Ammonia nitrogen and inorganic phosphorus excretion by the planktonic rotifers

Two series of experiments were carried out to determine the relation of the rate of phosphorus and nitrogen excretion by the planktonic rotifers to ambient temperature and individual body weights of these animals. The following formulas describing this relation were obtained: E_P=0.0154 W^?1.27 e^0.096T E_N=0.0879 W^?1.01 e^{0.088 T}, where E_P and E_N denote the rate of P and N excretion, respectively, in µg · mg dry wt^?1 · h^?1, W is body weight in µg dry weight, and T is temperature in °C.     

Disruption of planktonic phosphorus cycling by ultraviolet radiation

Ultraviolet radiation (UVR) may alter phosphorous (P) cycling by plankton through changes in the acquisition and/or regeneration of dissolved P. However, to date an effect of UVR on the uptake of P has not been observed at ambient phosphate (PO₄ ³⁻) concentrations. This has lead to the conclusion that the uptake of P by plankton may be insensitive to UVR. Past research has been limited to a few individual systems, prolonged incubations in bags, or lab cultures. We suspect that experimentation with natural plankton assemblages across broader environmental and/or chemical gradients is required to appreciably understand how UVR may alter P kinetics. Therefore, our study aimed to determine the effect of UVR on the turnover time of the dissolved PO₄ ³⁻ pool, the regeneration of dissolved P, the turnover rate of particulate P, and on PO₄ ³⁻ concentrations in natural plankton assemblages across broad environmental and chemical gradients. Second we aimed to assess how UVR may alter phosphatase activity and, determine if a change in phosphatase activity under UVR irradiance is correlated with a change in P uptake as proposed in the literature. Studies were conducted on 18 thermally stratified or polymictic lakes located in Ontario and Saskatchewan, Canada. Lake water samples were exposed to one of three experimental treatments: control, photosynthetically active radiation (PAR), or photosynthetically active radiation plus ultraviolet radiation (PAR + UVR). Our study is the first to demonstrate that UVR exposure has the potential to alter P cycling at ambient (picomolar) PO₄ ³⁻ concentrations. We have demonstrated that the turnover time of the PO₄ ³⁻ pool increases under UVR irradiance (i.e., P uptake decreases), while the regeneration rate of dissolved P and turnover rate of planktonic P are generally not affected; with the net effect being an increase in steady state PO₄ ³⁻ concentration (ssPO₄ ³⁻). Alkaline phosphatase activity (APA) in the dissolved and particulate fractions was significantly reduced in PAR + UVR treatments, but unrelated to changes in P uptake. In summary, we have demonstrated that the cycling of P may be disrupted by UVR, with a decrease in the uptake of P and the accumulation of PO₄ ³⁻ in the dissolved pool. This, in turn may exacerbate planktonic P limitation, alter the nutrient stoichiometry of plankton and/or indirectly alter rates of primary production in limnetic systems.     

Food selection and growth of the planktonic ciliate Coleps hirtus isolated from a monomictic subtropical lake

A strain of Coleps hirtus (Ciliophora, Prorodontida) was isolatedfrom the epilimnion of monomictic Lake Kinneret. Growth of thisciliate was tested in response to 12 species of planktonic algaeand seven species of cultured bacteria from lake isolates whichwere offered as food. Eight species of algae (one Cryptophyceaeand seven Chlorophyceae) and four bacteria supported good toexcellent growth of C.hirtus. Growth rates (µ) and doublingtimes (DT) ranged from 0.008 to 0.029 h^–1 and from 23.9to 90.8 h respectively. C.hirtus was able to grow on bacteriaat concentration levels as low as 2–8 x 10⁵ cells ml^–1.No correlation was observed between growth rate of C.hirtusand cell volume of the prey. ^aPresent address: Istituto di Ecologia, Universita di Parma,43100 Parma, Italy     

Physiological and environmental constraints in the ecology of the planktonic dinoflagellate Ceratium hirundinella

SUMMARY. Constraints upon the vertical distribution of a population of Ceratium hirundinella , in a productive English lake during the summer stratification of 1976, are considered. They are interpreted in relation to vertical gradients of temperature, dissolved oxygen and irradiance, and to rates of photosynthesis and respiration measured as oxygen exchange in long- and short-term exposures. The motile cells tended to aggregate at an intermediate depth in the epilimnion, associated with a relative irradiance level of c . 10% or c . 140 μ einsteins m⁻²s⁻¹ as measured with a horizontal PAR sensor. Higher irradiances, and conditions below the oxycline, were apparently unfavourable, but the intervening layer was severely compressed at the height of summer stratification, when concentrations of inorganic nitrogen were also minimal. Thus the population apparently passed through a critical period, at which the cellular content of chlorophyll-α was much reduced. The preferred irradiance level in the lake corresponded to that at which measured rates of net photosynthesis were maximal. Increased rates of oxygen evolution were measured at higher irradiances in very short exposures; this behaviour may be of importance to cells experiencing vertical movement in nature.     

Inter-strain differences in nitrogen use by the coccolithophore Emiliania huxleyi, and consequences for predation by a planktonic ciliate

Four strains of the coccolithophore Emiliania huxleyi (CCMP strains 370, 373, 374, 379) were tested for their ability to grow on various nitrogen sources. All strains grew on ammonium, nitrate, and urea, although growth of CCMP379 on urea was low. Responses to other dissolved organic nitrogen (DON) sources varied. CCMP379 did not grow on any DON source other than urea. All other strains grew on one of the two tested amino acids: CCMP370 and CCMP373 on glutamine, and CCMP374 on alanine. All three of these strains also grew on hypoxanthine; in addition, two grew well on acetamide and one on ethanolamine. E. huxleyi strains also differed in their susceptibility to predation by the ciliate Strobilidium sp. CCMP374 was ingested at substantially higher rates than CCMP373 regardless of E. huxleyi growth condition. Ciliate feeding rates also depended on E. huxleyi growth condition. For CCMP374, feeding rates were 2× higher on growing E. huxleyi cells than on non-growing cells (average 27.5 versus 15.6 cells ciliate⁻¹ h⁻¹, respectively). For CCMP373, a relationship between E. huxleyi growth rate and ciliate feeding rate was not evident, but E. huxleyi grown on some N sources (ammonium, nitrate, urea) were ingested at consistently higher rates than E. huxleyi grown on other sources (ethanolamine, glutamine). Interstrain differences in the ability to utilize DON and resist predation may contribute to maintenance of high genetic diversity within this cosmopolitan, bloom-forming species.     

Study of the marine planktonic dinoflagellate Ceratium divaricatum (Dinophyceae), a confused and considerably variable species

The species Ceratium divaricatum (Lemmermann) Kofoid has largely been subject to misidentification and taxonomic confusion. The history of the species is complex: originally illustrated by Bergh (1881) as Ceratium tripos var., for which Lemmermann (1899) gave it the name Ceratium tripos var. divaricatum; the name Ceratium divaricatum was used by Kofoid (1908) with no specification of authors or references. It shows a high degree of morphological variation and development of autotomy of the apical and antapical horns. This great morphological variation has led to misidentifications in routine examinations of phytoplankton materials, and several names have been used for this species, including Ceratium dens, Ceratium porrectum and Ceratium tripos var. ponticum, as well as Ceratium balechii, a proposed new species for intermediate forms. Here, the species is redescribed, on the basis of material from Mexican Pacific coasts. Morphological and ecologic differences exist among this species and other closely related ones. Distribution of C. divaricatum is wider than previously documented (mainly because of previous misidentifications): the North Pacific Ocean, from British Columbia in Canada to temperate or subtropical waters of Mexico, and then is interrupted to reappear again in coasts of Peru and Chile, and also in coasts of the Benguela area, the South‐west Atlantic Ocean. In tropical and equatorial areas of the Pacific Ocean, a more delicate form occurs, herein proposed as a variety of this species: Ceratium divaricatum var. balechii. C. divaricatum and var. balechii may be relatively abundant, even producing non‐toxic red tides, in various spots along coasts of the Pacific Ocean (Canada to Mexico). It appears to be a neritic form, with high sensibility to changes in water temperature, and presumably associated to upwelling areas.     

Predator–prey interactions between a planktonic ciliate Strombidium sp. (Ciliophora, Oligotrichida) and the dinoflagellate Pfiesteria piscicida (Dinamoebiales, Pyrrophyta)

The functional response of a planktonic ciliate, Strombidium sp. feeding on the dinoflagellate Pfiesteria piscicida non-toxic zoospores (NTZ) was experimentally studied with four different prey concentrations (43–3153 cells ml⁻¹). Data from direct observations (NTZ inside individual Strombidium sp.) was used to calculate predator–prey specific ingestion and clearance rates. The ingestion rates varied between 0.68 and 14.26 NTZ ind⁻¹ h⁻¹, and with the predator–prey specific handling time of 2.83 min the U_max was 21.18 NTZ ind⁻¹ h⁻¹. The increase in the prey concentration between approximately 700 and 3000 NTZ ml⁻¹ did not increase the uptake of prey, and at the lowest Pfiesteria NTZ concentrations the feeding efficiency of Strombidium sp. was lowered, possibly indicating a situation of threshold feeding. When data from direct observations of ingested Pfiesteria NTZ were compared with values of total NTZ loss from the experimental water during the experiment, ingestion was found to represent only a fraction of the total NTZ loss in the presence of ciliates. This discrepancy was concluded to be due to other grazer related factors than actual ciliate grazing. The control of the initial growth of Pfiesteria community, in a pre-bloom situation, would require only a small ciliate abundance (less than 5 ml⁻¹), but when the Pfiesteria NTZ are scarce, relatively more ciliates are needed to limit the population growth of the dinoflagellate community because of the apparent feeding threshold. It is concluded that the formation of non-toxic P. piscicida blooms require periods of low grazing pressure or a means to escape grazing.     

Bubble stimulation efficiency of dinoflagellate bioluminescence

Dinoflagellate bioluminescence , a common source of bioluminescence in coastal waters , is stimulated by flow agitation . Although bubbles are anecdotally known to be stimulatory , the process has never been experimentally investigated . This study quantified the flash response of the bioluminescent dinoflagellate Lingulodinium polyedrum to stimulation by bubbles rising through still seawater . Cells were stimulated by isolated bubbles of 0 . 3–3 mm radii rising at their terminal velocity , and also by bubble clouds containing bubbles of 0 . 06–10 mm radii for different air flow rates . Stimulation efficiency , the proportion of cells producing a flash within the volume of water swept out by a rising bubble , decreased with decreasing bubble radius for radii less than approximately 1 mm . Bubbles smaller than a critical radius in the range 0 . 275–0 . 325 mm did not stimulate a flash response . The fraction of cells stimulated by bubble clouds was proportional to the volume of air in the bubble cloud , with lower stimulation levels observed for clouds with smaller bubbles . An empirical model for bubble cloud stimulation based on the isolated bubble observations successfully reproduced the observed stimulation by bubble clouds for low air flow rates . High air flow rates stimulated more light emission than expected , presumably because of additional fluid shear stress associated with collective buoyancy effects generated by the high air fraction bubble cloud . These results are relevant to bioluminescence stimulation by bubbles in two‐phase flows , such as in ship wakes , breaking waves , and sparged bioreactors . Copyright © 2015 John Wiley & Sons, Ltd.     

Genotypic difference of potato in carbon budgeting as a mechanism of phosphorus utilization efficiency

Observed genotypic difference in P utilization efficiency in soil grown potatoes led to the present study to investigate possible mechanisms of P utilization efficiency in potato genotypes grown in nutrient solution under three P regimes (low, medium and high). For all genotypes relative growth rate (RGR), leaf P content, net assimilation rate (NAR) and leaf area ratio (LAR) increased while P utilization efficiency and leaf starch content decreased at the two higher P regimes compared to the low P regime. The P-efficient genotypes CGN 17903 and CIP 384321.3 had higher RGR compared to the P-inefficient genotypes CGN 22367 and CGN 18233, which resulted from enhanced NAR rather than from LAR. Net photosynthetic rate was similar for all genotypes. However, for P-inefficient genotype CGN 22367, the lower NAR could be explained by increased leaf dark respiration. For P-inefficient genotype CGN 18233 we speculate that increased carbon cost of root respiration or exudation or both, caused low NAR, since leaf dark respiration of this genotype was similar to that of P-efficient genotypes.     

A seasonal sequence of diel distribution patterns for the planktonic dinoflagellate Ceratium hirundinella in a eutrophic lake

SUMMARY. 1. Diel depth distribution patterns of Ceratium hirundinella were studied during eleven sampling periods, covering the seasonal growth cycle. They were shown to result from short-term periodic or non-periodic external factors, endogenous responses of the alga, and interactions between these.
2. Diel variations in wind stress resulted in the net transport of algae into or out of the sampling position due to lateral water movements. A progressive surface accumulation of Ceratium , leading to a 3-fold increase in cell numbers at the sampling site over a 24 h period, was due to wind-induced upwelling of deeper cells. Near-surface accumulation of Ceratium on a completely overcast afternoon, similar to that associated with migrations, was attributable to advection.
3. Under sufficiently calm conditions, depth-differentiation of Ceratium was regulated by its vertical swimming movements with a diel periodicity. Migration patterns observed in earlier work were confirmed and extended. The alga migrated towards the surface during the daytime and downward during the night; this rhythm had an endogenous component.
4. At high surface illumination, the alga retreated from the surface and formed discrete sub-surface maxima; at low irradiance Ceratium showed positive phototaxis and concentrated near the surface. Under either condition of irradiance Ceratium actively aggregated at depths associated with irradiance levels of about 125–155 μEinsteins m ⁻² s ⁻¹. Downward movement was restricted by anoxic conditions and possibly by thermal/ density gradients. However, given sufficient light penetration, dissolved oxygen and nutrient availability, the thermal density gradient does not apparently eliminate downward movement by Ceratium.     

A comparison of fixatives for the estimation of abundance and biovolume of marine planktonic ciliate populations

The effects of five treatments with four commonly used fixativeson the abundance and cell volume of marine planktonic ciliateswere investigated on a natural community from Plymouth Sound.The fixative treatments were 5% and 9% Bouin's solution, 0.4%acid Lugol's iodine, 1% buffered formaldehyde and 1% glutaraldehyde.The abundance of the aloricate ciliate community varied accordingto fixative treatment, with Lugol's maintaining the greatestcell numbers, followed by Bouin's, glutaraldehyde and formaldehyde.The effects of the fixatives on the abundance of the two mostcommon aloricate taxa, Balanion sp. and Strombidium epidemumwere similar to, and components of, those for the aloricatepopulation as a whole. However, there was little differencebetween the effects of different fixatives on the abundanceof the tintinnid community, or on the abundance of the mostcommon tintinnid, Tintinnopsis nana. Mean cell volumes of Balanionsp., S.epidemum and T.nana were greatest in samples fixed informaldehyde, followed by glutaraldehyde, Lugol's and Bouin's.The mean population volume of the aloricate and tintinnid populationsgenerally reflected this trend with greatest values recordedin formaldehyde- and glutaraldehyde-fixed samples, followedby Lugol's and Bouin's; however, the differential effects ofthe fixatives were not as great. Lugol's therefore appears tobe the most effective fixative tested for the estimation ofciliate abundance and population volume, the latter being afunction of abundance and cell volume. ³Present address: British Antarctic Survey, High Cross, MadingleyRoad, Cambridge CB3 OET, UK     

低盐度围隔调控环境浮游纤毛虫群落结构与动态

为了解施肥与水质调控对养殖水体中原生动物的影响,2008年6-10月,对低盐度围隔调控环境中浮游纤毛虫种群结构及动态变化进行了研究.通过活体观察和标本固定染色法共检测到浮游纤毛虫48种,分属于3纲11目37属,其中寡毛目纤毛虫种类8种;缘毛目7种,腹毛目和盾纤目均为6种;优势种多为富营养化水体中或耐污性种类,如圆筒状拟铃壳虫(Tintinnopsis cylindrata)、球形急游虫(Stranbidium globosaneum)、海洋帆口虫(Pleuronema marinum)、蚤状中缢虫(Mesodinium pulex)、毛板壳虫(Coleps hirtus)、瓜形膜袋虫(Cyclidium citrullus)等.围隔不同施肥处理,对纤毛虫的群落组成与动态变化影响显著,试验期间,围隔中纤毛虫种类平均值最高为9种,最低为4种;密度平均值最高为112.30cells·ml-1,最低为19.50 cells·ml-1;10个围隔中纤毛虫种类平均分别为6～7种,密度平均为52.56 cells·ml-1;施有机肥培藻的围隔,优势种始终是嗜污性较强的纤毛虫.纤毛虫动态与浮游藻类动态变化密切相关,二者的密度变化特点为前期和后期低,中期较高;但多样性的变化规律相反,纤毛虫的多样性表现为前期和后期低,中期较高,藻类的多样性表现为前期和后期高,中期较低.     

Effects of nitrogen,phosphorus and carbon enrichment on planktonic and periphytic algae in a softwater,oligotrophic lake in Florida,USA

The objective of this study was to investigate nutrient limitation of algal abundance in Anderson-Cue Lake, a softwater clear oligotrophic lake in north-central Florida. Nutrient diffusing clay pots and cylindrical enclosures were used in the field to test effects of different combinations of nitrogen, phosphorus, silica, and carbon on algal standing crop and composition of periphytic and planktonic algae, respectively. Effects of nutrient enrichment on periphytic algae were examined in two studies conducted 31 May – 8 July and 10 June – 15 July 1991. Nutrient effects on planktonic algae were examined in one study from 13 June – 1 July 1991. Planktonic and periphytic algal biovolume was significantly higher (p<0.05) when nitrogen and carbon were added in combination than with treatments without nitrogen, carbon, or nitrogen and carbon. Treatments with nitrogen and carbon combined resulted in lower algal diversity and dominance by coccoid green algae andScenedesmus. Results indicate that carbon and nitrogen can be limiting factors to algal growth in Anderson-Cue Lake and possibly other lakes of similar water quality.     

Arbuscular mycorrhiza improves plant adaptation to phosphorus deficiency through regulating the expression of genes relevant to carbon and phosphorus metabolism

Aims Arbuscular mycorrhizal (AM) symbiosis plays an important role in plant adaptation to phosphorus (P) deficiency. The mycorrhizal fungi can directly regulate P stress response of the host plants, and can also indirectly influence neighbor plants via AM exudates. This study aimed to reveal the regulation mechanisms of plant response to P deficiency by AM associations. Methods In a compartmentation cultivation experiment with Zea mays ‘B73’ and AM fungus Rhizophagus irregularis ‘DAOM197198’, we investigated mycorrhizal effects on plant P nutrition and the expression of plant and fungal genes related to P and carbon (C) metabolisms under both low P (10 mg?kg^-1) and high P (100 mg?kg^-1) conditions. The cultivation system consisted of three compartments, namely donor compartment, buffer compartment and receiver compartment divided by two pieces of microporous filters with pore size of 0.45 μm. Maize plant in donor compartment inoculated with AM fungus served as a source of AM exudates. The microporous filters could restrict the development of extraradical mycelium of AM fungi, but allow diffusion of AM exudates. Real-time PCR was performed to quantify the gene expression levels both in maize plants and AM fungi. Important findings The experimental results indicated that under low P conditions mycorrhizal colonization increased plant dry weight and P concentration in donor plants, and up-regulated plant genes encoding P transporters Pht1;2, Pht1;6, phosphoenolpiruvate carboxylase (PEPC), inorganic pyrophosphatase (TC289), glycerol-3-phosphate transporter (G3PT) and malate synthase (MAS1). The expression of AM fungal genes encoding P transporter (GiPT), GlcNAc transporter (NGT1), GlcNAc kinase (HXK1b), GlcNAc phosphomutase (AGM1), UDP GlcNAc pyrophosphorylase (UAP1), chitin synthase (CHS1), GlcNAc-6-phosphate deacetylase (DAC1) and glucosamine-6-phosphate isomerase (NAG1) was significantly higher under low P conditions compared with high P conditions. However, for the receiver plants, plant dry mass and P concentration were only significantly increased by higher P addition, while inoculation treatment significantly up-regulated the expression of P transporter genes Pht1;2 and Pht1;6, C metabolism related genes G3PT, PEPC, TC289 and MAS1. The study proved that AM exudates could potentially stimulate plant response to P deficiency by regulating functional genes relevant to P and C metabolisms in the mycorrhizal associations.     

Feeding of planktonic rotifers on ciliates: a method using natural ciliate assemblages labelled with fluorescent microparticles

A method was developed to allow direct measurements of predationexerted by metazooplankton on ciliates. The method relied onthe use of ciliates labelled with fluorescent microparticles(FMP). Optimal labelling conditions were determined with ciliatesfrom cultures (Tetrahymena pyriformis) and with natural ciliateassemblages sampled in a river. Labelled T. pyriformis wereused as tracer food to determine gut passage time (GPT) andingestion rates of the rotifer Brachionus calyciflorus in thelaboratory. Predation of metazooplankton from the lowland riverMeuse (Belgium) was determined by labelling natural assemblagesof ciliates and using them as tracer food for metazooplankterssampled in the river. Optimal labels of ciliates, i.e. sharpdistribution of FMP in cells, were obtained with short incubations(10 min) and low FMP concentrations (1 x 10⁵ mL^–1). GPTvaried between 30 and 45 min for B. calyciflorus and from 25up to >35 min for rotifers from the river. The ingestionrate of B. calyciflorus fed with T. pyriformis was 3.3 ±0.6 ciliate rot^–1 h^–1, i.e. 1.4 ± 0.3 ngCrot^–1 h^–1. Metazooplankton species for which theingestion of ciliates could be measured were the rotifers Keratellacochlearis, Euchlanis dilatata and Synchaeta spp. Ingestionrates measured ranged from 0.4 to 12.5 ngC rot^–1 h^–1.The method proposed proved to be useful in estimating the predationof microplankton on ciliates in semi- in situ conditions; infurther developments, labelled natural assemblages of ciliatescould be used for in situ incubations with the Haney chamber.