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Selected AbstractsMultilayer Amorphous-Si-B-C-N/,-Al2O3/,-Al2O3 Membranes for Hydrogen Purification,,ADVANCED ENGINEERING MATERIALS, Issue 6 2010Ravi Mohan Prasad Abstract The hydrogen and carbon monoxide separation is an important step in the hydrogen production process. If H2 can be selectively removed from the product side during hydrogen production in membrane reactors, then it would be possible to achieve complete CO conversion in a single-step under high temperature conditions. In the present work, the multilayer amorphous-Si-B-C-N/,-Al2O3/,-Al2O3 membranes with gradient porosity have been realized and assessed with respect to the thermal stability, geometry of pore space and H2/CO permeance. The ,-Al2O3 support has a bimodal pore-size distribution of about 0.64 and 0.045 µm being macroporous and the intermediate ,-Al2O3 layer,deposited from boehmite colloidal dispersion,has an average pore-size of 8,nm being mesoporous. The results obtained by the N2 -adsorption method indicate a decrease in the volume of micropores,0.35 vs. 0.75,cm3,g,1,and a smaller pore size ,6.8 vs. 7.4 Å,in membranes with the intermediate mesoporous ,-Al2O3 layer if compared to those without. The three times Si-B-C-N coated multilayer membranes show higher H2/CO permselectivities of about 10.5 and the H2 permeance of about 1.05,×,10,8 mol m,2 s,1 Pa,1. If compared to the state of the art of microporous membranes, the multilayer Si-B-C-N/,-Al2O3/,-Al2O3 membranes are appeared to be interesting candidates for hydrogen separation because of their tunable nature and high-temperature and high-pressure stability. [source] Hide, rest or die: a light-mediated diapause response in Daphnia magna to the threat of fish predationFRESHWATER BIOLOGY, Issue 1 2005Miros, lusarczyk Summary 1. In a laboratory batch culture experiment, a diapause response of Daphnia magna to a simulated threat of fish predation was tested at various light intensities, which under natural conditions determine potential vulnerability of Daphnia to visual planktivorous fish. 2. Under moderate light intensity (1.4 ,mol m,2 s,1) that allows effective predation by fish, the proportion of females producing dormant eggs was significantly higher than under dim light conditions (0.001 ,mol m,2 s,1) that are not favourable for visual detection of prey. Production of dormant eggs was not observed in complete darkness or in treatments missing fish kairomones, irrespective of tested light conditions. 3. The observed phenomenon is interpreted as a flexible response of prey to the conditional risk of predation assessed by Daphnia according to the presence of fish-derived cues on the one hand and the presence of dark refugia on the other. Irrespective of the presence of fish kairomones, Daphnia may not produce resting eggs as long as a safe, dark, bottom zone is accessible. [source] Photoheterotrophy and light-dependent uptake of organic and organic nitrogenous compounds by Planktothrix rubescens under low irradianceFRESHWATER BIOLOGY, Issue 10 2003Tatiana Zotina Summary 1. Planktothrix rubescens is the dominant photoautotrophic organism in Lake Zürich, a prealpine, deep, mesotrophic freshwater lake with an oxic hypolimnion. Over long periods of the year, P. rubescens accumulates at the metalimnion and growth occurs in situ at irradiance near the photosynthesis compensation point. Experiments were conducted to evaluate the contribution of photoheterotrophy, heterotrophy and light-dependent uptake of nitrogenous organic compounds to the carbon and nitrogen budget of this cyanobacterium under conditions of restricted availability of light quanta. 2. We used both purified natural populations of P. rubescens from the depth of 9 m and an axenic culture grown under low irradiance at 11 ,mol m,2 s,1 on a light : dark cycle (10 : 14 h) to determine the uptake rates of various amino acids, urea, glucose, fructose, acetate and inorganic carbon. The components were added to artificial lake water in low amounts that simulated the naturally occurring potential concentrations. 3. The uptake rates of acetate and amino acids (glycine, serine, glutamate and aspartate) were strongly enhanced at low irradiance as compared with the dark. However, no difference was observed in the uptake of arginine, which was taken up at high rates under both treatments. The uptake rates of glucose, fructose and urea were very low under all conditions. Similar results were obtained for both axenic P. rubescens and for purified natural populations of P. rubescens that were separated from bacterioplankton and other phytoplankton. 4. Metalimnetic P. rubescens that was stratified at low irradiance for weeks exhibited much higher uptake rates than filaments that were entrained in the deepening surface mixed layer and experienced higher irradiance. The added organic compounds contributed up to 62% to the total carbon uptake of metalimnetic P. rubescens. On the basis of a molar C : N ratio of 4.9, the nitrogen uptake as organic compounds satisfied up to 84% of the nitrogen demand. 5. The experiments indicate that photoheterotrophy and light-dependent uptake of nitrogenous organic compounds may contribute significantly to the carbon and nitrogen budget of filaments at low irradiance typical for growth of P. rubescens in the metalimnion and at the bottom of the surface mixed layer. [source] Ecosystem CO2 exchange and plant biomass in the littoral zone of a boreal eutrophic lakeFRESHWATER BIOLOGY, Issue 8 2003T. Larmola Summary 1In order to study the dynamics of primary production and decomposition in the lake littoral, an interface zone between the pelagial, the catchment and the atmosphere, we measured ecosystem/atmosphere carbon dioxide (CO2) exchange in the littoral zone of an eutrophic boreal lake in Finland during two open water periods (1998,1999). We reconstructed the seasonal net CO2 exchange and identified the key factors controlling CO2 dynamics. The seasonal net ecosystem exchange (NEE) was related to the amount of carbon accumulated in plant biomass. 2In the continuously inundated zones, spatial and temporal variation in the density of aerial shoots controlled CO2 fluxes, but seasonal net exchange was in most cases close to zero. The lower flooded zone had a net CO2 uptake of 1.8,6.2 mol m,2 per open water period, but the upper flooded zone with the highest photosynthetic capacity and above-ground plant biomass, had a net CO2 loss of 1.1,7.1 mol m,2 per open water period as a result of the high respiration rate. The excess of respiration can be explained by decomposition of organic matter produced on site in previous years or leached from the catchment. 3Our results from the two study years suggest that changes in phenology and water level were the prime cause of the large interannual difference in NEE in the littoral zone. Thus, the littoral is a dynamic buffer and source for the load of allochthonous and autochthonous carbon to small lakes. [source] Isotopic and petrological evidence of fluid,rock interaction at a Tethyan ocean,continent transition in the Alps: implications for tectonic processes and carbon transfer during early ocean formationGEOFLUIDS (ELECTRONIC), Issue 4 2007A. ENGSTRÖM Abstract We report overprinting stable isotope evidence of fluid,rock interaction below two detachment faults along which mantle rocks were exhumed to the seafloor, between the respective landward and seaward limits of oceanic and continental crust, at a Tethyan ocean,continent transition (OCT). This OCT, which is presently exposed in the Tasna nappe (south-eastern Switzerland) is considered an on-land analogue of the well-studied Iberian OCT. We compare our results with the fault architecture (fault core,damage zone,protolith) described by Caine et al. [Geology (1996) Vol. 24, pp. 1025,1028]. We confirm the existence of a sharp boundary between the fault core and damage zone based on isotopic data, but the boundary between the damage zone and protolith is gradational. We identify evidence for: (1) pervasive isotopic modification to 8.4 ± 0.1, which accompanied or post-dated serpentinization of these mantle rocks at an estimated temperature of 67,109°C, (2) either (i) partial isolation of some highly strained regions [fault core(s) and mylonite] from this pervasive isotopic modification, because of permeability reduction (Caine et al.) or (ii) subsequent isotopic modification caused by structurally channelled flow of warm fluids within these highly strained regions, because of permeability enhancement, and (3) isotopic modification, which is associated with extensive calcification at T = 54,100°C, primarily beneath the younger of the two detachment faults and post-dating initial serpentinization. By comparing the volumetric extent of calcification with an experimentally verified model for calcite precipitation in veins, we conclude that calcification could have occurred in response to seawater infiltration, with a calculated flux rate of 0.1,0.2 m year,1 and a minimum duration of 0.2,4.0 × 104 years. The associated time-averaged uptake flux of carbon during this period was 8,120 mol m,2 year,1. By comparison with the estimated area of exhumed mantle rocks at the Iberian OCT, we calculate a maximum annual uptake flux for carbon of 2,30 Tg year,1. This is an order of magnitude greater than that for carbon exchange at the mid-ocean ridges and 0.1,1.4% of the global oceanic uptake flux for carbon. [source] Methane efflux in relation to plant biomass and sediment characteristics in stands of three common emergent macrophytes in boreal mesoeutrophic lakesGLOBAL CHANGE BIOLOGY, Issue 1 2005Paula Kankaala Abstract Methane efflux was studied in stands of three emergent macrophyte species (Equisetum fluviatile, Schoenoplectus lacustris and Phragmites australis) commonly found in the littoral zone of boreal lakes. In vegetation stands with relatively low methane (CH4) emissions (<0.3 mol m,2 (ice-free period),1), the seasonal variation of CH4 efflux was better correlated with the dynamics of plant growth than variation in sediment temperature. In dense and productive vegetation stands that released high amounts of CH4 (2.3,7.7 mol m,2 (ice-free period),1), the seasonal variation in CH4 efflux was correlated with sediment temperature, indicating that methanogens were more limited by temperature than substrate supply. The bottom type at the growth site of the emergent plants significantly influenced the ratio of CH4 efflux to aboveground biomass of plants (Eff : B). The lowest Eff : B ratio was found in E. fluviatile stands growing on sand bottom under experimental conditions and the highest in P. australis -dominated littoral areas accumulating detritus from external sources. The future changes expected in the hydrology of boreal lakes and rivers because of climatic warming may impact the growth conditions of aquatic macrophytes as well as decomposition and accumulation of detritus and, thus, CH4 effluxes from boreal lakes. [source] High rates of net ecosystem carbon assimilation by Brachiara pasture in the Brazilian CerradoGLOBAL CHANGE BIOLOGY, Issue 5 2004Alexandre J.B. Santos Abstract To investigate the consequences of land use on carbon and energy exchanges between the ecosystem and atmosphere, we measured CO2 and water vapour fluxes over an introduced Brachiara brizantha pasture located in the Cerrado region of Central Brazil. Measurements using eddy covariance technique were carried out in field campaigns during the wet and dry seasons. Midday CO2 net ecosystem exchange rates during the wet season were ,40 ,mol m,2 s,1, which is more than twice the rate found in the dry season (,15 ,mol m,2 s,1). This was observed despite similar magnitudes of irradiance, air and soil temperatures. During the wet season, inferred rates of canopy photosynthesis did not show any tendency to saturate at high solar radiation levels, with rates of around 50 ,mol m,2 s,1 being observed at the maximum incoming photon flux densities of 2200 ,mol m,2 s,1. This contrasted strongly to the dry period when light saturation occurred with 1500 ,mol m,2 s,1 and with maximum canopy photosynthetic rates of only 20 ,mol m,2 s,1. Both canopy photosynthetic rates and night-time ecosystem CO2 efflux rates were much greater than has been observed for cerrado native vegetation in both the wet and dry seasons. Indeed, observed CO2 exchange rates were also much greater than has previously been reported for C4 pastures in the tropics. The high rates in the wet season may have been attributable, at least in part, to the pasture not being grazed. Higher than expected net rates of carbon acquisition during the dry season may also have been attributable to some early rain events. Nevertheless, the present study demonstrates that well-managed, productive tropical pastures can attain ecosystem gas exchange rates equivalent to fertilized C4 crops growing in the temperate zone. [source] The contribution of bryophytes to the carbon exchange for a temperate rainforestGLOBAL CHANGE BIOLOGY, Issue 8 2003Evan H. DeLucia Abstract Bryophytes blanket the floor of temperate rainforests in New Zealand and may influence a number of important ecosystem processes, including carbon cycling. Their contribution to forest floor carbon exchange was determined in a mature, undisturbed podocarp-broadleaved forest in New Zealand, dominated by 100,400-year-old rimu (Dacrydium cupressimum) trees. Eight species of mosses and 13 species of liverworts contributed to the 62% cover of the diverse forest floor community. The bryophyte community developed a relatively thin (depth <30 mm), but dense, canopy that experienced elevated CO2 partial pressures (median 46.6 Pa immediately below the bryophyte canopy) relative to the surrounding air (median 37.6 Pa at 100 mm above the canopy). Light-saturated rates of net CO2 exchange from 14 microcosms collected from the forest floor were highly variable; the maximum rate of net uptake (bryophyte photosynthesis , whole-plant respiration) per unit ground area at saturating irradiance was 1.9 ,mol m,2 s,1 and in one microcosm, the net rate of CO2 exchange was negative (respiration). CO2 exchange for all microcosms was strongly dependent on water content. The average water content in the microcosms ranged from 1375% when fully saturated to 250% when air-dried. Reduction in water content across this range resulted in an average decrease of 85% in net CO2 uptake per unit ground area. The results from the microcosms were used in a model to estimate annual carbon exchange for the forest floor. This model incorporated hourly variability in average irradiance reaching the forest floor, water content of the bryophyte layer, and air and soil temperature. The annual net carbon uptake by forest floor bryophytes was 103 g m,2, compared to annual carbon efflux from the forest floor (bryophyte and soil respiration) of ,1010 g m,2. To put this in perspective of the magnitude of the components of CO2 exchange for the forest floor, the bryophyte layer reclaimed an amount of CO2 equivalent to only about 10% of forest floor respiration (bryophyte plus soil) or ,11% of soil respiration. The contribution of forest floor bryophytes to productivity in this temperate rainforest was much smaller than in boreal forests, possibly because of differences in species composition and environmental limitations to photosynthesis. Because of their close dependence on water table depth, the contribution of the bryophyte community to ecosystem CO2 exchange may be highly responsive to rapid changes in climate. [source] Response of Oryzacystatin I Transformed Tobacco Plants to Drought, Heat and Light StressJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 2 2010K. Demirevska Abstract Transformed tobacco plants expressing a rice cysteine proteinase inhibitor (OC-I) and non-transformed plants were grown in a controlled environment and subjected to various stresses. Two-month-old transformed and non-transformed plants were exposed for 5 days to drought conditions by withholding watering. High temperature (40 °C) was applied additionally at day 6th for 5 h either individually or in combination with drought. All stress treatments were applied under low (150 ,mol m,2 s,1 PPFD) and high light intensity (HL) of 1000 ,mol m,2 s,1 PPFD to determine if OC-I expression might provide protection under combination of stresses usually existing in nature. Drought stress led to diminution in leaf relative water content, photosynthesis inhibition, decrease in chlorophyll content and accumulation of malondialdehyde and proline. Heat stress alone did not affect the plants significantly, but intensified the effect of drought stress. HL intensity further increased the proline content. OC-I transformed plants grown under low light intensity had significantly higher total superoxide dismutase and guaiacol peroxidase activities as well as their isoforms than non-transformed control plants under non-stress and stress conditions. Catalase activity was not highly affected by OC-I expression. Results indicate that OC-I expression in tobacco plants provides protection of the antioxidative enzymes superoxide dismutase and guaiacol peroxidise under both non-stress and stress conditions. [source] Oxygen transfer effects in ,-lactamase fermentation by Bacillus licheniformis in a glucose-based defined mediumJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2005nar Çal Abstract The effects of oxygen transfer on the ,-lactamase production by Bacillus licheniformis were investigated in a glucose-based defined medium. The experiments were conducted in 3.0 dm3 batch bioreactor systems at three different air inlet (QO/VR = 0.2, 0.5 and 1.0 vvm) and agitation rates (N = 250, 500 and 750 min,1). During the fermentation, the concentrations of the cell, glucose, by-products, ie organic and amino acids, oxygen transfer coefficients (KLa), yield coefficients, specific rates and oxygen uptake rates (OUR) were determined, in addition to ,-lactamase activities. The highest ,-lactamase activity was obtained at QO/VR = 0.5 vvm and N = 500 min,1 and at QO/VR = 0.2 vvm and N = 500 min,1 conditions, as caA = 90 U cm,3. The highest cell concentration was obtained as CX = 0.67 kg m,3 at QO/VR = 0.5 vvm and N = 750 min,1 and at QO/VR = 0.2 vvm and N = 750 min,1 conditions. The values of KLa increased with increasing agitation and aeration rates and varied between 0.007 and 0.044 s,1, and the OUR varied between 0.4 and 1.6 mol m,3 s,1. With increasing QO/VR and/or N, the Damköhler number (ie the oxygen transfer limitation) decreased owing to the increase in mass transfer coefficients (KLa). The highest instantaneous yield of cell on substrate (YX/S) and yield of cell on oxygen (YX/O) values were respectively obtained at 0.5 vvm and 500 min,1 conditions at t = 2 h as YX/S = 0.72 kg kg,1 and YX/O = 1.49 kg kg,1. The highest instantaneous yield of substrate on oxygen (YS/O) was obtained at 0.5 vvm and 750 min,1 conditions at t = 20 h as YS/O = 8.07 kg kg,1. Copyright © 2005 Society of Chemical Industry [source] Biomass and leaf-level gas exchange characteristics of three African savanna C4 grass species under optimum growth conditionsAFRICAN JOURNAL OF ECOLOGY, Issue 4 2009K. B. Mantlana Abstract C4 savanna grass species, Digitaria eriantha, Eragrostis lehmanniana and Panicum repens, were grown under optimum growth conditions with the aim of characterizing their above- and below-ground biomass allocation and the response of their gas exchange to changes in light intensity, CO2 concentration and leaf-to-air vapour pressure deficit gradient (Dl). Digitaria eriantha showed the largest above- and below-ground biomass, high efficiency in carbon gain under light-limiting conditions, high water use efficiency (WUE) and strong stomatal sensitivity to Dl (P = 0.002; r2 = 0.5). Panicum repens had a high aboveground biomass and attained high light saturated photosynthetic rates (Asat, 47 ,mol m,2 s,1), stomatal conductance, (gsat, 0.25 mol m,2 s,1) at relatively high WUE. Eragrostis lehmanniana had almost half the biomass of other species, and had similar Asat and gsat but were attained at lower WUE than the other species. This species also showed the weakest stomatal response to Dl (P = 0.19, r2 = 0. 1). The potential ecological significance of the contrasting patterns of biomass allocation and variations in gas exchange parameters among the species are discussed. Résumé On a fait pousser des espèces herbeuses de savane de type C4, Digitaria eriantha, Eragrostis lehmanniana et Panicum repens, dans des conditions optimales dans le but de caractériser l'allocation de leur biomasse aérienne et racinaire et la réponse de leur échange gazeux à des changements d'intensité de la lumière, de concentrations de CO2, et à un gradient déficitaire (Dl) de pression de vapeur feuille-air. D. eriantha montrait la plus grande biomasse aérienne et racinaire, une grande efficience de l'assimilation de carbone dans des conditions de luminosité limitée, une grande efficience d'utilisation de l'eau (WUE) et une forte sensibilité des stomates à Dl (P = 0,002; r2 = 0,5). P. repens avait une grande biomasse aérienne et atteignait des taux photosynthétiques élevés en lumière saturée (Asat, 47 ,mol m,2 s,1), et une conductance stomatique (gsat 0.25 mol m,2 s,1) à une WUE relativement élevée. E. lehmanniana avait une biomasse qui était presque la moitié de celle des autres espèces et avait un Asat et un gsat similaires mais qui étaient atteints à une WUE plus basse que les autres espèces. Cette espèce montrait aussi la plus faible réponse stomatique àDl (P = 0,19, r2 = 0,1). L'on discute de la signification écologique potentielle de ces schémas contrastés d'allocations de biomasse et des variations des paramètres des échanges gazeux entre les espèces. [source] Xanthophyll Cycle and Inactivation of Photosystem II Reaction Centers Alleviating Reducing Pressure to Photosystem I in Morning Glory Leaves under Short-term High IrradianceJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 7 2007Xin-Guo Li Abstract Under 30-min high irradiance (1500 ,mol m,2 s,1), the roles of the xanthophyll cycle and D1 protein turnover were investigated through chlorophyll fluorescence parameters in morning glory (Ipomoea setosa) leaves, which were dipped into water, dithiothreitol (DTT) and lincomycin (LM), respectively. During the stress, both the xanthophyll cycle and D1 protein turnover could protect PSI from photoinhibition. In DTT leaves, non-photochemical quenching (NPQ) was inhibited greatly and the oxidation level of P700 (P700+) was the lowest one. However, the maximal photochemical efficiency of PSII (Fv/Fm) in DTT leaves was higher than that of LM leaves and was lower than that of control leaves. These results suggested that PSI was more sensitive to the loss of the xanthophyll cycle than PSII under high irradiance. In LM leaves, NPQ was partly inhibited, Fv/Fm was the lowest one among three treatments under high irradiance and P700+ was at a similar level as that of control leaves. These results implied that inactivation of PSII reaction centers could protect PSI from further photoinhibition. Additionally, the lowest of the number of active reaction centers to one inactive reaction center for a PSII cross-section (RC/CSo), maximal trapping rate in a PSII cross-section (TRo/CSo), electron transport in a PSII cross-section (ETo/CSo) and the highest of 1-qP in LM leaves further indicated that severe photoinhibition of PSII in LM leaves was mainly induced by inactivation of PSII reaction centers, which limited electrons transporting to PSI. However, relative to the LM leaves the higher level of RC/CSo, TRo/CSo, Fv/Fm and the lower level of 1-qP in DTT leaves indicated that PSI photoinhibition was mainly induced by the electron accumulation at the PSI acceptor side, which induced the decrease of P700+ under high irradiance. [source] Characteristics of ammonia permeation through porous silica membranesAICHE JOURNAL, Issue 5 2010Masakoto Kanezashi Abstract A sol,gel method was applied for the preparation of silica membranes with different average pore sizes. Ammonia (NH3) permeation/separation characteristics of the silica membranes were examined in a wide temperature range (50,400°C) by measurement of both single and binary component separation. The order of gas permeance through the silica membranes, which was independent of membrane average pore size, was as follows: He > H2 > NH3 > N2. These results suggest that, for permeation through silica membranes, the molecular size of NH3 is larger than that of H2, despite previous reports that the kinetic diameter of NH3 is smaller than that of H2. At high temperatures, there was no effect of NH3 adsorption on H2 permeation characteristics, and silica membranes were highly stable in NH3 at 400°C (i.e., gas permeance remained unchanged). On the other hand, at 50°C NH3 molecules adsorbed on the silica improved NH3 -permselectivity by blocking permeation of H2 molecules without decreasing NH3 permeance. The maximal NH3/H2 permeance ratio obtained during binary component separation was ,30 with an NH3 permeance of ,10,7 mol m,2 s,1 Pa,1 at an H2 permeation activation energy of ,6 kJ mol,1. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Timing and nature of fluid flow and alteration during Mesoproterozoic shear zone formation, Olary Domain, South AustraliaJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2005C. CLARK Abstract The development of shear zones at mid-crustal levels in the Proterozoic Willyama Supergroup was synchronous with widespread fluid flow resulting in albitization and calcsilicate alteration. Monazite dating of shear zone fabrics reveal that they formed at 1582 ± 22 Ma, at the end of the Olarian D3 deformational event and immediately prior to the emplacement of regional S-type granites. Two stages of fluid flow are identified in the area: first an albitizing event which involved the addition of Na and loss of Si, K and Fe; and a second phase of calcsilicate alteration with additions of Ca, Fe, Mg and Si and removal of Na. Fluid fluxes calculated for albitization and calcsilicate alteration were 5.56 × 109 to 1.02 × 1010 mol m,2 and 2.57 × 108,5.20 × 109 mol m,2 respectively. These fluxes are consistent with estimates for fluid flow through mid-crustal shear zones in other terranes. The fluids associated with shearing and alteration are calculated to have ,18O and ,D values ranging between +8 and +11,, and ,33 and ,42,, respectively, and ,Nd values between ,2.24 and ,8.11. Our results indicate that fluids were derived from metamorphic dehydration of the Willyama Supergroup metasediments. Fluid generation occurred during prograde metamorphism of deeper crustal rocks at or near peak pressure conditions. Shear zones acted as conduits for major crustal fluid flow to shallow levels where peak metamorphic conditions had been attained earlier leading to the apparent ,retrograde' fluid-flow event. Thus, the peak metamorphism conditions at upper and lower crustal levels were achieved at differing times, prior to regional granite formation, during the same orogenic cycle leading to the formation of retrograde mineral assemblages during shearing. [source] 133 Studies on the Life History of the Portuguese Red Alga Porphyra Dioica (Brodie and Irvine) Under Varying Environmental ConditionsJOURNAL OF PHYCOLOGY, Issue 2003R. Pereira The life history of Porphyra dioica collected in Porto, Portugal, was investigated under laboratory conditions. This is one of the most common Porphyra species on the North Coast of Portugal and can be found throughout the year. Field studies showed higher percentage cover, from 23 to 66%, during February through May. Varying temperature, light intensities and photoperiods were tested. The zygotospores germinated faster at 15°C, and at 25 ,mol m,2·s,1. Growth rate of the conchocelis was affected by temperature rather than by photoperiod. In the three photoperiods tested, growth rate was always higher at 15°C, under 25 to 75 ,mol m,2·s,1, although not significantly different from that at 20° C. Difference between these two temperatures and 5 and 10°C was significant. Conchosporangia formation was higher in 15°C and at short-day, 8:16, Light:Dark and 25 to 75 ,mol m,2·s,1 and was almost non-existent in free floating conditions. Optimal conditions for conchosporangia maturation, 15° C, 8:16, Light:Dark and 5 to 25 ,mol m,2·s,1 also promoted spore release after 18 weeks. Aeration appeared to be crucial for normal blade development. No archeospores were observed. The first findings of the optimal conditions for growth of the gametophyte stage will also be discussed. [source] Some cesium and potassium salts increase the water permeability of astomatous isolated plant cuticlesJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2007Salem Elshatshat Abstract Salts were applied as aqueous solution to the outer surfaces of astomatous isolated cuticles, and the water was allowed to evaporate. Effects of salt residues on the surfaces of cuticles on water permeability of cuticles were measured at 25°C. A surface dose of 0.2 mol m,2 Cs2CO3 and K2CO3 increased the water permeability of pear leaf cuticles by factors of 9.9 and 3.9, respectively. Na2CO3 was barely effective, and Li2CO3 as well as (NH4)2CO3 had no influence on water permeability. Potassium applied as sulfate, nitrate, or chloride had no effect on the water permeability of pear leaf cuticles, while K+ salts of weak acids (0.2 mol m,2) were effective, as they increased water permeability by factors of 5.4 (K+ -acetate), 3.9 (K2CO3), and 2.0 (K2HPO4), respectively. Sensitivity of Idesia polycarpa leaf cuticles to treatment with K2CO3 at 0.2 mol m,2 was greatest as water permeability was increased 35-fold, while the water permeability of cuticles from other species tested (astomatous leaf cuticles from Hedera helix, Citrus aurantium, Prunus laurocerasus, Pyrus communis, and Populus canescens; fruit cuticles from Capsicum annuum and Lycopersicon esculentum) increased only by factors ranging from 1.7 to 3.9. Data are discussed in relation to swelling and ion-exchange properties of cuticles. [source] The Heterotrimeric G-protein Complex Modulates Light Sensitivity in Arabidopsis thaliana Seed GerminationPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Javier F. Botto Release of dormancy and induction of seed germination are complex traits finely regulated by hormonal signals and environmental cues such as temperature and light. The Red (R):Far-Red (FR) phytochrome photoreceptors mediate light regulation of seed germination. We investigated the possible involvement of heterotrimeric G-protein complex in the phytochrome signaling pathways of Arabidopsis thaliana seed germination. Germination rates of null mutants of the alpha (G,) and beta (G,) subunits of the G-protein (Atgpa1-4 and agb1-2, respectively) and the double mutant (agb1-2/gpa1-4) are lower than the wildtype (WT) under continuous or pulsed light. The G, and G, subunits play a role in seed germination under hourly pulses of R lower than 0.1 ,mol m,2 s,1 whereas the G, subunit plays a role in higher R fluences. The germination of double mutants of G-protein subunits with phyA-211 and phyB-9 suggests that AtGPA1 seems to act as a positive regulator of phyA and probably phyB signaling pathways, while the role of AGB1 is ambiguous. The imbibition of seeds at 4°C and 35°C alters the R and FR light responsiveness of WT and G-protein mutants to a similar magnitude. Thus, G, and G, subunits of the heterotrimeric G-protein complex modulate light induction of seed germination by phytochromes and are dispensable for the control of dormancy by low and high temperatures prior to irradiation. We discuss the possible indirect role of the G-protein complex on the phytochrome-regulated germination through hormonal signaling pathways. [source] Comparison by PAM Fluorometry of Photosynthetic Activity of Nine Marine Phytoplankton Grown Under Identical Conditions,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2005P. Juneau ABSTRACT The photosynthetic activity of marine phytoplankton from five algal classes (Phaeodactylum tricornutum, Skeletonema costatum, Thalassiosira oceanica, Thalassiosira weissflogii, Dunaliella tertiolecta, Mantoniella squamata, Emiliania huxleyi, Pavlova lutheri and Heterosigma akashiwo) was investigated under identical growth conditions to determine interspecies differences. Primary photochemistry and electron transport capacity of individual species were examined by pulse amplitude-modulated (PAM) fluorescence. Although few differences were found in maximal photosystem II (PSII) photochemical efficiency between various species, large differences were noticed in their PSII-photosystem I (PSI) electron transport activity. We found that species such as T. oceanica and M. squamata have much lower photochemical activity than H. akashiwo. It appeared that processes involved in electron transport activity were more susceptible to change during algal evolution compared with the primary photochemical act close to PSII. Large variations in the nonphotochemical energy dissipation event among species were also observed. Light energy required to saturate photosynthesis was very different between species. We have shown that M. squamata and H. akashiwo required higher light energy (>1300 ,mol m,2 s,1) to saturate photosynthesis compared with S. costatum and E. huxleyi (ca 280 ,mol m,2 s,1). These differences were interpreted to be the result of variations in the size of lightharvesting complexes associated with PSII. These disparities in photosynthetic activity might modulate algal community structure in the natural environment where light energy is highly variable. Our results suggest that for an accurate evaluation of primary productivity from fluorescence measurements, it is essential to know the species composition of the algal community and the individual photosynthetic capacity related to the major phytoplankton species present in the natural phytoplankton assemblage. [source] Red ,Anjou' pear has a higher photoprotective capacity than green ,Anjou'PHYSIOLOGIA PLANTARUM, Issue 3 2008Pengmin Li Photoprotective function of anthocyanins along with xanthophyll cycle and antioxidant system in fruit peel was investigated in red ,Anjou' vs green ,Anjou' pear (Pyrus communis) during fruit development and in response to short-term exposure to high light. The sun-exposed peel of red ,Anjou' had higher maximum quantum yield of photosystem II (FV/FM) than that of green ,Anjou' and both the sun-exposed peel and the shaded peel of red ,Anjou' had smaller decreases in FV/FM after 2-h high light (photon flux density of 1500 ,mol m,2 s,1) treatment than those of green ,Anjou'. At the middle and late developmental stages, the xanthophyll cycle pool size on a chlorophyll basis, the activity of superoxide dismutase, ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) and the level of reduced ascorbate and total ascorbate pool in the sun-exposed peel were either the same or lower in red ,Anjou' than in green ,Anjou', whereas the xanthophyll cycle pool size on a chlorophyll basis and the activity of APX, catalase, MDAR, DHAR and GR in the shaded peel were higher in red ,Anjou' than in green ,Anjou'. It is concluded that red ,Anjou' has a higher photoprotective capacity in both the sun-exposed peel and the shaded peel than green ,Anjou'. While the higher anthocyanin concentration along with the larger xanthophyll cycle pool size and the higher activity of some antioxidant enzymes may collectively contribute to the higher photoprotective capacity in the shaded peel of red ,Anjou', the higher photoprotective capacity in the sun-exposed peel of red ,Anjou' is mainly attributed to its higher anthocyanin concentration. [source] Relative enhancement of photosynthesis and growth at elevated CO2 is greater under sunflecks than uniform irradiance in a tropical rain forest tree seedlingPLANT CELL & ENVIRONMENT, Issue 12 2002A. D. B. LEAKEY Abstract The survivorship of dipterocarp seedlings in the deeply shaded understorey of South-east Asian rain forests is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain. To investigate the effect of elevated CO2 upon photosynthesis and growth under sunflecks, seedlings of Shorealeprosula were grown in controlled environment conditions at ambient or elevated CO2. Equal total daily photon flux density (PFD) (,7·7 mol m,2 d,1) was supplied as either uniform irradiance (,170 µmol m,2 s,1) or shade/fleck sequences (,30 µmol m,2 s,1/,525 µmol m,2 s,1). Photosynthesis and growth were enhanced by elevated CO2 treatments but lower under flecked irradiance treatments. Acclimation of photosynthetic capacity occurred in response to elevated CO2 but not flecked irradiance. Importantly, the relative enhancement effects of elevated CO2 were greater under sunflecks (growth 60%, carbon gain 89%) compared with uniform irradiance (growth 25%, carbon gain 59%). This was driven by two factors: (1) greater efficiency of dynamic photosynthesis (photosynthetic induction gain and loss, post-irradiance gas exchange); and (2) photosynthetic enhancement being greatest at very low PFD. This allowed improved carbon gain during both clusters of lightflecks (73%) and intervening periods of deep shade (99%). The relatively greater enhancement of growth and photosynthesis at elevated CO2 under sunflecks has important potential consequences for seedling regeneration processes and hence forest structure and composition. [source] Measurement of gradients of absorbed light in spinach leaves from chlorophyll fluorescence profilesPLANT CELL & ENVIRONMENT, Issue 12 2000T. C. Vogelmann ABSTRACT Profiles of chlorophyll fluorescence were measured in spinach leaves irradiated with monochromatic light. The characteristics of the profiles within the mesophyll were determined by the optical properties of the leaf tissue and the spectral quality of the actinic light. When leaves were infiltrated with 10,4M DCMU [3-(3,4-dichlorophenyl)-1, 1-dimethyl-urea] or water, treatments that minimized light scattering, irradiation with 2000 ,mol m,2 s,1 green light produced broad Gaussian-shaped fluorescence profiles that spanned most of the mesophyll. Profiles for chlorophyll fluorescence in the red (680 ± 16 nm) and far red (, > 710 nm) were similar except that there was elevated red fluorescence near the adaxial leaf surface relative to far red fluorescence. Fluorescence profiles were narrower in non-infiltrated leaf samples where light scattering increased the light gradient. The fluorescence profile was broader when the leaf was irradiated on its adaxial versus abaxial surface due to the contrasting optical properties of the palisade and spongy mesophyll. Irradiation with blue, red and green monochromatic light produced profiles that peaked 50, 100 and 150 ,m, respectively, beneath the irradiated surface. These results are consistent with previous measurements of the light gradient in spinach and they agree qualitatively with measurements of carbon fixation under monochromatic blue, red and green light. These results suggest that chlorophyll fluorescence profiles may be used to estimate the distribution of quanta that are absorbed within the leaf for photosynthesis. [source] Changes in leaf photosynthetic parameters with leaf position and nitrogen content within a rose plant canopy (Rosa hybrida)PLANT CELL & ENVIRONMENT, Issue 4 2000M. M. Gonzalez-Real ABSTRACT This paper deals with changes in leaf photosynthetic capacity with depth in a rose (Rosa hybrida cv. Sonia) plant canopy. Measurements of leaf net CO2 assimilation (Al) and total nitrogen content (Nl) were performed in autumn under greenhouse conditions on mature leaves located at different layers within the plant canopy, including the flower stems and the main shoots. These leaves were subjected (i) to contrasting levels of CO2 partial pressure (pa) at saturating photosynthetic photon flux density (I about 1000 ,mol m,2 s,1) and (ii) to saturating CO2 partial pressure (pa about 100 Pa) and varying I, while conditions of temperature were those prevailing in the greenhouse (20,38 °C). A biochemical model of leaf photosynthesis relating Al to intercellular CO2 partial pressure (pi) was parameterized for each layer of leaves, supplying corresponding values of the photosynthetic Rubisco capacity (Vlm) and the maximum rate of electron transport (Jm). The results indicated that rose leaves growing at the top of the canopy had higher values of Jm and Vlm, which resulted from a higher allocation of nitrogen to the uppermost leaves. Mean values of total leaf nitrogen, Nl, decreased about 35% from the uppermost leaves of flower stem to leaves growing at the bottom of the plant. The derived values of non-photosynthetic nitrogen, Nb, varied from 76 mmolN m,2leaf (layer 1) to 60 mmolN m,2leaf (layer 4), representing a large fraction of Nl (50 and 60% in layer 1 and 4, respectively). Comparison of leaf photosynthetic nitrogen (Np=Nl,Nb) and I profiles supports the hypothesis that rose leaves acclimate to the time-integrated absorbed I. The relationships between I and Np, obtained during autumn, spring and summer, indicate that rose leaves seem also to acclimate their photosynthetic capacity seasonally, by allocating more photosynthetic nitrogen to leaves in autumn and spring than in summer. [source] Contributions of diffusional limitation, photoinhibition and photorespiration to midday depression of photosynthesis in Arisaema heterophyllum in natural high lightPLANT CELL & ENVIRONMENT, Issue 3 2000Hiroyuki Muraoka ABSTRACT Diurnal changes in photosynthetic gas exchange and chlorophyll fluorescence were measured under full sunlight to reveal diffusional and non-diffusional limitations to diurnal assimilation in leaves of Arisaema heterophyllum Blume plants grown either in a riparian forest understorey (shade leaves) or in an adjacent deforested open site (sun leaves). Midday depressions of assimilation rate (A) and leaf conductance of water vapour were remarkably deeper in shade leaves than in sun leaves. To evaluate the diffusional (i.e. stomatal and leaf internal) limitation to assimilation, we used an index [1,A/A350], in which A350 is A at a chloroplast CO2 concentration of 350 ,mol mol,1. A350 was estimated from the electron transport rate (JT), determined fluorometrically, and the specificity factor of Rubisco (S), determined by gas exchange techniques. In sun leaves under saturating light, the index obtained after the ,peak' of diurnal assimilation was 70% greater than that obtained before the ,peak', but in shade leaves, it was only 20% greater. The photochemical efficiency of photosystem II (,F/Fm,) and thus JT was considerably lower in shade leaves than in sun leaves, especially after the ,peak'. In shade leaves but not in sun leaves, A at a photosynthetically active photon flux density (PPFD) > 500 ,mol m,2 s,1 depended positively on JT throughout the day. Electron flows used by the carboxylation and oxygenation (JO) of RuBP were estimated from A and JT. In sun leaves, the JO/JT ratio was significantly higher after the ,peak', but little difference was found in shade leaves. Photorespiratory CO2 efflux in the absence of atmospheric CO2 was about three times higher in sun leaves than in shade leaves. We attribute the midday depression of assimilation in sun leaves to the increased rate of photorespiration caused by stomatal closure, and that in shade leaves to severe photoinhibition. Thus, for sun leaves, increased capacities for photorespiration and non-photochemical quenching are essential to avoid photoinhibitory damage and to tolerate high leaf temperatures and water stress under excess light. The increased Rubisco content in sun leaves, which has been recognized as raising photosynthetic assimilation capacity, also contributes to increase in the capacity for photorespiration. [source] Modulation by phytochrome of the blue light-induced extracellular acidification by leaf epidermal cells of pea (Pisum sativum L.): a kinetic analysisTHE PLANT JOURNAL, Issue 5 2000J. Theo M. Elzenga Summary Blue light induces extracellular acidification, a prerequisite of cell expansion, in epidermis cells of young pea leaves, by stimulation of the proton pumping-ATPase activity in the plasma membrane. A transient acidification, reaching a maximum 2.5,5 min after the start of the pulse, could be induced by pulses as short as 30 msec. A pulse of more than 3000 ,mol m,2 saturated this response. Responsiveness to a second light pulse was recovered with a time constant of about 7 min. The fluence rate-dependent lag time and sigmoidal increase of the acidification suggested the involvement of several reactions between light perception and activation of the ATPase. In wild-type pea plants, the fluence response relation for short light pulses was biphasic, with a component that saturates at low fluence and one that saturates at high fluence. The phytochrome-deficient mutant pcd2 showed a selective loss of the high-fluence component, suggesting that the high-fluence component is phytochrome-dependent and the low-fluence component is phytochrome-independent. Treatment with the calmodulin inhibitor W7 also led to the elimination of the phytochrome-dependent high-fluence component. Simple models adapted from the one used to simulate blue light-induced guard cell opening failed to explain one or more elements of the experimental data. The hypothesis that phytochrome and a blue light receptor interact in a short-term photoresponse is endorsed by model calculations based upon a three-step signal transduction cascade, of which one component can be modulated by phytochrome. [source] Osmotic adjustment of chickpea (Cicer arietinum) is not associated with changes in carbohydrate composition or leaf gas exchange under droughtANNALS OF APPLIED BIOLOGY, Issue 2 2007P.S. Basu Abstract Genetic differences in osmotic adjustment (OA) have been reported among chickpea (Cicer arietinum) cultivars. In this study eight advanced breeding lines (ABLs) derived from a cross between CTS 60543 (high OA) and Kaniva (low OA) and Tyson (medium OA) and Kaniva, along with the parents, were evaluated for OA, leaf carbohydrate composition and leaf gas exchange under dryland field conditions in India. The water potential (WP) decreased to lower values (less than ,2.5 MPa) in Tyson, M 110 and M 86 than in the other genotypes. With decrease in WP, OA increased by 0.5 MPa in Kaniva and CTS 60543 to 1.3 MPa in M 55. As the decrease in WP varied with genotype, when OA was regressed against WP M 39 and M 55 had greater increases in OA with decrease in WP than the remaining nine genotypes, including the parents. As WP decreased, leaf starch content decreased while total soluble sugars, hexoses and sucrose increased: the decrease in starch was much smaller in M 93 and M 129 than in Tyson and M 51, but genotypic differences could not be detected in the increase in total sugars, hexoses or sucrose. The rates of photosynthesis and transpiration decreased as the WP became more negative, but M 129 reached low rates of photosynthesis (2 ,mol m,2 s,1) and transpiration at a WP of ,1.7 MPa, whereas Tyson reached the same low rate at ,2.4 MPa. While OA varied among the chickpea genotypes, the differences were not associated with the changes in carbohydrate composition or the rates of gas exchange at low values of WP. Further, the degree of OA of the 11 genotypes was not the same as when they were selected for differences in OA under rainout shelter conditions in the field in Australia, suggesting that OA may show poor stability depending upon the stress level, location or physiological stage of the plant. This suggests that OA is not a valuable drought-resistance trait to select for in chickpea breeding programmes. [source] Pd,Ag membranes for auto-thermal ethanol reformingASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010Silvano Tosti Abstract The auto-thermal ethanol reforming was carried out at 200 kPa by a two-step process consisting of a traditional reformer operating at high temperature (700,740 °C) and a Pd,Ag multitube membrane module where the separation of hydrogen took place at 350,380 °C. The membrane module was a bundle of 11 thin-wall Pd,Ag tubes of wall thickness 50,60 µm, diameter 10 mm, and length 270 mm: permeation tests were performed at 300,395 °C with lumen pressure of 150,200 kPa, and nitrogen sweep flow rates in the shell side ranged from 10 to 30 l min,1 at atmospheric pressure. A hydrogen permeance Pe = 1.317 × 10,2 exp (,3.622 × 103/T(K)) mol m,2 s,1 Pa,0.5 was measured and complete hydrogen selectivity was verified. A water/ethanol mixture of molar ratio 2.50/1.00 was used as feed stream for carrying out ethanol reforming in the traditional fixed-bed reactor filled with a Ni on alumina catalyst. As a second step, the water gas shift (WGS) membrane reaction was carried out in the multitube membrane reactor: the Pd,Ag alloy of the membrane tubes worked for both catalyzing the reaction and for separating all the hydrogen produced in the reformer and in the membrane reactor itself. The hydrogen separated through the membrane was collected in the shell side of the membrane module: by operating with a water/ethanol feed flow rate of 200 g h,1, up to 1.2 l min,1 of pure hydrogen was produced. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Photosynthetic efficiency of Chlorella sorokiniana in a turbulently mixed short light-path photobioreactorBIOTECHNOLOGY PROGRESS, Issue 3 2010Anna M. J. Kliphuis Abstract To be able to study the effect of mixing as well as any other parameter on productivity of algal cultures, we designed a lab-scale photobioreactor in which a short light path (SLP) of (12 mm) is combined with controlled mixing and aeration. Mixing is provided by rotating an inner tube in the cylindrical cultivation vessel creating Taylor vortex flow and as such mixing can be uncoupled from aeration. Gas exchange is monitored on-line to gain insight in growth and productivity. The maximal productivity, hence photosynthetic efficiency, of Chlorella sorokiniana cultures at high light intensities (1,500 ,mol m,1 s,1) was investigated in this Taylor vortex flow SLP photobioreactor. We performed duplicate batch experiments at three different mixing rates: 70, 110, and 140 rpm, all in the turbulent Taylor vortex flow regime. For the mixing rate of 140 rpm, we calculated a quantum requirement for oxygen evolution of 21.2 mol PAR photons per mol O2 and a yield of biomass on light energy of 0.8 g biomass per mol PAR photons. The maximal photosynthetic efficiency was found at relatively low biomass densities (2.3 g L,1) at which light was just attenuated before reaching the rear of the culture. When increasing the mixing rate twofold, we only found a small increase in productivity. On the basis of these results, we conclude that the maximal productivity and photosynthetic efficiency for C. sorokiniana can be found at that biomass concentration where no significant dark zone can develop and that the influence of mixing-induced light/dark fluctuations is marginal. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] | ||||||||||||||||||||||||||||