Effects of different nitrogen, phosphorus, and iron concentrations and salinity on lipid production in newly isolated strain of the tropical green microalga, Scenedesmus dimorphus KMITL

The fatty acid composition, the effect of different concentrations of nitrogen (16.5-344 mg ?L^?1), phosphorus (9–45 mg? L^?1), iron (9–45 mg? L^?1) and salinity levels (0–20 psu) on lipid production in the green microalga Scenedesmus dimorphus KMITL, a new strain isolated from a tropical country, Thailand, were studied. The alga was isolated from a freshwater fish pond, and cultured in Chlorella medium by varying one parameter at a time. The main fatty acid composition of this strain was C16–C18 (97.52 %) fatty acids. A high lipid content was observed in conditions of 16.5 mg? L^?1-N, or 22 mg ?L^?1-P, or 45 mg ?L^?1-Fe, or 5 psu salinity, which accumulated lipids to 20.3?±?0.4, 19.4?±?0.2, 24.7?±?0.5, and 14.3?±?0.2 % of algal biomass, respectively. Increasing lipid content and lipid productivity was noted when the alga was cultured under high iron concentration and high salinity, as well as under reduced phosphorus conditions, whereas nitrogen limitation only resulted in an increased lipid content.     

Effects of cryopreservation of Phaseolus vulgaris L. seeds on early stages of germination

In this work, we studied the effects of cryopreservation on various parameters of early stages of germination of Phaseolus vulgaris seeds (0, 7 and 14?days). Percentages of germination, fresh mass of different plant parts, levels of chlorophyll pigments (a, b, total), malondialdehyde, other aldehydes, phenolics (cell wall-linked, free, and total) and protein were determined. No phenotypic changes were observed visually in seedlings recovered from cryopreserved seeds. However, several significant effects of seed liquid nitrogen exposure were recorded at the biochemical level. There was a significant negative effect of cryopreservation on shoot protein content, which decreased from 3.11?mg?g^?1 fresh weight for non-cryopreserved controls to 0.44?mg?g^?1 fresh shoot weight for cryopreserved seeds. On the other hand, cryopreservation significantly increased levels of other aldehydes than malondialdehyde in shoots at day 7, from 56.47?μmol?g^?1 for non-cryopreserved controls to 253.19?μmol?g^?1 fresh shoot weight for cryopreserved samples. Liquid nitrogen exposure significantly reduced phenolics contents (free, cell-wall linked, total) in roots at day 7 after onset of germination. In general, roots were more affected by cryostorage compared with other plant parts, while leaves were the least affected. The effects of seed cryopreservation seem to decline progressively along with seedling growth.     

The effect of nitrogen limitation on lipid productivity and cell composition in Chlorella vulgaris

Chlorella vulgaris accumulates lipid under nitrogen limitation, but at the expense of biomass productivity. Due to this tradeoff, improved lipid productivity may be compromised, despite higher lipid content. To determine the optimal degree of nitrogen limitation for lipid productivity, batch cultures of C. vulgaris were grown at different nitrate concentrations. The growth rate, lipid content, lipid productivity and biochemical and elemental composition of the cultures were monitored for 20 days. A starting nitrate concentration of 170 mg L^?1 provided the optimal tradeoff between biomass and lipid production under the experimental conditions. Volumetric lipid yield (in milligram lipid per liter algal culture) was more than double that under nitrogen-replete conditions. Interpolation of the data indicated that the highest volumetric lipid concentration and lipid productivity would occur at nitrate concentrations of 305 and 241 mg L^?1, respectively. There was a strong correlation between the nitrogen content of the cells and the pigment, protein and lipid content, as well as biomass and lipid productivity. Knowledge of the relationships between cell nitrogen content, growth, and cell composition assists in the prediction of the nitrogen regime required for optimal productivity in batch or continuous culture. In addition to enhancing lipid productivity, nitrogen limitation improves the lipid profile for biodiesel production and reduces the requirement for nitrogen fertilizers, resulting in cost and energy savings and a reduction in the environmental burden of the process.     

The effect of sodium bicarbonate supplementation on growth and biochemical composition of marine microalgae cultures

The addition of bicarbonate (NaHCO₃; 0, 1, or 2 g L^?1) to microalgal cultures has been evaluated for two species (Tetraselmis suecica and Nannochloropsis salina) in respect of growth and biochemical composition. In batch cultures, addition of bicarbonate (1 g L^?1) resulted in significantly (P?<?0.05) higher final mean cell abundances for both species. No differences in specific growth rates (SGRs) were recorded for T. suecica between treatments; however, increasing bicarbonate addition decreased SGR values in N. salina cultures. Bicarbonate addition (1 g L^?1) significantly improved nitrate utilisation from the external media and photosynthetic efficiency (F _v /F _m ) in both species. For both T. suecica and N. salina, bicarbonate addition significantly increased the cellular concentrations of total pigments (3,432–3,587 and 19–37 fg cell^?1, respectively) compared to cultures with no additional bicarbonate (1,727 and 11 fg cell^?1, respectively). Moreover, final concentrations of total cellular fatty acids in T. suecica and N. salina cultures supplemented with 2 g L^?1 bicarbonate (7.6?±?1.2 and 1.8?±?0.1 pg cell^?1, respectively) were significantly higher than those cells supplemented with 0 or 1 g L^?1 bicarbonate (3.2–3.5 and 0.9–1.0 pg cell^?1, respectively). In nitrate-deplete cultures, bicarbonate addition caused species-specific differences in the rate of cellular lipid production, rates of change in fatty acid composition and final lipid levels. In summary, the addition of sodium bicarbonate is a viable strategy to increase cellular abundance and concentrations of pigments and lipids in some microalgae as well as the rate of lipid accumulation in nitrate-deplete cultures.     

Effect of ammonium-N on malic enzyme and lipid production in Rhodotorula glutinis grown on monosodium glutamate wastewater

Rhodotorula glutinis, an oil producing strain, can utilize monosodium glutamate (MSG) wastewater as a raw material for lipid production. The effects of ammonium-N in the MSG wastewater (ammonium 15,000–25,000?mg/L, COD 30,000–50,000?mg/L) on cell growth, lipid accumulation and malic enzyme activity of R. glutinis have been studied. Four initial ammonium sulfate concentrations in the medium were set, which were 20, 60, 100, and 140?g/L. With an increase in the ammonium sulfate concentration, the uptake of ammonia nitrogen and lipid accumulation increased while the biomass decreased at 72?h. The maximum value of ammonia nitrogen consumption reached 5.77?g/L for an initial ammonium sulfate concentration of 140?g/L at 72?h. In addition, 60?g/L ammonium sulfate concentration may be an appropriate concentration for R. glutinis cultivation. The activity of the malic enzyme was measured and the results showed that there was a linear relationship between the intracellular lipid content and the total malic enzyme activity.     

Lipid productivity, settling potential and fatty acid profile of 11 microalgal species grown under nitrogen replete and limited conditions

Microalgae are a promising alternative source of oil for biodiesel production. Identification of a species with desirable characteristics is a key component towards achieving economic feasibility for the process. This has been compromised by a lack of data allowing effective interspecies comparison. Eleven species of microalgae, selected on the basis of available literature data, were tested for lipid productivity, gravity sedimentation and the suitability of their fatty acid profiles for biodiesel production. The response to nitrogen limitation was species-specific. Lipid yields and productivity were higher at 150?mg?L^?1 nitrate than at 1,500?mg?L^?1 for all species tested except Spirulina platensis. The Chlorophyta, particularly Chlorella vulgaris and Scenedesmus, had the highest growth rates and showed the greatest increase in lipid content in response to nitrogen limitation. Cylindrotheca fusiformis, S. platensis, Scenedesmus and Tetraselmis suecica had the fastest settling rates and highest biomass recoveries after 24?h of gravity sedimentation. For most species, the fuel would need to be blended or culture conditions to be optimised to achieve the correct lipid profile in order for microalgal fuel to meet the European standards for biodiesel production (EN 14214). The most promising species overall were the freshwater algae Scenedesmus and C. vulgaris and the marine algae C. fusiformis and Nannochloropsis.     

The effects of cultivation depth,areal density,and nutrient level on lipid accumulation of <Emphasis Type="Italic">Scenedesmus acutus</Emphasis> in outdoor raceway ponds

Lipid accumulation is critical in the production of biodiesel from microalgae. However, little work has been done on the assessment of lipid accumulation during nitrogen stress in large research-scale outdoor raceways during different seasons; most values for lipid accumulation are assumptions based on work completed in laboratory settings or outdoor photobioreactors. This study focused on the use of raceway ponds operated in batch cultivation mode with an area of 30.37 m² to determine the impacts of nitrate-nitrogen concentration and cultivation depth on the ability of Scenedesmus acutus strain LB 0414 to accumulate lipids. A concentration of less than 60 mg N-NO₃ ^??L^?1 was required for removal of nitrogen in the cultivation medium within 8 days to stimulate lipid accumulation and increase lipid productivity. When nitrate concentrations were increased to prevent nitrogen depletion, lipid productivity decreased, which demonstrates that stressing is needed to induce lipid accumulation for increased lipid productivity. Additionally, decreasing cultivation depth below 9 cm, compared to raceways operated at a depth of 20–24 cm, increased lipid productivity by 62 % in December 2014 and 38 % in February 2015. More desirable environmental conditions, mainly increased sunlight and temperature, in February, increased biodiesel productivity for all raceways and account for the decrease in productivity differences. This research highlights increased lipid productivity found by reducing cultivation depth and nitrogen concentrations in outdoor raceways and provides insight into the optimal conditions for large-scale biodiesel production.     

Contrasting nitrogen uptake by diatom and Phaeocystis-dominated phytoplankton assemblages in the North Sea

This paper documents ambient concentrations of nutrients in the Belgian coastal waters of the North Sea during the spring of 1996 and 1997. The paper elaborates the differences of uptake rates of oxidised nitrogen (NO₃⁻) and reduced nitrogen (NH₄ and urea) by Phaeocystis and diatoms. The nitrogen concentrations were dominated by NO₃⁻ with a maximum concentration of 30 μM (January 1997) and 40 μM (March 1996). In 1996, Phaeocystis dominated the spring biomass with a maximum of 521 μg C l⁻¹, while maximum diatom biomass was 174 μg C l⁻¹. In 1997, the maximum Phaeocystis spring biomass was 1600 μg C l⁻¹ and diatom maximum biomass was below 100 μg C l⁻¹. A maximum bacteria biomass of about 55 μg C l⁻¹ was observed in mid-May 1996. The maximum nitrogen uptake rates were recorded during spring and were dominated by NO₃⁻ (0.005 h⁻¹ in 1996 and 0.032 h⁻¹ in 1997). Maximum specific NH₄ uptake rates were between 0.005 h⁻¹ in May 1996 and 0.006 h⁻¹ in April 1997. The NO₃⁻ uptake rates displayed exponential decrease versus increasing ambient reduced nitrogen concentrations (ammonium and urea), whereas the reduced nitrogen uptake increased but never compensated the decreased nitrate uptake. The NH₄ uptake kinetics of diatoms displayed lower v_max compared to Phaeocystis. Consequently, Phaeocystis showed ability to increase their NH₄ uptake capacity when more NH₄ became available while diatoms failed to do so, after ammonium had exceeded their saturation concentration (>1 μM). Although reduced nitrogen has a negative effect on the uptake of NO₃⁻, Phaeocystis have more advantage than diatoms on the uptake of ammonium. This might be contributing to the biomass domination shown by Phaeocystis over extended periods in spring.     

Rapid estimation of lipid content in an Antarctic ice alga (Chlamydomonas sp.) using the lipophilic fluorescent dye BODIPY505/515

Chlamydomonas sp. ICE-L, isolated from Antarctic coastal marine environments, was selected as a high lipid producer, which may be useful for biodiesel production. The lipophilic fluorescent dye BODIPY505/515 was used to determine the algal lipid content. Lipid bodies stained with BODIPY505/515 have a characteristic green fluorescence, and their volumes were determined using the sphere volume formula. In this study, lipid accumulation by Chlamydomonas ICE-L was analyzed under different cultivation conditions (nitrogen deficiency and UV-B radiation). The results demonstrated that nitrogen deficiency and UV-B radiation could significantly promote the accumulation of lipid content per cell. The highest yields of total lipid content (reaching 84?μL?L^?1) were obtained in full Provasoli medium after 12?days of cultivation, but not in the nitrogen-deficient medium. The inoculum used in this experiment was obtained from the late-exponential growth phase. The main reason was that the cell numbers in nitrogen-deficient medium had not increased and total lipid contents were offset by the lower growth rate. Considering the high lipid content in Chlamydomonas sp. ICE-L, this alga might be a promising alternative species for production of microalgal oil for the production of renewable biodiesel in the future.     

In vitro regeneration in Sarcostemma acidum (Roxb.) –an important medicinal plant of semi-arid ecosystem of Rajasthan, India

An efficient regeneration protocol for Sarcostemma acidum – an important medicinal plant has been established. Callus initiated from nodal explant on MS medium with 2.0 mg?L^?1 of NAA + additives. Callus initiated was subcultured on MS medium containing various concentrations of NAA or 2,4-D. Out of these combinations, MS medium +1.0 mg?L^?1 of NAA + additives was found to be effective for the multiplication of callus. Subculture was done after an interval of 20–22 days. For differentiation of callus BAP or Kinetin alone was found to be less effective. Maximum frequency of shoot regeneration recorded on MS medium +1.0 mg?L^?1 of BAP?+?0.5 mg?L^?1 of Kinetin and 0.1 mg?L^?1 of NAA + additives. The in vitro differentiated shoots were excised and inoculated on 1/4 strength MS medium +2.0 mg?L^?1 of IBA?+?0.02 % activated charcoal for in vitro rooting. Maximum response (90 %) was recorded on this medium. In vitro differentiated shoots were inoculated on autoclaved soilrite® after treatment with root inducing auxins. Ex vitro rooting in this plant species has been reported for the first time. Eighty five percent of the shoots rooted under ex vitro conditions. Both in vitro and ex vitro rooted plantlets were hardened in a green house.     

Euglena sp. as a suitable source of lipids for potential use as biofuel and sustainable wastewater treatment

Prolific algal growth in sewage ponds with high organic loads in the tropical regions can provide cost-effective and efficient wastewater treatment and biofuel production. This work examines the ability of Euglena sp. growing in wastewater ponds for biofuel production and treatment of wastewater. The algae were isolated from the sewage treatment plants and were tested for their nutrient removal capability. Compared to other algae, Euglena sp. showed faster growth rates with high biomass density at elevated concentrations of ammonium nitrogen (NH₄-N) and organic carbon (C). Profuse growth of these species was observed in untreated wastewaters with a mean specific growth rate (μ) of 0.28 day^?1 and biomass productivities of 132 mg ?L^?1? day^?1. The algae cultured within a short period of 8 days resulted in the 98 % removal of NH₄-N, 93 % of total nitrogen 85 % of ortho-phosphate, 66 % of total phosphate and 92 % total organic carbon. Euglenoids achieved a maximum lipid content of 24.6 % (w/w) with a biomass density of 1.24 g ?L^?1 (dry wt.). Fourier transform infrared spectra showed clear transitions in biochemical compositions with increased lipid/protein ratio at the end of the culture. Gas chromatography and mass spectrometry indicated the presence of high contents of palmitic, linolenic and linoleic acids (46, 23 and 22 %, respectively), adding to the biodiesel quality. Good lipid content (comprised quality fatty acids), efficient nutrient uptake and profuse biomass productivity make the Euglena sp. as a viable source for biofuel production in wastewaters.     

An exploration of how litter controls drainage water DIN, DON and DOC dynamics in freely draining acid grassland soils

Surface and subsurface litter fulfil many functions in the biogeochemical cycling of C and N in terrestrial ecosystems. These were explored using a microcosm study by monitoring dissolved inorganic nitrogen (DIN) (NH₄ ⁺–N?+?NO₃ ^?–N), dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) concentrations and fluxes in drainage water under ambient outdoor temperatures. Subsurface litter remarkably reduced the DIN concentrations in winter, probably by microbial N uptake associated with higher C:N ratio of added litter compared with soil at 10–25?cm depth. Fluxes of DIN were generally dominated by NO₃ ^?–N; but NH₄ ⁺–N strongly dominated DIN fluxes during freeze–thaw events. Appreciable concentrations of NH₄ ⁺–N were observed in the drainage from the acid grassland soils throughout the experiment, indicating NH₄ ⁺–N mobility and export in drainage water especially during freeze–thaw. Litter contributed substantially to DOC and DON production and they were correlated positively (p?<?0.01) for all treatments. DOC and DON concentrations correlated with temperature for the control (p?<?0.01) and surface litter (p?<?0.001) treatments and they were higher in late summer. The subsurface litter treatment, however, moderated the effect of temperature on DOC and DON dynamics. Cumulative N species fluxes confirmed the dominance of litter as the source of DON and DOC in the drainage water. DON constituted 42, 46 and 62% of cumulative TDN flux for control, surface litter and subsurface litter treatments respectively.     

Dietary Supplementation of Zinc Nanoparticles and Its Influence on Biology,Physiology and Immune Responses of the Freshwater Prawn,Macrobrachium rosenbergii

The present study was conducted to assess the influence of dietary zinc nanoparticles (size 50 nm) on the growth, biochemical constituents, enzymatic antioxidant levels and the nonspecific immune response of the freshwater prawn, Macrobrachium rosenbergii post larvae (PL). The concentrations of dietary supplement zinc nanoparticles (ZnNPs) were 0, 10, 20, 40, 60 and 80 mg kg^?1 with the basal diet, and the level of Zn in ZnNP-supplemented diets were 0.71, 10.61, 20.73, 40.73, 60.61 and 80.60 mg kg^?1, respectively. ZnNP-incorporated diets were fed to M. rosenbergii PL (initial body weight, 0.18?±?0.02 g) in a triplicate experimental setup for a period of 90 days. ZnNP supplemented feed fed PL up to 60 mg kg^?1 showed significantly (P?<?0.05) improved performance in survival, growth and activities of digestive enzymes (protease, amylase and lipase). The concentrations of biochemical constituents (total protein, total amino acid, total carbohydrate and total lipid), total haemocyte count and differential haemocyte count were elevated in 10–60 mg kg^?1 ZnNP supplemented feed fed PL. However, the PL fed with 80 mg ZnNPs kg^?1 showed negative results. Activities of enzymatic antioxidants [superoxide dismutase (SOD) and catalase (CAT)], metabolic enzymes [glutamate–oxaloacetate transaminase (GOT) and glutamate–pyruvate transaminase (GPT)] and the process of lipid peroxidation (LPO) in the hepatopancreas and muscle showed no significant alterations in 10–60 mg kg^?1 ZnNP supplemented feed fed PL. Whereas, 80 mg ZnNPs kg^?1 supplemented feed fed PL showed significant elevations in SOD, CAT, LPO, GOT and GPT. Therefore, 80 mg ZnNPs kg^?1 was found to be toxic to M. rosenbergii PL. Thus, the study suggests that up to 60 mg ZnNPs kg^?1 can be supplemented for regulating survival, growth and immunity of M. rosenbergii.     

Airborne basidiospores of Coprinus and Ganoderma in a Caribbean region

The present study sought to examine Coprinus and Ganoderma airborne spore counts, analysing seasonal variations, the influence of meteorological variables and intraday behaviour with a view to charting the aerobiological dynamics of both genera in Havana (Cuba) during a 2-year period (November 2010–October 2012). A Hirst-type volumetric air sampler was used as sampling methodology. The spores registered in the air were identified and counted following the model proposed by the Spanish Aerobiological Network based on two longitudinal transects along the slides. Coprinus spores outnumbered those of the Ganoderma (28,468 annual total spores vs. 1,921 spores). Moreover, both genera were recorded in the atmosphere on a large number of days over the two-year study period, with daily maximum concentrations in the rainy months. The daily maximum value for Coprinus was 880 spores/m³ (30 September 2011), whereas for Ganoderma 44 spores/m³ (4 September 2011). The analysis of the Spearman correlation coefficient showed a significant positive correlation of the airborne Coprinus and Ganoderma spores with the temperature, relative humidity and rainfall, whereas the degree of association is negative with the wind speed. Regarding the intraday behaviour, both basidiospores were more abundant in the atmosphere during the night, with a maximum peak at 5–6 a.m.     

Phase Plane Trajectories of the Muscle Spike Potential

To facilitate a study of the transmembrane action current, the striated muscle spike potential was recorded against its first time derivative. The specialized recording methods are described, as well as several mathematical transformations between a coordinate system in V, t, and the present coordinate system in V, dV/dt. The particular properties of the present recording method permitted an estimation for the “sodium” potential in muscle fibers at +39 mv. The maximum membrane conductance during spike production is in the order of 150 to 200 mmhos/cm². The changes in the shape of the recorded response indicate that the ionic currents and membrane conductances are reduced by Tris buffer or hypertonic Ringer's fluid. However, no marked changes in the properties of active membrane were observed when chloride ion was replaced by sulfate.     

The effect of degree and timing of nitrogen limitation on lipid productivity in Chlorella vulgaris

Improvements in lipid productivity would enhance the economic feasibility of microalgal biodiesel. In order to optimise lipid productivity, both the growth rate and lipid content of algal cells must be maximised. The lipid content of many microalgae can be enhanced through nitrogen limitation, but at the expense of biomass productivity. This suggests that a two-stage nitrogen supply strategy might improve lipid productivity. Two different nitrogen supply strategies were investigated for their effect on lipid productivity in Chlorella vulgaris. The first was an initial nitrogen-replete stage, designed to optimise biomass productivity, followed by nitrogen limitation to enhance lipid content (two-stage batch) and the second was an initial nitrogen-limited stage, designed to maximise lipid content, followed by addition of nitrogen to enhance biomass concentration (fed-batch). Volumetric lipid yield in nitrogen-limited two-stage batch and fed-batch was compared with that achieved in nitrogen-replete and nitrogen-limited batch culture. In a previous work, maximum lipid productivity in batch culture was found at an intermediate level of nitrogen limitation (starting nitrate concentration of 170 mg L^?1). Overall lipid productivity was not improved by using fed-batch or two-stage culture strategies, although these strategies showed higher volumetric lipid concentrations than nitrogen-replete batch culture. The dilution of cultures prior to nitrogen deprivation led to increased lipid accumulation, indicating that the availability of light influenced the rate of lipid accumulation. However, dilution did not lead to increased lipid productivity due to the resulting lower biomass concentration.     

Lipid productivity and fatty acid composition in Chlorella and Scenepdesmus strains grown in nitrogen-stressed conditions

Thirty Chlorella and 30 Scenedesmus strains grown in nitrogen-stressed conditions (70 mg L^?1 N) were analyzed for biomass accumulation, lipid productivity, protein, and fatty acid (FA) composition. Scenedesmus strains produced more biomass (4.02?±?0.73 g L^?1) after 14 days in culture compared to Chlorella strains (2.57?±?0.12 g L^?1). Protein content decreased and lipid content increased from days 8 to 14 with an increase in triacylglycerol (TAG) accumulation in most strains. By day 14, Scenedesmus strains generally had higher lipid productivity (53.5?±?3.7 mg lipid L^?1 day^?1) than Chlorella strains (35.1?±?2.8 mg lipid L^?1 day^?1) with the lipids consisting mainly of C16–18 TAGs. Scenedesmus strains generally had a more suitable FA profile with higher amounts of saturated fatty acids and monounsaturated fatty acids (MUFAs) and a smaller polyunsaturated fatty acid (PUFA) component. Chlorella strains had a larger PUFA component and smaller MUFA component. The general trend in the FA composition of Chlorella strains was oleic > palmitic > α-linolenic = linoleic > eicosenoic > heptadecenoic > stearic acid. For Scenedesmus strains, the general trend was oleic > palmitic > linoleic > α-linolenic > stearic > eicosenoic > palmitoleic > heptadecenoic acid. The most promising strains with the highest lipid productivity and most suitable FA profiles were Scenedesmus sp. MACC 401, Scenedesmus soli MACC 721, and Scenedesmus ecornis MACC 714. Although Chlorella sp. MACC 519 had lower lipid productivity, the FA profile was good with a lower PUFA component compared to the other Chlorella strains analyzed and a low linolenic acid concentration.     

Lead dynamics in the forest floor and mineral soil in south-central Ontario

Recent studies have suggested that the residence time of Pb in the forest floor may not be as long as previously thought, and there is concern that the large pulse of atmospheric Pb deposited in the 1960s and early 1970s may move rapidly through mineral soils and eventually contaminate groundwater. In order to assess Pb mobility at a woodland (JMOEC) in south-central Ontario, a stable Pb isotope tracer ²⁰⁷Pb (8?mg?m^?2) was added to the forest floor in white pine (Pinus strobus) and sugar maple (Acer saccharum) stands, respectively, and monitored over a 2-year period. Excess ²⁰⁷Pb was rapidly lost from the forest floor. Applying first-order rate coefficients (k) of 0.57 (maple) and 0.32 (pine) obtained from the tracer study, and estimates of Pb deposition in the region, current predicted Pb concentrations in the forest floor are 1.5–3.1 and 2.1–5.8?mg?kg^?1 in the maple and pine plots, respectively. These values compare favorably with measured concentrations (corrected for mineral soil contamination) of 3.1–4.3?mg?kg^?1 in the maple stand and 2.6–3.6?mg?kg^?1 in the pine stand. The response time (1/k) of Pb in the forest floor at the sugar maple and white pine plots was estimated to be 1.8 and 3.1 years, respectively. The rapid loss of Pb from the forest floor at the JMOEC is much greater than previously reported, and is probably due to the rapid rate of litter turnover that is characteristic of forests with mull-type forest floors. In a survey of 23 forested sites that border the Precambrian Shield in south-central Ontario, Pb concentrations in the forest floor increased exponentially with decreasing soil pH. Lead concentrations in the forest floor at the most acidic survey sites, which exhibited mor-type forest floors, were approximately 10 times higher (～80?mg?kg^?1) than at the JMOEC, and pollution Pb burdens were up to 25 times greater. Despite the rapid loss of Pb from the forest floor at the JMOEC, the highest pollution Pb concentrations were found in the upper (0–1?cm) mineral soil horizon. Lead concentrations in the upper 30?cm of mineral soil were strongly correlated with organic matter content, indicating that pollution Pb does not move as a pulse down the soil profile, but instead is linked with organic matter distribution, indicating groundwater contamination is unlikely.     

Photosynthetic physiological performance and proteomic profiling of the oleaginous algae <Emphasis Type="Italic">Scenedesmus acuminatus</Emphasis> reveal the mechanism of lipid accumulation under low and high nitrogen supplies

In this study, we presented cellular morphological changes, time-resolved biochemical composition, photosynthetic performance and proteomic profiling to capture the photosynthetic physiological response of Scenedesmus acuminatus under low nitrogen (3.6 mM NaNO₃, N^?) and high nitrogen supplies (18.0 mM NaNO₃, N⁺). S. acuminatus cells showed extensive lipid accumulation (53.7% of dry weight) and were enriched in long-chain fatty acids (C16 & C18) under low nitrogen supply. The activity of PSII and photosynthetic rate decreases, whereas non-photochemical quenching and dark respiration rates were increased in the N^? group. In addition, the results indicated a redistribution of light excitation energy between PSII and PSI in S. acuminatus exists before lipid accumulation. The iTRAQ results showed that, under high nitrogen supply, protein abundance of the chlorophyll biosynthesis, the Calvin cycle and ribosomal proteins decreased in S. acuminatus. In contrast, proteins associated with the photosynthetic machinery, except for F-type ATPase, were increased in the N⁺ group (N⁺, 3 vs. 9 days and 3 days, N⁺ vs. N^?). Under low nitrogen supply, proteins involved in central carbon metabolism, fatty acid synthesis and branched-chain amino acid metabolism were increased, whereas the abundance of proteins of the photosynthetic machinery had decreased, with exception of PSI (N^?, 3 vs. 9 days and 9 days, N⁺ vs. N^?). Collectively, the current study has provided a basis for the metabolic engineering of S. acuminatus for biofuel production.     

Bioremediation potential of Palmaria palmata and Chondrus crispus (Basin Head): effect of nitrate and ammonium ratio as nitrogen source on nutrient removal

Palmaria palmata and Chondrus crispus were grown for 4 weeks in 1-L flasks at 10 °C to evaluate nutrient uptake and their potential application as nutrient biofilters in effluent from finfish culture. For greatest bioremediation benefit within an integrated system, we conclude that a seaweed biofilter using these species should be placed prior to bacterial biofiltration for exposure to greater proportions of ammonium than nitrate, though it is apparent that the productivity of both species is not influenced by the nitrogen source. Five combinations of ammonium– and nitrate–nitrogen were compared, each with a total N concentration of 300 μM (300:0, 270:30, 150:150, 30:270, 0:300). Molar nitrogen/phosphorus ratio was 10:1. The maximum growth rates were 8.9 and 6.0 % per day for P. palmata and C. crispus, respectively. For both species, the total nitrogen uptake was highest at 300 μM ammonium, 4.46 mgN gDW^?1 day^?1 for P. palmata and 3.40 mg?N? g?DW^?1?day^?1 for C. crispus. Over a 24-h period, 23–37 % of the available nitrate and 91–100 % of the available ammonium were taken up by P. palmata. In the same period, C. crispus took up 55–87 % of available nitrate and 89–100 % of ammonium. Tissue N in P. palmata was highest (4.1 %) at 270 and 300 μM ammonium, while the nitrogen source did not have a significant effect on the tissue N of C. crispus (mean of 4.6 %).