Annual cycle of CO2 exchange over a reed (Phragmites australis) wetland in Northeast China

Net ecosystem exchange of CO₂ (NEE) was measured during 2005 using the eddy covariance (EC) technique over a reed (Phragmites australis (Cav.) Trin. ex Steud.) wetland in Northeast China (121°54′E, 41°08′N). Diurnal NEE patterns varied markedly among months. Outside the growing season, NEE lacked a diurnal pattern and it fluctuated above zero with an average value of 0.07 mg CO₂ m⁻² s⁻¹ resulting from soil microbial activity. During the growing season, NEE showed a distinct V-like diel course, and the mean daily NEE was −7.48 ± 2.74 g CO₂ m⁻² day⁻¹, ranging from −13.58 g CO₂ m⁻² day⁻¹ (July) to −0.10 g CO₂ m⁻² day⁻¹ (October). An annual cycle was also apparent, with CO₂ uptake increasing rapidly in May, peaking in July, and decreasing from August. Monthly cumulative NEE ranged from −115 ± 24 g C m⁻² month⁻¹ (the reed wetland was a CO₂ sink) in July to 75 ± 16 g C m⁻² month⁻¹ (CO₂ source) in November. The annual CO₂ balance suggests a net uptake of −65 ± 14 g C m⁻² year⁻¹, mainly due to the gains in June and July. Cumulative CO₂ emission during the non-growing season was 327 g C m⁻², much greater than the absolute value of the annual CO₂ balance, which proves the importance of the wintertime CO₂ efflux at the study site. The ratio of ecosystem respiration (R_eco) to gross primary productivity (GPP) for this reed ecosystem was 0.95, indicating that 95% of plant assimilation was consumed by the reed plant or supported the activities of heterotrophs in the soil. Daytime NEE values during the growing season were closely related to photosynthetically active radiation (PAR) (r² > 0.63, p < 0.01). Both maximum ecosystem photosynthesis rate (A_max) and apparent quantum yield (α) were season-dependent, and reached their peak values in July (1.28 ± 0.11 mg CO₂ m⁻² s⁻¹, 0.098 ± 0.027 μmol CO₂ μmol⁻¹ photon, respectively), corresponding to the observed maximum NEE in July. Ecosystem respiration (R_eco) relied on temperature and soil water content, and the mean value of Q₁₀ was about 2.4 with monthly variation ranging from 1.8 to 4.1 during 2005. Annual methane emission from this reed ecosystem was estimated to be about 3 g C m⁻² year⁻¹, and about 5% of the net carbon fixed by the reed wetland was released to the atmosphere as CH₄.     

Investigation of biomass and lipids production with Neochloris oleoabundans in photobioreactor

The fresh water microalga Neochloris oleoabundans was investigated for its ability to accumulate lipids and especially triacylglycerols (TAG). A systematic study was conducted, from the determination of the growth medium to its characterization in an airlift photobioreactor. Without nutrient limitation, a maximal biomass areal productivity of 16.5 g m⁻² day⁻¹ was found. Effects of nitrogen starvation to induce lipids accumulation was next investigated. Due to initial N. oleoabundans total lipids high content (23% of dry weight), highest productivity was obtained without mineral limitation with a maximal total lipids productivity of 3.8 g m⁻² day⁻¹. Regarding TAG, an almost similar productivity was found whatever the protocol was: continuous production without mineral limitation (0.5 g m⁻² day⁻¹) or batch production with either sudden or progressive nitrogen deprivation (0.7 g m⁻² day⁻¹). The decrease in growth rate reduces the benefit of the important lipids and TAG accumulation as obtained in nitrogen starvation (37% and 18% of dry weight, respectively).     

Primary production, nutrient dynamics, and accretion of a coastal freshwater forested wetland assimilation system in Louisiana

This study reports on the response of a tidal, freshwater forested wetland ecosystem to long-term input of secondarily treated municipal effluent from the City of Mandeville, LA. Measurements of hydrology, nutrients, and aboveground net primary productivity were made from September 1998 through March 2002. Accretion measurements were made in October 2000 and October 2004. The major hydrologic inputs to the system were the effluent, precipitation, and back water flooding from Lake Pontchartrain. Nutrient levels were generally low except in the immediate vicinity of the outfall. Mean net primary production of the freshwater forest system was significantly higher downstream of the effluent discharge (1202 g m⁻² yr⁻¹) compared to the control site (799 g m⁻² yr⁻¹). Downstream of the outfall, accretion rates were double the rate of relative sea level rise in the area. Removal efficiencies of N and P were as high as 75% and 95%, respectively. The relatively constant flow of secondarily treated municipal effluent buffered the downstream area from salinity intrusion during a region-wide drought. Re-direction of nutrient-enhanced effluents from open water bodies to wetland ecosystems can maintain plant productivity, sequester carbon, and maintain coastal wetland elevations in response to sea-level rise in addition to improving overall surface water quality, reducing energy use, and increasing financial savings.     

Studies on mixed mass cultivation of Anabaena spp. (nitrogen-fixing blue-green algae, cyanobacteria) on a large scale

Studies on mixed mass cultivation of Anabaena spp. on a large scale (5170m²) were conducted continuously for 3 years. Under the continental monsoon climate in northern subtropics (30°N, 115°E), 7–11 g dry weight m⁻² day⁻¹ of microalgal biomass on average was harvested in simple plastic greenhouses in the effective growth days during the warmer seasons. The maximum productivity was 22 g m⁻² day⁻¹ in the middle of summer. Observations on the productive properties of strains of Anabaena spp. indicated that they were different from and could compensate for each other in their productivities and adaptations to the seasonal changes. With different lining materials (PVC sheets, concrete, sand and soil) in the culture ponds, no significant variation of productivity was found, but bubbling with biogas in the middle of the day and the application of some growth regulating substances (2,4-D, NaHSO₃ and extracts of oyster mushroom spawn) was able to improve the production. The cost of microalgal biomass in this way was around 0·75–1·0 US dollar(s) per kilogram.     

Tropical wetlands: seasonal hydrologic pulsing,carbon sequestration,and methane emissions

This paper summarizes the importance of climate on tropical wetlands. Regional hydrology and carbon dynamics in many of these wetlands could shift with dramatic changes in these major carbon storages if the inter-tropical convergence zone (ITCZ) were to change in its annual patterns. The importance of seasonal pulsing hydrology on many tropical wetlands, which can be caused by watershed activities, orographic features, or monsoonal pulses from the ITCZ, is illustrated by both annual and 30-year patterns of hydrology in the Okavango Delta in southern Africa. Current studies on carbon biogeochemistry in Central America are attempting to determine the rates of carbon sequestration in tropical wetlands compared to temperate wetlands and the effects of hydrologic conditions on methane generation in these wetlands. Using the same field and lab techniques, we estimated that a humid tropical wetland in Costa Rica accumulated 255 g C m⁻² year⁻¹ in the past 42 years, 80% more than a similar temperate wetland in Ohio that accumulated 142 g C m⁻² year⁻¹ over the same period. Methane emissions averaged 1,080 mg-C m⁻² day⁻¹ in a seasonally pulsed wetland in western Costa Rica, a rate higher than methane emission rates measured over the same period from humid tropic wetlands in eastern Costa Rica (120–278 mg-C m⁻² day⁻¹). Tropical wetlands are often tuned to seasonal pulses of water caused by the seasonal movement of the ITCZ and are the most likely to be have higher fire frequency and changed methane emissions and carbon oxidation if the ITCZ were to change even slightly.     

Influence of soft rush (Juncus effusus) on phosphorus flux in grazed seasonal wetlands

Livestock significantly affect wetland soils and vegetation but their impacts on wetland nutrient dynamics are poorly understood. We set up a full factorial laboratory experiment to assess the effects of Juncus effusus, grazing exclusion, and flooding on P flux from intact cores collected from seasonal wetlands in cattle pastures in south Florida. We collected intact cores from Juncus tussocks and plant interspaces inside and outside 4-year grazing exclosures in five replicate wetlands. We incubated the cores for 50 days under continuous flooding or weekly 1-day flooding cycles and measured P concentrations in surface and pore water. Grazing exclosures had less Juncus (17%) and bare ground (2%) than adjacent grazed areas (Juncus, 48%; bare ground, 12%), but did not affect P fluxes. Initial fluxes of soluble reactive P (SRP) were much higher in cores with Juncus (242 ± 153 mg P m⁻² day⁻¹) than without Juncus (14 ± 20 mg P m⁻² day⁻¹). In weekly flooded cores P fluxes fell to 19.7 ± 13.4 mg P m⁻² day⁻¹ in cores with and 2.7 ± 2.6 in cores without Juncus. The strong effect of Juncus on P flux was an indirect effect of cattle grazing, but 4 years of grazing exclusion did not have a significant effect on P fluxes.     

基于MODIS的中国陆地植被生长及其与气候的关系

基于MODIS2000~2005(缺2004年)5a每8d的GPP资料,分析了中国陆地植被生长特征,讨论了我国气候因子(温度、降水以及辐射)对同期植被生长的影响。研究结果显示,中国陆地植被的年均GPP分布范围在0~3252.6gC.m-.2a-1之间,5a平均值为491.1gC.m-.2a-1;年均GPP最大的地方主要分布于云南南部、海南、台湾以及东南沿海部分地区,最小值主要出现在青藏高原、新疆以及内蒙古西部等高寒、干旱地区。温度是影响同期我国陆地植被生长的主要因子,其次为降水,辐射对我国陆地植被的影响比较小,主要影响区域在华南地区。陆地植被GPP与温度和降水的相关系数在我国表现为自北向南逐渐减小的分布特征,与对应气候因子的分布呈反向关系;而GPP与云量的相关系数则自北向南逐渐增大。     

Immobilization of soybean (Glycine max) urease on alginate and chitosan beads showing improved stability: Analytical applications

The soybean (Glycine max) urease was immobilized on alginate and chitosan beads and various parameters were optimized and compared. The best immobilization obtained were 77% and 54% for chitosan and alginate, respectively. A 2% chitosan solution (w/v) was used to form beads in 1N KOH. The beads were activated with 1% glutaraldehyde and 0.5 mg protein was immobilized per ml of chitosan gel for optimum results. The activation and coupling time were 6 h and 12 h, respectively. Further, alginate and soluble urease were mixed to form beads and final concentrations of alginate and protein in beads were 3.5% (w/v) and 0.5 mg/5 ml gel. From steady-state kinetics, the optimum temperature for urease was 65 °C (soluble), 75 °C (chitosan) and 80 °C (alginate). The activation energies were found to be 3.68 kcal mol⁻¹, 5.02 kcal mol⁻¹, 6.45 kcal mol⁻¹ for the soluble, chitosan- and alginate-immobilized ureases, respectively. With time-dependent thermal inactivation studies, the immobilized urease showed improved stability at 75 °C and the t_1/2 of decay in urease activity was 12 min, 43 min and 58 min for soluble, alginate and chitosan, respectively. The optimum pH of urease was 7, 6.2 and 7.9 for soluble, alginate and chitosan, respectively. A significant change in K_m value was noticed for alginate-immobilized urease (5.88 mM), almost twice that of soluble urease (2.70 mM), while chitosan showed little change (3.92 mM). The values of V_max for alginate-, chitosan-immobilized ureases and soluble urease were 2.82 × 10² μmol NH₃ min⁻¹ mg⁻¹ protein, 2.65 × 10² μmol NH₃ min⁻¹ mg⁻¹ protein and 2.85 × 10² μmol NH₃ min⁻¹ mg⁻¹ protein, respectively. By contrast, reusability studies showed that chitosan–urease beads can be used almost 14 times with only 20% loss in original activity while alginate–urease beads lost 45% of activity after same number of uses. Immobilized urease showed improved stability when stored at 4 °C and t_1/2 of urease was found to be 19 days, 80 days and 121 days, respectively for soluble, alginate and chitosan ureases. The immobilized urease was used to estimate the blood urea in clinical samples. The results obtained with the immobilized urease were quite similar to those obtained with the autoanalyzer^®. The immobilization studies have a potential role in haemodialysis machines.     

Utilization of the cyanobacteria Anabaena sp. ATCC 33047 in CO2 removal processes

In this paper the utilization of the cyanobacteria Anabaena sp. in carbon dioxide removal processes is evaluated. For this, continuous cultures of this strain were performed at different dilution rates; alternatives for the recovery of the organic matter produced being also studied. A maximum CO₂ fixation rate of 1.45 g CO₂ L⁻¹ day⁻¹ was measured experimentally, but it can be increased up to 3.0 g CO₂ L⁻¹ day⁻¹ outdoors. The CO₂ is mainly transformed into exopolysaccharides, biomass representing one third of the total organic matter produced. Organic matter can be recovered by sedimentation with efficiencies higher than 90%, the velocity of sedimentation being 2 · 10⁻⁴ s⁻¹. The major compounds were carbohydrates and proteins with productivities of 0.70 and 0.12 g L⁻¹ day⁻¹, respectively. The behaviour of the cultures of Anabaena sp. has been modelized, also the characteristics parameters requested to design separation units being reported. Finally, to valorizate the organic matter as biofertilizers and biofuels is proposed.     

The effect of environmental factors on the growth rate of Karenia brevis (Davis) G. Hansen and Moestrup

The red tide dinoflagellate Karenia brevis (Davis) G. Hansen and Moestrup is noted for causing mass mortalities of marine organisms in the Gulf of Mexico. Most research has focused on culture isolates from the eastern Gulf of Mexico. In this investigation, we examine the effects of light, temperature and salinity on the growth rate of K. brevis from the western Gulf of Mexico. Growth rates of K. brevis were determined under various combinations of irradiance (19, 31, 52, 67, and 123 μmol m⁻² s⁻¹), salinity (25, 30, 35, 40 and 45), and temperature (15, 20, 25, and 30 °C). Maximum growth rates varied from 0.17 to 0.36 div day⁻¹ with exponential growth rates increasing with increasing irradiance. Little or no growth was supported at 19 μmol photons m⁻² s⁻¹ for any experiment. Maximum growth rates at 15 °C were much lower than at other temperatures. Maximum growth rates of the Texas clone (SP3) fell within the range of Florida clones reported in the literature (0.17–0.36 div day⁻¹ versus 0.2–1.0 div day⁻¹). The Texas clone SP3 had a very similar light saturation point compared to that of a Florida isolate (Wilson's clone) (67 μmol m⁻² s⁻¹ versus 65 μmol m⁻² s⁻¹), and light compensation (20–30 μmol m⁻² s⁻¹1). The upper and lower salinity tolerance of the Texas clone was similar than that of some Florida clones (45 versus 46 and 25 versus 22.5, respectively). In our study, the Texas clone had the same temperature tolerance reported for Florida clones (15–30 °C). While individual clones can vary considerably in maximum growth rates, our results indicate only minor differences exist between the Texas and Florida strains of K. brevis in their temperature and salinity tolerance for growth. While the literature notes lower salinity occurrences of K. brevis in nearby Louisiana, our isolate from the southern Texas coast has the higher salinity requirements typical of K. brevis in the eastern Gulf of Mexico.     

The routine metabolic rate of mulloway (Argyrosomus japonicus: Sciaenidae) and yellowtail kingfish (Seriola lalandi: Carangidae) acclimated to six different temperatures

This study compared the mass-specific routine metabolic rate (RMR) of similar sized mulloway (Argyrosomus japonicus), a sedentary species, and yellowtail kingfish (Seriola lalandi), a highly active species, acclimated at one of several temperatures ranging from 10–35 °C. Respirometry was carried out in an open-top static system and RMR corrected for seawater–atmosphere O₂ exchange using mass-balance equations. For both species RMR increased linearly with increasing temperature (T). RMR for mulloway was 5.78T − 29.0 mg O₂ kg^− 0.8 h^− 1 and for yellowtail kingfish was 12.11T − 39.40 mg O₂ kg^− 0.8 h^− 1. The factorial difference in RMR between mulloway and yellowtail kingfish ranged from 2.8 to 2.2 depending on temperature. The energetic cost of routine activity can be described as a function of temperature for mulloway as 1.93T − 9.68 kJ kg^− 0.8 day^− 1 and for yellowtail kingfish as 4.04T − 13.14 kJ kg^− 0.8 day^− 1. Over the full range of temperatures tested Q₁₀ values were approximately 2 for both species while Q₁₀ responses at each temperature increment varied considerably with mulloway and yellowtail kingfish displaying thermosensitivities indicative of each species respective niche habitat. RMR for mulloway was least thermally dependent at 28.5 °C and for yellowtail kingfish at 22.8 °C. Activation energies (E_a) calculated from Arrhenius plots were not significantly different between mulloway (47.6 kJ mol^− 1) and yellowtail kingfish (44.1 kJ mol^− 1).     

The effect of seasonality on oxidative metabolism in Nacella (Patinigera) magellanica

We studied the seasonal variation on aerobic metabolism and the response of oxidative stress parameters in the digestive glands of the subpolar limpet Nacella (P.) magellanica. Sampling was carried out from July (winter) 2002 to July 2003 in Beagle Channel, Tierra del Fuego, Argentina. Whole animal respiration rates increased in early spring as the animals spawned and remained elevated throughout summer and fall (winter: 0.09 ± 0.02 μmol O₂ h^− 1 g^− 1; summer: 0.31 ± 0.06 μmol O₂ h^− 1 g^− 1). Oxidative stress was assessed at the hydrophilic level as the ascorbyl radical content / ascorbate content ratio (A / AH⁻). The A / AH⁻ ratio showed minimum values in winter (3.7 ± 0.2 10^− 5 AU) and increased in summer (18 ± 5 10^− 5 AU). A similar pattern was observed for lipid radical content (122 ± 29 pmol mg^− 1 fresh mass [FW] in winter and 314 ± 45 pmol mg^− 1 FW in summer), iron content (0.99 ± 0.07 and 2.7 ± 0.6 nmol mg^− 1 FW in winter and summer, respectively) and catalase activity (2.9 ± 0.2 and 7 ± 1 U mg^− 1 FW in winter and summer, respectively). Since nitrogen derived radicals are thought to be critically involved in oxidative metabolism in cells, nitric oxide content was measured and a significant difference in the content of the Fe–MGD–NO adduct in digestive glands from winter and summer animals was observed. Together, the data indicate that both oxygen and nitrogen radical generation rates in N. (P.) magellanica are strongly dependent on season.     

The potential role of climate in the distribution and zonation of the introduced seagrass Zostera japonica in North America

The current distribution of the introduced seagrass Zostera japonica is restricted to the mid- to upper intertidal zone in the coastal Pacific Northwest region of North America. The climate in this region is cool and wet, becoming hotter and dryer with increasing distance southward. Since temperature is likely to be an important factor affecting distribution of this species, growth of two populations located near the northern and southern limits of its established range along the Pacific Coast of North America were measured in an experimental setting across a range of temperatures typical of those in the field during the growing season (10, 20, and 30 °C). The effects of temperature and population were both significant. Leaf elongation, growth, and areal productivity rates of the northern population were consistently lower than those of the southern population. Across the range of temperatures, mean leaf elongation rates ranged from 0.47 to 1.40 cm² shoot⁻¹ d⁻¹; mean growth rates ranged from 0.19 to 0.52 mg dry wt shoot⁻¹ d⁻¹. Mean areal productivity ranged from 0.54 to 1.92 g dry wt m⁻² d⁻¹. Maximum rates of leaf elongation, growth, and areal productivity for both populations were observed at 20 °C. However, leaf elongation, growth, and areal productivity of the northern population declined markedly at 30 °C, whereas no comparable declines were observed for the southern population. This suggests that Z. japonica populations near the southern limits of its established range may be better adapted to warmer temperatures than populations near the northern range limits and further range extensions southward along the California coast may be likely. These differences could be important in predicting the outcome of competitive interactions between native and introduced seagrass species, and in determining future patterns of distribution and zonation of Pacific Coast seagrasses.     

A comparison of soil carbon pools and profiles in wetlands in Costa Rica and Ohio

Wetlands are large carbon pools and play important roles in global carbon cycles as natural carbon sinks. This study analyzes the variation of total soil carbon with depth in two temperate (Ohio) and three tropical (humid and dry) wetlands in Costa Rica and compares their total soil C pool to determine C accumulation in wetland soils. The temperate wetlands had significantly greater (P < 0.01) C pools (17.6 kg C m⁻²) than did the wetlands located in tropical climates (9.7 kg C m⁻²) in the top 24 cm of soil. Carbon profiles showed a rapid decrease of concentrations with soil depth in the tropical sites, whereas in the temperate wetlands they tended to increase with depth, up to a maximum at 18–24 cm, after which they started decreasing. The two wetlands in Ohio had about ten times the mean total C concentration of adjacent upland soils (e.g., 161 g C kg⁻¹ were measured in a central Ohio isolated forested wetland, and 17 g C kg⁻¹ in an adjacent upland site), and their soil C pools were significantly higher (P < 0.01). Among the five wetland study sites, three main wetland types were identified – isolated forested, riverine flow-through, and slow-flow slough. In the top 24 cm of soil, isolated forested wetlands had the greatest pool (10.8 kg C m⁻²), significantly higher (P < 0.05) than the other two types (7.9 kg C m⁻² in the riverine flow-though wetlands and 8.0 kg C m⁻² in a slowly flowing slough), indicating that the type of organic matter entering into the system and the type of wetland may be key factors in defining its soil C pool. A riverine flow-through wetland in Ohio showed a significantly higher C pool (P < 0.05) in the permanently flooded location (18.5 kg C m⁻²) than in the edge location with fluctuating hydrology, where the soil is intermittently flooded (14.6 kg C m⁻²).     

Removal of municipal solid waste COD and NH4–N by phyto-reduction: A laboratory–scale comparison of terrestrial and aquatic species at different organic loads

Laboratory scale tests on phytodepuration of raw and pre-treated leachate from municipal sanitary waste were carried out with four vegetable aquatic and terrestrial species at different organic loads. We used the terrestrial species Stenotaphrum secundatum and the free-floating aquatic species Lemna minor, Eichhornia crassipes and Myriophyllum verticellatum to purify leachate from municipal solid waste. The organic load characterized by COD varied from 2–30 g m⁻² day⁻¹. Blanks using tap water served as controls. Duration of the experiments varied from 9–90 days. Maximum concentrations in the experiments were 1600 mg l⁻¹ COD and 300 mg l⁻¹ NH₄–N for S. secundatum. Best results in terms of COD, BOD, and ammonia removal were obtained for raw leachate with COD=2 g m⁻² day⁻¹ in free water surface (FWS) wetlands, and with 2 and 5 g m⁻² day⁻¹ in subsurface flow (SSF) wetlands. Results show that for pretreated leachate (labeled c) low in BOD and NH₄–N, the aquatic species showed low removal and stress even at the lowest load of COD=2 g m⁻² day⁻¹. We cannot say if this is due to the pretreatment itself or the chemical or microbial composition of this leachate. The Stenotaphrum system operated well with this load of leachate c. For untreated leachate (type a and b) the removal and plant growing conditions seemed good at COD=2 g m⁻² day⁻¹. For S. secundatum a load of COD=5 g m⁻² day⁻¹ operated well. All loads above COD=5 g m⁻² day⁻¹ caused low removal and stress, and the green parts of the plants disappeared. Oxygen was, however, consumed throughout the experimental period. For pretreated leachate (type c), the removal of COD were low (−24 to 17%) but good for NH₄–N (52–91%). This leachate also experienced high ammonia removal from the beginning of the experiments, probably due to existing consortia of nitrifying bacteria in it. Statistical analysis shows that the S. secundatum and L. minor systems maintained higher oxygen levels than the M. verticellatum and E. crassipes systems, when operated with tap water. For Lemna minor, this may be due to a better capacity for transporting oxygen into the water. With leachate all S. secundatum systems have higher oxygen levels than the aquatic systems, basically because the water content of the soil has been kept well below saturation. S. secundatum shows a significantly lower removal of COD than did the aquatic systems at a loading of COD=2 g m⁻² day⁻¹ of raw leachate. There is no significant difference between the systems in the removal of NH₄–N at a loading of COD=2 g m⁻² day⁻¹ of both types of leachate. E. crassipes has a lower removal of NH₄–N than M. verticellatum and S. secundatum at a loading of 5 g m⁻² day⁻¹ of COD of both types of leachate. In our experiments, it appears that the amount of free ammonia explains the toxicity of the leachate to the plants. This, however, does not exclude other possible toxic factors.     

Spacer elongation and plagiotropic growth are the primary clonal strategies used by Vallisneria spiralis to acclimate to sedimentation

The aim of this study is to identify how submerged macrophyte Vallisneria spiralis acclimate to sedimentation by investigating the growth, biomass allocation and clonal characteristics in a greenhouse experiment of 30 days. Experimental treatments combined two sediment types (mud and sand) with four sedimentation depths (0, 2, 4 and 8 cm) in a factorial design. Biomass accumulation (0.98–1.33 versus 0.36 g per plant) and relative growth rate (RGR, 0.082–0.093 versus 0.046 g g⁻¹ day⁻¹) decreased only in the 8 cm sand treatment. Neither sedimentation depth nor sediment type influenced biomass allocation. The ratio of spacer length to biomass was significantly higher in the 8 cm sand (20.4 cm g⁻¹) than in other treatments (6.0–8.5 cm g⁻¹). Branching angles and the depths between ramet basal and sediment surface were only affected by sedimentation depth. Clonal ramets developed nearly vertical branching angles (ranged from 78° to 101°) in the 0 cm sedimentation treatment, but the angles of treated plants decreased at the initial 3–5 ramets (ranged from 68° to 78° at the first ramet level), then remained a relatively constant value (about 90°) in the following spacers. These data indicate that plagiotropic stolons were formed to project the ramets to sediment surface and to escape sedimentation stress primarily by elongating spacer length and decreasing branching angle, rather than by adjusting biomass allocation.     

Ethylenesulfide as a useful agent for incorporation into the biopolymer chitosan in a solvent-free reaction for use in cation removal

Chitosan (Ch) was chemically modified with ethylenesulfide (Es) under solvent-free conditions to give (ChEs), displaying a high content of thiol groups due to opening of the three member cyclic reagent. Elemental analysis showed a decrease in nitrogen content. This result indicated the incorporation of two ethylenesulfide molecules for each unit of the polymeric structure of the precursor biopolymer. Infrared spectroscopy, thermogravimetry, and ¹³C NMR in the solid state demonstrated the effectiveness of the reaction, with signals at 30 ppm for ChEs due to the change in the methylene group environment. Divalent metal uptake by chemically modified biopolymer gave the order Cu > Ni > Co > Zn, reflecting the corresponding acidity of these cations in bonding to the sulfur and the basic nitrogen atoms available on the pendant chains. The equilibrium data were fitted to Freundlich, Temkin, and Langmuir models. The maximum monolayer adsorption capacity for the cations was found to be 1.54 ± 0.02, 1.25 ± 0.03, 1.13 ± 0.01, and 0.83 ± 0.03 mmol g⁻¹, respectively. The Langmuir model best explained the cation–sulfur bond interactions at the solid–liquid interface. The thermodynamics for these interactions gave exothermic enthalpic values of −43.02 ± 0.03, −28.72 ± 0.02, −26.27 ± 0.04, and −17.32 ± 0.02 kJ mol⁻¹, respectively. The spontaneity of the systems is given by negative Gibbs free energies of −31.2 ± 0.1, −32.7 ± 0.1, −31.7 ± 0.1, and −32.2 ± 0.1 kJ mol⁻¹, respectively, in spite of the unfavorable negative entropic values of −39 ± 1, −13 ± 1, −18 ± 1, and −49 ± 1 J K⁻¹ mol⁻¹ due to solvent ordering in the course of complexation. This newly synthesized biopolymer is presented as a chemically useful material for cation removal from aqueous solution.     

Simultaneous determination of dimethylamphetamine and its metabolites in rat hair by gas chromatography–mass spectrometry

In order to study the disposition of dimethylamphetamine (DMAP) and its metabolites, DMAP N-oxide, methamphetamine (MA) and amphetamine (AP), from plasma to hair in rats, a simultaneous determination method for these compounds in biological samples using gas chromatography–mass spectrometry with selected ion monitoring (GC–MS-SIM) was developed. As DMAP N-oxide partially degrades to DMAP and MA during GC–MS analysis, it was necessary to avoid conditions which co-extract the N-oxide in the sample preparation so as to assure no contribution of artifactual products from DMAP N-oxide in the detection of the other compounds. For confirmation of the satisfactory separation of DMAP N-oxide from the others, the internal standards used for quantification were labeled with different numbers of deuterium atoms. Determination of unchanged DMAP was performed without any derivatization, that of DMAP N-oxide was carried out after conversion into trifluoroacetyl-MA by reaction with trifluoroacetic anhydride, and MA and AP were quantified after trifluoroacetyl-derivatization.After intraperitoneal administration of DMAP HCl to pigmented hairy rats (5 mg kg⁻¹ day⁻¹, 10 days, n=3), concentrations of DMAP and its metabolites in urine, plasma and hair were measured by GC–MS-SIM. The area under the concentration versus time curves (AUCs) of DMAP, DMAP N-oxide, MA and AP in the plasma were 397.2±97.5, 279.7±68.3, 18.4±1.2 and 15.9±2.2 μg min ml⁻¹, while their concentrations in the hair newly grown for 4 weeks after administration were 4.82±0.67. 0.45±0.09, 3.25±0.36 and 0.89±0.05 ng mg⁻¹, respectively. This fact suggested that the incorporation tendency of DMAP N-oxide from plasma into hair was distinctly low in comparison with the other compounds.     

Net release of dissolved organic matter by the scleractinian coral Acropora pulchra

The net production of dissolved organic matter (DOM) and dissolved combined and free amino acids (DCAA and DFAA, respectively) by the hermatypic coral Acropora pulchra was measured in the submerged condition, and the production rates were normalized to the coral surface area, tissue biomass, and net photosynthetic rates by zooxanthellae. When normalized to the unit surface area, the production rates of dissolved organic carbon and nitrogen (DOC and DON, respectively) were 37 and 4.4 nmol cm^− 2 h^− 1, respectively. Comparing with the photosynthetic rate by zooxanthellae, which was measured by ¹³C-tracer accumulation in the soft tissue of the coral colony, the release rate of DOC corresponded to 5.4% of the daily net photosynthetic production. The tissue biomass of the coral colony was 178 µmol C cm^− 2 and 23 µmol N cm^− 2, indicating that the release of DOC and DON accounted for 0.021% h^− 1 and 0.019% h^− 1 of the tissue C and N, respectively. The C:N ratios of the released DOM (average 8.4) were not significantly different from those of the soft tissue of the coral colonies (average 7.7). While DFAA did almost not accumulate in the incubated seawater, DCAA was considerably released by the coral colonies at the rate of 2.1 nmol cm^− 2 h^− 1 on average. Calculating C and N contents of the hydrolyzable DCAA, it was revealed that about 20% and 50%–60% of the released bulk DOC and DON, respectively, were composed of DCAA.     

Main features of the oxidative metabolism in gills and liver of Odontesthes nigricans Richardson (Pisces, Atherinopsidae)

The aim of this work was to study comparatively the oxidative metabolism in gills and liver of a silverside, Odontesthes nigricans, in their natural environment, the Beagle Channel. Oxidative damage to lipids was evaluated by assessing TBARS and lipid radical content, in gills and liver. Gills showed a significantly higher degree of damage than liver. The content of α-tocopherol, β-carotene and catalase activity showed significantly higher values in the liver than in the gills. The ascorbyl radical (A^•) content showed no significant differences between gills and liver. The ascorbate (AH⁻) content was 12 ± 2 and 159 ± 28 nmol/mg FW in gills and liver, respectively. Oxidative metabolism at the hydrophilic level was assessed as the ratio A^•/AH⁻. The ratio A^•/AH⁻ was significantly different between organs, (6 ± 2)10^− 5 and (5 ± 2)10^− 6, for the gills and the liver, respectively. Both, lipid radical content/α-tocopherol content and lipid radical content/β-carotene content ratios were significantly higher in gills as compared to the values recorded for the liver, suggesting an increased situation of oxidative stress condition in the lipid phase of the gills. Taken as a whole, the O. nigricans liver exhibited a better control of oxidative damage than the gills, allowing minimization of intracellular damage when exposed to environmental stressing conditions.