Effects Of Different Phosphorus Compounds And Interspecific Competition On The Growth Of Bloom-forming Cyanobacterium Chrysosporum Ovalisporum

With the global warming,the frequency and intensity of cyanobacterial bloom in the world tend to increase,and caused the global expansion of many new bloom-forming cyanobacteria,among which the most attention has been paid to Cylindrospermopsis raciborskii and Chrysosporum ovalisporum.C.ovalisporum is a kind of floating filamentous cyanobacterium,mainly distributed in the tropics,subtropics and the Mediterranean region.In recent years,it has also outbroken in Shanghai,China.As a new type of bloom-forming cyanobacterium in China,the study on the diffusion and competition mechanism of C.ovalisporum are rarely reported.In general,phosphorus is considered to be the most restrictive element in limiting the growth of algae,and the effective utilization of phosphorus in water bodies may affect the diffusion and invasion of microalgae.It is of great significance to understand the bioavailability of different phosphorus compounds and the effects of interspecific competition for further understanding the mechanism of the outbreak of C.ovalisporum and preventing and controlling cyanobacterial blooms timely.Therefore,in this study,we took C.ovalisporum as the research object,studied its bioavailability to different forms of phosphorus compounds and the effect of interspecific competition on their growth,and tried to explain the reasons for the growth advantage of C.ovalisporum in different aquatic ecosystems from the perspective of phosphorus.The specific research contents and results are as follows,(1)Six types of phosphorus compounds(dipotassium hydrogen phosphate,terasodium pyrophosphate decahydrate,sodium tripolyphosphate,disodium ?-glycerol phosphate pentahydrate,(2-aminoethyl)-phosphonic acid and glyphosate)were used as phosphate sources to cultivate Chrysosporum strains in the laboratory.The results showed that after 15 days of cultivation,the concentration of dissoluble inorganic phosphate in the glyphosate treatment approached 0 mg/L,and the specific growth rate was significantly lower than that without P treatment(P < 0.05),indicating that glyphosate not only was not conducive to the uptake of phosphorus by algal cells,but also inhibited its growth.The biomass of C.ovalisporum in the sodium tripolyphosphate and(2-aminoethyl)-phosphonic acid treatments were highest among that in control,reaching 426.96 ± 47.42 and 411.51 ± 10.91 mg/L,respectively.The concentrations of chlorophyll a were also higher than other treatment groups.Moreover,there were no significant difference with dipotassium hydrogen phosphate(P > 0.05),indicating that C.ovalisporum had better utilization of these two kinds of phosphorus compounds.(2)The effects of phosphorus sources on the growth and competition of C.ovalisporum and Microcystis aeruginosa were studied by co-culture and filtrate culture with dipotassium hydrogen phosphate and(2-aminoethyl)-phosphonic acid as the phosphorus source in the medium,respectively.The results showed that M.aeruginosa had stronger competitive ability and its growth was dominant when two kinds of algae were co-cultured.while the growth of C.ovalisporum was inhibited.In the experiment of filtrate culture,the growth and photosynthetic activity of C.ovalisporum of Chr in Mic treatment group that under the conditions of inorganic phosphorus were inhibited.And under the condition of organic phosphorus,the filtrate of M.aeruginosa inhibited the synthesis of chlorophyll a,aphotosynthetic activity and alkaline phosphatase activity of C.ovalisporum,but its growth was not inhibited.In the Mic in Chr treatment group,the growth,photosynthetic activity and alkaline phosphatase activity of M.aeruginosa were promoted under the condition of inorganic phosphorus,while the growth and photosynthetic activity of M.aeruginosa under the condition of organic phosphorus culture were not significantly affected.(3)The effects of phosphorus sources on the growth and competition of C.ovalisporum and Scenedesmus quadricauda were studied by co-culture and filtrate culture with dipotassium hydrogen phosphate and(2-aminoethyl)-phosphonic acid as the phosphorus source in the medium,respectively.The results of mixed culture showed that under the condition of BG11 medium,the higher the initial biological volume ratio of C.ovalisporum,the higher the competition ability,and the stronger the inhibitory effect on S.quadricauda.Under the condition of organic phosphorus culture,C.ovalisporum also had a significant inhibition on the growth of S.quadricauda.Among them,S.quadricauda was more inhibited when the initial biological volume ratio of C.ovalisporum and S.quadricauda was 1:3 or 3:1.The results of filtrate culture showed that under the condition of organic phosphorus,the growth and alkaline phosphatase activity of C.ovalisporum in the Chr in Sce treatment group were significantly promoted,and the growth,synthesis of chlorophyll a and photosynthetic rate under inorganic phosphorus conditions were inhibited.In the Sce in Chr treatment group,the growth of S.quadricauda was promoted under the condition of inorganic phosphorus,while under the condition of organic phosphorus,the cell filtrate of C.ovalisporum inhibited the synthesis of chlorophyll a and the growth of S.quadricauda.