Is the maximum carbon number of long-chain n-alkanes an indicator of grassland or forest? Evidence from surface soils and modern plants

Abstract

The molecular distribution of long-chain n-alkanes in 62 soil samples collected from diverse locations across eastern China was analyzed. The long-chain n-alkanes were mostly dominated by n-C 29 or n-C 31 , regardless of the overlying vegetation type at each site. The results were compared with those summarized from the literature, covering more than 100 soil samples within China and more than 300 genera of modern plants distributed worldwide. There were similar n-alkane distribution patterns for most genera, with no clear differences among grasses, shrubs, and trees. The evidence from analyses of surface soils and modern plants indicates that the relationship between the molecular distribution of long-chain n-alkanes of surface soils and source vegetation is highly complex, and is influenced by many factors. Further, it is suggested that source vegetation types should not be simply inferred from distribution patterns of long-chain n-alkanes in sediments.

Opportunities and limitations related to the application of plant-derived lipid molecular proxies in soil science

“…In all studies, the straight-chain lipid patterns lacked the odd-over-even chain length predominance typical of higher plants Xie et al, 2009;Zhou et al, 2009). Nevertheless, in a large survey a clear odd-overeven chain length predominance was found in spite of such potentially intense aerosol-derived input (Rao et al, 2011). This indicates that even in areas under large aerosol deposition, as in the case of the intensive anthropogenic pollution associated with fossil fuel burning, the effect of aerosol deposition on n-alkane patterns in the soil is limited as a result of the large in situ input via the roots and leaves of the local vegetation.…”

Spatial and temporal variability in vegetation and coal facies as reflected by organic petrological and geochemical data in the Middle Miocene Çayirhan coal field (Turkey)

“…More specifically, it was suggested that long-chain n-alkanes dominated by n-C 27 or n-C 29 indicate forest, while those dominated by n-C 31 indicate grassland. However, the relationship between the molecular distribution of n-alkanes in sediments and vegetation has been found to be influenced by many factors (Rao et al, 2011).…”

Biogeochemical evidence for freshwater periods during the Last Glacial Maximum recorded in lake sediments from Nam Co, south-central Tibetan Plateau

“…Although n-C 29 has previously been interpreted as an indicator for tree vegetation (Schwark et al 2002), it probably represents herbaceous terrestrial vegetation at Nam Co because it is found mainly in alpine meadows and steppe grasses that dominate the local, treeless vegetation. A distinction between the signal of woody and herbaceous plants is not possible because of mixing of different organic matter sources within the lake sediment (Rao et al 2011). On the other hand, n-C 29 was also found in higher proportions in emergent macrophyte species Hippuris and lower abundances in submerged plants (Potamogeton, Batrachium), with more affinity to shallow lakes that experience dryer conditions (Ficken et al 2000;Aichner et al 2010a).…”