Distributions of Bacterial Branched Tetraether Lipids Associated with Bacterial Communities in Hummock and Hollow Soils from Southern Tibetan Peatland

Branched glycerol dialkyl glycerol tetraethers (brGDGTs), special membrane-spanning lipids derived from some bacteria, are widely used as molecular tools in paleoenvironmental studies to reconstruct terrestrial temperature and pH conditions. However, the impact of microtopography discrepancies on the accuracy and applicability of brGDGT-based proxies remains unclear. Here we investigated the distributional patterns of brGDGTs and bacterial communities within the hummock-hollow microtopography in the mid-southern Tibetan peatlands. Our results show that the methylation index of C5-methyl brGDGTs (MBT ' 5ME ) values are significantly correlated with the local mean annual air temperature (MAAT). However, the peat-specific temperature calibration exhibits an underestimation of MAAT peat compared to the present MAAT. We find the MBT ' 5ME values are significantly lower in the moist hollows than that in the drier hummocks. This discrepancy could be primarily attributed to the shifts in bacterial communities and the physiological adaptation of brGDGT-producing bacteria driven by the high soil water content. These findings highlight the remarkable variability of MBT ' 5ME values at small spatial scales, which holds profound implications for paleotemperature reconstruction in alpine peatlands.