1,384 research outputs found
Is it possible to attain the same soil organic matter content in arable agriculture soils as under natural vegetation?
Clearing natural vegetation to establish arable agriculture (cropland) almost invariably causes a loss of soil organic carbon (SOC). Is it possible to restore soil that continues in arable agriculture to the pre-clearance SOC level through modified management practices? To address this question we reviewed evidence from long-term experiments at Rothamsted Research, UK, Bad LauchstĂ€dt, Germany, Sanborn Field, USA and Brazil and both experiments and surveys of farmersâ fields in Ethiopia Australia, Zimbabwe, UK and Chile. In most cases SOC content in soil under arable cropping was in the range 38-67% of pre-clearance values. Returning crop residues, adding manures or including periods of pasture within arable rotations increased this, often to 60-70% of initial values. Under tropical climatic conditions SOC loss after clearance was particularly rapid, e.g. a loss of >50% in less than 10 years in smallholder farmersâ fields in Zimbabwe. If larger yielding crops were grown, using fertilizers, and maize stover returned instead of being grazed by cattle, the loss was reduced. An important exception to the general trend of SOC loss after clearance was clearing Cerrado vegetation on highly weathered acidic soils in Brazil and conversion to cropping with maize and soybean. Other exceptions were unrealistically large annual applications of manure and including long periods of pasture in a highly SOC-retentive volcanic soil. Also, introducing irrigated agriculture in a low rainfall region can increase SOC beyond the natural value due to increased plant biomass production. For reasons of sustainability and soil health it is important to maintain SOC as high as practically possible in arable soils, but we conclude that in the vast majority of situations it is unrealistic to expect to maintain pre-clearance values. To maintain global SOC stocks at we consider it is more important to reduce current rates of land clearance and sustainably produce necessary food on existing agricultural land
A global transition to ferruginous conditions in the early Neoproterozoic oceans
Eukaryotic life expanded during the Proterozoic eon1, 2.5 to 0.542 billion years ago, against a background of fluctuating ocean chemistry2, 3, 4. After about 1.8 billion years ago, the global ocean is thought to have been characterized by oxygenated surface waters, with anoxic and sulphidic waters in middle depths along productive continental margins and anoxic and iron-containing (ferruginous) deeper waters5, 6, 7. The spatial extent of sulphidic waters probably varied through time5, 6, but this surface-to-deep redox structure is suggested to have persisted until the first Neoproterozoic glaciation about 717 million years ago8, 9, 10, 11. Here we report an analysis of ocean redox conditions throughout the Proterozoic using new and existing iron speciation and sulphur isotope data from multiple cores and outcrops. We find a global transition from sulphidic to ferruginous mid-depth waters in the earliest Neoproterozoic, coincident with the amalgamation of the supercontinent Rodinia at low latitudes. We suggest that ferruginous conditions were initiated by an increase in the oceanic influx of highly reactive iron relative to sulphate, driven by a change in weathering regime and the uptake of sulphate by extensive continental evaporites on Rodinia. We propose that this transition essentially detoxified ocean margin settings, allowing for expanded opportunities for eukaryote diversification following a prolonged evolutionary stasis before one billion years ago
A short-lived oxidation event during the early Ediacaran and delayed oxygenation of the Proterozoic ocean
The Ediacaran Period was characterised by major carbon isotope perturbations. The most extreme of these, the âŒ570 Ma Shuram/DOUNCE (Doushantuo Negative Carbon isotope Excursion) anomaly, coincided with early radiations of benthic macrofauna linked to a temporary expansion in the extent of oxygenated seawater. Here we document an earlier negative excursion (the âŒ610 Ma WANCE (Weng'An Negative Carbon isotope Excursion)) anomaly in the Yangtze Gorges area, South China, that reached equally extreme carbon isotope values and was associated with a similar degree of environmental perturbation. Specifically, new uranium isotope data evidence a significant, but transient, shift towards more oxygenated conditions in tandem with decreasing carbon isotope values, while strontium and sulfur isotope data support an increase in continental weathering through the excursion. We utilize a biogeochemical modelling approach to demonstrate that the influx of such a weathering pulse into an organically-laden, largely anoxic ocean, fully reproduces each of these distinct isotopic trends. Our study directly supports the hypothesis that a large dissolved marine organic pool effectively buffered against widespread oxygenation of the marine environment through the Proterozoic Eon, and in doing so, substantially delayed the radiation of complex aerobic life on Earth
'Bring on the dancing horses!': Ambivalence and class obsession within British media reports of the dressage at London 2012
Boosting BCG with recombinant modified vaccinia ankara expressing antigen 85A: Different boosting intervals and implications for efficacy trials
Objectives. To investigate the safety and immunogenicity of boosting BCG with modified vaccinia Ankara expressing antigen
85A (MVA85A), shortly after BCG vaccination, and to compare this first with the immunogenicity of BCG vaccination alone and
second with a previous clinical trial where MVA85A was administered more than 10 years after BCG vaccination. Design. There
are two clinical trials reported here: a Phase I observational trial with MVA85A; and a Phase IV observational trial with BCG.
These clinical trials were all conducted in the UK in healthy, HIV negative, BCG naıšve adults. Subjects were vaccinated with BCG
alone; or BCG and then subsequently boosted with MVA85A four weeks later (short interval). The outcome measures, safety
and immunogenicity, were monitored for six months. The immunogenicity results from this short interval BCG primeâMVA85A
boost trial were compared first with the BCG alone trial and second with a previous clinical trial where MVA85A vaccination
was administered many years after vaccination with BCG. Results. MVA85A was safe and highly immunogenic when
administered to subjects who had recently received BCG vaccination. When the short interval trial data presented here were
compared with the previous long interval trial data, there were no significant differences in the magnitude of immune
responses generated when MVA85A was administered shortly after, or many years after BCG vaccination. Conclusions. The
clinical trial data presented here provides further evidence of the ability of MVA85A to boost BCG primed immune responses.
This boosting potential is not influenced by the time interval between prior BCG vaccination and boosting with MVA85A. These
findings have important implications for the design of efficacy trials with MVA85A. Boosting BCG induced anti-mycobacterial
immunity in either infancy or adolescence are both potential applications for this vaccine, given the immunological data
presented here. Trial Registration. ClinicalTrials.Oxford University was the sponsor for all the clinical trials reported here
Herschel observations of embedded protostellar clusters in the Rosette Molecular Cloud
The Herschel OB young stellar objects survey (HOBYS) has observed the Rosette
molecular cloud, providing an unprecedented view of its star formation
activity. These new far-infrared data reveal a population of compact young
stellar objects whose physical properties we aim to characterise. We compiled a
sample of protostars and their spectral energy distributions that covers the
near-infrared to submillimetre wavelength range. These were used to constrain
key properties in the protostellar evolution, bolometric luminosity, and
envelope mass and to build an evolutionary diagram. Several clusters are
distinguished including the cloud centre, the embedded clusters in the vicinity
of luminous infrared sources, and the interaction region. The analysed
protostellar population in Rosette ranges from 0.1 to about 15 Msun with
luminosities between 1 and 150 Lsun, which extends the evolutionary diagram
from low-mass protostars into the high-mass regime. Some sources lack
counterparts at near- to mid-infrared wavelengths, indicating extreme youth.
The central cluster and the Phelps & Lada 7 cluster appear less evolved than
the remainder of the analysed protostellar population. For the central cluster,
we find indications that about 25% of the protostars classified as Class I from
near- to mid-infrared data are actually candidate Class 0 objects. As a
showcase for protostellar evolution, we analysed four protostars of low- to
intermediate-mass in a single dense core, and they represent different
evolutionary stages from Class 0 to Class I. Their mid- to far-infrared
spectral slopes flatten towards the Class I stage, and the 160 to 70um flux
ratio is greatest for the presumed Class 0 source. This shows that the Herschel
observations characterise the earliest stages of protostellar evolution in
detail.Comment: Astronomy & Astrophysics letter, 6 pages, 4 figures, accepted for
publication in the Special Issue for Herschel first result
Cluster-formation in the Rosette molecular cloud at the junctions of filaments
For many years feedback processes generated by OB-stars in molecular clouds,
including expanding ionization fronts, stellar winds, or UV-radiation, have
been proposed to trigger subsequent star formation. However, hydrodynamic
models including radiation and gravity show that UV-illumination has little or
no impact on the global dynamical evolution of the cloud. The Rosette molecular
cloud, irradiated by the NGC2244 cluster, is a template region for triggered
star-formation, and we investigated its spatial and density structure by
applying a curvelet analysis, a filament-tracing algorithm (DisPerSE), and
probability density functions (PDFs) on Herschel column density maps, obtained
within the HOBYS key program. The analysis reveals not only the filamentary
structure of the cloud but also that all known infrared clusters except one lie
at junctions of filaments, as predicted by turbulence simulations. The PDFs of
sub-regions in the cloud show systematic differences. The two UV-exposed
regions have a double-peaked PDF we interprete as caused by shock compression.
The deviations of the PDF from the log-normal shape typically associated with
low- and high-mass star-forming regions at Av~3-4m and 8-10m, respectively, are
found here within the very same cloud. This shows that there is no fundamental
difference in the density structure of low- and high-mass star-forming regions.
We conclude that star-formation in Rosette - and probably in high-mass
star-forming clouds in general - is not globally triggered by the impact of
UV-radiation. Moreover, star formation takes place in filaments that arose from
the primordial turbulent structure built up during the formation of the cloud.
Clusters form at filament mergers, but star formation can be locally induced in
the direct interaction zone between an expanding HII--region and the molecular
cloud.Comment: A&A Letter, in pres
A review of structural brain abnormalities in Pallister-Killian syndrome
Background
Pallister-Killian syndrome (PKS) is a rare multisystem developmental syndrome usually caused by mosaic tetrasomy of chromosome 12p that is known to be associated with neurological defects.
Methods
We describe two patients with PKS, one of whom has bilateral perisylvian polymicrogyria (PMG), the other with macrocephaly, enlarged lateral ventricles and hypogenesis of the corpus callosum. We have also summarized the current literature describing brain abnormalities in PKS.
Results
We reviewed available cases with intracranial scans (n = 93) and found a strong association between PKS and structural brain abnormalities (77.41%; 72/93). Notably, ventricular abnormalities (45.83%; 33/72), abnormalities of the corpus callosum (25.00%; 18/72) and cerebral atrophy (29.17%; 21/72) were the most frequently reported, while macrocephaly (12.5%; 9/72) and PMG (4.17%; 3/72) were less frequent. To further understand how 12p genes might be relevant to brain development, we identified 63 genes which are enriched in the nervous system. These genes display distinct temporal as well as region-specific expression in the brain, suggesting specific roles in neurodevelopment and disease. Finally, we utilized these data to define minimal critical regions on 12p and their constituent genes associated with atrophy, abnormalities of the corpus callosum, and macrocephaly in PKS.
Conclusion
Our study reinforces the association between brain abnormalities and PKS, and documents a diverse neurogenetic basis for structural brain abnormalities and impaired function in children diagnosed with this rare disorder
Dynamic anoxic ferruginous conditions during the end-Permian mass extinction and recovery
The end-Permian mass extinction, ~252 million years ago, is notable for a complex recovery period of ~5 Myr. Widespread euxinic (anoxic and sulfidic) oceanic conditions have been proposed as both extinction mechanism and explanation for the protracted recovery period, yet the vertical distribution of anoxia in the water column and its temporal dynamics through this time period are poorly constrained. Here we utilize FeâSâC systematics integrated with palaeontological observations to reconstruct a complete ocean redox history for the Late Permian to Early Triassic, using multiple sections across a shelf-to-basin transect on the Arabian Margin (Neo-Tethyan Ocean). In contrast to elsewhere, we show that anoxic non-sulfidic (ferruginous), rather than euxinic, conditions were prevalent in the Neo-Tethys. The Arabian Margin record demonstrates the repeated expansion of ferruginous conditions with the distal slope being the focus of anoxia at these times, as well as short-lived episodes of oxia that supported diverse biota
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Marine oxygen production and open water supported an active nitrogen cycle during the Marinoan Snowball Earth
The Neoproterozoic Earth was punctuated by two low-latitude Snowball Earth glaciations. Models permit oceans with either total ice cover or substantial areas of open water. Total ice cover would make an anoxic ocean likely, and would be a formidable barrier to biologic survival. However, there are no direct data constraining either the redox state of the ocean or marine biological productivity during the glacials. Here we present iron-speciation, redox-sensitive trace element, and nitrogen isotope data from a Neoproterozoic (Marinoan) glacial episode. Iron-speciation indicates deeper waters were anoxic and Fe-rich, while trace element concentrations indicate surface waters were in contact with an oxygenated atmosphere. Furthermore, synglacial sedimentary nitrogen is isotopically heavier than the modern atmosphere, requiring a biologic cycle with nitrogen fixation, nitrification and denitrification. Our results indicate significant regions of open marine water and active biologic productivity throughout one of the harshest glaciations in Earth history
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