Highest Pmax Research Articles

Experimental and numerical study on vented H2/air explosion in an obstructed duct: Effects of hydrogen concentration and vent size

In this study, the effects of hydrogen concentration (C) and vent size (AV) on the vented H2/air explosion in an obstructed duct were investigated using experimental methods and FLACS simulation software at an initial pressure and temperature of 101 kPa and 291K, respectively. A vent coefficient KA is chosen to represent AV to illustrate its influence on the explosion venting of H2/air. The results demonstrate that the maximum internal overpressure (pmax) and the maximum external overpressure (pext) increase and then decrease with C increasing from 10% to 60%. The highest pmax and pext are reached at C = 35% in experiments, but achieved at C = 30% in simulations because incomplete chemical reactions were not taken into account. In the tests with C <50%, the flame evolution inside the duct includes five stages: spherical flame, elliptical flame, finger-shaped flame, near-planar flame, and tulip-shaped flame. No tulip flame is observed for C ≥50%. FLACS can simulate the flame structure evolution for various C, but it cannot accurately simulate the flame propagation speed. FLACS overestimates the flame propagation speed in the tests with C ≤25%, but underestimates the flame propagation speed for C ≥35%. Under the initial condition of C = 15%, the above-mentioned five stages of flame evolution can be simulated by FLACS for KA ≤0.4; however, neither the near-plane nor tulip flame is observed in simulations for KA >0.4.

Biomechanical effects of different miniplate use on bone and miniplate systems in multiple mandible fracture: A finite element study

The aim of this study is to evaluate the biomechanical efficiency of different miniplates in the treatment of multiple mandibula fractures. Mandible, miniplates, and screws were modeled using the Solid Works v2015 (Dassault Systèmes, France) program, Subsequently two fracture lines were created on the right parasymphysis and angulus mandible. Models were divided into two main groups according to the plates used in the anterior fracture line: group A, 2 piece 4-hole-bar-I plate, and group B, ellipse plate. Each group was divided into five subgroups according to the plates used in the posterior fracture line (I, X, G, 3D, E) and 10 study models were created in total. Under three different biting forces (anterior, right, left), maximum von-Mises stresses seen on miniplates/screws, and Pmax/Pmin stresses seen in the cortically/cancellous bone were analyzed using the Ansys 16.2 software (ANSYS, Inc., USA). Data was visualized using a color distribution scale and interpreted. The highest von-Mises stress, seen in plates, was found in the I plate (353.82 MPa) at the angulus region of model A1. The highest Pmax and Pmin stresses, revealed in cortical bone, were found respectively in model A1 (181.63 MPa) and model B2 (115.01 MPa). The ideal results on plates were seen in models B3 and B5, in which E plates were used in the parasymphysis and G/E plates were used in the angulus region. Grid and ellipse plates provide successful results and plate geometry is more critical than number in terms of stress distribution.

Photosynthetic responses of switchgrass to light and CO2 under different precipitation treatments

AbstractSwitchgrass (Panicum virgatum L.) is a prominent bioenergy crop with robust resilience to environmental stresses. However, our knowledge regarding how precipitation changes affect switchgrass photosynthesis and its responses to light and CO2 remains limited. To address this knowledge gap, we conducted a field precipitation experiment with five different treatments, including −50%, −33%, 0%, +33%, and +50% of ambient precipitation. To determine the responses of leaf photosynthesis to CO2 concentration and light, we measured leaf net photosynthesis of switchgrass under different CO2 concentrations and light levels in 2020 and 2021 for each of the five precipitation treatments. We first evaluated four light and CO2 response models (i.e., rectangular hyperbola model, nonrectangular hyperbola model, exponential model, and the modified rectangular hyperbola model) using the measurements in the ambient precipitation treatment. Based on the fitting criteria, we selected the nonrectangular hyperbola model as the optimal model and applied it to all precipitation treatments, and estimated model parameters. Overall, the model fit field measurements well for the light and CO2 response curves. Precipitation change did not influence the maximum net photosynthetic rate (Pmax) but influenced other model parameters including quantum yield (α), convexity (θ), dark respiration (Rd), light compensation point (LCP), and saturated light point (LSP). Specifically, the mean Pmax of five precipitation treatments was 17.6 μmol CO2 m−2 s−1, and the ambient treatment tended to have a higher Pmax. The +33% treatment had the highest α, and the ambient treatment had lower θ and LCP, higher Rd, and relatively lower LSP. Furthermore, precipitation significantly influenced all model parameters of CO2 response. The ambient treatment had the highest Pmax, largest α, and lowest θ, Rd, and CO2 compensation point LCP. Overall, this study improved our understanding of how switchgrass leaf photosynthesis responds to diverse environmental factors, providing valuable insights for accurately modeling switchgrass ecophysiology and productivity.

Dust Explosibility and Severity of Bayan and Tanito Coal

AbstractThe assessment of the explosibility and severity characteristics of Bayan coal and Tanito coal was investigated over various concentrations in a 20 L Siwek spherical explosion chamber. The coals tested in this study were also compared with other organic dusts such as palm‐based soap noodle, tea powder, black rice, and rice flour, which were tested using the same explosion chamber and procedures. The severity and explosibility of the coals increase as their concentration increases. The Pmax of Bayan coal (10.15 bar) is higher than that of Tanito coal (7.35 bar). The Kst of Bayan coal (48.04 bar m s−1) is also higher than that of Tanito coal (16.83 bar m s−1). Among all the dusts studied using the same chamber and procedures, palm‐based soap noodle has the highest Pmax at 16 bar, while tea powder has the lowest Pmax at 6.35 bar. The results show that the explosibility and severity of the coals increase as the concentrations increase, and the moisture content, coal ranking, and different types of organic dust have a significant influence on the severity characteristics of dust explosions.

Effect of lignocellulosic biomass components on the extracellular electron transfer of biochar-based microbe-electrode in microbial electrochemical systems

Biomass-derived carbon-based electrodes with good biocompatibility, sustainability, and low cost are competitive in microbial electrochemical systems. Unfortunately, biomass composition is complex, and biochar performance is dependent on the kind of biomass, making quantitative function control difficult. Three-dimensional (3D) lignocellulosic carbon-based electrodes were generated in this study by varying the ratios of three natural biopolymers (cellulose, lignin, and hemicellulose). The biopolymer contents significantly impacted the material's physicochemical and electrochemical properties. Only the proper ratio of these natural polymers can ensure the 3D structure's integrity and mechanical strength after carbonization. The greater the cellulose content and the lower the hemicellulose (xylan) content, the lower the ohmic and charge transfer resistance. The maximum power density (Pmax) of the microbial fuel cells equipped with the biopolymer-based anode ranged between 4.5 and 4.8 W m−2, setting a new record for biocarbon electrodes. The highest Pmax was observed when the cellulose, lignin, and xylan ratios were 1:3:2 (4.80 ± 0.04 W m−2). The Pmax correlates with cellulose content more than lignin and xylan and with material capacitance more than with other parameters. High cellulose content facilitates electron transfer but reduces the capacitance of carbon-based electrodes. The material's electron transfer resistance and capacitance contribute to the opposite of the Pmax. So, the interaction with multiple properties influences the electrode performance. This research revealed the effects of natural biopolymer compositions on electrode performance, which was helpful for quantitatively modifying functional carbon-based materials.

Terrestrial Trentepohlia sp. (Ulvophyceae) from alpine and coastal collection sites show strong desiccation tolerance and broad light and temperature adaptation.

For the present study, we collected the Ulvophyceae species Trentepohlia aurea from limestone rock near Berchtesgaden, Germany, and the closely related taxa T. umbrina from Tilia cordata tree bark and T. jolithus from concrete wall both in Rostock, Germany. Freshly sampled material stained with Auramine O, DIOC6, and FM 1-43 showed an intact physiological status. Cell walls were depicted with calcofluor white and Carbotrace. When subjected to three repeated and controlled cycles of desiccation over silica gel (~ 10% relative humidity) followed by rehydration, T. aurea recovered about 50% of the initial photosynthetic yield of photosystem II (YII). In contrast, T. umbrina and T. jolithus recovered to 100% of the initial YII. HPLC and GC analysis of compatible solutes found highest proportions of erythritol in T. umbrina and mannitol/arabitol in T. jolithus. The lowest total compatible solute concentrations were detected in T. aurea, while the C/N ratio was highest in this species, indicative of nitrogen limitation. The prominent orange to red coloration of all Trentepohlia was due to extremely high carotenoid to Chl a ratio (15.9 in T. jolithus, 7.8 in T. aurea, and 6.6. in T. umbrina). Photosynthetic oxygen production was positive up to ~ 1500µmol photons m-2s-1 with the highest Pmax and alpha values in T. aurea. All strains showed a broad temperature tolerance with optima for gross photosynthesis between 20 and 35°C. The presented data suggest that all investigated Trentepohlia species are well adapted to their terrestrial lifestyle on exposed to sunlight on a vertical substrate with little water holding capacity. Nevertheless, the three Trentepohlia species differed concerning their desiccation tolerance and compatible solute concentrations. The lower compatible solute contents in T. aurea explain the incomplete recovery of YII after rehydration.

Experimental study of the coupling effects of ignition position and nitrogen inerting on vented hydrogen-air deflagrations

In this paper, the flame evolution and pressure dynamics of hydrogen-nitrogen-air explosions with nitrogen addition ratio (χ) ranging from 0 to 40 %, ignited at three different positions (“central”, “back” or “front” with respect to the vent) in a vented cylindrical vessel, were experimentally studied. Experimental results reveal that the coupling effects of χ and ignition position significantly affect the pressure curves and flame behavior within and outside the vessel. The higher the χ, the smoother the internal flame captured by a high-speed schlieren system. When χ<30 %, the maximum reduced overpressure (Pmax) at different ignitions decreases with increasing χ, and the central explosion yields the best suppression of Pmax: when χ is increased from 0 to 30 %, Pmax monotonically decreases from 232 kPa to 38 kPa. However, the differences in Pmax among the three ignition positions become negligible when χ ≥ 30 %. The structure of the pressure peaks and the types of oscillations measured near the vent depend on the combinations of ignition location and χ. The formation of a shock wave generated by the external explosion and its effect on the internal pressure-time histories are described. In general, for a given ignition, the maximum external overpressure (Pe-max) decreases with χ is increased. The most pronounced decreasing trend of Pe-max is consistently observed in back explosions when χ ranging from 0 to 40 %. Furthermore, compared to other ignition positions, the highest Pmax is always attained in central-ignition with χ<30 %; while the highest Pe-max is always attained in back-ignition with χ ≤ 30 %; as χ ≥ 10 %, both Pmax and Pe-max recorded at front-ignitions are almost insensitive to χ.

Taxonomic and Morpho-Functional Photosynthetic Patterns of 18 Intertidal Macroalgal Species in the Guangdong–Hong Kong–Macao Greater Bay Area, China

Macroalgae provide food for microbial, meio- and macro-faunal communities in coastal ecosystems, thus mediating nutrient dynamics and functions in these ecosystems. Because of this vital role, it is important to clarify physiological information about macroalgae as it reflects their growth potential in the field. In this study, we examined the biomass, pigment content, and photosynthetic O2 evolution rate versus irradiance curves of 18 macroalgal species from the intertidal zone of the Guangdong–Hong Kong–Macao Greater Bay Area, China, and investigated their photosynthetic patterns in relation to phyla characteristics, morphology, and growth locations. The results showed that green algae had the highest maximum photosynthetic O2 evolution rate (Pmax), light utilization efficiency (α), and dark respiration (Rd) among the three macroalgal phyla; the sheet-like macroalgal species had the highest Pmax, α, and Rd among the four morphological categories. The macroalgal species in the upper intertidal zone showed higher Pmax and α and lower saturation irradiance (EK) and compensation irradiance (EC) than those species in the lower intertidal location. The PCA results showed that the biomass of sheet-like macroalgal species was positively correlated with factor PC1 (50.34%), and that of finely branched species was negatively correlated with factor PC2 (25.17%). In addition, our results indicate that the light absorption and utilization capabilities of macroalgae could determine whether they could dominate the intertidal zone and that their photosynthetic characteristics could be used as a potential indicator of their biomass distribution in the Greater Bay Area.

Effect of palm-based soap noodles dust concentration on dust explosion severity in a spherical vessel

The dust explosion propagation of palm-based soap noodles was experimentally studied in a 20-L spherical vessel. Understanding the effect of concentration on this metric is a prerequisite to characterizing the severity of the explosion. This study focused on the link between concentration and overpressure (Pmax), rate of pressure rise (dP/dt), and deflagration index (KST). The highest Pmax, dP/dt, and KST were recorded at 400 g/m3, corresponding to a class St-2 dust with a strong explosion. The agglomeration process evidently controlled the mass burning rate, which affected the dust explosion propagation. This data can help design preventive measures related to palm-based soap noodle dust explosions.

Investigation of the biomechanical stability of Cfr-PEEK in the treatment of mandibular angulus fractures by finite element analysis

The purpose of this study is to explore the effectiveness of Cfr-PEEK, in the fixation of unfavorable fractures of mandibular angulus by comparing it with the titanium and resorbable biomaterials. 8 different fixation models were created. In the first 4 groups, a single mini plate was applied to the upper edge of the fracture line by the Champy method. In the other 4 groups, an additional plate was placed on the lower edge of the fracture line. In these models, titanium, resorbable and Cfr-PEEK plate/screw systems were investigated by the finite element analysis method. The highest Von Mises stress was observed on the upper plate in the group 5 while the lowest was seen in the lower plate in the group 7. The highest stress values on the screws were observed on the screws placed closer to the fracture line. Considering the stresses on the bone around the screws, the highest Pmax and Pmin values were seen in group 5, and the lowest values were seen in the group 7. The highest displacement was observed in the group 3, while the lowest was observed in the group 5. According to the results it can be said that Cfr-PEEK plate/screw systems may provide advantages by decreasing the stresses on the fixation systems over the titanium plates and providing more stable fixation over the resorbable systems. Cfr-PEEK plates of 2 mm thickness seems to be a potential alternative to 1 mm thick titanium plates.

The Influence of Ethylene Gas Concentration on LDPE/C2H4 Hybrid Explosion Process and its Severity

The influence of ethylene (C2H4) gas concentration on the LDPE dust hybrid explosion in a 20-L spherical vessel, equipped with a chemical ignitor was analysed for the determination of maximum explosion overpressure, Pmax and deflagration index, KG. The LDPEC2H4 dust hybrid explosibility was evaluated based on the Pmax development, measured by the Kistler piezoelectric pressure transducer. The adiabatic flame temperature was calculated based on ideal gas law. It is speculated that the LDPE/C2H4 explosion undergoes three-phase process, starting with the ignition, followed by flame growth and flame regression. The highest Pmax (17.9 bar) and flame temperature (5200 K) was obtained at flame growth phase, recorded at C2H4 concentration of 3 vol/vol%. It was found that the Pmax and flame temperature is dependent on C2H4 concentration. The calculated KG values in a range of 14 – 60 bar.m/ms obtained in this study, suggesting that the LDPE/C2H4 dust hybrid explosion might subject to an extreme explosion characteristic.

Assessment on the severity of low density polyethylene (LDPE)/Ethylene hybrid explosion

The potential explosion for low-density polyethylene (LDPE) dust is greatly increased due to the presence of ethylene gas. Thus, this study was aimed to investigate the explosion severity of polyethylene/ethylene hybrid mixture in a 20-L spherical vessel. The explosion setup is equipped with two chemical ignitors and Kistler piezoelectric pressure sensors to ignite the hybrid mixture and to quantify the propagation of pressure wave during the explosion process respectively. The following hybrid explosion characteristics including the maximum explosion overpressure (Pmax), the maximum rate of pressure rise (dP/dT) and deflagration index (KST) were evaluated. This study concluded that the explosion severity of polyethylene/ethylene hybrid mixture steeply increases as the gas concentration and particle size increase to 15 g/m3 and 125 μm, beyond which the Pmax and dP/dT steadily decrease. The highest Pmax and dP/dt were recorded at 5.5 bar and, 50.5 bar/s with the KST value is 50 bar.m/s indicating the LDPE/ethylene hybrid dust explosion possess a weak explosion.

Simple heat profiles and biogeochemical patterns for analysis the influence on soil microbial community of plastic-greenhouse and open field condition

The diversity of the soil microbial community is remarkably sensitive to different cropping techniques. To examine the effects of cultivation in a greenhouse on the soil microbial activity and diversity, we collected soil samples from vegetable crops continuously grown in a plastic greenhouse (G) and an open field (N). Heat profiling was obtained using microcalorimeter in the presence of different carbon sources. Power time curves were recorded after glucose and ammonium sulphate supplementation. The total heat release QT (Jg-1), maximum heat flow Pmax (μW) and growth rate constant k (h-1) are higher in G treatment group than the in N treatment group. On the other hand, the time (tmax) to reach the peak heat flow is lower in G treatment group compared to N treatment group, as is cell specific heat rate JQ/N (J cell-1). Sample G1 has the highest Pmax (1246.07 μW) and the lowest tmax (11.86 h); in contrast, sample N5 has the lowest Pmax (411.03 μW) and the highest tmax (21.78 h). The microbial community in the soil was estimated from phospholipid fatty acid (PLFA) biomarkers analysis and a viable count, followed by a subsequent determination of the physicochemical parameters. The total average PLFA concentration range is found as 129.76 - 142.54 nmol g-1. Both thermodynamics properties and PLFA concentration was are significantly greater in G1, G2 and G3 treatment than in the other two (N5 &amp; N6) management systems (P &lt; 0.05). Combination of both thermodynamic and PLFA profiling determines that the microbial population is higher in the soil from the greenhouse fertilization than from the open field cultivation. This novel approach could be applicable to a better understanding of (i) the changes in the soil microbial community in green house and open field cultivation practices, and (ii) the relationship between physicochemical properties and soil microbial community’s diversity. Moreover, this would be a notable technique for the decision maker to choose the potential cultivation method for sustainable green-food development program.

On the reflectance of dust in comets

Reflectance of cometary dust is a key parameter used in the characterization of comets. In the literature, the reflectance of single-scattering cometary dust particles is widely assumed to be the same as that of the cometary nucleus. We discuss this assumption and demonstrate its inconsistency with photometric observations of comets, laboratory optical measurements, and numerical simulation of light scattering from single-scattering dust particles and particulate surfaces composed of the same particles. We estimate the reflectance of cometary dust particles using a comprehensive physical model of polarization measured in comets over wide range of phase angle and at different wavelengths in the visible. The model predicts that the reflectance of dust in comets inversely correlates with their maximum of positive polarization Pmax. We find that even the darkest dust particles appearing in comets with the highest Pmax, reflect considerably more incident solar-radiation energy, up to 200%, compared to what is thought for cometary nuclei. We also find that the reflectance retrieved from polarimetry in the visible appears in good quantitative accordance with previous estimations from infrared observations of comets. Our findings suggest that the dust production of comets is currently overestimated and may require revision.

Adsorption and desorption of phosphorus in subtropical soils as affected by management system and mineralogy

Phosphorus added to soil is only partly available to crops because it is sorbed to some extent by various soil components. The aim of this study was to assess the influence of mineralogy and soil management (either conventional tillage, CT, or no-tillage, NT) on the maximum P adsorption capacity (Pmax), remaining P (Prem), and maximum desorbable P (β) in a Rhodic Paleudult, a Rhodic Hapludox and a Humic Hapludox, all from southern Brazil. Pmax was estimated from the Langmuir equation describing the sorption curve for soil samples and β from a first-order kinetic equation describing successive P extraction with an anion-exchange resin following incubation of the soils with an amount of P equivalent to 30% of Pmax (Padded). Pmax and Prem were significantly correlated with the content of iron oxides (mainly in goethite, Gt). Pmax was lower under NT than under CT in the Rhodic Paleudult and Rhodic Hapludox. On the other hand, Prem was lower under CT than under NT, and exhibited significant differences between the 0–5 and 5–10cm layers under NT. Parameter β peaked in the soil with the highest Pmax but the β/Padded ratio was highest in the Rhodic Paleudult, which was the soil with the lowest content in iron oxides. These results suggest that the soil with the highest Pmax and Gt content (viz., the Humic Hapludox) supplies plants with P at a lower rate than the other two despite its high P desorption potential.

Microcalorimetric evaluation of soil microbiological properties under plant residues and dogmatic water gradients in Red soil

A study of 6 months duration was carried out to investigate the effect of water regimes and organic amendments on the soil microbial biomass and microbial population under Red soil collected from Hunan Providence, China. The soil microbial biomass and population were measured with traditional methods and results obtained by conventional methods, corroborated with microcalorimetry. The incorporation of rice (Oryza sativa L.) straw (RS) and green manure (GM), especially at high rates, enhanced the soil microbial activities. We observed that the use of GM exhibited more significant stimulating effects on microbial activities than RS. Similarly, water regimes, 25% (W1) and 200% (W2) of water holding capacity, also had significant effects on microbial activities. Comparing the effects of water levels, we noticed that W2 had a significant negative influence on soil microbial biomass and population. To compare the results of conventional methods and to check the sensitivity of microcalorimetry, the thermodynamic parameters, microbial growth rate constant (k), total heat evolution (Q), peak height (Pmax) and peak time (tmax) were calculated. Highest Pmax, k and Q were observed in GM treatments at water regime W1, while highest tmax values were recorded in CK (control) and RS treatments at W2. The microcalorimetric parameters, Pmax, k and Q were positively correlated, whereas tmax negatively linked with microbial biomass and population at p < 0.01. Our results suggest that microcalorimetry successfully verified the results obtained from customary methods and microcalorimetric parameters Pmax, tmax, Q and k proved that they are highly sensitive to microbial properties and could be used as indices of microbial community shifts and activities in soil ecosystems.

Effects of light quality on the accumulation of oil in a mixed culture of Chlorella sp. and Saccharomyces cerevisiae

AbstractBACKGROUND: Chlorella strains rather than terrestrial oil crops having higher oil content and shorter generation time have been considered as promising candidates for alternative biodiesel. Since the influence of light quality on oil formation of microalgae in either monoculture or mixed culture has been shown to be either inconsistent or ambiguous, a light‐emitting diode (LED) photo‐bioreactor with different light sources and intensities was used in this study to investigate a cost‐effective lipid production process.RESULTS: The oil accumulation in a mixed culture of Chlorella sp. and Saccharomyces cerevisiae was higher than that in the monoculture under the different light sources used. Results of the influence of light quality on the mixed culture indicated that the optimal light wavelength and intensity for biomass formation was red LED light at 1000 lux, whereas the optimum for oil formation was blue LED light at 1000 lux. A novel two‐stage LED photo‐bioreactor was thus proposed and the highest Pmax and productivity in this study were obtained as 261 mg L−1 and 8.16 mg L−1 h−1, respectively.CONCLUSION: A novel two‐stage LED photo‐bioreactor using a mixed culture to optimize microalgal oil production was proposed and successfully demonstrated in this study. Copyright © 2011 Society of Chemical Industry

Modeling leaf maximum net photosynthetic rate of Festuca pallescens, the dominant perennial grass of Patagonian pine-based silvopastoral systems

The integrated relationship in a simple mechanistic model between the critical environmental factors controlling leaf photosynthesis of understory species would be a useful tool to optimize the management of the silvopastoral systems. Individual effect of leaf temperature, water stress and light environment over net maximum photosynthetic rate (Pmax) was evaluated on Festuca pallescens leaves grown in a silvopastoral system of two Pinus ponderosa canopy covers (350 and 500 trees ha−1) and natural grassland. The aim was to integrate individual functions for Pmax against these environmental factors into a multiplicative model. We measured pre-dawn water potential (ψpd), leaf temperature and net photosynthetic rate (Pn), stomatal conductance (gs) and intercellular CO2 concentration (Ci) as a function of photosynthetic photon flux density (PPFD). The highest Pmax under non-limiting conditions was 20.4 μmol CO2 m−2 s−1 and was defined as standardized dimensionless Pmaxs = 1 for comparison of environmental factors. The leaf temperature function showed an optimum range between 20.2 and 21.8°C where Pmaxs = 1. Then, Pmaxs declined by an average 1 μmol CO2 m−2 s−1 C−1 from the optimum to 4.7 and 38.5°C. Pmaxs decreased at a rate of 9.49 μmol CO2 m−2 s−1 MPa−1 as water potential reaches −1.9 MPa and showed a lower slope as water potential decreased down to −4.3 MPa. The light environment was estimated from hemispherical photograph analysis. Pmaxs was 20% higher in leaves of open control plants than under the maximum tree canopy cover. The simple multiplicative model accounted for 0.82 of the variation in Pmax. Such a simple mechanistic model is the first step towards a more effective decision support tool.

HIGH PHOTOSYNTHETIC RATES UNDER A COLIMITATION FOR INORGANIC PHOSPHORUS AND CARBON DIOXIDE1

Inorganic phosphorus (Pi) and carbon (here, CO2) potentially limit the photosynthesis of phytoplankton simultaneously (colimitation). A single Pi limitation generally reduces photosynthesis, but the effect of a colimitation is not known. Therefore, photosynthesis was measured under Pi-limited conditions and high and low CO2, and osmo-mixotrophic (i.e., growth in the presence of glucose) conditions that result in colimiting conditions in some cases. The green alga Chlamydomonas acidophila Negoro was used as a model organism because low Pi and CO2 concentrations likely influence its photosynthetic rates in its natural environment. Results showed a decreasing maximum photosynthetic rate (Pmax) and maximum quantum yield (ΦII) with increasing Pi limitation. In addition, a Pi limitation enhanced the relative contribution of dark respiration to Pmax (Rd:Pmax) but did not influence the compensation light intensity. Pmax positively correlated with the cellular RUBISCO content. Osmo-mixotrophic conditions resulted in similar Pmax, ΦII, and RUBISCO content as in high-CO2 cultures. The low-CO2 cultures were colimited by Pi and CO2 and had the highest Pmax, ΦII, and RUBISCO content. Colimiting conditions for Pi and CO2 in C. acidophila resulted in an enhanced mismatch between photosynthesis and growth rates compared to the effect of a single Pi limitation. Primary productivity of colimited phytoplankton could thus be misinterpreted.

Integrated Effects of Root-Zone Temperatures and Phosphorus Levels on Aeroponically-Grown Lettuce (Lactuca sativa L.) in the Tropics

In this study, butterhead lettuce (Lactuca sativa L. cv. Baby Butter) plants were grown at three root-zone tem- peratures (RZTs): 25 o C, 30 o C and ambient-RZT (A-RZT) ranging from 26 o C-42 o C while their shoots were maintained at hot ambient temperature ranging from 26 o C-42 o C. Three phosphorus (P) concentrations: -25% P (minus P, 23.25ppm), control (31.00ppm) and +25% P (plus P, 38.75ppm) were supplied to the plants at each RZT using Netherlands Standard Nutrient Solution. Interactions between RZT and P concentrations on productivity, root morphology, maximum photosyn- thetic O2 evolution (Pmax), P uptake and its partitioning between shoot and root were studied. Lettuce plants grown with the plus P concentration at 25 o C-RZT had the highest productivity, highest Pmax, highest shoot and root P concentrations. However, all the root morphological parameters studied were the greatest in plants grown with the minus P at 25 o C-RZT. Higher P concentration in the solution and 25 o C-RZT resulted in higher portion of the absorbed P partitioned to the shoots. Integrated effects of RZT and P concentration on the productivity, root morphology, photosynthesis and P uptake were discussed.