Coupling Spatiotemporal Community Assembly Processes to Changes in Microbial Metabolism

Abstract

Community assembly processes generate shifts in species abundances that influence ecosystem cycling of carbon and nutrients, yet our understanding of assembly remains largely separate from ecosystem-level functioning. Here, we investigate relationships between assembly and changes in microbial metabolism across space and time in hyporheic microbial communities. We pair sampling of two habitat types (i.e., attached and planktonic) through seasonal and sub-hourly hydrologic fluctuation with null modeling and temporally explicit multivariate statistics. We demonstrate that multiple selective pressures—imposed by sediment and porewater physicochemistry—integrate to generate changes in microbial community composition at distinct timescales among habitat types. These changes in composition are reflective of contrasting associations of Betaproteobacteria and Thaumarchaeota with ecological selection and with seasonal changes in microbial metabolism. We present a conceptual model based on our results in which metabolism increases when oscillating selective pressures oppose temporally stable selective pressures. Our conceptual model is pertinent to both macrobial and microbial systems experiencing multiple selective pressures and presents an avenue for assimilating community assembly processes into predictions of ecosystem-level functioning.

Colonization Habitat Controls Biomass, Composition, and Metabolic Activity of Attached Microbial Communities in the Columbia River Hyporheic Corridor

“…A subset of these taxa was present in comparable numbers in all three habitats, whereas others showed major variations connected to differential organic matter input and metabolism. Metabolically diverse heterotrophic Proteobacteria (31) were abundant in all the colonized sands, which is consistent with other hyporheic microbial communities (22,29,30) as well as previous Hanford 300 Area studies (15)(16)(17), and indicates a central role of these organisms in organic carbon (OC) decomposition across the HC. The abundance of Pseudomonadaceae relative to all Gammaproteobacteria was particularly high in the GWS, which is consistent with a previous sand colonization study in Hanford 300 Area groundwater (32), where Pseudomonadaceae accounted for 60 to 80% of all Proteobacteria.…”

“…Although the sand packs did not reproduce in situ groundwater, riverbed, or hyporheic zone sediment properties, the sand is from the same geological (Hanford) formation and provided a clean substratum on which microbial community development as a function of in situ habitat could be assessed (16). NMDS analysis of the 16S rRNA gene amplicon libraries indicated that distinct attached microbial communities did in fact arise in the three different in situ colonization habitats (Fig.…”

“…Based on this work and recent microbial community assembly studies in the Hanford 300 Area HC (15)(16)(17), deterministic selection imposed by the various DOC sources/ amounts in the three different habitats was expected to lead to distinct microbial assemblages in the colonized sand materials. Stegen et al (15) showed (using highresolution Fourier transform-ion cyclotron resonance mass spectrometry) significant differences in the properties of DOC among groundwater, river water, and hyporheic zone fluids, which were correlated with both microbial respiration and community composition.…”

Biogeochemical cycling at the aquatic–terrestrial interface is linked to parafluvial hyporheic zone inundation history

“…Previous studies of biogeochemical cycling in the parafluvial zone have sampled gravel bars to investigate hydrologic flow paths (Claret and Boulton, 2008;Deforet et al, 2009;Zarnetske et al, 2011) and have sampled during saturated conditions utilizing well/piezometer transects (Baker et al, 1999;Deforet et al, 2009;Briody et al, 2016;Graham et al, 2016;Stegen et al, 2016). Such studies have indicated that the parafluvial hyporheic zone is an active region of diverse biogeochemical transformations (Zarnetske et al, 2011;Briody et al, 2016) and microbial community dynamics (Baker et al, 1999;Graham et al, 2016Graham et al, , 2017Stegen et al, 2016), often influenced by residence times (Claret and Boulton, 2008;Deforet et al, 2009;Zarnetske et al, 2011).…”

“…Such studies have indicated that the parafluvial hyporheic zone is an active region of diverse biogeochemical transformations (Zarnetske et al, 2011;Briody et al, 2016) and microbial community dynamics (Baker et al, 1999;Graham et al, 2016Graham et al, , 2017Stegen et al, 2016), often influenced by residence times (Claret and Boulton, 2008;Deforet et al, 2009;Zarnetske et al, 2011). However, studies that have compared biogeochemical cycling in the parafluvial zone to other floodplain environments (e.g., forest, ponds, islands, wetlands) have found that stream and nearby gravel habitats have had lower respiration, bacterial abundance, enzyme activities, and sediment nitrogen nutrient leaching than adjacent pasture/grassland, vegetated islands, and/or mature forest habitats, but short flood pulses (24 h) have increased bacterial extracellular enzymes in sediment from both flooded riverbanks and wetlands (Burns and Ryder, 2001;Doering et al, 2011;Ostojić et al, 2013;Bodmer et al, 2016).…”