed growing in peatland conditions in Dajiuhu. For Q. aliena growing in both habitats and C. wilsonii growing in peatland, 2 or 3 independent samples were collected and analyzed, while only one specimen was collected for C. wilsonii growing in non-peatland and the other two species growing in both habitats.

    Figure 1.  Map of sampling sites in the Dajiuhu Basin. The square pattern represents the sampling location of the non-peat plant, and the circular pattern represents the sampling location of the peatland plant.

  • The lipid extraction and separation procedures were identical with Zhao et al. (2018). Briefly, the plant samples (ca. 1 g) were freeze-dried and ultrasonically extracted six times with dichloromethane (DCM)/MeOH (9 : 1, volume/volume) for 15 min. Before extraction, 5β-cholane (Chiron, Norway) was added as an internal standard. After solvent removal under reduced pressure, the extract was fractionated into aliphatic, aromatic and polar fractions using silica gel column chromatography. The aliphatic fraction containing long-chain n-alkanes was eluted with n-hexane.

  • The instrumental analysis procedures were identical to those published in Zhao et al. (2018). The aliphatic fraction containing n-alkanes was analyzed in a Shimadzu GC-2010 gas chromatograph (GC) equipped with a flame ionization detector (FID) and a DB-5 column (30 m×0.25 mm i.d., 0.25 μm film thickness). Each sample was injected in splitless mode with the injector temperature at 300 ℃. The initial oven temperature was 70 ℃, then ramped to 210 ℃ at 10 ℃/min, and it was finally raised to 300 ℃ (held 25 min) at 3 ℃/min. Quantification was achieved by comparison of peak areas with the internal standard (cholane) after adjustment for the relevant response factors.

    Gas chromatography-mass spectrometry (GC-MS) analysis was performed with a Hewlett Packard 6890 gas chromatograph interfaced with a Hewlett Packard 5973 mass selective detector. The chromatograph was equipped with a DB-5 MS column (30 m×0.25 mm, film thickness 0.25 μm). Samples were injected in splitless mode. The oven temperature was programmed from 70 ℃ (1 min hold) to 200 ℃ at 10 ℃/min and then to 300 ℃ at 3 ℃/min and held for 10 min. Helium was used as the carrier gas at a constant 1 mL/min. The ionization energy of the mass spectrometer was set at 70 eV, and the scan range was m/z 50–550. Compound identification was based on mass spectra and the relative retention times from the literature.

  • Compound-specific carbon isotope analysis was conducted using a Finnigan Trace GC attached to a Finnigan Delta Plus XP isotope ratio mass spectrometer, equipped with a DB-5MS capillary column (30 m×0.25 mm×0.25 μm) in the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (CUG), Wuhan. Samples were injected in splitless mode (1 μL), with the injector at 290 ℃. Instrumental performance was checked every four runs using the A6 n-alkane mixture (C16–C30) obtained from Arndt Schimmelmann (Indiana University, USA), and an inhouse mixture containing C23, C25, C27, C29, C31, and C33 n-alkanes. Squalane (δ13C, -19.8‰) was used as the internal standard. Reproducibility for the n-alkane standards was better than 0.5‰ (standard deviation) based on at least duplicate analyses. Results were reported in the notation (‰) relative to the VPDB standard.

  • Compound-specific hydrogen isotope compositions of n-alkanes were determined using a Trace GC coupled with a Delta V advantage isotope ratio mass spectrometer also in the State Key Laboratory of Biogeology and Environmental Geology, CUG, Wuhan. Samples were injected in splitless mode (1 μL), with the injector temperature at 290 ℃, and they were separated with a DB-5ms column (30 m×0.25 mm×1.0 μm film thickness). The analytical procedures were identical to that of Zhao et al. (2018). The high temperature conversion (HTC) system was operated at 1 400 ℃, and the HTC tube was conditioned with methane. H3+ factor was monitored daily, with daily values variation <±0.1. Instrument performance was verified before and after each sample run using a n-alkane standard mixture with known δ2H values (C16–C30, obtained from Indiana University). Reproducibility for specific compounds was <5‰ for δ2H (standard deviation), based on at least duplicate analyses. Squalane (δ2H, -167‰) was used as the internal standard. Results are reported in the delta notation (‰) relative to the VSMOW standard.

  • Long-chain n-alkanes ranging from C21 to C33 are the dominant constituents of the aliphatic fractions in all plant samples, showing a strong odd-over-even predominance (Fig. 2). The total concentrations of the C21 to C33 n-alkanes in the leaf samples vary greatly, ranging from 46.2 to 476.0 μg/g dry weight (Table 1). In general, G. pretense growing in both habitats (dominated by C31 and C33) and M. hupehensis growing in the non-peatland habitat (dominated by C29 and C31) have a higher concentration of n-alkanes than Q. aliena (dominated by C25 and C27) and C. wilsonii (dominated by C29). The three tree species all show higher n-alkanes concentrations in non-peatland than peatland habitats, while the herb species (G. pretense) displays comparable n-alkane concentrations in both conditions (Fig. 2).

    Figure 2.  Histograms showing the distribution patterns of n-alkanes in four plant species growing in peatland (wet) and non-peatland (relatively dry) conditions. The standard deviation in (a) was calculated on duplicate analyses. (a) Q. aliena; (b) G. pretense; (c) M. hupehensis; (d) C. wilsonii.

    Sample Habitat type Concentration (μg/g) Sum (μg/g) ACL CPI
    C21 C23 C25 C27 C29 C31 C33
    Q. aliena Peatland 0.3 4.15 10.4 24.3 21.2 4.25 0.3 74.9 27.3 6.0
    Non-peatland 0.5 4.1 66.4 56.3 33.4 3.9 0.3 188.4 26.6 6.7
    G. pretense Peatland 0.4 0.7 4.0 27.5 65.2 168.8 173.6 476.0 31.2 9.9
    Non-peatland 4.7 16.3 10.0 31.6 61.3 151.6 157.3 459.5 30.6 13.1
    M. hupehensis Peatland 0.8 2.5 3.5 5.1 14.7 9.1 0.5 46.2 28.3 3.5
    Non-peatland 0.5 2.2 3.0 7.1 176.9 215.5 19.6 451.8 30.1 15.4
    C. wilsonii Peatland 0.2 1.1 3.0 5.1 33.2 8.4 1.0 61.5 28.8 5.4
    Non-peatland 0.8 4.4 9.7 13.9 67.9 10.9 1.3 131.4 28.3 4.8

    Table 1.  Concentration of odd-numbered n-alkanes and the total n-alkanes (C21–C33), and the results of alkane ratios

    The above distribution differences between habitats are also clearly revealed by the values of average chain length (ACL) and carbon preference index (CPI). The ACL values of

    the plant samples in this study range from 26.6 to 31.2, with the highest ACL value occurring in G. pretense growing in the peatland condition (Table 1, Fig. 3). The plant species except M. hupehensis have relatively higher ACL values in the wet conditions than in the dry conditions (Fig. 3), although the difference is not significant for the quite small dataset (t-test, p > 0.05). The CPI values in the plant samples vary from 3.5 to 15.4 (Table 1, Fig. 3). G. pretense and M. hupehensis have higher CPI values in the dry environment than in the wet one. In contrast, the CPI values of Q. aliena and C. wilsonii are similar in both conditions.

    Figure 3.  Comparisons of ACL and CPI vales in the species growing in the peatland and non-peatland habitats. Filled symbols refer to peatland, while unfilled symbols refer to non-peatland. Distribution of ACL and CPI in the different types of plants collected from the Dajiuhu peatland. The ACL and CPI values were calculated as follows

  • In the peatland habitat, the δ13Calk values of the four species fall into the range previously reported in the same peatland (Zhao et al., 2018). M. hupehensis has been investigated in both studies, and shows quite similar δ13Calk values of C29 and C31 n-alkanes, ranging from -32.3‰ to -33.2‰ (Zhao et al., 2018; Table 2, Fig. 4). The difference in δ13Calk values among individual homolog in the same species is less than 1‰ (Fig. 4). The M. hupehensis specimen has the least negative δ13Calk values, while the δ13Calk values of G. pretense are near 4‰ more negative relative to those of M. hupehensis. In our previous study, the life-form averaged δ13Calk values of C29 and C31 n-alkanes are similar for forb, graminoid and shrub plants (Zhao et al., 2018). For the four species, the δ13Calk values of long-chain n-alkanes are comparable between the peatland and non-peatland habitats (Figs. 4a and 4b). Only the δ13Calk value of C27 n-alkane in M. hupehensis growing in the non-peatland is >1‰ negative than that in the peatland habitat (Fig. 4). Moreover, the plant n-alkanes in this study show a slight decrease in their δ13C values with longer chain lengths, although limited by the small number of samples. This trend has also been found in previous studies (Zhao et al., 2018; Smith et al., 2007). In summary, the habitats do not affect the δ13Calk values in the four species investigated in this study.

    Sample Habitat type Carbon number
    C25 C27 C29 C31 C33
    Q. aliena Peatland -33.4±0.5 -36.0±0.2 -33.9±0.4
    Non-peatland -33.2±0.7 -33.0±0.5 -32.6±0.3
    G. pretense Peatland -36.0±0.4 -35.6±0.1 -36.0 -36.0±0.9
    Non-peatland -35.8±0.4 -35.5±0.4 -37.0±0.2
    M. hupehensis Peatland -32.0±0.4 -32.5 -32.3±0.5 -33.0
    Non-peatland -34.3 -32.6±0.4 -33.8±0.6
    C. wilsonii Peatland -32.4±0.1
    Non-peatland -32.1±0.2 -32.4±0.2

    Table 2.  Individual carbon isotope values of odd-numbered n-alkanes (‰, VPDB) in the plant samples.

    Figure 4.  Patterns of δ2Halk and δ13Calk values of long-chain n-alkanes in the four plant species growing in peatland (a) and (c) and non-peatland (b) and (d) conditions.

  • Different from δ13Calk, the δ2Halk values are distinctive between the two habitats. The δ2Halk values of three of the four species are more negative in the non-peatland habitat than their counterparts in the peatland (Figs. 4c and 4d). Taking G. pretense as an example, the differences of the δ2Halk values of C29 and C31 n-alkanes between the two habitats are as large as near 50‰ (Table 3). For Q. aliena, the δ2Halk values of the predominant C27 and C29 n-alkanes are 15‰–20‰ more negative in the non-peatland habitat than those in the peatland. Different from the other three species, the M. hupehensis species show less negative δ2Halk values in the non-peatland habitat than in the peatland (Fig. 4c and 4d). Notably, the δ2Halk values among the species growing in the peatland habitat vary in a quite narrow range; however, the δ2Halk values in the non-peatland habitat are scattered. Such a finding is consistent with the results in Zhao et al. (2018), which reports similar life-form averaged δ2Halk values between forb and shrub plants. In the non- peatland habitat, the forb species (G. pretense) has more negative δ2Halk values (C31, -227‰; C33, -242‰) than the other three tree species, and is also more negative than the life-form averaged δ2Halk values for forb plants in the Dajiuhu (Zhao et al., 2018). Different from δ13Calk values, the relation of the chain lengths with δ2Halk values is scattered, especially for plant samples collected from non-peatland.

    Sample Habitat type Carbon number
    C25 C27 C29 C31 C33
    Q. aliena Peatland -159±3 -167 -162±3
    Non-peatland -187±5 -177±1
    G. pretense Peatland -174±6 -181±2 -185±2
    Non-peatland -228±1 -218 -227 -242±1
    M. hupehensis Peatland -141±1 -158±4 -169 -173±1
    Non-peatland -159±1 -142
    C. wilsonii Peatland -177±1 -158±4
    Non-peatland -179±3 -202 -178±1 -160±3

    Table 3.  Individual hydrogen isotope values of odd-numbered n-alkanes (‰, VSMOW) in the plant samples

  • This study reveals that the δ2H values of long-chain n-alkanes are generally less depleted in the peatland than in the non-peatland habitat (Fig. 4). For a single plant species, its δ2Halk values are mainly controlled by the isotopic compositions of source water, the influence of transpiration on soil water and leaf water, and the isotope fractionation during biosynthesis (Sessions, 2016; Sachse et al., 2012). Since the plant samples in this study were collected in the same area, the relevant environmental factors such as mean annual temperature and precipitation are identical. Besides, the soil pH values in these two habitats are quite similar. For a batch of surface soil (0–5 cm; n=24) collected across a habitat gradient (from peatland, wet meadow to dry meadow) in Dajiuhu Basin in 2018, the pH averages at 4.3 with a standard deviation of 0.5 (measured in deionized water/soil volume ratio of 5, unpublished data). Thus, the different patterns of δ2Halk values in the same species growing in the peatland and non-peatland habitats may result from the influence of water content.

    The groundwater level and water level retention time in peatland and non-peatland are quite different. Our high- resolution monitoring in the peatland clearly showed that the water level was always near the peat surface except for some extreme drought intervals (Huang and Meyers, 2019). In addition, the monitoring of δ2H values in porewater collected from different peat layers reveals that the δ2H values in porewater do not act as an important factor to affect the δ2Halk values in peat-forming plants (Huang and Meyers, 2019). Such a setting results in relatively small changes of δ2Halk values in forb and shrub plants except graminoids (Zhao et al., 2018).

    In the relatively dry habitat surrounding the peatland, the groundwater level is entirely below the surface. In this setting, the water deficit will affect the δ2Halk values in leaf wax n-alkanes through the influence on soil water evaporation and leaf transpiration processes (Kahmen et al., 2013a, b). Herein the physiological difference among different species or different plant life forms acts as an essential factor to control the variations of δ2Halk values, as the previous studies on mineral soil growing conditions (e.g., Liu and An, 2019; Sachse et al., 2012).

    Besides, it is cautioned that vascular plants growing in the inundation peatland habitat may be inhibited by the supply of photosynthetic products. In this way, vascular plants may utilize storage sugars for the lipid synthesis. The seasonal monitoring of leaf wax δ2Halk values in tree species from the subtropical region (Huang et al., 2018a) and other regions (Freimuth et al., 2017; Newberry et al., 2015) also observed less negative δ2Halk values in the early stage of leaf development, due to the shortage of photosynthetic supply. Greenhouse experiments also verified that plants growing in a heterotrophic condition frequently had less negative δ2Halk values, using more H atom from the sugar derived NADPH for lipid synthesis (Cormier et al., 2019, 2018). The δ2H valuesof NADPH originating from stored carbohydrates are almost less negative than those from new photosynthetic production (Schmidt et al., 2003).

  • Though the difference of the ACL values between habitats does not pass the t-test, we should be cautious about the interpretation of ACL records in peat sequences. Leaf waxes often play a role in mediating the water loss of leaves, herein the ACL values have been frequently utilized to reflect paleoenvironmental changes (e.g., Diefendorf and Freimuth, 2017; Carr et al., 2014; Bush and McInerney, 2013). Higher ACL values frequently occur in warmer and/or drier conditions (Diefendorf and Freimuth, 2017). The condition seems a little different in the Dajiuhu Basin. Plants growing in the relatively dry setting do not show higher ACL values than their counterparts growing in the peatland. In this way, the influence of plant life forms may play an important role in the ACL changes, as argued in our previous study (Zhao et al., 2018).

    Different from δ2Halk, the δ13Calk values are quite similar between the same species growing in the peatland and non-peatland habitats (Table 2, Fig. 4). Since C29 n-alkane is a significant component in all plant samples, here it is taken as an example for comparisons. For the paired plant samples, the δ13C values of C29 n-alkane only deviate <0.5‰, not distinct with the instrumental error (Table 2). In the synthesis of more plant data from the Dajiuhu Basin, the δ13C values of C29 n-alkane in forbs are a little negative than those in graminoids and shrubs, while the δ13C values of C31 and C33 n-alkanes are quite similar among the life form types (Zhao et al., 2018). These features are consistent with the previous studies in peat sequences, which show quite small deviations of the δ13Calk values of C29 and C31 n-alkanes (<2‰; Wang et al., 2016; Yamamoto et al., 2010a, b). An exception is the ZK-5 peat core retrieved from the Dajiuhu, the large variations of δ13Calk values of C29 n-alkane are interpreted as the uptake of respiration carbon during a drying interval in the mid-Holocene (Huang et al., 2018b).

    In a latest synthesis of results from the Dajiuhu peatland, we argue that the δ2H values of source water and plant life forms (i.e., graminoid vs. forb/shrub) are important factors to control the δ2Halk signals in the surface peat (Huang and Meyers, 2019). This study further suggests the influence of inundation conditions and possibly limited supply of photosynthetic products. Indeed, due to the relatively small sample number in this study, the above discussion is not supported by the statistical analysis. More data are required to testify the habitat influence on the leaf wax molecular, carbon and hydrogen isotope compositions in the near future. In addition, greenhouse incubation experiments are deserved to quantify the influences of various factors on leaf waxes of peat-forming plants.

  • We investigated changes in the leaf wax molecular distributions and hydrogen/carbon isotopic compositions of long-chain n-alkanes in different habitats and different species. The main findings are as follows.

    (1) The alkane ratios (ACL and CPI) and δ13Calk values of long-chain n-alkanes are not distinctive in the same species growing in the peatland and non-peatland habitats. In contrast, three of the four species show quite higher total concentrations of n-alkanes in the relatively dry non-peatland setting than in the peatland.

    (2) The δ2Halk values of long-chain n-alkanes are generally less depleted in the peatland and are comparable among different plant species, which is interpreted as the influence of inundation condition and the possible limited supply of photosynthetic products.

    These results raise caution for the interpretation of leaf- wax-based proxies in the peat deposits. Certainly, more data are required to testify the findings in this study, and to improve the understanding of leaf-wax-based proxies in the peat deposits.

  • This work was supported by the National Natural Science Foundation of China (No. 41877317), the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan (No. GBL1 1612), and the fundamental research funds for the central universities (Nos. CUGCJ1703, CUGQY 1902). Binyan Zhao, Meiling Zhao, Xiaofang Yu, and Kui Wang are thanked for their help in the field and during lipid extraction and analysis. The final publication is available at Springer via https://doi.org/10.1007/s12583-020-1322-x.

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