Structure of planktonic microbial food web in a brackish stratified Siberian lake

The distribution of primary components of the microbial community (autotrophic pico- and nanoplankton, phototrophic bacteria, heterotrophic bacteria, microscopic fungi, heterotrophic flagellates, ciliates and heliozoa) in the water column of Lake Shira, a steppe brackish-water, stratified lake in Khakasia, Siberia (Russia), were assessed in midsummer. Bacterioplankton was the main component of the planktonic microbial community, accounting for 65.3 to 75.7% of the total microbial biomass. The maximum concentration of heterotrophic bacteria were recorded in the monimolimnion of the lake. Autotrophic microorganisms contributed more significantly to the total microbial biomass in the pelagic zone (20.2–26.5%) than in the littoral zone of the lake (8.7–14.9%). First of all, it is caused by development of phototrophic sulphur bacteria at the oxic-anoxic boundary. The concentrations of most aerobic phototrophic and heterotrophic microorganisms were maximal in the upper mixolimnion. Heterotrophic flagellates dominated the protozoan populations. Ciliates were minor component of the planktonic microbial community of the lake. Heterotrophic flagellates were the most diverse group of planktonic eucaryotes in the lake, which represented by 36 species. Facultative and obligate anaerobic flagellates were revealed in the monimolimnion. There were four species of Heliozoa and only three of ciliates in the lake.     

Polar bears make little use of terrestrial food webs: evidence from stable-carbon isotope analysis

Summary The mean stable-carbon isotope ratios (¹³C) for polar bear (Ursus maritimus) tissues (bone collagen –15.7, muscle –17.7, fat –24.7) were close to those of the same tissues from ringed seals (Phoca hispida) (–16.2, –18.1, and –26.1, respectively), which feed exclusively from the marine food chain. The ¹³C values for 4 species of fruits to which polar bears have access when on land in summer ranged from –27.8 to –26.2, typical of terrestrial plants in the Arctic. An animal's ¹³C signature reflects closely the ¹³C signature of it's food. Accordingly, the amount of food that polar bears consume from terrestrial food webs appears negligible, even though some bears spend 1/3 or more of each year on land during the seasons of greatest primary productivity.     

Nutrient removal from sewage by an artificial food web system composed of phytoplankton and Daphnia magna

In order to remove nutrients from sewage, ecotechnology with an artificial food web composed of phytoplankton and Daphnia magna was used. To optimise performance of the system, phytoplankton growth, zooplankton growth, and a continuous-flow system were used. For phytoplankton growth, stirring was 6.7 times faster than the settling in growth rate of Scenedesmus. Zooplankton growth was not influenced by phytoplankton succession, and the specific production coefficient of D. magna was 110.4 mg Daphnia dry weight (DW) per mg chlorophyll a (Chl a). Results indicated that removal of nutrients was better in a long hydraulic residence time (HRT) system than in a system with short HRT. The optimum retention time was found to be 3 days for the phytoplankton chamber and 1.5 days for the subsequent D. magna chamber, respectively, with total retention time of the combined chambers being kept at 4.5 days. When a pilot plant was operated under these conditions, the removal rates of total nitrogen (TN) and total phosphorus (TP) were 68 and 56%, respectively. In the material budget of TN, 32% of inputs passed on to effluent, 39% to sludge, 27% to air and 2% to harvested Daphnia. For TP, 44% of inputs passed on to effluent, 51% to sludge and 4% to Daphnia.     

连作条件下毛鸡骨草根际土壤微生物群落功能多样性变化特征

毛鸡骨草是治疗肝病的重要中草药之一,而连作障碍致其产量和品质下降。从主产区广西玉林分别采集正茬、重茬和连作三年的毛鸡骨草根际土壤样品,以种植前水稻土壤为对照,采用Biolog GN2 平板碳源分析技术,研究连作条件下根际土壤微生物群落功能多样性变化特征,以揭示其连作障碍的原因。结果表明,连作导致根际土壤微生物功能多样性显著降低,微生物利用各类碳源的能力下降。主成分分析(PCA)表明,不同种植年限的毛鸡骨草根际土壤微生物群落结构之间存在显著差异,且均与种植前对照明显不同,而同一种植年限不同生长期土壤微生物碳代谢群落结构虽有差异,但并不显著。相关分析表明,其产量与微生物功能多样性指数(如Shannon,Simpson,Mclntosh)以及平均吸光值(AWCD)值正相关,而与第一主成分(PC1)呈显著负相关,说明连作条件下其产量的降低在一定程度上与土壤微生物功能多样性的降低和群落结构的改变有关。     

Evaluation of Microcystis as food for zooplankton in a eutrophic lake

Four experiments were conducted to evaluate Microcystis as food for zooplankton in Lake Kasumigaura, and the following results were obtained. (1) Moina micrura (Cladocera) showed little growth and no reproduction when the animal was reared with Microcystis cultured in the laboratory. The animal did not grow nor reproduce well when Chlorella was mixed with Microcystis as food. (2) Moina micrura assimilated Microcystis much less than Chlorella when the animal fed on single species of Microcystis or a mixture with Chlorella. (3) Microcystis collected from Lake Kasumigaura could not be utilized by Moina micrura even though the colonies were broken up into edible sizes. However, the alga turned into utilizable food when it was decomposed. (4) No inhibitors of Moina micrura population growth could be found in the non-filtered water of Lake Kasumigaura where Microcystis was blooming heavily. Decomposed Microcystis seemed to be utilized by zooplankton as an important food source in Lake Kasumigaura.     

两种代表性蚯蚓对设施菜地土壤微生物群落结构及理化性质的影响

不同生态型蚯蚓的取食偏好和生境有所差异,因此蚯蚓的生态型差异可能关乎其对土壤性质的不同影响;有关不同生态型蚯蚓对土壤性质尤其是微生物学性质影响的研究有助于了解蚯蚓生态功能的作用机制。在野外调控试验的第4年采集土壤,研究了牛粪混施和表施处理下内层种威廉腔环蚓(Metaphire guillelmi)和表层种赤子爱胜蚓(Eisenia foetida)对设施菜地土壤微生物群落结构和主要理化性质的影响。结果表明,土壤微生物群落结构同时受到蚯蚓种类和牛粪施用方式的影响。牛粪表施时,两种蚯蚓均显著降低了菌根真菌、真菌生物量和原生动物生物量(P0.05);牛粪混施时,不同蚯蚓的影响有所差异,威廉腔环蚓明显增加了菌根真菌、真菌生物量和放线菌生物量,而赤子爱胜蚓的作用不明显。此外,两种蚯蚓均提高了土壤孔隙度、团聚体稳定性和土壤p H、矿质氮以及微生物生物量碳氮水平,但提高幅度取决于蚯蚓种类和牛粪施用方式。冗余分析表明蚯蚓影响下土壤微生物群落结构的变化与团聚体稳定性、p H、速效磷、矿质氮呈正相关,而与土壤容重呈负相关。     

Photoperiod and food regulate termination of diapause in the squash bug, Anasa tristis

The squash bug, Anasa tristis DeGeer (Heteroptera: Coreidae), is a major pest of cultivated cucurbits in much of North America. Its seasonal population dynamics are determined in large part by the early season phenological adaptations of the overwintered adults. Squash bugs were maintained on pumpkin, Cucurbita moschata Duchesne (Cucurbitaceae), seedlings. Factors influencing the termination of diapause in squash bugs were studied. Squash bugs transferred from outdoors to long-day conditions during their prediapause period in October (when the respiratory rate declines to diapause levels) required longer to terminate diapause than squash bugs transferred in the winter after the prediapause period was completed. Females did not oviposit after up to 150 days in short-day conditions. Squash bugs maintained outdoors under natural photoperiods remained in diapause until at least late April. Food was shown to be necessary for the prompt termination of diapause.

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Résumé A. tristis (Hétéropt.: Coreidae) est un ravageur important des cucurbitacées dans une grande partie de l'Amérique du Nord, particulièrement de Cucurbita spp. Les événements phénologiques du début de la saison conditionnent la dynamique de population pour la saison entière. Cette étude concerne l'influence de la photopériode et de l'alimentation dans l'achèvement de la diapause. Les adultes ont été maintenus sur des plantules de Cucurbita moschata Duchesne (var. Libbey's Select). La diapause était établie par la mesure du taux respiratoire et par l'absence de ponte. La diapause était surveillée chez des insectes maintenus à l'extérieur en conditions naturelles, leurs taux respiratoires se maintenaient au taux correspondant à la diapause jusqu'à la fin avril au moins. Placés après novembre en jours longs et à 25°C, la diapause s'interrompait rapidement. Ceux transférés en jours longs plus tôt ont interompu leur diapause mais ont demandé plus de temps pour réagir au changement de photopériode. Transférés à 25°C mais en jours courts, leur diapause n'était pas interrompue jusqu'à la fin de l'expérience 150 jours plus tard. L'alimentation est nécessaire pour une interruption rapide de la diapause en jours longs. L'alimentation associée à des jours longs ou croissants semble nécessaire à l'achèvement de la diapause de A. tristis dans les conditions naturelles.

     

An in situ test of the effects of food quality on Daphnia population growth

The temporal variation of the surface deposit feeders in a mudflat of Chuwei Mangrove Forest showed a significant input of populations from the recruitments in the spring. The chemical analysis of the sediment in the top 8 cm showed that the sedimentary organic content had a subsurface maximum value in the deeper layer in most cases. Most of the temporal variations in the organic carbon and nitrogen contents occurred in the top few centimeters. The high C:N ratio and low organic nitrogen content in the sediment suggests the supply of carbon (or energy) to the benthos was low. The increase of labile protein content in the deep layer might be due to the downcore transport of sediment nutrients by the bioturbation. Laboratory growth experiment suggests that some the chemical characters examined in this study may represent the sediment nutrients to the animals.     

Feeding behaviour and food selection in the horseshoe crab,Tachypleus gigas (Müller)

The Indian horseshoe crab, Tachypleus gigas (Müller), is a benthic feeder which subsists mainly on molluscs, decayed organic matter and polychaetes, in order of prevalence. A strong and positive preference was recorded for molluscs over other food organisms. The intensity of feeding was maximum during the north-east monsoon (November to January) in females and during the intermonsoon season (February to May) in males. It was minimum during the south-west monsoon (June to September).     

肉苁蓉寄主梭梭根际土壤微生物种类及群落结构特征

为探索梭梭根际土壤微生物结构特征及其与肉苁蓉寄生的关系,应用磷脂脂肪酸(PLFA)法分析了5—8月份梭梭生长季节的根际土壤微生物种类及群落结构特征,采用湿筛倾注-蔗糖离心法对其根际土壤AM真菌进行了初步分离和鉴定,并分析了肉苁蓉寄生与梭梭根际微生物及环境因子间的相关性。结果表明,5—7月3个月份的梭梭根际土壤微生物磷脂脂肪酸种类及含量均显著高于8月份,总磷脂脂肪酸和AM真菌磷脂脂肪酸以6月份含量最高。梭梭根际土壤共鉴定出AM真菌4属35种,它们分别为球囊霉属(Glomus)22种、无梗囊霉属(Acaulospora)7种、多孢囊霉属(Diversispora)3种和巨孢囊霉属(Gigaspora)3种。其中以黑球囊霉(Glomus melanosporum)和双网无梗囊霉(Acaulospora bireticulata)为优势种群,并且发现了与寄生有关的巨孢囊霉属AM真菌。6月份和8月份的AM真菌孢子数量最多,而5月份的AM真菌孢子数量最低。6月份梭梭根际土壤提取液得到的肉苁蓉种子萌发率(65.94%)和田间接种寄生率(59.19%)均为最高值,而5月份土壤提取液测试得到的肉苁蓉种子萌发率最低。因此,推测梭梭根际AM真菌可能参与了肉苁蓉的寄生过程。相关分析表明梭梭根际土壤微生物种类和数量主要与土壤温湿度和土壤理化性质相关性较大,其中可能与寄生有关的真菌数量与土壤温度呈显著正相关;肉苁蓉寄生率与土壤温度及土壤养分呈显著负相关。研究为解析梭梭根际土壤微生物在肉苁蓉寄生过程中的作用以及指导肉苁蓉人工种植提供参考。