Physiological Response Of Typical Diatoms In The Yellow Sea To The Long-term Ocean Acidification And Warming

Ocean acidification and warming are generally considered to be the two main factors affecting marine diatoms,which have significant effects on marine ecosystems.However,little is known about how marine diatoms adapt to ocean acidification and warming.In this study,we compared the adaptation strategies of different diatoms to short-term temperature changes and long-term ocean acidification and warming.This study was divided into two parts.In the first part,the effects of short-term temperature changes(5,10,15,20,25,30 and 35 ℃)on three diatoms with different sizes(Thalassiosira pseudonana,Thalassiosira weissflogii and Thalassiosira punctigera)were studied.In the second part,the effects of long-term acidification and warming on three typical diatoms(Phaeodactylum tricornutum,T.pseudonana and Skeletonema costatum)were studied.The results showed that after 15 generations of acclimation at different temperatures,the optimum growth temperature,maximum growth rate and thermal niche width of T.pseudonana,T.weissflogii and T.punctigera decreased with increased cell size.The cell volume of each species diminished significantly and linearly with increased levels of temperature,being most pronounced in the largest diatom,T.punctigera.Beyond the growth optimum temperature,the physiological performances were significantly depressed,with the larger diatoms declined more.While respiration increased when the cells were exposed to acute temperature rise,it decreased with increased growth(acclimated)temperature levels,indicating that the acclimation resulted in less energetic cost as the cells became smaller with to increased levels of temperature.larger diatoms are more sensitive to temperature rise and diatoms respond to ocean warming by making tradeoffs between up-regulating carbon use efficiency,down-regulating physiological properties,and reducing particle size.Under long-term ocean acidification and warming conditions,ocean warming was the main factor affecting the growth rates of P.tricornutum,T.pseudonana and S.costatum.Ocean acidification is promoted only under warming conditions.Different diatoms have different adaptation strategies to environmental changes.P.tricornutum and T.pseudonana showed a strategy of trade-offs between different thermal physiological performance,while warming significantly promoted the thermal physiological performance in S.costatum.However,during adaptation,diatoms need to allocate carbon to physiological processes such as growth by downregulating carbon metabolic such as the Calvin cycle,tricarboxylic acid cycle and glycolysis to improve carbon use efficiency.In summary,marine diatoms have the potential to rapidly adapt to environmental changes,but the adaptation of diatoms is usually accompanied by the trade-off of resources and energy.Ocean warming,rather than acidification,is the main driver for the adaptation of marine diatoms.The effects of ocean acidification are mediated by temperature.This paper investigates the adaptation strategies of marine diatoms to ocean acidification and warming from different time scales,long-term and short-term.We provide important data for studying the adaptation mechanisms of phytoplankton to environment changes.The paper has 26 figures,11 tables,and 191 references.