Soil water repellency and its implications for organic matter decomposition – is there a link to extreme climatic events?

Earth system models associate the ongoing global warming with increasing frequency and intensity of extreme events such as droughts and heat waves. The carbon balance of soils may be more sensitive to the impact of such extremes than to homogeneously distributed changes in soil temperature (T_s) or soil water content (θ_s). One parameter influenced by more pronounced drying/rewetting cycles or increases in T_s is the wettability of soils. Results from laboratory and field studies showed that low θ_s, particularly in combination with high T_s can increase soil water repellency (SWR). Recent studies have provided evidence that the stability of soil organic matter (SOM) against microbial decomposition is substantially enhanced in water repellent soils. This review hypothesizes that SWR is an important SOM stabilization mechanism that could become more important because of the increase in extreme events. We discuss wettability‐induced changes in soil moisture distribution and in soil aggregate turnover as the main mechanisms explaining the reduced mineralization of SOM with increasing SWR. The creation of preferential flow paths and subsequent uneven penetration of rainwater may cause a long‐term reduction of soil water availability, affecting both microorganisms and plants. We conclude that climate change‐induced SWR may intensify the effects of climatic drought and thus affects ecosystem processes such as SOM decomposition and plant productivity, as well as changes in vegetation and microbial community structure. Future research on biosphere–climate interactions should consider the effects of increasing SWR on soil moisture and subsequently on both microbial activity and plant productivity, which ultimately determine the overall carbon balance.     

Host genotype affects the relative success of competing lines of aphid parasitoids under superparasitism

1. In solitary parasitoids, only one individual can complete development in a given host. Therefore, solitary parasitoids tend to prefer unparasitised hosts for oviposition, yet under high parasitoid densities, superparasitism is frequent and results in fierce competition for the host's limited resources. This may lead to selection for the best intra‐host competitors. 2. Increased intra‐host competitive ability may evolve under a high risk of superparasitism if this trait exhibits genetic variation, and if competitive differences among parasitoid genotypes are consistent across environments, e.g. different host genotypes. 3. These assumptions were addressed in the aphid parasitoid Lysiphlebus fabarum (Hymenoptera: Braconidae: Aphidiinae) and its main host, the black bean aphid, Aphis fabae (Scopoli) (Hemiptera: Aphididae). Three parthenogenetic lines of L. fabarum were allowed to parasitise three aphid clones singly and in all pairwise combinations (superparasitism). The winning parasitoid in superparasitised aphids was determined by microsatellite analysis. 4. The proportions of singly parasitised aphids that were mummified were similar for the three parasitoid lines and did not differ significantly among host clones. 5. Under superparasitism, significant biases in favour of one parasitoid line were observed for some combinations, indicating that there is genetic variation for intra‐host competitive ability. However, the outcome of superparasitism was inconsistent across aphid clones and thus influenced significantly by the host clone in which parasitoids competed. 6. Overall, this study shows that the fitness of aphid parasitoids under superparasitism is determined by complex interactions with competitors as well as hosts, possibly hampering the evolution of improved intra‐host competitive ability.     

Effect of ambient temperature on mechanosensory host location in two parasitic wasps of different climatic origin

Abstract.  Several parasitic wasps of the Pimplinae (Ichneumonidae) use self-produced vibrations transmitted through plant substrate to locate their concealed immobile hosts (lepidopteran pupae) by reflected signals. This mechanosensory mechanism of host location, called vibrational sounding, depends on the physical characteristics of the plant substrate and the wasp's body and is postulated to depend on ambient temperature. Adaptations of two parasitoid species to thermal conditions of their habitats and the influence of temperature on the trophic interaction during host location are investigated in the tropical Xanthopimpla stemmator (Thunberg) and compared with the temperate Pimpla turionellae (L.). Plant-stem models with hidden host mimics are offered to individual wasps under defined temperature treatments and scored for the number and location of ovipositor insertions. Significant effects of temperature are found on host-location activity and its success. The tropical species possesses an optimum temperature range for vibrational sounding between 26 and 32 °C, whereas the performance decreases both at low and high temperatures. The temperate species reveals substantial differences with respect to performance at the same thermal conditions. With increasing temperature, P. turionellae shows a reduced response to the host mimic, reduced numbers of ovipositor insertions, and decreased precision of mechanosensory host location. In the tropical X. stemmator , the female wasps are able to locate their host with high precision over a broad range of ambient temperatures, which suggests endothermic thermoregulation during vibrational sounding. Environmental physiology may therefore play a key role in adaptation of the host location mechanism to climatic conditions of the species' origin.     

Late Cretaceous follicular fruits from southern Sweden with systematic affinities to early diverging eudicots

Eight new species in seven new genera of follicular fruits are described from the Late Cretaceous of southern Sweden. They are Agapitocarpus emisxus , Chontrocarpus pachytoichus , Maiandrocarpus moirasmenus , Malliocarpus batrachoides , Mitocarpus elegans , Xylocarpus rhitidoides , Zeugarocarpus adroagathus and Z. leptoagathus . The fossil follicles are borne along infructescence axes or more commonly occur as isolated, dispersed fruits. Three genera, Maiandrocarpus , Mitocarpus and Zeugarocarpus , have follicles in distinct pairs borne spirally on an infructescence axis. Each follicle of a pair faces the axis with its ventral slit, which strongly indicates that the paired follicles were derived from two separate, monocarpellate flowers rather than from a single, bicarpellate flower. One genus ( Malliocarpus ) has follicles borne individually in the infructescence and three others ( Agapitocarpus , Chontrocarpus and Xylocarpus ) are known only as dispersed follicles. The paired follicles share many features with most of the dispersed follicles, including a sessile stigmatic area, a three-layered simple follicle wall, a simple vascular system composed of one dorsal and two lateral bundles, as well as a marginal-linear placentation bearing several anatropous ovules. Accordingly they are thought to belong to the same complex of taxa. The general structure of the fossils and comparison with modern angiosperms suggest that the fossils might represent an extinct lineage within or close to basal eudicots and many characters are shared with members of extant Proteaceae.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 148 , 377–407.     

Trefoil factor 3 stimulates human and rodent pancreatic islet beta-cell replication with retention of function

Both major forms of diabetes involve a decline in beta-cell mass, mediated by autoimmune destruction of insulin-producing cells in type 1 diabetes and by increased rates of apoptosis secondary to metabolic stress in type 2 diabetes. Methods for controlled expansion of beta-cell mass are currently not available but would have great potential utility for treatment of these diseases. In the current study, we demonstrate that overexpression of trefoil factor 3 (TFF3) in rat pancreatic islets results in a 4- to 5-fold increase in [(3)H]thymidine incorporation, with full retention of glucose-stimulated insulin secretion. This increase was almost exclusively due to stimulation of beta-cell replication, as demonstrated by studies of bromodeoxyuridine incorporation and co-immunofluorescence analysis with anti-bromodeoxyuridine and antiinsulin or antiglucagon antibodies. The proliferative effect of TFF3 required the presence of serum or 0.5 ng/ml epidermal growth factor. The ability of TFF3 overexpression to stimulate proliferation of rat islets in serum was abolished by the addition of epidermal growth factor receptor antagonist AG1478. Furthermore, TFF3-induced increases in [3H]thymidine incorporation in rat islets cultured in serum was blocked by overexpression of a dominant-negative Akt protein or treatment with triciribine, an Akt inhibitor. Finally, overexpression of TFF3 also caused a doubling of [3H]thymidine incorporation in human islets. In summary, our findings reveal a novel TFF3-mediated pathway for stimulation of beta-cell replication that could ultimately be exploited for expansion or preservation of islet beta-cell mass.     

THE MIDDLE ORDOVICIAN PROVENTOCITUM PROCERULUM RADIOLARIAN ASSEMBLAGE OF SPITSBERGEN AND ITS BIOSTRATIGRAPHIC CORRELATION

Abstract: The Proventocitum procerulum radiolarian assemblage from the Valhallfonna Formation of Spitsbergen is described for the first time in some detail from material investigated in transmitted light. A number of species are recognized in the well‐preserved material, showing unexpected diversity. The age of the fauna is restricted to the early Darriwilian (Da1‐2), based on comparison with precisely dated radiolarian assemblages from the Cow Head and Table Head Groups of western Newfoundland. Most species, however, are left in open nomenclature until additional material is available for SEM investigation. Inanigutta magnifica n. sp. is described as new.     

The performance of fungal xylan-degrading enzyme preparations in elemental chlorine-free bleaching for Eucalyptus pulp

Cellulase-free xylan-degrading enzyme preparations from Acrophialophora nainiana, Humicola grisea var. thermoidea and two Trichoderma harzianum strains were used as bleaching agents for Eucalyptus kraft pulp, prior to a chlorine dioxide and alkaline bleaching sequence. In comparison to the control sequence (performed without xylanase pretreatment), the sequence incorporating enzyme treatment was more effective. Removal of residual lignin was indicated by a reduction in kappa number. Overall, enzyme preparations from T. harzianum were marginally more effective in reducing pulp viscosity and chlorine chemical consumption and improving the brightness of the kraft pulp. However, the highest reduction in pulp viscosity was mediated by the xylanase preparation from A. nainiana. Xylanase pretreatment compares very favorably with that of chemical pulping. Journal of Industrial Microbiology & Biotechnology (2002) 28, 204–206 DOI: 10.1038/sj/jim/7000227 Received 27 April 2001/ Accepted in revised form 03 November 2001     

Role of the phenylalanine B24 side chain in directing insulin interaction with its receptor. Importance of main chain conformation

We have investigated (by use of semisynthetic insulin analogs and isolated canine hepatocytes) the role of invariant residue PheB24 in determining the affinity of insulin-receptor interactions. Our results confirm that replacement of PheB24 by D-Phe is not detrimental to ligand binding to receptor, show that D-Ala is well tolerated at position B24 (whereas Ala is not), and demonstrate that [GlyB24]insulin retains as much as 78% of the receptor binding potency of native insulin. Additional findings show that replacement of PheB24 by D-Pro or by alpha-aminoisobutyric acid results in analogs with severely decreased binding potency, and that the COOH-terminal domain containing residues B26-B30 plays a positive role in determining receptor binding potency in GlyB24-substituted insulin (whereas it plays a negative role in determining the receptor binding potency of its GlyB25-substituted counterpart). We interpret our results as identifying (a) a critical role for the insulin main chain near residue B24 in determining the affinity of receptor for ligand, (b) the importance of main chain flexibility in achieving a high affinity state of receptor-bound hormone, and (c) a potential interaction of the PheB24 side chain with receptor which initiates main chain structural changes in the natural hormone, but which does not itself confer affinity to ligand-receptor interactions.