巢湖夏季和冬季有毒微囊藻和无毒微囊藻种群丰度研究

Studies on the abundance of toxic and non-toxic Microcystis population of Lake Chaohu in summer and winter

应用荧光定量PCR技术研究了巢湖夏季和冬季有毒微囊藻和无毒微囊藻种群丰度的空间分布,分析了有毒微囊藻和无毒微囊藻种群丰度与环境因子之间的关系,同时应用HPLC方法分析了水体中溶解性微囊藻毒素浓度.结果表明:巢湖有毒微囊藻和无毒微囊藻种群丰度存在季节和空间差异.总的来说,夏季有毒微囊藻和无毒微囊藻种群丰度高于冬季,西湖区高于东湖区.有毒微囊藻占总微囊藻种群丰度的比例在夏季和冬季分别为8.4%～65.8%和0.5%～8.1%.微囊藻毒素浓度及其组成具有显著的季节和空间差异,在夏季,总微囊藻浓度低于0.5μg·L-1,西湖区和东湖区浓度高于湖心;在冬季,总微囊藻毒素浓度从东湖区向西湖区呈逐渐增加趋势,最高浓度为2.21μg·L-1,高于WHO规定的安全浓度阈值(<1.0μg·L-1).相关分析表明,有毒微囊藻、无毒微囊藻和叶绿素a呈极显著正相关(p<0.01);微囊藻毒素浓度与总氮、总磷、正磷酸盐、硝态氮、氨态氮和溶解氧呈极显著正相关(p<0.01),与电导率和pH呈极显著负相关(p<0.01).

It has been known that Microcystis exists as a mixed population of potentially toxic and non-toxic genotypes in a water body,but toxic and non-toxic Microcystis can not be distinguished by microscopy methods.In this study,we performed real time PCR assays to investigate the densities of the potential toxic subpopulation and the total Microcystis in Lake Chaohu,targeting the microcystin synthetase gene（mcyD） and the phycocyanin intergeic spacer,respectively.Water samples were collected from seven sampling sites,including a transect from eastern to western lake along with different trophic levels.QPCR data showed a marked spatio-temporal difference in the abundance of toxic and non-toxic Microcystis,which was much higher in summer than in winter and as well as in west lake areas than in east lake areas.The proportion of toxic Microcystis in total Microcystis population ranged from 8.4% to 65.8% and from 0.5% to 8.1%,in summer and winter,respectively.Using high-pressure liquid chromatography with diode array detection,we found that the concentration and composition of three microcystin variants（MC-RR,MC-YR,and MC-LR） varied significantly in different sampling sites.The total microcystin concentration was low（0.5 μg · L^-1） in summer.In contrast,it was relatively high in winter,with the peak value reaching 2.21 μg · L^-1 in CW3 sampling site.Correlation analysis showed that the abundance of toxic and non-toxic Microcystis were significantly related to chlorophyll a concentration（p〈0.01）.Microcystin concentration were positively related to total nitrogen,total phosphorus,orthophosphate,nitrate,ammonium and dissolved oxygen（p〈0.01）,but were negatively correlated with conductivity and pH（p〈0.01）.