Estimation of CO2 diffusion coefficient at 0–10 cm depth in undisturbed and tilled soils

Diffusion coefficients (D) of CO₂ at 0–10 cm layers in undisturbed and tilled soil conditions were estimated using the Penman (Penman HL. 1940. Gas and vapor movement in soil, 1. The diffusion of vapours through porous solids. J Agric Sci. 30:437–463), Millington–Quirk (Millington RJ, Quirk JP. 1960. Transport in porous media. In: Van Baren FA, editor. Transactions of the 7th International Congress of Soil Science. Vol. 1. Amsterdam: Elsevier. p. 97–106), Ridgwell et al. (Ridgwell AJ, Marshall SJ, Gregson K. 1999. Consumption of atmospheric methane by soils: A process-based model. Global Biogeochem Cy. 13:59–70), Troeh et al. (Troeh FR, Jabro JD, Kirkham D. 1982. Gaseous diffusion equations for porous materials. Geoderma. 27:239–258) and Moldrup et al. (Moldrup P, Kruse CW, Rolston DE, Yamaguchi T. 1996. Modeling diffusion and reaction in soils: III. Predicting gas diffusivity from the Campbell soil–water retention model. Soil Sci. 161:366–375) models. Soil bulk density and volumetric soil water content (θ_v) at 0–10 cm were measured on 14 April, 2 June and 12 July 2005 at 0–10 cm depth in no-till (NT) and conventional till (CT) malt barley and undisturbed soil grass–alfalfa (UGA) systems. Air-filled porosity (ε) was calculated from total soil porosity and θ_v measurements. Both soil air porosity and estimated CO₂ diffusivity at the 0–10 cm depth were significantly affected by tillage. Results of CO₂ diffusion coefficients in the soil followed trends similar to those for soil ε data. The CT tended to have significantly greater estimated soil CO₂ diffusion coefficients than the NT and UGA treatments. The relationship between D/D ₀, and air-filled porosity was well described by a power (R ² = 0.985) function. The model is useful for predicting CO₂ gas-diffusion coefficients in undisturbed and tilled soils at various ranges of ε where actual gas D measurements are time-consuming, costly and infeasible.     

The Introduced Fish Problem and the Aquarium Fish Industry

Of the 46 species of foreign fishes known to be established as reproducing populations in open waters of the contiguous United States, approximately 65% are known or presumed to have originated from the aquarium fish trade. Many escaped or were released from aquarium fish culture facilities and some were introduced by aquarists. More than 50 additional, non-established fishes, mostly aquarium species, have been collected in the wild. These introductions, with established populations, have not been restricted to the so-called Sun Belt states, but have occurred throughout the U.S.
Because many introductions have resulted in serious negative impcts to native fishes, and most have the potential to do so, it is imperative that the aquarium fish industry and trade take measures to curtail such releases. The means of accomplishing this goal are relatively inexpensive. Industry must assist in public education to reduce introductions by aquarists.     

Effect of Lipid Source and Concentration on Somatic Growth of Juvenile Green Sea Urchins, Strongylocentrotus droebachiensis

Supplying juvenile sea urchins with an abundant supply of resources and essential nutrients for growth will facilitate somatic growth and, hence, improve the success of the sea urchin aquaculture industry. Lipids are essential in physical processes such as membrane production and are a concentrated source of energy. This study, using prepared diets, tested the effects of lipid sources containing different major fatty acids (i.e., n‐3 and/or n‐6) (Part 1) and lipid concentration (i.e., 1, 3, 7, and 10%) (Part 2) on the somatic (i.e., test or shell) growth of two size cohorts (7.0‐ and 15.3‐mm average initial test diameter [TD]) of juvenile green sea urchins, Strongylocentrotus droebachiensis. The growth of the sea urchins fed prepared diets was compared to the growth of sea urchins fed a kelp reference diet, Laminaria longicruris. After both feeding trials, the kelp‐fed sea urchins had superior test growth and were more similar in physical appearance to wild sea urchins (i.e., test color, spine length, and gonad color). The sea urchins fed the prepared diets had pale test color, short, stubby spines, and large, pale‐colored gonads compared to wild sea urchins. The smaller cohort of sea urchins grew at a faster rate, but growth patterns for both cohorts were similar. The juveniles fed the prepared diets (in both feeding trials) had high initial growth rates that decreased after approximately 100 d compared to the kelp‐fed juveniles. Differences in test growth were not shown to be affected by sea urchin size (i.e., similar results for both cohorts) or by differences in dietary lipid sources (i.e., the presence of n‐3 and/or n‐6 fatty acids). However, the sea urchins fed diets with lower lipid concentration (≤3%) had larger average TDs than those fed diets with higher lipid concentrations (≥7%). Differences in test growth and physical appearance among those fed the prepared diets and kelp may have been because of nutritional deficiencies in the prepared diets.     

Seasonal,reproductive, and nutritional influences on muscle “buffering capacity” in yellow perch (Perca flavescens)

Effective non-bicarbonate buffering capacity (or buffer value) was measured in white muscle of yellow perch (Perca flavescens) by titrations with mineral acid and base in a carbon-dioxide free, closed system. Yellow perch were collected at three month intervals throughout 1983 from an acidic lake (pH 4.6) and two alkaline lakes (pH 7.8) in northern Wisconsin. Buffering capacity was also determined for white muscle of perch kept in the laboratory under different regimes of temperature and ration. The mean buffering capacity of white muscle from yellow perch taken directly from natural environments ranged from 40.7 ± 3.1 (SD) slykes in March of 1983 to 53.7 ± 2.8 (SD) slykes in July of that year. These changes in buffering capacity were strongly correlated with water temperature. Egg production and thirty-day laboratory starvation produced significant decreases in buffering capacity and increases in the water content of yellow perch muscle. Fed perch in the laboratory had a temperature dependent buffering capacity similar to field caught fish. Buffering capacity of white muscle did not differ between yellow perch from acidic and alkaline lakes. Investigators using buffering capacity as a gauge of species differences in metabolic potential, should be wary of seasonal and reproductive factors that might alter their conclusions.     

Early-life blockade of the 5-HT transporter alters emotional behavior in adult mice

Reduced serotonin transporter (5-HTT) expression is associated with abnormal affective and anxiety-like symptoms in humans and rodents, but the mechanism of this effect is unknown. Transient inhibition of 5-HTT during early development with fluoxetine, a commonly used serotonin selective reuptake inhibitor, produced abnormal emotional behaviors in adult mice. This effect mimicked the behavioral phenotype of mice genetically deficient in 5-HTT expression. These findings indicate a critical role of serotonin in the maturation of brain systems that modulate emotional function in the adult and suggest a developmental mechanism to explain how low-expressing 5-HTT promoter alleles increase vulnerability to psychiatric disorders.     

Chemistry. Inventing the nanomolecular wheel

The wheel is considered the canonical invention leading to all manner of mechanical devices. Rotating machinery is also being investigated at the nanoscale as researchers attempt to create molecular analogs of wheels and motors. But will these devices be merely imitations of macroscopic machines? In his Perspective, Siegel discusses results reported in the same issue by Fletcher et al. in which a four-stroke chemical nanoengine is reported. By a series of bond-breaking and bond-forming steps, a molecular structure is caused to undergo directed rotation. The development of structures of this kind, which are not merely miniaturized macromachines, may lead to other devices for executing controlled oscillatory motion.     

Comparative metagenomics of microbial communities

The species complexity of microbial communities and challenges in culturing representative isolates make it difficult to obtain assembled genomes. Here we characterize and compare the metabolic capabilities of terrestrial and marine microbial communities using largely unassembled sequence data obtained by shotgun sequencing DNA isolated from the various environments. Quantitative gene content analysis reveals habitat-specific fingerprints that reflect known characteristics of the sampled environments. The identification of environment-specific genes through a gene-centric comparative analysis presents new opportunities for interpreting and diagnosing environments.