Specific growth rate of Chlamydomonas reinhardtii and Chlorella sorokiniana under medium duration light/dark cycles: 13–87 s

The specific growth rate of Chlamydomonas reinhardtii and Chlorella sorokiniana decreased under square-wave light/dark cycles of medium duration, 13–87 s, in comparison to continuous illumination. Three experiments were done in three different turbidostats at saturating and sub-saturating light intensities during the light period, 240–630 μmol m⁻² s⁻¹. Within each experiment the light intensity during the light periods of the intermittent light regimes was equal and this intensity was also applied under continuous illumination. The specific growth rate decreased proportional or more than proportional to the fraction of time the algae were exposed to light; this light fraction ranged from 0.32 to 0.88. We conclude that under these light regimes the chlorophyta C. reinhardtii and C. sorokiniana are not able to store light energy in the light period to sustain growth in the dark period at the same rate as under continuous illumination. C. reinhardtii increased its specific light absorbing surface by increasing its chloropyll-a content under light/dark cycles of 13 s duration and a light fraction of 0.67 at 240 μmol m⁻² s⁻¹; the chloropyll-a content was twice as high under intermittent illumination in comparison to continuous illumination. The combination of a higher specific light absorption together with a lower specific growth rate led to a decrease of the yield of biomass on light energy under intermittent illumination.     

Laboratory culture of the Nudibranch Tritonia diomedea bergh (Tritoniidae: Opisthobranchia) and some aspects of its behavioral development

Tritonia diomedea Bergh was reared from oviposition, through metamorphosis to reproductive maturity in the laboratory. The larvae of T. diomedea are planktotrophic and undergo considerable shell growth (from 144.6–329 μ average maximum shell length). Metamorphosis does not require induction, but there may be a preference to metamorphose in the presence of the probable adult prey, a small Virgularia sp. Larvae in cultures fed no food, Dunaliella tertiolecta Butcher Isochrysis galbana Parke, or Monochrysis lutheri Droop did not achieve metamorphic competence at near ambient sea-water temperatures (11.9±1.3 and 13.0±0.8°C). Larvae from cultures fed Monochrysis at room temperature (20.8±1.5°C) or fed a 1 : 1 mixture of Isochrysis and Monochrysis at near ambient sea-water temperatures did metamorphose. Even so, only those larvae fed the 1 : 1 mixture survived more than a few days following metamorphosis. Adult behavioral patterns developed gradually, feeding being first observed at 5 days, swimming in response to NaCl crystals at about 60 days, copulation at about 272 days, and oviposition at about 277 days after metamorphosis. Growth rates were determined for field collected Tritonia diomedea; smaller animals gained and lost weight relatively faster than larger animals.     

Nutrient removal by thermophilic Fischerella (Mastigocladus laminosus) in a simulated algaculture process

A novel nutrient removal/waste heat utilization process was simulated using semicontinuous cultures of the thermophilic cyanobacterium Fischerella. Dissolved inorganic carbon (DIC)-enriched cultures, maintained with 10 mg l⁻¹ daily productivity, diurnally varying temperature (from 55°C to 26–28°C), a 12:12 light cycle (200 μE sec⁻¹ m⁻²) and 50% biomass recycling into heated effluent at the beginning of each light period, removed > 95% of NO₃⁻ + NO₂⁻−N, 71% of NH₃-N, 82% of PO₄³⁻ −P, and 70% of total P from effluent water samples containing approximately 400 μg l⁻¹ combined N and 60 μg l⁻¹ P. Nutrient removal was not severely impaired by an altered temperature gradient, doubled light intensity, or DIC limitation. Recycling 75% of the biomass at the end of each light period resulted in unimpaired NO₃⁻ + NO₂⁻ removal, 38–45% P removal and no net NH₃ removal. Diurnally varying P removal, averaging 50–60%, and nearly constant > 80% N removal, are therefore projected for a full-scale process with continuous biomass recycling.     

杉木和木荷种子萌发及幼苗生长对光梯度的响应

光是影响种子萌发和幼苗生长的关键因素.为理解不同树种种子萌发及幼苗生长对光梯度变化的响应机制,本文研究了不同光照强度(分别为自然光强的100%、60%、40%、15%和5%)对杉木和木荷种子萌发及幼苗生长的影响,探讨了两树种种子萌发和幼苗生长对光照响应的差异性.结果表明: 光照强度对两树种的种子萌发和幼苗生长均具有显著影响. 随着光照强度的减弱, 杉木种子萌发率增大,萌发指数增大,木荷种子萌发率和萌发指数则先增大后减小,在40%光照强度下达到最大值.两树种幼苗存活率在全光照(100%光照)下均为0,在5%～60%光照处理下则随着光照强度的减弱而显著降低.两树种幼苗根长、地径和株高对光梯度变化的响应趋势一致,随着光照强度的减弱,根长显著减小,地径和株高则先增大后减小,在5%光照强度下达到最小.随着光照强度的减弱,杉木幼苗根、茎、叶及总生物量降低,木荷幼苗生物量积累在15%～60%光照强度下较高, 5%光照强度下最小,且相同光照强度下,木荷幼苗各部分生物量均大于杉木.两树种幼苗应对低光环境时,表现出较大的茎和叶的生物量分配比,而根生物量比和根冠比降低.表明杉木苗期生长不耐阴,需要相对较强的光照,而木荷苗期具有较强的耐阴性,对弱光环境的适应性更强,能够在郁闭的林冠下定植和正常生长.     

Effect of culture conditions on lipid and gamma-linolenic acid production by mucoraceous fungi

The effect of various culture conditions on growth, lipid production and fatty acid composition in Mucor rouxii and Mucor sp.1b were studied. Total lipid production was higher in media containing potassium nitrate for both the cultures (30%) and cultures grown on plant seed oil produced more than 44% lipid. Among the carbon sources tested, γ-linolenic acid (GLA) production was maximal in cultures grown on glucose. The major fatty acids produced by these two cultures were palmitic, stearic and oleic acids. Levels of GLA in M. rouxii and M. sp.1b was in the range of 3–17% under different culture conditions. Lactose was a poor promoter for biomass and lipid production in both cultures. No GLA was found in fungal cultures grown on sesame oil. The optimal conditions for the production of GLA was standardised in these cultures.     

Metal–salt co-tolerance and metal removal by indigenous cyanobacterial strains

Chromium and salt tolerance in five indigenous cyanobacterial strains isolated from contaminated sites was investigated along with their metal bioaccumulative potential. All the five species showed significantly better growth when the medium was spiked with salt or chromium. As compared to single metal or salt treatment, the binary metal–salt (MS) treatments had more favorable effect on cyanobacterial growth as indicated by significantly higher concentration of the primary photosynthetic pigment chlorophyll at M₂₀S₂₀₀₀ (9.9–25.3 μg/mL) as compared to that at M₀S₀ (4.0–12.3 μg/mL). Similarly biomass was much higher at M₂₀S₁₀₀₀ and M₂₀S₂₀₀₀ (41.8–86.2 mg/10 mL) as compared to that at control, M₀S₀ (21.5–36.3 mg/10 mL). Accessory pigments like carotenoids and phycobilinproteins too tended to increase significantly in response to both metal and salts in the two species of Lyngbya (L. putealis and L. ceylanica var. constricta) and Gloeocapsa. These species also showed greater potential of chromium bioaccumulation, which increased further as both salt and metal concentration increased. In the two species of Nostoc however, bioaccumulative potential improve at higher metal concentration, but not affected significantly by salt concentration.     

A screening model to predict microalgae biomass growth in photobioreactors and raceway ponds

A microalgae biomass growth model was developed for screening novel strains for their potential to exhibit high biomass productivities under nutrient‐replete conditions in photobioreactors or outdoor ponds. Growth is modeled by first estimating the light attenuation by biomass according to Beer‐Lambert's Law, and then calculating the specific growth rate in discretized culture volume slices that receive declining light intensities due to attenuation. The model uses only two physical and two species‐specific biological input parameters, all of which are relatively easy to determine: incident light intensity, culture depth, as well as the biomass light absorption coefficient and the specific growth rate as a function of light intensity. Roux bottle culture experiments were performed with Nannochloropsis salina at constant temperature (23°C) at six different incident light intensities (10, 25, 50, 100, 250, and 850 µmol/m² s) to determine both the specific growth rate under non‐shading conditions and the biomass light absorption coefficient as a function of light intensity. The model was successful in predicting the biomass growth rate in these Roux bottle batch cultures during the light‐limited linear phase at different incident light intensities. Model predictions were moderately sensitive to minor variations in the values of input parameters. The model was also successful in predicting the growth performance of Chlorella sp. cultured in LED‐lighted 800 L raceway ponds operated in batch mode at constant temperature (30°C) and constant light intensity (1,650 µmol/m² s). Measurements of oxygen concentrations as a function of time demonstrated that following exposure to darkness, it takes at least 5 s for cells to initiate dark respiration. As a result, biomass loss due to dark respiration in the aphotic zone of a culture is unlikely to occur in highly mixed small‐scale photobioreactors where cells move rapidly in and out of the light. By contrast, as supported also by the growth model, biomass loss due to dark respiration occurs in the dark zones of the relatively less well‐mixed pond cultures. In addition to screening novel microalgae strains for high biomass productivities, the model can also be used for optimizing the pond design and operation. Additional research is needed to validate the biomass growth model for other microalgae species and for the more realistic case of fluctuating temperatures and light intensities observed in outdoor pond cultures. Biotechnol. Bioeng. 2013; 110: 1583–1594. © 2012 Wiley Periodicals, Inc.     

不同光强对棱角山矾幼苗生长及光合特性的影响

通过比较不同遮阴处理下棱角山矾幼苗生长及光合特性的差异,以探讨不同光强对棱角山矾生长及光合作用的影响及其适应机制。结果表明：棱角山矾幼苗的生物量分配对光强的反应敏感,在强光处理下,比叶面积减小,总叶面积变小;弱光处理下通过增大叶生物量比、叶面积比,支持结构生物量比,提高捕光能力。但L100、L30、L10处理下总生物量的积累显著小于L50处理,L30、L50、L100光强处理下总叶面积显著高于L10光强处理。并且10%和100%光强下棱角山矾叶片的最大净光合速率（P_max）、光饱和点（LSP）、表观量子效率（AQY）均显著低于30%和50%光强处理;而光补偿点（LCP）则随光强的增大而升高;总叶绿素和类胡萝卜素含量在10%~100%随着光强增大而显著降低（P<0.05）。说明棱角山矾幼苗在不同光环境下具有一定适应性,但过强或过弱的光环境均会对棱角山矾的生长产生负面影响,其中50%光强是棱角山矾幼苗生长的最佳光强;棱角山矾为中性树种,苗木适宜生长在荫蔽的环境下。     

Effects of light intensity variation on nitrogen and phosphorus contents,allocation and limitation in five shade-enduring plants

Aims To enhance the understanding on nitrogen (N) and phosphorus (P) physiological responses to different light environments in shade-enduring plants and provide references to improve the stand structure and ecosystem functions of plantation forests.Methods We selected seedlings of five shade-enduring species with high ecological and economic value in subtropical area of China to study the effects of light intensity on leaf N and P contents, allocation and nutrient limitation in shade-enduring plants. A light intensity gradient of five different levels was set to simulate the varying understory light environment.Important findings With decreasing light intensity, the total biomass and total N and P accumulation of five shade-enduring plants all showed a decreasing trend, but N, P contents in different organs increased. Among them, Gardenia jasminoides (GJ) had the highest while Illicium henryi (IH) had the lowest N content; The P contents of Quercus phillyraeoides (QP) and GJ were significantly higher than Elaeocarpus sylvestris (ES), Ardisia crenata (AC) and IH. QP and GJ had the highest N, P contents under extremely low light intensity (6% natural light intensity) condition (LIC), while AC and IH had the highest N and P contents in low (15% natural light intensity) and moderate (33% and 52% natural light intensity) LIC. ES demanded differently for LIC on N and P, which were 52% and 6% natural light intensity, respectively. N and P allocation of ES, AC and IH followed leaf > root > stem, but for QP and GJ were root > leaf > stem. Decreasing LIC significantly affected N and P allocation. N content variations shown good consistency among different organs under higher LIC (100% natural light intensity) while distinct variability under lower LIC (15% and 6% natural light intensity) in all five species. Phosphorus contents exhibited good consistency in IH, QP and GJ but varied in ES and AC. Decreasing LIC significantly affected organ N/P ratios of shade-enduring plants, but the fundamental growth restriction patterns remained. Light intensity variation and tree species co-regulated N, P utilization and allocation in shade-enduring plants, and then affected the total biomass and total N, P accumulation, which might result from the change of N and P utilization strategy. Therefore, light intensity preference and N, P nutrient balances in shade-enduring plants should be taken into account when constructing multiple layer and uneven-aged forests.     

Light adaptation and the role of autotrophic epiphytes in primary production of the temperate seagrass, Zostera marina L.

Photosynthetic features of Zostera marina L. and its autotrophic epiphyte community were investigated in a population inhabiting a shallow (1.3 m depth) water meadow in Great Harbor, Woods Hole, MA (U.S.A.). Photosynthesis versus irradiance (P-I) relationships were measured with respect to leaf age determined by the leaf position in the shoot bundle and by location of the tissue along the leaf axis. Therefore both age and light intensity gradients along the leaf axis were considered. The maximum photosynthesis (P_max) per dm² typically increased nearly two-fold along the leaf axis from leaf bases to apices. Photosynthetic rate on a chlorophyll (Chl) basis did not increase as dramatically along the leaf axis, and rates were usually lowest in tissues with the highest Chl content. The P-I relationships of leaves of different ages did not reveal photoinhibition even at light intensities > 1400 μE • m⁻² • s ⁻¹. Furthermore, no photoinhibition was observed in tissues from leaf blade bases, which never experienced high light levels (> 500 μE • m ⁻² • s⁻¹) in situ in Great Harbor. The initial slopes of the P-I curves and light compensation and saturation values varied along the leaf axis in relation to in situ light intensity gradients and in relation to leaf or tissue age. It appeared that leaf and/or tissue age was more important than light environment in determining P-I responses. The contribution of the autotrophic epiphyte community on Z. marina leaves to total photosynthesis per dm² was between 27 and 50%, and between 10 and 44% per mg chlorophyll. These levels of epiphyte photosynthesis can double the primary production of Z. marina leaves. No detrimental effects of epiphyte cover were realized in leaf maximal photosynthesis or P-I relationships. Non-epiphytized leaves and leaves from which epiphytes were removed showed essentially identical photosynthetic features. Light intensity and age gradients along the leaf axis control both the photosynthetic performance of the leaves and epiphyte biomass and photosynthesis.     

Carbon,nitrogen and phosphorus stoichiometry of Myrica nana in Yunnan,China

Aims Carbon (C), nitrogen (N) and phosphorus (P) play important roles in plant growth and physiological functions. We aimed at exploring the intrinsic relationships of C, N and P in Myrica nana—a common shrub in Yunnan Province—as well as their relationships with pant biomass and soil nutrients.
Methods We measured the concentration of C, N and P of M. nana from 29 sites for their magnitudes and correlations with soil nutrients.
Important findings 1) The arithmetic mean value of C, N and P concentration in the roots, stems and leaves of M. nana was 45.94%, 0.54%, 0.03%, and 46.32%, 0.58%, 0.03%, and 49.05%, 1.70%, 0.06%, respectively. C, N and P concentrations in the leaves were significantly higher than those in the roots and the stems. The C:N:P in roots, stems and leaves was 1531:18:1, 1544:19:1, and 818:10:1, respectively. 2) The C concentration and N:P in leaves of M. nana decreased with the increase of biomass of M. nana; the leaf C concentration was significantly correlated with biomass (p < 0.01), while the correlation between N:P and biomass was not significant (p > 0.05). The leaf N increased with the increase of plant biomass, the P was significantly correlated with biomass (p < 0.05), but the correlation between N concentration and biomass was not significant (p > 0.05). N:P in leaves was 34.2, suggesting that plant growth was limited by P. 3) C, N and P concentration in the roots were significantly correlated with soil P (p < 0.05), with N, P concentrations correlated with soil P positively (p < 0.01) and C negatively (p < 0.05). C concentration in the stems was significantly and negatively correlated with soil C, N, with significant correlation with C, N, and P concentration (p < 0.01). P concentration in the stems was significantly and positively correlated with soil P concentration (p < 0.01), while leaf P significantly and positively correlated with soil C, N and P (p < 0.01); leaf C concentration was significantly and negatively correlated with soil P (p < 0.01).     

Growth and biochemical characterization of microalgal biomass produced in bubble column and airlift photobioreactors: studies in fed-batch culture

Relatively large (0.19 m column diameter, 2 m tall, 0.06 m³ working volume) outdoor bubble column and airlift bioreactors (a split-cylinder and a draft-tube airlift device) were compared for monoseptic fed-batch culture of the microalga Phaeodactylum tricornutum. The three photobioreactors produced similar biomass versus time profiles and final biomass concentration (4 kg m⁻³). The maximum specific growth rate observed within a daily illuminated period in the exponential growth phase, had a value of 0.08 h⁻¹ on the third day of culture. Because of night-time losses of biomass, the specific growth rate averaged over the 4-days of exponential phase was 0.021 h⁻¹ for the three reactors.

The biomass in the vertical column reactors did not experience photoinhibition under conditions (photosynthetically active daily averaged irradiance value of 1150±52 μE m⁻² s⁻¹) that are known to cause photoinhibition in conventional thin-tube horizontal loop reactors. Because of good gas-liquid mass transfer, the dissolved oxygen concentration in the reactors at peak photosynthesis remained <120% of air saturation; thus, oxygen inhibition of photosynthesis and photo-oxidation of the biomass did not occur. Carbohydrate accumulation (up to 13% w/w) by the biomass was favored during light-limited linear growth. A declining light intensity caused a more than five-fold increase in cellular carotenoids but the chlorophylls increased only by about 2.5-fold during the course of the culture. In the stationary phase, up to 2% of the biomass was chlorophylls and carotenoids constituted up to 0.5% of the biomass dry weight.     

The influence of benthic microalgae on the stability of a subtidal sediment

The relationship between benthic microalgae and the stabilisation of sediment was studied using a straight-channel laboratory flume tank. To establish different densities of microalgal biomass, sieved sediment collected from a shallow bay was kept in a laboratory flow-through aquarium either in darkness or with a 16/8 light/dark cycle. The relation between shear velocities causing sediment transport (u_*(crit)) and chlorophyll a content, content of colloidal polysaccharides, biomass and composition of microalgae in the top 5 mm of the sediment were studied. Microalgal samples were also collected using the cover-glass technique. Erosion tests were also made on undisturbed field samples. The investigation showed that the stabilizing effect of microalgae, previously reported for intertidal areas, may also apply for shallow-water sediments lacking regular tidal emersion. Initially, sieving decreased sediment stability by destroying consolidating structures. Within 5 days, however, values of u_*(crit) approached those of the undisturbed field samples (2.8 cm · s⁻¹). The sediment that was exposed to light, became more stable against erosion (higher u_*(crit)) than sediment kept in darkness. This difference is suggested to be caused by different densities of microalgae, as several sediment variables related to algae (content of chlorophyll a, polysaccharide content and algal biomass caught on cover glasses) were significantly different in light and dark treatments. The increased stability was mainly induced by the increased biovolume of motile diatoms within the size groups 20–40 μm and > 100 μm, as well as by filamentous cyanobacteria. Only the biovolume of algae trapped on cover glasses correlated significantly with critical shear velocity, while chlorophyll a, polysaccharides and biovolume in core samples showed positive, but non-significant correlations with critical shear velocity. Although the cover glasses harvested only a minor portion (5–10%) of the algal biovolume in the top 5 mm sediment, at least the motile diatom flora was better assessed by the cover-glass technique. Consequently, this appears to be a better indicator of sediment stability than total biomass or chlorophyll a content in the lop 5 mm sediment. Although there is a methodological uncertainty as to what components the variable “polysaccharides” include, polysaccharide content can be used to give at least a qualitative prediction of sediment stability. It is doubtful, however, whether any reasonable specific quantitative prediction about sediment stability can be made without an extensive knowledge about several factors, such as sediment structure, the quantity and the quality, as well as the physiological status of the organisms.     

Annual nitrogen budget of a temperate coastal barrier salt-marsh system along a productivity gradient at low and high marsh elevation

An annual nitrogen budget was established for a temperate back barrier salt-marsh system along a productivity gradient at low and high marsh elevation. We measured plant biomass and nitrogen content in three plant compartments to deduce plant N-allocation patterns. Measurements were done along a successional sequence in a salt-marsh system. In addition, N-mineralization, wet and dry atmospheric N-deposition and sediment N-deposition were measured.

Plant-species dominance changed along the successional sequence. In early stages, Elymus farctus and Spergularia media formed a large part of total plant biomass. Festuca rubra and Puccinellia maritima were dominant at intermediate stages, whereas Elymus pycnanthus and Limonium vulgare were dominant at late stages of succession. Shoot biomass was highest in June, whereas litter biomass was highest in September and December. Root biomass formed by far the largest fraction of total plant biomass, especially at a low-marsh elevation.

Wet deposition of nitrate and ammonium was 1.7 g N m⁻² yr⁻¹, whereas throughfall deposition (dry and wet deposition) amounted to 2.1–3.6 g N m⁻² yr⁻¹, and was positively related to the height of an artificial plant canopy. Sediment organic nitrogen deposition rate was 0.3–5.4 g N m⁻² yr⁻¹, and negatively related to marsh elevation. Nitrogen mineralization rate increased from 2.5–2.8 g N m⁻² yr⁻¹ in young marshes towards 8.0–12.7 g N m⁻² yr⁻¹ at older marshes, depending on marsh elevation.

At a low-marsh elevation, plant N-availability depended equally on tidal N, atmospheric N and mineralized N, especially in young marshes, whereas the decomposition pathway became more important in older marshes. Tidal N contributed most to ecoystem N-accumulation rate at early successional stages, whereas atmospheric N was more important at later stages. Tidal influence was low at high-marsh elevation sites. Here, atmospheric deposition was the dominant exogenous nitrogen source both in young and old marshes.     

Influence of the degree and mode of light limitation on growth characteristics of the Rhodobacter capsulatus continuous cultures

The influence of the degree and mode of light limitation on growth characteristics of turbidostat cultures of Rhodobacter capsulatus was investigated using mass and energy balance regularities. Light limitation was achieved by increasing the steady-state biomass concentration at constant incident light intensity ( approximately 100 W/m(2)) or by decreasing the incident light intensity at constant steady-state biomass concentration ( approximately 500 mg of dry biomass/L). It was shown that under conditions of light limitation of Rh. capsulatus, the content of P and N in the biomass as well as the biomass degree of reduction were determined by the growth rate of the cultures. The energetic yield of biomass of Rh. capsulatus and total bacteriochlorophyll a content increased when light limitation increased. These parameters were higher in the cultures, in which light limitation was achieved by lowering the incident light intensity at low biomass concentration. This seems to be due to different distribution of light within the photobioreactor when dissimilar modes of light limitation were used.     

Maximum quantum yield and action spectrum of photosynthesis and fluorescence in chlorella

The maximum yield of oxygen production in Chlorella was found, in new, systematic experiments, not to exceed 0.12, under a great variety of conditions. Measurements were made on autospores and other synchronous cultures, at different CO₂ concentrations, at very low light intensities, and in the presence of ‘catalytic’ amounts of blue light. The action spectra (quantum yield as a function of wavelength) of photosynthesis, and of chlorophyll a fluorescence in vivo, were measured on the same Chlorella cell suspensions. In both cases, a decline in the yield was observed in the red beginning at about 675–680 nm. The yield declines to 50% of the maximum, on both curves, at 690–695 nm. A strong dip was observed in the action spectra of both fluorescence and photosynthesis at 660–665 nm.     

Distinction of water-soluble constituents between natural and cultured Cordyceps by capillary electrophoresis

Cordyceps is an expensive traditional Chinese medicine, which has anti-tumor activity and significant effects on the immune system. In Southeast Asia, Cordyceps is commonly sold in capsule form as a health food product. Most of these products are derived from cultured Cordyceps mycelia. Because of the price difference, some manufacturers claim their products are from natural Cordyceps. In order to distinguish among various types of Cordyceps in the market, the profiles of water-soluble constituents derived from different sources of Cordyceps were determined by capillary electrophoresis (CE). Both natural and cultured Cordyceps showed three peak clusters migrated at 5–7, 9–11 and 12–13 min, and the height and resolution of these peak clusters were rather distinct. Peak cluster at 9–11 min was identified as adenosine, guanosine and uridine, and shared a similarity between natural and cultured products. In contrast, the peak cluster at 5–7 min was characteristic of natural Cordyceps, regardless of hosts and sources. By using the peak characteristics of CE profiles of different Cordyceps samples, hierarchical clustering analysis was performed. The result shows that those samples of natural Cordyceps were grouped together distinct from the cultured and commercial products. Thus, the CE profiles could serve as fingerprints for the quality control of Cordyceps.     

Growth and photosynthetic rates of Phaeodactylum tricornutum Bohlin in a cyclical light field

Growth rates, cell chlorophyll a concentrations, and carbon uptake rates of Phaeodactylum tricornutum Bohlin grown in cyclical and constant light regimes at three mean irradiances (PFD) were compared. Light cycles with periods 5–38 min were used. Under high PFD the cyclical light regime resulted in both increased and decreased growth rates dependent on the signal frequency. Growth rates were universally depressed under mid and low PFD. Minimal influence of the light field was apparent on cell chlorophyll concentrations. The most marked effect of the fluctuating light was recorded on the carbon uptake rates with maximal influence demonstrated in those samples both grown and incubated in fluctuating light at high as opposed to mid and low PFDs. From the combination of light fields employed, the existence of both short and long term physiological controls of the carbon uptake rates were deduced, these being related to the time scales of carbon uptake and cell growth. A partial explanation to account for the observed increases in carbon uptake in terms of short period non-linear uptake kinetics was derived from two further experiments.     

Gas exchange and photosynthetic water use efficiency in response to light, CO2 concentration and temperature in Vicia faba

Light and temperature-response curves and their resulting coefficients, obtained within ecophysiological characterization of gas exchanges at the leaf level, may represent useful criteria for breeding and cultivar selection and required tools for simulation models aimed at the prediction of potential plant behaviour in response to environmental conditions.

Leaf-scale gas exchanges, by means of an IRGA open-flow system, were measured in response to light intensity (8 levels from 0 up to 2000 μmol m⁻² s⁻¹), CO₂ concentrations (ambient—350 μmol mol⁻¹ and short-term enriched—700 μmol mol⁻¹) and air temperature (from 7 up to 35 °C) on three Vicia faba L. genotypes, each representing one of the three cultivated groups: major, equina and minor. The net assimilation rate response to light intensity was well described by an exponential rise to max function. The short-term CO₂ enrichment markedly increased the values of light response curve parameters such as maximum photosynthetic rate (+80%), light saturation point (+40%) and quantum yield (+30%), while less homogenous behaviour was reported for dark respiration and light compensation point. For each light intensity level, the major and minor genotypes studied showed assimilation rates at least a 30% higher than equina.

The positive effects of short-term CO₂ enrichment on photosynthetic water use efficiency (WUE) indicate a relevant advantage in doubling CO₂ concentration. In the major and minor genotypes studied, similar assimilation rates, but different WUE were observed.

The optimum leaf temperature for assimilation process, calculated through a polynomial function, was 26–27 °C and no relevant limitations were observed in the range between 21 and 32 °C.

Analysis at the single leaf level provided both rapid information on the variations in gas exchange in response to environmental factors and selection criteria for the screening of genotypes.     

Species- and clone-specific responses to environmental stimuli in the cladocerans Bosmina cornuta and B. pellucida - a comparison with Daphnia

We studied the variation of small-scale swimming behaviour in eight Bosmina cornuta and ten B. pellucida clones in response to key environmental factors to test whether swimming behaviour and genotypes are linked in non-Daphnia cladocerans. We quantified (1) the short-term responses to changes in temperature, light intensity and pH, (2) the response to long-term temperature acclimation, and (3) the pH-related survival rates. Vertical swimming activity S was quantified in cuvette experiments as crossings of a line at 2 cm height per individual an hour. S differed significantly among species and conspecific clones. At any temperature, light intensity and pH tested, B. cornuta (clone variation: 40-58 crossings/ind.× h) showed a higher vertical swimming activity than B. pellucida (clone variation: 25-48 crossings/ind.× h). A short-term change of water temperature (range tested: 10-25°C) only affected S of B. cornuta, whereas that of B. pellucida remained unaltered. In contrast, S increased with rising temperature following long-term temperature acclimation (range tested: 10-20°C) in both species. Swimming activity was inversely related to the light intensity (range tested: 60-60,000 lux), but decrease of activity was stronger in B. pellucida (44 → 12 crossings/ind × h) than in B. cornuta (50 → 40 crossings/ind.× h). Short-term changes of pH (range tested: 4-6) did not influence swimming activity in any species, although a prolonged exposure (24 h) to pH 4 was lethal. Thus, Bosmina showed behavioural responses which permit to distinguish between the species and which are related to their seasonal succession and distribution pattern.