Branched glycerol dialkyl glycerol tetraether (brGDGT) distributions influenced by bacterial community composition in various vegetation soils on the Tibetan Plateau

Branched glycerol dialkyl glycerol tetraether (brGDGT) lipids are membrane-spanning lipids of some bacteria that are sensitive to environmental gradients, which makes it possible to use brGDGT proxies to estimate changes in environmental temperatures in paleoenvironmental studies. However, it is currently unknown whether the observed correlations of temperature and brGDGT distribution in natural samples are driven by directly changing bacterial membrane fluidity and permeability, or by a shift in the bacterial community. Here we present brGDGT distributions along an elevation gradient (704-3760 m) in the southeastern Tibetan Plateau, spanning gradients in temperature and vegetation. Analysis of brGDGTs shows that their distributions are significantly influenced by vegetation-intermediated soil temperature, in addition to mean annual air temperature, soil pH, and other environmental variables. Different vegetation types contribute to soil temperature and bacterial community changes. Consequently, these different groups of bacteria result in changes in the relative abundance of brGDGTs. Our results show that temperature and pH indirectly influence cyclopentane-containing brGDGTs via changes in the bacterial community. Genetic analyses reveal that in addition to Acidobacteria, Proteobacteria, Nitrospira, Bacteroidetes, Actinobacteria, and Verrucomicrobia could be potential candidates as brGDGT producers. These results indicate that changes in the vegetation and bacterial community should be taken into consideration when applying brGDGT proxies to reconstruct past changes in climate.