太湖水华期间有毒和无毒微囊藻种群丰度的动态变化

Abstract

Lake Taihu is a large(2338 km2),shallow(mean depth 2.0 m),hypereutrophic and well mixed year-round(polymictic) lake.For the past three decades,seasonal blooms of Microcystis spp.have regularly formed in the lake,usually starting around April and persisting through October.It has long been known that microcystin-producing and non microcystin-producing strains can be isolated from one water sample,and the waxing and waning of microcystin-producing versus non-microcystin-producing strains has been suggested as a most important factor regulating net microcystin production in water.However,the quantification of microcystin producers versus non-microcystin-producers was for a long time impeded because of the morphological similarity between strains differing in microcystin production.Quantitative real-time PCR(qPCR) has been successfully applied to track quantities of microcystin-producing Microcystis genotypes in natural populations.So far,the effects of environmental factors on the abundance of microcystin-producing and non-toxic Microcystis genotypes have been studied in a relatively limited scale.In this study,We attempted to verify the environmental factors related to the spatial and temporal dynamics of the abundance of toxic and non-toxic Microcystis in the Lake Taihu.Water samples were collected in three sampling sites(Meiliang Bay(N2),Gonghu Bay(N4) and the center area(S4) at monthly intervals from April to September,2010.The abundance and subpopulation proportion of toxic Microcystis genotypes was quantified using a quantitative real-time PCR with two primers sets for the cpcBA-IGS and mcyA gene.QPCR data showed that the abundance and proportion of toxic Microcystis genotypes in three studying sites increased gradually from April to August,and then decreased in September,with both values being higher in Meiliang Bay than in the other two sites.The proportion of toxic Microcystis genotypes in Meiliang,GonghuBay and the center area varied considerably,ranging from(26.2± 0.8)% to(64.3 ±2.2)%,from(4.4±0.2)% to(22.1±1.8)% and from(10.4±0.4)% to(20.6±1.5)%,respectively.Correlation analysis revealed a significantly positive relationship between chlorophyll a,toxic Microcystis and total Microcystis.Meanwhile all the three components were strongly related to water temperature(P0.05).The change of the proportion of toxic Microcystis genotypes was closed related to water temperature(P0.01) and phosphorus concentration(P0.05),suggesting that water temperature and phosphorus concentration are critical environmental factors for determining the abundance and proportion of toxic Microcystis genotypes in Lake Taihu.