Effect of Warming on Growth, Grazing, and Community Composition of Free-Living Bacterioplankton in Subtropical Coastal Waters During Winter and Summer.

Bowei Gu,Candy Lee,Yehui Tan,Xiaomin Xia,Hongbin Liu,Xiao Ma

doi:10.3389/fmicb.2020.534404

Abstract

Global warming is considered a major threat to marine ecosystems, which affects bacterioplankton activity, diversity, and community composition. However, few studies focus on the potential effects of warming on bacterioplankton in subtropical coastal waters in different seasons. Here we investigated the influences of warming on growth, grazing and community composition of bacterioplankton in Hong Kong coastal waters during winter and summer via 1-day incubation experiments. Our results revealed that without grazers, bacterioplankton displayed higher growth rate during summer compared to winter, while warming only significantly increased the growth rate of bacterioplankton in winter. Grazers with size <5 μm were major predators of bacterioplankton. Warming had little effect on grazing in summer but significantly enhanced grazing rates of >5 μm grazers in winter. In both seasons, warming had little influence on bacterial diversity and community composition. Nevertheless, in family and OTU levels, bacterioplankton had different responses to grazing and warming which may result from the selective grazing preference of predators and different temperature optima for bacterioplankton. Furthermore, the presence of >5 μm and <5 μm grazers would result in significant increase of some bacterial families under warming condition. Together, our results suggest that warming have direct impacts on bacterioplankton in subtropical coastal waters during winter and may thus affect global biogeochemical cycles.

Highlights

Bacterioplankton are fundamental ingredients in marine ecosystems and play an important role in biogeochemical cycling (Azam et al, 1983; Cotner and Biddanda, 2002; Azam and Malfatti, 2007)
Compared with in situ temperature incubation, bacterial abundance increased markedly in warming treatment during winter, especially in the 5 μm-prefiltration (W-
There was no significant difference of grazing rates between winter and summer whereas this difference become significant in warming treatment (Figure 1)

Summary

Introduction

Bacterioplankton are fundamental ingredients in marine ecosystems and play an important role in biogeochemical cycling (Azam et al, 1983; Cotner and Biddanda, 2002; Azam and Malfatti, 2007). Recent studies of grazing effects on natural bacteria have suggested that grazing affects the abundance of bacterioplankton and the bacterial community composition via selective ingestion and digestion (Jürgens et al, 1999; Pernthaler, 2005; Gong et al, 2016). Gong et al (2016) showed that Alteromonadaceae, Pseudoalteromonadaceae, and Vibrionaceae are digestion-resistant bacteria, which could survive from protistan bacterivore feeding and accumulate in the community. It is generally believed that the size of bacteria is a factor that affects grazing (González et al, 1990; Posch et al, 2001). The grazing pressure can trigger the change of the size structure of bacterial community (Jürgens et al, 1999). Whether grazing would affect bacterioplankton community in subtropical waters remains unknown

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Discussion

Conclusion