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1.
Gulati  R. D.  Ejsmont-Karabin  J.  Rooth  J.  Siewertsen  K. 《Hydrobiologia》1989,(1):347-354
Phosphorus (PO4-P) and nitrogen (NH4-N) excretion rates of Euchlanis dilatata lucksiana, a rotifer, isolated from Lake Loosdrecht (The Netherlands) and cultured in the lake water at 18–19 °C, were measured in the laboratory.In a series of experiments, the effects of experiment duration on the P and N excretion rates were examined. The rates measured in the first half-hour were about 2 times higher for P and 2–4 times for N than the rates in the subsequent three successive hours which were quite comparable.Eight experiments were carried out in triplicate, 4 each for P and N excretion measurements, using animals of two size ranges: 60–125 µm and > 125 µm. The specific excretion rates varied from 0.06 to 0.18 µg P.mg–1 DW.h–1 and 0.21 to 0.76 µg N.mg–1 DW.h–1. Generally an inverse relationship was observed between the specific excretion rates and the mean individual weight. The excretion rates of Euchlanis measured by us are lower than those reported for several other rotifer species, most of which are much smaller than Euchlanis.Extrapolating the excretion rates of Euchlanis to the other rotifer species in Lake Loosdrecht, and accounting for their density, size and temperature, rotifer excretion appears to be a significant, potential nutrient (N,P) source for phytoplankton growth in the lake. The excretion rates for the rotifers appear to be about two thirds of the total zooplankton excretion, even though the computed rotifer mean biomass is about one-third of the total zooplankton biomass.  相似文献   

2.
Summary Single fast fibres and small bundles of slow fibres were isolated from the trunk muscles of an Antarctic (Notothenia neglecta) and various warm water marine fishes (Blue Crevally,Carangus melampygus; Grey Mullet,Mugil cephalus; Dolphin Fish,Coryphaena hippurus; Skipjack-tuna,Katsuwonus pelamis and Kawakawa,Euthynuus affinis). Fibres were chemically skinned with the nonionic detergent Brij 58.For warm water species, maximum Ca2+-activated tension (P 0) almost doubled between 5–20°C with little further increase up to 30°C. However, when measured at their normal body temperatures,P 0 values for fast fibres were similar for all species examined, 15.7–22.5 N · cm–2. Ca2+-regulation of contraction was disrupted at temperatures above 15°C in the Antarctic species, but was maintained at up to 30°C for warm water fish.Unloaded (maximum) contraction speeds (V max) of fibres were determined by the slacktest method. In general,V max was approximately two times higher in white than red muscles for all species studied, except Skipjack tuna. For Skipjack tuna,V max of superficial red and white fibres was similar (15.7 muscle lengths · s–1 (L 0 · s–1)) but were 6.5 times faster than theV max of internal red muscle fibres (2.4±0.2L 0 · s–1) (25°C). V max forN. neglecta fast fibres at 0–5°C (2–3L 0 · s–1) were similar to that of warm water species measured at 10–20°C. However, when measured at their normal muscle temperatures, theV max for the fast muscle fibres of the warm water species were 2–3 times higher than that forN. neglecta.In general,Q 10(15–30°C) values forV max were in the range 1.8–2.0 for all warm water species studied except Skipjack tuna.V max for the internal red muscle fibres of Skipjack tuna were much more temperature dependent (Q 10(15–30°C)=3.1) (P<0.01) than for superficial red or white muscle fibres. The proportion of slower red muscle fibres in tuna (28% for 1 kg Skipjack) is 3–10 times higher than for most teleosts and is related to the tuna's need to sustain high cruising speeds. We suggest that the 8–10°C temperature gradient that can exist in Skipjack tuna between internal red and white muscles allows both fibre types to contract at the same speed. Therefore, in tuna, both red and white muscle may contribute to power generation during high speed swimming.  相似文献   

3.
Undaria pinnatifida gametophytes were grown in 2.5 l bubble column and airlift reactor at 25 °C and light intensity of 40 mol m–2 s–1 for 6 days. With aeration at 1 l min–1, the airlift reactor yielded higher growth rate (0.12 mg DW ml–1 d–1) than a bubble column (0.08 mg DW ml–1 d–1). The advantages were related to the more homogeneous fluid dynamic characteristics of the airlift reactor.  相似文献   

4.
Data on phosphate excretion rates of zooplankton are based on measurements using the pelagic crustacean zooplankton of Lake Vechten and laboratory-cultured Daphnia galeata. In case of Daphnia sp we measured the effects of feeding on P-rich algae and P-poor algae (Scenedesmus) as food on the P-excretion rates at 20°C. The excretion rates of the natural zooplankton community, irrespective of the influence of the factors mentioned, varied by an order of magnitude: 0.025–0.275µg PO4-Pmg–1C in zooplankton (C zp ) h–1. The temperature accounted for about half the observed variation in excretion rates. The mean excretion rates in the lake, computed for 20°C, varied between 0.141 and 0.260 µg Pmg–1C zp h–1. Based on data of zooplankton biomass in the lake the P-regeneration rates by zooplankton covered between 22 and 239% of the P-demand of phytoplankton during the different months of the study period.In D. galeata, whereas the C/P ratios of the Scenedesmus used as food differed by a factor 5 in the experiments, the excretion rates differed by factor 3 only. Despite the higher P-excretion rates (0.258± 0.022 µg PO4-P mg–1 C h–1) of the daphnids fed with P-rich food than those fed with P-poor food (0.105 ± 0.047 µg PO4-P mg–1 C hp–1), both the categories of the animals were apparently conserving P. A survey of the literature on zooplankton excretion shows that in Daphnia the excretion rates vary by a factor 30, irrespective of the species and size of animals and method of estimation and temperature used.About two-thirds of this variation can be explained by size and temperature. A major problem of comparability of studies on P-regeneration by zooplankton relates to the existing techniques of P determination, which necessitates concentrating the animals several times above the in situ concentration (crowding) and prolonged experimental duration (starving), both of which manifest in marked changes that probably lead to underestimation of the real rates.  相似文献   

5.
Methanobacterium thermoautotrophicum was grown on a defined mineral salts medium under strictly anaerobic conditions with H2 and CO2 as the sole energy and carbon sources, respectively. The cultivation medium was optimized with respect to non-organic components including Se(IV), W(VI), N, Ni(II), Fe(II), Co(II) and Mo(VI). Sulphide concentration in the medium was maintained constant using an on-line regulatory system by the addition of 0.5 M Na2S. A maximum supply rate of 0.6 vvm of a mixture of 80% H2 and 20% CO2 was achieved for the gaseous substrates. Under these conditions a specific growth rate of 0.30 h–1 and a cell concentration of 4.8 g cell dry weight (DW) l–1, representing a 140% increase over previously published results, were obtained. The growth yield of 2.3 g DW mol–1 CH4 was similar to published values. However, the overall specific productivity was enhanced from 11 mmol CH4 g–1 DW h–1 to 24 mmol CH4 g–1 DW h–1, corresponding to an improvement of 120%. Correspondence to: U. von Stockar  相似文献   

6.
The life history and production characteristics of Neomysis mercedis from two British Columbia lakes were examined for their potential influence on zooplankton and limnetic fish communities. During the day, mysids in shallow Muriel Lake (45 m) were on or near the bottom; in Kennedy Lake (> 100 m), mysids remained deeper than 50 m. In both lakes, mysids spent summer nights at 0–15 m depths despite > 20 °C temperatures. Mysid density was not strongly correlated with lake depth. Mysids generally displayed spring to early summer minima and late summer to fall maxima in numbers and biomass. Single peaks in gravid females and juvenile mysid abundance, and the absence of pronounced seasonal size changes of gravid females suggest that N. mercedis produced a single generation each year. Fecundities of study lake mysids are the lowest on record, and although size-dependent, exhibited unusually high variability. Annual productivity of mysids averaged 485 mg m–2 y–1 (range 205–690). Calculations indicate mysids consume several times more zooplankton per annum than limnetic fish do. N. mercedis is likely an important competitor of juvenile sockeye salmon (Oncorhynchus nerka) since: (i) sockeye exhibit food limited growth and survival patterns in coastal lakes, (ii) mysids and sockeye consume similar zooplankton prey and (iii) mysids do not contribute greatly to sockeye diet (i.e. < 26% of summer and fall diets by numbers or weight).  相似文献   

7.
Gelidium sesquipedale is the most important raw material used for extraction of agar in Spain. Based on chemostats, a system of culture for macroalgae with a continuous flow of culture medium has been developed. A stressed morphotype from the South of Spain was cultured, and the effects of different rates of NO 3 flow on growth and internal constituents were investigated in the laboratory. Cultivation was successful after optimizing factors affecting growth, such as irradiance level, renewal rate and water movement. Mass production was dependent on N supply. With a flow of 35 mol NO3 g–1 DW d–1, optimal values of growth (2.1% d–1) and biomass yield were obtained. In these conditions, biomass yield resembled the values observed in natural populations (about 500 g DW m–2 y–1). When the flow of N was reduced to 15 mol NO 3 g–1 DW d–1, growth rate and biomass yield were reduced three-fold, and were null when N was supplied as 7 mol NO 3 g–1 DW d–1. C:N ratio was an index of the physiological status of the tissue, remaining low when N was sufficient and raised to critical values when N supply was limited. Phycobiliproteins, kept at a constant irradiance level, were affected by N supply, acting as an internal nitrogen reserve, unlike chlorophylla. An effective phycobiliprotein synthesis took place when the flow of N was sufficient. Agar yield, on dry weight basis, was similar as a function of N flow, whereas agar yield of the culture was higher when N was sufficient as a result of growth not being limited by N.This system of culture, commonly used in microalgal studies, may have an important use in macroalgae as a system to obtain biomass of high quality as well as a good tool for physiological studies in conditions of continuous and controlled flow of nutrients.  相似文献   

8.
Plant nitrogen (N)deficiency often limits crop productivity. Early detection of plant N deficiency is important for improving fertilizer N-use efficiency and crop yield. An experiment was conducted in sunlit, controlled environment chambers in the 2001 growing season to determine responses of corn (Zea mays L. cv. 33A14) growth and leaf hyperspectral reflectance properties to varying N supply. Four N treatments were: (1) half-strength Hoagland's nutrient solution applied throughout the experiment (control); (2) 20% of control N starting 15 days after emergence (DAE); (3) 0% N starting 15 DAE; and (4) 0% N starting 23 DAE (0% NL). Plant height, the number of leaves, and leaf lengths were examined for nine plants per treatment every 3–4 days. Leaf hyperspectral reflectance, concentrations of chlorophyll a, chlorophyll b,and carotenoids, leaf and canopy photosynthesis, leaf area, and leaf N concentration were also determined during the experiment. The various N treatments led to a wide range of N concentrations (11 – 48 g kg–1 DW) in uppermost fully expanded leaves. Nitrogen deficiency suppressed plant growth rate and leaf photosynthesis. At final harvest (42 DAE), plant height, leaf area and shoot biomass were 64–66% of control values for the 20% N treatment, and 46-56% of control values for the 0% N treatment. Nitrogen deficit treatments of 20% N and 0% N (Treatment 3) could be distinguished by changes in leaf spectral reflectance in wavelengths of 552 and 710 nm 7 days after treatment. Leaf reflectance at these two wavebands was negatively correlated with either leaf N (r = –0.72 and –0.75**) or chlorophyll (r = –0.60 and –0.72**) concentrations. In addition, higher correlations were found between leaf N concentration and reflectance ratios. The identified N-specific spectral algorithms may be used for image interpretation and diagnosis of corn N status for site-specific N management.  相似文献   

9.
About 650 zooplankton samples were collected from Lake Inarijärvi in 1977–1979 from the littoral and pelagial zones of the lake. One hundred and twenty-three zooplankton taxa were found and most of them can be considered euplanktonic.The most important species were Holopedium gibberum, Daphnia cristata, Cyclops spp. and Eudiaptomus spp. Mean pelagial zooplankton biomass was 0.29 g m–3 in the 0–5 m depth zone, 0.17 g m–3 in 5–10 m and 0.11 g m–3 in 10–20 m.The zooplankton biomass at a sandy shore was about 0.09 g m–3, at a stony shore 0.05 g m–3 and at a vegetated shore 0.76 g m–3. About 70% of the whole zooplankton production consisted of crustaceans.The sum of herbivore and carnivore zooplankton production in the pelagial area during the summer was 210–330 kg ha–1 × 3 months.  相似文献   

10.
Palma-Silva  C.  Albertoni  E.F.  Esteves  F.A. 《Plant Ecology》2000,148(2):157-164
This investigation of the aquatic macrophyte Eleocharis mutata (L.) Roem. Et Schult. was carried out in Imboassica lagoon, a coastal lagoon in Macaé (22°50S; 44°42W), in the northern part of Rio de Janeiro, Brazil. The sandbar separating this lagoon from the ocean has been opened several times for flood control and to allow the entrance of marine species of commercial interest. The barrier bar has been breached without appropriate planning, and the consequences of breaching for the lagoon ecosystem are poorly understood. These openings drastically affect the structure and functioning of the lagoon, but there are no data on possible effects on macrophyte communities. In this project, we obtained data on the increase of the distribution, biomass accumulation and production rates of E. mutata in the establishment of a new stand, in an effort to relate effects of sandbar breach events to the expansion of this species. During 22 months of sampling, 4 breachings of the sandbar occurred, and E. mutata increased its area of coverage by about 8104 m2, or 2.5% of the total area of the lagoon. The total aerial biomass reached a maximum of 1515 g DW m–2, and the underground biomass reached 583 g DW m–2. During the establishment and development of the stand, both dead and live aerial biomass and underground biomass tended to accumulate. Aerial net primary production (ANPP) was quite variable, reaching a maximum of 18.9 g DW m–2 d–1. We conclude that the sudden variations in water level caused by breaches in the sandbar were beneficial to the expansion of this species in Imboassica lagoon.  相似文献   

11.
The seasonal variation in primary production, individual numbers, and biomass of phyto- and zooplankton was studied in the River Danube in 1981. The secondary production of two dominant zooplankton species (Bosmina longirostris and Acanthocyclops robustus) was also estimated. In the growing season (April–Sept.) individual numbers dry weights and chlorophyll a contents of phytoplankton ranged between 30–90 × 106 individuals, l–1, 3–12 mg l–1, and 50–170 µg l–1, respectively. Species of Thalassiosiraceae (Bacillariophyta) dominated in the phytoplankton with a subdominance of Chlorococcales in summer. Individual numbers and dry weights of crustacean zooplankton ranged between 1400–6500 individuals m–3, and 1.2–12 mg m–3, respectively. The daily mean gross primary production was 970 mg C m–3 d–1, and the net production was 660 mg C m–3 d–1. Acanthocyclops robustus populations produced 0.2 mg C m–3 d–1 as an average, and Bosmina longirostris populations 0.07 mg C m–3 d–1. The ecological efficiency between phytoplankton and crustacean zooplankton was 0.03%.  相似文献   

12.
Ultraviolet sunscreen compounds in epiphytic red algae from mangroves   总被引:3,自引:0,他引:3  
Karsten  Ulf  Sawall  Thomas  West  John  Wiencke  Christian 《Hydrobiologia》2000,432(1-3):159-171
Epiphytic red algae of the order Ceramiales from mangroves and salt marshes (nine species from Bostrychia, three from Stictosiphonia and four from Caloglossa) produce varying levels of the UV-absorbing compounds mycosporine-glycine, shinorine, porphyra-334, palythine, asterina-330 and palythinol, a suite of substances chemically assigned as mycosporine-like amino acids (MAAs). Mean MAA levels varied from 0.02 to 12.8 mg g–1 DW in field-collected and laboratory cultured specimens. While in field samples of Bostrychia montagneiHarvey, Bostrychia radicans (Montagne) Montagne and Caloglossa apomeiotica J.West et G.Zuccarello MAA concentrations were generally higher compared to cultured plants of the same taxa, Bostrychia tenella(Lamouroux) J.Agardh did not show such a difference. Catenella caespitosa (Withering) L.Irvine, Catenella impudica (Montagne) J.Agardh and Catenella nipae Zanardini (Gigartinales, Caulacanthaceae) produce two novel UV-absorbing compounds: MAA-1 (1.4–4.3 mg g –1 DW) and MAA-2 (0.1–1.0 mg g–1 DW), which absorb at 334 nm and 320 nm, respectively. In laboratory culture of Bostrychia moritziana when photosynthetically active radiation (PAR) was increased from 20 to 40 mol photons m–2 s–1, the total level of palythinol increased by 85% (from 2.0 to 3.7 mg g–1 DW). In a culture of Caloglossa leprieurii when PAR was increased from 40 to 80 mol m–2 s–1the porphyra-334 content increased by 77% (from 3.1 to 5.5 mg g–1 DW). Extremely high MAA contents of >30 mg g–1 DW were detected in mature tetrasporangial sori prepared from two isolates of laboratory-cultured reproductive Caloglossa apomeiotica compared to vegetative plants (about 10 mg MAAs g–1 DW) indicating tetraspores loaded up with UV-sunscreens. All data demonstrate that mangrove red algae contain high MAA concentrations, particularly the reproductive structures, and hence these compounds may act as biochemical photoprotectants against exposure to UV-radiation.  相似文献   

13.
The productivity and ecological role of benthos in man-made Lake Kariba was assessed through the use of P/B-ratios and by measuring the metabolism (respiration, N and P excretion) of the most abundant mussel species (Aspatharia wahlbergi, Corbicula africana and Caelatura mossambicensis) in laboratory experiments. For A. wahlbergi also filtration rate was estimated.The annual production of benthos for the populated 0–12 m interval was estimated at 11.0 g m –2 yr–1 (shellfree dry weight) of which mussels contributed for 8.81 g (80%), snails 2.16 g (20%) and insects 0.03 g (0.3%) respectively. The most important mussel species in the lake were Caelatura mossambicensis (4.97 g m–2 yr–1) and Corbicula africana (3.33 g). The dominant snail species was Melanoides tuberculata (1.63 g). For the total lake, also including deeper unpopulated bottoms, the annual production of benthos was 2.70 g m–2 yr–1 (shell-free dry weight).Respiration and excretion varied with temperature displaying a bell-shaped relationship. Metabolic rates in Aspatharia wahlbergi increased about 5× between 16.5 °C and the maximum at 34.0 °C and then decreased again at 39.0 °C, when the mussels showed signs of severe stress. Metabolism in Corbicula africana had a lower optimum with fairly constant activity between 18.6 and 29.2 °C, rapidly decreasing above this temperature.The average respiration, nutrient excretion and water filtration rates for mussels in Lake Kariba at 25.2 °C were estimated to about 0.6 mg O2 85 µg NH4–N, 1.5 µg PO4–P and 0.51 water filtered h–1 g–1 shellfree dry weight. This gives that a volume corresponding to about the total epilimnion of the lake is filtered by the mussels annually. Further, mussels can be estimated to remineralise % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaGymaiaac+% cacaaI0aaaaa!3A2B!\[1/4\] of the total load of phosphate, and 8 times the total load of nitrogen every year. The population needs 3.5 × 104 tons of organic carbon for its maintainance, which indicates that about 5% of the annual phytoplankton production is channeled through mussels. We conclude that the mussels, rather than being an important food source for fish, seem to play a large role in the nutrient dynamics of Lake Kariba.  相似文献   

14.
Photosynthetic activity, in leaf slices and isolated thylakoids, was examined at 25° C after preincubation of the slices at either 25° C or 4° C at a moderate photon flux density (PFD) of 450 mol·m–2·s–1, or at 4° C in the dark. The plants used wereSpinacia oleracea L.,Cucumis sativus L. andNerium oleander L. which was acclimated to growth at 20° C or 45° C. The plants were grown at a PFD of 550 mol·m–2·s–1. Photosynthesis, measured as CO2-dependent O2 evolution, was not inhibited in leaf slices from any plant after preincubation at 25° C at a moderate PFD or at 4° C in the dark. However, exposure to 4° C at a moderate PFD induced an inhibition of CO2-dependent O2 evolution within 1 h inC. sativus, a chilling-sensitive plant, and in 45° C-grownN. oleander. The inhibition in these plants after 5 h reached 80% and 40%, respectively, and was independent of the CO2 concentration but was reduced at O2 concentrations of less than 3%. Methyl-viologen-dependent O2 exchange in leaf slices from these plants was not inhibited. There was no photoxidation of chlorophyll, in isolated thylakoids, or any inhibition of electron transport at photosystem (PS)II, PSI or through both photosystems which would account for the inhibition of photosynthesis. The conditions which inhibit photosynthesis in chilling-sensitive plants do not cause inhibition inS. oleracea, a chilling-insensitive plant, or in 20° C-grownN. oleander. The CO2-dependent photosynthesis, measured at 5° C, was reduced to about 3% of that recorded at 25° C in chilling-sensitive plants but only to about 30% in the chilling-insensitive plants. Methyl-viologen-dependent O2 exchange, measured at 5° C, was greater than 25% of the activity at 25° C in all the plants. The results indicate that the mechanism of the chilling-induced inhibition of photosynthesis does not involve damage to PSII. That inhibition of photosynthesis is observed only in the chilling-sensitive plants indicates it is related, in some way, to the disproportionate decrease in photosynthetic activity in these plants at chilling temperatures.Abbreviations Chl chlorophyll - DPIPH reduced form of 2,6-dichlorophenol-indophenol - DMQ 2,5-dimethyl-p-benzoquinone - MV methyl viologen - 20°-oleander Nerium oleander grown at 20° C - 45°-oleander N. oleander grown at 45° C - PFD photon flux density (photon fluence rate) - PSI and PSII photosystem I and II, respectively  相似文献   

15.
Phosphorus and nitrogen excretion rates by zooplankton communities from two eutrophic and shallow Dutch lakes were measured in laboratory. The variations in excretion rates in the lakes (May–October) were caused mainly by fluctuation in zooplankton biomass. Mean summer excretion rates (June–September) were 2.4 and 0.9 µg PO4P·1–1·d–1 in Lake Loosdercht and Lake Breukeleveen, respectively. This difference between the lakes was caused mainly by the lower zooplankton biomass in Lake Breukeleveen. The excretion of 2.4 µg PO4P·1–1·d compared with the calculated P-demand of phytoplankton of 8.0 µg PO4P·1–1·d–1 is substantial in the summer (June–September) and far more important than the external P-supply of 0.4 µg P·1–1·d–1 and sediment release of 0.5 µg P·1–1·d–1. Both temperature and composition of zooplankton affected the weight specific excretion rates of the zooplankton community. The weight specific community excretion rates of P and N increased with temperature (exponential model); 1–8 g PO4P·mg–1 zooplankton-C·d–1 and 5–42 µg NH3N·mg–1 zooplankton-C·d–1 (10°C–20°C).  相似文献   

16.
Ulva rigida was cultivated in 7501 tanks at different densities with direct and continuous inflow (at 2, 4, 8 and 12 volumes d–1) of the effluents from a commercial marine fishpond (40 metric tonnes, Tm, of Sparus aurata, water exchange rate of 16 m3 Tm–1) in order to assess the maximum and optimum dissolved inorganic nitrogen (DIN) uptake rate and the annual stability of the Ulva tank biofiltering system. Maximum yields (40 g DW m–2 d–1) were obtained at a density of 2.5 g FW 1–1 and at a DIN inflow rate of 1.7 g DIN m–2 d–1. Maximum DIN uptake rates were obtained during summer (2.2 g DIN M–2 d–1), and minimum in winter (1.1 g DIN m–2 d–1) with a yearly average DIN uptake rate of 1.77 g DIN m–2 d–1 At yearly average DIN removal efficiency (2.0 g DIN m–2 d–1, if winter period is excluded), 153 m2 of Ulva tank surface would be needed to recover 100% of the DIN produced by 1 Tm of fish.Abbreviations DIN= dissolved inorganic nitrogen (NH inf4 sup+ + NO inf3 sup– + NO inf2 sup– ); - FW= fresh weight; - DW= dry weight; - PFD= photon flux density; - V= DIN uptake rate  相似文献   

17.
Summary Gossypium hirsutum L. var. Delta Pine 61 was cultivated in controlled-environment chambers at 1000–1100 mol photosynthetically active photons m-2 s-1 (medium photon flux density) and at 1800–2000 mol photons m-2 s-1 (high photon flux density), respectively. Air temperatures ranged from 20° to 34°C during 12-h light periods, whereas during dark periods temperature was 25° C in all experiments. As the leaf temperature decreased from about 33° to 27° C, marked reductions in dry matter production, leaf chlorophyll content and photosynthetic capacity occurred in plants growing under high light conditions, to values far below those in plants growing at 27° C and medium photon flux densities. The results show that slightly suboptimum temperatures, well above the so-called chilling range (0–12° C), greatly reduce dry matter production in cotton when combined with high photon flux densities equivalent to full sunlight.Abbreviations DW dry weight - F v variable fluorescence yield - F M maximum fluorescence yield - PFD photon flux density (400–700 nm)  相似文献   

18.
Field observations on temperature and pH of a small pond showed that a amphipod population of Hyalella azteca was exposed to variable seasonal pH between 5.10–5.85, and water temperatures between 2–21 °C. Laboratory experiments were designed to simulate seasonal temperatures and field pHs of a small pond habitat. Laboratory bioassay experiments were conducted to determine the survival of Hyalella azteca at pHs 4, 5, 6 and 7, and varying temperatures of 5°, 10°, 15°, 20° and 25 °C.The LT100 at pH 4 and 25 °C was 5.7 ± 0.47 days, compared to 47.3 ± 2.49 days at 5 °C. An Analysis of Variance (ANOVA) showed temperature was a significant (p > 0.0001) source of variation in the acute lethality of pH to H. azteca. A Duncans Multiple Range Test (DMRT) further showed that in laboratory experiments at pH 4, there was a significant difference ( = 0.01) between the LT100s at 5°, 10°, 15° and 20 °C, but not between temperatures 20° and 25 °C.  相似文献   

19.
Julian D. Olden 《Hydrobiologia》2000,436(1-3):131-143
Artificial neural networks are used to model phytoplankton succession and gain insight into the relative strengths of bottom-up and top-down forces shaping seasonal patterns in phytoplankton biomass and community composition. Model comparisons indicate that patterns in chlorophyll aconcentrations response instantaneously to patterns in nutrient concentrations (phosphorous (P), nitrite and nitrate (NO2/NO3–N) and ammonium (NH4–H) concentrations) and zooplankton biomass (daphnid cladocera and copepoda biomass); whereas lagged responses in an index of algal community composition are evident. A randomization approach to neural networks is employed to reveal individual and interacting contributions of nutrient concentrations and zooplankton biomass to predictions of phytoplankton biomass and community composition. The results show that patterns in chlorophyll aconcentrations are directly associated with P, NO2/NO3–N and daphnid cladocera biomass, as well as related to interactions between daphnid cladocera biomass, and NO2/NO3–N and P. Similarly, patterns in phytoplankton community composition are associated with NO2/NO3–N and daphnid cladocera biomass; however show contrasting patterns in nutrient– zooplankton and zooplankton–zooplankton interactions. Together, the results provide correlative evidence for the importance of nutrient limitation, zooplankton grazing and nutrient regeneration in shaping phytoplankton community dynamics. This study shows that artificial neural networks can provide a powerful tool for studying phytoplankton succession by aiding in the quantification and interpretation of the individual and interacting contributions of nutrient limitation and zooplankton herbivory on phytoplankton biomass and community composition under natural conditions.  相似文献   

20.
He  Z.H.  Qin  J.G.  Wang  Y.  Jiang  H.  Wen  Z. 《Hydrobiologia》2001,457(1-3):25-37
Moina mongolica, 1.0-1.4 mm long and 0.8 mm wide, is an Old World euryhaline species. This paper reviewed the recent advances on its autecology, reproductive biology, feeding ecology and perspective as live food for marine fish larviculture. Salinity tolerance of this species ranges from 0.4–1.4 to 65.2–75.4. Within 2–50 salinity, Moina mongolica can complete its life cycle through parthenogenesis. The optimum temperature is between 25 °C and 28 °C, while it tolerates high temperature between 34.4 °C and 36.0 °C and lower temperature between 3.2 °C and 5.4 °C. The non-toxic level of unionised ammonia (24 h LC50) for M. mongolica is <2.6 mg NH3–N l–1. Juvenile individuals filter 2.37 ml d–1 and feed 9.45×106 algal cells d–1, while mature individuals filter 9.45 ml d–1 and consume 4.94×106 algal cells d–1. At 28 °C, M. mongolica reaches sex maturity in 4 d and gives birth once a day afterward; females carry 7.3 eggs brood–1 and spawn 2.8 times during their lifetime. A variety of food can be used for M. mongolica culture including unicellular algae, yeast and manure, but the best feeding regime is the combination of Nannochloropsis oculata and horse manure. Moina mongolica reproduces parthenogenetically during most lifetime, but resting eggs can be induced at temperature (16 °C) combined with food density at 2000–5000 N. oculata ml–1. The tolerance to low dissolved oxygen (0.14–0.93 mg l–1) and high ammonia makes it suitable for mass production. Biochemical analyses showed that the content of eicospantanoic acid (20:53) in M. mongolica accounts for 12.7% of total fatty acids, which is higher than other live food such as Artemia nauplii and rotifers. This cladoceran has the characteristics of wide salinity adaptation, rapid reproduction and ease of mass culture. The review highlights its potential as live food for marine fish larvae.  相似文献   

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