Molecular and isotope characterization of soil lipids along a savannah (C4)/eucalyptus (C3) chronosequence (Pointe-Noire, Congo)

The surfaces dedicated to forestry plantations are rapidly increasing throughout the world, especially in the tropics [1]. The impacts of such a rapid afforestation on global carbon cycle and on soil that constitutes one of its key compartment, is therefore a critical issue [2]. Stable carbon isotope characterization of C4/C3 chronosequences has proven useful in assessing the dynamics of organic carbon in soils [3]. Lipids are important contributors to organic matter in soils since they can influence aggregate stability, water retention and fertility. Nevertheless, little is known on the effects of afforestation on lipid composition and dynamics in tropical soils. The eucalyptus plantation located in the area of Pointe-Noire (Republic of Congo) is a prime field to study the impact of afforestation on organic carbon dynamics. Indeed, a eucalyptus forest (C3) has been progressively planted on savannah (C4) during the last 30 years [4]. Lipids were solvent-extracted from the top soil (0-20 cm) of stands planted for 7, 17, 30 years, and of a reference plot of the initial savannah. They were also extracted from the main savannah species and from eucalyptus.