Phosphate uptake capacity of summer phytoplankton of the Loosdrecht Lakes in relation to phosphorus loading and irradiance

Summer populations of the phytoplankton of the Loosdrecht Lakes were enclosed in laboratory scale enclosures (LSE), supplied with 7.5 g P.l^–1.d^–1 and 105 g P.l^–1.d^–1, respectively. The maximum initial phosphate uptake rate (V_m) was related to irradiance and primary production. At phosphate uptake saturating light-irradiance V_m values up to 4 times the V_m values in the dark were measured.The phosphate uptake capacity per unit dry weight remained more or less constant throughout the experiments in the LSE receiving the lower amount of phosphorus, and declined in the LSE receiving the higher amount of phosphorus. Within the range of V_m values measured (<10 g P.mg DW^–1.h^–1 or 1,3 g P. g chla ^–1.h^–1), the growth rate of the phytoplankton was not influenced by alterations in phosphorus availability.     

Population dynamics of Limnothrix redekei,Oscillatoria lanceaeformis,Planktothrix agardhii and Pseudanabaena limnetica (cyanobacteria) in a shallow hypertrophic lake (Spain)

Populations of Limnothrix redekei, Oscillatoria lanceaeformis, Planktothrix agardhii and Pseudanabaena limnetica were found in a hypertrophic, gravel-pit lake near Madrid (Spain), throughout a one year sampling at weekly intervals. Physico-chemical factors, phytoplankton biomass and net growth rates were measured. Oscillatoria lanceaeformis was only observed a few weeks, probably being related to phosphorus limitation. Planktothrix agardhii biomass was related to PhAR irradiances, light attenuation coefficient in the water, Brunt-Väisäla frequency and decrease of soluble reactive phosphorus. Limnothrix redekei and Pseudanabaena limnetica biomass values were related to a decrease of inorganic nitrogen and temperature. A different lag response of populations was observed in relation to the environmental features.     

Growth and phosphate uptake kinetics of the toxic dinoflagellate Alexandrium tamarense from Hiroshima Bay in the Seto Inland Sea, Japan

Shellfish poisoning by the toxic dinoflagellate Alexandrium tamarense (Lebour) Balech occurred for the first time in Hiroshima Bay, Japan, in 1992. Oyster culture in the bay produces as much as 60% of the total production in Japan, and it suffered severe damage. In the present study, we experimentally investigated the growth rate and phosphate uptake kinetics of A. tamarense, Hiroshima Bay strain. A short-term phosphate uptake experiment revealed that the maximum uptake rate was 1.4 pmol P cell^-1 per h and the half-saturation constant was 2.6 umol L^-1. In semicontin-uous culture, the maximum specific growth rate and the minimum phosphorus cell quota were 0.54 day^-1 and 0.56 pmol P cell^-1, respectively. These uptake rates suggest that A. tamarense is a poor phosphorus competitor compared with other species. However, the large phosphorus storage capacity (Q_pmax/q_o= 36), the surge phosphorus uptake ability (V_s/V_i= 4.1) and the low growth rate would be advantageous for surviving brief periods of phosphorus limitation which frequently occur in Hiroshima Bay.     

N2-fixing cyanobacteria: Why they do not become dominant in shallow hypertrophic lakes

Summary Phytoplankton species shifts and succession phenomenona in lakes of increasing trophic state were considered, using the basic information on the growth kinetics of the species involved. One of the most obvious signs of advanced eutrophication is the dominance of cyanobacteria (blue-green algae). Striking examples are the shallow, hypertrophic Dutch lakes The Veluwerandmeren (e.g., Wolderwijd and Veluwemeer), whereOscillatoria agardhii, a non-N₂-fixing cyanobacterium, has become dominant over the green algae, diatoms and N₂-fixing cyanobacteria (BERGER, 1975).We have studied the natural population ofO.agardhii during the growing season, by using physiological indicators, and could adduce that the natural population was successively growing under phosphorus, light, or nitrogen limitation (ZEVENBOOM and MUR, 1978a,b; ZEVENBOOMet al., 1982). One might expect that during the period of nitrogen limitation the N₂-fixing speciesAphanizomenon flos-aquae would be favoured and would be able to outgrow the nitrogen-limitedO.agardhii. However, in these lakes,A. flos-aquae was present only in few numbers and a succession fromO. agardhii toA. flos-aquae did not occur. Although field observations may give some indication, they cannot give decisive answers to the question which factor is triggering the observed species shifts and species dominance in natural waters. Such answers can only be obtained from growth kinetic and physiological data of the species involved. In our opinion, the most important factor to consider is the availability of light energy, which decreases with increasing eutrophication.The hypothesis was proposed by Mur and coworkers (MURet al., 1978) that in hypertrophic lakes the prevailing light conditions (low light irradiance) are more favourable forO.agardhii, since this species has a much lower requirement of light energy for growth than green algae as a consequence of its lower specific maintenance rate constant, _e (VAN LIERE, 1979; GONS, 1977). Competition experiments, performed withO. agardhii andScenedesmus protuberans under lightlimiting conditions, confirmed the hypothesis (MURet al., 1978), Continuous culture experiments withA. flos-aquae showed that also this species had a higher energy requirement thanO. agardhii (ZEVENBOOM, 1980). The differences were not found in the value of _e, but in the growth efficiency. The higher energy requirement ofA.flos-aquae was expected, since energy is needed for heterocyst production and N₂ fixation. Under light-limiting conditions and nutrient sufficiency (including nitrogen-nitrate) it can thus be expected that the N₂-fixer will be outcompeted by the non-N₂-fixing cyanobacterium. This was indeed observed (ZEVENBOOM et al., 1981).We further investigated the competitive interactions betweenA.flos-aquae, O. agardhii andS. protuberans under different sets of irradiance values and nitrate concentrations. We used the growth kinetic data of the species involved, which were obtained by means of continuous culture experiments (GONS, 1977; VAN LIERE. 1979; VAN LIERE and MUR, 1979; GONS and MUR, 1980; ZEVENBOOM and MUR, 1980; ZEVENBOOMet al., 1980; ZEVENBOOMet al., 1981). The competing species could be placed along the gradients of light irradiance values and nitrate concentrations, their positions being defined by their energy requirements and half-saturation constants for nitrate-limited growth, respectively. Distinct niches for the three species were found with respect to light and nitrate. Under conditions of low irradiance values and low (realistic) nitrate concentrations, nitrogen-limitedO.agardhii was able to outgrowA. flos-aquae andS. protuberans as a consequence of its low energy requirement and its high affinity for nitrate. The growth rates of the last two species were restricted by the limited availability of light. However, at high irradiance values,O.agardhii was inhibited in its growth rate and therefore failed to outgrow the other two species. The competition was then restricted to nitrogen-limitedS.protuberans and light-limitedA.flos-aquae; the latter could dominate at low nitrate concentrations. The results of competition experiments withO.agardhii andA.flos-aquae under different sets of irradiance values and nitrate concentrations agreed well with the niche-model described above (Zevenboom, unpubl. results).In conclusion, kinetic data of growth, obtained with continuous culture experiments, can provide basic information to explain species shifts and dominance in lakes with increasing eutrophication. Nitrogen-limiting conditions favour N₂-fixing cyanobacteria only when sufficient light is available for their growth (in less hypertrophic waters). The trophic state is thus of major importance and decisive with regard to which species will dominate.     

Phosphate-limited growth of Chromatium vinosum in continuous culture

Chromatium vinosum DSM 185 was grown in continuous culture at a constant dilution rate of 0.071 h^-1 with sulfide as the only electron donor. The organism was subjected to conditions ranging from phosphate limitation (S _R-phosphate=2.7 M and S _R-sulfide=1.8 mM) to sulfide limitation (S _R-phosphate=86 M and S _R-sulfide=1.8 mM). At values of S _R-phosphate below 7.5 M the culture was washed out, whereas S _R-phosphate above this value resulted in steady states. The saturation constant (K ) for growth on phosphate was estimated to be between 2.6 and 4.1 M. The specific phosphorus content of the cells increased from 0.30 to 0.85 mol P mg^-1 protein with increasing S _R-phosphate. The specific rate of phosphate uptake increased with increasing S _R-phosphate, and displayed a non-hyperbolic saturation relationship with respect to the concentration of phosphate in the inflowing medium. Approximation of a hyperbolic saturation function yielded a maximum uptake rate (V _max) of 85 nmol P mg^-1 protein h^-1, and a saturation constant for uptake (K _t) of 0.7 M. When phosphate was supplied in excess 8.5% of the phosphate taken up by the cells was excreted as organic phosphorus at a specific rate of 8 nmol P mg^-1 protein h^-1.Non-standard abbreviations BChla bacteriochlorophyll a - D dilution rate; _max, maximum specific growth rate - maximum specific growth rate if the substrate were not inhibitory - K saturation constant for growth on phosphate - V _max maximum rate of phosphate uptake - K _i saturation constant for phosphate uptake - K _i inhibition constant for growth in the presence of sulfide - S _R concentration of substrate in the inflowing medium     

Effects of photoperiodicity and light irradiance on phosphate-limited Oscillatoria agardhii in chemostat cultures

The cyanobacterium Oscillatoria agardhii was grown in continuous culture under various light conditions in order to study the interactions of light on phosphorus-limited growth. Under severe P-limiting (light-saturating) conditions, a low chlorophyll a and C-phycocyanin content was found. In addition, the light-harvesting capacity, reflected in the values of P _max (maximum light-saturated oxygen production rate) and (photosynthetic affinity), were low compared to light-limited cultures.Reduction of the light climate, either by reduction of the length of the photoperiod or light-intensity, resulted in an increase in light-harvesting capacity (higher pigment content, P _m and ) during growth under P-limiting conditions. Light-induced changes in P _max and could be related to the relative growth rate, being the actual growth rate as a fraction of the growth rate which would be observed under light-limiting conditions.Under P-limiting conditions, reduction of the light-climate caused a reduction in dry weight of the culture. This decrease was mainly due to a decrease in carbohydrate content of the cells. Under all conditions tested, carbohydrates were found to accumulate during the light-period and to be consumed during the dark-period.Evaluation of carbohydrate consumption in the dark yielded a specific maintenance rate constant of 0.001 h^-1. This observation leads to the conclusion that the specific maintenance rate constant is independent on the character of the growth rate limiting nutrient for O. agardhii.     

PHYSIOLOGICAL RESPONSES TO PHOSPHORUS LIMITATION IN BATCH AND STEADY-STATE CULTURES OF DUNALIELLA TERTIOLECTA (CHLOROPHYTA): A UNIQUE STRESS PROTEIN AS AN INDICATOR OF PHOSPHATE DEFICIENCY1

A protein unique to phosphorus stress observed in Dunaliella tertiolecta Butcher was studied in the context of phosphate-limited cell physiology and is a potential diagnostic indicator of phosphate deficiency in this alga. Cells were grown over a range of limited, steady-state growth rates and at maximum (replete) and zero (phosphate-starved) growth rates. The stress protein, absent in nutrient-replete cells, was produced under all steady-state phosphate-limited conditions and increased in abundance with increasing limitation (decreasing growth rate). Cellular carbon: phosphorus ratios and the maximum uptake rate of phosphate (V_m) increased with increasing limitation, whereas the ratio of chlorophyll a: carbon decreased. Alkaline phosphatase activity did not respond to limitation but was measurable in starved, stationary-phase cells. F_v/F_m, a measure of photochemical efficiency, was a nonlinear, saturating function of p, as commonly observed under N limitation. The maximum F_v/F_m of 0.64 was measured in nutrient-replete cells growing at μ_max, and a value of zero was measured in stationary-phase starved cells. When physiological parameters were compared, the P-stress protein abundance and F_v/F_m were the most sensitive indicators of the level of deficiency. The stress protein was not produced under N- or Fe-limited conditions. It is of high molecular weight (>200) and is associated with internal cell membranes. The stress protein has several characteristics that make it a potential diagnostic indicator: it is 1) unique to phosphorus limitation (i.e. absent under all other conditions), 2) present under limiting as well as starved conditions, 3) sensitive to the level of limitation, and 4) observable without time-course incubation of live samples.     

Growth characteristics and growth modeling of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> and <Emphasis Type="Italic">Planktothrix agardhii</Emphasis> under iron limitation

Although iron is a key nutrient for algal growth just as are nitrogen and phosphorus in aquatic systems, the effects of iron on algal growth are not well understood. The growth characteristics of two species of cyanobacteria, Microcystis aeruginosa and Planktothrix agardhii, in iron-limited continuous cultures were investigated. The relationships between dissolved iron concentration, cell quota of iron, and population growth rate were determined applying two equations, Monod’s and Droop’s equations. Both species produced hydroxamate-type siderophores, but neither species produced catechol-type siderophores. The cell quota of nitrogen for both M. aeruginosa and P. agardhii decreased with decreasing cell quota of iron. The cell quota of phosphorus for M. aeruginosa decreased with decreasing cell quota of iron, whereas those for P. agardhii did not decrease. Iron uptake rate was measured in ironlimited batch cultures under different degrees of iron starvation. The results of the iron uptake experiments suggest that iron uptake rates are independent of the cell quota of iron for M. aeruginosa and highly dependent on the cell quota for P. agardhii. A kinetic model under iron limitation was developed based on the growth characteristics determined in our study, and this model predicted accurately the algal population growth and iron consumption. The model simulation suggested that M. aeruginosa is a superior competitor under iron limitation. The differences in growth characteristics between the species would be important determinants of the dominance of these algal species.     

The effect of nitrate concentration in a flowing solution system on growth and nitrate uptake of twoPlantago species

Summary Juvenile plants ofPlantago lanceolata andP. major ssp.major were grown in a flowing solution system at 7.5 mM or 9.5 M NO₃. The parameters investigated were: RGR, shoot weight percentage, leaf length, length of main root axis, shoot concentrations of major ions and organic N, and the specific uptake rate for NO₃. At 9.5 M NO₃ growth ofP. major was not hampered, whereas shoot growth and leaf length ofP. lanceolata were reduced. The NO₃ concentration ofP. lanceolata decreased more than that ofP. major. The different performances of the species at 9.5 M NO₃ were associated with different specific uptake rates. In both treatments the root system ofP. major was shorter than that ofP. lanceolata. P. lanceolata accumulated more NO₃ in the leaves. The performance of thePlantago species is discussed in relation to the availability of nutrients in their habitats.Grassland Species Research Group. Publication no. 37.     

EFFECT OF THE SINKING RATE OF TWO DIATOMS (THALASSIOSIRA SPP.) ON UPTAKE FROM LOW CONCENTRATIONS OF PHOSPHATE1

The effect of the sinking rate, or rate of medium flow (φ) on the rate of phosphate incorporation (V) by the planktonic diatoms Thalassiosira fluviatilis Hust. and T. pseudonana Hasle & Heimdal in batch and chemostat cultures was determined by passing medium at defined flow rates (0.5–25.0 mm·min^?1) over algae on membrane filters. At concentrations from 1 to 100 μg phosphorus·l^?1 V, increases with increasing velocity of flow, approaching a maximum value (V_m) as described by the empirical relationship: where K_φ is the sinking rate value when V = 1/2 V_m+ V_o and V_o is the uptake at 0 rate of flow. By comparing uptake at controlled flow with uptake in a vigorously stirred medium, the phosphate concentration in the cell boundary layer can be determined. The sinking rate that reduces the phosphate concentration in the boundary layer to half of nominal concentration in the medium is much lower for the larger T. fluviatilis than for T. pseudonana. For both diatoms, it is inversely related to the nominal concentration.     

Regulation of phosphate uptake reveals cyanobacterial bloom resilience to shifting N:P ratios

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Kinetics of sulfate uptake by freshwater and marine species ofDesulfovibrio

Apparent half-saturation constants (K _m) and maximum uptake rates (V _max) for sulfate were determined in four species ofDesulfovibrio of freshwater and marine origin using a³⁵S-sulfate tracer technique. The lowerstK _m (5 M) was found in the freshwater speciesDesulfovibrio vulgaris (Marburg) and the highestK _m (77 M) in the marine speciesDesulfovibrio salexigens. Maximum specific rates of sulfate uptake (i.e.,V _max) were proportional to the growth rates observed in batch cultures. The halophilicDesulfovibrio salexigens did not change itsK _m andV _max between 1 and 6,000 M SO ₄ ^2- , and apparently did not induce a low-affinity uptake system at high sulfate concentrations. The low half-saturation constants measured for sulfate uptake explain why high rates of bacterial sulfate reduction occur in surface sediments of freshwater lakes, and why sulfate reduction can be a quantitatively important process in anaerobic carbon mineralization in low-sulfate environments. The results shows that extremely low sulfate concentrations must occur before sulfate reduction is completely outcompeted by methanogenesis.Abbreviations MPB methane producing bacteria - SRB sulfate reducing bacteria     

SIZE-DEPENDENT PHOSPHORUS UPTAKE KINETICS AND CELL QUOTA IN PHYTOPLANKTON1

The allometric equation, y = aX^b, described the interspecific variation of phosphate uptake kinetics and cell quota with phytoplankton cell size and showed that smaller cells are superior in uptake rate to large. Species-specific measurements, made by track autoradiography in phosphorus deficient cultures of communities from a phosphorus-limited lake, revealed that eight different species did not differ significantly in the Michaelis-Menten half-saturation constant, K_m. However, both saturated uptake rates (V_max) and the initial slope of the uptake curve (V_max:K_m) decreased per unit biomass with increasing cell size. Biomass-specific cell phosphorus quotas also decreased with increasing cell volume, but less rapidly than did V_max or V_max: K_m. Comparable data from the literature showed that marine species were superior in phosphorus uptake to freshwater species of similar size, but allometric variation of kinetics appeared to exist within both groups. Together with a variable internal stores model of phosphorus-limited growth, the allometric relationships of uptake kinetics and quotas predicted competition to favor smaller cells, with a differential in growth rate diminishing as competitive intensity increased.     

The influence of phosphate concentration on the kinetics of uptake by maize roots

In an experiment with native maize roots depending on different phosphorus concentration in the external solution (0.001 … 50 mM P), the multiphasic character of the kinetics of phosphate uptake has been stated. The single phases are characterized by the different values of K_m and V_max. In the wide range of concentrations the isotherm of the phosphate uptake has five evident phases. The character of kinetics for the uptake of phosphate is analogical to the kinetics of the enzymatic reactions described by the Michaelis-Menten equation. On the other hand the linear dependence for the inactivated root was determined,i.e. the uptake of phosphate versus different phosphorus concentration in the external solution. The graphic representation of the logarithmic values for the phosphorus taken up versus the different phosphorus concentration in the external solution gives the biphasic course including concentration less than 1.0 mM P and more than 1.0 mM P. Within the framework of the concentration range the following values of V_max, K_m and ϕ_in were calculated under the conditions if the concentration of phosphorus is less than 1.0mMP: V_max = 1.705 μmol P × g^-1h^-1, K_m = 0.057 mM P and ϕ_in = 0.83,i.e. if the concentration of phosphorus is more than 1.0mM P: V_max = 40 μmol P × g^-1 h^-1, K_m = 16.66 mM and ϕ_in = 20. According to these results, the phosphate concentration in the external solution influences the activity of the transport mechanisms concerning their conformative changes which discretely change their working regime of membrane transport. This is also demonstrated in the change of values V_max, K_m and ϕ_in.     

Uptake of phosphate by symbiotic and free-living dinoflagellates

Uptake of phosphate in the light by Amphidinium carterae, Amphidinium klebsii, cultured and symbiotic Gymnodinium microadriaticum conformed to Michaelis-Menten type saturation kinetics with all organisms showing similar K _m values, namely 0.005 to 0.016 M phosphorus. V _max values were 0.009–0.32 nmol phosphorus · 10⁵ cells^-1 · 10 min^-1. Phosphate uptake by all the dinoflagellates was greater in the dark than in the light. The metabolic inhibitor 3-(3,4-dichlorophenyl) 1,1-dimethylurea stimulated phosphate uptake in the light by A. carterae and A. klebsii, but inhibited uptake by cultured and symbiotic G. microadriaticum. Carbonylcyanide 3-chlorophenylhydrazone (CCCP) inhibited phosphate uptake by A. carterae and A. klebsii under both light and dark conditions. Uptake of phosphate by cultured and symbiotic G. microadriaticum in the light, but not in the dark, was inhibited by CCCP. Low concentrations of arsenate (5 g As · l^-1) stimulated phosphate by A. carterae and A. klebsii, but inhibited uptake by cultured and symbiotic G. microadriaticum. High concentrations of arsenate (100 g As · l^-1) did not affect uptake of phosphate by A. carterae and A. klebsii.     

COMPARATIVE KINETIC STUDIES OF NITRATE-LIMITED GROWTH AND NITRATE UPTAKE IN PHYTOPLANKTON IN CONTINUOUS CULTURE1

A comparative study of nitrate-limited growth and nitrate uptake was carried out in chemostat cultures of Ankistrodesmus falcatus (Corda) Ralfs., Asterionella formosa Hass., and Fragilaria crotonensis Kit. In each species growth rate (μ) was related to total cell nitrogen or cell quota (q) by the empirical Droop growth function. Nitrate uptake was a function of both external N concentration and q. The apparent maximum uptake rate (V_m') at a given μ was inversely related to q – q₀, where q₀ is the minimum quota. The apparent half-saturation constant for uptake, (K_m') appears to show a slight inverse trend with μ, although statistical analysis shows that this trend is inconclusive. When q approaches q₀, V_m' is several orders of magnitude greater than μq, the calculated steady-state uptake rate. As q increases, however, the difference between these two variables decreases sharply until q approaches q_m, the cell quota for nitrogen-rich cells. At this point the difference between μq and V_m' disappears. This behavior is explained by the feedback regulation of N uptake. The inverse relationship between V_m' and q – q₀ can be described by an empirical three-parameter equation.     

Comparative structure of the gas-vacuoles of blue-green algae

Summary An investigation was made of 5 species of blue-green algae reported to contain gas-vacuoles. All organisms were grown and harvested under standard conditions. Gas-vacuoles were characterised as reddish structures which are destroyed by applying pressure. Using a simple direct preparation technique gascylinders were observed with the transmission electron microscope in gas-vacuolate cells. Gas-vacuoles were present in the strains of Anabaena flos-aquae, Gloeotrichia echinulata and Oscillatoria agardhii studied and absent from Microcystis aeruginosa and Nostoc linckia. The reddish, refractile central area of N. linckia and M. aeruginosa cells was tentatively identified as nucleoplasm. Gas-vacuoles are collections of gas-cylinders 70 m wide, which in A. flos-aquae and G. echinulata are clearly bounded by photosynthetic lamellae and associated with -granules. The presence of bounding photosynthetic lamellae in these species is suggested as a causal factor of the unusual optical properties of their gas-vacuoles. The range of lengths of gas-cylinders in G. echinulata and O. agardhii is from 100 m to 500 m and in A. flos-aquae it is from 100 m to 1300 m. The percentage of cell volume occupied by gas-vacuoles was estimated by direct measurement. In A. flos-aquae and G. echinulata it was 22%. In O. agardhii gas-cylinders were not clearly associated with photosynthetic lamellae and -granules and occupied 39% of cell volume. Gascylinder membranes showed reasonable preservation in KMnO₄ and excellent preservation in OsO₄. The widths of membranes after treatment with these two fixatives was 3 m and 2 m respectively.     

Some observations on the diet and food selection ofDaphnia hyalina (Cladocera) in an eutrophic lake

Summary The food composition in the guts ofDaphnia hyalina was compared with the phytoplankton composition in the lake water on several dates during the year. The guts contained almost exclusively algae; detritus was not an important food item. ExceptOscillatoria agardhii, all large algal forms were generally avoided. On a whole,Scenedesmus was the most preferred taxon, but as numbers or biomass ingestedO. agardhii was more important. The filamentous blue-green algae>60 m (range: 60–1500 m) were strongly avoided byDaphnia. The observed size selective feeding is probably the result of limitations in their filtering apparatus rather than active selection.     

Uptake ofpara-tyramine andmeta-tyramine into slices of the caudate nucleus and hypothalamus of the rat

The kinetics of the uptake ofp-tyramine,m-tyramine, and dopamine were investigated in slices of the hypothalamus and striatum of the rat in the presence of nialamide. When uptake was analyzed by a least-squares fit to a Lineweaver-Burk plot, each amine appeared to be concentrated by both a low-affinity and a high-affinity system in both brain regions. The obtainedK _m andV _max values for the high-affinity uptake system for each amine in both brain regions were similar. In general terms, the uptake systems in the striatum exhibited largerK _m andV _max values, with the velocity of uptake being in the order dopamine>m-tyramine>p-tyramine. 2,4-Dinitrophenol (DNP) and ouabain reduced all uptakes in the caudate, but reduced only the high-affinity uptake ofm-tyramine and the low-affinity uptake of dopamine in the hypothalamus.