Life form-specific gradients in compound-specific hydrogen isotope ratios of modern leaf waxes along a North American Monsoonal transect

Abstract

The use of hydrogen isotope ratios (δ(2)H) of sedimentary n-alkanes from leaf waxes has become an important tool for reconstructing paleoenvironmental and ancient hydrologic conditions. Studies of modern plant waxes can elucidate driving ecological mechanisms behind geologic deposits. Here, we used a transect across the North American Monsoon region of the western USA from Tucson, Arizona to Salt Lake City, Utah to study variations in leaf wax δ(2)H among co-occurring plants. Three co-occurring life forms were selected: perennial shrub (rabbit brush, Chrysothamnus nauseosus; sagebrush, Artemisia tridentata); tree (Gambel's oak tree, Quercus gambelii); and annual (sunflower, Helianthus annuus). Our results showed that the distributions and abundances of n-alkanes in perennial plants were similar across all sites and generally did not vary with environmental conditions (e.g., precipitation and temperature). In contrast, variations in n-alkane δ(2)H were significantly correlated with the fraction of the annual precipitation coming during the summer monsoon period. We use a modified Craig-Gordon model to speculate on the possible drivers of the δ(2)H values of leaf wax n-alkanes of plants across the region. The model results suggest that the most likely explanation for variation in wax δ(2)H values was a combination of seasonal source water usage and subsequent environmental conditions.

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

“…Plant δD wax shows a range of ~100‰ along a 20‰ δD r rainfall gradient (Figure a). Such a large range agrees with previous published data (Berke et al, ; Sachse et al, ), underscoring the complex processes involved in the fractionation process (Sachse et al, ). Partitioning the data based upon growth habit shows that trees group in a relatively narrow range (~30‰), while shrubs, forbs, and graminoids show a much larger range (Figure a).…”

“…). Such a large range agrees with previous published data(Berke et al, 2015;Sachse et al, 2012), underscoring the complex processes…”

“…The amplitude of the seasonal rainfall cycle and δD r and timing of leaf production within the growing cycle of the plant have been proposed as important contributors to δD wax , δ 13 C wax , and chain length distribution variability (Berke et al, ; Collins et al, ; Freimuth et al, ; Schwab et al, ; Tipple et al, ). To address this issue, we chose a sampling location that has only one rainy season and a large majority of the plants produce their leaves during or directly after the rainy season.…”

Hydrogen isotope fractionation of leaf wax n-alkanes in southern African soils

“…Several studies show a correlation between δDwax and δDp for different ecosystems (Sachse et al, 2006;Smith and Freeman, 2006;Polissar and Freeman, 2010;Garcin et al, 2012;Berke et al, 2015;Schwab et al, 2015;Feakins et al, 2016).…”

“…However, δDwax has also been shown to be influenced by other factors, such as evapotranspiration or plant growth form, which may bias its signal (e.g. Hou et al, 2008;Feakins and Sessions, 2010a;Seki et al, 2010;Douglas et al, 2012;Kahmen et al, 2013b;Berke et al, 2015). To reliably reconstruct hydrological changes in specific settings it is thus essential to understand the factors affecting δDwax in specific environments.…”