Hydrologic History Regulates Microbial Biofilm Diversity and Ecosystem Function

Aquatic 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 hydrologic history influences biofilm diversity and functional genes. This study was conducted in a long-term water table manipulation that simulates drought (lowered water table treatment) and flooding (raised water table treatment) conditions relative to a control treatment (no manipulation). We used a combination of metabarcoding and metagenomic approaches to (1) examine the diversity of eukaryotic algae, cyanobacteria, bacteria and fungi within the biofilm and (2) identify functional genes associated with alternating wet-dry transitional states. Historical flooding, but not drought, led to broad changes in composition and functional genes, especially those associated with carbon metabolism and nitrogen cycling. Differences were related to changes in relative abundance rather than the presence/absence of individual taxa or genes. Hydrologic history influenced community diversity by reducing interspecific competition or by alleviating resource limitation. These findings show that hydrologic history regulates species membership of the community (and thereby associated genes) but differences in water chemistry and interspecific interactions alter the relative abundance of species and their functional potential.