Effects Of Different Environmental Factors On Growth And Photosynthesis Of Karenia Mikimotoi

The global climate change and human activities have significant impacts on the ecological environment of the estuarine and coastal areas, such as seawater acidification, entrophication, seawater temperature rising and so on. Those changes greatly influence the photosynthetic physiology of the phytoplankton. As we all know, photosynthesis is an essential way for phytoplankton to acquire energy, which is vital to its growth and competition and also affects the outbreak of red tide. In order to understand the effects of those changing environmental factors on the the physiological state of phytoplankton, in this study, we used K.mikimotoi, one of the most common red tide species in East China Sea, as our research object. Based on our results, we can provide some primary knowledge for the effects of the environment changes on K.mikimotoi bloom. The major research results are as follows:1. pH had significant effects on K.mikimotoi’s growth and photosynthetic physiology. Cultured in pH=8.2, the algae’s growth rate, the N (nitrate) and P (phosphrous) absorption and the maximum rate of the photosynthesis were the largest compared to those in pH=7.2 and pH=6.2. At the same time, its growth rate, the N and P absorption, the maximum rate of the photosynthesis and the affinity to the inorganic carbon were the lowest when cultured in pH=6.2. When pH of the culture solution was 7.2, the cells have the highest affinity to the inorganic carbon. Hence, pH affected the algae’s nutrition absorption which further affected its cellular content of chlorophyll. Although the algae’s photosynthetic rate was not very fast, it can also maintain high growth in high pH.2. Salinity also affected the algae’s growth and photosynthesis significantly. The optimum salinity for the algae is 26-34. The algae can adjust the pigments content to maintain its growth. The lower salinity reduced the cell’s PS Ⅱ photochemical activity and energy conversion efficiency. The low salinity had a limitation on the algae’s photosynthesis and then limited the algae’s growth.3. The N and P content and ratio of the culture medium and their interaction also had great impact on the studied algae’s growth. In this experiment, the algae grew fastest in the concentration of N=800 μmol/L and P=8 μmol/L, while slowest in the concentration of N=25μmol/L and P=1μmol/L. The algae’s growth declined in advance in the late exponential growth phase when cultured with the increasing N and P concentration. Low N concentration limited the algae’s growth and high P concentration increased its pigment content. With the concentration of N and P increasing, the algae’s dark respiration per cell decreased but the photosynthesis rate increased. Only in a suitable P concentration range can the cells have a higher PSII photochemical efficiency.4. The carbon dioxide (CO2) concentration significantly affected the algae’s growth and photosynthesis. When cultured under high carbon dioxide concentration, the algae’s growth rate and the affinity to the inorganic carbon decreased, while the celluar content of chlorophyll a (Chla), and chlorophyll c (Chic), the maximum photosynthesis, the dark respiration and photosynthesis rate increased.5. The light and carbon dioxide concentration’ interation didn’t affect the algae’s cell growth and photosynthesis significantly. But high carbon dioxide concentration and high light were good to stimulate the cell’s growth.