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Undesired coupling to the surrounding environment destroys long-range correlations in quantum processors and hinders coherent evolution in the nominally available computational space. This noise is an outstanding challenge when leveraging the computation power of near-term quantum processors1. It has been shown that benchmarking random circuit sampling with cross-entropy benchmarking can provide an estimate of the effective size of the Hilbert space coherently available2–8. Nevertheless, quantum algorithms’ outputs can be trivialized by noise, making them susceptible to classical computation spoofing. Here, by implementing an algorithm for random circuit sampling, we demonstrate experimentally that two phase transitions are observable with cross-entropy benchmarking, which we explain theoretically with a statistical model. The first is a dynamical transition as a function of the number of cycles and is the continuation of the anti-concentration point in the noiseless case. The second is a quantum phase transition controlled by the error per cycle; to identify it analytically and experimentally, we create a weak-link model, which allows us to vary the strength of the noise versus coherent evolution. Furthermore, by presenting a random circuit sampling experiment in the weak-noise phase with 67 qubits at 32 cycles, we demonstrate that the computational cost of our experiment is beyond the capabilities of existing classical supercomputers. Our experimental and theoretical work establishes the existence of transitions to a stable, computationally complex phase that is reachable with current quantum processors.By implementing random circuit sampling, experimental and theoretical results establish the existence of transitions to a stable, computationally complex phase that is reachable with current quantum processors. [ABSTRACT FROM AUTHOR]

Indistinguishability of particles is a fundamental principle of quantum mechanics1. For all elementary and quasiparticles observed to date—including fermions, bosons and Abelian anyons—this principle guarantees that the braiding of identical particles leaves the system unchanged2,3. However, in two spatial dimensions, an intriguing possibility exists: braiding of non-Abelian anyons causes rotations in a space of topologically degenerate wavefunctions4–8. Hence, it can change the observables of the system without violating the principle of indistinguishability. Despite the well-developed mathematical description of non-Abelian anyons and numerous theoretical proposals9–22, the experimental observation of their exchange statistics has remained elusive for decades. Controllable many-body quantum states generated on quantum processors offer another path for exploring these fundamental phenomena. Whereas efforts on conventional solid-state platforms typically involve Hamiltonian dynamics of quasiparticles, superconducting quantum processors allow for directly manipulating the many-body wavefunction by means of unitary gates. Building on predictions that stabilizer codes can host projective non-Abelian Ising anyons9,10, we implement a generalized stabilizer code and unitary protocol23 to create and braid them. This allows us to experimentally verify the fusion rules of the anyons and braid them to realize their statistics. We then study the prospect of using the anyons for quantum computation and use braiding to create an entangled state of anyons encoding three logical qubits. Our work provides new insights about non-Abelian braiding and, through the future inclusion of error correction to achieve topological protection, could open a path towards fault-tolerant quantum computing.A unitary protocol for braiding projective non-Abelian Ising anyons in a generalized stabilizer code is implemented on a superconducting processor, allowing for verification of their fusion rules and realization of their exchange statistics. [ABSTRACT FROM AUTHOR]

Ribosome rescue pathways recycle stalled ribosomes and target problematic mRNAs and aborted proteins for degradation1,2. In bacteria, it remains unclear how rescue pathways distinguish ribosomes stalled in the middle of a transcript from actively translating ribosomes3–6. Here, using a genetic screen in Escherichia coli, we discovered a new rescue factor that has endonuclease activity. SmrB cleaves mRNAs upstream of stalled ribosomes, allowing the ribosome rescue factor tmRNA (which acts on truncated mRNAs3) to rescue upstream ribosomes. SmrB is recruited to ribosomes and is activated by collisions. Cryo-electron microscopy structures of collided disomes from E. coli and Bacillus subtilis show distinct and conserved arrangements of individual ribosomes and the composite SmrB-binding site. These findings reveal the underlying mechanisms by which ribosome collisions trigger ribosome rescue in bacteria.In bacteria, a newly identified endonuclease activated by ribosome collisions truncates mRNA to trigger rescue of stalled ribosomes. [ABSTRACT FROM AUTHOR]

Presents research measuring the linear polarization at a spatial resolution of about 2 kpc in Very Large Array observations of 20-cm continuum radio emission from the bright, nearly face-on, spiral galaxy M83. Low polarization in the center of the galaxy indicates disorder in the interstellar magnetic field. Method.

Rupture imaging of megathrust earthquakes with global seismic arrays revealed frequency-dependent rupture signatures1–4, but the role of high-frequency radiators remains unclear3–5. Similar observations of the more abundant crustal earthquakes could provide critical constraints but are rare without ultradense local arrays6,7. Here we use distributed acoustic sensing technology8,9 to image the high-frequency earthquake rupture radiators. By converting a 100-kilometre dark-fibre cable into a 10,000-channel seismic array, we image four high-frequency subevents for the 2021 Antelope Valley, California, moment-magnitude 6.0 earthquake. After comparing our results with long-period moment-release10,11 and dynamic rupture simulations, we suggest that the imaged subevents are due to the breaking of fault asperities—stronger spots or pins on the fault—that substantially modulate the overall rupture behaviour. An otherwise fading rupture propagation could be promoted by the breaking of fault asperities in a cascading sequence. This study highlights how we can use the extensive pre-existing fibre networks12 as high-frequency seismic antennas to systematically investigate the rupture process of regional moderate-sized earthquakes. Coupled with dynamic rupture modelling, it could improve our understanding of earthquake rupture dynamics.Distributed acoustic sensing technology is utilized to image four high-frequency rupture subevents of the 2021 Antelope Valley, California, earthquake; the results indicate that the subevents are due to the breaking of fault asperities. [ABSTRACT FROM AUTHOR]

Achieving food-system sustainability is a multidimensional challenge. In China, a doubling of crop production since 1990 has compromised other dimensions of sustainability1,2. Although the country is promoting various interventions to enhance production efficiency and reduce environmental impacts3, there is little understanding of whether crop switching can achieve more sustainable cropping systems and whether coordinated action is needed to avoid tradeoffs. Here we combine high-resolution data on crop-specific yields, harvested areas, environmental footprints and farmer incomes to first quantify the current state of crop-production sustainability. Under varying levels of inter-ministerial and central coordination, we perform spatial optimizations that redistribute crops to meet a suite of agricultural sustainable development targets. With a siloed approach—in which each government ministry seeks to improve a single sustainability outcome in isolation—crop switching could realize large individual benefits but produce tradeoffs for other dimensions and between regions. In cases of central coordination—in which tradeoffs are prevented—we find marked co-benefits for environmental-impact reductions (blue water (−4.5% to −18.5%), green water (−4.4% to −9.5%), greenhouse gases (GHGs) (−1.7% to −7.7%), fertilizers (−5.2% to −10.9%), pesticides (−4.3% to −10.8%)) and increased farmer incomes (+2.9% to +7.5%). These outcomes of centrally coordinated crop switching can contribute substantially (23–40% across dimensions) towards China’s 2030 agricultural sustainable development targets and potentially produce global resource savings. This integrated approach can inform feasible targeted agricultural interventions that achieve sustainability co-benefits across several dimensions.Spatial optimizations of high-resolution data from China on crop-specific yields, harvested areas, environmental footprints and farmer incomes shows that crop switching can enhance environmental sustainability and farmer incomes, and contribute substantially towards China’s agricultural sustainable development targets. [ABSTRACT FROM AUTHOR]

Accurate quantification of global land evapotranspiration is necessary for understanding variability in the global water cycle, which is expected to intensify under climate change1–3. Current global evapotranspiration products are derived from a variety of sources, including models4,5, remote sensing6,7 and in situ observations8–10. However, existing approaches contain extensive uncertainties; for example, relating to model structure or the upscaling of observations to a global level11. As a result, variability and trends in global evapotranspiration remain unclear12. Here we show that global land evapotranspiration increased by 10 ± 2 per cent between 2003 and 2019, and that land precipitation is increasingly partitioned into evapotranspiration rather than runoff. Our results are based on an independent water-balance ensemble time series of global land evapotranspiration and the corresponding uncertainty distribution, using data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) satellites13. Variability in global land evapotranspiration is positively correlated with El Niño–Southern Oscillation. The main driver of the trend, however, is increasing land temperature. Our findings provide an observational constraint on global land evapotranspiration, and are consistent with the hypothesis that global evapotranspiration should increase in a warming climate.Using a global mass-balance approach to calculate evapotranspiration, it is shown that global land evapotranspiration increased by 10% between 2003 and 2019, driven mainly by warming land temperatures. [ABSTRACT FROM AUTHOR]

Freshwater blooms of phytoplankton affect public health and ecosystem services globally1,2. Harmful effects of such blooms occur when the intensity of a bloom is too high, or when toxin-producing phytoplankton species are present. Freshwater blooms result in economic losses of more than US$4 billion annually in the United States alone, primarily from harm to aquatic food production, recreation and tourism, and drinking-water supplies3. Studies that document bloom conditions in lakes have either focused only on individual or regional subsets of lakes4–6, or have been limited by a lack of long-term observations7–9. Here we use three decades of high-resolution Landsat 5 satellite imagery to investigate long-term trends in intense summertime near-surface phytoplankton blooms for 71 large lakes globally. We find that peak summertime bloom intensity has increased in most (68 per cent) of the lakes studied, revealing a global exacerbation of bloom conditions. Lakes that have experienced a significant (P < 0.1) decrease in bloom intensity are rare (8 per cent). The reason behind the increase in phytoplankton bloom intensity remains unclear, however, as temporal trends do not track consistently with temperature, precipitation, fertilizer-use trends or other previously hypothesized drivers. We do find, however, that lakes with a decrease in bloom intensity warmed less compared to other lakes, suggesting that lake warming may already be counteracting management efforts to ameliorate eutrophication10,11. Our findings support calls for water quality management efforts to better account for the interactions between climate change and local hydrological conditions12,13. Analyses show that the peak intensity of summertime phytoplankton blooms has increased in 71 large lakes globally over the past three decades, revealing a worldwide exacerbation of bloom conditions. [ABSTRACT FROM AUTHOR]

Embryonic development is a crucial period in the life of a multicellular organism, during which limited sets of embryonic progenitors produce all cells in the adult body. Determining which fate these progenitors acquire in adult tissues requires the simultaneous measurement of clonal history and cell identity at single-cell resolution, which has been a major challenge. Clonal history has traditionally been investigated by microscopically tracking cells during development, monitoring the heritable expression of genetically encoded fluorescent proteins and, more recently, using next-generation sequencing technologies that exploit somatic mutations, microsatellite instability, transposon tagging, viral barcoding, CRISPR-Cas9 genome editing and Cre-loxP recombination. Single-cell transcriptomics provides a powerful platform for unbiased cell-type classification. Here we present ScarTrace, a single-cell sequencing strategy that enables the simultaneous quantification of clonal history and cell type for thousands of cells obtained from different organs of the adult zebrafish. Using ScarTrace, we show that a small set of multipotent embryonic progenitors generate all haematopoietic cells in the kidney marrow, and that many progenitors produce specific cell types in the eyes and brain. In addition, we study when embryonic progenitors commit to the left or right eye. ScarTrace reveals that epidermal and mesenchymal cells in the caudal fin arise from the same progenitors, and that osteoblast-restricted precursors can produce mesenchymal cells during regeneration. Furthermore, we identify resident immune cells in the fin with a distinct clonal origin from other blood cell types. We envision that similar approaches will have major applications in other experimental systems, in which the matching of embryonic clonal origin to adult cell type will ultimately allow reconstruction of how the adult body is built from a single cell. [ABSTRACT FROM AUTHOR]

Dodders (Cuscuta spp.) are obligate parasitic plants that obtain water and nutrients from the stems of host plants via specialized feeding structures called haustoria. Dodder haustoria facilitate bidirectional movement of viruses, proteins and mRNAs between host and parasite, but the functional effects of these movements are not known. Here we show that Cuscuta campestris haustoria accumulate high levels of many novel microRNAs (miRNAs) while parasitizing Arabidopsis thaliana. Many of these miRNAs are 22 nucleotides in length. Plant miRNAs of this length are uncommon, and are associated with amplification of target silencing through secondary short interfering RNA (siRNA) production. Several A. thaliana mRNAs are targeted by 22-nucleotide C. campestris miRNAs during parasitism, resulting in mRNA cleavage, secondary siRNA production, and decreased mRNA accumulation. Hosts with mutations in two of the loci that encode target mRNAs supported significantly higher growth of C. campestris. The same miRNAs that are expressed and active when C. campestris parasitizes A. thaliana are also expressed and active when it infects Nicotiana benthamiana. Homologues of target mRNAs from many other plant species also contain the predicted target sites for the induced C. campestris miRNAs. These data show that C. campestris miRNAs act as trans-species regulators of host-gene expression, and suggest that they may act as virulence factors during parasitism. [ABSTRACT FROM AUTHOR]

Volatile element delivery and retention played a fundamental part in Earth's formation and subsequent chemical differentiation. The heavy halogens-chlorine (Cl), bromine (Br) and iodine (I)-are key tracers of accretionary processes owing to their high volatility and incompatibility, but have low abundances in most geological and planetary materials. However, noble gas proxy isotopes produced during neutron irradiation provide a high-sensitivity tool for the determination of heavy halogen abundances. Using such isotopes, here we show that Cl, Br and I abundances in carbonaceous, enstatite, Rumuruti and primitive ordinary chondrites are about 6 times, 9 times and 15-37 times lower, respectively, than previously reported and usually accepted estimates. This is independent of the oxidation state or petrological type of the chondrites. The ratios Br/Cl and I/Cl in all studied chondrites show a limited range, indistinguishable from bulk silicate Earth estimates. Our results demonstrate that the halogen depletion of bulk silicate Earth relative to primitive meteorites is consistent with the depletion of lithophile elements of similar volatility. These results for carbonaceous chondrites reveal that late accretion, constrained to a maximum of 0.5 ± 0.2 per cent of Earth's silicate mass, cannot solely account for present-day terrestrial halogen inventories. It is estimated that 80-90 per cent of heavy halogens are concentrated in Earth's surface reservoirs and have not undergone the extreme early loss observed in atmosphere-forming elements. Therefore, in addition to late-stage terrestrial accretion of halogens and mantle degassing, which has removed less than half of Earth's dissolved mantle gases, the efficient extraction of halogen-rich fluids from the solid Earth during the earliest stages of terrestrial differentiation is also required to explain the presence of these heavy halogens at the surface. The hydropilic nature of halogens, whereby they track with water, supports this requirement, and is consistent with volatile-rich or water-rich late-stage terrestrial accretion. [ABSTRACT FROM AUTHOR]

This Review highlights how we can build upon the relatively new and rapidly developing field of research into bacterial quorum sensing (QS). We now have a depth of knowledge about how bacteria use QS signals to communicate with each other and to coordinate their activities. In recent years there have been extraordinary advances in our understanding of the genetics, genomics, biochemistry, and signal diversity of QS. We are beginning to understand the connections between QS and bacterial sociality. This foundation places us at the beginning of a new era in which researchers will be able to work towards new medicines to treat devastating infectious diseases, and use bacteria to understand the biology of sociality. [ABSTRACT FROM AUTHOR]

RNA has important and diverse roles in biology, but molecular tools to manipulate and measure it are limited. For example, RNA interference can efficiently knockdown RNAs, but it is prone to off-target effects, and visualizing RNAs typically relies on the introduction of exogenous tags. Here we demonstrate that the class 2 type VI RNA-guided RNA-targeting CRISPR-Cas effector Cas13a (previously known as C2c2) can be engineered for mammalian cell RNA knockdown and binding. After initial screening of 15 orthologues, we identified Cas13a from Leptotrichia wadei (LwaCas13a) as the most effective in an interference assay in Escherichia coli. LwaCas13a can be heterologously expressed in mammalian and plant cells for targeted knockdown of either reporter or endogenous transcripts with comparable levels of knockdown as RNA interference and improved specificity. Catalytically inactive LwaCas13a maintains targeted RNA binding activity, which we leveraged for programmable tracking of transcripts in live cells. Our results establish CRISPR-Cas13a as a flexible platform for studying RNA in mammalian cells and therapeutic development. [ABSTRACT FROM AUTHOR]

The human body carries vast communities of microbes that provide many benefits. Our microbiome is complex and challenging to understand, but evolutionary theory provides a universal framework with which to analyse its biology and health impacts. Here we argue that to understand a given microbiome feature, such as colonization resistance, host nutrition or immune development, we must consider how hosts and symbionts evolve. Symbionts commonly evolve to compete within the host ecosystem, while hosts evolve to keep the ecosystem on a leash. We suggest that the health benefits of the microbiome should be understood, and studied, as an interplay between microbial competition and host control. [ABSTRACT FROM AUTHOR]

Mantle plumes are buoyant upwellings of hot rock that transport heat from Earth's core to its surface, generating anomalous regions of volcanism that are not directly associated with plate tectonic processes. The best-studied example is the Hawaiian-Emperor chain, but the emergence of two sub-parallel volcanic tracks along this chain, Loa and Kea, and the systematic geochemical differences between them have remained unexplained. Here we argue that the emergence of these tracks coincides with the appearance of other double volcanic tracks on the Pacific plate and a recent azimuthal change in the motion of the plate. We propose a three-part model that explains the evolution of Hawaiian double-track volcanism: first, mantle flow beneath the rapidly moving Pacific plate strongly tilts the Hawaiian plume and leads to lateral separation between high- and low-pressure melt source regions; second, the recent azimuthal change in Pacific plate motion exposes high- and low-pressure melt products as geographically distinct volcanoes, explaining the simultaneous emergence of double-track volcanism across the Pacific; and finally, secondary pyroxenite, which is formed as eclogite melt reacts with peridotite, dominates the low-pressure melt region beneath Loa-track volcanism, yielding the systematic geochemical differences observed between Loa- and Kea-type lavas. Our results imply that the formation of double-track volcanism is transitory and can be used to identify and place temporal bounds on plate-motion changes. [ABSTRACT FROM AUTHOR]

In the cold dark matter cosmology, the baryonic components of galaxies-stars and gas-are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius-a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated. [ABSTRACT FROM AUTHOR]

Arising from: E. L. Olson & R. M. Allen 438, 212–215 (2005); Olson & Allen replyIt is essential in an earthquake early-warning system to be able rapidly to determine the size and location of an earthquake. Olson and Allen claim that the size of large earthquakes (magnitude (M) greater than 5.5) can be estimated from the seismic energy radiated during the first several seconds of fault rupture, implying that the earthquake process is deterministic. But here we analyse waveform data from more than 50 events (M≥6.0) recorded by the Japanese Hi-net seismic network and find no evidence that earthquake magnitude can be estimated before the rupture has completed. This bears on the difficult problem of understanding the physics of the earthquake process. [ABSTRACT FROM AUTHOR]

Helium isotopes provide an important tool for tracing early-Earth, primordial reservoirs that have survived in the planet's interior. Volcanic hotspot lavas, like those erupted at Hawaii and Iceland, can host rare, high 3He/4He isotopic ratios (up to 50 times the present atmospheric ratio, Ra) compared to the lower 3He/4He ratios identified in mid-ocean-ridge basalts that form by melting the upper mantle (about 8Ra; ref. 5). A long-standing hypothesis maintains that the high-3He/4He domain resides in the deep mantle, beneath the upper mantle sampled by mid-ocean-ridge basalts, and that buoyantly upwelling plumes from the deep mantle transport high-3He/4He material to the shallow mantle beneath plume-fed hotspots. One problem with this hypothesis is that, while some hotspots have 3He/4He values ranging from low to high, other hotspots exhibit only low 3He/4He ratios. Here we show that, among hotspots suggested to overlie mantle plumes, those with the highest maximum 3He/4He ratios have high hotspot buoyancy fluxes and overlie regions with seismic low-velocity anomalies in the upper mantle, unlike plume-fed hotspots with only low maximum 3He/4He ratios. We interpret the relationships between 3He/4He values, hotspot buoyancy flux, and upper-mantle shear wave velocity to mean that hot plumes-which exhibit seismic low-velocity anomalies at depths of 200 kilometres-are more buoyant and entrain both high-3He/4He and low-3He/4He material. In contrast, cooler, less buoyant plumes do not entrain this high-3He/4He material. This can be explained if the high-3He/4He domain is denser than low-3He/4He mantle components hosted in plumes, and if high-3He/4He material is entrained from the deep mantle only by the hottest, most buoyant plumes. Such a dense, deep-mantle high-3He/4He domain could remain isolated from the convecting mantle, which may help to explain the preservation of early Hadean (>4.5 billion years ago) geochemical anomalies in lavas sampling this reservoir. [ABSTRACT FROM AUTHOR]

Plastic bioelectronics is a research field that takes advantage of the inherent properties of polymers and soft organic electronics for applications at the interface of biology and electronics. The resulting electronic materials and devices are soft, stretchable and mechanically conformable, which are important qualities for interacting with biological systems in both wearable and implantable devices. Work is currently aimed at improving these devices with a view to making the electronic-biological interface as seamless as possible. [ABSTRACT FROM AUTHOR]

The lifetime of man-made materials is controlled largely by the wear and tear of everyday use, environmental stress and unexpected damage, which ultimately lead to failure and disposal. Smart materials that mimic the ability of living systems to autonomously protect, report, heal and even regenerate in response to damage could increase the lifetime, safety and sustainability of many manufactured items. There are several approaches to achieving these functions using polymer-based materials, but making them work in highly variable, real-world situations is proving challenging. [ABSTRACT FROM AUTHOR]

The concept of a weak asthenospheric layer underlying Earth's mobile tectonic plates is fundamental to our understanding of mantle convection and plate tectonics. However, little is known about the mechanical properties of the asthenosphere (the part of the upper mantle below the lithosphere) underlying the oceanic crust, which covers about 60 per cent of Earth's surface. Great earthquakes cause large coseismic crustal deformation in areas hundreds of kilometres away from and below the rupture area. Subsequent relaxation of the earthquake-induced stresses in the viscoelastic upper mantle leads to prolonged postseismic crustal deformation that may last several decades and can be recorded with geodetic methods1-3. The observed postseismic deformation helps us to understand the rheological properties of the upper mantle, but so far such measurements have been limited to continental-plate boundary zones. Here we consider the postseismic deformation of the very large (moment magnitude 8.6) 2012 Indian Ocean earthquake4-6 to provide by far the most direct constraint on the structure of oceanic mantle rheology. In the first three years after the Indian Ocean earthquake, 37 continuous Global Navigation Satellite Systems stations in the region underwent horizontal northeastward displacements of up to 17 centimetres in a direction similar to that of the coseismic offsets. However, a few stations close to the rupture area that had experienced subsidence of up to about 4 centimetres during the earthquake rose by nearly 7 centimetres after the earthquake. Our three-dimensional viscoelastic finiteelement models of the post-earthquake deformation show that a thin (30-200 kilometres), low-viscosity (having a steady-state Maxwell viscosity of (0.5-10) ? 1018 pascal seconds) asthenospheric layer beneath the elastic oceanic lithosphere is required to produce the observed postseismic uplift. [ABSTRACT FROM AUTHOR]

Understanding the causes of intraplate earthquakes is challenging, as it requires extending plate tectonic theory to the dynamics of continental deformation. Seismicity in the western United States away from the plate boundary is clustered along a meandering, north-south trending 'intermountain' belt. This zone coincides with a transition from thin, actively deforming to thicker, less tectonically active crust and lithosphere. Although such structural gradients have been invoked to explain seismicity localization, the underlying cause of seismicity remains unclear. Here we show results from improved mantle flow models that reveal a relationship between seismicity and the rate change of 'dynamic topography' (that is, vertical normal stress from mantle flow). The associated predictive skill is greater than that of any of the other forcings we examined. We suggest that active mantle flow is a major contributor to seismogenic intraplate deformation, while gravitational potential energy variations have a minor role. Seismicity localization should occur where convective changes in vertical normal stress are modulated by lithospheric strength heterogeneities. Our results on deformation processes appear consistent with findings from other mobile belts, and imply that mantle flow plays a significant and quantifiable part in shaping topography, tectonics, and seismic hazard within intraplate settings. [ABSTRACT FROM AUTHOR]

Plant resistance (R) genes are a crucial component in plant defence against pathogens. Although R genes often fail to provide durable resistance in an agricultural context, they frequently persist as long-lived balanced polymorphisms in nature. Standard theory explains the maintenance of such polymorphisms through a balance of the costs and benefits of resistance and virulence in a tightly coevolving host-pathogen pair. However, many plant-pathogen interactions lack such specificity. Whether, and how, balanced polymorphisms are maintained in diffusely interacting species is unknown. Here we identify a naturally interacting R gene and effector pair in Arabidopsis thaliana and its facultative plant pathogen, Pseudomonas syringae. The protein encoded by the R gene RPS5 recognizes an AvrPphB homologue (AvrPphB2) and exhibits a balanced polymorphism that has been maintained for over 2 million years (ref. 3). Consistent with the presence of an ancient balanced polymorphism, the R gene confers a benefit when plants are infected with P. syringae carrying avrPphB2 but also incurs a large cost in the absence of infection. RPS5 alleles are maintained at intermediate frequencies in populations globally, suggesting ubiquitous selection for resistance. However, the presence of P. syringae carrying avrPphB is probably insufficient to explain the RPS5 polymorphism. First, avrPphB homologues occur at very low frequencies in P. syringae populations on A. thaliana. Second, AvrPphB only rarely confers a virulence benefit to P. syringae on A. thaliana. Instead, we find evidence that selection for RPS5 involves multiple non-homologous effectors and multiple pathogen species. These results and an associated model suggest that the R gene polymorphism in A. thaliana may not be maintained through a tightly coupled interaction involving a single coevolved R gene and effector pair. More likely, the stable polymorphism is maintained through complex and diffuse community-wide interactions. [ABSTRACT FROM AUTHOR]

A unique property of many adult stem cells is their ability to exist in a non-cycling, quiescent state. Although quiescence serves an essential role in preserving stem cell function until the stem cell is needed in tissue homeostasis or repair, defects in quiescence can lead to an impairment in tissue function. The extent to which stem cells can regulate quiescence is unknown. Here we show that the stem cell quiescent state is composed of two distinct functional phases, G0 and an 'alert' phase we term GAlert. Stem cells actively and reversibly transition between these phases in response to injury-induced systemic signals. Using genetic mouse models specific to muscle stem cells (or satellite cells), we show that mTORC1 activity is necessary and sufficient for the transition of satellite cells from G0 into GAlert and that signalling through the HGF receptor cMet is also necessary. We also identify G0-to-GAlert transitions in several populations of quiescent stem cells. Quiescent stem cells that transition into GAlert possess enhanced tissue regenerative function. We propose that the transition of quiescent stem cells into GAlert functions as an 'alerting' mechanism, an adaptive response that positions stem cells to respond rapidly under conditions of injury and stress, priming them for cell cycle entry. [ABSTRACT FROM AUTHOR]

Seismic and geodetic observations in subduction zone forearcs indicate that slow earthquakes, including episodic tremor and slip, recur at intervals of less than six months to more than two years. In Cascadia, slow slip is segmented along strike and tremor data show a gradation from large, infrequent slip episodes to small, frequent slip events with increasing depth of the plate interface. Observations and models of slow slip and tremor require the presence of near-lithostatic pore-fluid pressures in slow-earthquake source regions; however, direct evidence of factors controlling the variability in recurrence times is elusive. Here we compile seismic data from subduction zone forearcs exhibiting recurring slow earthquakes and show that the average ratio of compressional (P)-wave velocity to shear (S)-wave velocity (vP/vS) of the overlying forearc crust ranges between 1.6 and 2.0 and is linearly related to the average recurrence time of slow earthquakes. In northern Cascadia, forearc vP/vS values decrease with increasing depth of the plate interface and with decreasing tremor-episode recurrence intervals. Low vP/vS values require a large addition of quartz in a mostly mafic forearc environment. We propose that silica enrichment varying from 5 per cent to 15 per cent by volume from slab-derived fluids and upward mineralization in quartz veins can explain the range of observed vP/vS values as well as the downdip decrease in vP/vS. The solubility of silica depends on temperature, and deposition prevails near the base of the forearc crust. We further propose that the strong temperature dependence of healing and permeability reduction in silica-rich fault gouge via dissolution-precipitation creep can explain the reduction in tremor recurrence time with progressive silica enrichment. Lower gouge permeability at higher temperatures leads to faster fluid overpressure development and low effective fault-normal stress, and therefore shorter recurrence times. Our results also agree with numerical models of slip stabilization under fault zone dilatancy strengthening caused by decreasing fluid pressure as pore space increases. This implies that temperature-dependent silica deposition, permeability reduction and fluid overpressure development control dilatancy and slow-earthquake behaviour. [ABSTRACT FROM AUTHOR]

Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations. Our ability to understand and predict changes in the forest carbon cycle-particularly net primary productivity and carbon storage-increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands. Yet, despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree, in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth (and thus carbon accumulation) decrease, remain constant, or increase as trees increase in size and age. Here we present a global analysis of 403 tropical and temperate tree species, showing that for most species mass growth rate increases continuously with tree size. Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees; at the extreme, a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree. The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-level productivity can be explained, respectively, by increases in a tree's total leaf area that outpace declines in productivity per unit of leaf area and, among other factors, age-related reductions in population density. Our results resolve conflicting assumptions about the nature of tree growth, inform efforts to undertand and model forest carbon dynamics, and have additional implications for theories of resource allocation and plant senescence. [ABSTRACT FROM AUTHOR]

Equilibrium climate sensitivity refers to the ultimate change in global mean temperature in response to a change in external forcing. Despite decades of research attempting to narrow uncertainties, equilibrium climate sensitivity estimates from climate models still span roughly 1.5 to 5 degrees Celsius for a doubling of atmospheric carbon dioxide concentration, precluding accurate projections of future climate. The spread arises largely from differences in the feedback from low clouds, for reasons not yet understood. Here we show that differences in the simulated strength of convective mixing between the lower and middle tropical troposphere explain about half of the variance in climate sensitivity estimated by 43 climate models. The apparent mechanism is that such mixing dehydrates the low-cloud layer at a rate that increases as the climate warms, and this rate of increase depends on the initial mixing strength, linking the mixing to cloud feedback. The mixing inferred from observations appears to be sufficiently strong to imply a climate sensitivity of more than 3 degrees for a doubling of carbon dioxide. This is significantly higher than the currently accepted lower bound of 1.5 degrees, thereby constraining model projections towards relatively severe future warming. [ABSTRACT FROM AUTHOR]

The niche is a conserved regulator of stem cell quiescence and function. During ageing, stem cell function declines. To what extent and by what means age-related changes within the niche contribute to this phenomenon are unknown. Here we demonstrate that the aged muscle stem cell niche, the muscle fibre, expresses Fgf2 under homeostatic conditions, driving a subset of satellite cells to break quiescence and lose their self-renewing capacity. We show in mice that relatively dormant aged satellite cells robustly express sprouty?1 (Spry1), an inhibitor of fibroblast growth factor (FGF) signalling. Increasing FGF signalling in aged satellite cells under homeostatic conditions by removing Spry1 results in the loss of quiescence, satellite cell depletion and diminished regenerative capacity. Conversely, reducing niche-derived FGF activity through inhibition of Fgfr1 signalling or overexpression of Spry1 in satellite cells prevents their depletion. These experiments identify an age-dependent change in the stem cell niche that directly influences stem cell quiescence and function. [ABSTRACT FROM AUTHOR]