Molecular and carbon isotopic composition of leaf wax in vegetation and aerosols in a northern prairie ecosystem

Abstract

We measured the molecular and carbon isotopic composition of major leaf wax compound classes in northern mixed mesic prairie species (Agropyron smithii, Stipa viridula, Bouteloua gracilis, Tragopogon dubius) and in selected crops (Triticum aestivum, Brassica napus, Hordeum vulgare, Medicago sativa) of southern Alberta and also in aerosols collected 4 m above the prairie canopy. Our aims were to better constrain the wax biosynthetic carbon isotopic fractionation relative to the plant's carbon isotopic discrimination and to quantitatively assess the correspondence between wax composition in vegetation and in boundary layer aerosols. Wax molecular composition of the C(3)prairie species and bulked vegetation was characterized by high abundance of C(28) n-alkanol and C(31) n-alkane compounds whereas the C(4) species B. gracilis had several co-dominant n-alkanol and n-alkane compounds. Wax molecular composition of crop species differed significantly from that of prairie vegetation and was often dominated by a single compound. Results indicate that leaf wax isotopic composition is quantitatively related to the plant's carbon isotopic discrimination. Although species variations were evident, n-alcohol, n-acid and n-alkane wax compounds were on average depleted in (13)C by approximately 6.0+/-1 per thousand relative to total plant carbon. The magnitude of the depletion in wax delta(13)C was unaffected by environmental factors which altered photosynthetic carbon isotopic discrimination. No consistent difference in the magnitude of wax biosynthetic fractionation was observed between C(3) and C(4) species, indicating that photosynthetic pathway has little influence on the isotopic fractionation of wax during biosynthesis. The isotopic composition of ablated waxes in aerosols collected above the canopy was similar to that of the grassland vegetation but the molecular composition differed significantly and indicated that the source "footprint" of the ablated leaf wax particles we sampled in boundary layer air masses was of a regional or larger spatial scale.

Strengthening of North American dust sources during the late Pliocene (2.7 Ma)

“…Lastly, the CPI values, molecular distribution, as well as the δ 13 C values for the n-alkanes and n-alkan-1-ols are similar to those found at present in air masses originating from the North American continent (Conte and Weber, 2002;Conte et al, 2003) and significantly different from those found in dust originating from Northern Africa (Conte and Weber, 2002;Huang et al, 2000;Schefuss et al, 2003a), at present the largest source of dust in the world. In this regard, the most distinct features are the dominance of the C 26 -homologues in the n-alkan-1-ol and n-alkanoic acid molecular distributions (Fig.…”

“…Long-chain n-alkanes (C 21 − C 33 ) with a clear odd over even predominance and n-alkan-1-ols (C 22 − C 32 ) with a clear even over odd predominance are common constituents of the epicuticular waxes of terrestrial higher plants such as angiosperms and gymnosperms (e.g., Bianchi, 1995;Eglinton and Hamilton, 1967; see review in Diefendorf et al, 2011). They are a major component of modern dust even in remote ocean areas (Conte and Weber, 2002;Conte et al, 2003;Gagosian et al, 1981;Simoneit et al, 1977) as they can easily be removed from the leaf surface by wind or rain, especially by sandblasting during dust storms, or entrained as part of soil and transported over large distances. Numerous studies therefore used the accumulation of these lipids in distal marine sediments far from major fluvial inputs to infer changes in aeolian input to the open ocean (e.g., López-Martínez et al, 2006;Madureira et al, 1997;Martínez-Garcia et al, 2009.…”

“…, and n-alkan-1-ols (C 26 +C 28 ) (orange and purple arrow), together with the range of δ 13 C in these compounds in aerosol measurements from Bermuda (green box) and off the coast of Africa (pink box). In addition, average δ 13 C values for long-chain n-alkanes and n-alkan-1-ols in dust samples obtained off the coast of Africa (star 1-3) and from within the North American continent (star 4) are shown (Conte and Weber, 2002;Conte et al, 2003;Huang et al, 2000;Simoneit, 1997). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)…”

Exploiting Natural Variation to Uncover an Alkene Biosynthetic Enzyme in Poplar

“…D leaf was lower in AM trees versus AP trees, suggesting lower long-term WUE ( Figure 7B). However, wax composition itself can affect carbon discrimination measurements, as wax is depleted in 13 C relative to total plant carbon (Conte et al, 2003). As such, the higher D leaf in AP could also be a consequence of the higher wax load per surface area.…”

Decomposition, δ13C, and the “lignin paradox”

“…Isotopic fractionation also occurs during subsequent biosynthesis, with depletion generally increasing with the number of steps required for biosynthesis. Thus, lignin of wood is typically depleted by 3.0-4.4‰ relative to cellulose (Benner et al 1987;Goñi and Eglinton 1996;Spiker and Hatcher 1987;Loader et al 2003), and plant lipids are even more depleted in 13 C (Conte et al 2003).…”