Deterministic influences exceed dispersal effects on hydrologically‐connected microbiomes

Abstract

Subsurface groundwater-surface water mixing zones (hyporheic zones) have enhanced biogeochemical activity, but assembly processes governing subsurface microbiomes remain a critical uncertainty in understanding hyporheic biogeochemistry. To address this obstacle, we investigated (a) biogeographical patterns in attached and waterborne microbiomes across three hydrologically-connected, physicochemically-distinct zones (inland hyporheic, nearshore hyporheic and river); (b) assembly processes that generated these patterns; (c) groups of organisms that corresponded to deterministic changes in the environment; and (d) correlations between these groups and hyporheic metabolism. All microbiomes remained dissimilar through time, but consistent presence of similar taxa suggested dispersal and/or common selective pressures among zones. Further, we demonstrated a pronounced impact of deterministic assembly in all microbiomes as well as seasonal shifts from heterotrophic to autotrophic microorganisms associated with increases in groundwater discharge. The abundance of one statistical cluster of organisms increased with active biomass and respiration, revealing organisms that may strongly influence hyporheic biogeochemistry. Based on our results, we propose a conceptualization of hyporheic zone metabolism in which increased organic carbon concentrations during surface water intrusion support heterotrophy, which succumbs to autotrophy under groundwater discharge. These results provide new opportunities to enhance microbially-explicit ecosystem models describing hyporheic zone biogeochemistry and its influence over riverine ecosystem function.

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.…”

“…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.…”

Hyporheic Zone Microbiome Assembly Is Linked to Dynamic Water Mixing Patterns in Snowmelt‐Dominated Headwater Catchments

“…We hypothesize that physical streambed characteristics, namely, lower permeability, limit the extent to which fluid-entrained microbes can travel, resulting in more spatially constrained communities. Supporting this inference, homogenizing selection was found to play a significant role in microbial community assembly in Columbia River sediments near Hanford, WA (Graham et al, 2017). In contrast to the Colorado River, the sampling location in the Columbia River is characterized by high permeability owing to the Hanford formation underlying the Columbia River (Table 1; Hammond & Lichtner, 2010).…”

Linking microbial co‐occurrences to soil ecological processes across a woodland‐grassland ecotone

“…Microbial co-occurrence networks can reveal associations among network members and yield insight into microbiome functioning (Bissett, Brown, Siciliano, & Thrall, 2013;Cardona, Weisenhorn, Henry, & Gilbert, 2016;Faust & Raes 2012;Fuhrman, 2009;). For example, patterns of microbial co-occurrence have been demonstrated for a diverse range of aquatic and terrestrial environments (Banerjee, Baah-Acheamfour et al, 2016;Barberán, Bates, Casamayor, & Fierer, 2012;De Menezes et al, 2015;Graham et al, 2017;Shi et al, 2016). Previous studies using network analysis have often only assessed bacterial communities and not fungal or archaeal communities (Banerjee, Baah-Acheamfour et al, 2016;Barberán et al, 2012;Shi et al, 2016;Vick-Majors, Priscu, & Amaral-Zettler, 2014).…”