Variation in δD values of a single, species‐specific molecular biomarker: a study of miliacin throughout a field of broomcorn millet (Panicum miliaceum L.)

Abstract

Compound-specific δD analyses of land plant-derived biomarkers preserved in lake sediments are gaining increasing interest in paleoclimatic studies because of their potential to record essential information on the climatic conditions that prevailed at the time of their synthesis. The accuracy of inferences about climate from these analyses could be better constrained with more study of the variability in the δD values of possible inputs at catchment scales. We measured the δD values of miliacin (olean-18-en-3β-ol methyl ether) extracted from the seeds of millet plants collected in 21 stands spatially distributed in a field with visually heterogeneous soil organic matter contents. The use of a single molecular biomarker extracted from a single plant species eliminates the possibility of variability caused by differences in plant type. The δD values differed between plants by as much as 50‰ and the average δD values per stand differed from one another by a maximum of 30‰. Thus, the δD values of a single, species-specific biomarker can vary markedly among plants even within a similar climate. Differences in δD values within stands could be as high as between stands, suggesting that the δD values are not related to macroscale heterogeneities in soil organic matter content. In addition, δD values were unrelated to factors indicative of differences in environment such as plant height, seed weight or miliacin concentration. The average miliacin δD value was representative of the area sampled, however, since it was normally distributed (p < 0.05).

Hydrogen isotopic fractionations during syntheses of lipid biomarkers in the seeds of broomcorn millet (Panicum miliaceum L.) under controlled environmental conditions

“…The total extract was separated into neutral, acidic and polar fractions by ion exchange chromatography on aminopropyl-bonded silica, as per Jacob et al (2005). The different classes of compounds (nalkanes and miliacin) were purified from the neutral fraction by flash chromatography on activated silica using solvents of increasing polarity (as per Bossard et al, 2011). Aliphatic hydrocarbons, such as n-alkanes, were first eluted with 2 mL of heptane, then aromatic hydrocarbons were eluted with 1 mL heptane and then 2 mL heptane:toluene 2:1.…”

“…1), a pentacyclic triterpene methyl ether, is a specific biomarker of broomcorn millet (Panicum miliaceum), which is a C4 plant. This biomarker was found in the sediments of lake Le Bourget dated as prior to the Bronze Age (Jacob et al, 2008a,b;Bossard et al, 2011;Bossard, 2013). It was also used as a tracer of C4 grasses in tropical soils (Schwab et al, 2015).…”

Paleohydrological and paleoenvironmental changes recorded in terrestrial sediments of the Paleocene–Eocene boundary (Normandy, France)

“…According to Sachse et al (2012), the hydrogen isotopic composition (δD) of higher plantderived leaf wax n-alkanes is impacted, in order of increasing importance, by: (i) the δD values of meteoric waters, which are affected by the source of moisture, the temperature at the precipitation site and the amount of precipitation (Dansgaard 1964;Epstein and Yapp, 1976;Sauer et al, 2001;Chikaraishi and Naraoka, 2003;Sachse et al, 2004); (ii) the extent of soil-water evaporation and leaf-water transpiration, which depend on temperature and humidity (Smith and Freeman, 2006;Feakins and Sessions, 2010); (iii) interspecific variability, which depends on the plant photosynthetic pathway, physiology and biochemistry (Smith and Freeman, 2006;Chikaraishi and Naraoka, 2007); (iv) local environmental parameters that are very likely buffered when molecular biomarkers are integrated into sedimentary archives (Bossard et al, 2011).…”

Distribution of miliacin (olean-18-en-3β-ol methyl ether) and related compounds in broomcorn millet (Panicum miliaceum) and other reputed sources: Implications for the use of sedimentary miliacin as a tracer of millet

“…P. miliaceum seeds of the "sunrise" subspecies were collected from 76 plants at maturity from a cultivated field in Mézières-lez-Cléry, France (Bossard et al, 2011). For two of them, leaves, roots and stems were also analysed.…”