High CO2 dampens then amplifies N-induced diversity loss over 24 years.

Rising levels of atmospheric carbon dioxide (CO2) and nitrogen (N) deposition affect plant communities in numerous ways1-11. Nitrogen deposition causes local biodiversity loss globally12-14, but whether, and if so how, rising CO2 concentrations amplify or dampen those losses remains unclear and is almost entirely unstudied. We addressed this knowledge gap with an open-air experiment in which 108 grassland plots were grown for 24 years under different CO2 and N regimes. We initially found that adding N reduced plant species richness less at elevated than at ambient CO2. Over time, however, this interaction reversed, and elevated CO2 amplified losses in diversity from enriched N, tripling reductions in species richness from N addition over the last eight years of the study. These interactions resulted from temporal changes in the drivers of diversity, especially light availability, that were in turn driven by CO2 and N inputs and associated changes in plant biomass. This mechanism is likely to be similar in many grasslands, because additions of the plant resources CO2 and N are likely to increase the abundance of the dominant species. If rising CO2 generally exacerbates the widespread negative impacts of N deposition on plant diversity, this bodes poorly for the conservation of grassland biodiversity worldwide.

Global spatially explicit yield gap time trends reveal regions at risk of future crop yield stagnation.

Yield gaps, here defined as the difference between actual and attainable yields, provide a framework for assessing opportunities to increase agricultural productivity. Previous global assessments, centred on a single year, were unable to identify temporal variation. Here we provide a spatially and temporally comprehensive analysis of yield gaps for ten major crops from 1975 to 2010. Yield gaps have widened steadily over most areas for the eight annual crops and remained static for sugar cane and oil palm. We developed a three-category typology to differentiate regions of 'steady growth' in actual and attainable yields, 'stalled floor' where yield is stagnated and 'ceiling pressure' where yield gaps are closing. Over 60% of maize area is experiencing 'steady growth', in contrast to ∼12% for rice. Rice and wheat have 84% and 56% of area, respectively, experiencing 'ceiling pressure'. We show that 'ceiling pressure' correlates with subsequent yield stagnation, signalling risks for multiple countries currently realizing gains from yield growth.

Higher versus lower oxygenation targets in adult ICU patients: A rapid practice guideline.

The aim of this Intensive Care Medicine Rapid Practice Guideline (ICM-RPG) was to provide evidence-based clinical guidance about the use of higher versus lower oxygenation targets for adult patients in the intensive care unit (ICU). The guideline panel comprised 27 international panelists, including content experts, ICU clinicians, methodologists, and patient representatives. We adhered to the methodology for trustworthy clinical practice guidelines, including the use of the Grading of Recommendations Assessment, Development, and Evaluation approach to assess the certainty of evidence, and used the Evidence-to-Decision framework to generate recommendations. A recently published updated systematic review and meta-analysis constituted the evidence base. Through teleconferences and web-based discussions, the panel provided input on the balance and magnitude of the desirable and undesirable effects, the certainty of evidence, patients' values and preferences, costs and resources, equity, feasibility, acceptability, and research priorities. The updated systematic review and meta-analysis included data from 17 randomized clinical trials with 10,248 participants. There was little to no difference between the use of higher versus lower oxygenation targets for all outcomes with available data, including all-cause mortality, serious adverse events, stroke, functional outcomes, cognition, and health-related quality of life (very low certainty of evidence). The panel felt that values and preferences, costs and resources, and equity favored the use of lower oxygenation targets. The ICM-RPG panel issued one conditional recommendation against the use of higher oxygenation targets: "We suggest against the routine use of higher oxygenation targets in adult ICU patients (conditional recommendation, very low certainty of evidence). Remark: an oxygenation target of SpO2 88%-92% or PaO2 8 kPa/60 mmHg is relevant and safe for most adult ICU patients."

Accounting for herbaceous communities in process-based models will advance our understanding of "grassy" ecosystems.

Grassland and other herbaceous communities cover significant portions of Earth's terrestrial surface and provide many critical services, such as carbon sequestration, wildlife habitat, and food production. Forecasts of global change impacts on these services will require predictive tools, such as process-based dynamic vegetation models. Yet, model representation of herbaceous communities and ecosystems lags substantially behind that of tree communities and forests. The limited representation of herbaceous communities within models arises from two important knowledge gaps: first, our empirical understanding of the principles governing herbaceous vegetation dynamics is either incomplete or does not provide mechanistic information necessary to drive herbaceous community processes with models; second, current model structure and parameterization of grass and other herbaceous plant functional types limits the ability of models to predict outcomes of competition and growth for herbaceous vegetation. In this review, we provide direction for addressing these gaps by: (1) presenting a brief history of how vegetation dynamics have been developed and incorporated into earth system models, (2) reporting on a model simulation activity to evaluate current model capability to represent herbaceous vegetation dynamics and ecosystem function, and (3) detailing several ecological properties and phenomena that should be a focus for both empiricists and modelers to improve representation of herbaceous vegetation in models. Together, empiricists and modelers can improve representation of herbaceous ecosystem processes within models. In so doing, we will greatly enhance our ability to forecast future states of the earth system, which is of high importance given the rapid rate of environmental change on our planet.

Stomatal behaviour moderates the water cost of CO2 acquisition for 21 boreal and temperate species under experimental climate change.

The linkage of stomatal behaviour with photosynthesis is critical to understanding water and carbon cycles under global change. The relationship of stomatal conductance (gs ) and CO2 assimilation (Anet ) across a range of environmental contexts, as represented in the model parameter (g1 ), has served as a proxy of the marginal water cost of carbon acquisition. We use g1 to assess species differences in stomatal behaviour to a decade of open-air experimental climate change manipulations, asking whether generalisable patterns exist across species and climate contexts. Anet -gs measurements (17 727) for 21 boreal and temperate tree species under ambient and +3.3°C warming, and ambient and ~40% summer rainfall reduction, provided >2700 estimates of g1 . Warming and/or reduced rainfall treatments both lowered g1 because those treatments resulted in lower soil moisture and because stomatal behaviour changed more in warming when soil moisture was low. Species tended to respond similarly, although, in species from warmer and drier habitats, g1 tended to be slightly higher and to be the least sensitive to the decrease in soil water. Overall, both warming and rainfall reduction consistently made stomatal behaviour more conservative in terms of water loss per unit carbon gain across 21 species and a decade of experimental observation.

Enhanced light interception and light use efficiency explain overyielding in young tree communities.

Diverse plant communities are often more productive than mono-specific ones. Several possible mechanisms underlie this phenomenon but their relative importance remains unknown. Here we investigated whether light interception alone or in combination with light use efficiency (LUE) of dominant and subordinate species explained greater productivity of mixtures relative to monocultures (i.e. overyielding) in 108 young experimental tree communities. We found mixed-species communities that intercepted more light than their corresponding monocultures had 84% probability of overyielding. Enhanced LUE, which arose via several pathways, also mattered: the probability of overyielding was 71% when, in a mixture, species with higher 'inherent' LUE (i.e. LUE in monoculture) intercepted more light than species with lower LUE; 94% when dominant species increased their LUE in mixture; and 79% when subordinate species increased their LUE. Our results suggest that greater light interception and greater LUE, generated by inter and intraspecific variation, together drive overyielding in mixed-species forests.

Prospective, observational study of carbon dioxide gaps and free energy change and their association with fluid therapy following cardiac surgery.

Background Venoarterial carbon dioxide pressure (pv-a CO2 ) and content (Cv-a CO2 ) differences, including the ratio to arteriovenous oxygen content difference (Ca-v O2 ), and free energy changes (-∆∆Ga-v ) may reflect tissue hypoperfusion. The associations with changes in cardiac output (CO) or oxygen consumption (VO2 ) following fluid bolus administration were investigated. Methods Single-centre, observational study of 89 adult post-operative cardiac surgical patients admitted to ICU. The pv-a CO2 , Cv-a CO2 and their ratios to Ca-v O2 as well as the -∆∆Ga-v were determined before and after a 250-500 mL fluid bolus using arterial, central venous and mixed venous blood gas analyses. Responses associated with changes ≥ or <15% in CO or oxygen consumption (VO2 ) were compared. Results In 234 boluses, the mixed venous to arterial pv-a CO2 and its ratio to Ca-v O2 were independently associated with an increase in CO; odds ratio 1.3 (95% CI 1.1-1.5) and 1.7 (95% CI 1.5-1.9) respectively, P < .001) and VO2 ; odds ratio 2.1 (95% CI 1.3-3.1), P < .001 for Ca-v O2 . No measures of pv-a CO2 , Cv-a CO2 or related ratios to the Ca-v O2 were associated with an increase in CO ≥15% following a single volume bolus. The mixed venous and central venous Cv-a CO2 to Ca-v O2 ratios were different for the first bolus episode only; mean differences 0.81 (95% CI 0.13-1.5), P = .02 and 0.44 (95% CI 0.06-0.82), P = .02, respectively, for increased VO2  ≥ 15%. The -∆∆Ga-v did not change. Conclusion The venoarterial carbon dioxide gradients and related calculations to assess the adequacy of tissue perfusion before a fluid bolus were not associated with subsequent increases in CO of oxygen consumption. Editorial Comment In some shock conditions, regional tissue hypoperfusion can be obvious and arterio-venous differences for CO2 or O2 may reflect this. This is not always the case; sometimes there are A-V differences or even a high lactate level without any obvious regional tissue hypoperfusion. Fluid therapy is a cornerstone in shock resuscitation treatment, but determining optimal fluid therapy is challenging, particularly as fluid overload may be detrimental. Fluid challenges are used as an "ex juvantebus" method to dose fluid therapy, but it is not clear if a positive response reflects a state of hypoperfusion or the existence of a cardiac reserve. Still, a better understanding on how to target and guide fluid therapy is welcome, and studies digging into the problem are needed. Here, invasively monitored post-operative cardiac surgery patients are assessed as a model to investigate if carbon dioxide gaps and free energy charge may be useful in detecting possible tissue hypoperfusion.

The effect of systemic corticosteroids on the incidence of gastrointestinal bleeding in critically ill adults: a systematic review with meta-analysis.

PURPOSE: To assess the effect of systemic corticosteroids on the incidence of gastrointestinal bleeding in adult critically ill patients. METHODS: We systematically reviewed randomised clinical trials comparing systemic corticosteroids administered for more than 24 h with placebo/no treatment in adult critically ill patients. Trial selection, data abstraction and risk of bias assessments were performed in duplicate. We used trial sequential analysis (TSA) to assess the risk of random errors and the grading of recommendations, assessment, development, and evaluations (GRADE) approach to assess the quality of evidence. The primary outcome was the incidence of clinically important gastrointestinal bleeding within 90 days. The secondary outcome was the incidence of gastrointestinal bleeding of any severity within 90 days. RESULTS: Twenty-five trials (n = 14,615) reported data for the primary outcome and 55 trials (n = 21,792) for the secondary outcome. The pooled incidence of clinically important gastrointestinal bleeding was 2.3% in the corticosteroid group and 1.8% in the control group (RR, 1.26; 95% CI, 1.01-1.57; I2 = 0%, TSA-adjusted CI 0.51-3.14). We observed no difference in the risk of gastrointestinal bleeding of any severity (RR, 1.10; 95% CI, 0.92-1.32; I2 = 0%, TSA-adjusted CI 0.87-1.38). The GRADE quality of evidence was low (risk of bias and imprecision). CONCLUSIONS: We observed an overall low incidence of clinically important gastrointestinal bleeding among adult critically ill patients. Corticosteroids may slightly increase the incidence of clinically important gastrointestinal bleeding, but not bleeding of any severity. Rarity of events, infrequent trial reporting and high risk of bias reduced the quality of evidence.

Peculiarly pleasant weather for US maize.

Continuation of historical trends in crop yield are critical to meeting the demands of a growing and more affluent world population. Climate change may compromise our ability to meet these demands, but estimates vary widely, highlighting the importance of understanding historical interactions between yield and climate trends. The relationship between temperature and yield is nuanced, involving differential yield outcomes to warm ([Formula: see text]C) and hot ([Formula: see text]C) temperatures and differing sensitivity across growth phases. Here, we use a crop model that resolves temperature responses according to magnitude and growth phase to show that US maize has benefited from weather shifts since 1981. Improvements are related to lengthening of the growing season and cooling of the hottest temperatures. Furthermore, current farmer cropping schedules are more beneficial in the climate of the last decade than they would have been in earlier decades, indicating statistically significant adaptation to a changing climate of 13 kg·ha-1· decade-1 All together, the better weather experienced by US maize accounts for 28% of the yield trends since 1981. Sustaining positive trends in yield depends on whether improvements in agricultural climate continue and the degree to which farmers adapt to future climates.

Low-dose corticosteroids for adult patients with septic shock: a systematic review with meta-analysis and trial sequential analysis.

PURPOSE: To assess the effect of low dose corticosteroids on outcomes in adults with septic shock. METHODS: We systematically reviewed randomised clinical trials (RCTs) comparing low-dose corticosteroids to placebo in adults with septic shock. Trial selection, data abstraction and risk of bias assessment were performed in duplicate. The primary outcome was short-term mortality. Secondary and tertiary outcomes included longer-term mortality, adverse events, quality of life, and duration of shock, mechanical ventilation and ICU stay. RESULTS: There were 22 RCTs, including 7297 participants, providing data on short-term mortality. In two low risk of bias trials, the relative risk (RR) of short-term mortality with corticosteroid versus placebo was 0.98 [95% confidence interval (CI) 0.89-1.08, p = 0.71]. Sensitivity analysis including all trials was similar (RR 0.96; 95% CI 0.91-1.02, p = 0.21) as was analysis of longer-term mortality (RR 0.96; 95% CI 0.90-1.02, p = 0.18). In low risk of bias trials, the risk of experiencing any adverse event was higher with corticosteroids; however, there was substantial heterogeneity (RR 1.66; 95% CI 1.03-2.70, p = 0.04, I2 = 78%). No trials reported quality of life outcomes. Duration of shock [mean difference (MD) -1.52 days; 95% CI -1.71 to -1.32, p < 0.0001], duration of mechanical ventilation (MD -1.38 days; 95% CI -1.96 to -0.80, p < 0.0001), and ICU stay (MD -0.75 days; 95% CI -1.34 to -0.17, p = 0.01) were shorter with corticosteroids versus placebo. CONCLUSIONS: In adults with septic shock treated with low dose corticosteroids, short- and longer-term mortality are unaffected, adverse events increase, but duration of shock, mechanical ventilation and ICU stay are reduced. PROSPERO registration no. CRD42017084037.

Microvascular reactivity, assessed by near-infrared spectroscopy and a vascular occlusion test, is associated with patient outcomes following cardiac surgery: A prospective observational study.

BACKGROUND: Microvascular dysfunction in patients admitted to the ICU following cardiac surgery may be related to perioperative complications and increased resource utilisation even in the presence of acceptable systemic haemodynamic variables. OBJECTIVES: To assess the relationship between microvascular impairment using peripheral near-infrared spectroscopy at ICU admission and 6 h postadmission and the duration of mechanical ventilatory support, length of stay in ICU and in hospital. DESIGN: Prospective, observational cohort study. SETTING: Single-centre, tertiary-level cardiac ICU. PATIENTS: Sixty-nine adult patients following elective cardiac surgery excluding patients with on-going extracorporeal support or in whom tissue haemoglobin oxygen saturation (StO2) measurements were not feasible. MAIN OUTCOME MEASURES: Thenar and forearm StO2 in response to a vascular occlusion test to calculate desaturation and reperfusion slopes. A logistic regression model was used to ascertain the associations between StO2, desaturation and reperfusion slopes as well as cardiac index, mean arterial pressure, arterial lactate concentrations and prolonged (≥75th percentile) duration of mechanical ventilation, ICU length of stay and hospital length of stay. RESULTS: A reduced reperfusion slope at ICU admission was associated independently with prolonged mechanical ventilation at thenar (OR 0.08; 95% CI [0.02 to 0.47], P = 0.003) and forearm [OR 0.2 (0.04 to 0.59), P = 0.006] sites. Similarly, a reduced Rres was associated with prolonged ICU LOS at both thenar [OR 0.3 (0.13 to 0.77), P = 0.007] and forearm [OR 0.2 (0.05 to 0.62), P = 0.007] sites at ICU0 h, as well as ICU6 h [OR 0.2 (0.05 to 0.66), P = 0.004 and OR 0.05 (0.008 to 0.34), P = 0.002]. An increased Rdes was associated with prolonged hospital LOS at the thenar eminence at ICU0 h [OR 1.9 (1.4 to 2.3), P = 0.004] and ICU6 h [OR 6.7 (2.0 to 23), P = 0.002] as well as the forearm at ICU0 h [OR 1.5 (1.3 to 1.9), P = 0.004] and ICU6 h [OR 1.6 (1.3 to 2.1), P = 0.004]. CONCLUSION: In the early postoperative period following cardiac surgery, changes in thenar and forearm tissue oxygenation variables are associated with patient resource utilisation outcomes.

Fluid Responsiveness After CArdiac Surgery (FRACAS): A Prospective Observational Study Using Peripheral Near-Infrared Spectroscopy.

OBJECTIVES: To describe tissue oxygen saturation (StO2) in response to a vascular occlusion test using thenar eminence and forearm near-infrared spectroscopy (NIRS) and the association with volume responsiveness after cardiac surgery. DESIGN: Single-center, prospective, observational cohort study. SETTING: Cardiothoracic intensive care unit. PARTICIPANTS: Seventy-six post-cardiac surgical adults. INTERVENTIONS: Immediately before and 10 minutes after a 250-to-500 mL fluid bolus, StO2 was measured in response to a vascular occlusion test to calculate tissue deoxygenation (Rdes) and reoxygenation (Rres) rates. Concurrently, systemic hemodynamic, metabolic, and blood gas variables were collected. MEASUREMENTS AND MAIN RESULTS: A total of 203 boluses were captured using thenar NIRS and 141 boluses using forearm NIRS. Approximately 25% of boluses increased cardiac output by ≥15% (volume responders). Thenar and forearm Rdes decreased in responders, but increased (thenar) or remained unchanged (forearm) in nonresponders. A logistic regression model of the association among StO2, Rdes and Rres, and volume responsiveness was significant for thenar measurements (p = 0.001) with an area under the receiver operating characteristic of 0.69 (95% confidence interval: 0.62-0.75). It also was significant (p = 0.02) for forearm measurements, with an area under the receiver operating characteristic of 0.71 (0.62-0.79). Rdes was an independent variable in both instances (odds ratio 0.31 [0.14-0.69], thenar; odds ratio 0.60 [0.45-0.80], forearm). Thenar and forearm NIRS variables were correlated poorly with cardiac output, stroke volume, systemic oxygen delivery and consumption index, mixed venous, and central venous oxygen saturation (Spearman׳s coefficients, r = 0.17-0.46, p < 0.002). CONCLUSION: In post-cardiac surgical patients, thenar and forearm NIRS variables were associated with volume responsiveness although not achieving precision necessary for clinical management.

Mapping local and global variability in plant trait distributions.

Our ability to understand and predict the response of ecosystems to a changing environment depends on quantifying vegetation functional diversity. However, representing this diversity at the global scale is challenging. Typically, in Earth system models, characterization of plant diversity has been limited to grouping related species into plant functional types (PFTs), with all trait variation in a PFT collapsed into a single mean value that is applied globally. Using the largest global plant trait database and state of the art Bayesian modeling, we created fine-grained global maps of plant trait distributions that can be applied to Earth system models. Focusing on a set of plant traits closely coupled to photosynthesis and foliar respiration-specific leaf area (SLA) and dry mass-based concentrations of leaf nitrogen ([Formula: see text]) and phosphorus ([Formula: see text]), we characterize how traits vary within and among over 50,000 [Formula: see text]-km cells across the entire vegetated land surface. We do this in several ways-without defining the PFT of each grid cell and using 4 or 14 PFTs; each model's predictions are evaluated against out-of-sample data. This endeavor advances prior trait mapping by generating global maps that preserve variability across scales by using modern Bayesian spatial statistical modeling in combination with a database over three times larger than that in previous analyses. Our maps reveal that the most diverse grid cells possess trait variability close to the range of global PFT means.

Implications of improved representations of plant respiration in a changing climate.

Land-atmosphere exchanges influence atmospheric CO2. Emphasis has been on describing photosynthetic CO2 uptake, but less on respiration losses. New global datasets describe upper canopy dark respiration (R d) and temperature dependencies. This allows characterisation of baseline R d, instantaneous temperature responses and longer-term thermal acclimation effects. Here we show the global implications of these parameterisations with a global gridded land model. This model aggregates R d to whole-plant respiration R p, driven with meteorological forcings spanning uncertainty across climate change models. For pre-industrial estimates, new baseline R d increases R p and especially in the tropics. Compared to new baseline, revised instantaneous response decreases R p for mid-latitudes, while acclimation lowers this for the tropics with increases elsewhere. Under global warming, new R d estimates amplify modelled respiration increases, although partially lowered by acclimation. Future measurements will refine how R d aggregates to whole-plant respiration. Our analysis suggests R p could be around 30% higher than existing estimates.

Random Forests for Global and Regional Crop Yield Predictions.

Accurate predictions of crop yield are critical for developing effective agricultural and food policies at the regional and global scales. We evaluated a machine-learning method, Random Forests (RF), for its ability to predict crop yield responses to climate and biophysical variables at global and regional scales in wheat, maize, and potato in comparison with multiple linear regressions (MLR) serving as a benchmark. We used crop yield data from various sources and regions for model training and testing: 1) gridded global wheat grain yield, 2) maize grain yield from US counties over thirty years, and 3) potato tuber and maize silage yield from the northeastern seaboard region. RF was found highly capable of predicting crop yields and outperformed MLR benchmarks in all performance statistics that were compared. For example, the root mean square errors (RMSE) ranged between 6 and 14% of the average observed yield with RF models in all test cases whereas these values ranged from 14% to 49% for MLR models. Our results show that RF is an effective and versatile machine-learning method for crop yield predictions at regional and global scales for its high accuracy and precision, ease of use, and utility in data analysis. RF may result in a loss of accuracy when predicting the extreme ends or responses beyond the boundaries of the training data.

Exploiting multi-layered vector spaces for signal peptide detection.

Analysing and classifying sequences based on similarities and differences is a mathematical problem of escalating relevance and importance in many scientific disciplines. One of the primary challenges in applying machine learning algorithms to sequential data, such as biological sequences, is the extraction and representation of significant features from the data. To address this problem, we have recently developed a representation, entitled Multi-Layered Vector Spaces (MLVS), which is a simple mathematical model that maps sequences into a set of MLVS. We demonstrate the usefulness of the model by applying it to the problem of identifying signal peptides. MLVS feature vectors are generated from a collection of protein sequences and the resulting vectors are used to create support vector machine classifiers. Experiments show that the MLVS-based classifiers are able to outperform or perform on par with several existing methods that are specifically designed for the purpose of identifying signal peptides.