【作者】 陈晓玲；

【导师】 韩博平；

【作者基本信息】 暨南大学 ， 环境科学， 2012， 硕士

【摘要】 超微型浮游植物是指细胞直径在0.2-3μm之间的浮游植物，包括原绿球藻、超微蓝藻和真核超微藻类，通常在贫营养水体中是初级生产力的重要贡献者。为了解南亚热带地区深水水库中超微浮游植物的群落结构及其影响因素，在广东省贫-中营养型的流溪河水库设置了5个采样点和4个深度分层，于2011年6月至2012年4月每月一次调查水库的超微浮游植物群落结构，并分别在流溪河水库进行了3次围隔（体积约为85m~3）实验，考察浮游动物以及鱼类牧食、营养盐加富和水体物理扰动对超微浮游植物群落的影响。第一个实验以了解溞属的盔形溞（Daphnia galeata）对超微浮游植物的影响为目的，设置空白对照组和3个添加不同密度盔形溞的处理组。第二个实验以了解营养盐加富和鱼类对超微浮游植物的影响为目的，设置对照组和4个处理组，添加氮、磷和不同密度组合的鲢（Hypophthalmichthys molitrix）、鳙（Aristichthys nobilis）、罗非鱼（Tilapia nilotica）。第三个实验以了解水体物理扰动的营养盐加富对超微浮游植物的影响为目的，在围隔底部添加磷盐，设置不同频率的扰动处理。流溪河水库超微浮游植物年平均丰度为1.44×105cells/mL，占浮游植物总丰度99.39%，生物量平均为0.23μg/L，占总生物量0.023%。流溪河水库的超微浮游植物主要由超微蓝藻和超微真核藻类两大类组成，其中超微蓝藻共占超微浮游植物总丰度95%。超微蓝藻在春季和秋季有峰值，超微真核藻类春季丰度最高。河流区与湖泊区丰度之间存在差异，超微真核藻类表现与小-微型浮游植物（>3μm）一致，全年河流区丰度高于湖泊区，超微蓝藻春季刚开始降雨后湖泊区显著高于河流区，其他季节河流区较高。从超微浮游植物在大坝的垂直分布来看，多数情况下其丰度均在10m深处最高，只有春季透明度较低和温跃层较高时，超微浮游植物在5m处最高。这说明超微浮游植物对光和温度敏感性较高。在添加盔形溞的围隔实验中，超微蓝藻和超微真核藻类变化趋势一致，而与小-微型浮游植物变化不一致，小-微型浮游植物在第1周下降而超微浮游植物第1周上升，说明在食物丰富时浮游动物选择性牧食较大的浮游植物，超微浮游植物可获得更多资源因而生物量增长。第2周各个粒径的浮游植物生物量均下降，可能是食物有限时浮游动物降低对食物的选择，同时营养盐限制了浮游植物生物量增长。第3周超微浮游植物持续下降，小-微型浮游植物停止下降，而浮游动物大幅度增长，可能是由于浮游动物开始大量繁殖，动物幼体更多牧食超微浮游植物所导致的。在添加营养盐和3种鱼类的实验中，无论是否加鱼类，营养盐的添加使各个粒径的浮游植物均在第1周增长，超微蓝藻增长速度较快并且持续增长至第2周，其他浮游植物第2周开始下降，这是由于第2周磷的下降和浮游动物的牧食导致的。对照组超微蓝藻生物量有小幅度增长，超微真核小幅度下降，小-微型浮游植物大幅度下降，同样说明了超微蓝藻在资源限制和浮游动物的牧食中的竞争优势。鱼类的添加使水体营养盐水平提高，同时各个粒径的浮游植物丰度生物量均更高，鲢、鳙及罗非鱼混养对超微蓝藻有最明显的促进作用，单养鲢在实验末期显著促进超微真核藻类和小-微型浮游植物的生长。鱼类通过下行效应和排泄物加速营养盐循环等途径影响超微浮游植物，其中加速营养盐循环对超微浮游植物的促进作用最为明显。在水体物理扰动实验中，各个粒径的浮游植物均在第1周生物量上升，超微蓝藻增长率显著高于其他浮游植物和不添加营养盐组，表现营养盐对其的促进作用和其对营养盐的快速利用。第2周各个粒径的浮游植物均下降，超微蓝藻随着种群密度增长到顶峰，其丰度和比重均开始下降至实验结束。超微真核藻类和小-微型浮游植物表现相似，均实验后期增长，表明超微真核藻类对营养盐加富反应较缓慢，但对其适应性更强。不同频率的扰动不能使营养盐浓度差异显著，但扰动促进营养盐均匀分布和循环，因此促进超微浮游植物的生长。综合野外观测和围隔实验，在流溪河水库中，影响超微浮游植物群落生物量的主要因子是营养盐，磷是超微浮游植物生长的限制因子，磷的加富促进超微浮游植物的生长，超微蓝藻对磷加富的响应最为敏感。在浮游动物食物丰富时，超微浮游植物受成体浮游动物的牧食压力较小。鱼类对超微浮游植物群落有正面影响，主要是通过其排泄物加速营养盐循环，提高营养盐的浓度而促进超微浮游植物生长。物理扰动主要通过底泥营养盐再悬浮和释放影响超微浮游植物的群落生物量。更多还原

【Abstract】 The picophytoplankton is the fraction of phytoplankton composed by cells between0.2-3μm,including Prochloroccus, picocyanobacteria and picoeukaryotes. It is especially important inoligotrophic water bodies. The effect of nutrients, zooplankton, fish prey and turbulence on thepicophytoplankton community in oligotrophic reservoirs was investigated by annual surveys andenclosure experiments of the picophytoplankton in Liuxihe Reservoir, a large and deepoligo-mesotrophic reservoir in southern China. The field samples were taken every month forseasonal variation, the observations ranging from June2011to April2012. And three enclosureexperiments were performed separately.The first enclosure experiment was designed to check the predation pressure of Daphnia onpicophytoplankton. The experiment had one control without adding Daphnia galeata and threetreatments with adding low, middle and high density of Daphnia galeata, respectively. In thesecond experiment, nitrogen and phosphorus were added to detect the effect of increase ofnutrients on picophytoplankton communites, Hypophthalmichthys molitrix （silver carp）,Aristichthys nobilis（bighead carp）and Tilapia nilotica（nile tilapia）were added solely or inmixture to detect their effects on picophytoplankton communites. The vertical mixing experimentwas carried out by adding phosphorous to the bottom of the enclosure and combined with differentvertical mixing.Both picocyanobacteria and picoeukaryotes were found in Liuxihe Reservoir. The annual averagepicophytoplankton cell number was1.44×105cells/mL，of which95%were cyanobacteria, whichcontributed to99.39%of the total phytoplankton abundance. Average biomass was0.23μg/L,contributed0.023%of total. The abundance of picocyanobacteria had peaks in both spring andautumn, when more species were found than in winter. Picocyanobacteria were more abundant inthe riverine zone and the transition zone than in the lacustrine zone except in spring, andpicoeukaryotes were more abundant in the riverine zone all year as well as that ofmicro-nanophyplankton（>3μm）. The vertical distribution of picophytoplankton showed a peakabundance at10m depth in all the samples except in spring. The results indicate that thepicophytoplankton was sensitive to light and temperature in Liuxihe Reservoir.The results of the zooplankton adding experiment showed no significant difference between thetreatments. Daphnia galeata increased quickly in the first three weeks and reduced the differencebetween four treatments. The abundance and biomass of picophytoplankton increased whenmicro-nanophytoplankton decreased in the first week and then both markedly descreased. Theresult indicates that the picophytoplankton can assimilate nutrients more efficiently when they arelimited, and they can also avoid from grazing by Daphnia who prefers the larger phytoplankton.But when micro-nanophytoplankton were less abundant, Daphnia may prey on both pico-andmicro-nanophytoplankton.In the second experiment, all fractions of phytoplankton increased in nutrient enriched treatmentswith or without fish. The results showed that the abundance and biomass of picophytoplanktonwere related to phosphorous concentration, while other phytoplankton were influenced by bothphosphorous concentration and zooplankton biomass. The nutrients were higher in the fishtreaments, which coincided with the picophytoplankton abundance. The picocyanobacteria was highest in HAT all the time and picoeukaryotes abundance was highest in H in the end of theexperiment.After adding nutrients in the treatments in the third experiment, the abundance and the biomass ofall phytoplankton increased. The abundance of picocyanobacteria was much higher than that ofothers in the first week and then decreased towards the end. The picoeukaryotes andmicro-nanophytoplankton decreased in the second week then increased later. Picocyanobacteriawas sensitive to nutrients but could not adapt to the high nutrient concentration. In contrast,picoeukaryotes has relatively low assimilation rate but higher affinity to nutrients. Theconcentration of nutrient showed no significant difference between different vertical mixingfrequency, and all significantly higher than in H. The density of picophytoplankton was higher inthe mixing treatments and highest in HP, which shows that vertical mixing can increasepicophytoplankton abundance.In conclusion, nutrient enrichment especially for phosphorous can increase picophytoplanktonabundance and biomass. Picocyanobacteria response more quickly than picoeukaryotes andmicro-nanophytoplankton. Picophytoplankton is not selectively grazed by zooplankton whichprefers the larger phytoplankton. However, zooplankton may graze on both pico-andmicro-nanophytoplankton when micro-nanophytoplankton was less abundant. The mostsignificant impact by the omnivorous fish to picophytoplanton was not the change of predationpressure, but the increase of nutrient concentration. Vertical mixing can increasepicophytoplankton abundance. Among all the possible factors, it seems that the nutrients,especially phosphorous, make up the most influencial factor to picophytoplankton abundance andcommunity structure in Liuxihe Reservoir.更多还原