The fate of plant wax lipids in a model forest ecosystem under elevated CO2 concentration and increased nitrogen deposition

Abstract

Atmospheric CO2 concentration and nitrogen (N) deposition have been altered by anthropogenic activity and they affect global biogeochemical cycles. It is still not clear how these environmental changes influence the storage and cycling of organic matter (OM) in soils, although this plays a key role in the biogeochemistry of terrestrial ecosystems. Here, we used nalkanes as biomarkers for plant-derived OM in specific soil fractions. We investigated the effect of elevated CO2 concentration and increased N deposition on the molecular and isotopic (δ 13 C) composition of n-alkanes in above-ground and below-ground tree biomass (beech and spruce) and soil density fractions. The n-alkane distribution patterns of spruce needles and root biomass were well reflected in those of particulate soil OM. Long chain (C27-34) nalkanes were preserved in soil by association with soil minerals, while midchain (C20-27) n-alkanes from plant biomass and particulate soil OM were ultimately degraded due to lack of physical protection. Renewal of n-alkanes was lower in roots and spruce needles than in beech leaves. Similar low renewal of n-alkanes in soil reflected the low input of n-alkanes from plant biomass to the soil n-alkane pool. n-Alkane biosynthesis in beech leaves was modified under high N deposition and similar effects were observed for nalkanes in mineral soil fractions and bulk soil. Here, different biosynthesis of n-alkanes in beech leaves under high N deposition consequently led to a modified input of n-alkanes from plant biomass to soil, with a relatively low 3 proportion of new (experimentally-derived) n-alkanes bound to soil minerals.

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

“…The differences could be related to the different biomass input on the one hand and large amount of lignite dust and the low biomass input on the other hand, thus hampering degradation at this site. The faster turnover of n-fatty acids than nalkanes was also confirmed by Wiesenberg et al (2008a) and Griepentrog et al (2015Griepentrog et al ( , 2016. This may also offer opportunities to apply such differences between molecular classes and their response to external factors to trace transformations and input of organic matter in soils (Feng and Simpson, 2007).…”

“…Regardless of these differences, they too found the aliphatic compounds to be preferentially preserved in the silt and clay fractions and again linked this to strong interactions with the present clay minerals. In a recent study, Griepentrog et al (2015Griepentrog et al ( , 2016 confirmed the higher residence time of organic matter in small size density fractions when compared to macroaggregates as a result of interaction with the mineral phase. This implies an improved preservation of organic matter associated with higher density and thus mineral association when compared to organic matter associated with lower density.…”

“…Greenhouse experiments showed that elevated CO 2 concentration affects the relative composition of saturated and unsaturated fatty acids in wheat plants (Williams et al, 1994(Williams et al, , 1995(Williams et al, , 1998. However, rising nitrogen fertilization and rising temperature can lead to competing trends (Williams et al, 1995;Griepentrog et al, 2016). Although specific abundances of individual long-chain alkanes and alcohols changed under elevated CO 2 concentration, the overall lipid composition expressed as ACL and CPI did not change (Huang et al, 1999).…”

Understanding the effects of early degradation on isotopic tracers: implications for sediment source attribution using compound-specific isotope analysis (CSIA)

“…Sediment fingerprinting based on CSIA utilizes the vegetation-specific isotopic signatures of the lipid biomarkers to discriminate the sediment sources by the fraction attributable to the major land uses present in the catchment. In particular, carbon isotopic composition (δ 13 C values) of individual long-chain fatty acids (Gibbs, 2008;Blake et al, 2012;Hancock and Revill, 2013;Alewell et al, 2016;Brandt et al, 2016;Mabit et al, 2018), long-chain n-alkanes (Seki et al, 2010;Cooper et al, 2015;Chen et al, 2016), and plant-family-specific biomarkers (e.g. triterpenyl acetates produced by Asteraceae) (Lavrieux et al, 2019) has been used to trace freshwater sediments (Lavrieux et al, 2019).…”

“…Also, it has been shown that within the soil particle size fractions and density fractions, the stability and composition of the tracer signal may change (Cayet and Lichtfouse, 2001;Quénéa et al, 2006;Griepentrog et al, 2016). In previous CSIA-based fingerprinting studies, the silt-clay fraction (< 63 µm) or < 100 µm fraction has been chosen to extract the representative source signature (Gibbs, 2008;Blake et al, 2012;Hancock and Revill, 2013;Cooper et al, 2015). The bulk soil fraction (< 2 mm) has also been used (Alewell et al, 2016).…”