45,189 research outputs found
Fungal community survey of Fraxinus excelior in New Zealand
The European Ash tree (Fraxinus excelsior) is widely grown throughout Europe. As a large deciduous tree species, it grows a tall, domed crown and has an attractive tree shape, so it is considered as a popular amenity tree species. European Ash is planted as an important forestry species in some European countries, and also often used for furniture making, due to its excellent wood quality. Ash species were introduced into New Zealand upon colonization in the 1800s.
Recently, ash trees throughout Europe have been observed to become damaged or die due to a severe disease known as ash dieback, caused by the fungus Chalara fraxinea. We are concerned about what will happen to the introduced ash tree in New Zealand. To our knowledge, there have been no studies on the fungi that inhabit ash trees in New Zealand. It is unknown which fungal species were present in ash at the time of the introduction to New Zealand, or which New Zealand fungi colonized ash tree after the introduction. Currently, ash dieback is not believed to be present in New Zealand.
The aim of this project was to determine the possible fungal communities on ash trees in New Zealand. We collected bark, bud and wood from three healthy ash trees, and used DNA-based methods to identify the fungi that inhabited these trees. We compared our study with a similar Swedish study to find differences and similarities in the fungi present on New Zealand and European ash trees. In total, we found 90 different fungal species. Of these species found, seven fungi could be species that came to New Zealand with the introduced ash tree. We also found one fungus that could possibly be said to have come from New Zealand. The pathogen causing ash dieback, Chalara fraxinea, was not detected
Ion-mediated RNA structural collapse: effect of spatial confinement
RNAs are negatively charged molecules residing in macromolecular crowding
cellular environments. Macromolecular confinement can influence the ion effects
in RNA folding. In this work, using the recently developed tightly bound ion
model for ion fluctuation and correlation, we investigate the confinement
effect on the ion-mediated RNA structural collapse for a simple model system.
We found that, for both Na and Mg, ion efficiencies in mediating
structural collapse/folding are significantly enhanced by the structural
confinement. Such an enhancement in the ion efficiency is attributed to the
decreased electrostatic free energy difference between the compact conformation
ensemble and the (restricted) extended conformation ensemble due to the spatial
restriction.Comment: 22 pages, 5 figure
Universal central extensions of over -graded algebras
We study central extensions of the Lie superalgebra , where
is a -graded superalgebra over a commutative ring . The Steinberg Lie
superalgebra plays a crucial role. We show that is
a central extension of for . We use a -graded
version of cyclic homology to show that the center of the extension is
isomorphic to as -modules. For , we prove that
is the universal central extension of . For
, we prove that and are both centrally
closed. The universal central extension of is constructed
explicitly.Comment: 18 pages; section 7 added; reference [KT] added; the authors thank
the referee for comments on the previous versio
- β¦