Effects of enhanced temperature on algae cells recruitment from sediment and their physiological characteristics

Many reports have suggested that the recruitment of some overwintered phytoplankton in the sediment may be important for the pelagic populations and may even be responsible for bloom formation. However, so far no single overwhelming environmental factor has been reported to trigger the recruitment of algal cells. And no study focused on the variation of Na+K+-ATPase and Ca2+Mg2+-ATPase activities, which may be of crucial importance for the process of algal recruitment. Besides, the sediment in lakes suffered from algal blooms could be considered as seed bank as many studies reported, could provide seed for the pelagic populations in the lake and is also significance for bloom formation. Therefore, the growth and the photosynthetic activity of the seed triggered by the favorable outside conditions, the variation of Na+K+-ATPase and Ca2+Mg2+-ATPase activities during the period of algal recruitment, all have critical significance for further research on the process of recruitment. The article mainly focused on the environmental factors and the characteristics of the recruited algal cells, and wanted to study their effects in the process of algal recruitment. Sediment in the experiment was collected from Meiliang Bay (3126'14 N, 12011'04 E) in Lake Taihu suffered from cyanobacaterial blooms. Three media with different N:P ratio (45:1, 29:1, 7:1) based on the BG11 medium were prepared. In the condition of enhancing temperature, the abundance of recruited algal cells and the variation of algal community in the three different media with laying the sediment were detected. What is more, algal cells photosynthetic activity measured with PHYTO-PAM-2000 in the three different media was compared. The variation of Na+K+-ATPase and Ca2+Mg2+-ATPase activities in the algal cells were also detected using the ATPase kit. The results showed that there were 62 species of algae in the study, belonging to 7 phyla. Therefore, the sediment in Lake Taihu should be considered as seed bank, and would provide seed for algal recruitment in the eutrophic lake. The cyanobacteria began to recruit in 6℃ and 16℃ was the optimum temperature for algal cells recruitment. Under experimental conditions, the photosynthetic efficiency of recruited cyanobacterial cells from sediment increased with the enhancing temperature, which suggested that the higher the temperature the better the recruitment of cyanobacterial cells from sediment. However, the photosynthetic efficiency of recruited Green algae andDiatom were both inhibited. The abundance of recruited algal cells in low N:P ratio medium was much larger than that in the other two media, and low N:P ratio could significantly trigger algal recruitment from sediment. Meanwhile, the Na+K+-ATPase and Ca2+Mg2+-ATPase activities of recruited algal cells in the low N:P ratio medium were significantly higher than that in the other two media. The rapid increases of the Na+K+-ATPase and Ca2+Mg2+-ATPase activities in 16℃ coincided with the optimum temperature for algal cells recruitment. Furthermore, the specific growth rate of recruited algal cells had significantly correlation with the Na+K+-ATPase and Ca2+Mg2+-ATPase activities (*P0.05). Therefore, the restored and increased activities of both Na+K+-ATPase and Ca2+Mg2+-ATPase should play important role in algal cells recruitment from the sediment.