925 research outputs found
The dynamic consequences of invasion: negative plant-soil feedbacks on natives increase ver the time course of invasion
*a) Background/Questions/Methods*
Exotic species can negatively impact native community members, directly through interference competition, or indirectly by altering interactions between native species and other species such as pathogens and mutualists. Soil microbial communities have been shown to respond to invasive species, yet are relatively stable and may take time to respond to perturbations. For this reason, microbe-mediated effects of invasives on natives may take time to develop and may change throughout the invasion process. Few studies have investigated how species interactions between natives and exotics change during invasions.

_Acer platanoides_ was introduced into the US from Europe in 1756 and has since invaded intact forests, lowering understory diversity and inhibiting native tree species regeneration. We hypothesize that _A. platanoides_ invasion will decrease seedling survival in the native _A. saccharum_ by changing the soil microbial community through plant-soil feedbacks (PSF), and this relationship will intensify over the course of an invasion. We collected soil samples from beneath the canopies of both species co-occurring in Michigan forests that had been invaded by _A. platanoides_ for varying time periods. In the greenhouse, we inoculated seedlings of both species with the microbial communities to determine how the soil community affects seedling survival and growth.

*b) Results/Conclusion*
The microbe-mediated negative effects of _A. platanoides_ on survival of the native congener _A. saccharum_ increased with increasing invasion age (negative correlation between invasion age and _A. saccharum_ survival; r = -0.806, R^2^ = 0.65, p = 0.032). This result was not related to _A. platanoides_ density, suggesting that age of invasion drives this pattern. Contrastingly, invasion age did not significantly influence survival of _A. platanoides_ seedlings, indicating that _A. platanoides’_ PSF impacts native species but not on conspecific regeneration. Overall, _A. platanoides_ seedlings had increased growth (more and larger leaves) when grown in soil communities collected from the native _A. saccharum_, but _A. saccharum_ seedlings had reduced growth when grown in conspecific soil (p = 0.044). These results suggest that invasive species may have increased performance in exotic ranges by their ability to modify the soil microbial community in a manner that suppresses the growth of native species.

We show the microbial community cultivated by an invader alters the performance of a native plant species, and this effect increases over the course of an invasion. In future work, we plan to identify changes in microbial community composition and the relative abundances of mutualists versus antagonists in response to invasion to identify potential mechanisms
Abundances of disk and bulge giants from hi-res optical spectra: II. O, Mg, Ca, and Ti in the bulge sample
Determining elemental abundances of bulge stars can, via chemical evolution
modeling, help to understand the formation and evolution of the bulge. Recently
there have been claims both for and against the bulge having a different
[/Fe] vs. [Fe/H]-trend as compared to the local thick disk possibly
meaning a faster, or at least different, formation time scale of the bulge as
compared to the local thick disk. We aim to determine the abundances of oxygen,
magnesium, calcium, and titanium in a sample of 46 bulge K-giants, 35 of which
have been analyzed for oxygen and magnesium in previous works, and compare them
to homogeneously determined elemental abundances of a local disk sample of 291
K-giants. We use spectral synthesis to determine both the stellar parameters as
well as the elemental abundances of the bulge stars analyzed here. The method
is exactly the same as was used for analyzing the comparison sample of 291
local K-giants in Paper I of this series. Compared to the previous analysis of
the 35 stars in our sample, we find lower [Mg/Fe] for [Fe/H]>-0.5, and
therefore contradict the conclusion about a declining [O/Mg] for increasing
[Fe/H]. We instead see a constant [O/Mg] over all the observed [Fe/H] in the
bulge. Furthermore, we find no evidence for a different behavior of the
alpha-iron trends in the bulge as compared to the local thick disk from our two
samples.Comment: Accepted for publication in A&
Evidence against anomalous compositions for giants in the Galactic Nuclear Star Cluster
Very strong Sc I lines have been found recently in cool M giants in the
Nuclear Star Cluster in the Galactic Center. Interpreting these as anomalously
high scandium abundances in the Galactic Center would imply a unique
enhancement signature and chemical evolution history for nuclear star clusters,
and a potential test for models of chemical enrichment in these objects. We
present high resolution K-band spectra (NIRSPEC/Keck II) of cool M giants
situated in the solar neighborhood and compare them with spectra of M giants in
the Nuclear Star Cluster. We clearly identify strong Sc I lines in our solar
neighborhood sample as well as in the Nuclear Star Cluster sample. The strong
Sc I lines in M giants are therefore not unique to stars in the Nuclear Star
Cluster and we argue that the strong lines are a property of the line formation
process that currently escapes accurate theoretical modeling. We further
conclude that for giant stars with effective temperatures below approximately
3800 K these Sc I lines should not be used for deriving the scandium abundances
in any astrophysical environment until we better understand how these lines are
formed. We also discuss the lines of vanadium, titanium, and yttrium identified
in the spectra, which demonstrate a similar striking increase in strength below
3500 K effective temperature.Comment: 11 pages, 6 figures, accepted for publication in Ap
Detailed Abundances for the Old Population near the Galactic Center: I. Metallicity distribution of the Nuclear Star Cluster
We report the first high spectral resolution study of 17 M giants
kinematically confirmed to lie within a few parsecs of the Galactic Center,
using R=24,000 spectroscopy from Keck/NIRSPEC and a new linelist for the
infrared K band. We consider their luminosities and kinematics, which classify
these stars as members of the older stellar population and the central cluster.
We find a median metallicity of =-0.16 and a large spread from
approximately -0.3 to +0.3 (quartiles). We find that the highest metallicities
are [Fe/H]<+0.6, with most of the stars being at or below the Solar iron
abundance. The abundances and the abundance distribution strongly resembles
that of the Galactic bulge rather than disk or halo; in our small sample we
find no statistical evidence for a dependence of velocity dispersion on
metallicity.Comment: 18 pages, 14 figures, accepted for publication in A
A three dimensional extinction map of the Galactic Anticentre from multi-band photometry
We present a three dimensional extinction map in band. The map has a
spatial angular resolution, depending on latitude, between 3 -- 9\,arcmin and
covers the entire XSTPS-GAC survey area of over 6,000\, for Galactic
longitude and latitude . By cross-matching the photometric catalog of the Xuyi Schmidt
Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC) with those
of 2MASS and WISE, we have built a multi-band photometric stellar sample of
about 30 million stars and applied spectral energy distribution (SED) fitting
to the sample. By combining photometric data from the optical to the
near-infrared, we are able to break the degeneracy between the intrinsic
stellar colours and the amounts of extinction by dust grains for stars with
high photometric accuracy, and trace the extinction as a function of distance
for low Galactic latitude and thus highly extincted regions. This has allowed
us to derive the best-fit extinction and distance information of more than 13
million stars, which are used to construct the three dimensional extinction
map. We have also applied a Rayleigh-Jeans colour excess (RJCE) method to the
data using the 2MASS and WISE colour . The resulting RJCE extinction
map is consistent with the integrated two dimensional map deduced using the
best-fit SED algorithm. However for individual stars, the amounts of extinction
yielded by the RJCE method suffer from larger errors than those given by the
best-fit SED algorithm.Comment: 20 pages, 18 figures, accepted in MNRA
Interstellar extinction towards the inner Galactic Bulge
DENIS observations in the J (1.2 micron) and K_S (2.15 micron) bands together
with isochrones calculated for the RGB and AGB phase are used to draw an
extinction map of the inner Galactic Bulge. The uncertainty in this method is
mainly limited by the optical depth of the Bulge itself. A comparison with
fields of known extinction shows a very good agreement. We present an
extinction map for the inner Galactic Bulge (approx. 20 sq. deg.)Comment: 4 pages, 4 figures, accepted for publication in A&A as a letter, see
also http://www-denis.iap.fr/articles/extinction
Abundances of disk and Bulge giants from high-resolution optical spectra III. Sc, V, Cr, Mn, Co, Ni
Context. Recent observations of the Bulge, e.g., its X-shape, cylindrical
stellar motions, and a potential fraction of young stars propose that it formed
through secular evolution of the disk and not through gas dissipation and/or
mergers, as thought previously. Aims. We measure abundances of six iron-peak
elements (Sc, V, Cr, Mn, Co and Ni) in the local thin and thick disks as well
as the Bulge to provide additional observational constraints for Galaxy
formation and chemical evolution models. Methods. We use high-resolution
optical spectra of 291 K giants in the local disk mostly obtained by the FIES
at NOT (signal-to-noise (S/N) ratio of 80-100) and 45 K giants in the Bulge
obtained by the UVES/FLAMES at VLT (S/N ratio of 10-80). We measure abundances
in SME and apply NLTE corrections to the [Mn/Fe] and [Co/Fe] ratios. To
discriminate between the thin and thick, we use stellar metallicity,
[Ti/Fe]-ratios, and kinematics from Gaia DR2 (proper motions and the radial
velocities). Results. The observed disk trend of V is more enhanced in the
thick disk, while the Co disk trend shows a minor enhancement in the thick
disk. The Bulge trends of V and Co appear even more enhanced w.r.t. the thick
disk, but within the uncertainties. The [Ni/Fe] ratio seems slightly
overabundant in the thick disk and the Bulge w.r.t. the thin disk, although the
difference is minor. The disk and Bulge trends of Sc, Cr and Mn overlap
strongly. Conclusions. The somewhat enhanced [(V,Co)/Fe] ratios observed in the
Bulge suggest that the local thick disk and the Bulge might have experienced
different chemical enrichment and evolutionary paths. However, we are unable to
predict the exact evolutionary path of the Bulge solely based on these
observations. Galactic chemical evolution models could, on the other hand,
provide that using these results.Comment: Accepted for publication in A&A; 25 pages, 15 figure
Bibliothekswesen in Südamerika - Chile im Jahr 2014
Librarianship in South America - Chile in 2014 (translation of the title). The historian and librarian Alexander H.T. Schultheis is living since nine years in Santiago de Chile and he is observing the Chilean librarianship. Although Chile is doing well economically, no improvement can be seen in the field of culture and education. On the contrary, the public libraries are still poorly equipped. Chance can be seen as small bright spots on the horizon, for example, the new opened cultural center GAM in the city of Santiago. Therefore, the Goethe-Institut in Santiago de Chile will continue provide intensive work with Chile at the sector of library science and public libraries
Bibliothekswesen in Südamerika - Chile im Jahr 2014
Librarianship in South America - Chile in 2014 (translation of the title). The historian and librarian Alexander H.T. Schultheis is living since nine years in Santiago de Chile and he is observing the Chilean librarianship. Although Chile is doing well economically, no improvement can be seen in the field of culture and education. On the contrary, the public libraries are still poorly equipped. Chance can be seen as small bright spots on the horizon, for example, the new opened cultural center GAM in the city of Santiago. Therefore, the Goethe-Institut in Santiago de Chile will continue provide intensive work with Chile at the sector of library science and public libraries
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