Effect of short-term, diel changes in environmental conditions on active microbial communities in a salt marsh pond

Microbial subnetworks related to short-term diel O2fluxes within geochemically distinct freshwater wetlands

“…These data suggested that the dominantly active microbial community may not be driving daily shifts in microbial community structure found in MM, and that a subset of less abundant microbial taxa could be driving community-level changes in MM. Overall, these results contrast with those found by Kearns et al (2017), where it was established that the active microbial community shifted over a daily cycle within salt marsh water. However, salt marshes are unique in that they are transient systems which alternate between influxes of saltwater and periods of stagnation, whereas the freshwater wetlands studied here were closed, stable systems.…”

“…Microbial dormancy may also be contributing to a lack of community structure differences between dawn and dusk within wetland water. Inactive community members have been found to constitute close to 30% of communities within freshwater systems (Lennon & Jones, 2011) and estimated at up to 62% of community membership in a saltwater marsh which experienced diel fluxes (Kearns et al, 2017). Further, DNA within freshwater environments can remain detectable for several days after removal of the DNA source (Dejean et al, 2011), thus persistence of microbial community DNA from dead cells may contribute to masking fine-scale community composition shifts.…”

“…Diel O 2 fluctuations have been observed within aquatic systems, including freshwater wetlands, with near anoxic levels occurring at night and elevated O 2 concentrations occurring during daytime hours (Cornell & Klarer, 2008; Reeder, 2011; Maynard et al, 2012). In aquatic ecosystems other than wetlands (such as oceans and salt marshes), microbial community activity and structure can respond to short-term daily changes in environmental conditions (Ghiglione et al, 2007; Ottesen et al, 2014; Andrade et al, 2015; Morris et al, 2016; Kearns et al, 2017). As a consequence, geochemical processes can respond daily to diel environmental fluxes (Jørgensen et al, 1979; Laursen & Seitzinger, 2004; Harrison et al, 2005), as many geochemical transformations are driven by microbial communities that are sensitive to shifting environmental variables such as O 2 , pH, temperature, and light levels.…”

“…While insights have been gained on microbial community response to diel fluxes in studies of wetland rhizospheres, it is necessary to examine the influence of diel fluxes on microbial communities in the water column of freshwater wetlands. Recent research in a salt marsh has highlighted that active soil microbial communities remain stable in the face of diel environmental fluxes, while active microbial communities shift with diel fluxes within the water column (Kearns et al, 2017).…”

A low proportion of rare bacterial taxa responds to abiotic changes compared with dominant taxa

“…While some rare bacterial taxa have been shown to support specific ecosystem processes more strongly than would be expected from their abundance, it has also been demonstrated that many have the ability to become dominant in space and time (Caporaso et al, 2012). At increased abundances, these formerly rare taxa have higher functional importance and take over or supplement functions performed by other dominant taxa (Campbell et al, 2011;Kearns et al, 2017). By increasing in abundance and supporting important functions, rare species are supposed to maintain ecosystem functioning under changes in environmental conditions-also called the insurance effect (Yachi and Loreau, 1999).…”