oa Intact Polar Lipids in Tropical Peatland Depth Profiles: Insights in the Microbial Community and Lipid Production

Peatlands play a pivotal function in the global carbon cycle and are sensitive to human intervention, rapidly turning from a carbon sink into a carbon source when perturbed. Large changes in peatland ecosystem functioning over geological time have been explored using fossil lipid biomarkers that are important proxies of microbial activity. However, the producers and processes that underpin these biomarker shifts are often elusive. Intact polar lipids (IPL) are the building blocks of cells therefore indicative of living biomass, with the polar headgroup quickly degrading after cell death. IPL distributions in peat provide insight into the composition of the microbial community and reveal microbial adaptations to environmental conditions, including pH, O2 nutrient or energy limitation, expressed as microorganisms’ membrane modification strategies e.g. maintaining structural integrity. Here, we determine IPL depth profiles from globally representative tropical peatlands and one temperate peatland, with varying pH and vegetation composition. All sites feature a distinct shift in the glycerol backbone structure of phospho- and betaine lipids from an ester-dominance in shallow peat to ether-dominance at depth. This shift corresponds to the transition from aerobic conditions to anaerobic conditions and could be a consequence of a changing microbial community or an adaptation to energy conservation.