A preliminary study of the bioremediation potential of Codium fragile applied to seaweed integrated multi-trophic aquaculture (IMTA) during the summer

In integrated multi-trophic aquaculture (IMTA), seaweeds have the capacity to reduce the environmental impact of nitrogen-rich effluents in coastal ecosystems. To establish such bioremediation systems, selection of suitable seaweed species is important. The distribution and productivity of seaweeds vary seasonally based on water temperature and photoperiod. In Korea, candidate genera such as Pophyra, Laminaria, and Undaria grow from autumn to spring. In contrast, Codium grows well at relatively high water temperatures in summer. Thus, aquaculture systems potentially could capitalize on Codium’s capacity for rapid growth in the warm temperatures of late summer and early fall. In this study, we investigated ammonium uptake and removal efficiency by Codium fragile. In laboratory experiments, we grew C. fragile under various water temperatures (10, 15, 20, and 25°C), irradiances (dark, 10, and 100 μmol photons m⁻² s⁻¹), and initial ammonium concentrations (150 and 300 μM); in all cases, C. fragile exhausted the ammonium supply for 6 h. At 150 μM of , ammonium removal efficiency was greatest (99.5 ± 2.6%) when C. fragile was incubated at 20°C under 100 μmol photons m⁻² s⁻¹. At 300 μM of , removal efficiency was greatest (86.3 ± 2.1%) at 25°C under 100 μmol photons m⁻² s⁻¹. Ammonium removal efficiency was significantly greater at 20 and 25°C under irradiance of 100 μmol photons m⁻² s⁻¹ than under other conditions tested.     

Factors affecting denitrification in agricultural headwater streams in Northeast Ohio,USA

As a result of increased anthropogenic nitrogen (N) loading in surface waters of agricultural watersheds, there is enhanced interest to understand and quantify N removal mechanisms. Denitrification, an important N removal mechanism in aquatic systems, may contribute to reducing N pollution in agricultural headwater streams. However, the key factors controlling this process in lotic systems remain unclear. The objective of our study was to examine the factors regulating rates of denitrification in the sediments of agricultural headwater streams in the mid-western USA. Denitrification rates were variable among streams and treatments (<0.1–28.0 μg N g AFDM⁻¹ h⁻¹) and on average, were higher than those reported for similar headwater streams. Carbon quantity and quality, and pH had no effect on denitrification, while temperature and nitrate ( ) concentrations had a positive effect on rates of denitrification. Specifically, controlled denitrification following Michaelis-Menten kinetics. We calculated a value of k_m (1.0 mg -N L^-1) that was comparable to other studies in aquatic sediments but was well below the median in-stream concentrations (5.2–17.4 mg -N L⁻¹) observed at the study sites. Despite high rates of denitrification, this removal mechanism is most likely saturated in the agricultural headwater streams we examined, suggesting that these systems are not effective at removing in-stream N. Handling editor: D. Ryder     

Effects of common soil anions and pH on the uptake and accumulation of perchlorate in lettuce

A mechanistic understanding of perchlorate () entry into plants is important for establishing the human health risk associated with consumption of contaminated produce and for assessing the effectiveness of phytoremediation. To determine whether common soil anions affect uptake and accumulation in higher plants, a series of competition experiments using lettuce (Lactuca sativa L.) were conducted between (50 nM) and (4–12 mM), (1–10 mM), or Cl⁻ (5–15 mM) in hydroponic solution. The effects of (0–5 mM) and pH (5.5–7.5) on uptake were also examined. Increasing in solution significantly reduced the amount of taken up by green leaf, butter head, and crisphead lettuces. Sulfate and Cl⁻ had no significant effects on uptake in lettuce over the concentrations tested. Increasing pH significantly reduced the amount of taken up by crisphead and green leaf lettuces, whereas increasing significantly reduced uptake in butter head lettuce. The inhibition by across all lettuce genotypes suggests that may share an ion carrier with , and the decrease in uptake with increasing pH or provides macroscopic evidence for cotransport across the plasma membrane.     

Leaching losses of inorganic N and DOC following repeated drying and wetting of a spruce forest soil

Forest soils are frequently subjected to dry–wet cycles, but little is known about the effects of repeated drying and wetting and wetting intensity on fluxes of , and DOC. Here, undisturbed soil columns consisting of organic horizons (O columns) and organic horizons plus mineral soil (O + M columns) from a mature Norway spruce stand at the Fichtelgebirge; Germany, were repeatedly desiccated and subsequently wetted by applying different amounts of water (8, 20 and 50 mm day⁻¹) during the initial wetting phase. The constantly moist controls were not desiccated and received 4 mm day⁻¹ during the entire wetting periods. Cumulative inorganic N fluxes of the control were 12.4 g N m⁻² (O columns) and 11.4 g N m⁻² (O + M columns) over 225 days. Repeated drying and wetting reduced cumulative and fluxes of the O columns by 47–60 and 76–85%, respectively. Increasing (0.6–1.1 g N m⁻²) and decreasing fluxes (7.6–9.6 g N m⁻²) indicate a reduction in net nitrification in the O + M columns. The negative effect of dry–wet cycles was attributed to reduced net N mineralisation during both the desiccation and wetting periods. The soils subjected to dry–wet cycles were considerably drier at the final wetting period, suggesting that hydrophobicity of soil organic matter may persist for weeks or even months. Based on results from this study and from the literature we hypothesise that N mineralisation is mostly constrained by hydrophobicity in spruce forests during the growing season. Wetting intensity did mostly not alter N and DOC concentrations and fluxes. Mean DOC concentrations increased by the treatment from 45 mg l⁻¹ to 61–77 mg l⁻¹ in the O tlsbba columns and from 12 mg l⁻¹ to 21–25 mg l⁻¹ in the O + M columns. Spectroscopic properties of DOC from the O columns markedly differed within each wetting period, pointing to enhanced release of rather easily decomposable substrates in the initial wetting phases and the release of more hardly decomposable substrates in the final wetting phases. Our results suggest a small additional DOC input from organic horizons to the mineral soil owing to drying and wetting.     

Insect cells respiratory activity in bioreactor

Specific respiration rate ( ) is a key parameter to understand cell metabolism and physiological state, providing useful information for process supervision and control. In this work, we cultivated different insect cells in a very controlled environment, being able to measure . Spodoptera frugiperda (Sf9) cells have been used through virus infection as host for foreign protein expression and bioinsecticide production. Transfected Drosophila melanogaster (S2) cells can be used to produce different proteins. The objective of this work is to investigate respiratory activity and oxygen transfer during the growth of different insect cells lines as Spodoptera frugiperda (Sf9), Drosophila melanogaster (S2) wild and transfected for the expression of GPV and EGFP. All experiments were performed in a well-controlled 1-L bioreactor, with SF900II serum free medium. Spodoptera frugiperda (Sf9) cells reached 10.7 × 10⁶ cells/mL and maximum specific respiration rate () of 7.3 × 10⁻¹⁷ molO₂/cell s. Drosophila melanogaster (S2) cells achieved 51.2 × 10⁶ cells/mL and of 3.1 × 10^–18 molO₂/cell s. S2AcGPV (expressing with rabies virus glycoprotein) reached 24.9 × 10⁶ cells/mL and of 1.7 × 10^–17 molO₂/cell s, while S2MtEGFP (expressing green fluorescent protein) achieved 15.5 × 10⁶ cells/mL and  = 1.9 × 10⁻¹⁷ molO₂/cell s. Relating to the Sf9, S2 cells reached higher maximum cell concentrations and lower specific respiration rate, which can be explained by its smaller size. These results presented useful information for scale-up and process control of insect cells.     

A Novel Approach for Bioremediation of a Coastal Marine Wastewater Effluent Based on Artificial Microbial Mats

A novel alternative for wastewater effluent bioremediation was developed using constructed microbial mats on low-density polyester. This biotechnology showed high removal efficiencies for nitrogen and phosphorous in a short retention time (48 h): 94% for orthophosphate (7.78 g m³ d⁻¹), 79% for ammonium (11.30 g m⁻³ d⁻¹), 78% for nitrite (7.46 g m⁻³ d⁻¹), and 83% for nitrate (8.55 g m⁻³ d⁻¹). The microbial mats were dominated by Cyanobacteria genera such as Chroococcus sp., Lyngbya sp., and bacteria of the subclass Proteobacteria representative of the Eubacteria Domain. Nitzschia sp. was the dominant Eukaryote Domain. Various N and P substrates in the wastewater permit the growth of self-forming and self-sustaining bacterial, microalgal, and cyanobacterial communities on a polyester support. The result is the continuous, self-sufficient growth of microbial mats. This is an innovative, economical, and environmentally safe alternative for the treatment of wastewater effluents in coastal marine environments.     

Can biological nitrification inhibition (BNI) genes from perennial Leymus racemosus (Triticeae) combat nitrification in wheat farming?

Using a recombinant luminescent Nitrosomonas europaea assay to quantify biological nitrification inhibition (BNI), we found that a wild relative of wheat (Leymus racemosus (Lam.) Tzvelev) had a high BNI capacity and releases about 20 times more BNI compounds (about 30 ATU g⁻¹ root dry weight 24 h⁻¹) than Triticum aestivum L. (cultivated wheat). The root exudate from cultivated wheat has no inhibitory effect on nitrification when applied to soil; however, the root exudate from L. racemous suppressed formation and kept more than 90% of the soil’s inorganic-N in the -form for 60 days. The high-BNI capacity of L. racemosus is mostly associated with chromosome Lr#n. Two other chromosomes Lr#J, and Lr#I also have an influence on BNI production. Tolerance of L. racemosus to is controlled by chromosome 7Lr#1-1. Sustained release of BNI compounds occurred only in the presence of in the root environment. Given the level of BNI production expressed in DALr#n and assuming normal plant growth, we estimated that nearly 87,500,000 ATU of BNI activity ha⁻¹ day⁻¹ could be released in a field of vigorously growing wheat; this amounts to the equivalent of the inhibitory effect from the application of 52.5 g of the synthetic nitrification inhibitor nitrapyrin (one AT unit of BNI activity is equivalent to 0.6 μg of nitrapyrin). At this rate of BNI production it would take only 19 days for a BNI-enabled wheat crop to produce the inhibitory power of a standard commercial application of nitrapyrin, 1 kg ha⁻¹. The synthetic nitrification inhibitor, dicyandiamide, blocked specifically the AMO (ammonia monooxygenase) pathway, while the BNI from L. racemosus blocked the HAO (hydroxylamine oxidoreductase) pathway in Nitrosomonas. Here we report the first finding of high production of BNI in a wild relative of any cereal and its successful introduction and expression in cultivated wheat. These results demonstrate the potential for empowering the new generation of wheat cultivars with high-BNI capacity to control nitrification in wheat-production systems. Responsible Editor: Hans Lambers.     

Epipelic and pelagic primary production in Alaskan Arctic lakes of varying depth

We compared on eight dates during the ice-free period physicochemical properties and rates of phytoplankton and epipelic primary production in six arctic lakes dominated by soft bottom substrate. Lakes were classified as shallow ( < 2.5 m), intermediate in depth (2.5 m <  < 4.5 m), and deep ( > 4.5 m), with each depth category represented by two lakes. Although shallow lakes circulated freely and intermediate and deep lakes stratified thermally for the entire summer, dissolved oxygen concentrations were always >70% of saturation values. Soluble reactive phosphorus and dissolved inorganic nitrogen (DIN = NO₃ ⁻–N + NH₄ ⁺–N) were consistently below the detection limit (0.05 μmol l⁻¹) in five lakes. However, one lake shallow lake (GTH 99) periodically showed elevated values of DIN (17 μmol l⁻¹), total-P (0.29 μmol l⁻¹), and total-N (33 μmol l⁻¹), suggesting wind-generated sediment resuspension. Due to increased nutrient availability or entrainment of microphytobenthos, GTH 99 showed the highest average volume-based values of phytoplankton chlorophyll a (chl a) and primary production, which for the six lakes ranged from 1.0 to 2.9 μg l⁻¹ and 0.7–3.8 μmol C l⁻¹ day⁻¹. Overall, however, increased resulted in increased area-based values of phytoplankton chl a and primary production, with mean values for the three lake classes ranging from 3.6 to 6.1 mg chl a m⁻² and 3.2–5.8 mmol C m⁻² day⁻¹. Average values of epipelic chl a ranged from 131 to 549 mg m⁻² for the three depth classes, but levels were not significantly different due to high spatial variability. However, average epipelic primary production was significantly higher in shallow lakes (12.2 mmol C m⁻² day⁻¹) than in intermediate and deep lakes (3.4 and 2.4 mmol C m⁻² day⁻¹). Total primary production (6.7–15.4 mmol C m⁻² day⁻¹) and percent contribution of the epipelon (31–66%) were inversely related to mean depth, such that values for both variables were significantly higher in shallow lakes than in intermediate or deep lakes. Handling editor: L. Naselli-Flores     

Bifurcation Analysis of Genetically Engineered Pacemaking in Mammalian Heart

Genetically engineered pacemaking in ventricular cells has been achieved by down-regulation of the time independent inward rectifying current (I _K1), or insertion of the hyperpolarisation-activated funny current (I _f). We analyse the membrane system (i.e. ionic concentrations clamped) of an epicardial Luo-Rudy dynamic cell model using continuation algorithms with the maximum conductance () of I _K1 and I _f as bifurcation parameters. Pacemaker activity can be induced either via Hopf or homoclinic bifurcations. As _K1 is decreased by ≈74%, autorhythmicity emerged via a homoclinic bifurcation, i.e., the periodicity first appear with infinitely large periods. In contrast, the insertion of _f induced periodicity via a subcritical Hopf bifurcation at _f≈ 0.25 mSμF⁻¹. Stable autorhythmic action potentials occurred at _f > 0.329 mSμF⁻¹.     

The effect of temperature on post-feeding ammonia excretion and oxygen consumption in the southern catfish

The post-prandial rates of ammonia excretion (TAN) and oxygen consumption in the southern catfish (Silurus meridionalis) were assessed at 2 h intervals post-feeding until the rates returned to those of the fasting rates, at 17.5, 22.5, 27.5, and 32.5°C, respectively. Both fasting TAN and increased with temperature, and were lower than those previously reported for many fish species. The relationship between fasting TAN (mmol NH₃–N kg⁻¹ h⁻¹) and temperature (T, °C) was described as: fasting TAN = 0.144e ^0.0266T (r = 0.526, n = 27, P < 0.05). The magnitude of ammonia excretion and its ratio to total N intake during the specific dynamic action (SDA) tended to increase initially, and then decrease with increasing temperature. The ammonia quotient (AQ), calculated as mol NH₃–N/mol O₂, following feeding decreased as temperature increased. The relationship between AQ during SDA and temperature was described as: AQ_{during SDA} = 0.303e ^−0.0143T (r = 0.739, n = 21, P < 0.05). Our results suggest that ammonia excretion and oxygen consumption post-feeding are operating independently of each other. Furthermore, it appears that the importance of protein as a metabolic substrate in postprandial fish decreases with temperature.     

A Combined Patch-Clamp and Electrorotation Study of the Voltage- and Frequency-Dependent Membrane Capacitance Caused by Structurally Dissimilar Lipophilic Anions

Interactions of structurally dissimilar anionic compounds with the plasma membrane of HEK293 cells were analyzed by patch clamp and electrorotation. The combined approach provides complementary information on the lipophilicity, preferential affinity of the anions to the inner/outer membrane leaflet, adsorption depth and transmembrane mobility. The anionic species studied here included the well-known lipophilic anions dipicrylamine (DPA⁻), tetraphenylborate (TPB⁻) and [W₂(CO)₁₀(S₂CH)]⁻, the putative lipophilic anion and three new heterocyclic W(CO)₅ derivatives. All tested anions partitioned strongly into the cell membrane, as indicated by the capacitance increase in patch-clamped cells. The capacitance increment exhibited a bell-shaped dependence on membrane voltage. The midpoint potentials of the maximum capacitance increment were negative, indicating the exclusion of lipophilic anions from the outer membrane leaflet. The adsorption depth of the large organic anions DPA⁻, TPB⁻ and increased and that of W(CO)₅ derivatives decreased with increasing concentration of mobile charges. In agreement with the patch-clamp data, electrorotation of cells treated with DPA⁻ and W(CO)₅ derivatives revealed a large dispersion of membrane capacitance in the kilohertz to megahertz range due to the translocation of mobile charges. In contrast, in the presence of TPB⁻ and no mobile charges could be detected by electrorotation, despite their strong membrane adsorption. Our data suggest that the presence of oxygen atoms in the outer molecular shell is an important factor for the fast translocation ability of lipophilic anions.     

Concentration-Dependent Effects on Intracellular and Surface pH of Exposing <Emphasis Type="Italic">Xenopus</Emphasis> oocytes to Solutions Containing NH<Subscript>3</Subscript>/NH<Subscript>4</Subscript><Superscript>+</Superscript>

Others have shown that exposing oocytes to high levels of (10–20 mM) causes a paradoxical fall in intracellular pH (pH_i), whereas low levels (e.g., 0.5 mM) cause little pH_i change. Here we monitored pH_i and extracellular surface pH (pH_S) while exposing oocytes to 5 or 0.5 mM NH₃/NH₄ ⁺. We confirm that 5 mM causes a paradoxical pH_i fall (−ΔpH_i ≅ 0.2), but also observe an abrupt pH_S fall (−ΔpH_S ≅ 0.2)—indicative of NH₃ influx—followed by a slow decay. Reducing [NH₃/NH₄ ⁺] to 0.5 mM minimizes pH_i changes but maintains pH_S changes at a reduced magnitude. Expressing AmtB (bacterial Rh homologue) exaggerates −ΔpH_S at both levels. During removal of 0.5 or 5 mM NH₃/NH₄ ⁺, failure of pH_S to markedly overshoot bulk extracellular pH implies little NH₃ efflux and, thus, little free cytosolic NH₃/NH₄ ⁺. A new analysis of the effects of NH₃ vs. NH₄ ⁺ fluxes on pH_S and pH_i indicates that (a) NH₃ rather than NH₄ ⁺ fluxes dominate pH_i and pH_S changes and (b) oocytes dispose of most incoming NH₃. NMR studies of oocytes exposed to ¹⁵N-labeled show no significant formation of glutamine but substantial accumulation in what is likely an acid intracellular compartment. In conclusion, parallel measurements of pH_i and pH_S demonstrate that NH₃ flows across the plasma membrane and provide new insights into how a protein molecule in the plasma membrane—AmtB—enhances the flux of a gas across a biological membrane.

Immobilization of the recombinant invertase INVB from <Emphasis Type="Italic">Zymomonas mobilis</Emphasis> on Nylon-6

The recombinant invertase INVB (re-INVB) from Zymomonas mobilis was immobilized on microbeads of Nylon-6, by means of covalent bonding. The enzyme was strongly and successfully bound to the support. The activity of the free and immobilized enzyme was determined, using 10% (w/v) sucrose, at a temperature ranging between 15 and 60 °C and a pH ranging between 3.5 and 7. The optimal pH and temperature for the immobilized enzyme were 5.5 and 25 °C, respectively. Immobilization of re-INVB on Nylon-6 showed no significant change in the optimal pH, but a difference in the optimal temperature was evident, as that for the free enzyme was shown to be 40 °C. The values for kinetic parameters were determined as: 984 and 98 mM for of immobilized and free re-INVB, respectively. values for immobilized and free enzymes were 6.1 × 10² and 1.2 × 10⁴ s⁻¹, respectively, and immobilized re-INVB showed of 158.73 μmol h min⁻¹ mg⁻¹. Immobilization of re-INVB on Nylon-6 enhanced the thermostability of the enzyme by 50% at 30 °C and 70% at 40 °C, when compared to the free enzyme. The immobilization system reported here may have future biotechnological applications, owing to the simplicity of the immobilization technique, the strong binding of re-INVB to the support and the effective thermostability of the enzyme.     

Determination of the chemical composition of ulvan, a cell wall polysaccharide from Ulva spp. (Ulvales, Chlorophyta) by FT-IR and chemometrics

The water-soluble cell wall polysaccharides from green seaweeds of Ulva spp. (Ulvales, Chlorophyta), referred to as ulvan, demonstrate composition- and structure-related functional properties. Mid-infrared spectroscopy combined with chemometric techniques was investigated as a means to rapidly predict the chemical composition of ulvan extracts. A calibration was realized with 41 ulvan extracts from two Ulva species. The variables studied included the constituent sugars (rhamnose, xylose, glucose, galactose, glucuronic acid, iduronic acid), protein, and sulfate contents. The correlation between Fourier transform infrared and chemical data was developed using partial least squares (PLS) regression with full cross-validation (leave one out). The coefficients of determination in cross-validation () and the standard error in cross-validation were determined for each variable. The PLS model validation resulted in a coefficient of determination () and a standard error in prediction. Good predictions were obtained for rhamnose ( = 0.9244), xylose ( = 0.8758), glucuronic acid ( = 0.9415), and sulfate ( = 0.9218), which are the main ulvan constituents. However, minor components such as proteins, glucose, galactose, and iduronic acid were not correctly predicted. This study showed that mid-infrared spectroscopy combined with PLS regression is a reliable and fast method for the quantification of the main chemical constituents of ulvan extracts.     

Hydrochemical fluctuations and crustacean community composition in an ephemeral saline lake (Sua Pan,Makgadikgadi Botswana)

Fluctuating hydrochemistry, as a result of extreme hydrological regimes, imposes major physiological constraints on the biota of ephemeral saline lakes. While the inverse relationship between salinity and zooplankton species richness is well-known across salinity gradients, few studies have documented closely the response of zooplankton to seasonal changes in salinity. Weekly sampling during two flood seasons at Sua Pan, an intermittent saline lake in central Botswana demonstrated the importance of spatial and temporal salinity gradients for crustacean community composition, associated with a decline in species richness, from 11 to three species. Conductivity ranged between 320 and 125,800 μS cm⁻¹ during seasonal flooding; changing from dominance by and , Ca²⁺ and Mg²⁺, at the beginning of the floods, to NaCl dominated waters as the lake dried out and salinities increased. pH estimates generally ranged between 8.6 and 10, with maximum values recorded during initial flooding. Crustaceans comprised mainly Branchinella spinosa, Moina belli, Lovenula africana and Limnocythere tudoranceai, all of which occurred across a wide range of salinities, while halotolerant freshwater species (Metadiaptomus transvaalensis, Leptestheria striatochonca and the ostracods Plesiocypridopsis aldabrae, Cypridopsis newtoni and a newly identified Potamocypris species) disappeared above conductivities of 1,500 μS cm⁻¹. A unique crustacean composition in southern Africa was attributed to Sua Pans’ rare chemical composition among southern African saline lakes; flood waters on Sua Pan contained a higher proportion of Na⁺ and , and less K⁺, Mg²⁺ and than over 80% of records from salt pans elsewhere in southern African. The freshwater species of crustaceans in Sua Pan were similar to those found in other southern Africa lakes, and these similarities decreased in lakes with higher pH and proportions of Na, and less SO₄ and Mg in their chemical composition. The predominant saline tolerant species on Sua Pan, however, showed a greater similarity to those in saline lakes in southern and East Africa with higher proportions of and, particularly, Mg²⁺ in their chemical composition. Handling editor: J. M. Melack     

Theoretical study of AlH(2+)n (n=1-7) dications

The structures and stability of 1–7 dications were calculated at the ab initio MP2/aug-cc-pVTZ level of theory. The dications AlH²⁺ 1 and 2 were characterized to be unstable thermodynamically. However, these and the stable dications, 3–7 have considerable kinetic barriers for deprotonation. Each of the structures 3–7 contains one or more two-electron three-center (2e–3c) bonds. Aluminum atoms of these dications carry most of the positive charges, as indicated by NBO charge calculations.Dedicated to Professor Dr. Paul von Ragué Schleyer on the occasion of his 75th birthday     

The role of body surfaces and ventilation in gas exchange of the abalone, <Emphasis Type="Italic">Haliotis iris</Emphasis>

The archaeogastropod Haliotis iris possesses paired bipectinate gills and normally four to six shell holes. In still water, endogenous water flow entered the branchial chamber anteriorly to the left of the head and was exhaled primarily from the three most posterior holes. The first or second anterior aperture was occasionally weakly inhalant. Cardiac interaction superimposed an oscillatory component upon ciliary ventilation but did not augment mean flow. At normal endogenous flow rates 49% of oxygen was extracted from the branchial flow, increasing to 71% at lower flows. In still water, normoxic was 0.47 μmol g⁻¹ h⁻¹. Oxyregulation occurred down to with partial oxyregulation down to 45 Torr (P _crit), and oxyconformity below this. The oxyregulatory plateau was absent in artificially ventilated animals but normoxic was higher (0.65 μmol g⁻¹ h⁻¹). Endogenous ventilation was unaffected by hypoxia to 15 Torr. Heart rate decreased by ~20% at 26 Torr before falling more steeply. Oxygen uptake from the branchial ventilation stream fully accounted for normoxic In hypoxia (<30 Torr), no uptake occurred from the head or foot despite extensive eversion of the epipodium. Blood oxygen measurements excluded the right mantle as a significant gas exchange organ. Changes in oxygen uptake caused by changes in the velocity of external water currents support the concept of induced ventilation and suggest that in still water aerobic respiration was ventilation-limited. Although ciliary ventilation appears adequate to support resting aerobic metabolism, induced ventilation may provide increased aerobic scope for activity and repayment of oxygen debt. An erratum to this article can be found at     

Soil Respiration in European Grasslands in Relation to Climate and Assimilate Supply

Soil respiration constitutes the second largest flux of carbon (C) between terrestrial ecosystems and the atmosphere. This study provides a synthesis of soil respiration (R _s) in 20 European grasslands across a climatic transect, including ten meadows, eight pastures and two unmanaged grasslands. Maximum rates of R _s ( ), R _s at a reference soil temperature (10°C; ) and annual R _s (estimated for 13 sites) ranged from 1.9 to 15.9 μmol CO₂ m⁻² s⁻¹, 0.3 to 5.5 μmol CO₂ m⁻² s⁻¹ and 58 to 1988 g C m⁻² y⁻¹, respectively. Values obtained for Central European mountain meadows are amongst the highest so far reported for any type of ecosystem. Across all sites was closely related to . Assimilate supply affected R _s at timescales from daily (but not necessarily diurnal) to annual. Reductions of assimilate supply by removal of aboveground biomass through grazing and cutting resulted in a rapid and a significant decrease of R _s. Temperature-independent seasonal fluctuations of R _s of an intensively managed pasture were closely related to changes in leaf area index (LAI). Across sites increased with mean annual soil temperature (MAT), LAI and gross primary productivity (GPP), indicating that assimilate supply overrides potential acclimation to prevailing temperatures. Also annual R _s was closely related to LAI and GPP. Because the latter two parameters were coupled to MAT, temperature was a suitable surrogate for deriving estimates of annual R _s across the grasslands studied. These findings contribute to our understanding of regional patterns of soil C fluxes and highlight the importance of assimilate supply for soil CO₂ emissions at various timescales.     

Mimosine Mitigates Oxidative Stress in Selenium Deficient Seedlings of Vigna radiata. Part II: Mitochondrial Uptake of 75Selenium and Mimosine

During the growth of selenium (Se)-deficient seedlings of Vigna radiata, exposure to mimosine [2-amino-3-(3-hydroxy-4-oxo-1H-pyridin-1-yl)-propanoic acid], a nonprotein plant amino acid, effectively mitigated stress at 0.1 mM, as reflected in enhancement of growth and efficiency of mitochondrial functions. Since the changes in the seedlings elicited by exposure to mimosine were similar to those effected by Se at an optimal exposure level of 0.75 ppm (Sreekala et al., Biol Trace Elem Res 70:193–207, 1999), the uptake of Se and that of mimosine itself was individually studied in the respiring mitochondria of Se-deficient seedlings (−Se-stressed group) in comparison with those exposed to mimosine during growth at 0.1 mM (Mim 0.1 group). In both groups, the mitochondrial uptake of ⁷⁵Se at 10 μM added increased linearly up to 2 min, attaining steady-state levels thereafter. Uptake levels were 2.3-fold higher in the Mim 0.1 group than in the −Se-stressed group. Double-reciprocal plots of mitochondrial ⁷⁵Se uptake against 2–20 μM in the medium were nonlinear and negative cooperative effects during the uptake were confirmed by Scatchard plots, whereas Hill coefficients were 0.8 and 0.85 for the two groups. Mitochondrial uptake of mimosine, at added levels of 25 or 50 μM, increased linearly up to 1 min and decelerated thereafter. Initial uptake levels of mimosine at 1 min were higher by 6.5-fold at 25 μM and 4-fold at 50 μM in the Mim 0.1 group than those in the −Se-stressed group. Initial uptake levels with added mimosine up to 50 or 100 μM yielded nonlinear double-reciprocal plots; and kinetic analyses at 5 to 50 μM revealed the prevalence of positive cooperativity in the −Se-stressed group and negative cooperativity in the Mim 0.1 group. Involvement of active thiol groups in the uptake of both Se and mimosine were indicated by inhibition studies. Evidence presented for mimosine mediated increase in mitochondrial Se uptake and cooperative interactions thereof underscores the metabolic significance of mimosine.     

Use of isotopic signatures to assess the food web in a tropical shallow marine ecosystem of Southeastern Brazil

A dual isotope approach was used to assess the relative importance of terrestrial vegetation detritus and other primary producers in the trophic web of Flamengo Sound (Ubatuba, SP), SE Brazil, surrounded by the Atlantic Rain Forest. Primary producers showed distinct C signatures and the observed values suggest that little terrestrial or bulk sediment organic matter enter the food web of the sound. Suspended particulate organic matter (POM, supports the bulk of the consumers, with some contribution by macroalgae . Consumers C values ranged from −17.4 to . At least three trophic levels were detectable in the food web. The N value of POM was , while that of sediment and detritus was . The N values of suspension feeding benthic invertebrates were 8.2–, deposit feeders 8.3–, and carnivores 10.7–. Values for fishes were for detritivore, 11.4– for benthic feeders, 12.4– for zooplanktivores, and for piscivores/benthic invertebrate feeders. Squid mean value was . There is a reasonable agreement between feeding habits information from the literature and N values from this study. In the sound, the first and second trophic steps seem to be about 1– higher than those of similar organisms studied in temperate waters and this may reflect an input of allochtonous anthropogenic nitrogen enriched in ¹⁵N from human activities.