流溪河水库的盔形潘和舌状叶镖水蚤对浮游植物的牧食影响研究

盔形溞Daphnia galeata和舌状叶镖Phyllodiaptomus tunguidus是流溪河水库的两种大型的滤食物性的浮游动物,P.tunguidus也是中国特有种,他们的牧食直接影响浮游植物种类组成和群落结构.为了解这两种浮游动物在自然水体中对浮游植物牧食的作用及营养盐水平对牧食作用的影响,将D.galeata和P.mnguidus 4.4 ind.L-1的密度,分别在两个营养水平(不添加与添加营养盐)中用4.5L的透明塑料瓶培养10天(2008年3月28-4月8日).在不添加营养盐的实验中,水样为用64um孔径的筛绢过滤后的水库水,在添加营养盐的实验中,为过滤后的水样再加入KH2PO4和NaNO3,使TN:TP=16:1(TN=34.86 μmol·L-1,TP=2.18 μmol·L-1).10天后,计数和分析浮游植物四个粒径级别(＜20μm,20-30μm,30-50μm,＞50μm)和各门类及优势种类的生物量组成,比较两组动物在两种营养状态中对浮游植物生物量的影响. 在不添加营养盐的实验中,两种浮游动物对浮游植物总生物量的抑制均不明显,但＜30μm的浮游植物生物量均下降,且D.galeata处理组中,小于20μm的浮游植物生物量低于P.tunguidus处理组,P.tunguidus处理组中20-30μm的浮游植物生物量低于D.galeata组,说明两种浮游动物对＜30μm的浮游植物均有抑制作用,但D.galeata对＜20μm的浮游植物抑制强于P.tunguidus而P.tunguidus对20-30μm的浮游植物抑制强于D.galeata. 在添加营养盐的实验中,营养盐对浮游植物生物量,尤其对＜20μm的浮游植物生物量的促进作用明显.但两种浮游动物对浮游植物的抑制作用在不同种类之间产生差异.D.galeataa处理组的浮游植物总生物量明显高于P.tunguidus组,表明P.tunguidus对浮游植物的抑制作用强于D.galeata.D.galeata处理组中,蓝藻生物量比例(15%)远低于绿藻(41%)和硅藻(37%),但在P.tunguidus组蓝藻生物量比例(36%)远高于绿藻(18%)和硅藻(32%),与不添加营养盐实验的t检验表明D.galeata对绿藻和蓝藻抑制明显,而P.tunguidus对绿藻和硅藻的抑制明显(t-test,p＞0.05).D.galeata对衣藻chlamydgmonas sp.,绿球藻chlorococcum sp.,单细胞蓝藻抑制作用明显,而P.tunguidus对小球藻chlorella sp.,衣藻chlamydomonas sp.,绿球藻chlorococcum sp.,小环藻cyclotella sp.,曲壳藻achnanthes sp.,针杆藻Syneara sp.的抑制明显. 实验结果表明两种浮游动物影响不同的浮游植物种类,对浮游植物的群落结构的影响具有差异.     

Grazing resistance in nutrient-stressed phytoplankton

Grazing experiments were performed with the zooplankters Daphnia pulex and Daphnia magna, feeding on phosphorus-saturated and phosphorus-limited cells of two green algae (Scenedesmus subspicatus and Selenastrum capricornutum). P-limited algal cells passed largely intact through the gut and were thus spared from heavy grazing pressure. P-saturated algal cells, in contrast, were efficiently assimilated. Structural and morphological changes in the P-limited cells most probably reduced their digestibility. This phenomenon may be an important factor in zooplankton production and competition, and may serve as an example of a highly efficient strategy of P-limited algae to resist heavy grazing pressure.     

Dynamics of a stable, large volume, laboratory ecosystem containing Daphnia and phytoplankton

Daphnia magna and phytoplankton were maintained in stable, large-volume(3400 l), indoor, planktonic model ecosystems for up to 20 weeks.Ecosystem stability was demonstrated by damped oscillationsin population abundance, and by a return to steady-state conditionsif the system was perturbed. The steady-state biomass of daphniaand algae responded to variations in nutrient loading ratesand daphnia harvesting rates in accordance with predictionsfrom a mathematical model. Increased nutrient addition resultedin an increase in biomass of daphnia, but not phytoplankton,if both were present. Increased harvesting caused an increasein chlorophyll and decreased daphnia biomass. Phosphorus additionswere balanced by sedimentation losses which were proportionalto daphnia biomass. Increased harvesting rates resulted in decreasedphosphorus loss rates and increased efficiency of phosphorusconversion into harvested daphnia. Damped oscillations had aperiodicity of 3.5 weeks and could be successfully modelledassuming a half-saturation constant for phosphorus control ofalgal growth of 1 µg l^–1. The ecosystem became unstableif nutrient loading rates exceeded a defined limit which wasa function of harvesting rates. Steady-state chlorophyll anddaphnia biomass levels were similar to levels approached inLake Michigan in summer in 1983 and 1984, when the zooplanktonbiomass was dominated by Daphnia pulicaria.     

Results Regarding the Food of the Planktic Crustaceans Daphnia hyalina and Eudiaptomus gracilis

The graph of maximum filtering and grazing rates versus particle size shows that Daphnia hyalina is a microfiltrator and Eudiaptomus gracilis is a macrofiltrator. In contrast to Eudiaptomus gracilis, Daphnia hyalina is also able to utilize larger bacteria (c. 1 μm³) as a food source.     

The influence of year-to-year variations in winter weather on the dynamics of Daphnia and Eudiaptomus in Esthwaite Water, Cumbria

1. Micro-crustacea of the genus Daphnia and Eudiaptomus have evolved different physiological mechanisms for coping with life in a rapidly changing environment. In this paper, we analyse some of the physical and biological factors influencing the winter abundance of the two species in a small lake (Esthwaite Water in Cumbria).
2. The results demonstrate that much of the year-to-year variation in their relative abundance can be related to long-term changes in the weather. The highest numbers of Daphnia were typically found in cold, calm winters when small flagellates were relatively abundant. In contrast, the highest numbers of Eudiaptomus were found in mild, windy winters when the phytoplankton community was dominated by colonial diatoms.
3. Year-to-year variations in the winter abundance of Eudiaptomus had no effect on their subsequent development but the numbers of overwintering Daphnia had a significant effect on the size of their first spring 'cohort'. The most important factor influencing the overwintering performance of the two species was the water temperature.
4. Winter air temperatures over much of Europe are influenced by the atmospheric pressure variation known as the North Atlantic Oscillation (NAO). Winter water temperatures in Esthwaite Water were strongly correlated with this empirical index and there was a significant positive correlation between the NAO and the number of overwintering Eudiaptomus.     

海洋微型浮游动物对浮游植物和初级生产力的摄食压力

综述了国际上研究微型浮游动物对浮游植物和初级生产力摄食的方法,并重点介绍了稀释法的理论和在实践中遇到的问题。各种方法的微型浮游动物对浮游植物和初级生产力摄食压力的估计表明,微型浮游动物在海洋生态系统中的扮演重要角色。     

Detection, cultivation and maintenance of Gallionella in laboratory microcosms

A simple circulating system was developed whereby growth medium or stream water was circulated through vessels containing putative Gallionella specimens. An iron source was provided, separate from the growth vessel. Removal of the iron source resulted in a rapid depletion of iron II ions indicative of Gallionella activity. Presence and viability of Gallionella were confirmed microscopically and by culture. The system is suitable for corrosion studies under conditions of controlled water chemistry, as well as for studies involving removal of metal ions from waste waters and aquifers.     

Convergent succession of phytoplankton in microcosms with different inoculum species composition

Summary Different initial mixtures of phyto-and zooplankton from different lakes were grown under identical chemical and physical conditions in medium size (8-and 12–1) laboratory microcosm cultures until convergence of phytoplankton species composition was attained. Five such experiments with four (four experiments) or three (one experiment) microcosm cultures were run. Three experiments were performed with weak stirring which permitted sedimentary elimination of the diatoms. Two experiments were conducted with stronger stirring to prevent sedimentation. In the three sedimentation intensive experiments, the final phytoplankton community was composed of the filamentous chlorophyte Mougeotia thylespora together with a smaller biomass of nanoplanktic algae. In the two sedimentation free experiments the final phytoplankton community consisted of pennate diatoms. Both dissolved nutrient concentrations and the chemical composition of biomass suggested strong nutrient limitation of algal growth rates in the final phase of the experiments. The zooplankton communities at the end of the experiments were composed of species that were apparently unable to ingest the large, dominant algae and that presumably fed on the nanoplanktic undergrowth and the bacteria. There was a distinct sequence of events in all experiments: first, the large zooplankton species (Daphnia and Copepoda) were replaced by smaller ones (Chydorus, Bosmina, rotifers); second, all cultures within one experiment developed the same nutritional status (limitation by the same nutrient); and third, the taxonomic composition of phytoplankton of the different cultures within one experiment converged. The last took 7–9 weeks, with is about 2–3 times as long as the time needed in a phytoplankton competition experiment to reach the final outcome.     

The impact of regional-scale changes in the weather on the long-term dynamics of Eudiaptomus and Daphnia in Esthwaite Water, Cumbria

1. Year‐to‐year changes in the weather have a profound effect on the seasonal dynamics of zooplankton in lakes. Here, I analyse some zooplankton data from Esthwaite Water in Cumbria and demonstrate that much of the recorded inter‐annual variation can be related to regional‐scale changes in the weather.
2. The first data set analysed shows the effect of changes in the water temperature on the winter abundance of the calanoid copepod Eudiaptomus gracilis. The highest numbers of Eudiaptomus were recorded when the winters were mild and the lowest when the winters were cold.
3. Winter temperatures in northern and western Europe are now known to be influenced by the atmospheric feature known as the North Atlantic Oscillation (NAO). Positive values of the NAO are associated with mild winters and westerly winds and there was a significant positive correlation between the winter abundance of Eudiaptomus in Esthwaite Water and this empirical index of change.
4. The second data set analysed shows the effect of wind‐induced mixing on the summer abundance of Daphnia. The highest numbers of Daphnia were recorded in years when the early summer thermocline was deep and the lowest number in years when the thermocline was shallow.
5. One of the most important factors influencing the depth of the early summer thermocline in the English lakes is the position of the north‐wall of the Gulf Stream. Southerly movements of the Gulf Stream are typically associated with higher winds, whilst northerly movements are associated with stable conditions. In Esthwaite Water, a significant positive correlation was recorded between the abundance of Daphnia and the depth of the early summer thermocline and significant negative correlations between the same variables and the position of the Gulf Stream.
6. A detailed analysis of the seasonal variations recorded in one calm and one windy year suggest that the main factor responsible for these correlations was the entrainment of nutrients which then stimulated the growth of edible algae. Daphnia numbers were low in 1968 (a ‘north’ Gulf Stream year which was relatively calm) and high in 1972 (a ‘south’ Gulf Stream year with intense wind‐mixing).     

Food quality influences habitat selection in Daphnia

1. The vertical distribution of Daphnia in stratified lakes strongly depends on the depth profiles of temperature and food resources. However, ecological requirements for these factors are slightly different for juvenile and adult Daphnia. 2. Here, I investigated whether food quality influences the habitat selection of Daphnia pulicaria at night and whether the habitat selection of juvenile and adult D. pulicaria is different. Daphnia were allowed to choose their optimal habitat in large, stratified water columns (plankton towers, Plön) that held either the green alga Scenedesmus obliquus (high quality) in the cold hypolimnion (Hypo‐treatment) or S. obliquus in the warm epi‐ and cold hypolimnion (SCEN‐treatment) or the non‐toxic cyanobacterium Synechococcus elongatus (low quality) in the warm epilimnion and S. obliquus in the cold hypolimnion (SYN treatment). 3. When food (S. obliquus) was present only in the hypolimnion (Hypo‐treatment), juveniles and adults distributed similarly in the water column and spent most of their time in the interface between the warm and the food rich layer. 4. When food was present in the epilimnion and hypolimnion (SCEN‐ and SYN‐treatments), juvenile and adult D. pulicaria moved into the warm and now also food‐rich epilimnion, however, the magnitude of this shift depended on the food type and age class of Daphnia. Adult and juvenile D. pulicaria spent most of their time in the epilimnion when food there was of a high quality (S. obliquus; SCEN‐treatment). However, compared to the juveniles, adult Daphnia spent significantly more time in the colder hypolimnion when epilimnetic food was of a low quality (S. elongatus; SYN‐treament). 5. Therefore, habitat selection of adult D. pulicaria was affected by food quality whereas the habitat selection of juveniles was not. 6. Additional growth and reproduction experiments show that the food quality is likely to be responsible for the different habitat selection of juveniles and adults in the SYN‐treatment. 7. In conclusion, my experiments show that D. pulicaria behaviourally reacts to the quality of its food source.     

Releases of ingested phytoplankton carbon by Daphnia magna

1. The carbon budgets and assimilation efficiencies (AEs) of adults and juveniles of Daphnia magna were quantified using ¹⁴C as a tracer. Animals were fed pure Chlamydomonas reinhardtii or Scenedesmus obliquus at different food concentrations. Carbon AEs (46–70%) were comparable at food concentrations of 0.03–0.30 mg C L^?1 for both algal species, but decreased to 34–49% when the food concentration further increased by 10‐fold. The carbon AEs were significantly and negatively correlated with the food level. 2. During the postdigestive period, partitioning of ingested carbon into different compartments including excretion, respiration and egestion was not influenced by the food species and life stage. There was a negative correlation between respiration (as % of total loss) and food concentration and a positive correlation between egestion (as % of total loss) and food concentration. Dissolved organic carbon (DOC) and CO₂ accounted for 55–72% and 9–37%, respectively, of the total carbon loss from juveniles fed both algal diets. For adults, DOC and CO₂ contributed to 44–64% and 20–47% of the total carbon loss, respectively. Particulate organic carbon (POC) was a minor pathway for the overall carbon loss. 3. The turnover and release budget of structural carbon (as moults and neonate reproduction) were further evaluated in long‐term experiments at different algal concentrations. Food concentration did not affect the carbon efflux or the carbon allocation into different physiological compartments except for respiration. Juveniles had twofold lower carbon turnover rate (0.12–0.16 day^?1) than those of the adults (0.32–0.35 day^?1). In adults, comparable carbon was allocated into DOC (35–42%) and reproduction (27–35%), which were the dominant routes for carbon loss. For the juveniles, DOC accounted for 42–64% of the total carbon loss. 4. About 21–38% of the total DOC released by adults and juveniles was associated with the high molecular weight organic carbon fraction (>5 kDa). Our results show that carbon was mainly lost by D. magna in the form of DOC during assimilation process as well as from the structural materials. Reproduction or maternal transfer was another major drain of body carbon for adult D. magna.     

Investigations into the Food Selectivity of the Planktic Crustaceans Daphnia hyalina,Eudiaptomus gracilis and Cyclops vicinus

The food selectivity of Daphnia hyalina, Eudiaptomus gracilis and Cyclops vicinus was investigated in laboratory experiments using algae of different sizes and at different concentrations as food sources. Vanderploeg and Scavia's (1979a, b) coefficient, which is most suitable for characterising selectivity, was selected from the literature and used to analyze the results. None of the three species was found to feed selectivity, however. The results show, on the other hand, that the leaky-sieve model can be used to describe the feeding patterns of these species. There were clear differences between the particle size ranges consumed by our experimental species, and these showed that, during the experiments, Daphnia hyalina acted as a microfilter-feeder, whereas Eudiaptomus gracilis and Cyclops vicinus acted as macrofilter-feeders.     

Life history consequences for Daphnia pulex feeding on nutrient-limited phytoplankton

1. The growth and feeding of Daphnia pulex De Geer on different algal species was examined. The green algae Chlamydomonas reinhardtii Dangeard and Scenedesmus acutus Meyen, the diatom Synedra tenuissima Kützing, the cryptophyte Cryptomonas pyrenoidifera Geitler and the cyanobacterium Microcystis aeruginosa Kützing were cultured in non-limiting and in N- or P-limiting medium and used as food for D. pulex.
2. Growth limitations were reflected in the elemental and biochemical composition and the morphological characteristics of the algal resources.
3. The clearance rates of D. pulex feeding on nutrient-limited algae were reduced. This was not observed when nutrient-limited mutant Chlamydomonas cells without cell walls were used as food, indicating that the cell wall may play an important part.
4. In comparison with animals grown on nutrient-sufficient cells, nutrient-limited algae resulted in smaller body length, reduced brood sizes, reduced size at maturity, increased age at first reproduction and, consequently, in reduced Daphnia population growth rates.
5. Daphnia population growth rates ( r ) were negatively correlated with the C : P ratio and the carbohydrate content of the food. Moreover, significant correlations between r and clearance rates were found.
6. The observed differences in the grazing and the life history parameters of Daphnia feeding on non-limited and nutrient-limited algae may be the result of both reduced nutritional value and reduced digestibility of nutrient-limited algae.     

罗非鱼对微型生态系统营养物水平的影响

本文总结了罗非鱼不同放养密度的微型生态系统中N、P浓度及P分布动态观测结果。在罗非鱼的影响下,微型生态系统中氨氮、颗粒磷和总磷浓度不同程度地高于对照组,而正磷酸盐浓度和沉积物磷的量显著地低于对照组。不同密度组某些指标的观测值虽有显著差异,但未见任何指标依罗非鱼放养密度而有规律地变动。微型生态系统中正磷酸盐浓度同浮游动、植物密度和初级生产力显著相关,氨氮浓度与浮游植物密度之间亦有显著的相关关系。然而,浮游植物密度与总磷浓度之间不存在营养级联假说所预见的下行影响,相反有前者决定于后者的上行影响的趋向。微型生态系统中P分布的变化可揭示罗非鱼促进系统中营养物循环,从而加速其富营养化的主要机制。     

Thermal adaptation of heterotrophic soil respiration in laboratory microcosms

Respiration of heterotrophic microorganisms decomposing soil organic carbon releases carbon dioxide from soils to the atmosphere. In the short term, soil microbial respiration is strongly dependent on temperature. In the long term, the response of heterotrophic soil respiration to temperature is uncertain. However, following established evolutionary trade‐offs, mass‐specific respiration (R_mass) rates of heterotrophic soil microbes should decrease in response to sustained increases in temperature (and vice‐versa). Using a laboratory microcosm approach, we tested the potential for the R_mass of the microbial biomass in six different soils to adapt to three, experimentally imposed, thermal regimes (constant 10, 20 or 30 °C). To determine R_mass rates of the heterotrophic soil microbial biomass across the temperature range of the imposed thermal regimes, we periodically assayed soil subsamples using similar approaches to those used in plant, animal and microbial thermal adaptation studies. As would be expected given trade‐offs between maximum catalytic rates and the stability of the binding structure of enzymes, after 77 days of incubation R_mass rates across the range of assay temperatures were greatest for the 10 °C experimentally incubated soils and lowest for the 30 °C soils, with the 20 °C incubated soils intermediate. The relative magnitude of the difference in R_mass rates between the different incubation temperature treatments was unaffected by assay temperature, suggesting that maximum activities and not Q₁₀ were the characteristics involved in thermal adaptation. The time taken for changes in R_mass to manifest (77 days) suggests they likely resulted from population or species shifts during the experimental incubations; we discuss alternate mechanistic explanations for those results we observed. A future research priority is to evaluate the role that thermal adaptation plays in regulating heterotrophic respiration rates from field soils in response to changing temperature, whether seasonally or through climate change.     

Composition of inorganic and organic nutrient sources influences phytoplankton community structure in the New River Estuary, North Carolina

The New River Estuary, NC, is a nutrient-sensitive, eutrophic water body that is prone to harmful algal blooms. High annual loading from the watershed of varying nutrient forms, including inorganic phosphorus and inorganic and organic nitrogen, may be linked to the persistence of algal blooms in the estuary. In order to evaluate phytoplankton response to nutrient inputs, a series of in situ nutrient addition experiments were carried out during June 2010 to July 2011 on water from an estuarine site known to support algal blooms. Estuarine water was enriched with nutrients consisting of individual and combined sources of dissolved inorganic nitrogen, orthophosphate, urea, and a natural dissolved organic nitrogen (DON) addition derived from upstream New River water. The combined inorganic N and P addition most frequently stimulated phytoplankton biomass production as total chlorophyll a. The responses of diagnostic (of major algal groups) photopigments were also evaluated. Significant increases in peridinin (dinoflagellates), chlorophyll b (chlorophytes), and myxoxanthophyll (cyanobacteria) were most frequently promoted by additions containing riverine DON. Significant increases in zeaxanthin (cyanobacteria) were more frequently promoted by inorganic nitrogen additions, while increases in fucoxanthin (diatoms) and alloxanthin (cryptophytes) were not promoted consistently by any one nutrient treatment. Evaluating the impact of varying nutrient forms on phytoplankton community dynamics is necessary in order to develop strategies to avoid long-term changes in community structure and larger-scale changes in ecosystem condition.     

How Daphnia cope with algae selected for inedibility in long- running microcosms

Macro video records of restrained feeding Daphnia enabled usto measure simultaneously carapace gape, claw rejection rate,filter limb beat rate, and mandible movement rate. We comparedthe effects of high and low concentrations of highly ediblealgae and of inedible algae, the latter selected by long-termDaphnia grazing in oligotrophic microcosms. Inedible algae slowedthe filtering process and influenced the carapace gape (wideningat low concentration and narrowing at high), but did not affectthe rejection rate.     

Understanding interactive inducible defenses of Daphnia and its phytoplankton prey

Cyanobacterial and zooplankton inducible defenses are important but understudied process that regulate the trophic interactions of freshwater ecosystem. Daphnia due to its large size is considered an important zooplankton with the high potential to control cyanobacterial blooms. It has been shown that Daphnia through maternal induction transfer tolerance to their next generation against Microcystis toxicity. Maternal induction has been investigated in different Daphnia species without considering phenotypic plasticity of prey. Laboratory experiments were performed to explore cyanobacteria-Daphnia inducible defenses in order to better understand their interactions. Two Daphnia species were fed either with Microcystis aeruginosa PCC7806 (Ma) or Microcystis flos-aquae (Mf) mixed with Chlorella vulgaris (Cv) (exposed Daphnia), and or pure Cv (unexposed Daphnia). Exposed prey cultures were produced by prior exposure to Daphnia infochemicals. Neonates produced by exposed and unexposed Daphnia were fed with mixed diet (Microcystis + Cv) of either exposed and or unexposed prey. Growth parameters and toxin production of exposed prey cultures were significantly different than that of control. Exposed Daphnia fecundity and survival was higher as compared to unexposed Daphnia. Growth and reproduction was reduced in exposed Daphnia when fed with exposed prey as compared to those fed with unexposed prey. This study provides information on the interactive inducible defenses between cyanobacteria and its grazer under laboratory conditions and may increase our understanding of cyanobacteria and Daphnia interactions in the freshwater ecosystem.