Photosynthetic productivity of conical helical tubular photobioreactor incorporating Chlorella sorokiniana under field conditions.

The photosynthetic performance of a conical, helical tubular photobioreactor (HTP) incorporating Chlorella sorokiniana was investigated under conditions of high temperature and light intensity during midsummer in an outdoor environment. Although the culture medium temperature exceeded 40 degrees C for approximately 5 h each day, peaking at 47.5 degrees C under sunny conditions, a photosynthetic productivity of 30.0 g x m(-2) (installation area) x day(-1) and a photosynthetic efficiency of 8.66% [photosynthetically active radiation (PAR), 400-700 nm] were achieved. A maximum photosynthetic productivity of 33.2 g x m(-2) x day(-1) was achieved on a sunny day, when solar energy input was also maximal (11.5 MJ x m(-2) x day(-1) [PAR]). On the other hand, a maximum photosynthetic efficiency of 9.54% was obtained on a day that was rainy in the morning and cloudy in the afternoon, and there was relatively little solar energy input. The average daily photosynthetic efficiency over the two culture periods (August 4 to 7 and August 10 to 13, 1999) was 7.25%. Thus, a high level of photosynthetic performance was achieved in the conical HTP incorporating Chlorella sorokiniana despite the fact that culture medium temperature was not controlled. The use of Chlorella sorokiniana in the conical HTP should be a good choice to produce microalgal biomass during the summer under field conditions.     

Photosynthetic performance of a helical tubular photobioreactor incorporating the cyanobacterium spirulina platensis

The photosynthetic performance of a helical tubular photobioreactor ("Biocoil"), incorporating the filamentous cyanobacterium Spirulina platensis, was investigated. The photobioreactor was constructed in a cylindrical shape (0.9 m high) with a 0.25-m(2)basal area and a photostage comprising 60 m of transparent PVC tubing of 1.6-cm inner diameter (volume = 12.1 L). The inner surface of the cylinder (area = 1.32 m(2)) was illuminated with cool white fluorescent lamps; the energy input of photosynthetically active radiation(PAR, 400 to 700 nm) into the photobioreactor was 2920 kJ per day. An air-lift system ncorporating 4%CO(2) was used to circulate the growth medium in the tubing. The maximum productivity achieved in batch culture was 7.18 g dry biomass per day [0.51 g . d biomass/L . day, or 5.44 g . d biomass/m(2)(inner surface of cylindrical shape)/day] which corresponded to a photosynthetic (PAR) efficiency of 5.45%. The CO(2) was efficiently removed from the gaseous stream; monitoring the CO(2) the outlet and inlet gas streams showed a 70% removal of CO(2) from the inlet gas over an 8-h period with almost maximum growth rate. (c) 1995 John Wiley & Sons, Inc.     

Outdoor helical tubular photobioreactors for microalgal production: modeling of fluid-dynamics and mass transfer and assessment of biomass productivity

The production of the microalga Phaeodactylum tricornutum in an outdoor helical reactor was analyzed. First, fluid dynamics, mass-transfer capability, and mixing of the reactor was evaluated at different superficial gas velocities. Performance of the reactor was controlled by power input per culture volume. A maximum liquid velocity of 0.32 m s(-1) and mass transfer coefficient of 0.006 s(-1) were measured at 3200 W m(-3). A model of the influence of superficial gas velocity on the following reactor parameters was proposed: gas hold-up, induced liquid velocity, and mass transfer coefficient, with the accuracy of the model being demonstrated. Second, the influence of superficial gas velocity on the yield of the culture was evaluated in discontinuous and continuous cultures. Mean daily values of culture parameters, including dissolved oxygen, biomass concentration, chlorophyll fluorescence (F(v)/F(m) ratio), growth rate, biomass productivity, and photosynthetic efficiency, were determined. Different growth curves were measured when the superficial gas velocity was modified-the higher the superficial gas velocity, the higher the yield of the system. In continuous mode, biomass productivity increased by 35%, from 1.02 to 1.38 g L(-1) d(-1), when the superficial gas velocity increased from 0.27 to 0.41 m s(-1). Maximal growth rates of 0.068 h(-1), biomass productivities up to 1.4 g L(-1) d(-1), and photosynthetic efficiency of up to 15% were obtained at the higher superficial gas velocity of 0.41 m s(-1). The fluorescence parameter, F(v)/F(m), which reflects the maximal efficiency of PSII photochemistry, showed that the cultures were stressed at average irradiances within the culture higher than 280 microE m(-2) s(-1) at every superficial gas velocity. For nonstressed cultures, the yield of the system was a function of average irradiance inside the culture, with the superficial gas velocity determining this relationship. When superficial gas velocity was increased, higher growth rates, biomass productivities, and photosynthetic efficiencies were obtained for similar average irradiance values. The higher the superficial gas velocity, the higher the liquid velocity, with this increase enhancing the movement of the cells inside the culture. In this way the efficiency of the cells increased and higher biomass concentrations and productivities were reached for the same solar irradiance.     

Airlift column photobioreactors for Porphyridium sp. culturing: Part II. verification of dynamic growth rate model for reactor performance evaluation

Dynamic growth rate model has been developed to quantify the impact of hydrodynamics on the growth of photosynthetic microorganisms and to predict the photobioreactor performance. Rigorous verification of such reactor models, however, is rare in the literature. In this part of work, verification of a dynamic growth rate model developed in Luo and Al-Dahhan (2004) [Biotech Bioeng 85(4): 382-393] was attempted using the experimental results reported in Part I of this work and results from literature. The irradiance distribution inside the studied reactor was also measured at different optical densities and successfully correlated by the Lambert-Beer Law. When reliable hydrodynamic data were used, the dynamic growth rate model successfully predicted the algae's growth rate obtained in the experiments in both low and high irradiance regime indicating the robustness of this model. The simulation results also indicate the hydrodynamics is significantly different between the real algae culturing system and an air-water system that signifies the importance in using reliable data input for the growth rate model.     

Minimization of carbon losses in pilot-scale outdoor photobioreactors by model-based predictive control

The optimization of carbon use in pilot-scale outdoor tubular photobioreactors is investigated in this study. The behavior of a 0.20-m(3) tubular photobioreactor was studied, with and without algae, by steady-state and pulse dynamic-response analysis experiments. A model of the system was obtained and implemented in a programmable control unit and was used to control the reactor under normal production conditions. Results showed that, using and on-off control, the mean daily CO(2) flow in the reactor was 0.86 g min(-1), 19.7% of this being lost. By using a predictive control algorithm the mean daily CO(2) flow was reduced to 0.74 g min(-1), with losses being reduced to 15.6%. In this case, pH tracking was not adequate, especially at the beginning and end of the daylight period, because the variation in solar irradiance was not considered. Taking solar irradiance into account resulted in better performance, with mean daily CO(2) flow reduced to 0.70 g min(-1), and carbon losses reduced to 5.5%. pH tracking was improved and valve actuation was reduced. Improvement of pH control reduced pH gradients in the culture, which increased the photosynthesis rate and biomass productivity of the system. Biomass productivity increased from 1.28 to 1.48 g L(-1) day-(1) when on-off control was replaced by model-based predictive control plus solar irradiance effect mode. Implementation of this methodology in outdoor photobioreactors can increase productivity by 15% and reduce the cost of producing biomass by >6%. Clearly, application of effective control techniques, such as model-based predictive control (MPC), must be considered when developing these processes.     

Continuous production of diatom Entomoneis sp. in mechanically stirred tank and flat-panel airlift photobioreactors

Continuous production of diatom Entomonies sp. was performed in mechanically stirred tank and flat-panel airlift photobioreactors (FPAP). The maximum specific growth rate of diatom from the batch experiment was 0.98 d^?1. A series of dilution rate and macronutrient concentration adjustments were performed in a stirred tank photobioreactor and found that the dilution rate ranged from 0.7 to 0.8 d^?1 and modified F/2 growth media containing nitrate at 3.09?mg N/L, phosphate at 2.24?mg P/L, and silicate at 11.91?mg Si/L yielded the maximum cell number density. Finally, the continuous cultivation of Entomonies sp. was conducted in FPAP using the optimal conditions determined earlier, resulting in the maximum cell number density of 19.69?×?10⁴ cells/mL, which was approximately 47 and 73% increase from the result using the stirred tank photobioreactor fed with modified and standard F/2 growth media, respectively.     

Evaluation of photobioreactor heat balance for predicting changes in culture medium temperature due to light irradiation

Microalgal photosynthesis requires appropriate culture medium temperatures to achieve high photosynthetic performance and to maintain production of a high-quality biomass product. Enclosed systems, such as our conical, helical tubular photobioreactor (HTP), can accomplish high photosynthetic efficiency and the small amount of culture medium used by these systems means that the culture medium temperature may be effectively controlled. On the other hand, because a high ratio of surface area to culture medium volume leads to rapid heating under the illumination condition and substantial heat loss at night, maintaining a suitable culture medium temperature is necessary to achieve efficient, commercially practical biomass production. In order to predict changes in the culture medium temperature caused by changes in solar irradiance and ambient temperature, it is necessary to understand the heat balance within the photobioreactor. We therefore investigated the heat balance in three major parts (photostage, degasser, and helical heat exchanger) of our conical HTP, analyzed the time-dependent changes in medium temperature at various room temperatures and radiant energy inputs, and predicted changes in the culture medium temperature based on the characteristics of heat transfer among the three parts. Using this model, the predicted changes in culture medium temperature were very similar to the changes observed experimentally in the laboratory and under field conditions. This means that by calculating the time-dependent changes in the culture medium temperature, based on measurements of solar energy input and ambient temperature, we should be able to estimate the energy required to maintain the culture medium temperature within a range where photosynthetic performance of microalgae is high.     

钝顶螺旋藻在不同光照条件下的放氧特性

钝顶螺旋藻在持续照光和中等频率 (0.01~20 Hz) 的光/暗交替照光下的放氧特性对光生物反应器的设计和操作具有重要意义。构建了一套可实现光/暗交替的光生物反应器系统对此进行研究,结果显示：根据与放氧速率的关系,可以将光强分为4个区：光限制区 (0~335 μmol/(m2·s)),过渡区 (335~875 μmol/(m2·s)),光饱和区 (875~2 775 μmol/(m2·s)) 以及光抑制区 (2 775 μmol/(m2·s)以上)。提高光/暗频率能否提高微藻光合速率取决于所采用的光强和     

Photosynthetic acclimation of maize to growth under elevated levels of carbon dioxide

The effects of elevated CO₂ concentrations on the photochemistry, biochemistry and physiology of C₄ photosynthesis were studied in maize (Zea mays L.). Plants were grown at ambient (350 μL L⁻¹) or ca. 3 times ambient (1100 μL L⁻¹) CO₂ levels under high light conditions in a greenhouse for 30 d. Relative to plants grown at ambient CO₂ levels, plants grown under elevated CO₂ accumulated ca. 20% more biomass and 23% more leaf area. When measured at the CO₂ concentration of growth, mature leaves of high-CO₂-grown plants had higher light-saturated rates of photosynthesis (ca. 15%), lower stomatal conductance (71%), higher water-use efficiency (225%) and higher dark respiration rates (100%). High-CO₂-grown plants had lower carboxylation efficiencies (23%), measured under limiting CO₂, and lower leaf protein contents (22%). Activities of a number of C₃ and C₄ cycle enzymes decreased on a leaf-area basis in the high-CO₂-grown plants by 5–30%, with NADP-malate dehydrogenase exhibiting the greatest decrease. In contrast, activities of fructose 1,6-bisphosphatase and ADP-glucose pyrophosphorylase increased significantly under elevated CO₂ condition (8% and 36%, respectively). These data show that the C₄ plant maize may benefit from elevated CO₂ through acclimation in the capacities of certain photosynthetic enzymes. The increased capacity to synthesize sucrose and starch, and to utilize these end-products of photosynthesis to produce extra energy by respiration, may contribute to the enhanced growth of maize under elevated CO₂. Received: 30 April 1999 / Accepted: 17 June 1999     

Carbon dioxide fixation by Chlorella kessleri, C. vulgaris, Scenedesmus obliquus and Spirulina sp. cultivated in flasks and vertical tubular photobioreactors

CO₂ at different concentrations were added to cultures of the eukaryotic microalgae, Chlorella kessleri, C. vulgaris and Scenedesmus obliquus, and the prokaryotic cyanobacterium, Spirulina sp., growing in flasks and in a photobioreactor. In each case, the best kinetics and carbon fixation rate were with a vertical tubular photobioreactor. Overall, Spirulina sp. had the highest rates. Spirulina sp., Sc. obliquus and C. vulgaris could grow with up to 18% CO₂.     

Heterotrophic production of Chlorella sp. TISTR 8990—biomass growth and composition under various production conditions

The green microalga Chlorella sp. TISTR 8990 was grown heterotrophically in the dark using various concentrations of a basal glucose medium with a carbon‐to‐nitrogen mass ratio of 29:1. The final biomass concentration and the rate of growth were highest in the fivefold concentrated basal glucose medium (25 g L^?1 glucose, 2.5 g L^?1 KNO₃) in batch operations. Improving oxygen transfer in the culture by increasing the agitation rate and decreasing the culture volume in 500‐mL shake flasks improved growth and glucose utilization. A maximum biomass concentration of nearly 12 g L^?1 was obtained within 4 days at 300 rpm, 30°C, with a glucose utilization of nearly 76% in batch culture. The total fatty acid (TFA) content of the biomass and the TFA productivity were 102 mg g^?1 and 305 mg L^?1 day^?1, respectively. A repeated fed‐batch culture with four cycles of feeding with the fivefold concentrated medium in a 3‐L bioreactor was evaluated for biomass production. The total culture period was 11 days. A maximum biomass concentration of nearly 26 g L^?1 was obtained with a TFA productivity of 223 mg L^?1 day^?1. The final biomass contained (w/w) 13.5% lipids, 20.8% protein and 17.2% starch. Of the fatty acids produced, 52% (w/w) were saturated, 41% were monounsaturated and 7% were polyunsaturated (PUFA). A low content of PUFA in TFA feedstock is required for producing high quality biodiesel. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1589–1600, 2017     

Field productivity of a CAM plant, Agave salmiana, estimated using daily acidity changes under various environmental conditions

Nocturnal acidity increases of the Crassulaceae acid metabolism succulent Agave salmiana Otto ex Salm. ssp. crassispina (Trel.) Gentry were determined for various photosynthetically active radiation (PAR) levels in the field and various day/night temperatures and soil water potentials in the laboratory. When a particular factor was optimal for nocturnal acid accumulation, it was assigned an index value of unity. The product of the three indices was termed the environmental productivity index (EPI), which summarizes the effect of PAR, temperature, and water status on nocturnal acid accumulation. A monthly value for EPI was determined using microclimatic conditions at the field site near Salinas de Hidalgo, San Luis Potosf, Mexico. EPI was highly correlated with the number of leaves unfolding monthly from plants in the field (r²= 0.95), where monitoring of such leaf unfolding is a non-destructive technique for assessing plant productivity. By using the measured leaf area index for four groups of A. salmiana and a relationship between acid accumulation and net CO₂ up-take, the EPI acidity data were converted to dry weight gain per unit ground area. This measure of productivity closely agreed with the 1.05 kg m⁻² year⁻¹ determined by conventional harvesting techniques. The productivity is also in agreement with studies on other desert agaves, but about 10-fold higher than that generally considered for desert ecosystems.     

Studies of Elodea nuttallii grown under photorespiratory conditions. I. Photosynthetic characteristics

Abstract. The photosynthetic characteristics of Elodea nuttallii grown in wastewater in continuous flow reactors in a greenhouse were investigated. The diurnal changes in dissolved inorganic carbon (DIC), dissolved oxygen (DO) and pH were monitored. Photosynthesis removed both CO₂(aq) and HCO₃^? from the reactors. A stoichiometry of 1.19:1 was observed between HCO₃^? removal during photosynthesis and OH^? production during photosynthesis, consistent with theories regarding direct bicarbonate utilization. In laboratory experiments, the light compensation points (г_PPFD) were similar (31–35μmol m^?2 s^?1) to reported values for other macrophytes; however, the light saturation level was high (1100μmol m^?2 s^?1) and similar to values reported for aerial portions Of heterophyllous macrophytes. The kinetics of photosynthetic oxygen evolution (K_m (CO₂) = 96mmol m^?3; V_max= 133mmol g^?1 Chl h^?1) and the CO₂ compensation point (г= 44cm³ m^?3) suggested an adaptive, low photorespiratory state in response to low carbon concentrations. Photosynthetic V_max values were slightly, but significantly higher (P 0.001) at pH 8.0 compared to pH 4.5. While CO₂ utilization at pH 8 could account for most of the observed phototsynthetic rates, an HCO₃^? component was present, suggesting two separate transport systems for HCO₃^? and CO₂(aq) in E. nuttallii. The activity of RUBISCO (160.3 mmol g^?1 Chl h^?1 was one of the highest reported values for aquatic macrophytes. Compared to RUBISCO, we observed lower activities of the β-carboxylating enzymes phopho enolpyruvate carboyxlase (PEPcase), 24.1 mmol g^?1 Chl h^?1; phosphor enol pyruvate carboxykinase (PEPCKase), 14 mmol g^?1 Chl h^?1. This suggests that the potential light-independent fixation of carbon in E. nuttallii was much less than RUBISCO-dependent fixation. The RUBISCO/PEPcase ratio was 6.6, indicating that E. nuttallii was similar to Myriophyllum sp. in possessing a physiological adaptation to low CO₂ levels which is hypothesized to include carbonic anhydrase (CA) and an active transport system for HCO₃^?. CA levels were surprisingly low in E. nuttallii (14.2 EUmg Chl^?).     

灌溉条件下藏北紫花针茅光合特性及其对温度和CO2浓度的短期响应

利用LI-6400便携式光合作用测定仪, 测定不同灌溉措施下紫花针茅(Stipa purpurea)的光合特性对CO₂浓度和温度的响应, 探讨了土壤水分、温度和CO₂浓度升高对藏北高寒草地紫花针茅光合作用的影响。结果表明: 1)紫花针茅各项光合特性参数对CO₂浓度、温度和土壤水分的变化响应显著, 并表现出明显的交互作用; 2) CO₂浓度升高促进光合速率, 但CO₂浓度过高时光合速率反而下降; 温度升高抑制光合速率, 土壤水分增加对高温条件下的光合作用具有补偿作用; 土壤水分增加促进紫花针茅光合速率的升高; 3)随着CO₂浓度的升高, 胞间CO₂浓度逐渐增大, 蒸腾速率降低, 水分利用效率升高, 气孔导度逐渐减小, 且温度升高加剧气孔导度下降的程度。各光合参数在不同温度水平和土壤水分下表现不同: 气孔导度在20 ℃时达到最大值, 且土壤水分增加利于气孔导度的增大; 温度上升抑制了胞间CO₂浓度, 且在土壤水分充足的条件下更显著; 蒸腾速率随着温度的上升而加快, 蒸腾速率与土壤水分的正相关关系明显; 叶片饱和水汽压亏缺与温度成正比, 充足的土壤水分会适当降低饱和水汽压亏缺; 水分利用效率随着温度上升和土壤水分增多而减小。不同土壤水分条件下光合参数对温度的响应结果表明, 土壤水分的增加对较高温度下光合及其生理参数与温度的关系具有一定的补偿作用。     

Photosynthetic competence of plantlets grown in vitro. An automated system for measurement of photosynthesis in vitro

An aseptic gas exchange and hydroponic system (AGEHS) has been developed in an attempt for characterization of physiological requirements for photoautotrophic growth in vitro and alleviation of the needs for ex vitro acclimatization. The AGEHS monitors and controls several parameters relevant to plant growth. Shootlets of Chrysanthemum × morifolium Ramat. cv. Envy were treated with flow of air or CO₂-enriched air under controlled relative humidity, elevated photosynthetic photon flux density (PPFD) and hydroponic irrigation. After 15 days of treatment, plantlets gained more than 3 times as much dry weight as those from a conventional culture tube treatment. This study shows that it is possible to favour photoautotrophic growth when elevated PPFD, enhanced air-exchange and hydroponic medium flow are provided concurrently. This enhancement is achievable through careful increments of light quanta, balanced with increments of humidified air flow and/or CO₂ content in air which seem to be necessary to avoid potential photoinhibition and premature water exhaustion from gelled media.     

Orthophosphate influx and efflux rates of Chlorella fusca measured in a continuous turbidostat culture with 32P under various conditions

The main objective of the experiments with Chlorella fusca strain 211-8b was to measure, with adequate time resolution, the unidirectional influx rates of phosphate into non-phosphate-starved algae under different steady state conditions (light, temperature, 3-phosphoglycerate influence) or following the addition of several photosynthesis and phosphate transport inhibitors (phenylmercuric acetate, p-chloromercuribenzoate, arsenate). the algae were cultivated in a phosphate rich medium in a continuous turbidostat culture. The phosphate exchange experiments with carrier-free ³²PO ₄ ^3- were performed directly in the continuous culture. The sampling intervals after the tracer addition were 15 s.For a continuous steady state culture grown in the light (25° C) the unidirectional influx rate measured with ³²P is 260 times higher than the net uptake rate (=influx minus efflux rate) calculated from the mass balance using the data of this culture. In all experiments, except the control experiment with trichloroacetic acid killed cells, the specific activity of the intracellular inorganic orthophosphate compartment oscillates around a constant mean value which never reaches the specific activity of the nutrient medium within the duration of the short-term experiments (7.5 min). The inhibitors strongly affect the characteristics of the oscillations. The unidirectional influx rates are constant. Oscillating flushing rates with unlabelled phosphate from a storage compartment have been postulates to explain the oscillations. Oscillating rates from the individual cells are apparently synchronized by an unknown mechanism.     

Responses of Photosynthetic and Defence Systems to High Temperature Stress in Quercus suber L Seedlings Grown under Elevated CO2

Abstract: Growth in elevated CO₂ led to an increase in biomass production per plant as a result of enhanced carbon uptake and lower rates of respiration, compared to ambient CO₂-grown plants. No down-regulation of photosynthesis was found after six months of growth under elevated CO₂. Photosynthetic rates at 15°C or 35 °C were also higher in elevated than in ambient CO₂-grown plants, when measured at their respective CO₂ growth condition. Stomata of elevated CO₂-grown plants were less responsive to temperature as compared to ambient CO₂ plants. The after effect of a heat-shock treatment (4 h at 45 °C in a chamber with 80% of relative humidity and 800–1000 tmol m^-2 s^-1 photon flux density) on A_max was less in elevated than in ambient CO₂-grown plants. At the photochemical level, the negative effect of the heat-shock treatment was slightly more pronounced in ambient than in elevated CO₂-grown plants. A greater tolerance to oxidative stress caused by high temperatures in elevated CO₂-grown plants, in comparison to ambient CO₂ plants, is suggested by the increase in superoxide dismutase activity, after 1 h at 45 °C, as well as its relatively high activity after 2 and 4 h of the heat shock in the elevated CO₂-grown plants in contrast with the decrease to residual levels of superoxide dismutase activity in ambient CO₂-grown plants immediately after 1 h at 45 °C. The observed increase in catalase after 1 h at 45 °C in both ambient and elevated CO₂-grown plants, can be ascribed to the higher rates of photorespiration and respiration under this high temperature.     

干旱胁迫下藜的光合特性研究

通过人工控制水分模拟干旱来研究生长期的藜对干旱胁迫的生理生化反应,以期望为干旱农业的高效生产提供理论依据。以盆栽的藜为材料,用称重控制浇水的方法,研究了干旱胁迫对藜叶片的光合特性。结果表明：干旱胁迫下藜的光合日变化呈双峰型,有“午休”现象（13:00）且受气孔限制;最大净光合速率出现在上午8:00。与正常条件下生长的藜相比,干旱胁迫下藜的光饱和点(LSP)、最大净光合速率(Pn)、表观量子效率(AQY)、二氧化碳饱和点(CSP)和羧化效率(CE)均降低,分别为1 200 μmolphoton·m^-2·s^-1、8.01 μmol CO₂·m^-2·s^-1、0.016 1 μmol CO₂·mol^-1 photons、1 200 μmol CO₂·mol^-1、0.017 6 μmol CO₂·m^-2·s^-1;光补偿点(LCP)、二氧化碳补偿点(CCP)升高,分别达到44.88 μmol photon·m^-2·s^-1、和46 μmol CO₂·mol^-1,干旱使藜的光合能力下降。干旱胁迫下藜的光合能力虽有所下降,但与其它C3植物相比仍具有较强的CO₂同化能力。藜是一种耐旱力较强的植物。     

Photosynthetic characteristics of leaves of male-sterile and hermaphrodite sex types of Plantago lanceolata grown under conditions of contrasting nitrogen and light availabilities

Plantago lanceolata is a gynodioecious species: In natural populations male steriles (MS) coexist with hermaphrodites (H). Since male steriles have a reproductive disadvantage, without any compensation for their loss in male function by an increase in female function, they are expected to disappear from the population. In this study we investigated the possibility that differences in ecologically important photosynthetic characteristics, between MS and H lines of P. lanceolata. play a role in maintaining gynodioecy. One MS line and two H lines were grown under conditions of high N and light availability, as well as under either N limitation or light limitation, to investigate whether the sex types respond differently to environmental constraints. Photosynthetic light-response and CO₂-response curves were made, together with leaf organic N and chlorophyll determinations. There were only few small differences between the lines and since the MS line did not differ in any of the determined photosynthetic characteristics from either H line, it is unlikely that these differences are involved in maintaining male sterility in populations of P. lanceolata. The low-light-grown plants showed a high degree of acclimation as shown by a two-fold higher leaf area to leaf weight ratio (SLA), a two-fold higher investment of N in light harvesting, and higher net photosynthetic rates under low-light conditions, as compared to the high-light-grown plants. The low-N-grown plants used their organic N more efficiently in photosynthesis compared to plants grown at an optimal N supply. This was mainly due to the N-limited plants having leaves with a lower organic N content and thus lower photosynthetic capacities. To a lesser extent it was due to the higher value for the curvature factor of the light-response curves of the N-limited plants, to their decreased rates of photorespiration and possibly to their relatively higher allocation of organic N to photosynthetic functions.