Maximum Nutrient Uptake Rate Research Articles

Effects of pH and nitrogen form on Nitzschia closterium growth by linking dynamic with enzyme activity

In this study, Nitzschia closterium was incubated in seawater at different pH values (8.10, 7.71, and 7.45) and using different nitrogen forms (NO3–N and NH4–N) in the laboratory. The results showed that the growth of N. closterium was inhibited by ocean acidification, with individuals under lower pH levels showing lower growth rates and lower nitrogen uptake rates for both nitrogen forms. The Vmax/Ks ratio decreased with decreasing pH, indicating the inhibition of nitrogen uptake, whereas the ratios for NH4–N cultures were higher than those for NO3–N cultures, implying the highly competitive position of NH4–N. Acidification might induce reactive oxygen species based on the result that the maximum enzyme activities of SuperOxide Dismutase (SOD) and CATalase (CAT) increased under lower pH levels. The SOD and CAT activities for the NO3–N cultures were higher than those for NH4–N cultures at the low pH level, indicating that acidification might cause more oxidative stress for NO3–N cultures than for NH4–N cultures. Thus, ocean acidification might have a more detrimental effect on the growth of N. closterium under NO3–N conditions than NH4–N conditions, with a lower ratio (γ) of the maximum growth rate to the maximum nutrient uptake rate, and a drop in nitrate reductase activity under lower pH levels.

Temporal phosphate gradients reveal diverse acclimation responses in phytoplankton phosphate uptake.

Phytoplankton face environmental nutrient variations that occur in the dynamic upper layers of the ocean. Phytoplankton cells are able to rapidly acclimate to nutrient fluctuations by adjusting their nutrient-uptake system and metabolism. Disentangling these acclimation responses is a critical step in bridging the gap between phytoplankton cellular physiology and community ecology. Here, we analyzed the dynamics of phosphate (P) uptake acclimation responses along different P temporal gradients by using batch cultures of the diatom Phaeodactylum tricornutum. We employed a multidisciplinary approach that combined nutrient-uptake bioassays, transcriptomic analysis, and mathematical models. Our results indicated that cells increase their maximum nutrient-uptake rate (Vmax) both in response to P pulses and strong phosphorus limitation. The upregulation of three genes coding for different P transporters in cells experiencing low intracellular phosphorus levels supported some of the observed Vmax variations. In addition, our mathematical model reproduced the empirical Vmax patterns by including two types of P transporters upregulated at medium-high environmental and low intracellular phosphorus levels, respectively. Our results highlight the existence of a sequence of acclimation stages along the phosphate continuum that can be understood as a succession of acclimation responses. We provide a novel conceptual framework that can contribute to integrating and understanding the dynamics and wide diversity of acclimation responses developed by phytoplankton.

Cell size as a key determinant of phytoplankton metabolism and community structure.

Phytoplankton size structure controls the trophic organization of planktonic communities and their ability to export biogenic materials toward the ocean's interior. Our understanding of the mechanisms that drive the variability in phytoplankton size structure has been shaped by the assumption that the pace of metabolism decreases allometrically with increasing cell size. However, recent field and laboratory evidence indicates that biomass-specific production and growth rates are similar in both small and large cells but peak at intermediate cell sizes. The maximum nutrient uptake rate scales isometrically with cell volume and superisometrically with the minimum nutrient quota. The unimodal size scaling of phytoplankton growth arises from ataxonomic, size-dependent trade-off processes related to nutrient requirement, acquisition, and use. The superior ability of intermediate-size cells to exploit high nutrient concentrations explains their biomass dominance during blooms. Biogeographic patterns in phytoplankton size structure and growth rate are independent of temperature and driven mainly by changes in resource supply.

Reassessment of the cell surface area limitation to nutrient uptake in phytoplankton

In many past theoretical and empirical studies of phytoplankton nutrient allometry, cell surface area has been considered the main limiting factor to nutrient uptake rates because of an assumption that the cell surface area is not large enough to accommodate enough uptake sites to meet the uptake demand. However, calculations in this paper show that the required uptake sites may only cover approximately 76% of the surface area of a typical phytoplankton cell. Cell volume could be the main factor controlling the maximum nutrient uptake rates of phytoplankton cells with a cell volume of <40 μm3, while the cell surface becomes limiting for larger cells. The maximum nutrient uptake rate of phytoplankton cells generally increases almost linearly with cell volume, and that of smaller cells increases faster than that of larger cells.

Allometric scaling and taxonomic variation in nutrient utilization traits and maximum growth rate of phytoplankton

Nutrient utilization traits can be used to link the ecophysiology of phytoplankton to population dynamic models and the structure of communities across environmental gradients. Here we analyze a comprehensive literature compilation of four traits: maximum nutrient uptake rate; the half‐saturation constant for nutrient uptake; the minimum subsistence quota, measured for nitrate and phosphate; and maximum growth rate. We also use these traits to analyze two composite traits, uptake affinity and scaled uptake affinity. All traits tend to increase with cell volume, except for scaled uptake affinity and maximum growth rate, which tend to decline with cell volume. Most scaling relationships are the same for freshwater and marine species, although important differences exist. Most traits differ on average between major taxa, but between‐taxon variation is nearly always due to between‐taxon variation in volume. There is some evidence for between‐trait correlations that could constrain trait evolution, but these correlations are difficult to disentangle from correlation driven by cell volume. These results should enhance the parameterization of models that use size or taxonomic group to structure physiological variation in phytoplankton communities.

Going for the slow burn: why should possession of a low maximum growth rate be advantageous for microalgae?

Background: Phytoplankton show a wide range of maximum growth rates (μmax), with no obvious advantage to having a low μmax. Aims: To explore advantages for phytoplankton in having μmax values commensurate with the rate of nutrient supply in their environment, making use of a mechanistic model describing their growth. Methods : In contrast with the typical construction of quota-based models of microalgal growth, which scale the maximum nutrient uptake rate to μmax, a more realistic description of excess nutrient transport capacity endows organisms of lower μmax with a competitive advantage for nutrient acquisition. This, in turn, enables the retention of a higher organismal nutrient status at low-nutrient concentrations. Thence low μmax organisms may be expected to have lower intrinsic death rates, and also faster response times to capitalise on nutrient spikes. Results: Of the traits modelled, the lowering of death rate appears the most important, enabling cells of low μmax to out-compete their high μmax counterparts at low-nutrient concentration. An ability to recover more rapidly from nutrient stress is of lesser importance, and is unable to counter differences in μmax. Conclusions: Descriptions of features such as those modelled define properties of plankton functional types and also provide trade-off characteristics for placement within models considering emergent properties of plankton communities.

Differential cell size optimization strategies produce distinct diatom richness–body size relationships in stream benthos and plankton

Summary The relationship between species richness and body size is one of the most thoroughly studied subjects in animal ecology; however, this relationship and its underlying mechanisms are largely unknown in photosynthetic organisms, especially protists. In this continental study, I first examined the number of diatom species across the cell size spectrum in benthic and planktonic stream habitats. The relationship was right‐skewed unimodal and was significantly different between the benthos and the plankton; larger sizes were more speciose in the benthos, and smaller sizes in the plankton. The species richness peaks were explained with allometric trade‐offs between maximum nutrient uptake rate and dispersal in the benthos but maximum nutrient uptake rate and sinking resistance in the phytoplankton. I also explored the cell size similarity among species and across environments. Small diatoms were significantly more similar in size than large diatoms, and benthic diatoms were significantly more similar than planktonic diatoms. This is the first continental study on the richness–body size relationship in algae, which suggests that the environmental differences between benthic and planktonic habitats generated allometric trade‐offs that have driven the cell size optimization towards larger species in the benthos but smaller in the plankton. The patterns of cell size similarity revealed a higher niche overlap in the benthos than in the phytoplankton and among small species than among large species. These findings indicate that interspecific competition in stream diatoms, which is a function of niche differentiation, is habitat‐specific and inversely related to cell size.

Seasonal Biomass Accumulation and Nutrient Uptake of Pea and Lentil on a Black Chernozem Soil in Saskatchewan

ABSTRACT Close relationships usually exist among biomass accumulation, nutrient uptake, and seed yield during the growing season. Field experiments with pea (Pisum sativum L.) and lentil (Lens cultinaris L.) were conducted in 1998 and 1999 at Melfort, Saskatchewan, Canada, to determine relationships of biomass accumulation and nutrient uptake with days after emergence (DAE) or growing degree days (GDD). For both biomass accumulation and nutrient uptake, maximum rates and amounts increased with time at early growth stages and reached a maximum value at late growth stages. The R2 values for cubic polynomial regressions were highly significant, indicating their suitability to estimate the progression of biomass accumulation and nutrient uptake as a function of days after emergence (DAE). Both pulse crops followed a similar pattern in biomass accumulation and nutrient uptake, which increased in the early growth stages and reached a maximum late in the growth cycle. Pulse crops usually reached their maximum biomass accumulation rate and amount at early to late bud formation (42–56 DAE or 390–577 GDD) and at medium pod formation to early seed filling (75–82 DAE or 848–858 GDD) growth stages, respectively. Maximum biomass accumulation rate was 175–215 kg ha− 1d−1 for pea and 109–140 kg ha− 1d− 1 for lentil. Maximum nutrient uptake rate and amount usually occurred at branching to early bud formation (28–49 DAE or 206–498 GDD) and at the flowering to seed filling (66–85 DAE or 672–986 GDD) growth stages, respectively. Maximum uptake rate of nitrogen (N), phosphorus (P), potassium (K), and sulfur (S), respectively, was 4.6–4.9, 0.4–0.5, 5.0–5.3 and 0.3 kg ha− 1d− 1 for pea, and 2.4–3.8, 0.2–0.3, 2.0–3.4 and 0.2 kg ha− 1d− 1 for lentil. In general, maximum nutrient uptake rate and amount occurred earlier than maximum biomass accumulation rate and amount, respectively; and the maximum accumulation rates of both biomass and nutrients occurred earlier than maximum amounts. The findings suggest that adequate supply of nutrients from soil and fertilizers at early growth stages, and translocation of biomass and nutrients to seed at later growth stages are of great importance for high seed yield of pulse crops.

Seasonal Biomass Accumulation and Nutrient Uptake of Canola, Mustard, and Flax on a Black Chernozem Soil in Saskatchewan

ABSTRACT Seed yield and nutrient use efficiency are related to biomass accumulation and nutrient uptake in the growing season. Biomass accumulation and nutrient uptake of canola (Brassica napus L. and Brassica rapa L.), mustard (Brassica juncea L.) and flax (Linum usitatissimum L.) and the relationship to days after emergence (DAE) or growing degree days (GDD) were determined during the 1998 and 1999 growing seasons in field experiments at Melfort, Saskatchewan, Canada. In general, biomass accumulation and nutrient uptake increased with time at early growth stages and reached a maximum at late growth stages. Significant R2 values for both biomass accumulation and nutrient uptake indicated that a cubic polynomial type equation was suitable to represent these parameters as a function of DAE. All oilseed crops maximized biomass at mid way to the end of pod forming stages (74–84 DAE or 750–973 GDD). Maximum biomass accumulation rate occurred at the early to late bud forming stage (42–49 DAE or 390–498 GDD), and it was 146–190 kg ha−1d−1 for canola, 158–182 kg ha−1d−1 for mustard, and 174–189 kg ha−1d−1 for flax. Maximum nutrient uptake occurred during flowering to early ripening (59–82 DAE or 597–945 GDD). Maximum nutrient uptake rate normally occurred at branching to early bud formation (21–42 DAE or 142–399 GDD). There was a close correlation between biomass accumulation and nutrient uptake, and among nutrients, suggesting interrelated absorption. For nitrogen (N), phosphorus (P), potassium (K), sulfur (S), and boron (B), respectively, maximum nutrient uptake rate was 2.3–4.5, 0.3–0.5, 2.5–5.7, 0.7–1.1, and 0.005–0.008 kg ha−1d−1 for canola; 2.3–3.9, 0.4–0.5, 2.6–4.9, 1.2–1.4, and 0.006–0.008 kg ha−1d−1 for mustard; and 3.2–4.0, 0.3–0.4, 2.9–4.1, 0.3–0.5, and 0.004–0.009 kg ha−1d−1 for flax. In general, maximum nutrient uptake rate and amount occurred earlier than maximum biomass accumulation rate and amount, and maximum rates of both nutrient uptake and biomass accumulation occurred earlier than their maximum amounts. The findings suggest that for high seed yields, there should be adequate supply of nutrients for plants, particularly to sustain high nutrient uptake rate at branching to bud forming stage and high biomass accumulation rate at early to late bud forming stage.

Seasonal biomass accumulation and nutrient uptake of wheat, barley and oat on a Black Chernozem Soil in Saskatchewan

Dry matter and nutrient accumulation in the growing season are the main factors in the determination of seed yield and nutrient use efficiency. Field experiments were conducted with spring wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and oat (Avena sativa L.) in 1998 and 1999 at Melfort, Saskatchewan, Canada, to determine the biomass accumulation and plant nutrient uptake at different growth stages, and their relationship with days after emergence (DAE) and growing degree days (GDD). All crops generally followed a similar pattern of biomass and nutrient accumulation in the growing season, which increased continuously with growing time, with much faster increase at early growth stages than at late growth stages. Maximum biomass accumulation rate and amount usually occurred at late boot stage (46–47 DAE or 443–460 GDD) and ripening stage (89–90 DAE or 948–1050 GDD), respectively. Maximum rate of nutrient uptake occurred at tillering to stem elongation stages (22–36 DAE or 149–318 GDD). Maximum amount of nutrient uptake generally occurred at the beginning of flowering to medium milk stages (61–75 DAE or 612–831 GDD), except for P in 1998 when it occurred at late milk to ripening stages (80–90 DAE or 922–1050 GDD). In general, the maximum nutrient uptake rate and amount, respectively, occurred earlier than maximum biomass accumulation rate and amount. For various cereal species/cultivars, maximum biomass accumulation rate was 204–232 kg ha-1 d-1, and maximum uptake rate of N, P, K and S, respectively, was 3.2–5.7, 0.30–0.60, 3.85–7.05 and 0.45–0.60 kg ha-1 d-1. The findings suggest that a sufficient supply of nutrients from soil and fertilizers at early growth stages is of great importance for optimum crop yield. Key words: Barley, biomass accumulation, cereals, growth stages, nutrient uptake, oat, wheat

Phytoplankton nutrient competition under dynamic light regimes

Many physiological processes in phytoplankton, including nutrient uptake, vary on a number of temporal scales. Experiments show that the daily cycle in irradiance affects nutrient uptake rates. We used a Droop‐based model of resource competition to investigate how diel variability in nutrient uptake influences phytoplankton competition and community structure. The analytical approximation we derive shows that if nutrient uptake is light dependent, the minimum nutrient requirements and, hence, nutrient competitive abilities depend on light regime in a species‐specific way. Consequently, daily variations in irradiance may slow rates of competitive exclusion or reverse the identity of the superior competitor but not allow stable coexistence. Irradiance‐induced fluctuations in the maximum nutrient uptake rate of the superior competitor can lead to fluctuations in ambient nutrient concentration and an increase in the average nutrient concentration compared to constant light conditions. This can enhance nutrient use by inferior competitors. These results may be applicable to bacteria‐phytoplankton nutrient competition as well. Depending on the costs and benefits of maintaining nutrient uptake in the dark, different strategies of nutrient use are optimal under different light regimes. Our results suggest that by mediating limiting nutrient use, fluctuations in irradiance may alter the structure of phytoplankton communities.

Safety factors and nutrient uptake by seaweeds

The differences in the kinetic characteristics of nutrient (nitrate, ammonium and phosphate) uptake by seaweeds are evaluated using published half-saturation constants (K m ), maximum rates of uptake (V max ) and calculated safety factors for nitrate, ammonium and phosphate uptake. The safety factor is the ratio of maximum nutrient uptake rate to uptake rate at maximum ambient concentration of nutrient and provides a simple estimate of the amount of surplus capacity of a nutrient uptake system. Frequency distributions of K m values for nitrate, ammonium and phosphate uptake show similar patterns, though values tend to be lower for phosphate uptake and greater for ammonium uptake. There is no relationship between the K m values for nitrate or ammonium uptake and seaweed surface area:volume ratio (SA:V). Frequency distributions of V max :K m values for nitrate, ammonium and phosphate uptake show similar patterns, but V max :K m values tend to be lower for phosphate uptake and greater for ammonium uptake. Moreover, rates of nitrate uptake (at 5 μM nitrate) are comparable to rates of ammonium uptake (at 1.5 μM ammonium) at any value of seaweed SA:V ratio, i.e. the efficiency of ammonium uptake is greater. For nitrate and phosphate uptake by seaweeds and ammonium uptake by phytoplankton values for safety factors are low. In contrast, values for ammonium uptake by seaweeds are high. It is suggested that the reason for the high surplus capacity for ammonium uptake in seaweeds is a combination of the size of the plant and the spatially and temporally variable concentration of ammonium in the seawater that surrounds these plants.

Ammonium-Limited Continuous Culures of Skeletonema Costatum in Steady and Transitional State: Experimental Results and Model Simulations

The physiological response of ammonium-limited continuous cultures of Skeletonema costatum (Grev.)Cleve to steady-state and transient conditions was tested and compared to simulations with a Droop-type quota model and a four-state variable model (internal amino acid pool added to the quota model). External ammonium, free internal amino acids, protein, silicate and culture-cell volume were measured.All cultures showed reproducible changes in growth and uptake kinetics due to spontaneous cell-cycle synchronization of the populations. Under steady-state conditions protein decreased with increasinggrowth rate from 82%; cell-nitrogen to 52% and free internal amino acids increased from 2·5% cell-nitrogen to 8%. Under transient conditions amino acids could reach 25% of cell-nitrogen.A comparison of model and culture results yielded the following information: Both models could simulate steady-state and most transient conditions. The dependence of the quota on steady-state growth rate is not the result of changes in amino acid or protein pool size. The amino acid pool, an intermediary step in the nitrogen assimilation, does not serve to increase the time lag in growth response significantly. The four-state variable model reproduced under most conditions the behaviour of theamino acid pool without the use of feedback control mechanisms on the rate of uptake. The models could simulate a strong increase in growth rate except when it was initiated by impulse dilution of the culture. Then growth response was controlled by epigenetic mechanisms induction of enzyme synthesis). (6) The maximum nutrient uptake rate per culture cell volume of Skeletonema is inversely related to cell size.

Ammonium-Limited Continuous Culures of Skeletonema Costatum in Steady and Transitional State: Experimental Results and Model Simulations

The physiological response of ammonium-limited continuous cultures of Skeletonema costatum (Grev.)Cleve to steady-state and transient conditions was tested and compared to simulations with a Droop-type quota model and a four-state variable model (internal amino acid pool added to the quota model). External ammonium, free internal amino acids, protein, silicate and culture-cell volume were measured.All cultures showed reproducible changes in growth and uptake kinetics due to spontaneous cell-cycle synchronization of the populations. Under steady-state conditions protein decreased with increasinggrowth rate from 82%; cell-nitrogen to 52% and free internal amino acids increased from 2·5% cell-nitrogen to 8%. Under transient conditions amino acids could reach 25% of cell-nitrogen.A comparison of model and culture results yielded the following information: Both models could simulate steady-state and most transient conditions. The dependence of the quota on steady-state growth rate is not the result of changes in amino acid or protein pool size. The amino acid pool, an intermediary step in the nitrogen assimilation, does not serve to increase the time lag in growth response significantly. The four-state variable model reproduced under most conditions the behaviour of theamino acid pool without the use of feedback control mechanisms on the rate of uptake. The models could simulate a strong increase in growth rate except when it was initiated by impulse dilution of the culture. Then growth response was controlled by epigenetic mechanisms induction of enzyme synthesis). (6) The maximum nutrient uptake rate per culture cell volume of Skeletonema is inversely related to cell size.