| Chlorophyll fluorescence is based on the theory of photosynthesis, using chlorophyll fluorescence as a natural probe for detection and study of the physiological status of plant photosynthesis, as well as a variety of external environmental factors affected their new minor in vivo determination of and diagnostic technology, a rapid, sensitive, no damage to the cells the characteristics of studies are a good probe of photosynthesis. At present, both at home and abroad of plant chlorophyll fluorescence kinetics in vivo research has become very hot .In 2008, photosynthetic performances of young seedlings of Sargassum horneri were investigated under various temperature, light and salinity conditions by use of chlorophyll fluorescence measurements. Results showed that:(1)Under the condition of our investigation, the photosynthetic system of young seedlings of Sargassum horneri can be obviously destroyed without resuming in short time by high temperature of 35℃. the upper survival temperature limit of young seedlings was 28℃, the appropriate growth temperature ranged from 22 to 24℃. Optimal chlorophyll fluorescence quantum yields (Fv/Fm) of seedlings of S.horneri after exposure to 35℃for 1 h was 63.0% compared to the control and the corresponding recovered values after 24 h was 4.96% compared to the control. And some parameters even reduced to 0. The filemot leaves became shriveling, and some leaves dropped. The initial and finial optimal chlorophyll fluorescence quantum yields (Fv/Fm) of the seedlings of S.horneri after exposed to 28℃for 10d and corresponding recovered values after 24 h almost have no difference. Relative-growth rates in weights of S.horneri seedlings after exposure to 28℃for 10d was 0.83 d-1, and the 30℃was -0.88 d-1. Relative-growth rates in weights was 4.53,5.99和2.59% d-1 and the longest leaves of S.horneri seedlings after exposure to three temperatures for 10 days was 2.32,2.04和0.52% d-1(2)Fluorescence quantum yield measured in the presence of actinic light (Fm′) of S.horneri seedlings in reduced ambient solar irradiance reduced with the increasing of light intensities, when the highest light intensities 320μmol photons m-2s-1, Fm′decreased to 0.4, but the Fm′gradually increased to 0.73 when the irradiance declined over time. Under full spectrum of solar irradiance in outdoor measurement, S.horneri seedlings was exposed to the outdoor tank only 1h, Fv/Fm decreased to 0.36, and Fv/Fm tempestuously decreased with the increasing of active radiation (PAR) and UV radiation above the outdoor tank, the Fm′of the seedlings decreased to 0.11 When the highest active radiation (PAR) was 1 490μmol photons m-2s-1 and UV radiation was 4720μw cm-2, and was only 15% compared to the indoor tank as the control , but recovered to 0.5 after 24 h in standard culture condition. After 24 h recovery, Fm′of S.horneri seedling exposed 1h basically recovered to the control, although the Fm′exposed over 1h also recovered, the leaves became shriveling.(3)osmotic changes had no evidently effect on S.horneri seedlings. Six hour treatments in 9-60‰salinities and 1 hour in fresh water did not affect the optimal chlorophyll fluorescence quantum yields (Fv/Fm). Although the Fv/Fm of S.horneri seedlings obviously reduced with the salinity and exposed time increased, after 24h recovery, the Fv/Fm recovered to the control after exposed to 60‰salinity for 6h treatments. decreased with the salinity decreased and exposed time increased. Fv/Fm was 95.77%, 78.38%, 50.00% and 36.49% compared to the control after exposed to fresh water for 0.5, 1, 3 and 6 h, and after 24h recovery Fv/Fm was 97.18%, 76.71%, 44.44%和28.38%.In our study, the appropriate growth temperature ranged from 22 to 24℃, this result accord to the fact that wild seedings basically grow in the early summer. Because commercially cultivation and cosmically reconstruct the subtidal algal flora has not come true, and has no and relational study up to the present, so our study supply valuable information. Another relevant issue regards to the contamination and removal of epiphytic algae such as Ulva spp., Polysiphonia sp., Ecotocarpus spp., Enteromorpha spp., and These algae are usually very resistant to ambient solar irradiance, to desiccation and to change of temperature. It is usually very difficult to filter out spores of these algae even with the help of sand-filter water treatment system in a commercial farm. The epiphytic algae compete with seedlings for substrate space, photons, CO2 and nutrients in the artificial raising system and therefore must be removed from time to time until the erect thalli of the seedlings stands up. Therefore epiphytic algae that are sensitive to osmotic changes could be removed by such treatments at fixed time intervals.Chlorophyll fluorescence emitted from algal sample under various stressful conditions could be taken as a diagnostic approach to estimate the physiological state, especially the photosynthetic efficiency. Although these parameters could not give the changes on molecular or cellular processes, they provide a faster, economic, non-damaging and most of all sufficient means to estimate the in situ state of the algae. So chlorophyll fluorescence will be universality used in the stress physiology of algaeThis research is supported by (1) the 863 Hi-Tech Research and Development Program of China (Nr.: 2006AA10A416), (2) the Natural Science Foundation of China (NSFC., Nr.: 30471327), and (3) the Basic conditions of National Science and Technology platform for the work of the project - the standardization of aquatic resources, organize, integrate and share issues (2006DKA30470-017) support.
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