Will trees or grasses profit from changing rainfall regimes in savannas?

Increasing rainfall variability is widely expected under future climate change scenarios. How will savanna trees and grasses be affected by growing season dry spells and altered seasonality and how tightly coupled are tree-grass phenologies with rainfall? We measured tree and grass responses to growing season dry spells and dry season rainfall. We also tested whether the phenologies of 17 deciduous woody species and the Soil Adjusted Vegetation Index of grasses were related to rainfall between 2019 and 2023. Tree and grass growth was significantly reduced during growing season dry spells. Tree growth was strongly related to growing season soil water potentials and limited to the wet season. Grasses can rapidly recover after growing season dry spells and grass evapotranspiration was significantly related to soil water potentials in both the wet and dry seasons. Tree leaf flushing commenced before the rainfall onset date with little subsequent leaf flushing. Grasses grew when moisture became available regardless of season. Our findings suggest that increased dry spell length and frequency in the growing season may slow down tree growth in some savannas, which together with longer growing seasons may allow grasses an advantage over C3 plants that are advantaged by rising CO2 levels.

Reassessing the alternative ecosystem states proposition in the African savanna-forest domain.

Ecologists are being challenged to predict how ecosystems will respond to climate changes. According to the Multi-Colored World (MCW) hypothesis, climate impacts may not manifest because consumers such as fire and herbivory can override the influence of climate on ecosystem state. One MCW interpretation is that climate determinism fails because alternative ecosystem states (AES) are possible at some locations in climate space. We evaluated theoretical and empirical evidence for the proposition that forest and savanna are AES in Africa. We found that maps which infer where AES zones are located were contradictory. Moreover, data from longitudinal and experimental studies provide inconclusive evidence for AES. That is, although the forest-savanna AES proposition is theoretically sound, the existing evidence is not yet convincing. We conclude by making the case that the AES proposition has such fundamental consequences for designing management actions to mitigate and adapt to climate change in the savanna-forest domain that it needs a more robust evidence base before it is used to prescribe management actions.

Plant-Derived, Nodule-Specific Cysteine-Rich Peptides as a Novel Source of Biopesticides for Controlling Citrus Greening Disease.

Nodule-specific cysteine-rich (NCR) peptides, encoded in the genome of the Mediterranean legume Medicago truncatula (barrelclover), are known to regulate plant-microbe interactions. A subset of computationally derived 20-mer peptide fragments from 182 NCR peptides was synthesized to identify those with activity against the unculturable vascular pathogen associated with citrus greening disease, 'Candidatus Liberibacter asiaticus' (CLas). Grounded in a design of experiments framework, we evaluated the peptides in a screening pipeline involving three distinct assays: a bacterial culture assay with Liberibacter crescens, a CLas-infected excised citrus leaf assay, and an assay to evaluate effects on bacterial acquisition by the nymphal stage of hemipteran vector Diaphorina citri. A subset of the 20-mer NCR peptide fragments inhibits both CLas growth in citrus leaves and CLas acquisition by D. citri. Two peptides induced higher levels of D. citri mortality. These findings reveal 20-mer NCR peptides as a new class of plant-derived biopesticide molecules to control citrus greening disease.

Providing multimedia information to children and young people increases recruitment to trials: pre-planned meta-analysis of SWATs.

BACKGROUND: Randomised controlled trials are often beset by problems with poor recruitment and retention. Information to support decisions on trial participation is usually provided as printed participant information sheets (PIS), which are often long, technical, and unappealing. Multimedia information (MMI), including animations and videos, may be a valuable alternative or complement to a PIS. The Trials Engagement in Children and Adolescents (TRECA) study compared MMI to PIS to investigate the effects on participant recruitment, retention, and quality of decision-making. METHODS: We undertook six SWATs (Study Within A Trial) within a series of host trials recruiting children and young people. Potential participants in the host trials were randomly allocated to receive MMI-only, PIS-only, or combined MMI + PIS. We recorded the rates of recruitment and retention (varying between 6 and 26 weeks post-randomisation) in each host trial. Potential participants approached about each host trial were asked to complete a nine-item Decision-Making Questionnaire (DMQ) to indicate their evaluation of the information and their reasons for participation/non-participation. Odds ratios were calculated and combined in a meta-analysis. RESULTS: Data from 3/6 SWATs for which it was possible were combined in a meta-analysis (n = 1758). Potential participants allocated to MMI-only were more likely to be recruited to the host trial than those allocated to PIS-only (OR 1.54; 95% CI 1.05, 2.28; p = 0.03). Those allocated to combined MMI + PIS compared to PIS-only were no more likely to be recruited to the host trial (OR = 0.89; 95% CI 0.53, 1.50; p = 0.67). Providing MMI rather than PIS did not impact on DMQ scores. Once children and young people had been recruited to host trials, their trial retention rates did not differ according to intervention allocation. CONCLUSIONS: Providing MMI-only increased the trial recruitment rate compared to PIS-only but did not affect DMQ scores. Combined MMI + PIS instead of PIS had no effect on recruitment or retention. MMIs are a useful tool for trial recruitment in children and young people, and they could reduce trial recruitment periods.

Identification of genes required for gold and silver tolerance in Burkholderia cenocepacia H111 by transposon sequencing.

Members of the genus Burkholderia show remarkable abilities to adapt to a wide range of environmental conditions and is frequently isolated from soils contaminated with heavy metals. In this study, we used a transposon sequencing approach to identify 138 and 164 genes that provide a benefit for growth of the opportunistic pathogen Burkholderia cenocepacia H111 in the presence of silver and gold ions respectively. The data suggest that arginine metabolism and citrate biosynthesis are important for silver tolerance, while components of an ABC transporter (BCAL0307-BCAL0308) and de novo cysteine biosynthesis are required for tolerance to gold ions. We show that determinants that affect tolerance to both metal ions include the two-component systems BCAL0497/99 and BCAL2830/31 and genes that are involved in maintaining the integrity of the cell envelope, suggesting that membrane proteins represent important targets of silver and gold ions. Furthermore, we show that that the P-type ATPase CadA (BCAL0055), which confers tolerance to cadmium contributes to silver but not gold tolerance. Our results may be useful for improving the antibacterial effect of silver and gold ions to combat drug-resistant pathogens.

Strain Tracking of 'Candidatus Liberibacter asiaticus', the Citrus Greening Pathogen, by High-Resolution Microbiome Analysis of Asian Citrus Psyllids.

The Asian citrus psyllid, Diaphorina citri, is an invasive insect and a vector of 'Candidatus Liberibacter asiaticus' (CLas), a bacterium whose growth in Citrus species results in huanglongbing (HLB), also known as citrus greening disease. Methods to enrich and sequence CLas from D. citri often rely on biased genome amplification and nevertheless contain significant quantities of host DNA. To overcome these hurdles, we developed a simple pretreatment DNase and filtration (PDF) protocol to remove host DNA and directly sequence CLas and the complete, primarily uncultivable microbiome from D. citri adults. The PDF protocol yielded CLas abundances upward of 60% and facilitated direct measurement of CLas and endosymbiont replication rates in psyllids. The PDF protocol confirmed our lab strains derived from a progenitor Florida CLas strain and accumulated 156 genetic variants, underscoring the utility of this method for bacterial strain tracking. CLas genetic polymorphisms arising in lab-reared psyllid populations included prophage-encoding regions with key functions in CLas pathogenesis, putative antibiotic resistance loci, and a single secreted effector. These variants suggest that laboratory propagation of CLas could result in different phenotypic trajectories among laboratories and could confound CLas physiology or therapeutic design and evaluation if these differences remain undocumented. Finally, we obtained genetic signatures affiliated with Citrus nuclear and organellar genomes, entomopathogenic fungal mitochondria, and commensal bacteria from laboratory-reared and field-collected D. citri adults. Hence, the PDF protocol can directly inform agricultural management strategies related to bacterial strain tracking, insect microbiome surveillance, and antibiotic resistance screening.

An Excised Leaf Assay to Measure Acquisition of 'Candidatus Liberibacter asiaticus' by Psyllids Associated with Citrus Huanglongbing Disease.

Huanglongbing, or citrus greening disease, is the most serious disease of citrus worldwide and is associated with plant infection by 'Candidatus Liberibacter asiaticus' (CLas) and other Liberibacter species. CLas is transmitted by Diaphorina citri, the Asian citrus psyllid, in a circulative propagative manner. Circulative propagative transmission is a complex process comprising at least three steps: movement of the pathogen into vector tissues, translocation and replication of the pathogen within the vector host, and pathogen inoculation of a new host by the vector. In this work, we describe an excised leaf CLas acquisition assay, which enables precise measurements of CLas acquisition by D. citri in a streamlined laboratory assay. Briefly, healthy fourth and fifth instar D. citri nymphs acquire CLas from excised CLas-positive leaves, where the insects also complete their developmental cycle. CLas titer in the resulting adults is measured using quantitative PCR and CLas-specific 16S rRNA gene primers. We observed positive correlations between CLas titer in each leaf replicate and the CLas titer that developed in the insects after acquisition (rs = 0.78; P = 0.0002). This simple assay could be used to detect CLas acquisition phenotypes and their underlying genotypes, facilitate assessment of plant factors that impact acquisition, and screen for compounds that interfere with CLas acquisition by delivering these compounds through the excised leaf.

Proteomic Polyphenism in Color Morphotypes of Diaphorina citri, Insect Vector of Citrus Greening Disease.

Diaphorina citri is a vector of "Candidatus Liberibacter asiaticus" (CLas), associated with citrus greening disease. D. citri exhibit at least two color morphotypes, blue and non-blue, the latter including gray and yellow morphs. Blue morphs have a greater capacity for long-distance flight and transmit CLas less efficiently as compared to non-blue morphs. Differences in physiology and immunity between color morphs of the insect vector may influence disease epidemiology and biological control strategies. We evaluated the effect of CLas infection on color morph and sex-specific proteomic profiles of D. citri. Immunity-associated proteins were more abundant in blue morphs as compared to non-blue morphs but were upregulated at a higher magnitude in response to CLas infection in non-blue insects. To test for differences in color morph immunity, we measured two phenotypes: (1) survival of D. citri when challenged with the entomopathogenic fungus Beauveria bassiana and (2) microbial load of the surface and internal microbial communities. Non-blue color morphs showed higher mortality at four doses of B. bassinana, but no differences in microbial load were observed. Thus, color morph polyphenism is associated with two distinct proteomic immunity phenotypes in D. citri that may impact transmission of CLas and resistance to B. bassiana under some conditions.

The eco-evolutionary significance of rainfall constancy for facultative CAM photosynthesis.

A flexible use of the crassulacean acid metabolism (CAM) has been hypothesised to represent an intermediate stage along a C3 to full CAM evolutionary continuum, when relative contributions of C3 vs CAM metabolism are co-determined by evolutionary history and prevailing environmental constraints. However, evidence for such eco-evolutionary interdependencies is lacking. We studied these interdependencies for the leaf-succulent genus Drosanthemum (Aizoaceae, Southern African Succulent Karoo) by testing for relationships between leaf δ13 C diagnostic for CAM dependence (i.e. contribution of C3 and CAM to net carbon gain), and climatic variables related to temperature and precipitation and their temporal variation. We further quantified the effects of shared phylogenetic ancestry on CAM dependence and its relation to climate. CAM dependence is predicted by rainfall and its temporal variation, with high predictive power of rainfall constancy (temporal entropy). The predictive power of rainfall seasonality and temperature-related variables was negligible. Evolutionary history of the tested clades significantly affected the relationship between rainfall constancy and CAM dependence. We argue that higher CAM dependence might provide an adaptive advantage in increasingly unpredictable rainfall environments when the anatomic exaptation (succulence) is already present. These observations might shed light on the evolution of full CAM.

Large uncertainties in future biome changes in Africa call for flexible climate adaptation strategies.

Anthropogenic climate change is expected to impact ecosystem structure, biodiversity and ecosystem services in Africa profoundly. We used the adaptive Dynamic Global Vegetation Model (aDGVM), which was originally developed and tested for Africa, to quantify sources of uncertainties in simulated African potential natural vegetation towards the end of the 21st century. We forced the aDGVM with regionally downscaled high-resolution climate scenarios based on an ensemble of six general circulation models (GCMs) under two representative concentration pathways (RCPs 4.5 and 8.5). Our study assessed the direct effects of climate change and elevated CO2 on vegetation change and its plant-physiological drivers. Total increase in carbon in aboveground biomass in Africa until the end of the century was between 18% to 43% (RCP4.5) and 37% to 61% (RCP8.5) and was associated with woody encroachment into grasslands and increased woody cover in savannas. When direct effects of CO2 on plants were omitted, woody encroachment was muted and carbon in aboveground vegetation changed between -8 to 11% (RCP 4.5) and -22 to -6% (RCP8.5). Simulated biome changes lacked consistent large-scale geographical patterns of change across scenarios. In Ethiopia and the Sahara/Sahel transition zone, the biome changes forecast by the aDGVM were consistent across GCMs and RCPs. Direct effects from elevated CO2 were associated with substantial increases in water use efficiency, primarily driven by photosynthesis enhancement, which may relieve soil moisture limitations to plant productivity. At the ecosystem level, interactions between fire and woody plant demography further promoted woody encroachment. We conclude that substantial future biome changes due to climate and CO2 changes are likely across Africa. Because of the large uncertainties in future projections, adaptation strategies must be highly flexible. Focused research on CO2 effects, and improved model representations of these effects will be necessary to reduce these uncertainties.

Human impact on the diversity and virulence of the ubiquitous zoonotic parasite Toxoplasma gondii.

A majority of emerging infectious diseases in humans are zoonoses. Understanding factors that influence the emergence and transmission of zoonoses is pivotal for their prevention and control. Toxoplasma gondii is one of the most widespread zoonotic pathogens known today. Whereas only a few genotypes of T. gondii dominate in the Northern Hemisphere, many genotypes coexist in South America. Furthermore, T. gondii strains from South America are more likely to be virulent than those from the Northern Hemisphere. However, it is not clear what factor(s) shaped modern-day genetic diversity and virulence of T. gondii Here, our analysis suggests that the rise and expansion of farming in the past 11,000 years established the domestic cat/mouse transmission cycle for T. gondii, which has undoubtedly played a significant role in the selection of certain linages of T. gondii Our mathematical simulations showed that within the domestic transmission cycle, intermediately mouse-virulent T. gondii genotypes have an adaptive advantage and eventually become dominant due to a balance between lower host mortality and the ability to superinfect mice previously infected with a less virulent T. gondii strain. Our analysis of the global type II lineage of T. gondii suggests its Old World origin but recent expansion in North America, which is likely the consequence of global human migration and trading. These results have significant implications concerning transmission and evolution of zoonotic pathogens in the rapidly expanding anthropized environment demanded by rapid growth of the human population and intensive international trading at present and in the future.

Evaluating the use of multimedia information when recruiting adolescents to orthodontics research: A randomised controlled trial.

OBJECTIVE: To compare two methods of providing information about the Bone Anchored Maxillary Protraction (BAMP) trial: standard printed information and multimedia websites, for their quality and ease of understanding, and impact on decision-making. DESIGN: Randomised controlled trial. SETTING: Orthodontic outpatient clinic in the UK. METHODS: Participants were 109 adolescents (aged 11-14 years) attending for orthodontic treatment. While awaiting treatment they were asked to imagine being recruited to the BAMP clinical trial. They were individually randomised to receive the printed or the multimedia website information (comprising text, animations and 'talking head' videos). After reading or viewing the information, they completed a 9-item Likert scale Decision-Making Questionnaire (DMQ) (score range 0-36) plus three free-text questions on their evaluation of the information. RESULTS: A total of 104 participants completed the questionnaire. Mean total DMQ scores were higher (more positive) in the website group (28.1 vs. 27.0), although the difference was small and not statistically significant (P = 0.20). Analysis of individual questionnaire items showed two statistically significant differences: the website information had higher ratings on 'easy to understand' (Z = 3.03; P = 0.003) and 'confidence in decision-making' (Z = 2.00; P = 0.044). On the three free-text questions, more positive and fewer negative comments were made about the websites than the printed information. CONCLUSION: In this hypothetical trial setting, adolescent patients found that trial information conveyed on a multimedia website was easier to understand and made them more confident in their decision about trial participation. Their subjective evaluations of the website were also more positive and less negative than about the printed information. Multimedia information has the potential to increase the quality of engagement and information exchange when seeking consent for research.

Metagenome-Guided Proteomic Quantification of Reductive Dehalogenases in the Dehalococcoides mccartyi-Containing Consortium SDC-9.

At groundwater sites contaminated with chlorinated ethenes, fermentable substrates are often added to promote reductive dehalogenation by indigenous or augmented microorganisms. Contemporary bioremediation performance monitoring relies on nucleic acid biomarkers of key organohalide-respiring bacteria, such as Dehalococcoides mccartyi (Dhc). Metagenome sequencing of the commercial, Dhc-containing consortium, SDC-9, identified 12 reductive dehalogenase (RDase) genes, including pceA (two copies), vcrA, and tceA, and allowed for specific detection and quantification of RDase peptides using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Shotgun (i.e., untargeted) proteomics applied to the SDC-9 consortium grown with tetrachloroethene (PCE) and lactate identified 143 RDase peptides, and 36 distinct peptides that covered greater than 99% of the protein-coding sequences of the PceA, TceA, and VcrA RDases. Quantification of RDase peptides using multiple reaction monitoring (MRM) assays with 13C-/15N-labeled peptides determined 1.8 × 103 TceA and 1.2 × 102 VcrA RDase molecules per Dhc cell. The MRM mass spectrometry approach allowed for sensitive detection and accurate quantification of relevant Dhc RDases and has potential utility in bioremediation monitoring regimes.

Assessing the Risks Associated with MRI in Patients with a Pacemaker or Defibrillator.

BACKGROUND: The presence of a cardiovascular implantable electronic device has long been a contraindication for the performance of magnetic resonance imaging (MRI). We established a prospective registry to determine the risks associated with MRI at a magnetic field strength of 1.5 tesla for patients who had a pacemaker or implantable cardioverter-defibrillator (ICD) that was "non-MRI-conditional" (i.e., not approved by the Food and Drug Administration for MRI scanning). METHODS: Patients in the registry were referred for clinically indicated nonthoracic MRI at a field strength of 1.5 tesla. Devices were interrogated before and after MRI with the use of a standardized protocol and were appropriately reprogrammed before the scanning. The primary end points were death, generator or lead failure, induced arrhythmia, loss of capture, or electrical reset during the scanning. The secondary end points were changes in device settings. RESULTS: MRI was performed in 1000 cases in which patients had a pacemaker and in 500 cases in which patients had an ICD. No deaths, lead failures, losses of capture, or ventricular arrhythmias occurred during MRI. One ICD generator could not be interrogated after MRI and required immediate replacement; the device had not been appropriately programmed per protocol before the MRI. We observed six cases of self-terminating atrial fibrillation or flutter and six cases of partial electrical reset. Changes in lead impedance, pacing threshold, battery voltage, and P-wave and R-wave amplitude exceeded prespecified thresholds in a small number of cases. Repeat MRI was not associated with an increase in adverse events. CONCLUSIONS: In this study, device or lead failure did not occur in any patient with a non-MRI-conditional pacemaker or ICD who underwent clinically indicated nonthoracic MRI at 1.5 tesla, was appropriately screened, and had the device reprogrammed in accordance with the prespecified protocol. (Funded by St. Jude Medical and others; MagnaSafe ClinicalTrials.gov number, NCT00907361 .).

An operational definition of the biome for global change research.

Biomes are constructs for organising knowledge on the structure and functioning of the world's ecosystems, and serve as useful units for monitoring how the biosphere responds to anthropogenic drivers, including climate change. The current practice of delimiting biomes relies on expert knowledge. Recent studies have questioned the value of such biome maps for comparative ecology and global-change research, partly due to their subjective origin. Here we propose a flexible method for developing biome maps objectively. The method uses range modelling of several thousands of plant species to reveal spatial attractors for different growth-form assemblages that define biomes. The workflow is illustrated using distribution data from 23 500 African plant species. In an example application, we create a biome map for Africa and use the fitted species models to project biome shifts. In a second example, we map gradients of growth-form suitability that can be used to identify sites for comparative ecology. This method provides a flexible framework that (1) allows a range of biome types to be defined according to user needs and (2) enables projections of biome changes that emerge purely from the individualistic responses of plant species to environmental changes.

Proteogenomics Reveals Novel Reductive Dehalogenases and Methyltransferases Expressed during Anaerobic Dichloromethane Metabolism.

Dichloromethane (DCM) is susceptible to microbial degradation under anoxic conditions and is metabolized via the Wood-Ljungdahl pathway; however, mechanistic understanding of carbon-chlorine bond cleavage is lacking. The microbial consortium RM contains the DCM degrader "Candidatus Dichloromethanomonas elyunquensis" strain RM, which strictly requires DCM as a growth substrate. Proteomic workflows applied to DCM-grown consortium RM biomass revealed a total of 1,705 nonredundant proteins, 521 of which could be assigned to strain RM. In the presence of DCM, strain RM expressed a complete set of Wood-Ljungdahl pathway enzymes, as well as proteins implicated in chemotaxis, motility, sporulation, and vitamin/cofactor synthesis. Four corrinoid-dependent methyltransferases were among the most abundant proteins. Notably, two of three putative reductive dehalogenases (RDases) encoded within strain RM's genome were also detected in high abundance. Expressed RDase 1 and RDase 2 shared 30% amino acid identity, and RDase 1 was most similar to an RDase of Dehalococcoides mccartyi strain WBC-2 (AOV99960, 52% amino acid identity), while RDase 2 was most similar to an RDase of Dehalobacter sp. strain UNSWDHB (EQB22800, 72% amino acid identity). Although the involvement of RDases in anaerobic DCM metabolism has yet to be experimentally verified, the proteome characterization results implicated the possible participation of one or more reductive dechlorination steps and methyl group transfer reactions, leading to a revised proposal for an anaerobic DCM degradation pathway.IMPORTANCE Naturally produced and anthropogenically released DCM can reside in anoxic environments, yet little is known about the diversity of organisms, enzymes, and mechanisms involved in carbon-chlorine bond cleavage in the absence of oxygen. A proteogenomic approach identified two RDases and four corrinoid-dependent methyltransferases expressed by the DCM degrader "Candidatus Dichloromethanomonas elyunquensis" strain RM, suggesting that reductive dechlorination and methyl group transfer play roles in anaerobic DCM degradation. These findings suggest that the characterized DCM-degrading bacterium Dehalobacterium formicoaceticum and "Candidatus Dichloromethanomonas elyunquensis" strain RM utilize distinct strategies for carbon-chlorine bond cleavage, indicating that multiple pathways evolved for anaerobic DCM metabolism. The specific proteins (e.g., RDases and methyltransferases) identified in strain RM may have value as biomarkers for monitoring anaerobic DCM degradation in natural and contaminated environments.

A Raman-Based Imaging Method for Characterizing the Molecular Adsorption and Spatial Distribution of Silver Nanoparticles on Hydrated Mineral Surfaces.

Although minerals are known to affect the environmental fate and transformation of heavy-metal ions, little is known about their interaction with the heavily exploited silver nanoparticles (AgNPs). Proposed here is a combination of hitherto under-utilized micro-Raman-based mapping and chemometric methods for imaging the distribution of AgNPs on various mineral surfaces and their molecular interaction mechanisms. The feasibility of the Raman-based imaging method was tested on two macro- and microsized mineral models, muscovite [KAl2(AlSi3O10)(OH)2] and corundum (α-Al2O3), under key environmental conditions (ionic strength and pH). Both AgNPs- and AgNPs+ were found to covalently attach to corundum (pHpzc = 9.1) through the formation of Ag-O-Al- bonds and thereby to potentially experience reduced environmental mobility. Because label-free Raman imaging showed no molecular interactions between AgNPs- and muscovite (pHpzc = 7.5), a label-enhanced Raman imaging approach was developed for mapping the scarce spatial distribution of AgNPs- on such mineral surfaces. Raman maps comprising of n = 625-961 spectra for each sample/control were rapidly analyzed in Vespucci, a free open-source software, and the results were confirmed via ICP-OES, AFM, and SEM-EDX. The proposed Raman-based imaging requires minimum to no sample preparation; is sensitive, noninvasive, cost-effective; and might be extended to other environmentally relevant systems.

Atmospheric CO2 forces abrupt vegetation shifts locally, but not globally.

It is possible that anthropogenic climate change will drive the Earth system into a qualitatively different state. Although different types of uncertainty limit our capacity to assess this risk, Earth system scientists are particularly concerned about tipping elements, large-scale components of the Earth system that can be switched into qualitatively different states by small perturbations. Despite growing evidence that tipping elements exist in the climate system, whether large-scale vegetation systems can tip into alternative states is poorly understood. Here we show that tropical grassland, savanna and forest ecosystems, areas large enough to have powerful impacts on the Earth system, are likely to shift to alternative states. Specifically, we show that increasing atmospheric CO2 concentration will force transitions to vegetation states characterized by higher biomass and/or woody-plant dominance. The timing of these critical transitions varies as a result of between-site variance in the rate of temperature increase, as well as a dependence on stochastic variation in fire severity and rainfall. We further show that the locations of bistable vegetation zones (zones where alternative vegetation states can exist) will shift as climate changes. We conclude that even though large-scale directional regime shifts in terrestrial ecosystems are likely, asynchrony in the timing of these shifts may serve to dampen, but not nullify, the shock that these changes may represent to the Earth system.

The Essential Genome of Burkholderia cenocepacia H111.

The study of the minimum set of genes required to sustain life is a fundamental question in biological research. Recent studies on bacterial essential genes suggested that between 350 and 700 genes are essential to support autonomous bacterial cell growth. Essential genes are of interest as potential new antimicrobial drug targets; hence, our aim was to identify the essential genome of the cystic fibrosis (CF) isolate Burkholderia cenocepacia H111. Using a transposon sequencing (Tn-Seq) approach, we identified essential genes required for growth in rich medium under aerobic and microoxic conditions as well as in a defined minimal medium with citrate as a sole carbon source. Our analysis suggests that 398 genes are required for autonomous growth in rich medium, a number that represents only around 5% of the predicted genes of this bacterium. Five hundred twenty-six genes were required to support growth in minimal medium, and 434 genes were essential under microoxic conditions (0.5% O2). A comparison of these data sets identified 339 genes that represent the minimal set of essential genes required for growth under all conditions tested and can be considered the core essential genome of B. cenocepacia H111. The majority of essential genes were found to be located on chromosome 1, and few such genes were located on chromosome 2, where most of them were clustered in one region. This gene cluster is fully conserved in all Burkholderia species but is present on chromosome 1 in members of the closely related genus Ralstonia, suggesting that the transfer of these essential genes to chromosome 2 in a common ancestor contributed toward the separation of the two genera.IMPORTANCE Transposon sequencing (Tn-Seq) is a powerful method used to identify genes that are essential for autonomous growth under various conditions. In this study, we have identified a set of "core essential genes" that are required for growth under multiple conditions, and these genes represent potential antimicrobial targets. We also identified genes specifically required for growth under low-oxygen and nutrient-limited environments. We generated conditional mutants to verify the results of our Tn-Seq analysis and demonstrate that one of the identified genes was not essential per se but was an artifact of the construction of the mutant library. We also present verified examples of genes that were not truly essential but, when inactivated, showed a growth defect. These examples have identified so-far-underestimated shortcomings of this powerful method.

Allometric equations for integrating remote sensing imagery into forest monitoring programmes.

Remote sensing is revolutionizing the way we study forests, and recent technological advances mean we are now able - for the first time - to identify and measure the crown dimensions of individual trees from airborne imagery. Yet to make full use of these data for quantifying forest carbon stocks and dynamics, a new generation of allometric tools which have tree height and crown size at their centre are needed. Here, we compile a global database of 108753 trees for which stem diameter, height and crown diameter have all been measured, including 2395 trees harvested to measure aboveground biomass. Using this database, we develop general allometric models for estimating both the diameter and aboveground biomass of trees from attributes which can be remotely sensed - specifically height and crown diameter. We show that tree height and crown diameter jointly quantify the aboveground biomass of individual trees and find that a single equation predicts stem diameter from these two variables across the world's forests. These new allometric models provide an intuitive way of integrating remote sensing imagery into large-scale forest monitoring programmes and will be of key importance for parameterizing the next generation of dynamic vegetation models.