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ABSTRACT The marine microalgaEmiliania huxleyiis widely distributed in the surface oceans and is prone to infection by coccolithoviruses that can terminate its blooms. However, little is known about how global change factors like solar UV radiation (UVR) and ocean warming affect the host‐virus interaction. We grew the microalga at 2 temperature levels with or without the virus in the presence or absence of UVR and investigated the physiological and transcriptional responses. We showed that viral infection noticeably reduced photosynthesis and growth of the alga but was less harmful to its physiology under conditions where UVR influenced viral DNA expression. In the virus‐infected cells, the combination of UVR and warming (+4°C) led to a 13‐fold increase in photosynthetic carbon fixation rate, with warming alone contributing a change of about 5–7‐fold. This was attributed to upregulated expression of genes related to carboxylation and light‐harvesting proteins under the influence of UVR, and to warming‐reduced infectivity. In the absence of UVR, viral infection downregulated the metabolic pathways of photosynthesis and fatty acid degradation. Our results suggest that solar UV exposure in a warming ocean can reduce the severity of viral attack on this ecologically important microalga, potentially prolonging its blooms. 

Abstract We conducted a mesocosm experiment to examine how ocean acidification (OA) affects communities of prokaryotes and eukaryotes growing on single‐use drinking bottles in subtropical eutrophic waters of the East China Sea. Based on 16S rDNA gene sequencing, simulated high CO 2 significantly altered the prokaryotic community, with the relative abundance of the phylum Planctomycetota increasing by 49%. Under high CO 2 , prokaryotes in the plastisphere had enhanced nitrogen dissimilation and ureolysis, raising the possibility that OA may modify nutrient cycling in subtropical eutrophic waters. The relative abundance of pathogenic and animal parasite bacteria also increased under simulated high CO 2 . Our results show that elevated CO 2 levels significantly affected several animal taxa based on 18S rDNA gene sequencing. For example, Mayorella amoebae were highly resistant, whereas Labyrinthula were sensitive to OA. Thus, OA may alter plastisphere food chains in subtropical eutrophic waters. 

Abstract. Trichodesmium species, as a group of photosynthetic N2 fixers(diazotrophs), play an important role in the marine biogeochemical cycles ofnitrogen and carbon, especially in oligotrophic waters. How ongoing oceanwarming may interact with light availability to affect Trichodesmium is not yet clear. Wegrew Trichodesmium erythraeum IMS 101 at three temperature levels of 23, 27, and 31∘C undergrowth-limiting and growth-saturating light levels of 50 and 160 µmol quanta m−2 s−1, respectively, for at least 10 generations and thenmeasured physiological performance, including the specific growth rate, N2fixation rate, and photosynthesis. Light availability significantly modulatedthe growth response of Trichodesmium to temperature, with the specific growth ratepeaking at ∼27∘C under the light-saturatingconditions, while growth of light-limited cultures was non-responsive acrossthe tested temperatures (23, 27, and 31∘C). Short-term thermalresponses for N2 fixation indicated that both high growth temperatureand light intensity increased the optimum temperature (Topt) forN2 fixation and decreased its susceptibility to supra-optimaltemperatures (deactivation energy – Eh). Simultaneously, alllight-limited cultures with low Topt and high Eh were unable tosustain N2 fixation during short-term exposure to high temperatures (33–34∘C) that are not lethal for the cells grown underlight-saturating conditions. Our results imply that Trichodesmium spp. growing under lowlight levels while distributed deep in the euphotic zone or under cloudyweather conditions might be less sensitive to long-term temperature changesthat occur on the timescale of multiple generations but are more susceptible toabrupt (less than one generation time span) temperature changes, such asthose induced by cyclones and heat waves. 

Abstract. Marine phytoplankton such as bloom-forming, calcite-producingcoccolithophores, are naturally exposed to solar ultraviolet radiation (UVR,280–400nm) in the ocean's upper mixed layers. Nevertheless, the effects ofincreasing carbon dioxide (CO₂)-induced ocean acidification and warming have rarelybeen investigated in the presence of UVR. We examined calcification andphotosynthetic carbon fixation performance in the most cosmopolitancoccolithophorid, Emiliania huxleyi, grown under high(1000µatm, HC; pH_T: 7.70) and low (400µatm,LC; pH_T: 8.02) CO₂ levels, at 15^∘C,20^∘C and 24^∘C with or without UVR. The HCtreatment did not affect photosynthetic carbon fixation at 15^∘C,but significantly enhanced it with increasing temperature. Exposure to UVRinhibited photosynthesis, with higher inhibition by UVA (320–395nm) thanUVB (295–320nm), except in the HC and 24^∘C-grown cells, in whichUVB caused more inhibition than UVA. A reduced thickness of the coccolith layerin the HC-grown cells appeared to be responsible for the UV-inducedinhibition, and an increased repair rate of UVA-derived damage in theHC–high-temperature grown cells could be responsible for lowered UVA-induced inhibition.While calcification was reduced with elevated CO₂ concentration,exposure to UVB or UVA affected the process differentially, with the formerinhibiting it and the latter enhancing it. UVA-induced stimulation of calcification washigher in the HC-grown cells at 15 and 20^∘C, whereas at24^∘C observed enhancement was not significant. The calcificationto photosynthesis ratio (Cal∕Pho ratio) was lower in the HC treatment,and increasing temperature also lowered the value. However, at 20 and24^∘C, exposure to UVR significantly increased the Cal∕Phoratio, especially in HC-grown cells, by up to 100%. This implies thatUVR can counteract the negative effects of the “greenhouse” treatment onthe Cal∕Pho ratio; hence, UVR may be a key stressor when considering theimpacts of future greenhouse conditions on E. huxleyi.