The Response of Archaeal Tetraether Membrane Lipids in Surface Soils to Temperature: A Potential Paleothermometer in Paleosols

Abstract

Isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs), major membrane lipids in some Archaea, have been widely used to examine past archaeal activity and infer ancient paleotemperature in aquatic environments. However, it is still unclear whether soil thaumarchaeotal iGDGTs also record temperature, and how thaumarchaeotal iGDGTs in the different climatic zones respond to temperature. Here we investigated iGDGTs in soils along an altitudinal transect of Mt. Shennongjia in central China, and determined the response of thaumarchaeotal membrane lipids to temperature in soils from a typical subtropical region. The TEX86 proxy, reflecting the number of GDGT cyclopentyl moieties, in these soils is significantly correlated with mean annual air temperature (MAT) at a given site, apparently recording a temperature response by Thaumarchaeota that dominate in soils. However, the TEX86 values are similar both at Mt. Shennongjia where a warm and humid climate prevails and at Mt. Xiangpi where a cold and dry climate is predominant. This could result from the seasonality of thaumarchaeotal production in soils from cold and (or) dry regions, and a local calibration is required if the TEX86 proxy is to be applied to reconstruct paleoaltimetry or paleotemperature in paleosols from cold and (or) dry regions. The TEX86 for soils from Mt. Rungwe (Tanzania), Mt. Jianfengling (China) and another climatic transect generally follows the rising trend of TEX86 vs. MAT for Mt. Shennongjia, suggesting that the thaumarchaeotal iGDGTs in soils from subtropical and tropical regions respond to temperature similarly among sites. However, the different calibrations of TEX86 paleothermometer among sites also reveal factors other than MAT may affect the TEX86 values in soils.