Secondary Metabolites of Flustra foliacea and Their Influence on Bacteria

The North Sea bryozoan Flustra foliacea was investigated to determine its secondary metabolite content. Gas chromatography-mass spectrometry analysis of a dichloromethane extract of the bryozoan enabled 11 compounds to be identified. Preparative high-performance liquid chromatography of the extract resulted in the isolation of 10 brominated alkaloids (compounds 1 to 10) and one diterpene (compound 11). All of these compounds were tested to determine their activities in agar diffusion assays against bacteria derived from marine and terrestrial environments. Compounds 1, 3 to 7, 10, and 11 exhibited significant activities against one or more marine bacterial strains originally isolated from F. foliacea but only weak activities against all of the terrestrial bacteria. By using the biosensors Pseudomonas putida(pKR-C12), P. putida(pAS-C8), and Escherichia coli(pSB403) the antagonistic effect on N-acyl-homoserine lactone-dependent quorum-sensing systems was investigated. Compounds 8 and 10 caused reductions in the signal intensities in these bioassays ranging from 50 to 20% at a concentration of 20 μg/ml.     

Seasonal patterns of partitioning and remobilization of 14C in the invasive rhizomatous perennial Japanese knotweed (Fallopia japonica (Houtt.) Ronse Decraene)

Resource partitioning between shoot growth, storage and reproduction is poorly understood in many clonal plant species. This study documents seasonal patterns of growth, ¹⁴C-labelled photoassimilate distribution and remobilization in the invasive rhizomatous species Fallopia japonica (Japanese knotweed). Biomass accumulation above- and below-ground in F. japonica was rapid. By September, rhizome biomass had increased 18-fold from the initial harvest in May (representing 48% of total plant biomass) and this was maintained over winter. Patterns of ¹⁴C allocation from F. japonica shoots labelled at different times of year show that as the season progressed, the rhizomes became an increasingly important sink for current assimilate (the percentage of ¹⁴C recovered from rhizomes was 35% in August and 67% in September) and the corresponding retention of assimilate by established shoots declined. The percentage of ¹⁴C exported to roots was greatest in August. Relatively little photoassimilate was exported to other shoots on the plant, or to flowers. Recycling of photoassimilate was fairly tight in this species and ¹⁴C fixed by shoots in early May 1999 or September 1999 was remobilized to the rhizome prior to shoot senescence and death. Some of this ¹⁴C was then remobilized to new shoots early the following spring. These characteristics may contribute to the success of F. japonica in colonizing a variety of contrasting habitats, often with serious management implications.     

Reduced clonal reproduction indicates low potential for establishment of hybrids between wild and cultivated strawberries (Fragaria vesca × F. × ananassa)

The genus Fragaria (Rosaceae) contains 24 species, including hybrid species such as the garden strawberry (Fragaria × ananassa Duch.). Natural hybridization between Fragaria species has repeatedly been reported, and studies on the hybridization potential between F. × ananassa and its wild relatives have become increasingly important with the outlook for genetically modified garden strawberries. In Europe, a candidate species for hybridization with garden strawberries is the common woodland strawberry (Fragaria vesca L.). Although a previous field survey indicated that the potential for hybridization between F. vesca and F. × ananassa is low, it is not clear whether the lack of natural hybrids is caused by known pre- and postzygotic barriers, or whether hybrid plants lack the fitness to establish in natural F. vesca populations. We grew different F. vesca and F. vesca × F. × ananassa hybrid clones with and without competition in a greenhouse and assessed biomass production, clonal reproduction, and sexual reproduction of plants. While some hybrid clones exceeded F. vesca in biomass production, general clonal reproduction was much lower and delayed in hybrids. Furthermore, hybrids were sterile. These results demonstrate a mechanism by which the general lack of F. vesca × F. × ananassa hybrids in natural habitats can be explained, in addition to the known low hybridization potential between garden and woodland strawberries. We conclude that hybrids have a competitive disadvantage against co-occurring F. vesca plants due to inferior and delayed clonal reproduction, and that the potential for hybrid establishment under natural conditions is low.     

Growth and loss of distal tissue in blades of Lessonia nigrescens and Lessonia trabeculata (Laminariales)

Meristematic growth and loss of distal tissue from blades of two ecologically important species in the south-east Pacific, Lessonia nigrescens and Lessonia trabeculata, was evaluated during 1 year. Comparative growth was determined by a hole-punch method, loss of distal tissue from the blades was determined by subtracting final blade length (with loss) from expected blade lengths (without loss); growth and tissue loss were transformed to fresh biomass units for calculation of inter-algae differences. The results showed that blade elongation rate increased at the beginning of spring, and declined towards the end of summer, with mean values between 0.40 and 0.08 cm day⁻¹ for L. nigrescens, and 0.65–0.17 cm day⁻¹ for L. trabeculata. Loss of distal tissue varied seasonally when examined as length units for both species; with mean values between 0.24 and 0.10 cm day⁻¹ for L. nigrescens, and 0.51–0.25 cm day⁻¹ for L. trabeculata. Variations in fresh biomass units were only observed in Lessonia trabeculata, increasing in spring, with mean values to 0.13 g (fresh weight) day⁻¹. Annual growth and loss of distal tissue were higher in L. trabeculata (0.41 and 0.39 cm day⁻¹, respectively) than in L nigrescens (0.19 and 0.15 cm day⁻¹). When growth and tissue loss were considered as fresh biomass, monthly gains significantly outweighed loss of distal tissue in both species, but parallel results based on length data followed a different trend. L. trabeculata released about 50% of its growth biomass as particulate organic matter, while the comparative value for L. nigrescens was about 20%.     

The influence of population density on fission and growth of Holothuria atra in natural mesocosms

Investigation of the population dynamics, asexual reproduction (fission) and growth of holothuroids has been impeded by the difficulty of tagging individuals. We conducted the first tests on the interactions between population density, fission and growth of holothuroids in experimental populations placed in natural mesocosms (microatolls) at One Tree Reef (OTR), Great Barrier Reef. Similarly sized Holothuria atra were translocated to the microatolls in low (LDT) and high (HDT) density treatments. We hypothesised that holothuroids in lower density treatments would have more resources per individual and that this would promote higher frequencies of asexual reproduction and smaller individuals. The seasonal pattern of fission was similar in natural (unmanipulated) and experimental populations, with the maximum number of fission products occurring in winter and spring. The overall density of the LDT (0.19 ind. m^- 2) and HDT (0.59 ind. m^- 2) did not vary over time. This ‘steady state’ suggested that some fission products died and that asexual reproduction compensated for overall mortality and emigration. There was no difference in sediment chlorophyll pigments between treatments indicating that the different densities of H. atra did not affect benthic microalgal biomass. The percentage of fission products was greater in the LDT than the HDT but this difference was not statistically significant, providing some support for the hypothesis that H. atra in the LDT exhibit a higher fission rates. At the end of the experiment H. atra in LDT were significantly longer and heavier than in HDT. H. atra surpassed their initial deployment weight and length after 13 months in the LDT by 115.2% and 45.2% respectively and in the HDT 86.9% and 24.6% respectively, changing from the small to the large phenotype known for this species. This differential growth may be linked to habitat stability and high benthic productivity and demonstrates the phenotypic plasticity of holothuroids and potential to achieve ‘Optimum Individual Size’ with respect to environmental conditions. Our results will assist in finetuning conceptual models on asexual reproduction and future experimental studies on the phenomena of fission and plastic growth in holothuroids.     

Colony Structure in Flustra foliacea (Linnaeus) (Bryozoa,Chéilostomata)

Encrusting forms presumably represent the original mode of growth in the bryozoans. They usually exhibit a relatively low degree of colony integration. The numerous different erect colony types, certainly independently derived from this stage, show a higher degree of integration. Eventually forms arise with a strict pattern only little influenced by the environment. The Flustra foliacea colony holds an intermediate position in this respect. It forms an initial crust on a foreign substratum such as rock. The crust forms marginal lobes. The lobes collide two and two. The two components of each collision then rise back to back, owing to lack of space, into bilaminar fronds. The two zooid layers composing these erect branches and mutually encrusting the “auto-substratum” of their respective basal walls, grow much more rapidly than the initial crust on the “heterosubstratum” of the rock to finally comprise more than 95 % of the colony volume. The different rate of growth on “auto-” and “heterosubstratum” respectively is interpreted as indicating a preference for the “autosubstratum” and as the main force in the formation of erect branches. The Fl. foliacea case indicates one of the pathways from encrusting to erect colonies in the bryozoans. It is probably valid for at least some of the erect bilaminar colonies appearing in different parts of the bryozoan system.     

Zoobenthos of the Cheshskaya Bay (southeastern Barents Sea): spatial distribution and community structure in relation to environmental factors

Structural and functional characteristics of zoobenthos of the Cheshskaya Bay (SE Barents Sea) were studied at 21 stations in June/July 1995. Strong prevailing cyclonic and tidal currents result in relatively uniform temperature and salinity in the area. Sediments consist mainly of sand and pebbles, while the flux of suspended matter from rivers locally increases the share of finer fractions. Analysis of species composition (419 taxa), abundance (up to 4,200 ind m⁻² and up to 29,000 ind m⁻² with juveniles) and biomass (up to >6,000 g wet wt m⁻²) indicates high species richness in most parts of the bay, especially in the northeast. Analysis of community structure using production characteristics of species revealed a general predominance of suspension feeders partitioned into seven communities. The dominant species of these communities were Mytilus edulis and Balanus crenatus (Type 1), B. crenatus (Type 2), Modiolus modiolus and Verruca stroemia (Type 3), Flustra foliacea and V. stroemia (Type 4), Hydrallmania falcata (Type 5), V. stroemia and Chirona hameri (Type 6), and Ophelia limacina (Type 7). The structure of the communities is mainly regulated by sediment type, water depth and, to some extent, by riverine input. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Bioreactor shoot cultures of <Emphasis Type="Italic">Rhododendron tomentosum</Emphasis> (<Emphasis Type="Italic">Ledum palustre</Emphasis>) for a large-scale production of bioactive volatile compounds

Rhododendron tomentosum Harmaja (Ledum palustre), a peat bog plant from Ericaceae family, has been used in traditional medicine as the anti-arthritis agent. Although modern researches confirm its anti-inflammatory properties, it remains threatened by habitat degradation and possibilities to collect this endangered species from its natural environment for further biological activity studies are limited. Therefore, R. tomentosum liquid in vitro cultures were established as the alternative source of that valuable plant material. Schenk–Hildebrandt medium with 24.60 μM 2-isopentenyladenine and 592.02 μM adenine provides intensive growth and proper morphology of the obtained microshoots. The R. tomentosum biomass was scaled up using the various bioreactors (immersion, temporary immersion and spraying systems) for better growth and improved volatile oil production. The largest biomass accumulation (fresh weight?=?250 g l^?1, growth index?=?280, dry weight?=?20 g l^?1) and essential oil content (0.5% v/m) were achieved with application of commercially available RITA^® bioreactor. GC/MS analysis revealed the high content of p-cymene (6.9%), alloaromadendrene (5.5%), shyobunone (8.2%) and ledene oxide (II) (13.0%) in the volatile fraction obtained from RITA^® system. The biomass growth parameters and production profile in terms of essential oil and selected terpenoid compounds were determined during the 2 month period. The influence of culture conditions and bioreactor construction on the growth and volatile oil production in R. tomentosum biomasses was discussed.     

Synthesis and evaluation of N(1)-alkylindole-3-ylalkylammonium compounds as nicotinic acetylcholine receptor ligands

In this study thirty-three novel indole derivatives were designed and synthesized based on the structure of deformylflustrabromine B (1), a metabolite isolated from the marine bryozoan Flustra foliacea L. The syntheses were carried out using standard methodologies and in good yields. The molecules were tested for their affinities for the α4β2¹, α3β4¹, α7¹ and (α1)₂β1γδ nicotinic acetylcholine receptor (nAChR) subtypes. Binding assays showed that, among these ligands, compound 7c exhibited the highest affinity with K_i = 136.1, 93.9 and 862.4 nM for the α4β2¹, α3β4¹, and α7¹ nAChRs subtypes, respectively. These results indicated that the indole core might be a useful scaffold for the development of new potent and selective nAChR ligands.     

Species screening and biomass trials of woody plants in the semi-arid southwest United States

Species screening and selection trials are being conducted to identify appropriate woody species and technology for biofuel farming in the southwest United States. During the initial phase of the program, 26 native and exotic species have been tested at sites in Texas, New Mexico and Arizona. Second season biomass estimates indicate that initial yields of 3·2–8·5 dry Mg ha⁻¹ year⁻¹ are possible without post-establishment irrigation. The species Atriplex canescens (Pursh) Nutt., Prosopis alba Griseb. and Leucaena leucocephala (Lam.) de Wit reached canopy closure within two seasons of growth and are identified as rapid initial biomass producers under the semi-arid conditions of the study area.     

The Distribution of Macrozoobenthos Taxa,as Potential Indicators of Vulnerable Marine Ecosystems in the Western Bering Sea: 1. Anadyr Bay Area

The composition of common species in some macrozoobenthos groups that are considered as potential indicators of vulnerable marine ecosystems (VME), in the Anadyr Bay area, Bering Sea have been determined based on the results of four benthic surveys using a benthic grab sampler (1985, 2005) and a bottom trawl (2008, 2012). These are soft corals (Gersemia rubiformis), sponges (Myxilla incrustans, Halichondria panicea, and Semisuberites cribrosa), ascidians (Halocynthia aurantium and Boltenia ovifera), bryozoans (Cystisella saccata and Flustra foliacea), barnacles (Chirona evermanni), and the brittle star (Gorgonocephalus eucnemis). The distribution of these animals has been mapped. Aggregations of immobile sestonophages (the former five groups) are formed on hard coarse-grained and mixed sediments in waters with higher hydrodynamic activity (along the southwestern and northeastern coasts of the Anadyr Bay, mainly at depths of 80–90 m). In some cases, sponges and bryozoans in the southern part of the area can descend to a depth of 250 m (in the Navarin Canyon). The mobile filterer G. eucnemis forms aggregations mainly on soft sediments in the central part of Anadyr Bay, at depths of 50–270 m, in the area of a localized spot of near-bottom cold water. According to the results of trawl surveys conducted in 2008 and 2012, the mean biomass of the sponges, the brittle star G. eucnemis, and the sea squirt B. ovifera did not change, whereas the mean biomass of the barnacle Ch. evermanni and sea peach H. aurantium decreased by 6.5 and 3.7 times, respectively. Since the level of trawl fishing activity in the region is not high, the hypothesis has been proposed that the decrease in the abundance of the latter two species is presumably caused by the natural dynamics of their population or can be related to the factor of randomness, as these species are caught in their mosaically distributed local aggregations.     

The epizoic diatom community on four bryozoan species from Helgoland (German Bight, North Sea)

The composition of the diatom community on the bryozoans Electra pilosa, Membranipora membranacea, Flustra foliacea, and Alcyonidium gelatinosum from the German Bight was studied by light and scanning electron microscopy. In total, members of 26 diatom genera were found, with Cocconeis, Tabularia, Licmophora, Amphora, and Navicula being the most abundant. The amount and the composition of the diatom covering seem to be typical for single bryozoan species. Electra pilosa and Membranipora membranacea showed a rather dense covering with 71–547 cells/mm² and 77–110 cells/mm², respectively. The most prominent genus on Electra pilosa was Cocconeis, reaching up to 58% of all diatoms in one sample, followed by Navicula, Tabularia and Amphora. The most abundant genera on Membranipora membranacea were Tabularia and Licmophora, making up almost 70% of all diatoms in one sample, followed by Navicula, Cocconeis and Amphora. The diatom composition was very stable on all Electra samples, but varied on Membranipora samples. With <1–27 cells/mm², diatoms were much less abundant on Alcyonidium gelatinosum. Members of the genera Tabularia and Navicula were the most frequently found benthic diatoms, whereas the planktonic forms Coscinodiscus, Cyclotella, and Thalassiosira made up 35% of the diatoms. On Flustra foliacea, diatoms were virtually absent, with fewer than 5 cells/mm². The low diatom numbers are probably due to toxic metabolites produced by the host. The same may be true for Alcyonidium gelatinosum, but here they might also be a consequence of the surface properties of the bryozoan. Electronic Publication     

Influence of salt stress on propagation,growth and nutrient uptake of typical aquatic plant species

Anthropogenic activities and natural causes contribute to an increase in the area and degree of degraded saline wetlands in arid/semi‐arid and coastal regions. The objective of this study was to determine the salt tolerance of the seven aquatic plant species Phragmites australis, Arundo donax, Canna indica, Scirpus validus, Alternanthera philoxeroides, Phyllostachys heteroclada and Potederia cordata during asexual reproduction and continuous growth. The species were exposed to five salinity treatments from 0.3 (control) to 20 dS m^?1 during a 30 day experiment. Data were collected on asexual reproduction and growth, chlorophyll content in leaves, Na⁺ and K⁺ concentrations, total nitrogen (TN) and total phosphorus (TP) concentrations in above‐ground biomass (AGB) and below‐ground biomass (BGB). The results showed that: 1) increase in salinity (especially at a salinity level of EC ≥15 dS m^?1) generally inhibited the capacity for asexual reproduction and reduced the chlorophyll content of leaves; 2) total dry biomass of plants was significantly negatively related to asexual reproduction; 3) species‐specific salt tolerance mechanisms were reflected by the Na⁺ and K⁺ concentrations and Na⁺/K⁺ ratios in different parts of the plants; and 4) the absorption of TN and TP were inhibited at high salinity (i.e. EC = 20 dS m^?1) in AGB and BGB of most tested plant species. However, salinity may enhance plant uptake of TN and TP under certain conditions (e.g. EC at 5, 10 and 15 dS m^?1). In general, as compared to the other species tested, giant reed A. donax and alligator weed A. philoxeroides showed relatively high asexual reproduction and growth capacity under high salt stress, and these species should thus be considered as candidates for restoration of degraded saline wetlands and/or for decontaminating saline wastewater.     

Early growth responses of mangroves to different rates of nitrogen and phosphorus supply

Experiments were conducted in an outdoor facility to quantify growth responses of six mangrove species to rates of dissolved inorganic nitrogen and phosphorus supply mimicking the range of N and P mineralization rates in natural soils. Growth of all six species on nitrogen was nonlinear. Stem extension rates of Rhizophora apiculata and Xylocarpus granatum were enhanced to the highest rate of N supply (50 mmol m^− 2 d^− 1); Bruguiera gymnorrhiza, Avicennia marina, and Xylocarpus moluccensis stem growth leveled off by 10 mmol m^− 2 d^− 1. Stem growth of Ceriops tagal peaked at 24-26 mmol N m^− 2 d^− 1. Except for A. marina and C. tagal, rates of biomass increase declined at the highest supply rate, indicating NH₄⁺ toxicity. At different rates of P supply, stem extension rates and rates of biomass increase of R. apiculata and C. tagal best-fit Gaussian curves and B. gymnorrhiza stem growth and biomass increase best-fit sigmoidal and Gaussian curves, respectively; X. moluccensis stem and biomass growth increased linearly, but stem and biomass growth rates of A. marina did not vary in relation to P supply. Stem growth of X. granatum was Gaussian but rates of biomass increase best-fit a quadratic equation. Changes in leaf and root N and P content mirrored the growth responses. As rates of N and P mineralization in natural mangrove soils overlap with the lowest rates of N and P supplied in these experiments, the growth responses imply that mangroves are intrinsically nutrient-limited at mineralization rates often encountered in nature. Such species specificity may have significant implications for recruitment success and the establishment of species gradients within mangrove forests.     

Recent changes in the seaweed community of Western Prince Edward Island: implications for the seaweed industry

Prior to 1980, seaweed beds of western Prince Edward Island, Canada, were dominated by Chondrus crispus Stackhouse, associated with 37 other species of common algae. Furcellaria lumbricalis (Huds.) Lamour. occurred in 4.6% of the samples from the Pleasant View bed but never reached measurable levels of cover. By 1991 F. lumbricalis was reported in 67% of the samples from this bed. Furcellaria lumbricalis biomass was negatively correlated with C. crispus biomass and positively correlated with Phyllophora Grev. spp. biomass. F. lumbricalis biomass and cover peaked in subtidal areas below 4 m at 359 ± 299 SD fresh g 0.25 m^–2. Harvesters avoid concentrations of F. lumbricalis, resulting in a 5% content of this species in the commercial harvest. Systematic harvesting located concentrations of F. lumbricalis in seven of 10 commercial beds. Proposed causes for change in species dominance from C. crispus to F. lumbricalis range from general environmental change, natural succession to excessive human perturbation.     

The Development and Influence of Meloidogyne incognita and M. javanica on Wheat

The effects of soil temperature and initial inoculum density (Pi) of Meloidogyne incognito and M. javanica on growth of wheat (Triticum aestivum cv. Anza) and nematode reproduction were studied in controlled temperature baths in the glasshouse. Nematode reproduction was directly proportional to temperature between 14 and 30 C for M. incognita and between 18 and 26 C for M. javanica. Reproduction rates (Pf/Pi, where Pf = final number of eggs) for Pi''s of 3,000, 9,000, and 30,000 eggs/plant were greatest at each temperature when Pi = 3,000. Maximum M. incognita reproduction rate (Pf/Pi = 51.12) was at 30 C. At 26 C, M. javanica reproduction (Pf/Pi = 14.82, 9.02, and 4.23 for Pi = 3,000, 9,000, and 30,000, respectively) was about half that of M. incognita when Pi = 3,000 or 9,000 but similar when Pi = 30,000. Reproduction of both species was depressed between 14 and 18 C. Shoot and root growth and head numbers were inversely related to soil temperature between 14 and 30 C but were not affected by the Pi of M. incognita when 7 d old seedlings were inoculated. When newly germinated seedlings were inoculated with M. incognita or M. javanica, the Pi did not affect shoot and root fresh weights, shoot/root ratio, and tillering, but it did reduce root dry weight (M. javanica at 26 C) and increase shoot dry weight (M. incognita at 18-22 C). The optimum temperature range is lower for wheat growth than for nematode reproduction. Wheat cv. Anza is a good host for M. incognita and M. javanica, but it is tolerant to both species.     

Biomass Partitioning in Tomato Plants Infected with Meloidogyne incognita

Tomato plants were inoculated with Meloidogyne incognita at initial populations (Pi) of 0, 1, 10, 50, 100, and 200 (x 1,000) eggs per plant and maintained in a growth chamber for 40 days. Total fresh biomass (roots + shoots) at harvest was unchanged by nematode inoculation with Pi of 1 x 10⁵ eggs or less. Reductions in fresh shoot weight with increasing Pi coincided with increases in root weight. Total fresh biomass declined with Pi above 1 x 10⁵ eggs, whereas total dry biomass declined at Pi above 1 x 10⁴ eggs. The greatest reduction percentages in fresh shoot biomass induced by root-knot nematodes occurred in the stem tissue, followed by the petiole + rachis; the least weight loss occurred in the leaflets. Although biomass varied among shoot tissues, the relationship between biomass of various shoot tissues and Pi was described by quadratic equations. The linear and quadratic coefficients of the equations (stem, petiole + rachis, or leaflets on Pi) did not differ among tissues when calculations were based on standardized values. Meloidogyne incognita-infected plants had thinner leaves (leaf area/leaf weight) than did uninfected plants. Reductions in leaf weight and leaf area with nematode inoculation occurred at nodes 5-15 and 4, 6-14, respectively. Losses in plant height and mass due to nematodes reflected shorter internodes with less plant mass at each node.     

Growing microalgae as aquaculture feeds on twin-layers: a novel solid-state photobioreactor

Four strains of marine microalgae commonly used as live feeds in hatcheries (Isochrysis sp. T.ISO, Tetraselmis suecica, Phaeodactylum tricornutum, Nannochloropsis sp.) were grown in a novel solid-state photobioreactor, the twin-layer system. Microalgae were immobilized by self adhesion to vertically oriented twin-layer modules which consisted of two different types of ultrathin layers, a macroporous source layer (glass fiber nonwoven) through which the culture medium was transported by gravity flow, and a microporous substrate layer (plain printing paper) which carried the algae on both surfaces of the source layer. This simple open cultivation system effectively separated the immobilized microalgae from the bulk of the growth medium and permitted prolonged cultivation of microalgae with average biomass yields of 10–15 g dry weight m^?2 growth area after 14–25 days of cultivation. Algal biomass was harvested as fresh weight (with 72–84 % water content) without the need to pre-concentrate algae. No aeration or external CO₂ supply was necessary, and due to the microporous substrate layer, no eukaryotic contaminations were observed during the experiment. All experiments were conducted in Germany under greenhouse conditions with natural sunlight. Small-scale growth experiments performed under the same conditions revealed that growth over most of the experimental period (24 days) was linear in all tested algae with growth rates (dry weight per square meter growth area) determined to be 0.6 g ?m^?2?day^?1 (Isochrysis), 0.8 g? m^?2?day^?1 (Nannochloropsis), 1.5 g ?m^?2?day^?1 (Tetraselmis), and 1.8 g? m^?2?day^?1 (Phaeodactylum). Due to its cost-effective construction and with further optimisation of design and productivity at technical scales, the twin-layer system may provide an attractive alternative to methods traditionally used to cultivate live microalgae.     

Photosynthetic Characteristics of C(3)-C(4) Intermediate Flaveria Species : III. Reduction of Photorespiration by a Limited C(4) Pathway of Photosynthesis in Flaveria ramosissima

The initial products of photosynthesis by the C₃ species Flaveria cronquistii, the C₄ species F. trinervia, and the C₃-C₄ intermediate species F. ramosissima were determined using a pulse-chase technique with ¹⁴CO₂-¹²CO₂. The intermediate species F. ramosissima incorporated at least 42% of the total soluble ¹⁴C fixed into malate and aspartate after 10 seconds of photosynthesis in ¹⁴CO₂, as compared with 90% for the C₄ species F. trinervia and 5% for the C₃ species F. cronquistii. In both F. ramosissima and F. trinervia, turnover of labeled malate and aspartate occurred during a chase period in ¹²CO₂, although the rate of turnover was slower in the intermediate species. Relative to F. cronquistii, F. ramosissima showed a reduced incorporation of radioactivity into serine and glycine during the pulse period. These results indicate that a functional C₄ pathway of photosynthesis is operating in F. ramosissima which can account for its reduced level of photorespiration, and that this species is a true biochemical intermediate between C₃ and C₄ plants.     

南岭小坑藜蒴栲群落地上部分生物量分配规律

采用皆伐法对南岭小坑750m2天然藜蒴栲群落的生物量进行了实测,该群落有43个树种,其中藜蒴栲为优势种,获得了胸径2.0 cm以上的267株树的树干、枝、叶烘干重数据以及实测的胸径（D）、树高（H）数据。揭示了该森林群落地上部分总生物量(AGB)在森林各层次、各树种及乔木层各器官中的分配规律,并建立了该群落的生物量模型。结果表明,南岭小坑流域藜蒴栲群落地上部分总生物量是131.149 t.hm-2,其中乔木层是129.895 t.hm-2,下木层是1.563 t.hm-2,层间植物是0.267 t.hm-2,凋落物层是2.424 t.hm-2。树干、树枝、树叶生物量分别是乔木层地上部分总生物量的85.0%、10.6%和4.4%。优势树种藜蒴栲和小红栲生物量是乔木层地上部分总生物量的46.3%和9.8%,这说明在早期演替的森林群落中生物量主要集中分布在少数的几个优势种。乔木各径阶（DBH<5,5~10,10~15,15~20,20~25,≥25cm）的生物量占乔木层地上部分总生物量的百分比分别是1.0%, 13.1%,52.2%,26.4%,4.6%和2.7%。天然次生藜蒴栲群落以D为自变量的模型是Wtagb=0.116D2.384,R2=0.934,模型估算值比皆伐实测值低5.0%;以D2H为自变量的总生物量模型是Wtagb=184.274(D2H)0.881,R2=0.952,模型估算值比皆伐实测值低6.9%;这说明针对天然藜蒴栲群落,采用以D为自变量的总生物量模型更为实用。