【作者】 孙育平；

【导师】 韩博平；

【作者基本信息】 暨南大学 ， 水生生物学， 2010， 博士

【摘要】 营养盐和捕食者是影响浮游植物群落结构特征的关键因素。为了解南亚热带贫-中营养型水库水体中营养盐和捕食作用(鱼、浮游动物)对浮游植物群落结构的影响,本文于2008-2009年在流溪河水库进行围隔(85m3)实验,研究和分析了营养盐加富、鲢、鳙、透明薄皮溞对浮游植物群落结构的影响。于2008年4-6月进行围隔实验,设置营养盐加富(N、P)、营养盐加富+4g／m3鲢、对照处理组。其中营养盐以N／P(质量比)为10／1,分别按低(P为30μg/L)、中(P为60μg/L)、高(P为90μg／L)浓度形式添加。分析了营养盐加富和鲢对浮游植物群落结构的作用。结果表明营养盐加富和鲢都将导致透明度降低,且无鱼围隔组高于有鱼围隔组。有鱼围隔TN低于无鱼围隔组,TP则与此相反。营养盐加富和鲢使Chla浓度升高,且无鱼围隔组低于有鱼围隔组。营养盐加富使浮游植物种类多样性降低,鲢使浮游植物多样性增加。营养盐加富和鲢都使浮游植物总生物量明显升高,但其作用大小均受营养水平的影响。营养盐加富导致蓝藻、绿藻和隐藻生物量升高,而鲢则使蓝藻、绿藻、硅藻、隐藻生物量升高。蓝藻、硅藻、绿藻、隐藻生物量无鱼围隔组低于有鱼围隔组；金藻、甲藻生物量变化大小受营养水平的影响。实验期间出现了硅藻-绿藻-隐藻模式过渡期,但营养盐加富和鲢都均使浮游植物群落以甲藻-硅藻-绿藻型向绿藻-硅藻-蓝藻型模式演替,优势种向可食性差或具快速生长能力的种类演替。营养盐加富和鲢使浮游植物群落个体大小组成发生变化,其作用大小也均受营养水平影响。营养盐加富使组成浮游植物生物量的个体大型化,且使>30μm个体的相对生物量上升；鲢使组成浮游植物生物量的个体小型化,导致<10μm个体的相对生物量明显上升。这是由于无鱼围隔中主要受浮游动物(盔形溞)、有鱼围隔中主要受鲢的捕食压力,从而导致浮游植物产生不同的响应所致。营养盐和鱼的交互作用仅对浮游植物种类数和金藻丰度具有明显的作用,对衣藻数量变化也产生一定的影响。于2008年11-12月进行围隔实验,设置营养盐加富(N、P)、营养盐加富+3g／m3鳙、空白、3g/m3鳙对照处理组。其中营养盐以N／P(质量比)为10／1,分别按低(P为10μg/L)、中(P为30μg/L)、高(P为50μg／L)浓度形式添加。分析了营养盐加富和鳙对浮游植物群落结构的影响。结果表明营养盐加富和鳙导致透明度降低,但其作用大小与营养水平有关。有鱼围隔TN高于无鱼围隔组,TP与此相反。营养盐加富和鳙使Chla浓度升高,无鱼围隔低于有鱼围隔组。营养盐加富和鳙使浮游植物种类多样性升高,但有鱼围隔组较无鱼围隔组丰富。营养盐加富和鳙使浮游植物总生物量升高。营养盐加富导致甲藻、金藻生物量下降,而使绿藻、硅藻、蓝藻、隐藻生物量上升；鳙使绿藻、甲藻、金藻、隐藻生物量升高,而使硅藻、蓝藻生物量下降,但二者作用大小与营养水平有关。营养盐加富和鳙使浮游植物群落由硅藻-甲藻-金藻型向硅藻-绿藻-蓝藻型演替,优势种类向可食性差或生长速度快的种类演替。营养盐加富和鳙使组成浮游植物生物量个体大小变化,但作用大小均受营养水平影响。营养盐加富使组成浮游植物生物量的个体小型化；其中低营养水平条件下10-30μm个体相对生物量增加；中、高营养水平条件下<10μm和>30μm个体相对生物量上升。鳙在低营养水平条件下使组成浮游植物生物量的个体大型化,使>30μm个体相对生物量上升,而在中营养水平条件下使组成浮游植物生物量的个体小型化,使<30μm个体的相对生物量上升。这主要是由于无鱼围隔中浮游动物所受捕食压力较有鱼围隔中小,无鱼围隔中浮游植物主要受大型浮游动物(枝角类)和营养盐的影响,而有鱼围隔中浮游植物主要受小型浮游动物(轮虫)、营养盐和鳙影响所致。此外,营养盐和鱼的交互作用对浮游植物种类数,蓝藻、硅藻、甲藻、隐藻数量变化具有一定的作用。于2009年1-4月进行大型围隔实验,实验设置对照组、添加2.0 ind／m3透明薄皮溞组、添加1.1g/m3鳙组、添加2.0 ind／m3透明薄皮溞+1.1g/m3鳙组共四组处理。每个处理至少三个平行,共15个围隔。分析了透明薄皮溞和鳙对浮游植物群落结构的影响和作用。结果表明浮游植物种类多样性鳙+透明薄皮溞最高,有鱼围隔组高于无鱼围隔组,但透明薄皮涵和对照组相似。浮游植物总生物量鳙+透明薄皮溞最高,透明薄皮溞最低。鳙、透明薄皮溞+鳙将导致浮游植物生物量一定程度增加；透明薄皮溞的级联效应对蓝藻、硅藻、绿藻生物量具有一定的抑制作用,而对甲藻和金藻具有一定的促进作用。透明薄皮溞和鳙使浮游植物群落由硅藻-金藻-甲藻型向硅藻-绿藻-甲藻型演替,优势种类向可食性差或生长速度快的种类演替。透明薄皮溞和鳙使组成浮游植物生物量个体大型化。其中,鳙、透明薄皮溞+鳙导致>30μm个体相对生物量上升、<30μm个体的相对生物量下降；透明薄皮涵导致10-30μm个体相对生物量上升、>30μm和<10μm个体相对生物量下降。这可能因无鱼围隔主要受盔形溞的影响,而有鱼围隔主要受桡足类、轮虫和鳙级联效应的影响；透明薄皮溞对小型枝角类及轮虫进行捕食,导致对浮游植物的群落结构产生了不同的级联效应。上述结果表明,浮游植物群落结构受营养盐和捕食者双重效应的共同影响。营养盐和捕食者作用的大小受营养水平和捕食者种类、数量的影响。因此,充分了解和掌握不同捕食者在不同营养水平条件下的作用是进行水库水质改善和管理的关键。更多还原

【Abstract】 It is now well recognized that nutrient and predation would play the key roles in phytoplankton structure and biomass, but most studies are conducted mainly in the temperate regions, less in the tropics and subtropics. In order to understand the trophic cascade effects of nutrient enrichment, filter-feeding fish and zooplankton on phytoplankton community in tropical and subtropical reservoirs, we performed three large enclousure experiments in Liuxihe Reservior, an oligo-mesotrophic reservoir, located in South China from 2008 to 2009. The enclosures were filled with about 85 m3 water from the reservoir. The trophic cascade effect of the nutrient enrichment, silver carp(Hypophthalmichthys molitrix,[val.]),bighead carp(Aristichthys nobilis) and Leptodora kindti on the phytoplankton community in the enclosure were examined and analysed.The first experiment was carried out with 21 large enclosures from April 24 to June 7,2008 (49 d,7weeks). It was designed with 7 treatments of nutrient enrichment and stocking silver carp. The experiment included 1)the nutrient additions of three different levels including low (P concentration 30μg/L) (LN), medium (P concentration 60μg/L)(MN) and high (P concentration 90μg/L)(HN)conditions, with a N/P(mass ratio) of 10/1 in all treatments;2)the above three levels of nutrient enrichment conditions with silver carp 4g/m3 stocked(LNF,MNF and HNF); 3)controls without nutrient enrichment and fish stocking(C). There were three replicates for each treatment. The response of phytoplankton to nutrient enrichment was analyzed through the nutrient added treatments and the controls. The trophic cascade effects of the filter-feeding fish on the phytoplankton were also investigated and analyzed between the only nutrient enriched treatments.The results showed that the Secchi disk depth in both nutrient enrichment treatments and silver carp+nutrient addition treatments descreased, and it was higher in the enclosures without fish than in the enclosures with fish. The total nitrogen(TN) in the water column decreased,while the total phosphorus(TP)increased with the presence of fish. Chlorophyll a concentration in nutrient enrichment with and without fish stocking increased, and it was higher in the enclosures stocked fish than the only nutrient addition. Nutrient enrichment resulted in a decrease in phytoplankton diversity, and fish stocking resulted in an increase. Nutrient enrichment and fish stocking both sustained high total phytoplankton biomass depending on nutrient concentrations. Responses of algal groups, such as Cyanobacteria, Chlorophyta and Cryptophyta, were similar in the nutrient enrichment enclosures with and without fish, but the biomass of diatoms (Bacillariophyta) increased solely in the nutrient enrichment with fish. Cyanobacteria, Bacillariophyta, Chlorophyta and Cryptophyta biomass was higher in the enclosures with fish than in the enclosures without fish, but Chrysophyta biomass and Dinophyta biomass were on the contrary. The structure of the phytoplankton community in the enclosures treatments with and without fish shifted from an initial dominance of Dinophyta-Bacillariophyta-Chlorophyta phytoplankton pattern to Bacillariophyta-Chlorophyta-Cryptophyta, and finally to Chlorophyta-Bacillariophyta-Cyanobacteria, while the dominant species shifted to inedible species or the species with rapid growth rate. The phytoplankton size structure and species composition in the enclosures of erichments with and without fish varied during the experiments, but the variability would depend on the nutrient concentrations. Nutrient enrichment only resulted in the dominance of large sized groups, especially increase in the relative biomass of>30μm fraction, while nutrient enrichment with fish reaulted in small size groups became dominant, especially increase in the relative biomass of<10μm fraction.These were because that the enclousure treatments only enrichment were mainly regulated by Daphnia geleata while the enclousure treatments enrichment with fish were regulated by silver carp and nutrient at the same time, so the trophic cascade would be different with the treatments.The second experiment was carried out in 21 large enclosures from December 26 to November 28,2008 (32d,5weeks). The experiment was designed with nutrient enrichment and bighead carp. The experiment included:1)the nutrient additions with three levels including low (P concentration 10μg/L)(LN), medium(P concentration 30μg/L)(MN) and high (P concentration 50μg/L)(HN)conditions, with a N/P(mass ratio) of 10/1 in all treatments; 2)the above nutrient enrichment conditions(LN and MN) with 3g/m3 bighead carp stocked(LNF and MNF); 3)controls without nutrient enrichment and fish stocked(C); 4) controls without nutrient enrichment but only with fish stocked(CF). There were three replicates for each treatment. The results showed that the Secchi disk depth in both nutrient enrichment treatments with and without fish stocking decreased, to the various extents regulated by the nutrient additon levels. Fish presence increased total nitrogen (TN) while decreased total phosphorus (TP). Chlorophyll a concentrations increased in nutrient enrichment treatments with and without fish, and it was higher in the enclosures with fish than in the only nutrient enrichments. Nutrient enrichment and stocking fish resulted in increase in phytoplankton diversity. And phytoplankton diversity was higher in the nutrient enrichment with stocking fish than in those with nutrient enrichment. Nutrient enrichment and stocking fish sustained high phytoplankton total biomass. Nutrient addition led to the increase of Chlorophyta,Bacillariophyta,Cyanobacteria and Cryptophyta,but the decrease of Dinophyta and Chrysophyta.On the other hand,addition of fish caused biomass increase of green algae, dinoflagellates,cryptophyta and chrysophytes,and decrease of diatoms and cyanobacteria,but the magnitude of the changes depended on the level of nutrients. The structure of the phytoplankton community in the treatment enclosures with and without fish stocking shifted from an initial pattern dominated by Bacillariophyta-Dinophyta-Chlorophyta to the final dominance of Bacillariophyta-Chlorophyta-Cyanobacteria, while the dominant species shifted to inedible species or the rapid-growing species. The phytoplankton size structure and community composition in the enrichments with and without fish stocking changed during the experiments, but the the extent depended on the nutrient concentration. Nutrient enrichment resulted in small size groups becoming dominant.Particulary,the low enrichments would increase the relative biomass of 10-30μm,while the medium and higher enrichments could increase the relative biomass in<10μm and >30μm fraction. Low enrichment with fish resulted in large size groups become dominant, especially increased the relative biomass in>30μm fraction, while in medium nutrient enrichments, smaller sized components become more dominant, especially cells of<30μm fraction. The predation pressure of zoophytoplankton to the phytoplankton was higher in the treatment enclosures without fish than the treatments enclosures with fish,sucn as the treatements without fish were mainly controlled by cladocear and nutrient,but the treatements with fish were mainly regulated by rotifera,bighead carp and nutrient,so theses would make the phytoplankton response different.The third experiment was carried out in 15 large enclosures from January 21 to April 17, 2009 (85 d). Leptodora kindti and bighead carp were used as predator treatments. The experiment included:1)the control (C).2) with 2.0 ind/m3 Leptodora kindti (L).3)with 1.1 g/m3 bighead carp (F).4) with 2.0 ind/m3 Leptodora kindti and 1.1 g/m3 bighead carp (LF). There are more than three replicates for each treatment. The response of phytoplankton to Leptodora kindti was analyzed through the Leptodora kindti added treatments and the other treatments. The trophic cascade effects of the filter-feeding fish on the phytoplankton were also investigated and analyzed between different treatments. Phytoplankton diversity in FL treatment was the hith3w5, and it was higher in the enclosures with fish than in the enclosures without fish, while the diversity in L and C treatments was similar. Total phytoplankton biomass was the most in FL, and was the least in the L treatment. Phytoplankton biomass increased in F and FL.Addition of Leptodora kindti would resulted in decrease in biomass of Cyanobacteria, Bacillariophyta, Chlorophyta, but improved Dionphyta and Chrysophyta biomass. The structure of the phytoplankton community in the enclosures treatments with Leptodora kindti and fish stocking shifted from an initial pattern with dominance of Bacillariophyta-Chrysophyta-Dinophyta to the final dominance of Bacillariophyta-Chlorophyta-Dinophyta, while the dominant species shifted to inedibile species or the species with fast-growing. The phytoplankton size structure and species composition in the enclosures with Leptodora kindti and bighead carp varied during the experiments, large sized groups became dominant. Fish stocking and Fish stocking+Leptodora kindti treatments would increase the relative biomass of>30μm fraction, and reduce the relative biomass of<30μm fraction. Leptodora kindti increased the relative biomass of 10-30μm fraction, but decreased the relative biomass of<10μm and>30μm fraction. Daphnia geleata in treatments without fish was more than treatments with fish,while copepods and rotifera were on the contrary. Leptodora kindti can prey rotifera and some small sized cladocera. So the different predation pressure would led to different trophic cascade to the phytoplankton.Our experiments indicated that phytoplankton community structures were regulated by both nutrients and predation. The interaction of nutrient and fish would also play a key role. However, the trophic cascade effects on phytoplankton community would mostly depend on the nutrient concentration, and the species and density of the predators. Consenquently, it is important to find out and understand the interaction between predators and nutrients.更多还原