Soil pH impact on microbial tetraether lipids and terrestrial input index (BIT) in China

The distributions of microbial tetraether lipids, i.e. glycerol dialkyl glycerol tetraethers (GDGTs), were investigated in a variety of Chinese soils featured by a wide range of pH values in different climate zones. The bacterial branched GDGTs and archaeal isoprenoid GDGTs were found to be widely distributed in Chinese soils and their relative abundance was controlled primarily by soil pH. The bacterial bGDGTs usually dominate over archaeal iGDGTs in abundance when the soil pH is below 8.0. However, archaeal iGDGTs become dominant and the abundance of halophilic archaea characterized by GDGT V without cyclopentyl ring increases dramatically in the alkaline soil with pH greater than 8.0. The relative abundance of archaeal iGDGTs to bacterial bGDGTs was defined here as RAI index. The RAI index decreases with elevated soil pH and a linear correlation is found between them, indicating that the relative abundance of archaeal iGDGTs to bacterial bGDGTs increases with increased pH. The RAI index thus could be a novel proxy of the pH values of paleosol. The terrestrial input index, BIT (Branched and Isoprenoid Tetraethers Index), decreases with increased soil pH, suggesting that soil pH should be taken into consideration when the terrestrial contribution to marine sediments is estimated by BIT index. Moreover, the TEX86 index cannot be used to reconstruct sea surface temperature in the sediments featured by a large terrestrial input.