Contrasting community assembly processes structure lotic bacteria metacommunities along the river continuum.

Hyun S Gweon,Anna E Oliver,Mark J Bailey,Heather L Moorhouse,Michael J Bowes,Daniel S Read,Michael C Acreman

doi:10.1111/1462-2920.15337

Abstract

SummaryThe heterogeneous nature of lotic habitats plays an important role in the complex ecological and evolutionary processes that structure the microbial communities within them. Due to such complexity, our understanding of lotic microbial ecology still lacks conceptual frameworks for the ecological processes that shape these communities. We explored how bacterial community composition and underlying ecological assembly processes differ between lotic habitats by examining community composition and inferring community assembly processes across four major habitat types (free‐living, particle‐associated, biofilm on benthic stones and rocks, and sediment). This was conducted at 12 river sites from headwater streams to the main river in the River Thames, UK. Our results indicate that there are distinct differences in the bacterial communities between four major habitat types, with contrasting ecological processes shaping their community assembly processes. While the mobile free‐living and particle‐associated communities were consistently less diverse than the fixed sediment and biofilm communities, the latter two communities displayed higher homogeneity across the sampling sites. This indicates that the relative influence of deterministic environmental filtering is elevated in sediment and biofilm communities compared with free‐living and particle‐associated communities, where stochastic processes play a larger role.

Highlights

Lotic habitats are characterized by high spatiotemporal variability caused by natural factors such as variations in hydrology, temperature, water chemistry and resource availability, including nutrients and both particulate and dissolved organic matter
We explored how bacterial community composition and underlying ecological assembly processes differ between lotic habitats by examining community composition and inferring community assembly processes across four major habitat types
Unlike soil bacterial communities where pH and organic matter have frequently been identified as the dominant drivers (Fierer et al, 2007), our understanding of lotic microbial ecology still lacks conceptual frameworks for the ecological processes and drivers that shape these communities

Summary

Introduction

Lotic habitats (i.e. flowing water) are characterized by high spatiotemporal variability caused by natural factors such as variations in hydrology, temperature, water chemistry and resource availability, including nutrients and both particulate and dissolved organic matter. River catchments represent a continuum of interlinked habitats that change considerably in abiotic and biotic character longitudinally, along the river continuum from source to sea (Vannote et al, 2008), laterally, via exchanges with the floodplain, and vertically, from freeflowing water through to the sediment–water interface and the saturated hyporheic zone (Stegen et al, 2016). Lotic habitats are found along a gradient of contrasting physicochemical conditions, from headwaters to downstream rivers (Vannote et al, 2008). As such, it is still unknown whether such consistency is preserved across this river continuum, and whether the processes that govern their community composition are consistent along this gradient

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