Influence of duration of incubation on zooplankton respiration and excretion results

Respiration (O), ammonium (NH₄), phosphate (PO₄), total nitrogen (N_T) and phosphorus (P_T) excretions were measured on mixed zooplankton during 3-, 6-, 9-, 12-, 21-, and 24-h incubation periods at 20–23 C. The excretion rates of PO₄, N_T. and P_T decrease during a 21-h period, while rates of respiration and excretion of NH{IN4} are constant. The percentage of inorganic nitrogen excreted increases regularly from 3 h (30–40% of total nitrogen) to 21 h (70–80%) and it could be either due to a bacterial activity which was measured or to a decrease with time of organic nitrogen excreted because of starvation. $\text{O}\text{N}{}_{\mathrm{T}}$, $\text{O}\text{PO}{}_4$, $\text{O}\text{P}{}_{\mathrm{T}}$, and $\text{NH}{}_4\text{PO}{}_4$ ratios increase during the first 9 h of incubation; the percentage of inorganic phosphorus excreted is higher at the very beginning and then remains constant from 6 to 24 h. $\text{O}\text{NH}{}_4$ and $\text{N}{}_{\mathrm{T}}\text{P}{}_{\mathrm{T}}$ ratios are constant during a 24-h term, which makes them useful metabolic indexes.     

Presence of nitrate-accumulating sulfur bacteria and their influence on nitrogen cycling in a shallow coastal marine sediment

Nitrate flux between sediment and water, nitrate concentration profile at the sediment-water interface, and in situ sediment denitrification activity were measured seasonally at the innermost part of Tokyo Bay, Japan. For the determination of sediment nitrate concentration, undisturbed sediment cores were sectioned into 5-mm depth intervals and each segment was stored frozen at -30 degrees C. The nitrate concentration was determined for the supernatants after centrifuging the frozen and thawed sediments. Nitrate in the uppermost sediment showed a remarkable seasonal change, and its seasonal maximum of up to 400 microM was found in October. The directions of the diffusive nitrate fluxes predicted from the interfacial concentration gradients were out of the sediment throughout the year. In contrast, the directions of the total nitrate fluxes measured by the whole-core incubation were into the sediment at all seasons. This contradiction between directions indicates that a large part of the nitrate pool extracted from the frozen surface sediments is not a pore water constituent, and preliminary examinations demonstrated that the nitrate was contained in the intracellular vacuoles of filamentous sulfur bacteria dwelling on or in the surface sediment. Based on the comparison between in situ sediment denitrification activity and total nitrate flux, it is suggested that intracellular nitrate cannot be directly utilized by sediment denitrification, and the probable fate of the intracellular nitrate is hypothesized to be dissimilatory reduction to ammonium. The presence of nitrate-accumulating sulfur bacteria therefore may lower nature's self-purification capacity (denitrification) and exacerbate eutrophication in shallow coastal marine environments.     

Model of copepod growth influenced by the food carbon:nitrogen ratio and concentration, under the hypothesis of strict homeostasis

This study describes a model which addresses the processes of ingestion, assimilation, respiration, excretion and growth of copepods as a function of the concentration of food and its elemental composition in terms of carbon and nitrogen (N). Two experimental data sets are used to estimate several parameters of the model concerned with the influence of food quality. The results of the model suggest that the concentration of food and its quality (i.e. the C:N ratio) largely determine copepod growth. Both the experimental data sets and the model output show that low carbon relative to the nitrogen content of food does not limit the production of copepods. Comparing the results of the model to those of a previous model on bacteria suggests large differences between bacterial and copepod physiological responses to a variable quality of the substrate or food. The results of these models suggest that the regeneration of ammonium performed by copepods always favors regenerated primary production, whereas that performed by bacteria, depending on the quality of assimilated substrates, can favor or limit regenerated production.      

Copepod and microzooplankton grazing in mesocosms fertilised with different Si:N ratios: no overlap between food spectra and Si:N influence on zooplankton trophic level

We hypothesized that the trophic level of marine copepods should depend on the composition of the protist community. To test this hypothesis, we manipulated the phytoplankton composition in mesocosms and measured grazing rates of copepods and mesozooplankton in those mesocosms. Twelve mesocosms with Northeast Atlantic phytoplankton were fertilised with different Si:N ratios from 0:1 to 1:1. After 1 week, ten of the mesocosms were filled with natural densities of mesozooplankton, mainly calanoid copepods, while two remained as mesozooplankton-free controls. Both before and after the addition of copepods there was a positive correlation of diatom dominance with Si:N ratios. During the second phase of the experiment, copepod and microzooplankton grazing rates on different phytoplankton species were assessed by a modification of the Landry-Hassett dilution technique, where the bottles containing the different dilution treatments were replaced by dialysis bags incubated in situ. The results indicated no overlap in the food spectrum of microzooplankton (mainly ciliates) and copepods. Ciliates fed on nanoplankton, while copepods fed on large or chain-forming diatoms, naked dinoflagellates, and ciliates. The calculated trophic level of copepods showed a significantly negative but weak correlation with Si:N ratios. The strength of this response was strongly dependent on the trophic levels assumed for ciliates and mixotrophic dinoflagellates.     

The role of arctic zooplankton in biogeochemical cycles: respiration and excretion of ammonia and phosphate during summer

The study of the structural and functional properties of key components of polar marine ecosystems has received increased attention in order to better understand the ecological consequences of future sea temperature rise and seasonal ice retraction. Owing to this purpose, during the ATOS-Arctic cruise, held in July 2007 in the framework of the 2007–2008 International Polar Year, we studied the respiratory carbon demand of mesozooplankton as well as their contribution to the regeneration of inorganic nitrogen and phosphorus (NH₄-N and PO₄-P) via excretion. The studied area comprised several stations along a latitudinal gradient in the East Greenland current, plus a network of stations NW of the Svalbard islands. The specific respiratory carbon losses and phosphorus (PO₄-P) excretion rates were similar or slightly higher than some reports for Arctic mesozooplankton, but the nitrogen (NH₄-N) excretion rates were higher by a factor of 3 when compared with previous data sets. The mesozooplankton respiratory losses were equivalent to 23% of primary production, and at turn zooplankton contributed by excretion to more than 50% of the N and P required by phytoplankton. Although C:N, C:P and N:P metabolic atomic quotients almost coincided with the average Redfield’s stoichiometric ratios, the low C:N values when compared to previous reports suggested a predominance of protein-related metabolic substrates. The potential consequences of changes observed in the C:N, N:P and C:P metabolic ratios of mesozooplankton for Arctic marine ecosystems are discussed.     

Intraspecific stoichiometric variability and the ratio of nitrogen to phosphorus resupplied by zooplankton

1. An in situ experiment was carried out in a high-mountain oligotrophic lake (La Caldera) to quantify the specific release rates of ammonium and phosphorus in different phases of the seasonal succession of plankton. The zooplankton community was dominated by the calanoid copepod Mixodiaptomus laciniatus .
2. The rates of release of N and P (from non-detectable to 3.58 μg N mg^–1 DW h^–1 and from 0.26 to 2.29 μg P mg^–1 DW h^–1, respectively) and the N : P released ratio (not detectable to 4.77) fell within the range typical of oligotrophic lakes dominated by copepodite assemblages.
3. The values of the zooplankton N : P ratio (5 : 1 to 10 : 1 by weight) were lower than those established for other species of calanoids, and followed a well-established pattern of seasonal variation from year to year with higher values after ice thaw and lower values as individual size increased (ontogenetic development).
4. The elemental composition of the zooplankton depended on individual size, while the released N : P ratio was inversely related to the N : P ratio of the food. This pattern conforms to the predictions of the homeostasis theory of Sterner (1990).
5. A feedback regulation was established between the stoichiometric composition of the zooplankton, their food and the released N : P ratio that can help explain changes in pelagic community structure during the ice-free period.     

Intraspecific stoichiometric variability and the ratio of nitrogen to phosphorus resupplied by zooplankton

1. An in situ experiment was carried out in a high-mountain oligotrophic lake (La Caldera) to quantify the specific release rates of ammonium and phosphorus in different phases of the seasonal succession of plankton. The zooplankton community was dominated by the calanoid copepod Mixodiaptomus laciniatus .
2. The rates of release of N and P (from non-detectable to 3.58 μg N mg^–1 DW h^–1 and from 0.26 to 2.29 μg P mg^–1 DW h^–1, respectively) and the N : P released ratio (not detectable to 4.77) fell within the range typical of oligotrophic lakes dominated by copepodite assemblages.
3. The values of the zooplankton N : P ratio (5 : 1 to 10 : 1 by weight) were lower than those established for other species of calanoids, and followed a well-established pattern of seasonal variation from year to year with higher values after ice thaw and lower values as individual size increased (ontogenetic development).
4. The elemental composition of the zooplankton depended on individual size, while the released N : P ratio was inversely related to the N : P ratio of the food. This pattern conforms to the predictions of the homeostasis theory of Sterner (1990).
5. A feedback regulation was established between the stoichiometric composition of the zooplankton, their food and the released N : P ratio that can help explain changes in pelagic community structure during the ice-free period.     

Prey selectivity and the influence of prey carbon:nitrogen ratio on microflagellate grazing

We investigated the influence of prey species and nutritional value, in terms of carbon:nitrogen (C:N) ratio, on prey selection by the predatory microflagellate Paraphysomonas vestita. Experiments were conducted with two phytoplankton prey species of similar diameter to remove size-specific grazing effects. Live cells of both low and high C:N ratio (ranging from 4.8 to 14; N-replete and N-deplete, respectively) were offered to the predator either individually or in combination. By utilising analytical flow cytometry, we were able to enumerate the two prey species and, hence, study selective predation in the mixed-prey assemblage. In single prey experiments, the maximum observed ingestion rates were found to be higher, at all prey C:N ratios, when Isochrysis galbana was the prey item when compared to Pavlova lutheri, whilst maximum specific predator division rates were similar for both prey. Ingestion rates were influenced by prey nutrient status, higher values being observed with N-replete than N-deplete prey. When the two prey species were presented to P. vestita as a mixture, I. galbana was ingested more rapidly than P. lutheri, although ingestion was found to be suppressed when compared to when this was the sole prey species. Conversely, the presence of I. galbana did not influence the rate of ingestion of P. lutheri. P. vestita was, therefore, able to modify its rate of ingestion on the basis of prey type and prey C:N ratio and to discriminate between alternative prey of similar size in mixed-prey assemblages.     

氮源及碳氮比对产朊假丝酵母合成谷胱甘肽的影响

研究了N源对产朊假丝酵母细胞生长和谷胱甘肽(GSH)合成的影响。在此基础上,分别以(NH4)2SO4和尿素作为单一N源,摇瓶条件下研究了不同C、N比对GSH发酵的影响。结果发现尿素有利于细胞生长,而(NH4)2SO4更有利于GSH的合成,并且酵母细胞在利用这2种N源合成GSH时,各自具有最佳的C、N比((NH4)2SO4为8.3 mol/mol,尿素为5.6 mol/mol)。最佳C、N比下的GSH分批发酵结果显示,尿素是更合适的N源,最终细胞干质量和GSH产量可以分别达到16.48 g/L和246.4 mg/L。最后分别采用发酵动力学模型和代谢网络分析对该结果产生的原因进行了定量解释。     

Nitrate respiration,denitrification, and utilization of nitrogen sources by aerobic carbon monoxide-oxidizing bacteria

We describe the ability of carboxydotrophic bacteria for nitrate respiration or denitrification. Four out of fourteen strains examined could denitrify heterotrophically forming N₂ (Pseudomonas carboxydoflava) or N₂O (Pseudomonas carboxydohydrogena, Pseudomonas compransoris, and Pseudomonas gazotropha). Three carried out a heterotrophic nitrate respiration (Arthrobacter 11/x, Azomonas B1, and Azomonas C2). P. carboxydohydrogena could use H₂ as electron donor for nitrate respiration under chemolithoautotrophic growth conditions. CO did not support denitrification or nitrate respiration of carboxydotrophic bacteria, although the free energy changes of the reactions would be sufficiently negative to allow growth. CO at 50 kPa was a weak inhibitor of N₂O-reduction in carboxydotrophic and non-carboxydotrophic bacteria and decelerated denitrifying growth. Carboxydotrophic bacteria could utilize a wide range of N-sources. Results obtained with a plasmid-cured mutant of Pseudomonas carboxydovorans OM5 showed, that genes involved in nitrogen assimilation entirely reside on the chromosome. In the presence of an suitable electron donor, most carboxydotrophic bacteria could carry out a reduction of nitrate to nitrite that did not support growth and did not lead to the formation of ammonia.This article is dedicated to Professor Hans G. Schlegel on the occasion of his 65th birthday and in admiration for his élan and eternal idealism     

The influence of soil C/N ratios on nitrogen mineralization during anaerobic incubation

Summary N-availability in 25 soils, spanning a wide range of C : N ratios, was estimated by maize growth in a pot experiment and ammonium-N production during anaerobic incubation. Discrepancies between the two indices were traced to soils with a high organic matter content and high C : N ratio. Whereas there existed a highly significant negative correlation between C : N ratio and incubation ammonium-N production, maize N-uptake was unrelated to C : N ratio. In particular, for soils of high C : N ratio, soil ammonium-N content after incubation gives a more reliable estimate of N-availability than does incubation ammonium-N production.     

Effects of kepone on growth and respiration of several estuarine bacteria

The toxicity of Kepone to mixed populations of estuarine microorganisms was determined by standard plate assays on Zobell marine medium containing 0.02, 0.20, and 2.0 mg of Kepone per liter. Under aerobic conditions, Kepone reduced the number of colony-forming units at all concentrations tested, but had no effect on the number of anaerobic microorganisms. Gram-positive organisms were more sensitive to Kepone than were gram-negative organisms. Growth of gram-negative isolates was not inhibited in nutrient broth, but was significantly inhibited in a minimal salts broth. Oxygen uptake by most isolates was reduced 25 to 100% by 20 ppm (20 mg/ml) of Kepone. Oxygen evolution was observed when several gram-positive isolates were exposed to Kepone concentrations of 20 ppm. Pentachlorophenol at concentrations above 28 ppm produced effects similar to those produced by Kepone. Inhibition of electron transport by Kepone was demonstrated by a significant reduction in the specific activities of NADH oxidases and succinooxidase.     

Feeding, growth and food conversion of the marine cladoceran Penilia avirostris

Ingestion and clearance rates, feeding behaviors and life historyvariables of the marine cladoceran Penilia avirostris were evaluatedover a range of food concentrations encountered in nature (0.01–3.0mm³ 1^–1 of Isochrysis galbana). Ingestion rates increasedand clearance rates decreased with increasing food concentration.No maximum feeding thresholds were observed over the range ofalgal concentrations offered. Weight-specific ingestion ratesdecreased with increasing body weight. Feeding behaviors suchas mandibular activity, abdominal claw rejections of cloggedfeeding structures and feeding appendage activity decreasedat a food level of 0.3 mm³ l^–1 of l. galbana. Peniliaavirostris had very poor survivorship at extremely low (0.01mm³ l^–1 and high (3.00 mm³ l^–1) food levels. Mortalitywas hardly affected at food levels of 0.03–1.0 mm³ l^–1Reproduction did not occur at food levels of     

Plant respiration in relation to growth, maintenance, ion uptake and nitrogen assimilation

Abstract Respiration in plants is generally observed to comprise two components: one proportional to the growth rate and the other to the plant dry mass. These components are usually interpreted as being related to the growth of new plant material and maintenance of existing plant material, respectively. By analysing data in this way, the respiratory costs of both structural synthesis and maintenance are observed to be greater in the root than the shoot. This contradicts current understanding of the biochemistry of the processes involved. The basic model is developed to incorporate three additional processes. The first is the cost of ion uptake for plant growth. The second allows for the fact that the site of nitrogen assimilation into amino acids may differ from the site of utilization for protein synthesis: when ammonium is supplied, this is incorporated immediately into amino acids owing to its toxicity to the plants; when nitrate is supplied it may be reduced either in the shoot or root, or both, and subsequently transported around the plant for utilization. The third process to be included is an energy cost for the uptake of ions to balance efflux from the root system. The theory is consistent with experimental observation and provides a means of understanding and interpreting respiration and nitrogen metabolism in plants.     

The influence of temperature and labile C substrates on heterotrophic respiration in response to elevated CO2 and nitrogen fertilization

Important effects of elevated [CO₂] on SOM are expected as a consequence of increased labile organic substrates derived from plants. The present study tests the hypotheses that, under elevated [CO₂]: 1) soil heterotrophic respiration will increase due to roots-microbes-soil interactions; 2) the increased labile C will boost soil heterotrophic respiration, depending on N availability; 3) the temperature sensitivity of soil respiration will change, depending on nitrogen inputs and plant activity. To test these hypotheses, we measured the heterotrophic respiration of intact soil cores collected in a poplar plantation exposed to elevated [CO₂] and two nitrogen inputs, at different temperatures. Additional physical (water content, root biomass) and biochemical parameters (microbial biomass, labile C) were determined on the same samples. The soil samples were collected at the POP-EuroFACE experimental site (Italy), where a Populus x euramericana plantation was exposed for 6 years to 550 ppm [CO₂] (Free Air CO₂ Enrichment) at two different nitrogen inputs (none or 290 kg ha^?1). The higher heterotrophic respiration under elevated [CO₂] (+30% on average) was driven by the larger pool of soil labile C (+57% on average). The temperature sensitivity of soil respiration was unaffected by elevated [CO₂], but was positively affected by N fertilization. Our results indicate that only a fraction of the extra carbon fixed by photosynthesis in elevated [CO₂] will contribute to enhanced carbon storage into the soil because of the contemporary stimulation of soil heterotrophic respiration. At the same time, the fraction remaining in the soil will enhance the pool of soil labile C.     

Modelling the influence of assimilate availability on root growth and architecture

A model has been designed to simulate rubber seedling root development as related to assimilate availability. Each root of the system is defined both as an element of a network of axes, characterized by its order, position and connections and as an individual sink competing for assimilates. At each time step, the growth of each root is calculated as a function of its own growth potential and of assimilate availability calculated within the whole plant. The potential elongation rate of a root is estimated by its apical diameter, which reflects the size of the meristem. When a root is initiated, the apical diameter depends on root type, but it varies thereafter according to assimilate availability. Thus, the latter controls both current and potential elongation. The model was able to simulate periodicity in root development as related to shoot growth and to reproduce differences in sensitivity to assimilate availability related to root type. It thereby validated the hypothesis that root growth but also root system architecture depend on assimilate allocation and that apical diameter is a good indicator of root growth potential. Provided that specific calibration is done, this model may be used for other species.     

Effect of carbon to nitrogen (C:N) ratio on nitrogen removal from shrimp production waste water using sequencing batch reactor

The United States Marine Shrimp Farming Program (USMSFP) introduced a new technology for shrimp farming called recirculating raceway system. This is a zero-water exchange system capable of producing high-density shrimp yields. However, this system produces wastewater characterized by high levels of ammonia, nitrite, and nitrate due to 40% protein diet for the shrimp at a high density of 1,000 shrimp per square meter. The high concentrations of nitrate and nitrite (greater than 25 ppm) are toxic to shrimp and cause high mortality. So treatment of this wastewater is imperative in order to make shrimp farming viable. One simple method of treating high-nitrogen wastewater is the use of a sequencing batch reactor (SBR). An SBR is a variation of the activated sludge process, which accomplishes many treatment events in a single reactor. Removal of ammonia and nitrate involved nitrification and denitrification reactions by operating the SBR aerobically and anaerobically in sequence. Initial SBR operation successfully removed ammonia, but nitrate concentrations were too high because of carbon limitation in the shrimp production wastewater. An optimization study revealed the optimum carbon to nitrogen (C:N) ratio of 10:1 for successful removal of all nitrogen species from the wastewater. The SBR operated with a C:N ratio of 10:1 with the addition of molasses as carbon source successfully removed 99% of ammonia, nitrate, and nitrite from the shrimp aquaculture wastewater within 9 days of operation.     

Decomposition of cellulose strips in relation to climate,litterfall nitrogen,phosphorus and C/N ratio in natural boreal forests

Isolates of Alternaria alternata, Botrytis cinerea, Fusarium oxysporum, Penicillium sp., Rhizoctonia solani, Stemphylium sp., Thielaviopsis basicola, and Verticillium dahliae were cultured on potato–dextrose agar (PDA), barley-sand and alfalfa-sand substrates in petri-dish or in column microcosms. N-mineralization by fungi and fungal-feeding nematodes in combination or fungi alone was assessed. Numbers of Aphelenchus avenae or Aphelenchoides composticola supported by the fungi were measured every 7 days. Times for full colonization of the substrates by fungi ranged from 5 to 15 days. Rhizoctonia solani and B. cinerea on PDA supported the largest A. avenae and A. composticola populations, respectively. Penicillium sp. was a nonhost for A. composticola and A. avenae. Rhizoctonia solani, B. cinerea, V. dahliae, and F. oxysporum supported significantly more nematodes than the other four fungal species. The ranked order of fungi based on the amount of N mineralized in columns free of nematodes was A. alternata (with a rate of 0.052 μg N/g-sand per day), Stemphylium sp., V. dahliae, T. basicola, B. cinerea, F. oxysporum, R. solani, and Penicillium sp. (with a rate of 0.0045 μg N/g-sand perday). The presence of A. avenae resulted in significant increases in mineral N, compared to nematode-free columns colonized by F. oxysporum, R. solani, and T. basicola alone. The presence of A. composticola resulted in significant increases in mineral N, compared to nematode-free columns colonized by A. alternata, B. cinerea, F. oxysporum, and R. solani alone. There was more mineral N incolumns in the presence of A. composticola than A. avenae in most cases. This revised version was published online in August 2006 with corrections to the Cover Date.     

Seasonal changes of C:P ratios of seston, bacteria, phytoplankton and zooplankton in a deep, mesotrophic lake

• 1 The C:P ratios of seston, bacteria, phytoplankton and zooplankton were measured twice a week in situ in mesotrophic, large and deep Lake Constance from April to December 1995. Except for zooplankton, a strong seasonality was exhibited with low C:P ratios during P‐enriched early spring conditions and high values during P‐depleted summer conditions.
• 2 Molar C:P ratios of seston varied between 180:1 and 460:1 demonstrating moderate phosphorus limitation in spring and during the clear‐water phase, and strong limitation for the rest of the season. The sestonic C:P ratio increased significantly during two decades of re‐oligotrophication of Lake Constance, reflecting an enhanced phosphorus limitation of the plankton community in summer. Molar C:P ratios of bacteria and phytoplankton varied seasonally between 50:1 and 130:1 and 180:1 and 500:1, respectively, and indicate carbon or light limitation in winter and phosphorus limitation in summer. Zooplankton had a molar C:P ratio of about 124:115 which was nearly constant throughout the seasons.
• 3 These differences in the C:P ratios of planktonic organisms have direct implications for phosphorus recycling within the food web as C:P ratios of excreta should be highly variable.