On-line estimation of O<Subscript>2</Subscript> production,CO<Subscript>2</Subscript> uptake,and growth kinetics of microalgal cultures in a gas-tight photobioreactor

Growth of the green algae Chlamydomonas reinhardtii and Chlorella sp. in batch cultures was investigated in a novel gas-tight photobioreactor, in which CO₂, H₂, and N₂ were titrated into the gas phase to control medium pH, dissolved oxygen partial pressure, and headspace pressure, respectively. The exit gas from the reactor was circulated through a loop of tubing and re-introduced into the culture. CO₂ uptake was estimated from the addition of CO₂ as acidic titrant and O₂ evolution was estimated from titration by H₂, which was used to reduce O₂ over a Pd catalyst. The photosynthetic quotient, PQ, was estimated as the ratio between O₂ evolution and CO₂ up-take rates. NH₄ ⁺, NO₂ ⁻, or NO₃ ⁻ was the final cell density limiting nutrient. Cultures of both algae were, in general, characterised by a nitrogen sufficient growth phase followed by a nitrogen depleted phase in which starch was the major product. The estimated PQ values were dependent on the level of oxidation of the nitrogen source. The PQ was 1 with NH₄ ⁺ as the nitrogen source and 1.3 when NO₃ ⁻ was the nitrogen source. In cultures grown on all nitrogen sources, the PQ value approached 1 when the nitrogen source was depleted and starch synthesis became dominant, to further increase towards 1.3 over a period of 3–4 days. This latter increase in PQ, which was indicative of production of reduced compounds like lipids, correlated with a simultaneous increase in the degree of reduction of the biomass. When using the titrations of CO₂ and H₂ into the reactor headspace to estimate the up-take of CO₂, the production of O₂, and the PQ, the rate of biomass production could be followed, the stoichiometrical composition of the produced algal biomass could be estimated, and different growth phases could be identified.     

CO2 Dynamics and Growth in Photoautotrophic and Photomixotrophic Apple Cultures

The daily dynamics of CO₂ concentration in the culture vessels and the photoautotrophic or photomixotrophic growth capacity of apple (Malus pumila hybrid MM 106 paradisiaca× Northern Spy) cultures were studied. The photoautotrophic cultures were grown on a sugar-free growth medium and submitted (0S+CO₂) or not (0S-CO₂) to periodic injections of exogenous CO₂. The photomixotrophic cultures were grown in the presence of 30 g dm⁻³ sucrose, with (30S+CO₂) or without (30S-CO₂) CO₂ enrichment. The photosynthetic photon flux density applied was of 210 ± 5 μmol m⁻²s⁻¹. In the 0S-CO₂ treatment, CO₂ showed rather uniform and narrow light-dark fluctuations throughout the culturing cycle. In the 30S-CO₂ treatment, the daily ratio between CO₂ produced during the dark period and that uptaken during the following light period, was almost always above 1 with the only exception of a few days (from the 5^th to the 9^th day) when the amount of photosynthesised CO₂ was equal to or higher than that produced during dark respiration. The 0S+CO₂ cultures needed to be enriched all days with exogenous CO₂ to avoid periods of gas deficiency while in 30S+CO₂ the CO₂ injected the first culturing day was uptaken over 5 d; thereafter, daily injections were necessary. Culture fresh and dry mass, number of newly formed shoots and number of nodes per shoot in 0S+CO₂ treatment did not statistically differ from the values obtained with 30S−CO₂. The highest growth was observed in 30S+CO₂ treatment. The increase in culture fresh mass due to 1 μmol of CO₂ added to the culture vessels was 1.54 and 1.36 mg for 30S and 0S respectively, while in terms of dry mass the increase was about 2.5 times higher in the sugar-enriched treatment. CO₂ enrichment accounted for 77.3 % and 21.2 % of the final fresh mass in 0S+CO₂ and 30S+CO₂, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Response of Photosynthetic Apparatus of Spring Barley (Hordeum vulgare L.) to Combined Effect of Elevated CO2 Concentration and Different Growth Irradiance

The response of barley (Hordeum vulgare L. cv. Akcent) to various photosynthetic photon flux densities (PPFDs) and elevated [CO₂] [700 μmol (CO₂) mol⁻¹; EC] was studied by gas exchange, chlorophyll (Chl) a fluorescence, and pigment analysis. In comparison with barley grown under ambient [CO₂] [350 μmol (CO₂) mol⁻¹; AC] the EC acclimation resulted in a decrease in photosynthetic capacity, reduced stomatal conductance, and decreased total Chl content. The extent of acclimation depression of photosynthesis, the most pronounced for the plants grown at 730 μmol m⁻² s⁻¹ (PPFD₇₃₀), may be related to the degree of sink-limitation. The increased non-radiative dissipation of absorbed photon energy for all EC plants corresponded to the higher de-epoxidation state of xanthophylls only for PPFD₇₃₀ barley. Further, a pronounced decrease in photosystem 2 (PS2) photochemical efficiency (given as F_V/F_M) for EC plants grown at 730 and 1 200 μmol m⁻² s⁻¹ in comparison with AC barley was related to the reduced epoxidation of antheraxanthin and zeaxanthin back to violaxanthin in darkness. Thus the EC conditions sensitise the photosynthetic apparatus of high-irradiance acclimated barley plants (particularly PPFD₇₃₀) to the photoinactivation of PS2. This revised version was published online in August 2006 with corrections to the Cover Date.     

Improved guggulsterone production from sugars, precursors, and morphactin in cell cultures of Commiphora wightii grown in shake flasks and a bioreactor

Cell cultures of Commiphora wightii (Arnott.) Bhandari were grown in shake flasks and a bioreactor and an increase in guggulsterone accumulation up to 18 μg l⁻¹ was recorded in cells grown in the production medium containing a combination of sucrose:glucose (4% total), precursors (phenylalanine, pyruvic acid, xylose, and sodium acetate), morphactin, and 2iP. A yield of 10 g l⁻¹ biomass and ∼200 μg l⁻¹ guggulsterone was recorded in a 3-l flask and in a 2-l stirred tank bioreactor compared with 6.6 g biomass and 67 μg l⁻¹ guggulsterone in 250-ml flasks. Increased vessel size was correlated with increased biomass and guggulsterone accumulation. 2iP alone was not effective for biomass and guggulsterone accumulation in cell cultures of C. wightii.     

Effect of nutritional parameters on laccase production by the culinary and medicinal mushroom, Grifola frondosa

Summary Extracellular laccase in cultures of Grifola frondosa grown in liquid culture on a defined medium was first detectable in the early/middle stages of primary growth, and enzyme activity continued to increase even after fungal biomass production had peaked. Laccase production was significantly increased by supplementing cultures with 100–500 (M Cu over the basal level (1.6 mM Cu) and peak levels observed at 300 mM Cu were ∼ ∼7-fold higher than in unsupplemented controls. Decreased laccase activity similar to levels detected in unsupplemented controls, as well as an adverse effect on fungal growth, occurred with further supplementation up to and including 0.9 mM Cu, but higher enzyme titres (2- to 16-fold compared with controls) were induced in cultures supplemented with 1–2 mM Cu²⁺. SDS-PAGE combined with activity staining revealed the presence of a single protein band (M _r ∼ ∼70 kDa) exhibiting laccase activity in control culture fluids, whereas an additional distinct second laccase protein band (M _r␣∼ ∼45 kDa) was observed in cultures supplemented with 1–2 mM Cu. Increased levels of extracellular laccase activity, and both laccase isozymes, were also detected in cultures of G. frondosa supplemented with ferulic, vanillic, veratric and 4-hydroxybenzoic acids, and 4-hydroxybenzaldehyde. The optimal temperature and pH values for laccase activity were 65 °C and pH 2.2 (using 2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonate) {ABTS} as substrate), respectively, and the enzyme was relatively heat stable. In solid-state cultures of G. frondosa grown under conditions adopted for industrial-scale mushroom production, extracellular laccase levels increased during the substrate colonization phase, peaked when the substrate was fully colonized, and then decreased sharply during fruit body development.     

Avocado shoot culture, plantlet development and net CO2 assimilation in an ambient and CO2 enhanced environment

Summary The proliferation and survival of avocado nodal cultures of juvenile origin were affected by the form and concentration of nitrogen. Optimum growth was achieved on modified Murashige and Skoog medium containing 67% KNO₃ and 33% NH₄NO₃ with total N of 40 mM supplemented with 100 mg l⁻¹ myo-inositol, 1 mg l⁻¹ thiamine HCl, 30 g l⁻¹ sucrose, and 4.44 μM BA with a 16-h photoperiod (120–150 μmol m⁻² s⁻¹). Proliferating shoots and plantlets were photosynthetically active. Better shoot growth and accumulation of higher biomass occurred in a CO₂-enriched environment than under ambient CO₂ conditions. CO₂ assimilation efficiency, however, was higher under the latter conditions than in a CO₂-enhanced environment, e.g., 31±7 and 17±2 μmol CO₂ m⁻² s⁻¹, respectively. The net CO₂ assimilation rates of in vitro grown plantlets were comparable to those of seedlings ex vitro.     

Interactive effects of elevated CO2 and drought stress on leaf water potential and growth in Caragana intermedia

We studied the responses of leaf water potential (Ψ_w), morphology, biomass accumulation and allocation, and canopy productivity index (CPI) to the combined effects of elevated CO₂ and drought stress in Caragana intermedia seedlings. Seedlings were grown at two CO₂ concentrations (350 and 700 μmol mol⁻¹) interacted with three water regimes (60–70%, 45–55%, and 30–40% of field capacity of soil). Elevated CO₂ significantly increased Ψ_w, decreased specific leaf area (SLA) and leaf area ratio (LAR) of drought-stressed seedlings, and increased tree height, basal diameter, shoot biomass, root biomass as well as total biomass under the all the three water regimes. Growth responses to elevated CO₂ were greater in well-watered seedlings than in drought-stressed seedlings. CPI was significantly increased by elevated CO₂, and the increase in CPI became stronger as the level of drought stress increased. There were significant interactions between elevated CO₂ and drought stress on leaf water potential, basal diameter, leaf area, and biomass accumulation. Our results suggest that elevated CO₂ may enhance drought avoidance and improved water relations, thus weakening the effect of drought stress on growth of C. intermedia seedings.     

Sagebrush and grasshopper responses to atmospheric carbon dioxide concentration

Summary Seed- and clonally-propagated plants of Big Sagebrush (Artemisia tridentata var.tridentata) were grown under atmospheric carbon dioxide regimes of 270, 350 and 650 μl l⁻¹ and fed toMelanoplus differentialis andM. sanguinipes grasshoppers. Total shrub biomass significantly increased as carbon dioxide levels increased, as did the weight and area of individual leaves. Plants grown from seed collected in a single population exhibited a 3–5 fold variation in the concentration of leaf volatile mono- and sesquiterpenes, guaianolide sesquiterpene lactones, coumarins and flavones within each CO₂ treatment. The concentration of leaf allelochemicals did not differ significantly among CO₂ treatments for these seed-propagated plants. Further, when genotypic variation was controlled by vegetative propagation, allelochemical concentrations also did not differ among carbon dioxide treatments. On the other hand, overall leaf nitrogen concentration declined significantly with elevated CO₂. Carbon accumulation was seen to dilute leaf nitrogen as the balance of leaf carbon versus nitrogen progressively increased as CO₂ growth concentration increased. Grasshopper feeding was highest on sagebrush leaves grown under 270 and 650 μl l⁻¹ CO₂, but varied widely within treatments. Leaf nitrogen concentration was an important positive factor in grasshopper relative growth but had no overall effect on consumption. Potential compensatory consumption by these generalist grasshoppers was apparently limited by the sagebrush allelochemicals. Insects with a greater ability to feed on chemically defended host plants under carbon dioxide enrichment may ultimately consume leaves with a lower nitrogen concentration but the same concentration of allelochemicals. Compensatory feeding may potentially increase the amount of dietary allelochemicals ingested for each unit of nitrogen consumed.     

Simultaneous flue gas bioremediation and reduction of microalgal biomass production costs

A flue gas originating from a municipal waste incinerator was used as a source of CO₂ for the cultivation of the microalga Chlorella vulgaris, in order to decrease the biomass production costs and to bioremediate CO₂ simultaneously. The utilization of the flue gas containing 10–13% (v/v) CO₂ and 8–10% (v/v) O₂ for the photobioreactor agitation and CO₂ supply was proven to be convenient. The growth rate of algal cultures on the flue gas was even higher when compared with the control culture supplied by a mixture of pure CO₂ and air (11% (v/v) CO₂). Correspondingly, the CO₂ fixation rate was also higher when using the flue gas (4.4 g CO₂ l⁻¹ 24 h⁻¹) than using the control gas (3.0 g CO₂ l⁻¹ 24 h⁻¹). The toxicological analysis of the biomass produced using untreated flue gas showed only a slight excess of mercury while all the other compounds (other heavy metals, polycyclic aromatic hydrocarbons, polychlorinated dibenzodioxins and dibenzofurans, and polychlorinated biphenyls) were below the limits required by the European Union foodstuff legislation. Fortunately, extending the flue gas treatment prior to the cultivation unit by a simple granulated activated carbon column led to an efficient absorption of gaseous mercury and to the algal biomass composition compliant with all the foodstuff legislation requirements.     

Concurrent measurements of oxygen- and carbon-dioxide exchange during lightflecks inAlocasia macrorrhiza (L.) G. Don

Oxygen and CO₂ exchange were measured concurrently in leaves of shade-grownAlocasia macrorrhiza (L.) G. Don during lightflecks consisting of short periods of high photon flux density (PFD) superimposed on a low-PFD background illumination. Oxygen exchange was measured with a zirconium-oxide ceramic cell in an atmosphere containing 1 600 bar O₂ and 350 bar CO₂. Following an increase in PFD from 10 to 500 mol photons·m^-2·s^-1, O₂ evolution immediately increased to a maximum rate that was about twice as high as the highest CO₂-exchange rates that were observed. Oxygen evolution then decreased over the next 5–10 s to rates equal to the much more slowly increasing rates of CO₂ uptake. When the PFD was decreased at the end of a lightfleck, O₂ evolution decreased nearly instantaneously to the low-PFD rate while CO₂ fixation continued at an elevated rate for about 20 s. When PFD during the lightfleck was at a level that was limiting for steady-state CO₂ exchange, then the O₂-evolution rate was constant during the lightfleck. This observed pattern of O₂ evolution during lightflecks indicated that the maximum rate of electron transport exceeded the maximum rate of CO₂ fixation in these leaves. In noninduced leaves, rates of O₂ evolution for the first fraction of a second were about as high as rates in fully induced leaves, indicating that O₂ evolution and the electron-transport chain are not directly affected by the leaf's induction state. Severalfold differences between induced and noninduced leaves in O₂ evolution during a lightfleck were seen for lightflecks longer than a few seconds where the rate of O₂ evolution appeared to be limited by the utilization of reducing power in CO₂ fixation.Abbreviation PFD photon flux density (of photosynthetically active radiation)     

Cultivation characteristics ofIsaria japonica

Cultivation characteristics of fruit-body (synnema) formation ofIsaria japonica were examined using liquid and solid media in order to produce fruit-bodies on a large scale. Mycelia grew well at 18–28°C on PDA medium with an initial pH of 7.0. The formation of fruit-bodies ofI. japonica was induced by lowering temperature to below 20°C in PD liquid medium. In sawdust-rice bran basal medium mixed with pupal powder prepared from silkworms (Bombyx mori), the fresh weight of fruit-bodies increased with increasing content of pupal powder. The highest yields of fruit-bodies were obtained in carbon-rich barley grain medium supplemented with pupal powder. The fruit-bodies grown under CO₂ concentrations of 1,000 μl/L had coral-like, many-branched synnemata with numerous conidiospores, whereas those formed under high concentrations (9,000 μl/L) of CO₂ had unbranched and longer synnemata. High concentrations of CO₂ remarkably inhibited conidiospore formation on synnemata. Continuous high-intensity illumination at 2.93 W·m⁻² inhibited the elongation of synnemata, and low-intensity illumination at 0.088 W·m⁻² slightly inhibited the branching of synnemata. Fruit-bodies were produced on the pupa metamorphosed from living larvae ofAgrotis fucosa placed on the surface of a culture ofI. japonica incubated in sawdust-rice bran medium.     

Light/dark cyclic movement of algal culture (<Emphasis Type="Italic">Synechocystis aquatilis</Emphasis>) in outdoor inclined tubular photobioreactor equipped with static mixers for efficient production of biomass

Synechocystis aquatilis SI-2 was grown outdoors in a 12.5cm diam. tubular photobioreactor equipped with static mixers. The static mixers ensured that cells were efficiently circulated between the upper (illuminated) and lower (dark) sections of the tubes. The biomass productivity varied from 22 to 45g m^–2d^–1, with an average of 35g m^–2d^–1, etc which corresponded to average CO₂ fixation rate of about 57 g CO₂ m^–2 d^–1. The static mixers not only helped in improving the biomass productivities but also have a high potential to lower the photoinhibitory effect of light during the outdoor cultures of algae. Revisions requested 27 July 2004; Revisions received 12 November 2004     

Evidence of de novo synthesis of maltose excreted by the endosymbiotic Chlorella from Paramecium bursaria

The endosymbiotic Chlorella sp. from Paramecium bursaria excretes maltose both in the light and in the dark. Experiments on photosynthetic ¹⁴CO₂ fixation and ¹⁴CO₂ pulse-chase experiments show that maltose is synthesized in the light directly from compounds of the Calvin cycle, whereas in the dark it results from starch degradation.     

Guggulsterone production in cell suspension cultures of the guggul tree, <Emphasis Type="Italic">Commiphora wightii</Emphasis>, grown in shake-flasks and bioreactors

Cell suspension cultures of Commiphora wightii, grown in modified MS medium containing 2,4-dichlorophenoxyacetic acid (0.5 mg l⁻¹) and kinetin (0.25 mg l⁻¹), produced ∼5 μg guggulsterone g⁻¹ dry wt. In a 2 l stirred tank bioreactor, the biomass was 5.5 g l⁻¹ and total guggulsterone was 36 μg l⁻¹.     

High photosynthetic photon flux and high CO2 concentration under increased number of air exchanges promote growth and photosynthesis of four kinds of orchid plantlets in vitro

Summary In vitro plantlets of Phalaenopsis ‘Happy Valentine’, Neofinetia falcate Hu, Cymbidium kanran Makino, and Cymbidium goeringii Reichb. f. were grown under photoautotrophic [high photosynthetic photon flux (PPF), high CO₂ concentration, and increased number of air exchanges] and heterotrophic (low PPF, low CO₂ concentration, no air exchanges) culture conditions. After 40 d of culture, a significant difference in plantlet growth was observed between the two cultures. Total fresh and dry mass were on average 1.5 times greater in photoautotrophic culture than in heterotrophic culture. Higher net photosynthetic rates were also observed for Phalaenopsis in photoautotrophic culture. In photoautotrophic culture, little difference was observed in air temperature between the inside and outside of the culture vessel, whereas in heterotrophic culture, air temperature inside the culture vessel was 1–2°C higher than that outside the culture vessel. Relative humidity inside the culture vessel was remarkably different between the two cultures: 83–85% in photoautotrophic culture and 97–99% in heterotrophic culture. These results indicated that growth and net photosynthetic rate of in vitro orchid plantlets were susceptible to the culture environments such as PPF, CO₂ concentration, relative humidity (RH), and the number of air exchanges, which would allow a more efficient micropropagation system for these orchid plants.     

Effects of periodic fluctuations of photon flux density on anatomical and photosynthetic characteristics of soybean leaves

The development of soybean leaves grown at fluctuating photon flux density between 100 and 1500M m^-2s^-1 with a period of 160 sec were compared to leaves developed under continuous light with the same mean photon flux density. Number of epidermal cells and stomata, leaf area and specific leaf weight were not affected by the periodic fluctuation of photon flux density. Chloroplastic pigment concentration and chlorophyll fluorescence reveal some photoinhibitory effects of the high photon flux density phase. Stomatal and internal CO₂ conductance and the quantum yield were not affected by the light regime. In contrast ribulose 1.5 bisphosphate carboxylase/oxygenase activity before in vitro activation by CO₂ and Mg⁺⁺ was stimulated by the periodic illumination whereas the total amount of the enzyme and the internal leaf CO₂ conductance remained steady. In conclusion, there was no major difference between leaves of plant grown either under a steady or under a periodic fluctuation of the photon flux density except some photoinhibitory symptoms under fluctuating illumination, and a higher in vivo level of activation of the Rubisco.     

Photosynthetic responses to elevated CO2and O3 in field-grown potato(Solanum tuberosum)

Potato plants (Solanum tuberosum L. cv. Bintje) were grown to maturity in open-top chambers under three carbon dioxide (CO₂; ambient and 24 h d⁻¹ seasonal mean concentrations of 550 and 680 μmol mol⁻¹) and two ozone levels (O₃; ambient and an 8 h d⁻¹ seasonal mean of 50 nmol mol⁻¹). Chlorophyll content, photosynthetic characteristics, and stomatal responses were determined to test the hypothesis that elevated atmospheric CO₂ may alleviate the damaging influence of O₃ by reducing uptake by the leaves. Elevated O₃ had no detectable effect on photosynthetic characteristics, leaf conductance, or chlorophyll content, but did reduce SPAD values for leaf 15, the youngest leaf examined. Elevated CO₂ also reduced SPAD values for leaf 15, but not for older leaves; destructive analysis confirmed that chlorophyll content was decreased. Leaf conductance was generally reduced by elevated CO₂, and declined with time in the youngest leaves examined, as did assimilation rate (A). A generally increased under elevated CO₂, particularly in the older leaves during the latter stages of the season, thereby increasing instantaneous transpiration efficiency. Exposure to elevated CO₂ and/or O₃ had no detectable effect on dark-adapted fluorescence, although the values decreased with time. Analysis of the relationships between assimilation rate and intercellular CO₂ concentration and photosynthetically active photon flux density showed there was initially little treatment effect on CO₂-saturated assimilation rates for leaf 15. However, the values for plants grown under 550 μmol mol⁻¹ CO₂ were subsequently greater than in the ambient and 680 μmol mol⁻¹ treatments, although the beneficial influence of the former treatment declined sharply towards the end of the season. Light-saturated assimilation was consistently greater under elevated CO₂, but decreased with time in all treatments. The values decreased sharply when leaves grown under elevated CO₂ were measured under ambient CO₂, but increased when leaves grown under ambient CO₂ were examined under elevated CO₂. The results obtained indicate that, although elevated CO₂ initially increased assimilation and growth, these beneficial effects were not necessarily sustained to maturity as a result of photosynthetic acclimation and the induction of earlier senescence.     

Distribution of reducing power between photosynthetic carbon and nitrogen assimilation in Scenedesmus

Fixation of CO₂ and N assimilation were studied in synchronous cultures of Scenedesmus obtusiusculus Chod. under saturating and limiting light. Within the photon-flux range studied, the cells maintained C to N assimilation ratios of 7–10 with either NO ₃ ^- , NO ₂ ⁺ or NH ₄ ⁺ as the N source. Competitive interactions between C and N assimilation were pronounced under light limitation and were proportional to the oxidation status of the N source. Fixation of CO₂ at saturating light was also slightly reduced by NO ₂ ^- and NH ₄ ⁺ . In the absence of CO₂, NO ₃ ^- uptake and reduction was light-saturated at a comparatively low photon flux, whereas NO ₂ ^- uptake and reduction was considerably faster in the absence of CO₂ than in its presence. The pools of reduced pyridine nucleotides (NADPH and NADH) were largely unaffected by the presence or absence of the different N sources. The regulatory influences of CO₂ fixation on N assimilation are discussed in terms of coupling between the rates of CO₂ fixation and NH ₄ ⁺ assimilation, as well as the existance of control mechanisms for NO ₃ ^- uptake and reduction.Abbreviations Chl chlorophyll - PF photon flux     

Use of response surface methodology to optimise carotenogenesis in the microalga,Haematococcus pluvialis

The factors controlling biomass production and the synthesis of astaxanthin esters in the microalga Haematococcus pluvialis (CCAP 34/7) have been investigated using a statistical approach employing response surface methodology (RSM). The culture conditions required for optimal growth and carotenogenesis in this alga are very different. Of particular importance is the photon flux density: for growth the optimum is 50–60 μmol m⁻² s⁻¹ whereas the optimum for astaxanthin synthesis is much higher at ∼-1600 μmol m⁻² s⁻¹. The addition of low levels of NaCl to the medium also stimulates to a small extent synthesis of astaxanthin, but photon flux density remains the overriding factor. The optimal temperature for this strain is quite low at 14–15 °C. RSM has been shown to be a rapid and effective technique leading to the optimisation of algal culture conditions. This statistical approach can be applied readily to the majority of microalgae and their products.     

Responses of C4 grasses to atmospheric CO2 enrichment

Summary The growth and photosynethetic responses to atmospheric CO₂ enrichment of 4 species of C₄ grasses grown at two levels of irradiance were studied. We sought to determine whether CO₂ enrichment would yield proportionally greater growth enhancement in the C₄ grasses when they were grown at low irradiance than when grown at high irradiance. The species studied were Echinochloa crusgalli, Digitaria sanguinalis, Eleusine indica, and Setaria faberi. Plants were grown in controlled environment chambers at 350, 675 and 1,000 l 1^-1 CO₂ and 1,000 or 150 mol m^-2 s^-1 photosynthetic photon flux density (PPFD). An increase in CO₂ concentration and PPFD significantly affected net photosynthesis and total biomass production of all plants. Plants grown at low PPFD had significantly lower rates of photosynthesis, produced less biomass, and had reduced responses to increases in CO₂. Plants grown in CO₂-enriched atmosphere had lower photosynthetic capacity relative to the low CO₂ grown plants when exposed to lower CO₂ concentration at the time of measurement, but had greater rate of photosynthesis when exposed to increasing PPFD. The light level under which the plants were growing did not influence the CO₂ compensation point for photosynthesis.