Abstract
Free-living (FL) and particle-associated (PA) bacterioplankton communities play critical roles in biogeochemical cycles in the ocean. However, their community composition, assembly process and functions in the continental shelf and slope regions are poorly understood. Based on 16S rRNA gene amplicon sequencing, we investigated bacterial communities’ driving factors, assembly processes and functional potentials at a subtropical marginal sea. The bacterioplankton community showed specific distribution patterns with respect to lifestyle (free living vs. particle associated), habitat (slope vs. shelf) and depth (surface vs. DCM and Bottom). Salinity and water temperature were the key factors modulating turnover in the FL community, whereas nitrite, silicate and phosphate were the key factors for the PA community. Model analyses revealed that stochastic processes outweighed deterministic processes and had stronger influences on PA than FL. Homogeneous selection (Hos) was more responsible for the assembly and turnover of FL, while drift and dispersal limitation contributed more to the assembly of PA. Importantly, the primary contributor to Hos in PA was Gammaproteobacteria:Others, whereas that in FL was Cyanobacteria:Bin6. Finally, the PICRUSt2 analysis indicated that the potential metabolisms of carbohydrates, cofactors, amino acids, terpenoids, polyketides, lipids and antibiotic resistance were markedly enriched in PA than FL.
Highlights
Microbial communities are highly diverse and play critical roles in biogeochemical cycling cycles across ecosystems, which are fundamental in maintaining climate and ecosystem stability [1,2,3]
Our results revealed that environmental drift overwhelmed homogeneous selection in the bacterioplankton community assembly regardless of freeliving or particle-associated fractions
Our results demonstrated that salinity and water temperature were the key factors modulating turnover in the Free living (FL) bacterioplankton, whereas nitrite, silicate and phosphate were the key factors modulating turnover in the particle associated (PA) counterparts
Summary
Microbial communities are highly diverse and play critical roles in biogeochemical cycling cycles across ecosystems, which are fundamental in maintaining climate and ecosystem stability [1,2,3]. Bacteria modulate carbon and nutrient cycling [4] and bacterial community composition is closely related to carbon export [5,6]. PA microbes rely on particulate organic matter (POM) as attachment substrate, which constitutes the hotspot microenvironment for the ecological process of marine microorganisms and biogeochemical cycle [8,9]. Particles of variable sizes, chemical compositions and physical properties conform to the microspatial architecture that structures the microbial environment, which differs from the bulk surrounding seawater in their chemistry and physics [4,10]. There are many different types of particles, such as living or dead protist cells, zooplankton and fish fecal pellets [4]
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