Phosphate Uptake Kinetics Research Articles

Assessing the nitrate and phosphate uptake kinetics potential and growth performance of Gracilaria corticata var. cylindrica in shrimp farm water (SFW)

Gracilaria corticata var. cylindrica (GCC) was studied as a biofilter in shrimp farm water (SFW) and its growth and biochemical attributes in the medium were evaluated. GCC showed significant nutrient absorption from SFW, with maximum nitrate and phosphate uptake observed after the first 48 h. Nitrate depletion happened faster than phosphate, thus showing a higher affinity for nitrate uptake (78.4% removal) by GCC. Nutrient uptake kinetics followed the Michaelis–Menten curve, with Vmax values of 43.16 μM g dw−1 h−1 for nitrate and 67.50 μM g dw−1 h−1 for phosphate. Also, GCC’s low Km values (12.53 µM for nitrate, 1.91 µM for phosphate) indicated efficient nutrient utilization. GCC showed rapid growth in SFW, with a daily growth rate of 2.93 ± 0.19% d−1, comparable to the commercial MP1 media (3.54 ± 0.19% d−1) and greater to seawater (2.23 ± 0.13% d−1). Proximate analysis revealed consistent biochemical compositions across all three media, with carbohydrate and protein contents of 2.24 ± 0.41% and 0.76 ± 0.12%, respectively, in SFW. Pigment analysis revealed that pigment concentrations varied, with SFW having the greatest R-PE concentration (182.25 ± 32.77 µg g−1), followed by MP1 media and saltwater. R-PC concentrations followed a similar pattern, with SFW having the greatest concentration (85.73 ± 19.33 µg g−1). These findings highlight GCC’s potential as an efficient biofilter for reducing nitrate and phosphate levels in SFW, therefore offering a sustainable solution for aquaculture effluent management and the potential integration of GCC into shrimp farming practices.

Two-dimensional solid-state NMR spectroscopy investigations of surface precipitation of phosphate onto calcite

The interaction of phosphate with typical soil minerals is important for understanding P cycling in natural and agricultural systems. We investigated the mechanisms of kinetics of phosphate uptake onto calcite using solid-state NMR spectroscopy. At a low phosphate concentration of 0.5 mM, the 31P single-pulse solid-state NMR peak revealed the formation of amorphous calcium phosphate (ACP) within the initial 30 min, which transformed to carbonated hydroxyapatite (CHAP) after 12 d. At a high phosphate concentration (5 mM), the results showed transformation from ACP to OCP, later to brushite, and eventually to CHAP. The formation of brushite is further supported by 31P{1H} heteronuclear correlation (HETCOR) spectra via a correlation of δP–31 = 1.7 ppm and the 1H peak at δH–1 = 6.4 ppm, which denotes the structure water of brushite. Furthermore, 13C NMR directly revealed both A-type and B-type CHAP. Generally, this work provides a detailed understanding of the aging effect on the phase transition scale of phosphate surface precipitation onto calcite in soil environments.

Kinetics of phosphate uptake in the dinoflagellate Karenia mikimotoi in response to phosphate stress and temperature

Phosphate (Pi) and temperature are two important environmental factors affecting algal growth and the occurrence of red tide. In this paper, we conduct experiments on Karenia mikimotoi under different Pi concentrations and temperatures and propose a novel Pi uptake model by incorporating Arrhenius function and Pi-stress function into the two-stage model presented in one of our recent paper (Jiang et al. (2019)). In both Pi-replete and Pi-deplete, the model parameters are obtained by fitting the experimental data at 24 °C and validated by the experimental data at 20 °C, respectively. K. mikimotoi under low Pi condition entered into the exponential growth phase earlier compared with Pi-replete groups. Under the Pi-replete condition, K. mikimotoi continually increased, while the Pi-deplete condition showed a wave trend. The experimental results and the fitting of experimental data both show that K. mikimotoi has an obvious response to temperature. In both Pi-replete and Pi-deplete, the peak values of the cell quota of intracellular Pi and surface-adsorbed Pi at 24 °C were higher than those at 20 °C. Using the luxury coefficient and growth potential, interspecific competition between K. mikimotoi and Prorocentrum donghaiense is also discussed. These results and conclusions are helpful to understand the Pi uptake characteristics of algae at different Pi concentrations and temperatures, and could effectively explain mechanisms of interspecific competition and succession between different algae species during red tide.

Differential Nutrient Uptake by Saltmarsh Plants Is Modified by Increasing Salinity.

In Southern European estuaries and associated salt marshes, the anthropogenic nutrient inputs, together with longer drought periods, are leading to increasing eutrophication and salinization of these coastal ecosystems. In this study, uptake kinetics of ammonium, nitrate, and phosphate by three common plants in Palmones salt marsh (Southern Spain), Sarcocornia perennis ssp. alpini, Atriplex portulacoides, and Arthrocnemum macrostachyum were measured in hydroponic cultures. We also determined how these uptakes could be modified by increasing salinity, adding NaCl to the incubation medium (from 170 to 1,025 mM). Kinetic parameters are analyzed to understand the competition of the three species for nutrient resources under realistic most frequent concentrations in the salt marsh. These results may also be useful to predict the possible changes in the community composition and distribution if trends in environmental changes persist. Atriplex portulacoides showed the highest Vmax for ammonium, the most abundant nutrient in the salt marsh, while the highest affinity for this nutrient was observed in A. macrostachyum. Maximum uptake rates for nitrate were much lower than for ammonium, without significant differences among species. The highest Vmax value for phosphate was observed in A. macrostachyum, whereas A. portulacoides presented the highest affinity for this nutrient. High salinity drastically affected the physiological response of these species, decreasing nutrient uptake. Sarcocornia perennis ssp. alpini and A. macrostachyum were not affected by salinity up to 510 mM NaCl, whereas A. portulacoides notably decreased its uptake capacity at 427 mM and even withered at 1,025 mM NaCl. At current most frequent concentrations of ammonium and phosphate in the salt marsh, S. perennis ssp. alpini is the most favored species, from the nutritional point of view. However, A. portulacoides could enhance its presence if the increasing ammonium load continues, although a simultaneous salinization would negatively affect its nutritional physiology.

Regulation of phosphate uptake kinetics in the bloom-forming dinoflagellates prorocentrum donghaiense with emphasis on two-stage dynamic process

Phosphorus is an essential element for the growth and reproduction of algae. In recent years, the frequent outbreaks of algal blooms caused by eutrophication have drawn much attention to the influence of phosphate (P) uptake on the growth of algal cells. The previous study only considered the effect of total P pools on the P uptake process of algal cells and considered the process as one stage, which is insufficient. P uptake by algae is actually a two-stage kinetic process because in many algae species, surface-adsorbed P pools account for a large proportion of total P pools. In this paper, we fit one-stage and two-stage models of P uptake by algae to our experimental data on short-term uptake kinetics of algae Prorocentrum donghaiense under P-deplete and P-replete conditions at 24°C. According to the experimental results, P. donghaiense possesses different P uptake characteristics under different P concentrations. P. donghaiense grows faster and exponentially for longer periods of time under P-replete condition. Ranges of change of Qc (cell quota of intracellular P) and Sp (cell quota of surface-adsorbed P) during the culture time are obviously larger under P-replete condition than those under P-deplete condition. The value of Kp (represents the impact of P-starvation on P uptake rate) in one-stage model under P-deplete condition is smaller than that under P-replete condition, which is opposite to results of two-stage model and does not meet the actual biological significance of Kp. The two-stage model gives more reasonable and realistic explanations to the process of P uptake by algae no matter from the perspective of intuitive fitting effect, biological significance of parameters, statistical test results or essential dynamic process. These results, combined with long-term lab and field data in ocean, could be used to effectively predict algal blooms.

Nitrogen availability facilitates phosphorus acquisition by bloom-forming cyanobacteria.

Cyanobacterial blooms are threatening freshwater ecosystems. The physiological basis involved in the onset of cyanobacterial bloom is fundamental to advance in bloom predictions. Generally, cyanobacteria grow until the availability of nitrogen (N), phosphorus (P) or both nutrients becomes limited. Population survival may depend on physiological adjustments to nutrient deficiency as well as on the efficient use of episodic N and P inputs. This study investigated the effect of N inputs on phosphate uptake affinity and activity of N-deficient bloom-forming cyanobacteria. Lake samples dominated by filamentous cyanobacteria were preincubated with and without nitrate addition, and the uptake of [32P] phosphate pulses was measured in the following days. Phosphate uptake kinetics were analyzed with a flow-force model that provides the threshold concentration, reflecting phosphate uptake affinity, and the membrane conductivity coefficient that corresponds to the activity of uptake systems. After 24 h of nitrate preincubation, phosphate uptake kinetics showed a progressive increase in affinity (nanomolar [Pe]A) and activity (25-fold) concomitant with cyanobacterial growth. It was demonstrated that the alleviation of N-deficiency by N inputs boosts the activation of phosphate uptake systems of non-N2-fixing cyanobacteria to sustain growth. Therefore, reduction of dissolved inorganic N levels in lakes is also mandatory to limit cyanobacterial phosphate uptake affinity and activity capabilities.

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

Abstract The resilience of cyanobacterial blooms challenges lake restoration programmes based on nutrient load reduction. The survival of organisms may depend on episodic short‐term fluctuations of nitrogen (N) and phosphorus (P). Insight into physiological responses to shifts in nutrient limitation will improve our understanding of cyanobacterial bloom resilience. This study investigated the resilience and collapse of a long‐term cyanobacterial bloom dominated by Planktothrix agardhii and Raphidiopsis mediterranea, subjected to different periods of dissolved inorganic nitrogen (DIN) and phosphorus (SRP) inputs in Lago Rodó, a polymictic, hypereutrophic (6.0 ± 1.6 μmol total P/L) and turbid lake (attenuation coefficient: 4.7 ± 1.7 m−1). Phytoplankton composition, nutrient dynamics and physiological monitoring of [32P] phosphate uptake kinetics were studied over four summers. The influence of environmental nutrient supply on phytoplankton net phosphate uptake kinetics was analysed with a flow–force model that gives the threshold value of phosphate uptake ([Pe]A), a limiting concentration below which incorporation is not energetically possible by organisms, and the membrane conductivity coefficient (LP). The [Pe]A reflects the affinity and LP the activity of the cellular uptake systems. Nutrient supply into the lake sustained high DIN:SRP ratios and high cyanobacterial biomass that showed P‐deficiency features characterised by low [Pe]A (5.4 ± 0.5 nm [32P] phosphate) and high LP. High cyanobacterial biomass persisted after external nutrient inflows were interrupted for 14 months, which resulted in low dissolved DIN:SRP ratios; however, N2‐fixers did not develop. The collapse of cyanobacterial populations occurred under the lowest N:P ratios, low affinity and activity of phosphate uptake systems and strong water outflows. Our study suggests that the alleviation of N‐deficiency under high N:P ratios enhances the activation of phosphate uptake systems by cyanobacteria. The flexible physiological response results in more efficient exploitation of limiting nutrients favouring cyanobacterial resilience under suboptimal conditions.

Uptake kinetics of nitrate, ammonia and phosphate by the dinoflagellate Heterocapsa circularisquama isolated from Hiroshima Bay, Japan

SUMMARY Heterocapsa circularisquama is a harmful dinoflagellate whose first bloom in Hiroshima Bay, Japan, appeared in 1992. As suggested by the authors’ group, in the Seto Inland Sea including Hiroshima Bay, oligotrophication particularly the reduction of phosphate starting 1980 is severe. The bloom caused serious damage to the bay's extensive oyster culture. In the present study, the uptake kinetics of nitrate, ammonia, and phosphate by this species were experimentally investigated. The maximum uptake rate (ρmax) and the half‐saturation constant (Ks) were 0.41 pmol cell−1 h−1 and 4.45 μM, respectively, for nitrate, 2.02 pmol cell−1 h−1 and 11.1 μM for ammonium, and 0.079 pmol cell−1 h−1 and 1.79 μM for phosphate. The maximum specific uptake rates (Vmax) for nitrate, ammonia, and phosphate were estimated to be 8.95, 44.1, and 21.3 day−1, respectively. A comparison of Vmax/Ks, which is also an index of affinity to nutrients, between this species and others suggested that H. circularisquama can utilize nitrate and ammonia efficiently, but not phosphate. Considering both reports describing that H. circularisquama has the ability to utilize dissolved organic phosphorus (DOP) and the DOP concentration is higher than phosphate in Hiroshima Bay, it was concluded that H. circularisquama became dominant due to the phosphate reduction measure.

Phosphate uptake kinetics and tissue-specific transporter expression profiles in poplar (Populus × canescens) at different phosphorus availabilities.

BackgroundPhosphorus (P) is a major plant nutrient. It is transported into and allocated inside plants by four families of phosphate transporters (PHT1 to PHT4) with high or low affinity to phosphate. Here, we studied whole-plant P uptake kinetics and expression profiles of members of the PHT families under high, intermediate and low P availability in the woody crop poplar (Populus × canescens) in relation to plant performance.ResultsPoplars exhibited strong growth reduction and increased P use efficiency in response to lower P availabilities. The relative P uptake rate increased with intermediate and decreased with low P availability. This decrease was not energy-limited because glucose addition could not rescue the uptake. The maximum P uptake rate was more than 13-times higher in P-starved than in well-supplied poplars. The Km for whole-root uptake ranged between 26 μM and 20 μM in poplars with intermediate and low P availability, respectively. In well-supplied plants, only low uptake rate was found. The minimum concentration for net P uptake from the nutrient solution was 1.1 μM. All PHT1 members studied showed significant up-regulation upon P starvation and were higher expressed in roots than leaves, with the exception of PtPHT1;3. PtPHT1;1 and PtPHT1;2 showed root- and P starvation-specific expression. Various members of the PHT2, PHT3 and PHT4 families showed higher expression in leaves than in roots, but were unresponsive to P deprivation. Other members (PtPHT3;1, PtPHT3;2, PtPHT3;6, PtPHT4;6 to PtPHT4;8) exhibited higher expression in roots than in leaves and were in most cases up-regulated in response to P deficiency.ConclusionsExpression profiles of distinct members of the PHT families, especially those of PHT1 were linked with changes in P uptake and allocation at whole-plant level. The regulation was tissue-specific with lower P responsiveness in leaves than in roots. Uptake efficiency for P increased with decreasing P availability, but could not overcome a threshold of about 1 μM P in the nutrient solution. Because the P concentrations in soil solutions are generally in the lower micro-molar range, even below the apparent Km-values, our findings suggest that bare-rooted poplars are prone to suffer from P limitations in most environments.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0892-3) contains supplementary material, which is available to authorized users.

Phosphate removal from solution by composite of MCM-41 silica with rice husk: Kinetic and equilibrium studies

Composite of MCM-41 silica with rice husk was synthesized under hydrothermal conditions using cetyltrimethylammonium bromide (CTAB) as an organic template, aqueous ammonia solution (NH4OH) and rice husk. Rice husk served as not only a silica source but also as a substrate for the deposition of MCM-41. The synthetic hybrid composites were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) and tested as sorbents for phosphate from aqueous solution. Kinetic data and equilibrium uptake isotherms were measured. The effects of different experimental parameters such as contact time, initial phosphate concentration, solution pH, adsorbent mass, and the presence of competitive ions on phosphate uptake were investigated. The phosphate uptake kinetics were found to be fast and equilibrium was achieved after 30 min. The phosphate uptake was found to be highly pH dependent. Studies on the effects of competing ions, without keeping the initial pH constant, indicated that phosphate uptake and Kd values decreased in the presence of CO32− and NO3−, but SO42− ions showed little or no effect. With keeping the initial pH constant at 6, the presence of these competing ions had no clear effect on the uptake of phosphate. The phosphate uptake by composite of rice husk with MCM-41 could be described well by the Langmuir isotherm equation. Adsorption kinetic data correlated well with pseudo-second-order model, which suggested that the uptake process might be chemical sorption.

Phosphate uptake kinetics for four species of submerged freshwater macrophytes measured by a 33P phosphate radioisotope technique

Phosphate (Pi) uptake kinetics were determined in shoot and root tissues for four freshwater macrophyte species, Littorella uniflora, Potamogeton perfoliatus, Myriophyllum alterniflorum and Elodea canadensis, using a radioactive 33P phosphate technique. Collection of plant material in the oligotrophic softwater lake, Lake Hampen, Denmark, where Pi limits macrophyte growth, enabled us to characterize and compare the Pi uptake kinetics and competitive characteristics of the four species in a low level Pi environment. The maximum Pi uptake rates (Vmax), the half saturation constants (Km) together with the affinity at low Pi concentrations (Vmax/Km) were determined by fitting data to the Michaelis-Menten kinetics.L. uniflora showed the highest Vmax/Km in the root tissue and the lowest Km. M. alterniflorum showed the highest and E. canadensis and P. perfoliatus the lowest Vmax/Km in leaf tissue. M. alterniflorum had the highest Vmax and, as the only species, a higher Vmax in leaves than in roots. Surface area explained about half of Vmax in M. alterniflorum leaves. Roots were the dominant organ for Pi assimilation for all species at the Lake Hampen Pi concentrations. Km showed positive correlation to%P content in root tissue.The results indicate that at low lake water Pi concentrations L. uniflora is able to survive on the Pi pools in the sediment porewater. M. alterniflorum showed high affinity for Pi at both low and high Pi concentrations by both roots and shoots, and suggests that M. alterniflorum is a strong competitor at both low and high Pi concentrations.

Differential nutrient uptake by two segregated red algae in an estuarine intertidal zone

SÁnchez de Pedro R., Niell F.X. and Carmona R. 2013. Differential nutrient uptake by two segregated red algae in an estuarine intertidal zone. Phycologia 52: 461–471. DOI: 10.2216/13-147.1Bostrychia scorpioides (Rhodophyta: Ceramiales) and Catenella caespitosa (Rhodophyta: Gigartinales) were segregated but slightly overlapping in the narrow intertidal of the Palmones River Estuary (Southern Spain). This study investigated whether there were interspecific differences in nutrient uptake capabilities and how meaningful these were to zonation. Uptake kinetics of ammonium, nitrate, and phosphate were measured over successive time intervals across a range of environmentally realistic concentrations. The interactions between ammonium and nitrate in mixed N source uptake were also tested. Using internal N and P content, turnover rates were calculated for each species for periods of emersion and submersion. Nutrient uptake kinetics were saturable for almost all nutrients except for ammonium in B. scorpioides, which showed surge uptake responses through linear kinetics. Vmax and affinity progressively decreased over 3 h for all nutrients in C. caespitosa and only for phosphate in B. scorpioides. At high dissolved inorganic nitrogen concentrations both species exhibited greater uptake rates for ammonium than nitrate; although, similar N uptake rates were obtained at the low ones. Ammonium contributed to the total N uptake in B. scorpioides to a greater extent; whereas, in C. caespitosa, this only occurred at high N concentrations. In mixed N source uptake experiments, ammonium and nitrate uptake rates by B. scorpioides decreased when the other N source was equimolarly supplied, while in C. caespitosa these interactions were absent. Catenella caespitosa showed a Vmax and affinity for phosphate fourfold higher than for B. scorpioides, with greater interspecific differences than those found for N uptake. Catenella caespitosa renewed internal nutrients faster and was more dependent on the external nutrient supply than B. scorpioides, which can withstand longer periods without nutrient supply due to its slower nutrient turnover rate. Different capabilities for nutrient acquisition in the two species suggested an adaptation to the nutrient availability at each intertidal position.

Steady‐state bioassay approach applied to phosphorus‐limited continuous cultures: A growth study of the marine chlorophyte Dunaliella salina

Phosphorus‐limited growth and phosphate uptake kinetics of the marine phytoplankter Dunaliella salina were studied using continuous‐culture techniques. Determination of residual phosphate concentrations in the cultures were made using a steady‐state bioassay approach in which short‐term phosphate uptake rates as measured by 33P‐radiotracer were balanced with the turnover of phosphorus in the culture. This allowed the determination of low‐nanomolar ambient phosphate concentrations (8–95 nmol P L−1) at seven unique specific growth rates, which agreed closely with an alternative kinetics bioassay phosphate determination. The relationship of specific growth rate to ambient phosphate concentration for the D. salina cultures was well‐described by the Monod growth equation with μmax = 1.8 d−1 and Kμ = 28 nmol P L−1. Phosphate uptake kinetics were evaluated at three growth rates and adhered to Michaelis‐Menten kinetics, with evidence of growth‐rate‐dependent variability of uptake affinities (1.9–3.0 L µmol−1 h−1) and half‐saturation constants (1.85–3.8 µmol P L−1). Maximum uptake rates were constant across growth rates when measured in either carbon‐specific (220 µmol P mol C−1 min−1), volume‐specific (7 amol P µm−3 min−1), cell‐specific (1 fmol P cell−1 min−1), or phosphorus‐specific units (7 h−1). This represents a phosphate uptake rate capacity between 200‐fold and 600‐fold greater than the requirements for growth. Finally, we compared the results from our study with previous studies across four phytoplankton species and found that the Monod half‐saturation constant for phosphorus‐limited growth (Kμ) is well‐predicted by the theoretical ratio of the maximum specific growth rate to the phosphorus‐specific uptake affinity.

Growth and uptake kinetics of nitrate and phosphate by benthic microalgae for phytoremediation of eutrophic coastal sediments

In the present study, the effect of monochromatic light (blue, yellow and red) and mixed wavelength on the nutrient uptake and growth kinetics of benthic microalgae Achnanthes sp., Amphora sp., Navicula sp. and Nitzschia sp. were investigated. The maximum uptake rate (ρmax) for nitrate and phosphate obtained by short-term experiments were high in the order of blue, mixed, red, yellow wavelength, and among the 4 benthic microalgae, Nitzschia sp. was the highest ρmax. The half-saturation constant (Ks) was higher than other taxon. The specific maximum growth rate (μmax′) and minimum cell quota (q0) for the nitrogen and phosphorus-limited condition, Nitzschia sp. showed the highest μmax′ and q0 values among the 4 benthic microalgae. These results suggest that the benthic microalgae are adapted to high nutrient concentration. In particular, Nitzschia sp., which have a higher capability of storage and uptake, may be a useful species for phytoremediation.

Growth and uptake kinetics of phosphate by benthic microalga Nitzschia sp. isolated from Hiroshima Bay, Japan

SUMMARYIn the present study, we experimentally investigated the phosphate uptake kinetics of benthic microalga Nitzschia sp. isolated from Hiroshima Bay, Japan. The maximum uptake rate (ρmax) obtained by short‐term experiments was 6.84 pmol cell−1 h−1 for phosphate. The half‐saturation constant for uptake (KS) was 61.2 µmol cell−1 h−1. Both the ρmax and Ks of this species were extremely high, suggesting that Nitzschia sp. is adapted to benthic environments, where nutrient concentrations are much higher than in the water column. The specific maximum growth rate (µ'max) and minimum cell quota (Q0) for the P‐limited condition, obtained by a semi‐continuous growth experiment, were 0.48 day−1 and 0.045 pmol cell−1, respectively. It is concluded that Nitzschia sp. could be a ‘storage strategist’ species, meaning it adapts so as to minimize the influence of fluctuations in phosphate conditions resulting from the change in redox conditions of sediment due to bioturbation.

Microbial Group Specific Uptake Kinetics of Inorganic Phosphate and Adenosine-5′-Triphosphate (ATP) in the North Pacific Subtropical Gyre

We investigated the concentration dependent uptake of inorganic phosphate (Pi) and adenosine-5′-triphosphate (ATP) in microbial populations in the North Pacific Subtropical Gyre (NPSG). We used radiotracers to measure substrate uptake into whole water communities, differentiated microbial size classes, and two flow sorted groups; Prochlorococcus (PRO) and non-pigmented bacteria (NPB). The Pi concentrations, uptake rates, and Pi pool turnover times (Tt) were (mean, ±SD); 54.9 ± 35.0 nmol L−1 (n = 22), 4.8 ± 1.9 nmol L−1 day−1 (n = 19), and 14.7 ± 10.2 days (n = 19), respectively. Pi uptake into >2 μm cells was on average 12 ± 7% (n = 15) of the total uptake. The kinetic response to Pi (10–500 nmol L−1) was small, indicating that the microorganisms were close to their maximum uptake velocity (Vmax). Vmax averaged 8.0 ± 3.6 nmol L−1 day−1 (n = 19) in the >0.2 μm group, with half saturation constants (Km) of 40 ± 28 nmol L−1 (n = 19). PRO had three times the cell specific Pi uptake rate of NPB, at ambient concentrations, but when adjusted to cells L−1 the rates were similar, and these two groups were equally competitive for Pi. The Tt of γ-P-ATP in the >0.2 μm group were shorter than for the Pi pool (4.4 ± 1.0 days; n = 6), but this difference diminished in the larger size classes. The kinetic response to ATP was large in the >0.2 μm class with Vmax exceeding the rates at ambient concentrations (mean 62 ± 27 times; n = 6) with a mean Vmax for γ-P-ATP of 2.8 ± 1.0 nmol L−1 day−1, and Km at 11.5 ± 5.4 nmol L−1 (n = 6). The NPB contribution to γ-P-ATP uptake was high (95 ± 3%, n = 4) at ambient concentrations but decreased to ∼50% at the highest ATP amendment. PRO had Km values 5–10 times greater than NPB. The above indicates that PRO and NPB were in close competition in terms of Pi acquisition, whereas P uptake from ATP could be attributed to NPB. This apparent resource partitioning may be a niche separating strategy and an important factor in the successful co-existence within the oligotrophic upper ocean of the NPSG.

Light-dependent phosphate uptake of a submersed macrophyte Myriophyllum spicatum L.

The uptake kinetics of phosphate (Pi) by Myriophyllum spicatum was determined from adsorption and absorption under light and dark conditions. Pi uptake was light dependent and showed saturation following the Michaelis–Menten relation (in light: V = 16.91 × [Pi](1.335 + [Pi]), R 2 = 0.90, p < 0.001; in the dark: V = 5.13 × [Pi](0.351 + [Pi]), R 2 = 0.77, p < 0.001). Around 77% of the loss of Pi in the water column was absorbed into the tissue of M. spicatum, and only 23% was adsorbed on the surface of the plant shoots. Our study shows that M. spicatum shoots have a much higher affinity (in light: 3.9 μmol g −1 dw h −1 μM −1; in the dark: 3.7 μmol g −1 dw h −1 μM −1) and V max (maximum uptake rate, shoot light) for Pi uptake than many other aquatic macrophytes (in light: 0.002–0.23 μmol g −1 dw h −1 μM −1; in the dark: 0.002–0.19 μmol g −1 dw h −1 μM −1), which may provide a competitive advantage over other macrophytes across a wide range of Pi concentrations.

A model and experimental study of phosphate uptake kinetics in algae: Considering surface adsorption and P-stress

Phosphorus is an important limiting nutrient in many ecosystems. Consequently, there is increasing interest on phosphate uptake and algal growth due to the increasing frequency and magnitude of algal blooms induced by eutrophication. The co-existence of surface adsorbed and intracellular phosphorus pools indicate that phosphate uptake by phytoplankton is, to some extent, a two-stage kinetic process. However, almost all previous uptake models considered the internal uptake stage only and ignored the possible impact of surface adsorption. In this article, a two-stage kinetic uptake model considering both surface adsorption and P-stress on phosphate uptake by algae was constructed and compared to conventional one-stage models, based on experimental data on short-term uptake kinetics of a green algae S. quadricauda. Results indicated that with suitable parameters, the two-stage uptake model not only fit the experimental data better, but also gave more reasonable and realistic explanations to the phosphate uptake process. The results are meaningful as surface-adsorption of phosphate may affect the uptake process of phosphate and assist in understanding realistic phosphate uptake kinetics in phytoplankton.

Kinetics of Ammonium, Nitrate and Phosphate Uptake by Candidate Plants Used in Constructed Wetlands

Abstract The constructed/artificial wetland system is a new sewage technique with low cost and less energy consumption for removal of nitrogen and phosphorus in wastewater, and the wetland plants have the important functions in the system. In wastewater purification, plants can absorb and utilize the nutrients (nitrogen and phosphorus) directly, and enhance nutrient transformation processes such as nitrification, denitrification, adsorption and desorption. In this study, a series of experiments for investigating the kinetics of ammonium, nitrate and phosphate uptake by 8 candidate wetland plants, such as Carex taliensis Franch, Dracaena sanderiana Virens, Impatiens balsamina, rush (Juncus effusus L.), mulberry (Morus indica L.), wetland rice (Oriza Sativa L.), Salvia plebeia R. Br., and Sesbania cannabina Poir, were carried out under controlled conditions (temperature 25-28, illumination 3000Lux, relative°C humidity 60-70%). The results indicated that the kinetic characteristics of ammonium, nitrate and phosphate uptake by the selected plants could be well illustrated with the Michaelis-Menten equation, and the kinetic parameters (maximum rate and Km value of absorption) could also be calculated using the regression equations. The orders of maximum uptake rate were as follows: Morus indica L. > Carex taliensis Franch > Oriza Sativa L. > Impatiens balsamina > Juncus effusus L. > Sesbania cannabina Poir > Salvia plebeia R. Br. > Dracaena sanderiana for ammonium; Carex taliensis Franch > Oriza Sativa L. > Sesbania cannabina Poir > Juncus effusus L. > Impatiens balsamina > Morus indica L. > Salvia plebeia R. Br. > Dracaena sanderiana for nitrate; Oriza Sativa L. > Juncus effusus L. > Salvia plebeia R. Br. > Dracaena sanderiana > Impatiens balsamina > Morus indica L. Sesbania cannabina Poir > Carex taliensis Franch for phosphate. Sesbania cannabina Poir., Dracaena sanderiana Virens and Salvia plebeia R. Br. had the smallest Km value for ammonium uptake, and Impatiens balsamina, Dracaena sanderiana Virens and Salvia plebeia R. Br. had the smallest Km value for nitrate uptake, Sesbania cannabina Poir., mulberry and Dracaena sanderiana Virens had the smallest Km value for phosphate uptake. According to the kinetic characteristics of N and P uptake, we suggested that plant species with higher maximum uptake rates could be used in the first section for cleaning up wastewater with high nutrient concentrations, and plant species with lower Km values could be used in subsequent sections for cleaning up wastewater with lower nutrient concentrations.

Nitrate and phosphate uptake kinetics of the harmful diatom Coscinodiscus wailesii, a causative organism in the bleaching of aquacultured Porphyra thalli

The large diatom Coscinodiscus wailesii is one of the problematic species which indirectly cause bleaching damage to “Nori” ( Porphyra thalli) cultivation through competitive utilization of nutrients during its bloom. In the present study, we experimentally investigated the nitrate (N) and phosphate (P) uptake kinetics of C. wailesii, Harima-Nada strain. Maximum uptake rates ( ρ max), obtained by short-term experiments, were 58.3 and 95.5 pmol cell −1 h −1 for nitrate and 41.9 and 59.1 pmol cell −1 h −1 for phosphate at 9 and 20 °C, respectively. The half saturation constants for uptake ( K s ) were 2.91 and 5.08 μM N and 5.62 and 6.67 μM P at 9 and 20 °C, respectively. The ρ max values of C. wailesii, much higher than those of other marine phytoplankton species, suggest that C. wailesii is able to take up large amounts of nutrients from the water column. On the other hand, V max/ K s ( V max; V max = ρ max/ Q 0, Q 0; minimum cell quota) values of C. wailesii, which is a better measure to evaluate the competitive ability for nutrient uptake, were low in dominant diatom species. This parameter indicates that C. wailesii is disadvantaged compared to other diatom species in competing for nutrients, and the decreasing nutrient concentrations from winter to spring is an important factor limiting C. wailesii blooming in early spring.