The Study Of Environmental Factors On Population Growth And Interspecific Competition Of Thalassionema Nitzschioides Under Laboratory Conditions

Plankton indicator species is a powerful tool to infer the marine environment. T. nitzschioides is a common world spread diatom species, which is distributed over all maritime space except the polar. It has been found that there is a good consistency between the composition ratio of T. nitzschioides in sedimentary diatoms of South China Sea and the original temperature records, which is a good indicator species of ancient temperatures. However, because T. nitzschioides distributed widely, the adaptability to environment and environmental implications of T. nitzschioides has not been given enough attention. To further understand the potential indication value of T. nitzschioides, it is selected to serve as target organisms in this study. The main objective of this work is to realize effects of the environmental factors, such as different nutrient concentrations and temperature, on population growth and interspecific competition of T. nitzschioides under laboratory conditions.The results are as follows:(A)The impact of environmental factors on population growth of T. nitzschioidesThe temperature has a appreciable impact on the population growth of T. nitzschioides. Its’ environmental load capacity (k) decreases as the temperature drops, and the intrinsic population growth rate (r) increases as temperature drops. At the minimum temperature below 10 degree, T. nitzschioides has a slowly population growth, and it’s population density essentially unchanged; in other 3 temperature groups, there is a trend that T. nitzschioides enter into the resting stage ahead of time, and the time (Tp) of enter into the resting stage and reached the inflection point are about the same.Under the conditions of different nutrient concentrations, the growth status of T. nitzschioides are diverse, the environmental load capacity (k) decreases with the nutrient concentration drops, while the intrinsic population growth rate (r) changes disorderly. In the 5 dealing groups, micro-algae enters into the exponential growth phase at the same time, but the time of reaches the inflection point (Tp) and enter into the resting stage are delay with the decreasing of nutrient concentration.(B) The impact of environmental factors on the interspecific competition between T. nitzschioides and Karenia mikimotoi.Environmental factors changes can impact the effect of interspecific competition. We made a numerical fitting to the population density change of the microalgae in the co-culture system. Result showed that:When the temperature was rising, we could observe a equilibrium state about the Interspecific competition between T. nitzschioides and K. mikimotoi, but the equilibrium wasn’t stable. So we got the concussion that temperature couldn’t impact the competitive relation between the two kinds of algae. When the concentration of the nutritive salt was rising, the competitive relation between the two kinds of algae was changing continually. This means that the nutritive salt can impact the competitive relation between the two kinds of algae obviously. But we still don’t know the specific changing rule. (C) The impact of environmental factors on the chlorophyll fluorescence parameters of T. nitzschioidesThe environmental factor has a significantly influence on the photosynthetic efficiency and the photosynthetic light use efficiency strong light of T. nitzschioides, which changes the distribution of excess light energy. Under different temperatures, the quick light response curves of convex height of T. nitzschioides is 10℃> 15℃>25℃>20℃; under temperature gradient of 10-25℃, the results of α,β and rETRmax are both 10℃> 15℃>25℃>20℃. The results trend of Ek and NPQ are15℃>10℃>25℃>20℃. This shows that T. nitzschioides input the main resource into photosynthesis to maintain itself faced with the cold stress.The exploration the fluorescence induction curves of T. nitzschioides under different temperature shows that, the Fv/Fm of T. nitzschioides increases with the temperature enlarges, while the Y(Ⅱ) reduced after the first rise. With this clarification the T. nitzschioides invest their excess resources into reproductive allocation at appropriate temperatures.In summary, temperature and nutrient concentrations have some impact on population growth, interspecific competition and photosynthesis of T. nitzschioides.What’s more, temperature and nutrient concentrations also change its’ reproductive strategies. T. nitzschioides can be regard as an indication of ancient temperature and nutrient concentrations changes of the South China Sea.