Nitrogen-limitation exacerbates the impact of ultraviolet radiation on the coccolithophore Gephyrocapsa oceanica

Warming and UV Radiation Alleviate the Effect of Virus Infection on the Microalga Emiliania huxleyi

The marine microalga Emiliania huxleyi is 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.

Gradient experiment reveals physiological stress from heavy metal zinc on the economically valuable seaweed Sargassum fusiforme

Zn is a common heavy metal pollutant in water bodies and accounts for the largest proportion of heavy metal pollutants in many rivers entering the sea. This study investigated the growth and physiological response characteristics of Sargassum fusiforme under different divalent Zn ion concentration gradients. We observed that low concentration Zn2+ treatment (<2 mg L-1) exerted no significant effect on the growth rate, photosynthesis, and nitrogen metabolism-related indicators of S. fusiforme. Treatment with medium to high Zn2+ concentrations (2-25 mg L-1) significantly affected the growth rate, photosynthetic activity, nitrogen absorption rate, antioxidant enzyme activity, membrane lipids, and DNA peroxidation damage-related indicators of S. fusiforme. Under medium-to-high concentration treatments, the SOD activity of S. fusiforme decreased with increasing concentration, and the CAT activity increased with increasing treatment concentration. The MDA and H2O2 contents increased with increasing Zn2+ concentrations. At a Zn2+ concentration of 5 mg L-1, the relative conductivity of S. fusiforme significantly increased. Treatment with higher Zn2+ concentrations significantly increased the 8-hydroxydeoxyguanosine (8-OHdG) content, poly ADP-ribose polymerase (PARP) activity, and Histone H2AX content of S. fusiforme, thus indicating that Zn2+ stress causes DNA damage. All Zn2+ concentrations induced mannitol accumulation, and soluble protein content decreased with increasing Zn2+ concentration. In summary, we observed that a Zn2+ concentration of 2-5 mg L-1 may be the critical value for the response of S. fusiforme to Zn2+ stress. Higher concentrations of Zn in the environment can exert toxic effects on the growth, development, and biomass accumulation of S. fusiforme. This study provides a reference for the risk assessment and aquaculture management of seaweeds.

The response of aquatic ecosystems to the interactive effects of stratospheric ozone depletion, UV radiation, and climate change

Variations in stratospheric ozone and changes in the aquatic environment by climate change and human activity are modifying the exposure of aquatic ecosystems to UV radiation. These shifts in exposure have consequences for the distributions of species, biogeochemical cycles, and services provided by aquatic ecosystems. This Quadrennial Assessment presents the latest knowledge on the multi-faceted interactions between the effects of UV irradiation and climate change, and other anthropogenic activities, and how these conditions are changing aquatic ecosystems. Climate change results in variations in the depth of mixing, the thickness of ice cover, the duration of ice-free conditions and inputs of dissolved organic matter, all of which can either increase or decrease exposure to UV radiation. Anthropogenic activities release oil, UV filters in sunscreens, and microplastics into the aquatic environment that are then modified by UV radiation, frequently amplifying adverse effects on aquatic organisms and their environments. The impacts of these changes in combination with factors such as warming and ocean acidification are considered for aquatic micro-organisms, macroalgae, plants, and animals (floating, swimming, and attached). Minimising the disruptive consequences of these effects on critical services provided by the world's rivers, lakes and oceans (freshwater supply, recreation, transport, and food security) will not only require continued adherence to the Montreal Protocol but also a wider inclusion of solar UV radiation and its effects in studies and/or models of aquatic ecosystems under conditions of the future global climate.

Light history modulates growth and photosynthetic responses of a diatom to ocean acidification and UV radiation

To examine the synergetic effects of ocean acidification (OA) and light intensity on the photosynthetic performance of marine diatoms, the marine centric diatom Thalassiosira weissflogii was cultured under ambient low CO₂ (LC, 390 μatm) and elevated high CO₂ (HC, 1000 μatm) levels under low-light (LL, 60 μmol m^-2 s^-1) or high-light (HL, 220 μmol m^-2 s^-1) conditions for over 20 generations. HL stimulated the growth rate by 128 and 99% but decreased cell size by 9 and 7% under LC and HC conditions, respectively. However, HC did not change the growth rate under LL but decreased it by 9% under HL. LL combined with HC decreased both maximum quantum yield (F _V/F _M) and effective quantum yield (Φ _PSII), measured under either low or high actinic light. When exposed to UV radiation (UVR), LL-grown cells were more prone to UVA exposure, with higher UVA and UVR inducing inhibition of Φ _PSII compared with HL-grown cells. Light use efficiency (α) and maximum relative electron transport rate (rETR_max) were inhibited more in the HC-grown cells when UVR (UVA and UVB) was present, particularly under LL. Our results indicate that the growth light history influences the cell growth and photosynthetic responses to OA and UVR.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-022-00138-x.