Terpenoid profiling of keystone plant species of the Bale Mountains, Ethiopia: Implications for chemotaxonomy and paleovegetation studies

The Sanetti Plateau is Africa's largest Afro-alpine ecosystem. As part of an ongoing effort to reconstruct the paleo-extent of Ericaceous vegetation in this ecosystem, we aim to identify unambiguous Erica biomarkers. Here, we present a respective study focusing on plant-derived terpenoids. Terpenoids from seven keystone plant species were identified and quantified using gas chromatography-mass spectrometry (GC-MS). Widely employed angiosperm biomarkers such as lupane, oleanane, ursane, and taraxastane-type triterpenoid alcohols, acids, and esters were detected with a more ample presence in Erica species and Lobelia rhynchopetalum. Ursolic acid is always the predominant triterpenoid, followed by oleanolic acid. The beta- and alpha-amyrin triterpenoids allowed distinguishing Erica trimera from the other plants in hierarchical cluster analysis (HCA). The nearly exclusive presence of amyrin acetate in particular and the total terpenoid content in Erica species corroborate the potential of terpenoid biomarkers for reconstructing the paleo-extent of Ericaceous vegetation in the soil and sediments. Moreover, 3beta-taraxerol may serve as a proxy to distinguish the morphologically and ecologically very similar Erica trimera and Erica arborea. Given that the diagenetic alteration of taraxerol as well as other terpenoid biomarkers should not be overlooked, ongoing research is needed and encouraged to address this issue.