| In recent years,with the rapid development of economy and human production activities,a large number of nitrogen,phosphorus nutrients and greenhouse gases are discharged.The eutrophication of water body is becoming more and more serious,and the climate warming is intensified,resulting in frequent outbreaks of cyanobacterial blooms.In particular,algal toxins have become one of the environmental pollution problems that have attracted much attention.Chaohu Lake in Anhui province is the fifth largest freshwater lake in China,but cyanobacterial blooms have become an urgent ecological and environmental problem to be solved in Chaohu Lake.In particular,microcystins are a serious threat to human and animal health.Toxicity and inactive cyanobacteria coexist in natural water and are affected by environmental factors.In this study,the concentration distribution characteristics of microcystins（MCs）,the changes of water quality indexes and the abundance distribution characteristics of microcystin-producing Microcystis detected by fluorescence quantitative PCR（q PCR）were investigated.Taking microcystin-producing Microcystis in Chaohu Lake as the research object,the effects of different temperatures and nitrogen and phosphorus nutrients on the growth and toxin production of Microcystis were explored.The results were as follows :（1）A one-year investigation of Chaohu Lake from March 2021 to January 2022 showed that microcystins（MCs）were composed of intracellular microcystins（IMCs）and extracellular microcystins（EMCs）,and had obvious spatial and temporal distribution characteristics.The concentration of IMCs in summer（6.690 μg/L）> autumn（3.533μg/L）> spring（0.282 μg /L）> winter（0.125 μg/L）,EMCs in summer（0.236μg/L）>autumn（0.235 μg/L）> winter（0.028 μg/L）> spring（0.025 μg/L）.Spatially,from the perspective of the whole year,IMCs West Lake（4.479 μg/L）> Middle Lake（1.876μg/L）> East Lake（1.010 μg/L）,EMCs West Lake（0.235 μg/L）> Middle Lake（0.067μg/L）> East Lake（0.055 μg/L）.However,the spatial distribution of EMCs is not completely consistent in different seasons,and the East Lake region is slightly larger than the Central Lake region in spring,autumn and winter.The annual average water temperature（T）of Chaohu Lake was 19.19 ℃,the average concentration of total nitrogen（TN）was 2.45 mg/L,and the average concentration of total phosphorus（TP）was 0.15mg/L.The annual average water temperature（T）of Chaohu Lake was 19.19 ℃,the average concentration of total nitrogen（TN）was 2.45 mg/L,and the average concentration of total phosphorus（TP）was 0.15 mg / L.Correlation analysis showed that IMCs and TP were significantly positively correlated（P < 0.01）and T,TN were significantly positively correlated（P < 0.05）,and TN/TP was significantly negatively correlated（P < 0.05）;e MCs showed extremely significant positive relationship with TP（P < 0.01）,significant positive relationship with TN（P < 0.05）,and significant negative relationship with TN/TP（P <0.05）.MCs were significantly positively correlated with TN,TP and T（P < 0.05）.It can be seen that TN,TP and T are the key factors affecting MCs in Chaohu Lake.（2）The abundance changes of toxic Microcystis in spring（April）,summer（August）,autumn（October）and winter（January）were analyzed by q PCR.The results showed that the abundance of toxic Microcystis also showed temporal and spatial distribution.The highest abundance was in summer,followed by autumn,spring and winter.In space,the overall west lake area > the lake center area > the east lake area.Toxic and non-toxic Microcystis coexist,and the abundance of toxic Microcystis accounts for the proportion of total Microcystis abundance.The abundance in summer is the highest in time,followed by autumn,spring and winter.In space,the overall West Lake area > the central lake area >the East Lake area,but there is no obvious spatial distribution law in spring and winter.The abundance of toxic Microcystis was significantly positively correlated with T（P <0.01）,TN and TP（P < 0.05）,and the proportion of toxic Microcystis in TN and TP was significantly positively correlated（P < 0.01）.（3）Temperature（20 ℃,25 ℃,30 ℃）and nitrogen and phosphorus nutrients（control : TN = 2.3 mg/L,TP = 0.18 mg/L;3 NP : TN = 6.9 mg/L,TP = 0.54 mg/L;6 NP :TN = 13.8 mg/L,TP = 1.08 mg/L;12 NP : TN = 27.6 mg/L,TP = 2.16 mg/L;24 NP : TN= 55.2 mg/L,TP = 4.32 mg/L）.The results of laboratory experiments on the growth and toxin production of Microcystis aeruginosa under the superposition effect showed that the growth and toxin production of Microcystis aeruginosa showed different response modes to the superposition effect of temperature and nutrients.At the same temperature,the number of Microcystis aeruginosa cells and the concentration of chlorophyll a（Chla）increased with the increase of nitrogen and phosphorus concentration,and the specific growth rate increased,showing a logistic growth mode.With the increase of temperature,the concentration of Chla and the specific growth rate of Microcystis aeruginosa cells increased continuously under the superposition effect of nitrogen and phosphorus nutrients.At the same temperature,although the microcystin production increased with the increase of nutrients,the microcystin concentration at 25 ℃ was significantly higher than that at30 ℃ and 20 ℃,and the microcystin concentration at 20 ℃ was the lowest.As the temperature increased to 25 ℃,Microcystis aeruginosa synthetic toxins were more obvious by the superposition of temperature and nitrogen and phosphorus nutrients.At20 ℃,the toxic production of a single Microcystis aeruginosa increased with the increase of nitrogen and phosphorus nutrient salt concentration,but with the increase of temperature,the growth trend of toxic production capacity of Microcystis aeruginosa was not obvious.The above results showed that the growth and toxin production of Microcystis aeruginosa had a significant response to the increase of temperature and nutrients,but the response of Microcystis aeruginosa synthetic toxins to temperature was not consistent with the growth.In the future,warming and eutrophication will significantly promote the growth of Microcystis aeruginosa and promote the expansion of cyanobacterial blooms,but the concentration of microcystins may not always increase,which may be related to its toxin production capacity.Figure [23] table [16] reference [80]... |
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