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 n-alkanes 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 (δ13C) 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) n-alkanes were preserved in soil by association with soil minerals, while mid-chain (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 n-alkanes 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 proportion of new (experimentally-derived) n-alkanes bound to soil minerals.