[Utilization and growth response of Chrysosporum ovalisporum to different phosphorus compounds]. / 卵孢金孢藻对不同磷化合物的利用及生长响应.

To explore the ability of bloom-forming cyanobacterium Chrysosporum ovalisporum to utilize different kinds of phosphorus compounds in the water column, we examined the growth response of C. ovalisporum in the laboratory by taking dipotassium hydrogen phosphate as the control and set different treatments of phosphorus substrates. The results showed that C. ovalisporum could utilize sodium tripolyphosphate and terasodium pyrophosphate decahydrate, with better utilization of sodium tripolyphosphate. After 15 days, it had the highest biomass and chlorophyll a concentrations under the treatment of sodium tripolyphosphate, with a value of (426.96±47.42) mg·L-1 and (1852.34±116.60) µg·L-1, respectively. Compared with the control, there was no significant difference in biomass of C. ovalisporum under both the (2-aminoethyl)-phosphonic acid and disodium ß-glycerol phosphate pentahydrate treatments. The change characteristics of dissolved inorganic phosphate were related to the alkaline phosphatase activity, indicating that C. ovalisporum was able to utilize these two organophosphorus compounds via enzyme hydrolysis. The concentration of dissolved inorganic phosphate reached 0 mg·L-1 during the whole experiment when the C. ovalisporum were fed with glyphosate. Biomass, specific growth rate, chlorophyll a concentration and photosynthetic activity of algal cells were significantly lower than those of the control, indicating that C. ova-lisporum could not uptake phosphorus compounds in the glyphosate substrate and thus their growth being inhibited. Our results present new insights to understand the diffusion mechanism of C. ovalisporum into different aquatic ecosystems and had theoretical reference value for the prevention and control of new cyanobacterial blooms.

[Succession Characteristics of Phytoplankton Functional Groups and Their Relationships with Environmental Factors in Dianshan Lake, Shanghai].

Dianshan Lake, a subtropical shallow lake, is one of the main drinking water sources of Shanghai City. In order to explore the characteristics of phytoplankton functional groups (PFGs) and their relationships with environmental factors in Dianshan Lake, phytoplankton and water samples collected from January 2015 to December 2016 were characterized. Results suggested that there were 26 PFGs during our study period. The biomasses of 15 PFGs (B, C, D, F, G, H1, J, Lo, M, MP, P, W1, W2, X1, and X2) were dominant and had marked annual succession patterns: D/C Lo/C/MP MP/J/P/W1 P in 2015 and P W2/Lo W2/G/M/H1 P in 2016. To elucidate the relationships of PFGs with the environmental factors, canonical correspondence analysis (CCA) was conducted. Results showed that water level fluctuation (WLF), dissolved oxygen (DO), water temperature (WT), total phosphorus (TP), electrical conductivity (EC), transparency (SD), and total nitrogen (TN) were the main impact factors associated with the composition variations of PFGs in Dianshan Lake. From this study, it is proposed that the effects of nitrogen, phosphorus, and WLF on the PFGs in Dianshan Lake should be paid more attention.

[Effects of Nutrient Addition on the Growth and Competition of Bloom Forming Cyanobacterium Chrysosporum ovalisporum: An In-situ Experiment].

An in-situ mesocosm experiment was conducted to study the growth dynamic of Chrysosporum ovalisporum and the other phytoplankton organisms under accelerated eutrophication conditions by using 39 buckets (100 L) in Lake Dishui, Shanghai. The results showed that the growth of both filamentous cyanobacteria (C. ovalisporum) and green algae were promoted with nutrient enrichment. The increase in the algal biomass rate in N plus P addition treatments was significantly higher than in treatments with N or P alone (P<0.05). Although the increasing biomass rate with P addition alone was higher than with N alone, there was no statistically significant difference (P>0.05). The relevant abundance of C. ovalisporum showed a significantly decreasing trend with N addition treatments and N plus P additions treatments (P<0.05), although it was slightly increased with the treatments with P alone (P>0.05). Nutrient addition could significantly improve the growth of small sized algae organisms (Chroococcus spp., Coelastrum spp., Chlorella spp., Tetraedron spp., and Scenedesmus spp.) rather than C. ovalisporum in all treatments (P<0.05). The small sized green algae overcoming C. ovalisporum indicated that small sized algae were more favored by hyper-eutrophicated, high water temperature and relatively undisturbed conditions. This is because small sized algal organisms have higher metabolic and growth rates compared to other sized algae, especially in stationary water regimens and high, light density conditions. We foresee that the small sized algae, Chlorophyte, dominating the small hyper-eutrophic aquatic system may be a potential succession pattern in the high water temperature seasons.