Alaska Peatland Experiment (APEX) aquatic biofilm microbiome
Aquatic microbial biofilms are an understudied component of northern peatlands and are expected to play a more prominent role in ecosystem processes in areas where aquatic habitat is expanding. The goal of this study was to investigate how water-driven transitional states (i.e., hydrologic history) influence biofilm diversity and functional genes. This study was conducted in a long-term water table manipulation experiment that simulates drought (via a lowered water table treatment), and flooding (raised water table treatment) conditions relative to a control treatment (no water table manipulation). We used a combination of metabarcoding and metagenomic approaches to 1) examine the diversity of producers (eukaryotic algae and cyanobacteria) and decomposers (bacteria and fungi) within the microbial biofilm, and 2) identify functional genes associated with alternating wet-dry transitional states. Historical flooding, but not drought, led to broad changes in biofilm diversity and functional genes. Positive and negative correlations among members of the biofilm provided evidence of interspecific interactions (cooperative vs. antagonistic) that were influenced by resource availability (e.g., nutrients). Genes associated with carbon metabolism (photosynthesis, fermentation, methanol oxidation) and nitrogen cycling (fixation, ureolysis) were particularly prevalent. Differences in biofilm community composition and metabolic functions were related to changes in relative abundance rather than the presence/absence of individual taxa or genes. These findings show that hydrologic history (long timescale) regulates species membership of the community (and thereby associated genes) but differences in water chemistry and interspecific interactions within the biofilm (short timescale) alter the relative abundance of species and their functional potential.