Figure 4 - available via license: Creative Commons Attribution 4.0 International
Content may be subject to copyright.
Geographic map showing sample sites in Heshui, Lantian and Xi’an and the distribution of compiled modern leaf wax δDn-alkane values of higher plants across the North hemisphere.: Black rectangles are data based upon Liu and Yang, (2008); red dots are additional data points. ( was created by CorelDRAW 12; My co-authors and I grant NPG to publish the image under an Open Acess license; We grant NPG to publish the image in all formats i.e. print and digital).
Source publication
Leaf wax δDn-alkane values have shown to differ significantly among plant life forms (e.g., among grasses, shrubs, and trees) in higher plants. However, the underlying causes for the differences in leaf wax δDn-alkane values among different plant life forms remain poorly understood. In this study, we observed that leaf wax δDn-alkane values between...
Citations
... Internal factors, linked to plant physiology (e.g., biosynthetic pathway, rooting depth) can also contribute to the variation in δ 2 H wax (Smith and Freeman, 2006;Gao et al., 2015;Cormier et al., 2018Cormier et al., , 2019Eley et al., 2018) and modulate the correlation between δ 2 H p and δ 2 H wax , normally expressed as the net (or apparent) 2 H-fractionation between n-alkanes and mean annual precipitation (e.g., ε 29/MAP ) (Liu et al., 2006(Liu et al., , 2016Hou et al., 2007b;Sachse et al., 2012;Gao et al., 2014a;Gamarra et al., 2016;Eley et al., 2018). Despite the resulting high inter-and intra-specific variability characterising δ 2 H wax (e.g., 40‰ between leaves of the same plant; Sachse et al., 2009;Newberry et al., 2015), larger datasets reveal a generally stable correlation between δ 2 H wax and δ 2 H p in plant communities and derived sediments (Chikaraishi and Naraoka, 2003;Sachse et al., 2006;Hou et al., 2008;Rao et al., 2009;Feakins and Sessions, 2010;Chen et al., 2022). ...
Many continental paleoclimate archives originate from wetland sedimentary sequences. While several studies have investigated biomarkers derived from peat-generating vegetation typical of temperate/boreal bogs (e.g., Sphagnum), only scant information is available on emergent plants predominant in temperate/subtropical coastal marshlands, peri-lacustrine and fen environments. Here, we address this gap, focusing on two wetlands in the Mediterranean (Nisí fen and Tenaghi Philippon, Greece). We examined the concentration, homologue distribution, and hydrogen stable isotopic composition (δ²H) of leaf wax n-alkanes in 13 fen plant species, their surrounding soil, and surface water during the wet growing season (spring) and the declining water table period (summer). Our findings indicate that local graminoid species primarily contribute to the soil n-alkane signal, with a lesser influence from forbs, likely owing to differences in morphology and vegetation structure. The δ²H values of surface and soil water align with local average annual precipitation δ²H, reflecting winter-spring precipitation. Consistently, the average δ²H of local surface, soil, and lower stem water showed negligible evaporative enrichment, confirming minimal ²H-fractionation during water uptake. We find that δ²H values of source water for wax compound synthesis in local fen plants accurately mirror local annual precipitation. Furthermore, despite differences between leaves and lower stems in n-alkane production rates, their δ²H values exhibit remarkable similarity, indicating a shared metabolic substrate, likely originating in leaves. Our net ²H-fractionation values (i.e., precipitation to leaf n-alkanes) align with those in Chinese highlands and other similar environments, suggesting consistency across diverse climatic zones. Notably, our data reveal a seasonal decrease in the carbon preference index (CPI) in plant samples, indicating wax lipid synthesis changes associated with increased aridity. Additionally, we introduce a new parity isotopic difference index (PID) based on the consistent δ²H difference between odd and even n-alkane homologues. The PID demonstrates a strong anticorrelation with plant CPI, suggesting a potential avenue to trace long-term aridity shifts through δ²H analysis of odd and even n-alkane homologues in sedimentary archives. While further development of the PID is necessary for broad application, these findings highlight the intricate interplay between plant physiology, environmental parameters, and sedimentary n-alkanes in unravelling past climatic conditions.
... Later, based on a study of modern vegetation in northwestern China, Liu et al. (2006) suggested that δ 2 H wax values manifest themselves as differences among different plant life forms (e.g., trees, shrubs, and herbs), instead of the photosynthetic pathways. Then, recent studies have observed that δ 2 H wax values differ markedly between plant lineage taxonomies (dicots vs. monocots) at both global and regional scales, with monocots being more negative compared to dicots by about 30‰ (Liu J Z et al., 2016(Liu J Z et al., , 2022. Again, given the isotopic differences mentioned above, δ 2 H wax and δ 13 C wax can also effectively reflect the contribution of different type plants. ...
Serving as one of the largest rivers in terms of both sediment and organic carbon transport fluxes in the world, the Yellow River plays a crucial role in regional biogeochemical process as well as in the global carbon cycle. However, although a large number of studies have been carried out on the flux, composition, source and seasonal variation of total particulate organic carbon in the Yellow River so far, studies on molecular biomarkers at different spatial and temporal scales are still scarce. In this study, we focus on the molecular and hydrogen isotopic properties of leaf wax n-alkanes among different types of samples which obtained from different seasons (flood vs. non-flood) along the lower Yellow River. The molecular distribution of n-alkanes show that the riparian topsoils are subject to inputs from the overlying vegetation, while the suspended sediments from the flood season are characterized by the mixing of soil materials which originate from various stratigraphy with different ages on the Chinese Loess Plateau. Due to the contrasting hydrodynamic conditions, the n-alkanes in suspended sediments also show distinct molecular composition between flood and non-flood seasons. Additionally, considering the effect of climatic factors, the proportion of monocots in flood-season suspended sediments is calculated from a semi-quantitative perspective using δ 2 H wax. Our findings may bring to light new considerations for the interpretation of leaf wax proxies in studies of organic matter sources of Yellow River.
... The ε app is also associated with the leaf-wax syntheses, which vary between plant functional type (PFT), species, and ecosystem (Kahmen et al., 2013a(Kahmen et al., , 2013b. The previous studies observed quite a large variation in δ 2 H n-alkane and ε app values of gymnosperms and angiosperms at species level (Kahmen et al., 2013a, b;Liu et al., 2016;Lane, 2017;Diefendorf and Freimuth, 2017). Additionally, higher δ 2 H n-alkane values are observed in gymnosperms compared to angiosperms (Liu et al., 2016) growing under similar environmental conditions. ...
... The previous studies observed quite a large variation in δ 2 H n-alkane and ε app values of gymnosperms and angiosperms at species level (Kahmen et al., 2013a, b;Liu et al., 2016;Lane, 2017;Diefendorf and Freimuth, 2017). Additionally, higher δ 2 H n-alkane values are observed in gymnosperms compared to angiosperms (Liu et al., 2016) growing under similar environmental conditions. The probable role of biological factors inherited from plant taxonomies has been suggested to control the 2 H enrichment in gymnosperms (Lui et al., 2016). ...
... Additionally, our study reveals a difference in for C 29 (C 31 ) homologues showing ∼ 45 ‰ (∼60 ‰) more fractionation in gymnosperms than angiosperms (Table S2). This opposes the findings of Liu et al. (2016), who reported similar values for both gymnosperms and angiosperms on a global scale. Therefore, our study suggests the need for region-specific fractionation values to improve the reliability of palaeo-rainfall reconstructions (e.g., Jha et al., 2020Jha et al., , 2021. ...
The responses of angiosperms and gymnosperms to environmental variables (e.g., rainfall [MAP], temperature [MAT] and pCO2) remain ambiguous and require systematic investigation. This study monitored the plants' responses to changing environments and measured variations in molecular n-alkane indices, δ13Cbulk, δ13Cn-alkanes, and δ2Hn-alkanes values in woody gymnosperms (n = 36) and angiosperms (n = 17) from an altitudinal gradient (0.9 to 3.8 km) in the Himalayas.
The results indicate that δ13Cbulk values in angiosperms show a moderate correlation with altitude, MAP, and pCO2, while gymnosperms show no response in their δ13Cbulk. The δ13Cn-alkanes values in angiosperms remain unaffected by MAP, MAT, and pCO2, whereas gymnosperms exhibit a moderate negative correlation. The fractionations between δ13Cn-alkanes and δ13Cbulk values (ɛalk/leaf) are approximately –4.0±1.6‰ and –5.6±1.5‰ for gymnosperms and angiosperms, respectively. In gymnosperm, the fractionation between δ2Hn-alkane and δ2Hrain (ɛalk/rain) is –133.2±39.8‰ and –122.8±38.0‰ (C31), while in angiosperm, it is –88.5±44.6‰ (C29) and –62.4±22.9‰ (C31). The δ2Hn-alkane values in gymnosperms and angiosperms are weakly and positively influenced by MAT and MAP, respectively. We found that gymnosperms are enriched in 13C (∼1.5-3.0‰) and depleted in 2H (∼56-60‰) compared to angiosperms; this pattern is consistent throughout the latitudes sampled in this study. The species-specific isotopic response to environmental factors is primarily driven by lower stomatal conductance, smaller leaf-size, and presence of complex tracheids in gymnosperms compared to angiosperms. The statistical K-means algorithm of dual isotope analysis (δ13Cn-alkanes and δ2Hn-alkane) provided two distinct clusters with an accuracy of 70% for angiosperms and gymnosperms, which has implications for studying past vegetation transitions.
... It has been suggested that these differences originate due to specific discrimination against 2 H between distinct photosynthetic pathways (Chikaraishi et al., 2004), as well as due to different pools of biosynthetic source waters fed by different mixtures of enriched leaf water and unenriched soil water (Kahmen et al., 2013a), or due to both processes. Moreover, studies analyzing plants by growth form (Griepentrog et al., 2019;Liu et al., 2016) or even at the species level (Gao et al., 2014) show a strong control of vegetation type or species on ε wax/pre , explained by physiological and biochemical factors that vary among different plant taxa (Gao et al., 2014;Liu et al., 2016). In addition to the vegetation effects, it has been identified that ε wax/pre values become higher as aridity intensifies (Douglas et al., 2012;Feakins and Sessions, 2010;Garcin et al., 2012;Goldsmith et al., 2019;Herrmann et al., 2017;Li et al., 2019;Polissar and Freeman, 2010;Smith and Freeman, 2006). ...
... It has been suggested that these differences originate due to specific discrimination against 2 H between distinct photosynthetic pathways (Chikaraishi et al., 2004), as well as due to different pools of biosynthetic source waters fed by different mixtures of enriched leaf water and unenriched soil water (Kahmen et al., 2013a), or due to both processes. Moreover, studies analyzing plants by growth form (Griepentrog et al., 2019;Liu et al., 2016) or even at the species level (Gao et al., 2014) show a strong control of vegetation type or species on ε wax/pre , explained by physiological and biochemical factors that vary among different plant taxa (Gao et al., 2014;Liu et al., 2016). In addition to the vegetation effects, it has been identified that ε wax/pre values become higher as aridity intensifies (Douglas et al., 2012;Feakins and Sessions, 2010;Garcin et al., 2012;Goldsmith et al., 2019;Herrmann et al., 2017;Li et al., 2019;Polissar and Freeman, 2010;Smith and Freeman, 2006). ...
The hydrogen isotope composition of leaf wax biomarkers (δ2Hwax) is a valuable tool for reconstructing continental paleohydrology, since it serves as a proxy for the hydrogen isotope composition of precipitation (δ2Hpre). To yield robust palaeohydrological reconstructions using δ2Hwax in marine archives, it is necessary to examine the impacts of regional climate on δ2Hwax and assess the similarity between marine sedimentary δ2Hwax and the source of continental δ2Hwax. Here, we examined an aridity gradient from hyperarid to humid along the Chilean coast. We sampled sediments at the outlets of rivers draining into the Pacific as well as soils within catchments and marine surface sediments adjacent to the outlets of the studied rivers and analyzed the relationship between climatic variables and δ2Hwax values. We found that apparent fractionation between leaf waxes and source water is relatively constant in humid and semiarid regions (average: −121 ‰). However, it becomes less negative in hyperarid regions (average: −86 ‰) as a result of evapotranspirative processes affecting soil and leaf water 2H enrichment. We also observed that along strong aridity gradients, the 2H enrichment of δ2Hwax follows a non-linear relationship with water content and water flux variables, driven by strong soil evaporation and plant transpiration. Furthermore, our results indicate that δ2Hwax values in marine surface sediments largely reflect δ2Hwax values from the continent, confirming the robustness of marine δ2Hwax records for paleohydrological reconstructions along the Chilean margin. These findings also highlight the importance of considering the effects of hyperaridity in the interpretation of δ2Hwax values and pave the way for more quantitative paleohydrological reconstructions using δ2Hwax.
... Despite the relatively steady ε app values overall, the ε app values became slightly lower at elevations above 3000 m asl (Fig. 4). ε app could be affected by complex factors such as soil evaporation, plant transpiration, biosynthesis processes (Sachse et al., 2012;Liu and An, 2018), mean annual precipitation (MAP) and aridity index (Liu et al., 2023a), and plant types or plant life forms (Liu et al., 2006(Liu et al., , 2016Hou et al., 2007Hou et al., , 2018Liu and Yang, 2008;Daniels et al., 2017;Zhang et al., 2017;Bai et al., 2020;He et al., 2020). Among these factors, soil evaporation and plant transpiration both controlled by hydroclimatic factors lead to 2 H-enrichment relative to precipitation (Feakins and Sessions, 2010;Kahmen et al., 2013aKahmen et al., , 2013b, counteracting the negative fractionation associated with leaf wax n-alkane biosynthesis (Sessions et al., 1999;Cormier et al., 2018). ...
... These processes synergistically resulted in relatively steady ε app values (Smith and Freeman, 2006;Hou et al., 2008;Daniels et al., 2017;Zhang et al., 2017; Liu and An, 2019). Thus, the variations of ε app probably resulted from the MAP or aridity index (Liu et al., 2023a) and plant types or plant life forms (Liu et al., 2006(Liu et al., , 2016Bai et al., 2020). ...
... Our ε app overlaps the reported ε app mean species value of -94 ± 21 ‰ by Feakins and Sessions (2010), -89 ± 28 ‰ by O'Connor et al. (2020) and -89 ± 14 ‰ by Daniels et al. (2017). The ε app calculated from our δ 2 H C29 (and δ 2 H LMWL ) is -99 ± 21 ‰ and falls within the error range of the mean high-latitude angiosperm ε app of -119 ± 29 ‰ by Liu et al. (2016), the data from which were later included in the global plant-scale data set mean values of -116 ± 5 ‰, reported by Liu and An (2019), also calculated from δ 2 H C29 values (Fig. 8). When comparing the sedimentary mean δ 2 H n-alk (δ 2 H C29 = -202 ‰, δ 2 H C27 = -189 ‰ and δ 2 H C25 = -182 ‰) in our study and the modern mean yearly δ 2 H precip values, these yield an ε app values of -133 ‰, -118 ‰ and -110 ‰, respectively, which have larger absolute values than the ε app calculated from our plant leaves (-93 ± 21 ‰). ...
... Typically, vegetation change can introduce variability in a region's ε app values and impact interpretation of paleo-precipitation δD values (Hou et al., 2007;Feakins and Sessions., 2010;Liu et al., 2016). In monsoonal climate past vegetation shifts from evergreen to deciduous taxa have been reported (Kumaran et al., 2013;Prasad et al., 2014). ...
... δD values reflect both the δD values of precipitation, deuteriumenriched leaf water, and evapotranspiration (Kahmen et al., 2011). Monocotyledonous (grasses) are deuterium depleted relative to dicotyledonous (forbs, shrubs, trees) species, and in general, more negative values indicate wetter conditions, and more positive values indicate drier conditions (Liu et al., 2016). Present-day δ 2 H (‰, V-SMOW) are estimates according to The Online Isotopes in Precipitation Calculator, version 3.1 (Bowen, 2022). ...
... Within a single geographic location, species variation ranges of up to 96 ‰ for n-alkane and 85 ‰ for cellulose δ 2 H values, and 18 ‰ for cellulose δ 18 O values, have been found (Wang et al., 1998;Chikaraishi et al., 2004;Gao et al., 2014;Liu et al., 2016;Eley et al., 2018;Griepentrog et al., 2019;Holloway-Phillips et al., 2022). Variation in precipitation and soil water δ 2 H and δ 18 O values is relatively small within a given region and timepoint, and similar for all species (Brinkmann et al., 2018(Brinkmann et al., , 2019Nelson et al., 2021), so the large observed species variation in organic compound δ 2 H and δ 18 O values must be attributed to species variation in leaf water δ 2 H and δ 18 O values, species variation in biosynthetic 2 H-and 18 O-fractionation, or to variation in both. ...
... This study indicated that the d 2 H wax proxy was probably not reliable by itself for paleoelevation studies in that region, thus the dual-proxy coupling of d 2 H wax -brGDGTs values was urgently required. Additionally, d 2 H wax values are also affected by evapotranspiration via soils and leaves (Feakins and Sessions, 2010;Kahmen et al., 2013), biosynthetic processes (Sachse et al., 2012;Sessions, 2016), and plant types from regional to global scales (dicots versus monocots; Liu et al., 2016Liu et al., , 2017Liu and An, 2019;Liu et al., 2022). Thus, the d 2 H wax proxy reflects both environmental (e.g., elevation) and biochemical conditions, but these combined factors make it complex for the d 2 H wax proxy to reconstruct paleoelevation. ...
The multi-proxy approach is becoming an effective means to reduce uncertainties and errors compared to the single proxy approach. In this study, we investigated leaf wax biomarker and brGDGTs in topsoils along a semiarid elevation transect on the Chinese Loess Plateau. We found that both leaf wax n-alkane d2Hwax values and brGDGTs-derived MBT0 5ME decreased significantly with elevation, and thus the coupled d2Hwax-MBT0 5ME proxy can improve correlation coefficients (R2 ¼ 0.96) compared to a single proxy (R2 ¼ 0.82 and 0.90 for d2Hwax and MBT05ME, respectively) and reduce the uncertainty (RMSE ¼ 230 m) relative to a single proxy (RMSE ¼ 275 m and 360 m for d2Hwax and MBT05ME, respectively) in elevation
estimates. Then we tested the effectiveness and advantages of coupled d2Hwax-MBT05ME proxy from surface soils on the Tibetan Plateau compared to a single proxy. Collectively, the coupled d2Hwax-MBT05ME proxy can be used as a potentially advantageous proxy for reconstructing paleoelevation in semiarid
conditions.
