Effects of flooding on photosynthesis and root respiration in saltcedar (Tamarix ramosissima), an invasive riparian shrub

The introduced shrub Tamarix ramosissima invades riparian zones, but loses competitiveness under flooding. Metabolic effects of flooding could be important for T. ramosissima, but have not been previously investigated. Photosynthesis rates, stomatal conductance, internal (intercellular) CO₂, transpiration, and root alcohol dehydrogenase (ADH) activity were compared in T. ramosissima across soil types and under drained and flooded conditions in a greenhouse. Photosynthesis at 1500 μmol quanta m⁻² s⁻¹ (A₁₅₀₀) in flooded plants ranged from 2.3 to 6.2 μmol CO₂ m⁻² s⁻¹ during the first week, but A₁₅₀₀ increased to 6.4–12.7 μmol CO₂ m⁻² s⁻¹ by the third week of flooding. Stomatal conductance (g_s) at 1500 μmol quanta m⁻² s⁻¹ also decreased initially during flooding, where g_s was 0.018 to 0.099 mol H₂O m⁻² s⁻¹ during the first week, but g_s increased to 0.113–0.248 mol H₂O m⁻² s⁻¹ by the third week of flooding. However, photosynthesis in flooded plants was reduced by non-stomatal limitations, and subsequent increases indicate metabolic acclimation to flooding. Root ADH activities were higher in flooded plants compared to drained plants, indicating oxygen stress. Lower photosynthesis and greater oxygen stress could account for the susceptibility of T. ramosissima at the onset of flooding. Soil type had no effect on photosynthesis or on root ADH activity. In the field, stomatal conductance, leaf water potential, transpiration, and leaf δ¹³C were compared between T. ramosissima and other flooded species. T. ramosissima had lower stomatal conductance and water potential compared to Populus deltoides and Phragmites australis. Differences in physiological responses for T. ramosissima could become important for ecological concerns.     

Protocorm culture of Dendrobium candidum in balloon type bubble bioreactors

Protocorm cultures of Dendrobium candidum were established in balloon type bubble bioreactors using Murashige and Skoog (MS) medium with 0.5 mg l⁻¹ α-naphthaleneacetic acid (NAA), 2.5% (w/v) sucrose, 5:25 mM NH₄:NO₃ and 1% (v/v) banana homogenate for the production of biomass and bioactive compounds. In 3 l bioreactor containing 2 l medium, a maximum protocorm biomass (21.0 g l⁻¹ dry biomass) and also optimum quantities of total polysaccharides (389.3 mg g⁻¹ DW), coumarins (18.0 mg g⁻¹ DW), polyphenolics (11.9 mg g⁻¹ DW), and flavonoids (4.5 mg g⁻¹ DW) were achieved after 7 weeks of culture. Based on these studies, 5 and 10 l bioreactor cultures were established to harvest 80 g and 160 g dry biomass. In 10 l bioreactors, the protocorms grown were accumulated with optimal levels of polysaccharides (424.1 mg g⁻¹ DW), coumarins (15.8 mg g⁻¹ DW), polyphenols (9.03 mg g⁻¹ DW) and flavonoids (4.7 mg g⁻¹ DW). The bioreactor technology developed here will be useful for the production of important bioactive compounds from D. candidum.     

Growth limitation of Lemna minor due to high plant density

The effect of high population densities on the growth rate of Lemna minor (L.) was studied under laboratory conditions at 23 °C in a medium with sufficient nutrients. At high population densities, we found a non-linear decreasing growth rate with increasing L. minor density. Above a L. minor biomass of ca. 180 g dry weight (DW) m⁻², the net growth rate became negative. At a density of 9 g DW m⁻², a maximum relative growth rate of ca. 0.3 d⁻¹ was found. At very low densities (<9 g m⁻²), we observed an inverse density dependence (or Allee effect). Probably, this lower growth rate was due to lower local temperatures within such partly covered L. minor decks. On the basis of these experimental results and literature data, a simple model was created. To test the model, the density of duckweed in three different Dutch ditches was monitored for 9 weeks in spring. Within this period, full coverage of the ditches by duckweed was reached. The maximum density increased with rising air temperature. The model described the field data well, suggesting that crowding is an important factor in limitation of duckweed growth.     

Abrupt changes in Potamogeton and Ruppia beds in a Mediterranean lagoon

Until the early 1990s, the Ichkeul lagoon (80 km², Tunisia) was characterised by the seasonal alternation of low and high salinity and by the presence (mainly in summer and autumn) of more or less extensive Potamogeton pectinatus beds (western and south-eastern zones). The yield was largely consumed by wintering waterfowl populations (almost exclusively phytophagous), making this lagoon one of the most important wintering places in northern Africa, and recognized as a high ecological value World Heritage site. Ruppia cirrhosa (together with Chaetomorpha linum floating mats) was confined to a small north-eastern or eastern zone of the lagoon. This is the distribution which the authors observed in 1993, in the course of a study running through 1998, with P. pectinatus covering 37 km² (28,236 t DW) and 30 km² (20,139 t DW) in summer and autumn, respectively. In 1994, P. pectinatus had disappeared, an event which had already occurred in the past; however, this situation was still apparent in 1998; such a 5 year absence had never been reported since at least the early 1960s. From 1996 onwards, R. cirrhosa and C. linum “moved” to the sites formerly occupied by P. pectinatus. Direct causes (shortage of freshwater input, salinity increase) and indirect ones (construction of dams in the water catchment area of the lagoon, a relative drought) can account for these abrupt changes. The persistence of this situation could threaten the Ichkeul lagoon, as a major site for the wintering of phytophagous waterfowl.     

An annual cycle of biomass and productivity of Vallisneria americana in a subtropical spring-fed estuary

An annual cycle of biomass and productivity of wild celery (Vallisneria americana) was studied in Kings Bay, FL, USA. In situ growth rates were measured monthly between March 2001 and June 2002 in high-density stands, using a modified hole-punching technique, and applied to shoot density data to obtain areal estimates of production. Mean shoot density varied greatly over the study period, ranging between 200 and 800 shoots m⁻². Mean total biomass ranged between 162 and 1013 g m⁻², with aboveground material comprising, on average, 70% of total biomass. Total annual estimated production of new attached shoots was 519 g m⁻². Leaf growth rates peaked at >50 mg shoot⁻¹ d⁻¹, and mass-specific leaf growth ranged 0.6–1.8% d⁻¹. Annually, individual shoots produced 7.4 g of leaf material and completely replaced standing leaf biomass 3.5 times. Areal leaf production was highest in late spring/summer of 2001, and ranged between 3.6 and 23.0 g m⁻² d⁻¹. Annual total leaf production was 2704 g m⁻². Seasonality was not apparent in most variables monitored monthly; only 1 of the 64 relationships we examined between environmental variables (nutrients, chlorophyll a, and irradiance) and Vallisneria biological variables were significant, with relative growth rate increasing linearly with irradiance. Peak biomass and productivity of Vallisneria in Kings Bay were high compared to literature values for other Vallisneria populations as well as global averages for well-studied seagrasses, emphasizing the potential importance of Vallisneria to whole ecosystem functioning in springs, lakes, and oligohaline reaches of many estuaries.     

Extent estimates and land cover relationships for functional indicators in non-wadeable rivers

Functional indicators are being increasingly used to assess waterway health but their responses to pressure in non-wadeable rivers have not been widely documented or applied in modern survey designs that provide unbiased estimates of extent. This study tests the response of river metabolism and loss in cotton strip tensile strength across a land use pressure gradient in non-wadeable rivers of northern New Zealand, and reports extent estimates for river metabolism and decomposition rates. Following adjustment for probability of selection, ecosystem respiration (ER) and gross primary production (GPP) for the target population of order 5–7 non-wadeable rivers averaged −7.3 and 4.8 g O₂ m⁻² d⁻¹, respectively, with average P/R < 1 indicating dominance by heterotrophic processes. Ecosystem respiration was <−3.3 g O₂ m⁻² d⁻¹ for 75% of non-wadeable river length with around 20% of length between −10 and −20 g O₂ m⁻² d⁻¹. Cumulative distribution functions of cotton strength loss estimates indicated a more-or-less linear relationship with river km reflecting an even spread of decay rates (range in k 0.0007–0.2875 d⁻¹) across non-wadeable rivers regionally. A non-linear relationship with land cover was detected for GPP which was typically <5 g O₂ m⁻² d⁻¹ where natural vegetation cover was below 20% and greater than 80% of upstream catchment area. For cotton strength loss, the relationship with land cover was wedge-shaped such that sites with >60% natural cover had low decay rates (<0.02 d⁻¹) with variability below this increasing as natural cover declined. Using published criteria for assessing waterway health based on ER and GPP, 232–298 km (20–29%) of non-wadeable river length was considered to have severely impaired ecosystem functioning, and 436–530 km (42–50%) had no evidence of impact on river metabolism.     

Freeze tolerance and accumulation of cryoprotectants in the enchytraeid Enchytraeus albidus (Oligochaeta) from Greenland and Europe

The freeze tolerance and accumulation of cryoprotectants was investigated in three geographically different populations of the enchytraeid Enchytraeus albidus (Oligochaeta). E. albidus is widely distributed from the high Arctic to temperate Western Europe. Our results show that E. albidus is freeze tolerant, with freeze tolerance varying extensively between Greenlandic and European populations. Two populations from sub Arctic (Nuuk) and high Arctic Greenland (Zackenberg) survived freezing at −15 °C, whereas only 30% of a German population survived this temperature. When frozen, E. albidus responded by catabolising glycogen to glucose, which likely acted as a cryoprotectant. The average glucose concentrations were similar in the three populations when worms were frozen at −2 °C, approximately 50 μg glucose mg⁻¹ tissue dry weight (DW). At −14 °C the glucose concentrations increased to between 110 and 170 μg mg⁻¹ DW in worms from Greenland. The average glycogen content of worms from Zackenberg and Nuuk were about 300 μg mg⁻¹ DW, but only 230 μg mg⁻¹ DW in worms from Germany showing that not all glycogen was catabolised during the experiment. Nuclear magnetic resonance spectrometry (NMR) was used to screen for other putative cryoprotectants. Proline, glutamine and alanine were up regulated in frozen worms at −2 °C but only in relatively small concentrations suggesting that they were of little significance for freeze survival. The present study confirms earlier reports that freeze tolerant enchytraeids, like other freeze tolerant oligochaete earthworms, accumulate high concentrations of glucose as a primary cryoprotectant.     

Effects of salt stress on volatile compounds,total phenolic content and antioxidant activities of Salvia mirzayanii

Salvia mirzayanii is a medicinal and aromatic plant belonging to the Lamiaceae family, which is an endemic plant in Iran. In this study, the effects of different salt concentrations on total phenolic content, antioxidant activities and volatile components of the aerial parts of S. mirzayanii were studied. The results showed that total phenolic content increased with the increase in salt concentration. The increase was more pronounced under moderate salinity (3.8 mg GAE g^− 1 DW at 6.8 dS m^− 1 NaCl). Plants grown at 6.8 dS m^− 1 NaCl displayed the highest DPPH˚ scavenging activity with the lowest IC₅₀ value (2.13 mg ml^− 1) compared to the control. The volatile components were identified and analyzed by HS (headspace)-GC–MS using the Combi PAL System technique. The main components of control plants were α-terpinyl acetate, 1,8-cineole and bicyclogermacrene. The proportions of these main compounds were differently affected by salinity stress. The results showed that the synthesis of both total phenolic and some important volatile components was induced by moderate salinity.     

Accumulation of phycocyanin in heterotrophic and mixotrophic cultures of the acidophilic red alga Galdieria sulphuraria

The relationship between light intensity, nitrogen availability and pigmentation was investigated in mixotrophic and heterotrophic cultures of the unicellular red alga Galdieria sulphuraria 074G, a potential host for production of the blue pigment, phycocyanin (PC). During the exponential growth phase of batch cultures, G. sulphuraria 074G contained 2–4 mg phycocyanin per g dry weight. In carbon-limited and nitrogen-sufficient batch cultures grown in darkness, this value increased to 8–12 mg g⁻¹ dry weight during the stationary phase, whereas the phycocyanin content in nitrogen-deficient cells decreased to values below 1 mg g⁻¹ dry weight during stationary phase. Light intensities between 0 and 100 μmol photons m⁻² s⁻¹ had no influence on phycocyanin accumulation in mixotrophic cultures grown on glucose or fructose, while light stimulated phycocyanin synthesis in cultures grown on glycerol, in which the phycocyanin content in stationary phase was increased from 10 mg g⁻¹ dry weight in darkness to 20 mg g⁻¹ dry weight at a light intensity of 80 μmol photons m⁻² s⁻¹. At higher light intensities, less phycocyanin accumulated than at lower intensities, irrespective of the carbon substrate used. In carbon-limited continuous flow cultures grown on glucose or glycerol at a dilution rate of 0.63 day⁻¹, corresponding to 50% of the maximum specific growth rate, the highest steady-state phycocyanin content of 15–28 mg g⁻¹ dry weight was found at 65 μmol photons m⁻² s⁻¹. In contrast to the apparent glucose repression of light-induced PC synthesis observed in batch cultures, no glucose repression of the light stimulation was observed in continuous flow cultures because the glucose concentration in the culture supernatant always remained at limiting levels. Despite the fact that G. sulphuraria 074G contains less phycocyanin than some other microalgae and cyanobacteria, the ability of G. sulphuraria 074G to grow and synthesize phycocyanin in heterotrophic or mixotrophic cultures makes it an interesting alternative to the cyanobacterium, Spirulina platensis presently used for synthesis of phycocyanin.     

Leaf growth and population dynamics of intertidal Zostera japonica on the western coast of Korea

Leaf production and population dynamics of Zostera japonica were examined at three elevations of an intertidal transect in Seungbongdo Island on the western coast of Korea. Morphometrics, shoot density, biomass, leaf production, reproductive effort and environmental factors were monitored from October 2001 to October 2002. Z. japonica grew well in the lower intertidal zone from 0.2 to 1.0 m above mean chart datum. The upper station (St. 1) exhibited a finer sediment grain size and richer organic content than the middle (St. 2) and lower stations (St. 3). The size of shoots and leaves was significantly greater at St. 1 than at St. 3, whereas the rhizome internodes were longer at St. 3. Despite differences in morphological characteristics among three stations, seagrass biomass and shoot density were not significantly different among study sites. Shoot density, biomass, morphometrics and leaf productivity exhibited clear seasonal variations, which varied along with seasonal changes of water and air temperature. Leaf productivity measured by the clip and reharvest method was highest in September (4.3 g DW m⁻² d⁻¹) and lowest in February (0.2 g DW m⁻² d⁻¹). Reproductive shoots rapidly increased to maximum density along with the high water temperature in July to September. In the intertidal zone, Z. japonica exhibited faster vegetative growth on muddy sand than on sand, probably due to the difference in nutrient supply. The seasonal changes of water and air temperature were considered to play an important role in the seasonal leaf growth of Z. japonica.     

Leaf growth and population dynamics of intertidal Zostera japonica on the western coast of Korea

Leaf production and population dynamics of Zostera japonica were examined at three elevations of an intertidal transect in Seungbongdo Island on the western coast of Korea. Morphometrics, shoot density, biomass, leaf production, reproductive effort and environmental factors were monitored from October 2001 to October 2002. Z. japonica grew well in the lower intertidal zone from 0.2 to 1.0 m above mean chart datum. The upper station (St. 1) exhibited a finer sediment grain size and richer organic content than the middle (St. 2) and lower stations (St. 3). The size of shoots and leaves was significantly greater at St. 1 than at St. 3, whereas the rhizome internodes were longer at St. 3. Despite differences in morphological characteristics among three stations, seagrass biomass and shoot density were not significantly different among study sites. Shoot density, biomass, morphometrics and leaf productivity exhibited clear seasonal variations, which varied along with seasonal changes of water and air temperature. Leaf productivity measured by the clip and reharvest method was highest in September (4.3 g DW m⁻² d⁻¹) and lowest in February (0.2 g DW m⁻² d⁻¹). Reproductive shoots rapidly increased to maximum density along with the high water temperature in July to September. In the intertidal zone, Z. japonica exhibited faster vegetative growth on muddy sand than on sand, probably due to the difference in nutrient supply. The seasonal changes of water and air temperature were considered to play an important role in the seasonal leaf growth of Z. japonica.     

Effect of nutrient pulses on photosynthesis of Chaetomorpha linum from a shallow Mediterranean coastal lagoon

The influence of nitrogen and phosphorus pulses on Chaetomorpha linum (Muller) Kutzing growth and photosynthesis was studied in laboratory experiments. Photosynthesis and growth of C. linum from Tancada lagoon seems limited by both nitrogen and phosphorus, as indicated by the high rate (4.7–11.6 mg O₂ g⁻¹ dry weight h⁻¹) of light-saturated photosynthesis (P_m) and growth rates observed under nitrogen plus phosphorus enrichment in relation to enrichment by nitrogen alone (2.9–7.6 mg O₂ g⁻¹ dry weight h⁻¹). Significant increase in nitrogen and phosphorus content as percentage of dry weight was observed in C. linum fertilized with a single nutrient or with nitrogen plus phosphorus. In Tancada lagoon, when availability of nitrogen to primary producers is by pulses, an increase of nitrate concentration in the water column (from 6 to 100 μM) has a greater effect on growth of C. linum (growth rate: 0.13 day⁻¹) than an increase in ammonium concentration (from 20 to 100 μM and growth rate: 0.11 day⁻¹). For a given thallus nitrogen content (0.6–1.4% N), both P_m and the photosynthetic efficiency (α) normalized to dry weight were correlated (r² = 0.73, p < 0.005) indicating that variations in electron transport were coupled to variations in C-fixation capacity. Optimizing both α and P_m may be a general characteristic of thin-structured opportunistic algae in more variable estuarine environments.     

Hydrogen sulphide removal from air by biotrickling filter using open-pore polyurethane foam as a carrier

A study was conducted on H₂S removal in a biotrickling filter packed with open-pore polyurethane foam. Thiobacillus denitrificans was used as inoculum and a mixed culture population was developed during the process. The inhibitory effect of sulphate concentration (1.8–16.8 g L⁻¹), pH (6.9–8.6), trickling liquid velocity (TLV, 9.1–22.8 m h⁻¹), H₂S inlet concentration (20–157 ppmv) and the empty bed residence time (EBRT, 9–57 s) on the H₂S removal efficiency (RE) were thoroughly investigated. An increase in pH from 6.9 to 8.5 led to a corresponding increase in H₂S removal. In addition, an inhibitory effect of sulphate concentration was observed from 16.8 g L⁻¹ and the maximum elimination capacity was found to be 22 gS m⁻³ h⁻¹ (RE 98%). The RE was constant (98.8 ± 0.30%) for EBRT ≥ 16 s, but a decrease in the EBRT from 16 to 9 s led to a corresponding decrease in RE from 98.2 to 89.6% for a TLV of 9.1 m h⁻¹ and from 97.9 to 94.9% for a TLV of 22.8 m h⁻¹ (inlet load of 11.0 ± 0.2 gS m⁻³ h⁻¹). The sulphur oxidation capacity in the biotrickling filter was not diminished by the presence of other bacteria.     

Seasonal variations in photosynthetic irradiance response curves of macrophytes from a Mediterranean coastal lagoon

The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Thau lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17 °C, 982 μmol O₂ g⁻¹ dw h⁻¹ and 9.1 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹, respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25 °C, 583 μmol O₂ g⁻¹ dw h⁻¹ and 2.6 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹ respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to R_d (ranging 6.7–794 μmol O₂ g⁻¹ dw h⁻¹, respectively for Rytiphlaea tinctoria at 7 °C and for Dasya sessilis at 25 °C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of P/I curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum).     

d- and l-lactic acid production from fresh sweet potato through simultaneous saccharification and fermentation

The aim of this study was to develop a bioprocess for l- and d-lactic acid production from raw sweet potato through simultaneous saccharification and fermentation by Lactobacillus paracasei and Lactobacillus coryniformis, respectively. The effects of enzyme and nitrogen source concentrations as well as of the ratio of raw material to medium were investigated. At dried material concentrations of 136.36–219.51 g L⁻¹, yields of 90.13–91.17% (w/w) and productivities of 3.41–3.83 g L⁻¹ h⁻¹ were obtained with lactic acid concentrations as high as 198.32 g L⁻¹ for l-lactic acid production. In addition, d-lactic acid was produced with yields of 90.11–84.92% (w/w) and productivities of 2.55–3.11 g L⁻¹ h⁻¹ with a maximum concentration of 186.40 g L⁻¹ at the same concentrations of dried material. The simple and efficient process described in this study will benefit the tuber and root-based lactic acid industries without requiring alterations in plant equipment.     

Ability of a perfluoropolymer membrane to tolerate by-products of ethanol fermentation broth from dilute acid-pretreated rice straw

A perfluoropolymer (PFP) membrane has been prepared for use in vapor permeation to separate aqueous ethanol mixtures produced from rice straw with xylose-assimilating recombinant Saccharomyces cerevisiae. PFP membranes commonly have been used for dehydration process and possess good selectivity and high permeances. The effects of by-products during dilute acid pretreatment, addition of yeast extract, and ethanol fermentation on PFP membrane performance were investigated. While feeding mixtures of ethanol (90 wt%) in water, to which individual by-products (0.1–2 g/L) were added, the PFP membrane demonstrated no clear change in permeation rate (439–507 g m⁻² h⁻¹) or separation factor (14.9–23.5) from 2 to 4 h of the process. The PFP membrane also showed no clear change in permeation rate (751–859 g m⁻² h⁻¹) or separation factor (12.5–13.8) while feeding the mixture (final ethanol conc.: 61 wt%) of ethanol and distillation of the fermentation broth using a suspended fraction of dilute acid-pretreated rice straw for 20 h. These results suggest that the PFP membrane can tolerate actual distillation liquids from ethanol fermentation broth obtained from lignocellulosic biomass pretreated with dilute acid.     

Evaluation of distant carbon sources in biosurfactant production by a gamma ray-induced Pseudomonas putida mutant

Pseudomonas putida 33 wild strain, subjected to gamma ray mutagenesis and designated as P. putida 300-B mutant was used as microbial rhamnolipid-producer by using distant carbon sources (viz. hydrocarbons, waste frying oils ‘WFOs’, vegetable oil refinery wastes and molasses) in the minimal media under shake flask conditions. The behavior of glucose as co-substrate and growth initiator was examined. The 300-B mutant strain showed its ability to grow on all the substrates tested and produced rhamnolipid surfactants to different extents however; soybean and corn WFOs were observed to be preferred carbon sources followed by kerosene and paraffin oils, respectively. The best cell biomass (3.5 g l⁻¹) and rhamnolipids yield (4.1 g l⁻¹) were obtained with soybean WFO as carbon source and glucose as growth initiator under fed-batch cultivation showing an optimum specific growth rate (μ) of 0.272 h⁻¹, specific product yield (q_p) of 0.318 g g⁻¹ h and volumetric productivity (P_V) of 0.024 g l⁻¹ h. The critical micelle concentration of its culture supernatant was observed to be 91 mg rhamnolipids l⁻¹ and surface tension as 31.2 mN m⁻¹.     

Thresholds for morphological response to light reduction for four tropical seagrass species

Seagrasses worldwide are highly vulnerable to, and at increasing risk from reduced light availability, and robust light thresholds are required for evaluating future impacts of changing light conditions. We tested the morphological response (shoot density and growth) of four Indo-West Pacific seagrass species (Cymodocea serrulata, Halodule uninervis, Halophila ovalis and Zostera muelleri) to six daily light levels ranging from 0 to 23 mol m⁻² d⁻¹ (0–70% surface irradiance) in cool (∼23 °C) and warm temperatures (∼28 °C) over 14 weeks. The impact of light limitation on shoot densities and growth rates was higher at warm than at cool temperatures, and for Z. muelleri and H. ovalis than for C. serrulata and H. uninervis, in terms of both the time taken for the low light treatment to take effect and the predicted time to shoot loss (e.g. 17–143 days at 0 mol m⁻² d⁻¹). Using fitted curves we estimated temperature-dependent thresholds (with estimates of uncertainty) for 50% and 80% protection of growth and shoot density, defined here as “potential light thresholds” in recognition that they were derived under experimental conditions. Potential light thresholds that maintained 50% and 80% of seagrass shoot density fell within the ranges 1.1–5.7 mol m⁻² d⁻¹ and 3.8–10.4 mol m⁻² d⁻¹, respectively, depending on temperature and species. Light thresholds calculated in separate in situ studies for two of the same species produced comparable results. We propose that the upper (rounded) values of 6 mol m⁻² d⁻¹ and 10 mol m⁻² d⁻¹ can be used as potential light thresholds for protecting 50% and 80% of shoot density for these four species over 14 weeks. As management guidelines should always be more conservative than thresholds for biological declines, we used error estimates to provide a quantitative method for converting potential light thresholds into guidelines that satisfy this criterion. The present study demonstrates a new approach to deriving potential light thresholds for acute impacts, describes how they can be applied in management guidelines and quantifies the timescales of seagrass decline in response to light limitation. This method can be used to further quantify cumulative impacts on potential light thresholds.     

Production of schisantherin A and gomisin G in in vitro cultures of Schisandra chinensis

Methanolic extracts from the biomass of shoot-differentiating and undifferentiating callus cultures of Schisandra chinensis growing respectively on six and two different variants of the Murashige and Skoog (MS) medium, with different concentrations of plant growth regulators, BA (N⁶-benzyladenine) and NAA (α-naphthaleneacetic acid) were analyzed for the accumulation of two lignans–schisantherin A and gomisin G, using the HPLC method. The amounts of the two compounds in the biomass extracts from shoot-differentiating callus cultures were dependent on the concentration of plant growth regulators in the MS medium. The highest amounts of both lignans were obtained on the MS medium supplemented with 3 mg l⁻¹ BA and 1 mg l⁻¹ NAA. The maximum amount of schisantherin A (33.45 mg 100 g⁻¹ DW) was about 1.3 times higher than in the extracts from the leaves and fruits of parent plants. This is the most important result potentially promising from a practical point of view.     

The effects of light intensity on the growth of Japanese Gambierdiscus spp. (Dinophyceae)

Marine toxic dinoflagellates of the genus Gambierdiscus are the causative agents of ciguatera fish poisoning (CFP), a form of seafood poisoning that is widespread in tropical, subtropical and temperate regions worldwide. The distributions of Gambierdiscus australes, Gambierdiscus scabrosus and two phylotypes of Gambierdiscus spp. type 2 and type 3 have been reported for the waters surrounding the main island of Japan. To explore the bloom dynamics and the vertical distribution of these Japanese species and phylotypes of Gambierdiscus, the effects of light intensity on their growth were tested, using a photoirradiation-culture system. The relationship between the observed growth rates and light intensity conditions for the four species/phylotypes were formulated at R > 0.92 (p < 0.01) using regression analysis and photosynthesis-light intensity (P-L) model. Based on this equation, the optimum light intensity (L_max) and the semi-optimum light intensity range (L_s-opt) that resulted in the maximum growth rate (μ_max) and ≥80% μ _max values of the four species/phylotypes, respectively, were as follows: (1) the L_max and L_s-opt of G. australes were 208 μmol photons m⁻² s⁻¹ and 91–422 μmol photons m⁻² s⁻¹, respectively; (2) those of G. scabrosus were 252 and 120–421 μmol photons m⁻² s⁻¹, respectively; (3) those of Gambierdiscus sp. type 2 were 192 and 75–430 μmol photons m⁻² s⁻¹, respectively; and (4) those of Gambierdiscus sp. type 3 were ≥427 and 73–427 μmol photons m⁻² s⁻¹, respectively. All four Gambierdiscus species/phylotypes required approximately 10 μmol photons m⁻² s⁻¹ to maintain growth. The light intensities in coastal waters at a site in Tosa Bay were measured vertically at 1 m intervals once per season. The relationships between the observed light intensity and depth were formulated using Beer’s Law. Based on these equations, the range of the attenuation coefficients at Tosa Bay site was determined to be 0.058–0.119 m⁻¹. The values 1700 μmol photons m⁻² s⁻¹, 500 μmol photons m⁻² s⁻¹, and 200 μmol photons m⁻² s⁻¹ were substituted into the equations to estimate the vertical profiles of light intensity at sunny midday, cloudy midday and rainy midday, respectively. Based on the regression equations coupled with the empirically determined attenuation coefficients for each of the four seasons, the ranges of the projected depths of L_max and L_s-opt for the four Gambierdiscus species/phylotypes under sunny midday conditions, cloudy midday conditions, and rainy midday conditions were 12–38 m and 12–54 m, 1–16 m and 1–33 m, and 0 m and 0–16 m, respectively. These results suggest that light intensity plays an important role in the bloom dynamics and vertical distribution of Gambierdiscus species/phylotypes in Japanese coastal waters.