Effects Of Warming And Temperature Fluctuation On Marine Phytoplankton

In this thesis,the dominant species of diatom and coccolithophore were cultured in semi-continuous culture incubation,and the phytoplankton communities in the coastal area of Tianjin in spring were cultured in continuous culture incubation.The effects of warming and temperature fluctuation on the physiology of diatoms and coccolithophores,and the effects of warming,temperature fluctuation and acidification on the physiological parameters of coastal phytoplankton communities were investigated.(1)The growth rates of Thalassiosira sp.and Nitzschiaclosterium f.minutissima were very sensitive to the changes of temperature.The results support that although both warming and fluctuating in low temperature inhibited the growth of diatoms,the growth rates increased significantly under the fluctuating in high temperature.The remarkable increase in growth rates during fluctuating in high temperature indicates that when the temperature exceeds the optimal growth temperature range,the fluctuation will help accelerate the adaptation of diatoms to a severely warming environment.The Thalassiosira sp.and Nitzschiaclosterium f.minutissima under fluctuating in high temperature can promote the accumulation of protein and PON,because the synthetic efficiency of protein increases rapidly under high temperature.In addition,other physiological parameters of Nitzschiaclosterium f.minutissima also increased significantly when the temperature was fluctuated,which indicated that the thermal tolerance and recovery ability of Nitzschiaclosterium f.minutissima was higher than that of Thalassiosira sp..The fluctuation of temperature weakens the carbon fixation ability of Thalassiosira sp.and affects the carbon deposition in the ocean.(2)The growth rates of two strains of coccolithophores were decreased significantly with the rise and fluctuation of temperature.The growth rates of coccolithophores were slowed down by temperature variation,and the inhibition of temperature variation on the growth of coccolithophores was more obvious at high temperature than at low temperature.The changes at both low(20℃)and high(25℃)mean temperature had different affects on the physiological indicators of coccolithophores.Calcified coccolithophores are more tolerance to high temperature than non-calcified due to their calcification ability.When the ability of calcification was weakened,the cellular physiological parameters changed significantly.The reduction of calcified ability will lead to the change of ballast,and then affect the carbon deposition.(3)The results showed that both warming and fluctuation inhibited the increase of Chl-a contents in coastal phytoplankton communities significantly.In addition to the group of high temperature,acidification also played a significant role in the inhibition,because environmental variations result in the changes in phytoplankton of different sizes.Diatom dominated the phytoplankton communities in the coastal area of Tianjin,and acidification promoted the growth of Skeletonema,while warming promoted the growth of Thalassiosira and Nitzschia.The response of element ratios to acidification was more significant,and the temperature of seawater in-situ was lower than the optimal growth temperature of most species.This indicated that the warming and acidification of seawater induced by climate change in the future will lead to the rapidly growth of small and medium sized phytoplankton in the phytoplankton communities in spring,and the nutrient limitation of seawater and the early appearance of summer bloom.These results indicate that the physiological responses of different species of marine phytoplankton to temperature changes are different.This difference may be an important role that affecting the calcification ability of coccolithophores,as well as a key factor affecting the abundance and community structure of coastal diatoms and affecting the biogeochemistry cycle in the ocean.