Abstract
Seasonal succession in bacterioplankton is a common process in marine waters. However, seasonality in their spatial turnover is largely unknown. Here, we investigated spatial turnover of surface bacterioplankton along a nearshore-to-offshore gradient in the East China Sea across four seasons. Although seasonality overwhelmed spatial variability of bacterioplankton composition, we found significant spatial turnover of bacterioplankton along the gradient as well as overall seasonal consistency in biogeographic patterns (including distance–decay relationship and covariation of community composition with distance to shore) with subtle changes. Bacterioplankton assembly was consistently dominated by deterministic mechanisms across seasons, with changes in specific processes. We found overall seasonal consistency in abiotic factors (mainly salinity and nitrogen and phosphorus nutrients) shaping bacterioplankton composition, while phytoplankton showed a similar influence as abiotic factors only in spring. Although key taxa responsible for bacterioplankton spatial turnover showed certain season-specificity, seasonal switching between closely related taxa occurred within most dominant families. Moreover, many close relatives showed different responding patterns to the environmental gradients in different seasons, suggesting their differences in both seasonally climatic and spatially environmental preferences. Our results provide insights into seasonal consistency and variability in spatial turnover of bacterioplankton in terms of biogeographic patterns, ecological processes, and external and internal drivers.
Highlights
Marine bacterioplankton are important contributors to biogeochemical cycles, and understanding their spatiotemporal variability and underlying mechanisms is fundamental in unveiling how they are functioning across space and time [1]
Clear seasonal succession was found in the composition of eukaryotic phytoplankton, which was dominated by Thalassiosirales, Bacillariales, and Pyrenomonadales in the summer; Thalassiosirales, Cymatosirales, and Pyrenomonadales in the autumn; Thalassiosirales and Pyrenomonadales in the winter and spring (Figure S2)
To understand how individual taxa as internal drivers of bacterioplankton spatial turnover rather than the whole community respond to environmental conditions, we identified the key driver OTUs responsible for a large amount of compositional variation of bacterioplankton in each season
Summary
Marine bacterioplankton are important contributors to biogeochemical cycles, and understanding their spatiotemporal variability and underlying mechanisms is fundamental in unveiling how they are functioning across space and time [1]. Seasonal succession in bacterioplankton community composition is commonly driven by seasonal changes in environmental conditions such as water temperature, nutrients, and phytoplankton (as reviewed in [9]). Seasonal variability of environmental conditions may depend on geographic factors such as latitude and distance to shore of the sampling stations [10,11]. With the change of latitude or distance to shore, multiple environmental gradients could be formed in coastal waters, leading to spatial turnover of bacterial communities [12,13]. Some previous studies have considered the coastal areas with ecological gradients as ideal models for understanding the interplay of seasonal and spatial variability in bacterioplankton communities [10,14]. The seasonality in biogeographic patterns and underlying processes of bacterioplankton along coastal environmental gradients is largely unknown
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