Terpenoids in surface soils from different ecosystems on the Tibetan Plateau

Abstract

Realizing the potential of terpenoid biomarkers as an unequivocal land ecosystem and floral diversity indicator calls for work to establish a direct link between the terpenoids extracted from the plants and those found in the underlying soils. To this end, we have characterized the triterpenoid profile of soils and vegetation along two altitudinal transects representing very different ecosystems. The first transect, comprising 31 sample sites, was on the eastern slopes of Mt Gongga (eastern Tibetan Plateau) rising from 1230 m to 4500 m above sea level, an area with a temperate monsoonal climate. The second transect, sampling 29 sites, was on the northern slopes of Mt West Kunlun, a region characterized by montane desert, meadow and alpine steppe (located between 1300 m and 5050 m above sea level). The dominant terpenoid biomarkers (polycyclic triterpenoids of the taraxerane, oleanane, friedelane, ursane, lupane, glutinane and lanostane series) identified in the soils were found to be consistent with the overlying vegetation. However, the discovery of some unusual triterpenoids, including the pentacyclic triterpene 3-methyl ethers (PTMEs), D:A-friedo-2,3-secoolean-2,3-dioic acid, methyl 3β-acetoxylup-20(29)-en-28-oate, 24-methylenecycloartan-3-one, 9,19-cyclolanostan-3-yl 24-methylene acetate, 3α-methoxy-9β-lanosta-7,24-dien-26,23-olide and 3α-methoxy-9β-lanost-7-en-26,23-olide in the Gongga soils, does not match the current vegetation and may be indicative of a long vanished forest-type vegetation. Thus, soil biomarkers may be a useful tool in the reconstruction of palaeo-vegetation.