A hierarchical framework for disentangling different controls on leaf wax δD_n-alkane values in terrestrial higher plants

Leaf wax δD_n-alkane values have been widely utilized in terrestrial paleoenvironmental research, and numerous studies have reported that leaf wax δD_n-alkane values were affected by a lot of factors. However, the current knowledge regarding the constructive relationships among these factors is still unclear. Based upon a limited compilation of available δD_n-alkane records from published literature across the world, we proposed a hierarchical framework of three-level controls on leaf wax δD_n-alkane values by using an Interpretive Structural Modeling (ISM). Precipitation δD, plant types and evapotranspiration are the first-level controls that serve as direct co-controls on leaf wax δD_n-alkane values in higher plants, on average contributing 47 ± 22%, 20 ± 9.8% and 33%, respectively. The proportions of different controls on leaf wax δD_n-alkane values vary significantly over the world, probably responsible for the across-site substantial variability of isotopic fractionation (ε_app) between leaf wax δD_n-alkane values and precipitation δD. Moreover, extra factors (e.g., salinity, aridity, seasonality etc.) and climate parameters (e.g., temperature, relative humidity, light intensity etc.) execute the second-level and third-level controls on leaf wax δD_n-alkane values, respectively. They play indirect controls, through affecting the first-level controls, and thus are translated into leaf wax δD_n-alkane values. To quantitatively disentangle these controls on leaf wax δD_n-alkane values is important for better understanding the spatial-temporal variability of sedimentary δD_n-alkane values.