Editors' Choice

Science  12 Aug 2005:
Vol. 309, Issue 5737, pp. 990
  1. ECOLOGY/EVOLUTION

    Hidden Long-Term Consequences

    Fires are becoming increasingly frequent in wet tropical forests as a result of human land use and other associated disturbances. In addition to their visibly destructive effects on aboveground biomass, tropical forest fires can smoulder underground for a long time. Thus, fire has a potential to alter soil properties directly, especially the concentration and spatial distribution of nutrients—both of which have ramifications for the subsequent ecological dynamics of forests.

    Blair has examined the effects of underground fires on the spatial patterns of soil constituents in a lowland wet forest in Nicaragua. Fire altered the spatial scale of nutrient distribution, generally reducing the patch size for key nutrients such as carbon, nitrogen, phosphorus, and potassium, with as yet unknown consequences for belowground competition between plants. Asbjornsen et al. describe the effects of fire on plant biomass in montane cloud forests in Mexico, a habitat type in which forest fires have been documented only in the past few years. Here, the belowground effects were substantial: Deep ground fires occurring in 1997-1998 resulted in a 50 to 75% reduction in live root biomass, as well as >80% reduction in aboveground biomass. Given the time scale of forest dynamics, the longer-term effects of these disturbances will unfold over decades. — AMS

    J. Trop. Ecol. 21, 435; 427 (2005).

  2. MATERIALS SCIENCE

    Stronger Steel

    Ferritic and martensitic steels are preferred structural materials for use at elevated temperatures in power plants. Their major advantage is good thermal behavior relative to other elevated-temperature alloys, but they suffer from not being strong enough at high temperature. Niobium, vanadium, and nitrogen have been added to push upward this maximum-use temperature, but alloying may have reached its limit for enhancing these steels. The development of alloys that are strengthened through the dispersion of oxide particles requires expensive manufacturing techniques. Under normal processing conditions, commercial steel alloys develop large metal (M) carbon precipitates or MX particles, where X is Nb or V. Small MX precipitates confer higher-temperature stability, and Klueh et al. have developed methods to increase their density. High-temperature rolling was used to create dislocations in the alloys that acted as nucleation sites for the MX particles, increasing the nanoparticle density by three orders of magnitude. Tests on treated commercial alloys showed increases in yield stress, particularly above 620°C, which is the upper use temperature for the untreated alloys. — MSL

    ScriptaMaterialia 53, 275 (2005).

  3. CHEMISTRY

    Avoiding Distortions

    The formation of silica zeolites usually requires some structural distortion, but what has been observed experimentally is that the bending within the SiO4 tetrahedra is minor and occurs mainly along the bonds connecting them. Zwijnenburg et al. performed a computational study of known zeolitic frameworks, as well as hypothetical frameworks built up of three-connected polyhedral tiles (simple tilings such as double 4-rings), whose packing can be used to represent known frameworks. They found that the experimental frameworks had minimal tetrahedral distortion (less than 2.5 × 10−2 Å2), but that hypothetical frameworks, even ones with enthalpies similar to those of experimental frameworks, had an order of magnitude or more tetrahedral distortion. They conclude that although a few of the hypothetical frameworks may be realizable, most of the more distorted ones will likely elude hydrothermal synthesis. — PDS

    J. Phys. Chem. B 10.1021/jp0531309 (2005).

  4. PSYCHOLOGY

    Of Morals and Mores

    What is it that makes moral beliefs nonnegotiable? Such beliefs are thought to transcend cultural variation—in short, to be universal— and they are often associated with intense emotion, as are strongly held attitudes. Across a range of situations, however, Skitka et al. find evidence consistent with their proposal that attitudes and moral convictions differ. When questioned about their social distance preferences, where in-laws were proximal and public officials were distal, study participants were less tolerant of social relations with people whose convictions disagreed with their own than when the discordant positions on issues were regarded merely as a clash of attitudes. This abstract type of preference could in fact be converted into a simple physical measure of how close to another person with known similar or dissimilar convictions a participant chose to sit. Furthermore, grouped participants demonstrated a greater willingness to engage in discussion and negotiation with others when opposing beliefs arose from nonmoral attitudes rather than convictions, in line with recent work suggesting distinct emotional versus cognitive neural substrates for intuitive versus reasoned social appraisals. — GJC

    J. Pers. Soc. Psych. 88, 895 (2005).

  5. GEOPHYSICS

    Gradation of Fabric

    The solid inner core of Earth grew larger over time as the liquid iron outer core crystallized. This process released latent heat that helps drives convection in the liquid outer core, producing Earth's magnetic field; the inner core now has a radius of about 1200 km. Recent seismic observations have started to reveal details of the inner parts of the inner core. Initial results showed that the core has a distinct and organized crystal fabric. More recently, it has been suggested that there may be a boundary deep in the inner core at a radius of about 300 km, which may indicate its episodic growth. Cormier and Stroujkova searched for additional evidence of such a structure in a series of waveforms of seismic waves passing through the inner core at various angles (thus sampling it through different depths). The data suggest, albeit not conclusively, more subtle variations in the fabric of the inner core with depth, consistent with an increase in organized crystal size with depth, instead of a sharp transition. — BH

    Earth Planet. Sci. Lett. 236, 96 (2005).

  6. CHEMISTRY

    ROMP with Restraint

    Ring-opening metathesis polymerization (ROMP) yields a versatile range of linear polymers from cyclic olefin starting materials. The reaction is driven by relief of the bonding strain inherent to the geometry, as a metal catalyst pries open the monomer rings and stitches them together one by one. Whereas molybdenum and tungsten catalysts are more active, ruthenium compounds can react selectively with a C=C bond in the presence of many other groups, such as ketones and esters. The tradeoff for such a tolerant catalyst is reduced reactivity toward low-strain rings, such as cyclopentene and cycloheptene, which are appealing substrates because they can be functionalized symmetrically to yield regioregular polymers.

    Hejl et al.show that by careful tuning of catalyst and monomer concentrations, some of these rings can be coaxed open by Ru-based systems. In particular, they achieve >80% yields for polymerization of the unsubstituted 5- and 7-membered cyclic alkenes, and >60% yields for several ketone- and ester-substituted variants. The authors used density functional theory to calculate the strain in each monomer variant and found that the threshold for Ru-catalyzed ROMP is a minimal strain of 3.4 to 4.4 kcal/mol. — JSY

    Macromolecules 10.1021/ma0501287 (2005).

  7. STKE

    Signaling Behavior of Dopamine

    Dopamine is a neurotransmitter in circuits that convey reward and motivation, and abnormalities in dopamine signaling have been associated with mental illness. In particular, reduced function of the D2-type dopamine receptor (D2DR) is thought to contribute to schizophrenia, addiction, and mood disorders. Park et al. used a yeast two-hybrid screen to uncover prostate apoptosis response 4 (Par-4) as a binding partner for D2DR. In striatal neurons from mice that expressed a mutant form of Par-4 (in which the domain mediating the interaction with D2DR had been deleted), activation of signaling through cAMP was disrupted. Furthermore, behavioral tests of the mutant mice showed a depression-like phenotype, but no effects on measures of anxiety. Beaulieu et al. examined another signaling pathway emanating from D2DR, and they find that β-arrestin 2 is important in mediating the behavioral effects of dopamine. In wild-type mice, β-arrestin 2 was shown to associate with protein phosphatase 2a (PP2A) and the protein kinase Akt; this interaction increased after treatment with dopamine, which produced a decrease in Akt activity. In contrast, in mice deficient in β-arrestin 2, PP2A and Akt did not associate with D2DR, and dopamine did not affect Akt activity; this latter set of mice also showed decreases in dopamine-dependent behaviors. D2DRs are targets of antipsychotic drugs, so both studies provide hope that understanding the complexities of dopamine signaling may lead to the development of therapeutics that would be more effective and have fewer side effects. - NRG

    Cell 122, 275; 261 (2005).