Tracing life at the dry limit using phospholipid fatty acids - does sampling matter?

Phospholipid fatty acids (PLFAs) have been used to trace bacterial life in extremely carbon-poor soils of the hyperarid Atacama Desert. However, the low abundances of bacteria and, thus, PLFAs increases the risk of contamination by exogenous PLFAs. Here, we assess whether field sampling strategies (super-clean, clean, and regular sampling protocols) have an effect on PLFA diversity and abundance in hyperarid Atacama soils or whether laboratory processing or true environmental heterogeneity control PLFA inventories. Our results show no exogenous PLFA contribution during sample processing in the lab and statistical analyses (ANOVA, Kruskal-Wallis) reveal that PLFA abundances do not differ significantly between replicate samples (n = 3) taken with the three different sampling strategies. Rather than sampling strategy, our results show that PLFA abundances in the investigated soil replicates rather reflect true environmental heterogeneity of primarily bacterial biomass (in the absence of indigenous fungi), potentially related to small-scale physicochemical differences.