Study On The Physiological Responses Of Three Marine Macroalgae To The Change Of Nutrients Supplies In Seawater

The eutrophication of coastal water is becoming a serious issue of ecological environment. There have been many studies on the responses of marine macroalgae to nitrogen supply, and it also arouses extensive interests that how the interaction between nitrogen and phosphorus affects the ecophysiological characteristics of marine macroalgae. However, little is known about the response of marine macroalgae to the changes of nutrient supplies, the uptake ability of nutrients and the characteristics of metabolism. This paper reviewed these responses of macroalgae, trying to explore the ecophysiological characteristics in three marine macroalgae, Gracilaria lemaneiformis (a red macroalga), Ulva lactuca (a green macroalga) and Hizikia fusiformis (a brown macroalga). In order to screen for efficient biofilter to treat coastal eutrophication, we focused on the rate of nutrients uptake, the kinetics of nutrients absorption and the regularity of nutrients metabolism. Major studies includes the following:(1) Effects of different nitrogen and phosphorus supplies on growth and physiological biochemical characteristics of Gracilaria lemaneiformis, Ulva lactuca and Hizikia fusiformis; (2) Effect on N and P uptake rates of starved and replete macroalgae at different lights and temperatures; (3) Effect on NO3-uptake kinetics of nitrogen starved and nitrogen replete Ulva lactuca at different lights and temperatures. The results were as follows:Ⅰ. When enriched nitrogen and phosphorus were simultaneously supplied, the growths of Gracilaria lemaneiformis and Ulva lactuca were significantly enhanced, producing higher amount of soluble proteins. Photosynthetic capacities were also promoted and the amount of pigments was significantly increased. Meantime, nitrogen enrichment inhibited the growth rate of Hizikia fusiformis, producing fewer soluble proteins. In all three macroalgae, the contents of soluble sugars were significantly decreased. These results show that simultaneously supplied nitrogen and phosphorus can promote the growth of Gracilaria lemaneiformis and Ulva lactuca, and also increase the accumulation of nitrogen. But nitrogen supply had toxic effects on Hizikia fusiformis and plays a negative role during its growth.Ⅱ. The uptake rates of nutrients in Gracilaria lemaneiformis, Ulva lactuca and Hizikia fusiformis were accelerated with increasing substrate concentrations. Both Gracilaria lemaneiformis and Hizikia fusiformis maintain higher uptake rates at low temperatures, while Ulva lactuca can only maintain similar rate at high temperature. Light intensity also influenced uptake efficiency. The uptake capacity and absorption efficiency of nutrients at the middle level of light intensity were higher than those at either dark or high light intensity. It is concluded that temperature, light and substrate concentration will affect the uptake characteristics of nitrogen and phosphorus in all three macroalgae.Ⅲ. Nitrogen-starved Ulva lactuca has higher uptake rates of NO3- than nitrogen-repleted one. Light and temperature can affect photosynthesis and other physiological processes, thereby affect the nutrients uptake.20℃is found to be the best temperature for nutrients uptake. Within appropriate temperature range, the uptake rates of Ulva lactuca were increased with increasing light intensity, but these effects were abolished at high tempareture. It is concluded that the physiological states of algae is a major factor affecting nitrate uptake. Meanwhile, temperature and light can both affect the characteristics of nitrogen and phosphorus uptake in all three algae.In conclusion, light, temperature and nutrient concentrations can affect the physiological characteristics of Gracilaria lemaneiformis, Ulva lactuca and Hizikia fusiformis, especially the uptake characteristics of nutrients. Our data suggests that Gracilaria lemaneiformis and Ulva lactuca are more appropriate species in dealing with coastal eutrophication. We propose that the environmental conditions during macroalgae growth should also be considered in related research and applications...