Effects Of Controlling C,N,and P On The Growth,Nutrient Absorption Of Chlorella Vulgaris And Its Competition With Microcystis

In the process of phytoplankton growth,carbon(C),nitrogen(N)and phosphorus(P)are the most important limiting factors affecting the growth of algae.Different algal species grow differently under variant nutrient conditions,and nutrient plays a key role in the growth competition between algae.In eutrophic culture waters,we can artificially provide the nutrient conditions suitable for the growth of beneficial algae(such as Chlorophyta),and proliferation of beneficial algae will inhibit harmful algae(such as Cyanobacteria)growth,which can not only be helpful for solving eutrophication problem in culture waters,but also be helpful for the prevention and control of cyanobacteria blooms.In this study,we explored the optimal C,N and P ratios for the growth of C.vulgaris under different P concentrations using response surface analysis.On this basis,the optimal C,N and P ratios for C.vulgaris growth,the absorption of C,N and P nutrients in C.vulgaris were investigated.Moreover,the growth competition between C.vulgaris and M.aeruginosa was also analyzed using corresponding competition model.The results are presented as follows:In the range of phosphorus concentrations(0.05-1 mg/L),with the same N:P ratio,the density of C.vulgaris increased first and then decreased with the increasing C:N ratios.With the same C:N ratio,the density of C.vulgaris in the control group gradually increased with the increase of N:P ratios,while the density of C.vulgaris in the other groups increased first and then decreased.Based on the results of response surface analysis,the optimal ratios of C,N and P for C.vulgaris growth at different P concentrations were obtained as follows: P=0.05 mg/L,N:P=124:1,C:N=3.3:1(T1);P=0.1 mg/L,N:P=119:1,C:N=3.9:1(T2);P=0.4 mg/L,N:P=101:1;C:N=3.6:1(T3);P=0.8 mg/L,N:P=44:1,C:N=5.6:1(T4);P=1 mg/L,N:P=31:1,C:N=3.7:1(T5).Comparing the changes in cell density,specific growth rate and chlorophyll a content of C.vulgaris cultured under above five optimal nutritional conditions,we found that with the increase of C,N and P concentrations,the cell density,specific growth rate and chlorophyll a content of C.vulgaris increased first and then decreased,reaching the maximum value at P= 0.8 mg/L,N:P=44:1,and C:N=5.6:1(T4).There was a significant difference in the absorption efficiency of total nitrogen and total organic carbon in C.vulgaris between groups(P<0.05),and the order from high to low was: T3 >T4 >T5 >T2 >T1 and T4 >T3 >T5 >T2 >T1,respectively.No significant difference in the absorption efficiency of total phosphorus in C.vulgaris between groups was observed(P>0.05).Under above five optimal nutritional conditions,C.vulgaris and M.aeruginosa were cultured separately and together in two different media.Results show that at low C,N and P concentrations,growth rates of M.aeruginosa cultured alone were significantly faster than those of C.vulgaris cultured alone in both two different media(P<0.05).With increasing concentrations of C,N and P,growth rates of C.vulgaris increased.At high C,N and P concentrations,cell density of C.vulgaris was significantly higher than that of M.aeruginosa(P<0.05);When C.vulgaris and M.aeruginosa were cultured together in two different media,the competitive inhibition parameters of M.aeruginosa to C.vulgaris were the largest at low C,N and P concentrations.With the increase of C,N and P concentrations,C.vulgaris gradually inhibited the growth of M.aeruginosa.Compared with BG-11 medium,C.vulgaris in simple medium showed greater competitive inhibition effects on M.aeruginosa.It was indicated that the growth of C.vulgaris changed with variant C,N and P nutrition conditions.Under the optimal C,N and P nutrition conditions for C.vulgaris growth,C.vulgaris achieved rapid proliferation via absorption of C,N and P nutrients,which will be contributed to solve eutrophication problem in culture waters.In addition,at the beginning phase of Microcystis bloom outbreak,we can stimulate C.vulgaris growth and competitively inhibit M.aeruginosa growth via adjusting C,N and P nutrition conditions.