Impact of farm management on the diversity of desulfonation genes and 16S rRNA genes in wheat rhizospheres

Worldwide the resources for mineral fertiliser are diminishing. Growth of healthy, high-yielding crop plants requires a stable input not only of nitrogen and phosphorus, but also of sulfur (S). In natural ecosystems, nutrient cycling is mainly mediated by soil microorganisms, and much research is devoted to optimisation of microbial nutrient cycling for agricultural ecosystems. Several rhizosphere microorganisms are able to mobilise plant-unavailable soil S, and two bacterial genes that may be involved in the process are atsA, which encodes arylsulfatase, and ssuD which encodes alkanesulfonate monooxygenase. This study investigated the impact of agricultural practices on the overall rhizosphere microbial community and on functional diversity of S-mobilising organisms. Five wheat genotypes with different root-structures were inoculated with different strains of Azospirillum brasilense to determine the influence of wheat genotype and inoculation treatment in a continuous wheat field trial at Narrabri, New South Wales (Australia). Pot trials with vertisol soil from the field-site were carried out to investigate the effect of wheat variety and different inoculation treatments under controlled conditions. For the analysis of the ssuD gene diversity degenerate primers were designed and tested for specificity through cloning and sequencing. Both exploratory NMDS-Analysis and redundancy analysis (RDA) of fingerprinting profiles obtained by T-RFLP (Terminal restriction fragment length polymorphism) showed that wheat variety has a significant (p< 0.05) impact on the ssuD gene diversity in the rhizosphere. No significant wheat-genotype related effect could be found for the rhizosphere diversity of the16S rRNA gene. A comparison of two crop rotations, (field pea/sorghum/wheat or Indian mustard/sorghum/wheat) also showed clear differences between the 16S rRNA gene and ssuD gene diversity in the two treatments. In addition, an effect of the interaction between crop rotation (field pea-sorghum-wheat and mustard-sorghum-wheat) and two different N fertiliser levels was found on ssuD gene diversity but not on overall bacterial diversity. These findings indicate that cropping measures, including plant genotype, rotation and N-fertiliser level influence not only overall bacterial, but also ssuD gene functional diversity. This study proves that changes in ssuD gene functional and overall bacterial diversity are not congruent, thus pointing out the importance of a detailed analysis of the functional microbial diversity involved in nutrient cycling. Furthermore major environmental drivers correlated with ssuD gene diversity in wheat and canola rhizospheres across NSW and Victoria were assessed with T-RFLP fingerprints. The information about treatment-related changes, and geographical changes in ssuD gene diversity offers the first information that sulfonate-mobilising communities in soil can be influenced. The development of ssuD degenerate primers for pyrosequencing approaches offers a tool to identify key organisms and to measure their behaviour in rhizospheres and impact on plant nutrition. Optimising farm management by taking into account the genetic potential of rhizosphere microorganisms can help to tailor more resource-efficient crop production systems

Dirac parameters and topological phase diagram of Pb1-xSnxSe from magneto-spectroscopy

Pb1-xSnxSe hosts 3D massive Dirac fermions across the entire composition range for which the crystal structure is cubic. In this work, we present a comprehensive experimental mapping of the 3D band structure parameters of Pb1-xSnxSe as a function of composition and temperature. We cover a parameter space spanning the band inversion that yields its topological crystalline insulator phase. A non-closure of the energy gap is evidenced in the vicinity of this phase transition. Using magnetooptical Landau level spectroscopy, we determine the energy gap, Dirac velocity, anisotropy factor and topological character of Pb1-xSnxSe epilayers grown by molecular beam epitaxy on BaF2 (111). Our results are evidence that Pb1-xSnxSe is a model system to study topological phases and the nature of the phase transition.Comment: Submitte

Massive and massless Dirac fermions in Pb1-xSnxTe topological crystalline insulator probed by magneto-optical absorption

Dirac fermions in condensed matter physics hold great promise for novel fundamental physics, quantum devices and data storage applications. IV-VI semiconductors, in the inverted regime, have been recently shown to exhibit massless topological surface Dirac fermions protected by crystalline symmetry, as well as massive bulk Dirac fermions. Under a strong magnetic field (B), both surface and bulk states are quantized into Landau levels that disperse as B^1/2, and are thus difficult to distinguish. In this work, magneto-optical absorption is used to probe the Landau levels of high mobility Bi-doped Pb0.54Sn0.46Te topological crystalline insulator (111)-oriented films. The high mobility achieved in these thin film structures allows us to probe and distinguish the Landau levels of both surface and bulk Dirac fermions and extract valuable quantitative information about their physical properties. This work paves the way for future magnetooptical and electronic transport experiments aimed at manipulating the band topology of such materials.Comment: supplementary material included, to appear in Scientific Report

Hole-LO phonon interaction in InAs/GaAs quantum dots

We investigate the valence intraband transitions in p-doped self-assembled InAs quantum dots using far-infrared magneto-optical technique with polarized radiation. We show that a purely electronic model is unable to account for the experimental data. We calculate the coupling between the mixed hole LO-phonon states using the Fr\"ohlich Hamiltonian, from which we determine the polaron states as well as the energies and oscillator strengths of the valence intraband transitions. The good agreement between the experiments and calculations provides strong evidence for the existence of hole-polarons and demonstrates that the intraband magneto-optical transitions occur between polaron states

Psychological and neurophysiological correlates of social vocal control

Flexible vocal behaviour is an important paralinguistic signal in social interactions, but it is unclear whether such social vocal control can occur volitionally and specifically, and which speaker characteristics contribute to this ability. In this dissertation, the psychological and neurophysiological mechanisms involved in social vocal control are addressed using a novel social vocal control task, behavioural ratings and functional neuroimaging. Speakers evoked specific social trait impressions in listeners through targeted vocal modulations. While speakers’ self-reported level of Machiavellianism predicted the ability to evoke favourable trait percepts in listeners, dispositional empathy was not related to vocal control performance. Processing regions involved in vocomotor control and social cognitive processing interacted on the level of the left inferior frontal gyrus during social vocal control, while performance was associated with activation in somatosensory and social feedback regions. Social vocal control might be a route for impression management and support successful social interactions