Photosynthetic and growth responses of three freshwater algae to phosphorus limitation and daylength

1. Three common species of freshwater phytoplankton, the diatom Nitzschia sp., green alga Sphaerocystis schroeteri and cyanobacterium Phormidium luridum, were grown under contrasting daylengths [18 : 6 h light : dark cycles (LD) versus 6 : 18 h LD] and phosphorus (P) regimes (P‐sufficient versus 1 μm P). The rates of growth and photosynthesis, as well as growth efficiencies and pigment concentrations, were compared among treatments. 2. The growth and photosynthetic parameters of the three species depended on both P status and daylength in a species‐specific way. The responses to P limitation depended on daylength and, conversely, the responses to daylength depended on P status. 3. Growth rates and the maximum rates of photosynthesis (P_max) of all species decreased under P limitation under both light regimes. However, the decrease of P_max because of P limitation was greater under long daylength. The P_max of the green alga S. schroeteri decreased the most (ca. sixfold) under P limitation compared with the other two species. The photosynthesis saturation parameter I_k also decreased under P limitation; the decline was significant in Nitzschia and Sphaerocystis. P‐limitation significantly increased photoinhibition (β) in Nitzschia and Sphaerocystis, but not in Phormidium. The excess photochemical capacity (the ratio of the maximum photosynthesis rate to the photosynthesis rate at the growth irradiance), characterising the ability to utilise fluctuating light, was significantly lower under P limitation. 4. The growth efficiency (growth rate normalised to daylength) declined with increasing daylength in all species. Under short daylength the cyanobacterium Phormidium had the lowest growth efficiency of the three species. 5. The cellular chlorophyll a concentration in both Nitzschia and Sphaerocystis was significantly higher under short daylength, but only under P‐sufficient conditions. In Nitzschia, under short daylength, P‐limitation significantly decreased cellular chlorophyll concentration. In contrast, P‐limitation increased cellular chlorophyll concentration in Sphaerocystis, but under long daylength only. The ratio of chlorophyll a to b in the green alga also declined under short daylength and under P‐limited conditions.     

Diversity in the influence of temperature on the growth rates of freshwater algae, and its ecological relevance

1. Growth rates of seven species of planktonic algae were determined in culture over a range of temperature from 2 to 35 °C. Additional observations on growth and viability were made for 13 species in the temperature range 20–35 °C. 2. There was a wide range of growth rates between species at their optimal temperatures, from 1.7 divisions day^?1 (Asterionella formosa) to 0.3 divisions day^?1 (Ceratium furcoides). 3. There were considerable differences between species for growth at low and high temperature. Certain algae, including the diatom A. formosa and the flagellates Cryptomonas marssonii, Dinobryon divergens and Eudorina unicocca var. unicocca, had growth rates of 0.4 divisions day^?1 or more at 5 °C. The cyanophyte Tychonema (formerly Oscillatoria) bourrellyi, the xanthophyte Tribonema sp., the desmid Staurastrum cingulum and the large dinoflagellate C. furcoides grew poorly or not at all at this temperature. All 21 species tested could grow at 25 °C, but many – including most of the diatoms, some cyanophytes, and all the flagellates – failed to grow persistently at 30 °C. Only Aphanizomenon flos‐aquae survived with moderate increase at 35 °C, a lethal temperature for the other species. 4. The applicability was considered of proposed quantitative formulations of the rate‐temperature relationship. Simple exponential relationships applied only to very limited lower ranges of temperature. The relationship proposed by B?lehrádek was a better fit over a wider temperature range, but still excluded rate‐decline at high temperature. 5. The interspecific differences found are of potential significance for restrictions in natural distributions associated with season, altitude (especially above 500 m) and latitude.     

Light and temperature effects on the growth rate of three freshwater [2pt] algae isolated from a eutrophic lake

Effects of light and temperature, on the growth of three freshwater green algae isolated from an eutrophic lake and identified as Selenastrum minutum, Coelastrum microporum f. astroidea and Cosmarium subprotumidumwere studied in batch cultures under non-nutrient limited conditions. Experiments were performed to determine the growth rate over a wide range of light intensities (30–456 mol m^–2 s^–1) and temperature (15–35°C), using a 15/9 (light/dark) photoperiod cycle. The maximum growth rates and the optimum light intensities at a temperature of 35°C were 1.73 d^–1 and 420 mol m^–2 s^–1for Selenastrum minutum, 1.64 d^–1 and 400 mol m^–2 s^–1 for Coelastrum microporum and 1.00 d^–1 and 400 mol m^–2 s¹ for Cosmarium subprotumidum. The results were fitted with the mathematical models of Steele (1965), Platt & Jassby (1976) and Peeters & Eilers (1978). Steele's function and equation of Platt & Jassby don't describe correctly the relationship between the growth and light intensity. In the opposite, the equation of Peeters & Eilers provides the best fit for the three species.     

Growth rates of phytoplankton under fluctuating light

• 1 The effect of light fluctuations on the growth rates of four species of freshwater phytoplankton was investigated. Experimental light regimes included constant irradiance and fluctuations of a step function form, with equal proportion of high (maximum of 240 µmol photons m^‐2 s^‐1) and low light (minimum of 5 µmol photons m^‐2 s^‐1) (or dark) in a period. Fluctuations of 1, 8 and 24‐h periods were imposed over several average irradiances (25, 50, 100 and 120 µmol photons m^‐2 s^‐1).
• 2 Growth rate responses to fluctuations were species‐specific and depended on both the average irradiance and the period of fluctuations. Fluctuations at low average irradiances slightly increased growth rate of the diatom Nitzschia sp. and depressed growth of the cyanobacterium Phormidium luridum and the green alga Sphaerocystis schroeteri compared to a constant irradiance.
• 3 Fluctuations at higher average irradiance did not have a significant effect on the growth rates of Nitzschia sp. and Sphaerocystis schroeteri (fluctuations around saturating irradiances) and slightly increased the growth rates of the cyanobacteria Anabaena flos‐aquae and Phormidium luridum (when irradiance fluctuated between limiting and inhibiting levels).
• 4 In general, the effect of fluctuations tended to be greater when irradiance fluctuated between limiting and saturating or inhibiting levels of a species growth‐irradiance curve compared to fluctuations within a single region of the curve.
• 5 The growth rates of species under fluctuating light could not always be predicted from their growth‐irradiance curves obtained under constant irradiance. When fluctuations occur between limiting and saturating or inhibiting irradiances for the alga and when the period of fluctuations is long (greater than 8 h), steady‐state growth‐irradiance curves may be insufficient to predict growth rates adequately. Consequently, additional data on physiological acclimation, such as changes in photosynthetic parameters, may be required for predictions under non‐constant light supply in comparison to constant conditions.

     

Dominance of phosphorus over nitrogen as the limiter to phytoplankton growth rate

Laboratory experiments with natural phytoplankton assemblages from three lakes (two mesotrophic and one oligotrophic) showed that added PO₄ predictably affected growth rate (μ, determined as P : B) while NO₃ had little effect even when the N P ratio approached one. The response to PO₄ followed the typical Monod-type function. The lack of effect of NO₃ on μ at such low N : P ratios is in striking contrast to the added effect of NO₃ Plus PO₄ on maximum biomass produced versus only PO₄ alone. Contribution No. 193 to the IBP-Coniferous Forest Biome. The work was supported in part by National Science Foundation Grant No. GB-20963 (IBP-Coniferous Forest Biome), and in part by Environmental Protection Agency Training Grant T900313-W P293-03,04. Contribution No. 193 to the IBP-Coniferous Forest Biome. The work was supported in part by National Science Foundation Grant No. GB-20963 (IBP-Coniferous Forest Biome), and in part by Environmental Protection Agency Training Grant T900313-W P293-03,04.     

Optical properties of some freshwater phytoplanktonic algae

Measurements of absorption and scattering of light by pure cultures of some New Zealand freshwater phytoplankters have been made with a spectrophotometer. An integrating sphere accessory was used to capture most of the light scattered by an algal cell suspension and thus give an indication of the true absorption coefficient, with only a small correction required for residual scattering. The purpose of this study was to investigate the factors affecting the relationships of chlorophyll-a concentration to absorption and scattering by a diverse selection of algae. Qualitative differences in absorption spectra of the different phytoplankton studied here can be related to differences in pigment composition. Quantitative differences in the specific absorption coefficients (absorption coefficient divided by Chl-a concentration) at the Chl-a red peak (676 nm in vivo) are explained in terms of different extents of packaging of pigment in cells or cell aggregates in the different cultures. Qualitative differences in scattering spectra are explained in terms of optical size of the particulates comprising the pure cultures. The green and diatom cultures displayed a complex-shaped but non-trending scattering spectrum with minima (troughs) in scattering associated with maxima (peaks) in absorption. The blue-green cultures behaved as optically small particles and displayed a pattern of decreasing scattering with increasing wavelength. Quantitative differences in specific scattering coefficients (scattering coefficient divided by Chl-a concentration) were related mainly to differences in the effective ratio of surface areas to Chl-a content of scattering centres in the different cultures. Overall, however, the specific absorption and scattering coefficients at any given wavelength were less variable between cultures than expected suggesting that the common assumption that absorption and scattering by the algal component of a lake water depends only on the Chl-a concentration may be a justifiable first approximation in field studies.     

Growth response of four freshwater algal species to dissolved organic nitrogen of different concentration and complexity

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The metabolic rate of roach in relation to body size and temperature

Standard and routine metabolic rates of roach Rutilus rutilus for a wide size and temperature range (3–200 g, 5–23° C) were analysed by automated, computerized intermittent flow respirometry. The mass exponent b ranged from 0·68 to 0·82 for standard metabolism, and from 0·65 to 0·92 for routine metabolism depending on the experimental temperature. For routine metabolism b was lowest at 10° C. At both decreasing and increasing temperatures, b increased significantly. Roach were exponentially temperature-dependent for both metabolic levels. For roach <20 g, however, an asymptotic relationship was observed between temperature and routine metabolic rate. The 'flattening of the curve' in the latter case may be explained by reduced spontaneous activities at the lower threshold of the preferred temperature range.     

Growth in a freshwater snail under laboratory conditions in relation to eutrophication

Shell growth in the snail Potamoryrgus jenkinsi (Prosobranchia, Hydrobiidae) was measured under laboratory conditions. Individuals of populations from two lakes differing in trophic status were kept in water with sandy substrates from each environment. Growth was faster in the environment of the more eutrophic lake, regardless of the origin of the snails; this held in particular for the smallest size class.     

富营养化水体中N、P浓度对浮游植物生长繁殖速率和生物量的影响

在浮游植物生长繁殖的高峰期（7—10月份）对3个富营养化水体的总氮、总磷和浮游植物生物量进行调查,统计分析了生物量与氮和磷浓度的关系。利用3种水样和梯度稀释的东湖水样培养玫瑰拟衣藻（Chloromonas rosae）,研究了氮、磷浓度对生长繁殖速率的影响。结果表明磷是生长繁殖速率的限制因子,求出了生长繁殖速率与磷浓度的对数回归方程y=0．08061nx＋0．4658,当磷浓度小于0．05mg／L时,生长繁殖速率随着磷浓度的升高而直线上升,当磷浓度进一步升高,生长繁殖速率仍然随之增加,但增加的幅度越来越小,当磷浓度达到0．2mg／L时,生长繁殖速率基本不再随着磷浓度的增加而升高。计算出生长速率为零时磷的浓度是0．003mg／L,接近贫营养化湖泊磷浓度的下限,计算结果与坂本的调查统计结果相吻合,说明回归方程具有代表性。在凋查的3个富营养化水体中,浮游植物中的氮占全部氮元素的53％,磷占全部磷元素的85％,是氮、磷存在的主要形式,所以,评价水体的营养程度,必须同时考虑水中溶解的氮、磷和生物体内的氮、磷。统计分析表明,3个富营养化水体中浮游植物的生物量由氮（溶解氮＋胞内氮）和磷（溶解磷＋胞内磷）的浓度共同决定,生物量与氮浓度的直线回归方程y=10．687x-7．8304,生物量与磷浓度的直线回归方程y=122．11x-12．069。实验结果为根据氮、磷浓度以Redfield值判断浮游植物限制性营养元素的相对性和绝对性提供了例证。对3个富营养化水体的比较表明,防止水体富营养的唯一办法是维持水体氮、磷等主要营养元素收支平衡,治理富营养化的根本办法是从水体中移走过量的氮、磷等主要营养元素。     

Seed weight and seed resources in relation to plant growth rate

Summary Relative growth rate in radish is not influenced by initial seed weight.     

Microscopic green algae and cyanobacteria in high-frequency intermittent light

The effects of fluctuations in the irradiance onScenedesmus quadricauda, Chlorella vulgaris andSynechococcus elongatus were studied in dilute cultures using arrays of red light emitting diodes. The growth rate and the rate of photoinhibition were compared using intermittent and equivalent continuous light regimes in small-size (30 ml) bioreactors. The CO₂ dependent photosynthetic oxygen evolution rates in the intermittent and continuous light regimes were compared for different light/dark ratios and different mean irradiances. The kinetics of the electron transfer reactions were investigated using a double-modulation fluorometer. The rates of photosynthetic oxygen evolution normalized to equal mean irradiance were lower or equal in the intermittent light compared to the maximum rate found in the equivalent optimal continuous light regime. In contrast, the growth rates in the intermittent light can be higher than the growth rate in the equivalent continuous light. Photoinhibition is presented as an example of a physiological process affecting the growth rate that occurs at different rates in the intermittent and equivalent continuous lights. The difference in the dynamics of the redox state of the plastoquinone pool is proposed to be responsible for the low photoinhibition rates observed in the intermittent light.     

Effect of temperature on photosynthesis-light response and growth of four phytoplankton species isolated from a tidal freshwater river

Three cyanobacteria (Microcystis aeruginosa Kütz. emend. Elenkin, Merismopedia tenuissima Lemmermann, and Oscillatoria sp.) and one diatom (Aulacoseira granulata var. angustissima O. Mull. emend. Simonsen) were isolated from the tidal freshwater Potomac River and maintained at 23° C and 40 μmol photons·m^?2·s^?1 on a 16:8 L:D cycle in unialgal culture. Photosynthetic parameters were determined in nutrient‐replete cultures growing exponentially at 15, 20, 25, and 30° C by incubation with ¹⁴C at six light levels. P ^B_max was strongly correlated with temperature over the entire range for the cyanobacteria and from 15 to 25° C for Aulacoseira, with Q₁₀ ranging from 1.79 to 2.67. The α values demonstrated a less consistent temperature pattern. Photosynthetic parameters indicated an advantage for cyanobacteria at warmer temperatures and in light‐limited water columns. P ^B_max and I_k values were generally lower than comparable literature and field values, whereas α was generally higher, consistent with a somewhat shade acclimated status of our cultures. Specific growth rate (μ), as measured by chlorophyll change, was strongly influenced by temperature in all species. Oscillatoria had the highest μ at all temperatures, joined at lower temperatures by Aulacoseira and at higher temperatures by Microcystis. Values of μ for Aulacoseira were near the low end of the literature range for diatoms consistent with the light‐limited status of the cultures. The cyanobacteria exhibited growth rates similar to those reported in other studies. Q₁₀ for growth ranged from 1.71 for Aulacoseira to 4.16 for Microcystis. Growth rate was highly correlated with P ^B_max for each species and the regression slope coefficients were very similar for three of the species.     

Effect of N, P concentration on growth rate

The total nitrogen, phosphorus, biomass, pH, dissolved oxygen in and temperatures of three eutrophic waters were investigated in the rapid-growth season of phytoplankton (July-October). Chloromonas rosae was cultivated in water samples from three eutrophic waters and diluted water samples from Lake Donghu to determine the effect of N and P concentrations on the growth rate. The relationship between the biomass and the N and P concentrations, analyzed by regression, showed that phosphorus was the limiting factor for algae growth in eutrophic water. The relationship between the growth rate and the P concentration can be described with the regression equation y=0.0806ln(x) 0.4658, (R²=0.889). The growth rate increased linearly with the increase of P concentration when it was below 0.05 mg/L. It increased less when the P concentration was above 0.05 mg/L, and was almost unchanged when the P concentration exceeded 0.2mg/L. The P concentration corresponding to the growth rate “0” (deduced from the regression equation) was 0.003mg/L, close to the minimal P concentration of poorly nutrient lakes. This indicated that the regression equation was representative. The average values for plankton cellular N and P in the three eutrophic waters were 53% and 85%, respectively. To evaluate the levels of eutrophy, N and P, both in the water and in the plants, must be considered. The biomass of phytoplankton is controlled by concentrations of both dissolved and cellular N and P. The following linear regression equations describe the relationship between biomass and N: y=10.687x-7.8304, (R²=0.950), and between biomass and P, y=122.11x-12.069, (R²=0.991). They exemplify the absolute and relative aspects of growth-limiting factors with Redfield values. We conclude that the only way to prevent eutrophication is to maintain a balance between the input and output of nutrients and to remove excessive dissolved N and P in the water.     

Effect of N, P concentration on growth rate

The total nitrogen, phosphorus, biomass, pH, dissolved oxygen in and temperatures of three eutrophic waters were investigated in the rapid-growth season of phytoplankton (July-October). Chloromonas rosae was cultivated in water samples from three eutrophic waters and diluted water samples from Lake Donghu to determine the effect of N and P concentrations on the growth rate. The relationship between the biomass and the N and P concentrations, analyzed by regression, showed that phosphorus was the limiting factor for algae growth in eutrophic water. The relationship between the growth rate and the P concentration can be described with the regression equation y=0.0806ln(x)+0.4658, (R²=0.889). The growth rate increased linearly with the increase of P concentration when it was below 0.05 mg/L. It increased less when the P concentration was above 0.05 mg/L, and was almost unchanged when the P concentration exceeded 0.2mg/L. The P concentration corresponding to the growth rate “0” (deduced from the regression equation) was 0.003mg/L, close to the minimal P concentration of poorly nutrient lakes. This indicated that the regression equation was representative. The average values for plankton cellular N and P in the three eutrophic waters were 53% and 85%, respectively. To evaluate the levels of eutrophy, N and P, both in the water and in the plants, must be considered. The biomass of phytoplankton is controlled by concentrations of both dissolved and cellular N and P. The following linear regression equations describe the relationship between biomass and N: y=10.687x?7.8304, (R²=0.950), and between biomass and P, y=122.11x?12.069, (R²=0.991). They exemplify the absolute and relative aspects of growth-limiting factors with Redfield values. We conclude that the only way to prevent eutrophication is to maintain a balance between the input and output of nutrients and to remove excessive dissolved N and P in the water.     

Kinetics of nitrate uptake by freshwater algae

The kinetics of nitrate (NO₃ ^–) uptake, the maximum uptake velocity (V_m) and the half-saturation constant (K_s), were determined for 18 species of batch-cultured freshwater algae grown without nitrogen limitation. Values of K_s ranged from 0.25 to 6.94 µM l^–1 Chlorella pyrenoidosa Chick, and Navicula pelliculosa (Breb.) Hilse, respectively. Values of V_m ranged from 0.51 to 5.07 µM l^–1 h^–1 for Anabaena A7214 and Nitzschia W-32 O'Kelley, respectively. The mean positive values of K_s for Chlorophyta, Cyanophyta and Chrysophyta were 1.89, 3.67 and 4.07 µM l^–1, respectively. The mean values of V_m for the same phyla were 1.61, 1.02 and 2.97 µM l^–1 h^–1 10⁵ cells^–1, respectively. The ranges of these kinetic parameters encompass values of kinetic parameters for marine and freshwater species in batch culture, for freshwater algae grown in N-limited chemostats and for natural populations of freshwater phytoplankton. Thus, in spite of variability between species, uptake parameters for both marine and freshwater algae are identical.     

Acclimation of respiration to temperature and CO2 in seedlings of boreal tree species in relation to plant size and relative growth rate

The role of acclimation of dark respiration to temperature and CO₂ concentration and its relationship to growth are critical in determining plant response to predicted global change. We explored temperature acclimation of respiration in seedlings of tree species of the North American boreal forest. Populus tremuloides, Betula papyrifera, Larix laricina, Pinus banksiana, and Picea mariana plants were grown from seed in controlled-environments at current and elevated concentrations of CO₂ (370 and 580 μmol mol^–1) in combination with three temperature treatments of 18/12, 24/18, and 30/24 °C (light/dark period). Specific respiration rates of roots and shoots acclimated to temperature, damping increases in rates across growth-temperature environments compared to short-term temperature responses. Compared at a standard temperature, root and shoot respiration rates were, on average, 40% lower in plants grown at the highest compared to lowest growth temperature. Broad-leaved species had a lower degree of temperature acclimation of respiration than did the conifers. Among species and treatment combinations, rates of respiration were linearly related to size and relative growth rate, and relationships were comparable among growth environments. Specific respiration rates and whole-plant respiratory CO₂ efflux as a proportion of daily net CO₂ uptake increased at higher growth temperatures, but were minimally affected by CO₂ concentration. Whole-plant specific respiration rates were two to three times higher in broad-leaved than coniferous species. However, compared to faster-growing broad-leaved species, slower-growing conifers lost a larger proportion of net daily CO₂ uptake as respiratory CO₂ efflux, especially in roots. Interspecific variation in acclimation responses of dark respiration to temperature is more important than acclimation of respiration to CO₂ enrichment in modifying tree seedling growth responses to projected increases in CO₂ concentration and temperature.     

Relative growth rate in relation to physiological and morphological traits for northern hardwood tree seedlings: species,light environment and ontogenetic considerations

The influence of ontogeny, light environment and species on relationships of relative growth rate (RGR) to physiological and morphological traits were examined for first-year northern hardwood tree seedlings. Three Betulaceae species (Betula papyrifera, Betula alleghaniensis and Ostrya virginiana) were grown in high and low light and Quercus rubra and Acer saccharum were grown only in high light. Plant traits were determined at four ages: 41, 62, 83 and 104 days after germination. In high light (610 mol m^–2 s^–1 PPFD), across species and ages, RGR was positively related to the proportion of the plant in leaves (leaf weight ratio, LWR; leaf area ratio, LAR), in situ rates of average canopy net photosynthesis (A) per unit mass (A_mass) and per unit area (A_area), and rates of leaf, stem and root respiration. In low light (127 mol m^–2 s^–1 PPFD), RGR was not correlated with A_mass and A_area whereas RGR was positively correlated with LAR, LWR, and rates of root and stem respiration. RGR was negatively correlated with leaf mass per area in both high and low light. Across light levels, relationships of CO₂ exchange and morphological characteristics with RGR were generally weaker than within light environments. Moreover, relationships were weaker for plant parameters containing a leaf area component (leaf mass per area, LAR and A_area), than those that were solely mass-based (respiration rates, LWR and A_mass). Across light environments, parameters incorporating the proportion of the plant in leaves and rates of photosynthesis explained a greater amount of variation in RGR (e.g. LWR^*A_mass, R²=0.64) than did any single parameter related to whole-plant carbon gain. RGR generally declined with age and mass, which were used as scalars of ontogeny. LWR (and LAR) also declined for seven of the eight species-light treatments and A declined in four of the five species in high light. Decreasing LWR and A with ontogeny may have been partially responsible for decreasing RGR. Declines in RGR were not due to increased respiration resulting from an increase in the proportion of solely respiring tissue (roots and stems). In general, although LWR declined with ontogeny, specific rates of leaf, stem, and root respiration also decreased. The net result was that whole-plant respiration rates per unit leaf mass decreased for all eight treatments. Identifying the major determinants of variation in growth (e.g. LWR^*A_mass) across light environments, species and ontogeny contributes to the establishment of a framework for exploring limits to productivity and the nature of ecological success as measured by growth. The generality of these relationships both across the sources of variation we explored here and across other sources of variation in RGR needs further study.     

Acclimation of thermotolerant algae to light and temperature interaction1

Here, we explore the responses of photosynthesis and related cellular processes in the thermotolerant microalga Micractinium sp. acclimated to limiting and saturating irradiances combined with elevated temperatures, using a novel computer-controlled multi-sensor system. This system allows for the monitoring of online values of oxygen exchange during photosynthesis and respiration with high accuracy. Micractinium sp. cells showed maximum growth and net oxygen production rates under the optimal temperature of 25°C regardless of the light acclimation conditions. Our results show that the upper thermal threshold for Micractinium sp. photosynthesis and growth ranges between 35°C and 40°C. This microalga exhibited stable photosynthetic efficiency and effective non-photochemical quenching (NPQ) under saturating light, and was more susceptible to temperature change when acclimated to limiting light levels. These results demonstrate that the acclimation of thermotolerant microalgae to saturating light helps to enhance the thermal tolerance of PSII. This feature results from enhanced heat stability of PSII photochemistry and oxygen evolution.