Predicting leaf wax n‐alkane ²H/¹H ratios: controlled water source and humidity experiments with hydroponically grown trees confirm predictions of Craig–Gordon model

Abstract

The extent to which both water source and atmospheric humidity affect δ(2)H values of terrestrial plant leaf waxes will affect the interpretations of δ(2)H variation of leaf waxes as a proxy for hydrological conditions. To elucidate the effects of these parameters, we conducted a long-term experiment in which we grew two tree species, Populus fremontii and Betula occidentalis, hydroponically under combinations of six isotopically distinct waters and two different atmospheric humidities. We observed that leaf n-alkane δ(2)H values of both species were linearly related to source water δ(2)H values, but with slope differences associated with differing humidities. When a modified version of the Craig-Gordon model incorporating plant factors was used to predict the δ(2)H values of leaf water, all modelled leaf water values fit the same linear relationship with n-alkane δ(2)H values. These observations suggested a relatively constant biosynthetic fractionation factor between leaf water and n-alkanes. However, our calculations indicated a small difference in the biosynthetic fractionation factor between the two species, consistent with small differences calculated for species in other studies. At present, it remains unclear if these apparent interspecies differences in biosynthetic fractionation reflect species-specific biochemistry or a common biosynthetic fractionation factor with insufficient model parameterization.

Evaluation of bacterial glycerol dialkyl glycerol tetraether and <sup>2</sup>H–<sup>18</sup>O biomarker proxies along a central European topsoil transect

“…8). Likewise, the ε bio values reported in the literature for 2 H of nalkanes can be off from −160 ‰ by tens of per mille (Feakins and Sessions, 2010;Tipple et al, 2015;Feakins et al, 2016;Freimuth et al, 2017). The degree to which hydrogen originates from NADPH rather than leaf water is important, because NADPH is more negative (Schmidt et al, 2003).…”

Leaf Wax δD and δ13C in Soils Record Hydrological and Environmental Information Across a Climatic Gradient in Israel

“…Across global data sets, rainfall δD (δD r ) is the strongest predictor of δD wax (Aichner et al, 2010;Polissar & Freeman, 2010;Sachse et al, 2004Sachse et al, , 2006Sachse et al, , 2012Smith & Freeman, 2006). However, at the local scale, plant type, leaf transpiration, and soil evaporation can modify the δD wax signal (Kahmen et al, 2013;Sachse et al, 2012;Tipple et al, 2014). Different plant types exhibit distinct offsets from rainfall δD and are an important factor to consider when interpreting fossil δD values.…”

Influence of salinity on hydrogen isotope fractionation in Rhizophora mangroves from Micronesia

“…The difference between δ 2 H Lipid values and δ 2 H Water values is expressed using the net fractionation factor, α Lipid-Water = ( 2 H/ 1 H) Lipid /( 2 H/ 1 H) Water . The magnitude of α Lipid-Water is sensitive to variables such as plant type (Luo et al, 2006;Smith and Freeman, 2006;Hou et al, 2007), relative humidity (Feakins and Sessions, 2010;Kahmen et al, 2013a, b;Tipple et al, 2014), and light levels (Luo and Yang, 2008;Yang et al, 2009;Yang et al, 2011). In order to reliably use sedimentary δ 2 H Lipid values to infer information about past changes in climate, it is important to better understand causes of variability in α Lipid-Water , which can result in changes to δ 2 H Lipid values that are not solely driven by changes in δ 2 H Precipitation values.…”