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Wan-Hsuan Cheng and Chih-hao Hsieh

A study on vertical variation of bacteria in the Kuroshio Current east of Taiwan across seasons, led by Ph.D. student Wan-Hsuan Cheng from Academia Sinica, and Profs. Chih-hao Hsieh and Jan Sen from IONTU, reveal that ocean stratification strength can mediate mechanisms shaping vertical beta diversity of bacterioplankton. This study is published in Frontiers in Microbiology.

One key concern of warming effects on ocean is enhanced water column stratification. Whether and how stratification strength would mediate community assembly mechanisms (e.g. environmental and spatial effects) driving bacterial beta diversity in a vertical dimension remain understudied. This research question is topical, as increasing evidence has indicated the importance of beta diversity at influencing ecosystem functioning. Here, the research team collected 78 bacterial communities from paired surface and deep chlorophyll maximum (DCM) layers along a transect of Kuroshio region east of Taiwan across multiple seasons.

The results indicated that stratification strength would mediate bacterial vertical beta diversity from both environmental and spatial effects. Specifically, while the environmental effect is prevalent in both strongly and weakly stratified periods, further analysis indicated that the determinisms of environmental effects differs between these two periods. During the weakly stratified periods, the environmental effect was attributed to vertical nutrient gradients caused by upwelling events (Fig 1A). In contrast, during the strongly stratified periods, the environmental effect resulted from water stratification and vertical distance (Fig 1B). Furthermore, the spatial effect was only observed when the stratification strength is strong, indicating that the strong stratification created dispersal barriers for bacteria (Fig 1B). These findings highlight the importance of considering water column physics for studying metacommunity structure in marine ecosystems. More importantly, as climate warming can intensify water column stratification, warming can potentially affect vertical beta diversity of microbes, which in turn likely affects ecosystem functioning in the ocean.

Figure 1. Conceptual scheme illustrating the mechanisms shaping vertical beta diversity of bacterioplankton during weakly and strongly stratified periods. (A) During the weakly stratified periods, the vertical beta diversity was driven by the environmental effect caused by nutrient upwelling in some nearshore sites. (B) During the strongly stratified periods, the vertical beta diversity was driven by both the spatial and environmental effects. The spatial effect was resulted from the vertical distance. The environmental effects were resulted from water stratification and vertical distance.

Reference:

Cheng, WH, Lu HP, Chen CC, Jan S, and Hsieh CH (2020) Vertical beta-diversity of bacterial communities depending on water stratification. Front. Microbiol. 11:449. doi: 10.3389/fmicb.2020.00449