An unusual occurrence of hydroxylated isoprenoid GDGTs in forest soils

Abstract

Hydroxylated isoprenoid glycerol dialkyl glycerol tetraethers (OH-GDGTs), a class of lipids that widely occur in global marine and lacustrine environments, have been used as tools for temperature reconstruction. Reports on their occurrence in soils, however, are rare. Here, we report the downward variation in distribution and concentration of OH-GDGTs in three soil profiles (SP) from Mount Yujiashan in Wuhan, central China. The OH-GDGT concentrations show significant correlations with that of crenarchaeol and decreased with soil depth, likely in relation to the decreased oxygen availability of OH-GDGT-producing archaea with depth. Crenarchaeol was likely to be produced primarily by several thaumarchaeotal lineages, e.g. group I.1a, I.1b, and SAGMCG (South Africa Gold Mine Crenarchaeotal Group)-1, whereas OH-GDGTs were presumed to be contributed primarily by SAGMCG-1 and to a lesser extent, by group I.1a Thaumarchaeota based on 16S rRNA gene amplicon sequencing. OH-GDGTs were dominated by OH-GDGT-2, differing significantly from aquatic settings. This results in markedly higher RI-OH and RI-OH′ (both expressing the ring index of OH-GDGTs) values in soils than in marine sediments, suggesting a different response of terrestrial OH-GDGTs to temperature and (or) a significant bias towards summer temperature in RI-OH and RI-OH′ for soils.