Microplastics Weaken the Adaptability of Cyanobacterium Synechococcus sp. to Ocean Warming

Increasedgrowth rates and carbon fixation were weakenedand triggered the transcriptomic adjustment of Synechococcus sp. in photosynthesis and CO2 fixation in response tomicroplastics under ocean warming. Ocean warming (OW) caused by anthropogenic activitiesthreatensocean ecosystems. Moreover, microplastic (MP) pollution in the globalocean is also increasing. However, the combined effects of OW andMPs on marine phytoplankton are unclear. Synechococcus sp., the most ubiquitous autotrophic cyanobacterium, was used toevaluate the response to OW + MPs under two warming scenarios (28and 32 degrees C compared to 24 degrees C). The enhancement of the cellgrowth rate and carbon fixation under OW were weakened by MP exposure.Specifically, OW + MPs reduced carbon fixation by 10.9 and 15.4% at28 and 32 degrees C, respectively. In addition, reduction in photosynthesispigment contents of Synechococcus sp. under OW wasintensified under OW + MPs, supporting the lower growth rate and carbonfixation under OW + MPs. Transcriptome plasticity (the evolutionaryand adaptive potential of gene expression in response to changingenvironments) enabled Synechococcus sp. to developa warming-adaptive transcriptional profile (downregulation of photosynthesisand CO2 fixation) under OW. Nevertheless, the downregulationof photosynthesis and CO2 fixation were alleviated underOW + MPs to increase responsiveness to the adverse effect. Due tothe high abundances of Synechococcus sp. and itscontributions to primary production, these findings are importantfor understanding the effects of MPs on carbon fixation and oceancarbon fluxes under global warming.