Wild Tropical Forest Soil Characteristics and Composition of Directly Extractable Soil Lipid Fraction
Résumé
Soil characteristics of a wild tropical forest from Cote d`Ivoire and composition of directly extractable soil lipid fraction were investigated. This study was undertaken with the aim to establish soil characteristics, structures and origin of directly extractable lipids components as the first step in understanding diagenesis processes in soil of Cote d`Ivoire. Studies required the use of particle size fractionation and spectrometric (GC/MS) methods. Main characteristics of the soil are the following: neutral pH (6.7), absence of carbonates, sandy texture (88% of sand consisting of silica) and low total organic matter content (4% including 644 mg kg-1 of extractable lipid) localized in fine fraction (90%). Directly extractable lipid fraction is composed by aliphatic series of alkanes, normal alcohols, fatty acids and triterpenes. The fatty acids, by their composition and the prominence of even carbon chains, could originate from higher plants and highlight a strong microbial activity. Long normal and odd carbon chains compose exclusively alkanes while long even carbon chains form alcohols. Such a distribution underlines the double origin (fungi and/or microbial) of these compounds. Few triterpenoids, found in directly extractable lipids, are formed exclusively by cholestene and derivatives. Such a structure indicates either the reductive character of this soil, or the triterpenes vegetal origin.