Microbial Degradation of Dimethylsilanediol in Soil

Dimethylsilanediol (DMSD) is the ultimate hydrolysis product of silicone (polydimethylsiloxane = PDMS) polymer in soil. Our previous paper showed that it would volatilize from soil, and the present study investigates the importance of microbial degradation in removing DMSD from soil. DMSD (¹⁴C-labeled) was thus incubated (1 mg kg^-1) for 30 wk at 25 °C in soils from a permanent grass field, a corn field, a deciduous woodland, and a pine woodland. Release of¹⁴ CO₂ varied from 0.4 to 1.6% wk^-1. For 3 of the soils, ¹⁴CO₂ increased with higher microbial biomass, while organisms in the deciduous woodland soil were more active in degrading DMSD than organisms in the other soils. After 30 weeks, most of the remaining ¹⁴C in the soil had moved from freely available water extractable to less available acid and base extractable fractions. Similar incubations with 2% plant litter showed extensive transfer of the DMSD into the litter layer. Incubations with a microbial inhibitor showed less DMSD degradation, while cold storage of soils almost completely stopped degradation. These results suggest that microbial degradation is an important mechanism of DMSD loss from soil.     

First-principles theory for the H + H2O, D2O reactions

A full quantum dynamical study of the reactions of a hydrogen atom with water, on an accurate ab initio potential energy surface, is reported. The theoretical results are compared with available experimental data for the exchange and abstraction reactions in H + D2O and H + H2O. Clear agreement between theory and experiment is revealed for available thermal rate coefficients and the effects of vibrational excitation of the reactants. The excellent agreement between experiment and theory on integral cross sections for the exchange reaction is unprecedented beyond atom-diatom reactions. However, the experimental cross sections for abstraction are larger than the theoretical values by more than a factor of 10. Further experiments are required to resolve this.     

Productivity is a poor predictor of plant species richness

For more than 30 years, the relationship between net primary productivity and species richness has generated intense debate in ecology about the processes regulating local diversity. The original view, which is still widely accepted, holds that the relationship is hump-shaped, with richness first rising and then declining with increasing productivity. Although recent meta-analyses questioned the generality of hump-shaped patterns, these syntheses have been criticized for failing to account for methodological differences among studies. We addressed such concerns by conducting standardized sampling in 48 herbaceous-dominated plant communities on five continents. We found no clear relationship between productivity and fine-scale (meters(-2)) richness within sites, within regions, or across the globe. Ecologists should focus on fresh, mechanistic approaches to understanding the multivariate links between productivity and richness.     

Malaria control with genetically manipulated insect vectors

At a recent workshop, experts discussed the benefits, risks, and research priorities associated with using genetically manipulated insects in the control of vector-borne diseases.     

Laboratory studies of crust development in irish and iraqi soils: I. moisture content,penetration resistance,aggregate size and seedling emergence of spring barley (hordeum vulgare L.)

Thirty soils differing widely in origin, texture and organic carbon content were used to study crust properties and development under laboratory conditions. Crust strength was measured as penetration resistance to an upward moving probe both with and without artificial rain treatment. The patterns of penetration resistance with time of drying under infra-red lamps varied considerably, the time taken to reach maximum and steady values for penetration resistance varying from 4 to 10 days. Maximum penetration resistance values ranged from approximately 50 to 500 kPa with one Iraqi soil recording a value of 800 kPa. The soils separated into 3 fairly distinct groups when penetration resistance was plotted against moisture content: Group I showed a sudden and sharp increase, Group II a gradual increase, whereas Group III did not show a definite relationship. A positive linear relationship was found between maximum penetration-resistance values of soils with and without artificial rain treatment. There was also a high positive correlation between small (2?0.53 mm) water-stable aggregates and penetration resistance and a negative correlation between penetration resistance and percentage water-stable aggregates of > 2 mm in size.In seedling emergence trials with spring barley (Hordeum vulgare L.), maximum emergence (90–98%) was recorded at penetration resistance (no rain treatment) of 75–110 kPa and zero emergence at approximately 300 kPa, with a good negative relationship between these values. There was a positive relationship between seedling emergence and penetration resistance values < 75 kPa, failure to emerge being due to a lack of anchorage and radial support for the shoot. Simulated rain treatment, which led to additional crust strength, reduced seedling emergence further for the limited number of soils tested.     

Amplification of surface temperature trends and variability in the tropical atmosphere

The month-to-month variability of tropical temperatures is larger in the troposphere than at Earth's surface. This amplification behavior is similar in a range of observations and climate model simulations and is consistent with basic theory. On multidecadal time scales, tropospheric amplification of surface warming is a robust feature of model simulations, but it occurs in only one observational data set. Other observations show weak, or even negative, amplification. These results suggest either that different physical mechanisms control amplification processes on monthly and decadal time scales, and models fail to capture such behavior; or (more plausibly) that residual errors in several observational data sets used here affect their representation of long-term trends.     

Characterization and agricultural utilization of swine waste lagoon effluents

This investigation was conducted to determine the elemental composition of effluents from three anaerobic swine waste lagoons and one aerobic swine waste lagoon and to evaluate effects of effluent application on growth of corn (Zea mays L.) Wide variation occurred in the elemental composition of effluents among the four lagoons and among four sampling dates from each lagoon. Use of these effluents as irrigation water would lead to application of a wide range in amounts of nutrients to soil. Effluent application increased corn grain yield on a Woodstown loamy fine sand. This yield increase was attributed to alleviation of moisture stress and to correction of N deficiency.     

Eye-specific retinogeniculate segregation independent of normal neuronal activity

The segregation of initially intermingled left and right eye inputs to the dorsal lateral geniculate nucleus (DLGN) during development is thought to be in response to precise spatial and temporal patterns of spontaneous ganglion cell activity. To test this hypothesis, we disrupted the correlated activity of neighboring ganglion cells in the developing ferret retina through immunotoxin depletion of starburst amacrine cells. Despite the absence of this type of correlated activity, left and right eye inputs segregated normally in the DLGN. By contrast, when all spontaneous activity was blocked, the projections from the two eyes remained intermingled. Thus, certain features of normal neural activity patterns are not required for the formation of eye-specific projections to the DLGN.     

NFAT binding and regulation of T cell activation by the cytoplasmic scaffolding Homer proteins

T cell receptor (TCR) and costimulatory receptor (CD28) signals cooperate in activating T cells, although understanding of how these pathways are themselves regulated is incomplete. We found that Homer2 and Homer3, members of the Homer family of cytoplasmic scaffolding proteins, are negative regulators of T cell activation. This is achieved through binding of nuclear factor of activated T cells (NFAT) and by competing with calcineurin. Homer-NFAT binding was also antagonized by active serine-threonine kinase AKT, thereby enhancing TCR signaling via calcineurin-dependent dephosphorylation of NFAT. This corresponded with changes in cytokine expression and an increase in effector-memory T cell populations in Homer-deficient mice, which also developed autoimmune-like pathology. These results demonstrate a further means by which costimulatory signals are regulated to control self-reactivity.