While increasing atmospheric CO2 concentration and associated ocean acidificationhave been predicted to stimulate marine primary production, little is known about theinterplay between ocean acidification and other climate change parameters, such asshoaling of upper mixing layer (UML), associated with global warming.Here, weshowed that the high CO2-grown cells showed higher growth rates at the lower lightlevels but reversed to much reduced rates under the higher light levels in all thediatoms tested, with reduced PAR threshold at which it becomes excessive andincreased NPQ, when the diatoms, Phaeodactylum tricornutum, Thalassiosirapseudonana and Skeletonema costatum grown under different levels (5-100％) ofsolar radiation, mimicking the PAR doses received by the cells during mixing withindifferent depths of UML.Future acidified and shoaled upper oceans will lead toincreased light stress for phytoplankton, would subsequently influence marinebiological CO2 pump and biogeochemical processes.　　It is important to understand the combined or interactive effects of multiple futureclimate change variables on phytoplankton in order to assess the net ecologicalinfluences of future ocean changes.We used a simultaneous multivariate “clusterexperiment” treatment approach to investigate the responses of growth rates,chlorophyll a, biogenic silica (BSi), and particulate organic carbon (POC) andnitrogen (PON) contents of the diatoms Thalassiosira pseudonana and Skeletonemacostatum grown under different cluster regimes of solar radiation, nutrients, and pCO2(pH).These conditions were chosen to simulate future expected reductions in thethickness of the upper mixed layer that will lead to increased light exposures anddecreased transport of nutrients, as well as CO2 increases and pH declines due toocean acidification.Present-day (cluster l), mid-century (cluster 2) and end-century(cluster 3) scenarios were simulated following future projections based on the IPCCA 1F 1 scenario (IPCC Climate change 2001).Our results showed that growth ratesdecreased by 8-18％ and chl a contents by 44-58％in cluster 2, and by 79-82％ and73-83％ in cluster 3, respectively, compared to cluster 1.And Cellular POCsignificantly increased in both species, being 1.3-1.4 times and 1.4-2.1 times higherunder cluster 2 and cluster 3, respectively, compared with the cells grown undercluster 1.However, no significant difference was found in cellular PON content,leading to increased C/N ratios under future conditions in both species.Cellular BSicontent showed no significant differences between treatments in T.pseudonana, butincreased by 40％ and 100％ in S.costatum under cluster 2 and cluster 3, respectively.Our results suggest that enhanced stratification may interact with ocean acidificationto influence diatom-relatedbiogeochemical processes by affecting their growth andbiochemical compositions in species-specific ways, although other global changevariables not examined such as ocean warming could also modify these responses. Marine green plants, though sharing similar photosynthetic machinery withterrestrial higher plants, may show differential responses to increasing CO2concentration due to associated seawater acidification.When the cosmopolitan greenalga, Ulva prolifera, was grown from its zoospore, under elevated CO2 concentrationof 1000 tatm for over 50 days, it reduced its maximal photosynthetic capacity andlight use efficiency as well as its ability to dissipate excessive light energy, thoughacclimation to the elevated CO2 led to higher electron transfer rate.Along with thedecreased photosynthetic affinity for HCO3-or/and CO2, photorespiration increased,Chl a and Chl b contents decreased and carotenoids contents increased remarkablyunder the elevated CO2.The increased photorespiration and carotenoid contents,together with the down-regulated CCM, implies that the green alga increased itsdefensive strategy against CO2-driven seawater acidification at the cost of reducedratio of carboxylation to oxygenation, which contrasts to reduced photorespirationobserved in its terrestrial green partners.From a physiological evolutionary point ofview, ancient ocean acidification event might be responsible for evolution of greenplants from marine to terrestrial environments.