The effects of arbuscular mycorrhizal fungi (AMF) and Rhizophagus irregularis on soil microorganisms assessed by metatranscriptomics and metaproteomics

Arbuscular mycorrhizal fungi (AMF) form symbioses with approximately 80% of plant species and potentially benefit their hosts (e.g. nutrient acquisition) and the soil environment (e.g. soil aggregation). AMF also affect soil microbiota and soil multifunctionality. We manipulated AMF presence (via inoculation of non-sterile soil with Rhizophagus irregularis and using a hyphal compartment design) and used RNA-seq and metaproteomics to assess AMF roles in soil. The results indicated that AMF drove an active soil microbial community expressing transcripts and proteins related to nine metabolic functions, including the metabolism of C and N. We suggest two possible mechanisms: 1) the AMF hyphae produce exudates that select a beneficial community, or, 2) the hyphae compete with other soil microbes for available nutrients and consequently induce the community to mineralize nutrients from soil organic matter. We also identified candidate proteins that are potentially related to soil aggregation, such as Lpt and HSP60. Our results bridge microbial ecology and ecosystem functioning. We show that the AMF hyphosphere contains an active community related to soil respiration and nutrient cycling, thus potentially improving nutrient mineralization from soil organic matter and nutrient supply to the plants

Experimental and theoretical electronic structure of EuRh2As2

The Fermi surfaces (FS's) and band dispersions of EuRh2As2 have been investigated using angle-resolved photoemission spectroscopy. The results in the high-temperature paramagnetic state are in good agreement with the full potential linearized augmented plane wave calculations, especially in the context of the shape of the two-dimensional FS's and band dispersion around the Gamma (0,0) and X (pi,pi) points. Interesting changes in band folding are predicted by the theoretical calculations below the magnetic transition temperature Tn=47K. However, by comparing the FS's measured at 60K and 40K, we did not observe any signature of this transition at the Fermi energy indicating a very weak coupling of the electrons to the ordered magnetic moments or strong fluctuations. Furthermore, the FS does not change across the temperature (~ 25K) where changes are observed in the Hall coefficient. Notably, the Fermi surface deviates drastically from the usual FS of the superconducting iron-based AFe2As2 parent compounds, including the absence of nesting between the Gamma and X FS pockets.Comment: 4 pages, 4 figure

The 2000 Periastron Passage of PSR B1259-63

We report here on a sequence of 28 observations of the binary pulsar system PSR B1259-63/SS2883 at four radio frequencies made with the Australia Telescope Compact Array around the time of the 2000 periastron passage. Observations made on 2000 Sep 1 show that the pulsar's apparent rotation measure (RM) reached a maximum of $-14800 \pm 1800$ rad m$^{-2}$, some 700 times the value measured away from periastron, and is the largest astrophysical RM measured. This value, combined with the dispersion measure implies a magnetic field in the Be star's wind of 6 mG. We find that the light curve of the unpulsed emission is similar to that obtained during the 1997 periastron but that differences in detail imply that the emission disc of the Be star is thicker and/or of higher density. The behaviour of the light curve at late times is best modelled by the adiabatic expansion of a synchrotron bubble formed in the pulsar/disc interaction. The expansion rate of the bubble $\sim 12$ km s$^{-1}$ is surprisingly low but the derived magnetic field of 1.6 G close to that expected.Comment: 8 pages, 6 figures, 3 tables, LaTeX (mn.sty). Accepted for publication in the Monthly Notices of the Royal Astronomical Society. Also available at http://astronomy.swin.edu.au/staff/tconnors/publications.htm

Absence of structural correlations of magnetic defects in heavy fermion LiV2O4

Magnetic defects have pronounced effects on the magnetic properties of the face-centered cubic compound LiV2O4. The magnetic defects arise from crystal defects present within the normal spinel structure. High-energy x-ray diffraction studies were performed on LiV2O4 single crystals to search for superstructure peaks or any other evidence of periodicity in the arrangement of the crystal defects present in the lattice. Entire reciprocal lattice planes are mapped out with help of synchrotron radiation. No noticeable differences in the x-ray diffraction data between a crystal with high magnetic defect concentration and a crystal with low magnetic defect concentration have been found. This indicates the absence of any long-range periodicity or short-range correlations in the arrangements of the crystal/magnetic defects.Comment: 6 pages, 4 figure

On the detectability of extragalactic fast radio transients

Recent discoveries of highly dispersed millisecond radio bursts by Thornton et al. in a survey with the Parkes radio telescope at 1.4 GHz point towards an emerging population of sources at cosmological distances whose origin is currently unclear. Here we demonstrate that the scattering effects at lower radio frequencies are less than previously thought, and that the bursts could be detectable at redshifts out to about $z=0.5$ in surveys below 1 GHz. Using a source model in which the bursts are standard candles with bolometric luminosities $\sim 8 \times 10^{44}$ ergs/s uniformly distributed per unit comoving volume, we derive an expression for the observed peak flux density as a function of redshift and use this, together with the rate estimates found by Thornton et al. to find an empirical relationship between event rate and redshift probed by a given survey. The non-detection of any such events in Arecibo 1.4 GHz survey data by Deneva et al., and the Allen Telescope Array survey by Simeon et al. is consistent with our model. Ongoing surveys in the 1--2 GHz band should result in further discoveries. At lower frequencies, assuming a typical radio spectral index $\alpha=-1.4$, the predicted peak flux densities are 10s of Jy. As a result, surveys of such a population with current facilities would not necessarily be sensitivity limited and could be carried out with small arrays to maximize the sky coverage. We predict that sources may already be present in 350-MHz surveys with the Green Bank Telescope. Surveys at 150 MHz with 30 deg$^2$ fields of view could detect one source per hour above 30 Jy.Comment: 5 pages, 2 figures, Accepted for publication in MNRAS on 2013 July 25. Received 2013 July 24; in original form 2013 May 3