Ocean Acidification Regulates the Activity, Community Structure, and Functional Potential of Heterotrophic Bacterioplankton in an Oligotrophic Gyre

Abstract

Ocean acidification (OA), a consequence of increased global carbon dioxide (CO 2 ) emissions, is considered a major threat to marine ecosystems. Its effects on bacterioplankton activity, diversity, and community composition have received considerable attention. However, the direct impact of OA on heterotrophic bacterioplankton is often masked by the significant response of phytoplankton due to the close coupling of heterotrophic bacterioplankton and autotrophs. Here we investigated the responses of a heterotrophic bacterioplankton assemblage to high pCO 2 (790-ppm) treatment in warm tropical western Pacific waters by conducting a microcosm experiment in dark for 12 days. Heterotrophic bacterioplankton abundance and production were enhanced by OA over the first 6 days of incubation, while the diversity and species richness were negatively affected. Bacterioplankton community composition in the high pCO 2 treatment changed faster than that in the control. The molecular ecological network analysis showed that the elevated CO 2 changed the overall connections among the bacterial community and resulted in a simple network under high CO 2 condition. Species-specific responses to OA were observed and could be attributed to the different life strategies and to the ability of a given species to adapt to environmental conditions. In addition, high-throughput functional gene array analysis revealed that genes related to carbon and nitrogen cycling were positively affected by acidification. Together, our findings suggest that OA has direct effects on heterotrophic bacterioplankton in a low-latitude warm ocean and may therefore affect global biogeochemical cycles.

Thermal discharge-induced seawater warming alters richness, community composition and interactions of bacterioplankton assemblages in a coastal ecosystem

“…Though a dearth of information is available on interactions among marine bacterial assemblages under elevated temperature conditions, several reports describing the potential impact of other environmental anomalies such as ocean acidification (reduction in seawater pH) are available. For example, alterations in microbial ecological networks under elevated CO 2 condition has been observed by Xia et al 72 . Nevertheless, this is not always the case, as few studies have also found that microbial intra-species interactions among marine microorganisms are either less affected or unaffected in climatic changes such as elevated partial pressure of CO 2 ( p CO2) 73 .…”

Effect of Ocean Acidification on Bacterial Metabolic Activity and Community Composition in Oligotrophic Oceans, Inferred From Short-Term Bioassays

“…The relative abundance of Alteromonadaceae and SAR86 increased under OA. Alteromonadaceae with relatively large cell size and the ability to thrive in nutrientdeficient situations (Lopez-Perez and Rodriguez-Valera, 2014) is repressed by ocean acidification (Xia et al, 2019). The different response of Alteromonadaceae to OA might result from the different environmental conditions, as Xia's experiment is conducted during a heterotrophic bloom phase, in which BP is 20-40 folds higher than at M8.…”

“…Westwood et al (2018) report that an increase in BP is attributed to the effect of OA on phytoplanktonderived DOC and the lower grazing pressure in highly productive waters. Xia et al (2019) suggest that enhanced BP under high pCO 2 is caused by the physiological adjustment of bacterial cells. Instead, in mesopelagic regions, high pCO 2 reduces BP in Hawaiian deep seawater (Coffin et al, 2004).…”

“…For example, high pCO 2 has little effect on bacterial community richness or diversity (Roth-Schulze et al, 2018). However, Xia et al (2019) report that OA reduces bacterial diversity and results in shifts in the bacterial community in a 12-day dark incubation experiment. Bacterial clades of Pseudoalteromonadaceae and Shewanellaceae increase in the relative abundance in high-pCO 2 treatments, accompanied by a decline in BGE (James et al, 2019).…”

Data_Sheet_1.zip

“…Previous studies have shown that responses of bacterioplankton communities to elevated pCO 2 are diverse and complex and even conflicting. Bacterioplankton communities were found to be susceptible to changes in pCO 2 or pH in some studies that were reflected in abundance, diversity, or composition (Krause et al, 2012;Zhang et al, 2013;Xia et al, 2019;Aguayo et al, 2020;Crummett, 2020), whereas other studies reported negligible effects (Roy et al, 2013;Oliver et al, 2014;Wang et al, 2015). Take coastal ecosystems for example, microbial community from coastal ecosystem with naturally low pH (average = 7.8) was still sensitive to acidification (Crummett, 2020).…”