Photosynthetic Responses Of Skeletonema Costatum To Salinity?Ocean Acidification And UV Radiation

Global climate change causes ocean warming,which reduces sea ice cover and global sea level rise,which may lead to changes in seawater salinity.Strong precipitation caused by climate change will also affect surface salinity.The continuous increase of atmospheric CO₂ concentration causes ocean acidification.At the same time,increased human activity leads to enhanced UV radiation in the ocean.Diatoms play a key role in the ecosystem cycle.Therefore,this paper simulates the visible light and UV in the sunlight using a full-band solar simulator(Sol 1200,Honle GmbH,Germany).Skeletonema costatum is studied,and the reduction of seawater salinity,enhanced UV radiation of the sun,and ocean acidification are discussed.And its coupling effect on photosynthetic physiological characteristics of Skeletonema costatum and its mechanism.The salinity of seawater decreased,and the growth rate of Skeletonema costatum decreased.The Fv/Fm values of high-light radiation(PAR,PAR+UVR)decreased with time,and the degree of inhibition was more obvious under PAR+UVR treatment.The decrease of seawater salinity would aggravate the decrease of Fv/Fm.The decrease in salinity had no significant effect on the PsbA protein content of Skeletonema costatum,but the UV radiation caused a significant decrease in the PsbA protein content of the PSII reaction center.PAR+UVR radiation treatment significantly increased the NPQs of algae cells,and the decrease in salinity exacerbated the increase in UV radiation and its NPQs.Moreover,the CAT and SOD values under PAR+UVR radiation were significantly higher than those under PAR treatment.Acidification promoted the growth rate of algae cells.Wherein rETR_max and I_K values are further increased by the coupling of highlights.Acidification significantly increased the NPQs of algal cells and further increased after coupling with salinity reduction.At the same time,increased CO₂ concentration increases PsbA removal rate(K_PsbA)of Skeletonema costatum,especially the K_PsbA value of algal cells under the condition of reduced salinity.At the same time,the acidification significantly increased the Krec value of the algae,indicating that acidification improved its repair ability.Under different salinity culture conditions,there was no significant difference in the maximum photochemical efficiency Fv/Fm of PSII after acidification conditions,and the Fv/Fm of PAR+UVR radiation treatment was significantly decreased.At the same time,UV radiation significantly reduced the content of PsbA?PsbD and Rubisco protein content in the PSII reaction center of algae cells.Under different culture conditions,the initial slope?of the fast light curve of Skeletonema costatum has little change.Under UV radiation,algae cells have higher relative maximum electron efficiency rETR_max and half-saturated light intensity I_K,and salinity decreases(15‰)and its coupling with PAR,PAR+UVR radiation further increased the rETR_max and I_K,and the acidification treatment also aggravated the decrease of salinity and UV radiation on the rETR_maxax and I_K values of algae cells.In addition,UV radiation further decreases K_PsbA value in salinity and ocean acidification,and UV radiation reduces the increase in Krec by acidification and salinity.In conclusion,the reduction in seawater salinity inhibits the growth of Skeletonema costatum,and UV radiation exacerbates this tendency.It was no difference on the Fv/Fm and photosynthetic efficiency of PSII after acidification.However,UV radiation would aggravate the inhibition of the coupling of salinity and ocean acidification to the photosynthetic efficiency of Skeletonema costatum.Therefore,in the future marine environment with reduced seawater salinity,enhanced UV radiation,and ocean acidification,the growth of Skeletonema costatum will be inhibited.However,the combined effects of environmental factors in the natural marine environment are much more complex,and more research is needed.