This study analyzed the influence of biocrusts on the chemical properties and bacterial diversity and community composition in the underlying soils along a depth gradient (the biocrust (C1), middle ...(S2) and deep (S3) soil layers) in two semi-arid Mediterranean ecosystems. Organic carbon, pH, electric conductivity and calcium carbonate content were estimated by wet oxidation, potentiometrically (pHmeter), with a conductivity-meter and volumetrically with a Bernard calcimeter, respectively. Bacterial diversity and community composition were estimated by 16S rRNA gene high-throughput amplicon sequencing. Chemical properties in C1 were significantly different from the other soil layers, showing higher organic carbon content and lower pH (p < 0.05). The relative abundance of several bacterial taxa, such as Bryocella, Methylobacterium, Segitebacter and Actinomycetospora showed significant positive correlations with organic carbon (r = 0.53 to 0.75) and negative with pH (r = −0.72 to −0.84), and were also highly correlated with each other (p < 0.01), suggesting a bacterial co-occurrence pattern associated with the biocrust. On the contrary, other bacterial taxa, such as Euzebyaceae, Truepera, Alphaproteobacteria and Caldinilaceae, showed positive correlations with electrical conductivity and calcium carbonate and were also correlated with each other (p < 0.01), in a second type of co-occurrence pattern associated with bare soil. The C1 and S2 layers had several taxa in common, while S3 layers had taxa common to bare soil, suggesting that the effect of biocrusts was limited to the first centimeters of soil and progressively decreased in depth. Bacterial diversity was lower in C1 than in the underlying layers and increased progressively from biocrust to deeper soil layers. The results suggest that the diversity and composition of soil microbial communities in biologically crusted sites in Mediterranean semi-arid environments are mainly controlled by chemical properties which in turn are modified by the biocrust along a depth gradient.
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•Lichen-dominating biocrusts control the composition of soil bacterial communities.•Biocrusts modify chemical soil properties influencing bacterial communities.•Biocrusts effects are limited to the first centimeters of soil and decreases in depth.•Two bacterial co-occurrence patterns were found controlled by chemical properties.•One pattern is related to organic carbon-pH and the other to conductivity-carbonates.
MAXI J1535−571 is a Galactic black hole candidate X-ray binary that was discovered going into outburst in 2017 September. In this paper, we present comprehensive radio monitoring of this system using ...the Australia Telescope Compact Array, as well as the MeerKAT radio observatory, showing the evolution of the radio jet during its outburst. Our radio observations show the early rise and subsequent quenching of the compact jet as the outburst brightened and then evolved toward the soft state. We constrain the compact jet quenching factor to be more than 3.5 orders of magnitude. We also detected and tracked (for 303 days) a discrete, relativistically moving jet knot that was launched from the system. From the motion of the apparently superluminal knot, we constrain the jet inclination (at the time of ejection) and speed to ≤45° and ≥0.69 c, respectively. Extrapolating its motion back in time, our results suggest that the jet knot was ejected close in time to the transition from the hard intermediate state to soft intermediate state. The launching event also occurred contemporaneously with a short increase in X-ray count rate, a rapid drop in the strength of the X-ray variability, and a change in the type-C quasi-periodic oscillation (QPO) frequency that occurs >2.5 days before the first appearance of a possible type-B QPO.
The selection of a suitable organic amendment for recovery of semi-arid soils degraded by mining is key to the success of an ecological restoration. The aim of this research is to study the ...short-term responses of physicochemical, biochemical and biological properties, as well as the changes of a soil bacterial community at the genus level after application of five types of organic amendments in a limestone quarry in Almería (SE, Spain). The relationship among bacterial taxa with biochemical and physicochemical properties and priming effect from restored soils was also analysed. Six months after the application of organic amendments, the values of different soil status, such as total organic carbon, total nitrogen, assimilable phosphorus and labile organic matter forms (carbohydrates and polyphenols), basal respiration (BR) and enzymatic activities increased significantly with respect to unrestored soils. Similarly, a positive priming effect of soil organic matter mineralisation was produced by all organic amendments, being significantly higher (p < 0.05) in sewage sludge-treated soils. Bacterial diversity was higher in restored than in control soils. The restoration caused changes in soil bacterial communities' composition at the phylum and genus levels. It was observed that soil bacterial communities were significantly related to several physical, chemical and biochemical soil properties, establishing two different co-occurrence patterns between restored and unrestored soils. A first bacterial co-occurrence pattern showed significant positive correlations to pH and C/N ratio and negativity with the rest of the soil properties. The second bacterial pattern was positively correlated with carbohydrates, μg of C, priming effect, BR, β-glucosidase and phosphatase and negatively with pH and C/N ratio. It was concluded that soil bacterial communities are clearly influenced by the types of organic amendments applied. Bacterial taxa such as Taibaiella or Pseudomonas could perform key functions in the carbon cycle in restored soils.
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•Recycled waste improved physico-chemical and biological quality in restored soils.•Organic amendment modifies soil bacterial communities composition in the short-term.•Two soil bacterial co-occurrence pattern were found in restored and degraded soils.•Specific soil bacterial taxa could perform key functions in the carbon cycle.
Mass accretion onto black holes releases energy in the form of radiation and outflows. Although the radiative flux cannot substantially exceed the Eddington limit, at which the outgoing radiation ...pressure impedes the inflow of matter, it remains unclear whether the kinetic energy flux is bounded by this same limit. Here, we present the detection of a radio-optical structure, powered by outflows from a non-nuclear black hole. Its accretion disk properties indicate that this black hole is less than 100 solar masses. The optical-infrared line emission implies an average kinetic power of 3 × 1040 erg second–1, higher than the Eddington luminosity of the black hole. These results demonstrate kinetic power exceeding the Eddington limit over a sustained period, which implies greater ability to influence the evolution of the black hole's environment.
Abstract
Many radio galaxies show the presence of dense and dusty gas near the active nucleus. This can be traced by both 21 cm H i absorption and soft X-ray absorption, offering new insight into the ...physical nature of the circumnuclear medium of these distant galaxies. To better understand this relationship, we investigate soft X-ray absorption as an indicator for the detection of associated H i absorption, as part of preparation for the First Large Absorption Survey in H i to be undertaken with the Australian Square Kilometre Array Pathfinder (ASKAP). We present the results of our pilot study using the Boolardy Engineering Test Array, a precursor to ASKAP, to search for new absorption detections in radio sources brighter than 1 Jy that also feature soft X-ray absorption. Based on this pilot survey, we detected H i absorption towards the radio source PKS 1657−298 at a redshift of z = 0.42. This source also features the highest X-ray absorption ratio of our pilot sample by a factor of 3, which is consistent with our general findings that X-ray absorption predicates the presence of dense neutral gas. By comparing the X-ray properties of active galactic nuclei with and without detection of H i absorption at radio wavelengths, we find that X-ray hardness ratio and H i absorption optical depth are correlated at a statistical significance of 4.71σ. We conclude by considering the impact of these findings on future radio and X-ray absorption studies.
Abstract
Black hole X-ray binaries undergo occasional outbursts caused by changing inner accretion flows. Here we report high angular resolution radio observations of the 2013 outburst of the black ...hole candidate X-ray binary system XTE J1908+094, using data from the Very Long Baseline Array and European VLBI Network. We show that following a hard-to-soft state transition, we detect moving jet knots that appear asymmetric in morphology and brightness, and expand to become laterally resolved as they move away from the core, along an axis aligned approximately −11° east of north. We initially see only the southern component, whose evolution gives rise to a 15-mJy radio flare and generates the observed radio polarization. This fades and becomes resolved out after 4 days, after which a second component appears to the north, moving in the opposite direction. From the timing of the appearance of the knots relative to the X-ray state transition, a 90° swing of the inferred magnetic field orientation, the asymmetric appearance of the knots, their complex and evolving morphology, and their low speeds, we interpret the knots as working surfaces where the jets impact the surrounding medium. This would imply a substantially denser environment surrounding XTE J1908+094 than has been inferred to exist around the microquasar sources GRS 1915+105 and GRO J1655−40.
Abstract
In outburst, neutron star X-ray binaries produce less powerful jets than black holes at a given X-ray luminosity. This has made them more difficult to study as they fade towards quiescence. ...To explore whether neutron stars power jets at low accretion rates (L
X ≲ 1036 erg s−1), we investigate the radio and X-ray properties of three accreting millisecond X-ray pulsars (IGR J17511−3057, SAX J1808.4−3658 and IGR J00291+5934) during their outbursts in 2015, and of the non-pulsing neutron star Cen X−4 in quiescence (2015) and in outburst (1979). We did not detect the radio counterpart of IGR J17511−3057 in outburst or of Cen X−4 in quiescence, but did detect IGR J00291+5934 and SAX J1808.4−3658, showing that at least some neutron stars launch jets at low accretion rates. While the radio and X-ray emission in IGR J00291+5934 seem to be tightly correlated, the relationship in SAX J1808.4−3658 is more complicated. We find that SAX J1808.4−3658 produces jets during the reflaring tail, and we explore a toy model to ascertain whether the radio emission could be attributed to the onset of a strong propeller. The lack of a universal radio/X-ray correlation, with different behaviours in different neutron star systems (with various radio/X-ray correlations; some being radio faint and others not), points at distinct disc–jet interactions in individual sources, while always being fainter in the radio band than black holes at the same X-ray luminosity.
ABSTRACT
Most ultraluminous X-ray sources (ULXs) are believed to be powered by super-Eddington accreting neutron stars and, perhaps, black holes. Above the Eddington rate the disc is expected to ...thicken and to launch powerful winds through radiation pressure. Winds have been recently discovered in several ULXs. However, it is yet unclear whether the thickening of the disc or the wind variability causes the switch between the classical soft and supersoft states observed in some ULXs. In order to understand such phenomenology and the overall super-Eddington mechanism, we undertook a large (800 ks) observing campaign with XMM-Newton to study NGC 247 ULX-1, which shifts between a supersoft and classical soft ULX state. The new observations show unambiguous evidence of a wind in the form of emission and absorption lines from highly ionized ionic species, with the latter indicating a mildly relativistic outflow (−0.17c) in line with the detections in other ULXs. Strong dipping activity is observed in the light curve and primarily during the brightest observations, which is typical among soft ULXs, and indicates a close relationship between the accretion rate and the appearance of the dips. The latter is likely due to a thickening of the disc scale height and the wind as shown by a progressively increasing blueshift in the spectral lines.
Ammonia is a potent neurotoxin that is detoxified mainly by the urea cycle in the liver. Hyperammonemia is a common complication of a wide variety of both inherited and acquired liver diseases. If ...not treated early and thoroughly, it results in encephalopathy and death. Here, we found that hepatic autophagy is critically involved in systemic ammonia homeostasis by providing key urea-cycle intermediates and ATP. Hepatic autophagy is triggered in vivo by hyperammonemia through an α-ketoglutarate–dependent inhibition of the mammalian target of rapamycin complex 1, and deficiency of autophagy impairs ammonia detoxification. In contrast, autophagy enhancement by means of hepatic gene transfer of the master regulator of autophagy transcription factor EB or treatments with the autophagy enhancers rapamycin and Tat-Beclin-1 increased ureagenesis and protected against hyperammonemia in a variety of acute and chronic hyperammonemia animal models, including acute liver failure and ornithine transcarbamylase deficiency, the most frequent urea-cycle disorder. In conclusion, hepatic autophagy is an important mechanism for ammonia detoxification because of its support of urea synthesis, and its enhancement has potential for therapy of both primary and secondary causes of hyperammonemia.
ABSTRACT
We present results from the major coordinated X-ray observing programme on the ULX NGC 1313 X-1 performed in 2017, combining XMM–Newton, Chandra, and NuSTAR, focusing on the evolution of the ...broad-band (∼0.3–30.0 keV) continuum emission. Clear and unusual spectral variability is observed, but this is markedly suppressed above ∼10–15 keV, qualitatively similar to the ULX Holmberg IX X-1. We model the multi-epoch data with two-component accretion disc models designed to approximate super-Eddington accretion, allowing for both a black hole and a neutron star accretor. With regards to the hotter disc component, the data trace out two distinct tracks in the luminosity–temperature plane, with larger emitting radii and lower temperatures seen at higher observed fluxes. Despite this apparent anticorrelation, each of these tracks individually shows a positive luminosity–temperature relation. Both are broadly consistent with L ∝ T4, as expected for blackbody emission with a constant area, and also with L ∝ T2, as may be expected for an advection-dominated disc around a black hole. We consider a variety of possibilities for this unusual behaviour. Scenarios in which the innermost flow is suddenly blocked from view by outer regions of the super-Eddington disc/wind can explain the luminosity–temperature behaviour, but are difficult to reconcile with the lack of strong variability at higher energies, assuming this emission arises from the most compact regions. Instead, we may be seeing evidence for further radial stratification of the accretion flow than is included in the simple models considered, with a combination of winds and advection resulting in the suppressed high-energy variability.
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