Path-dependence of the Plio-Pleistocene glacial/interglacial cycles.

We find strong path dependence in the evolution of the Plio-Pleistocene glaciations using CLIMBER-2 Earth System Model simulations from the mid-Pliocene to modern preindustrial (3 My-0 My BP) driven by a gradual decrease in volcanic carbon dioxide outgassing and regolith removal from basal ice interaction. Path dependence and hysteresis are investigated by alternatively driving the model forward and backward in time. Initiating the model with preindustrial conditions and driving the model backward using time-reversed forcings, the increase in volcanic outgassing back-in-time (BIT) does not generate the high CO2 levels and relatively ice-free conditions of the late Pliocene seen in forward-in-time (FIT) simulations of the same model. This behavior appears to originate from nonlinearities and initial state dependence in the carbon cycle. A transition from low-amplitude sinusoidal obliquity (~41 ky) and precession (~23 ky) driven glacial/interglacial cycles to high-amplitude ~100 ky likely eccentricity-related sawtooth cycles seen between -1.25 My and -0.75 My BP (the Mid-Pleistocene transition or "MPT") in FIT simulations disappears in BIT integrations depending on the details of how the regolith removal process is treated. A transition toward depleted regolith and lowered atmospheric CO2 levels are both required to reproduce the MPT.

Episodic fluid venting from sedimentary basins fueled by pressurized mudstones.

Subsurface sandstone reservoirs sealed by overlying, low-permeability layers provide capacity for long-term sequestration of anthropogenic waste. Leakage can occur if reservoir pressures rise sufficiently to fracture the seal. Such pressures can be generated within the reservoir by vigorous injection of waste or, over thousands of years, by natural processes. In either case, the precise role of intercalated mudstones in the long-term evolution of reservoir pressure remains unclear; these layers have variously been viewed as seals, as pressure sinks, or as pressure sources. Here, we use the geological record of episodic fluid venting in the Levant Basin to provide striking evidence for the pressure-source hypothesis. We use a Bayesian framework to combine recently published venting data, which record critical subsurface pressures since ∼2 Ma, with a stochastic model of pressure evolution to infer a pressure-recharge rate of ∼30 MPa/Myr. To explain this large rate, we quantify and compare a range of candidate mechanisms. We find that poroelastic pressure diffusion from mudstones provides the most plausible explanation for these observations, amplifying the ∼3 MPa/Myr recharge caused primarily by tectonic compression. Since pressurized mudstones are ubiquitous in sedimentary basins, pressure diffusion from mudstones is likely to promote seal failure globally.

A bioenergy-focused versus a reforestation-focused mitigation pathway yields disparate carbon storage and climate responses.

Limiting global warming to 2 °C requires urgent action on land-based mitigation. This study evaluates the biogeochemical and biogeophysical implications of two alternative land-based mitigation scenarios that aim to achieve the same radiative forcing. One scenario is primarily driven by bioenergy expansion (SSP226Lu-BIOCROP), while the other involves re/afforestation (SSP126Lu-REFOREST). We find that overall, SSP126Lu-REFOREST is a more efficient strategy for removing CO2 from the atmosphere by 2100, resulting in a net carbon sink of 242 ~ 483 PgC with smaller uncertainties compared to SSP226Lu-BIOCROP, which exhibits a wider range of -78 ~ 621 PgC. However, SSP126Lu-REFOREST leads to a relatively warmer planetary climate than SSP226Lu-BIOCROP, and this relative warming can be intensified in certain re/afforested regions where local climates are not favorable for tree growth. Despite the cooling effect on a global scale, SSP226Lu-BIOCROP reshuffles regional warming hotspots, amplifying summer temperatures in vulnerable tropical regions such as Central Africa and Southeast Asia. Our findings highlight the need for strategic land use planning to identify suitable regions for re/afforestation and bioenergy expansion, thereby improving the likelihood of achieving the intended climate mitigation outcomes.

Southern Ocean drives multidecadal atmospheric CO2 rise during Heinrich Stadials.

The last glacial period was punctuated by cold intervals in the North Atlantic region that culminated in extensive iceberg discharge events. These cold intervals, known as Heinrich Stadials, are associated with abrupt climate shifts worldwide. Here, we present CO2 measurements from the West Antarctic Ice Sheet Divide ice core across Heinrich Stadials 2 to 5 at decadal-scale resolution. Our results reveal multi-decadal-scale jumps in atmospheric CO2 concentrations within each Heinrich Stadial. The largest magnitude of change (14.0 ± 0.8 ppm within 55 ± 10 y) occurred during Heinrich Stadial 4. Abrupt rises in atmospheric CO2 are concurrent with jumps in atmospheric CH4 and abrupt changes in the water isotopologs in multiple Antarctic ice cores, the latter of which suggest rapid warming of both Antarctica and Southern Ocean vapor source regions. The synchroneity of these rapid shifts points to wind-driven upwelling of relatively warm, carbon-rich waters in the Southern Ocean, likely linked to a poleward intensification of the Southern Hemisphere westerly winds. Using an isotope-enabled atmospheric circulation model, we show that observed changes in Antarctic water isotopologs can be explained by abrupt and widespread Southern Ocean warming. Our work presents evidence for a multi-decadal- to century-scale response of the Southern Ocean to changes in atmospheric circulation, demonstrating the potential for dynamic changes in Southern Ocean biogeochemistry and circulation on human timescales. Furthermore, it suggests that anthropogenic CO2 uptake in the Southern Ocean may weaken with poleward strengthening westerlies today and into the future.

Long- and short-term coupling of sea surface temperature and atmospheric CO2 during the late Paleocene and early Eocene.

The late Paleocene and early Eocene (LPEE) are characterized by long-term (million years, Myr) global warming and by transient, abrupt (kiloyears, kyr) warming events, termed hyperthermals. Although both have been attributed to greenhouse (CO2) forcing, the longer-term trend in climate was likely influenced by additional forcing factors (i.e., tectonics) and the extent to which warming was driven by atmospheric CO2 remains unclear. Here, we use a suite of new and existing observations from planktic foraminifera collected at Pacific Ocean Drilling Program Sites 1209 and 1210 and inversion of a multiproxy Bayesian hierarchical model to quantify sea surface temperature (SST) and atmospheric CO2 over a 6-Myr interval. Our reconstructions span the initiation of long-term LPEE warming (~58 Ma), and the two largest Paleogene hyperthermals, the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) and Eocene Thermal Maximum 2 (ETM-2, ~54 Ma). Our results show strong coupling between CO2 and temperature over the long- (LPEE) and short-term (PETM and ETM-2) but differing Pacific climate sensitivities over the two timescales. Combined CO2 and carbon isotope trends imply the carbon source driving CO2 increase was likely methanogenic, organic, or mixed for the PETM and organic for ETM-2, whereas a source with higher δ13C values (e.g., volcanic degassing) is associated with the long-term LPEE. Reconstructed emissions for the PETM (5,800 Gt C) and ETM-2 (3,800 Gt C) are comparable in mass to future emission scenarios, reinforcing the value of these events as analogs of anthropogenic change.

Modeling direct air carbon capture and storage in a 1.5 °C climate future using historical analogs.

Limiting the rise in global temperature to 1.5 °C will rely, in part, on technologies to remove CO2 from the atmosphere. However, many carbon dioxide removal (CDR) technologies are in the early stages of development, and there is limited data to inform predictions of their future adoption. Here, we present an approach to model adoption of early-stage technologies such as CDR and apply it to direct air carbon capture and storage (DACCS). Our approach combines empirical data on historical technology analogs and early adoption indicators to model a range of feasible growth pathways. We use these pathways as inputs to an integrated assessment model (the Global Change Analysis Model, GCAM) and evaluate their effects under an emissions policy to limit end-of-century temperature change to 1.5 °C. Adoption varies widely across analogs, which share different strategic similarities with DACCS. If DACCS growth mirrors high-growth analogs (e.g., solar photovoltaics), it can reach up to 4.9 GtCO2 removal by midcentury, compared to as low as 0.2 GtCO2 for low-growth analogs (e.g., natural gas pipelines). For these slower growing analogs, unabated fossil fuel generation in 2050 is reduced by 44% compared to high-growth analogs, with implications for energy investments and stranded assets. Residual emissions at the end of the century are also substantially lower (by up to 43% and 34% in transportation and industry) under lower DACCS scenarios. The large variation in growth rates observed for different analogs can also point to policy takeaways for enabling DACCS.

Application of New Lineage Tracing Techniques in Cardiovascular Development and Physiology.

Cardiovascular disease has been the leading cause of mortality and morbidity worldwide in the past 3 decades. Multiple cell lineages undergo dynamic alternations in gene expression, cell state determination, and cell fate conversion to contribute, adapt, and even modulate the pathophysiological processes during disease progression. There is an urgent need to understand the intricate cellular and molecular underpinnings of cardiovascular cell development in homeostasis and pathogenesis. Recent strides in lineage tracing methodologies have revolutionized our understanding of cardiovascular biology with the identification of new cellular origins, fates, plasticity, and heterogeneity within the cardiomyocyte, endothelial, and mesenchymal cell populations. In this review, we introduce the new technologies for lineage tracing of cardiovascular cells and summarize their applications in studying cardiovascular development, diseases, repair, and regeneration.

Differential processing of a chemosensory cue across life stages sharing the same valence state in Caenorhabditis elegans.

Many chemosensory cues evoke responses of the same valence under widely varying physiological conditions. It remains unclear whether similar or distinct neural mechanisms are involved in the detection and processing of such chemosensory cues across contexts. We show that in Caenorhabditis elegans, a chemosensory cue is processed by distinct neural mechanisms at two different life stages that share the same valence state. Both starved adults and dauer larvae are attracted to carbon dioxide (CO2), but CO2 evokes different patterns of neural activity and different motor outputs at the two life stages. Moreover, the same interneuron within the CO2 microcircuit plays a different role in driving CO2-evoked motor output at the two life stages. The dauer-specific patterns of CO2-evoked activity in this interneuron require a dauer-specific gap junction complex and insulin signaling. Our results demonstrate that functionally distinct microcircuits are engaged in response to a chemosensory cue that triggers the same valence state at different life stages, revealing an unexpected complexity to chemosensory processing.

An alcove at the acetyl-CoA synthase nickel active site is required for productive substrate CO binding and anaerobic carbon fixation.

One of the seven natural CO2 fixation pathways, the anaerobic Wood-Ljungdahl pathway (WLP) is unique in generating CO as a metabolic intermediate, operating through organometallic intermediates, and in conserving (versus utilizing) net ATP. The key enzyme in the WLP is acetyl-CoA synthase (ACS), which uses an active site [2Ni-4Fe-4S] cluster (A-cluster), a CO tunnel, and an organometallic (Ni-CO, Ni-methyl, and Ni-acetyl) reaction sequence to generate acetyl-CoA. Here, we reveal that an alcove, which interfaces the tunnel and the A-cluster, is essential for CO2 fixation and autotrophic growth by the WLP. In vitro spectroscopy, kinetics, binding, and in vivo growth experiments reveal that a Phe229A substitution at one wall of the alcove decreases CO affinity thirty-fold and abolishes autotrophic growth; however, a F229W substitution enhances CO binding 80-fold. Our results indicate that the structure of the alcove is exquisitely tuned to concentrate CO near the A-cluster; protect ACS from CO loss during catalysis, provide a haven for inhibitory CO, and stabilize the tetrahedral coordination at the Nip site where CO binds. The directing, concentrating, and protective effects of the alcove explain the inability of F209A to grow autotrophically. The alcove also could help explain current controversies over whether ACS binds CO and methyl through a random or ordered mechanism. Our work redefines what we historically refer to as the metallocenter "active site". The alcove is so crucial for enzymatic function that we propose it is part of the active site. The community should now look for such alcoves in all "gas handling" metalloenzymes.

Associations Between End-Tidal Carbon Dioxide During Pediatric Cardiopulmonary Resuscitation, Cardiopulmonary Resuscitation Quality, and Survival.

BACKGROUND: Supported by laboratory and clinical investigations of adult cardiopulmonary arrest, resuscitation guidelines recommend monitoring end-tidal carbon dioxide (ETCO2) as an indicator of cardiopulmonary resuscitation (CPR) quality, but they note that "specific values to guide therapy have not been established in children." METHODS: This prospective observational cohort study was a National Heart, Lung, and Blood Institute-funded ancillary study of children in the ICU-RESUS trial (Intensive Care Unit-Resuscitation Project; NCT02837497). Hospitalized children (≤18 years of age and ≥37 weeks postgestational age) who received chest compressions of any duration for cardiopulmonary arrest, had an endotracheal or tracheostomy tube at the start of CPR, and evaluable intra-arrest ETCO2 data were included. The primary exposure was event-level average ETCO2 during the first 10 minutes of CPR (dichotomized as ≥20 mm Hg versus <20 mm Hg on the basis of adult literature). The primary outcome was survival to hospital discharge. Secondary outcomes were sustained return of spontaneous circulation, survival to discharge with favorable neurological outcome, and new morbidity among survivors. Poisson regression measured associations between ETCO2 and outcomes as well as the association between ETCO2 and other CPR characteristics: (1) invasively measured systolic and diastolic blood pressures, and (2) CPR quality and chest compression mechanics metrics (ie, time to CPR start; chest compression rate, depth, and fraction; ventilation rate). RESULTS: Among 234 included patients, 133 (57%) had an event-level average ETCO2 ≥20 mm Hg. After controlling for a priori covariates, average ETCO2 ≥20 mm Hg was associated with a higher incidence of survival to hospital discharge (86/133 [65%] versus 48/101 [48%]; adjusted relative risk, 1.33 [95% CI, 1.04-1.69]; P=0.023) and return of spontaneous circulation (95/133 [71%] versus 59/101 [58%]; adjusted relative risk, 1.22 [95% CI, 1.00-1.49]; P=0.046) compared with lower values. ETCO2 ≥20 mm Hg was not associated with survival with favorable neurological outcome or new morbidity among survivors. Average 2 ≥20 mm Hg was associated with higher systolic and diastolic blood pressures during CPR, lower CPR ventilation rates, and briefer pre-CPR arrest durations compared with lower values. Chest compression rate, depth, and fraction did not differ between ETCO2 groups. CONCLUSIONS: In this multicenter study of children with in-hospital cardiopulmonary arrest, ETCO2 ≥20 mm Hg was associated with better outcomes and higher intra-arrest blood pressures, but not with chest compression quality metrics.

Charting C-C coupling pathways in electrochemical CO2 reduction on Cu(111) using embedded correlated wavefunction theory.

The electrochemical CO2 reduction reaction (CO2RR) powered by excess zero-carbon-emission electricity to produce especially multicarbon (C2+) products could contribute to a carbon-neutral to carbon-negative economy. Foundational to the rational design of efficient, selective CO2RR electrocatalysts is mechanistic analysis of the best metal catalyst thus far identified, namely, copper (Cu), via quantum mechanical computations to complement experiments. Here, we apply embedded correlated wavefunction (ECW) theory, which regionally corrects the electron exchange-correlation error in density functional theory (DFT) approximations, to examine multiple C-C coupling steps involving adsorbed CO (*CO) and its hydrogenated derivatives on the most ubiquitous facet, Cu(111). We predict that two adsorbed hydrogenated CO species, either *COH or *CHO, are necessary precursors for C-C bond formation. The three kinetically feasible pathways involving these species yield all three possible products: *COH-CHO, *COH-*COH, and *OCH-*OCH. The most kinetically favorable path forms *COH-CHO. In contrast, standard DFT approximations arrive at qualitatively different conclusions, namely, that only *CO and *COH will prevail on the surface and their C-C coupling paths produce only *COH-*COH and *CO-*CO, with a preference for the first product. This work demonstrates the importance of applying qualitatively and quantitatively accurate quantum mechanical method to simulate electrochemistry in order ultimately to shed light on ways to enhance selectivity toward C2+ product formation via CO2RR electrocatalysts.

The importance of hydrology in routing terrestrial carbon to the atmosphere via global streams and rivers.

SignificanceStream/river carbon dioxide (CO2) emission has significant spatial and seasonal variations critical for understanding its macroecosystem controls and plumbing of the terrestrial carbon budget. We relied on direct fluvial CO2 partial pressure measurements and seasonally varying gas transfer velocity and river network surface area estimates to resolve reach-level seasonal variations of the flux at the global scale. The percentage of terrestrial primary production (GPP) shunted into rivers that ultimately contributes to CO2 evasion increases with discharge across regions, due to a stronger response in fluvial CO2 evasion to discharge than GPP. This highlights the importance of hydrology, in particular water throughput, in terrestrial-fluvial carbon transfers and the need to account for this effect in plumbing the terrestrial carbon budget.

Coupled CH4 production and oxidation support CO2 supersaturation in a tropical flood pulse lake (Tonle Sap Lake, Cambodia).

Carbon dioxide (CO2) supersaturation in lakes and rivers worldwide is commonly attributed to terrestrial-aquatic transfers of organic and inorganic carbon (C) and subsequent, in situ aerobic respiration. Methane (CH4) production and oxidation also contribute CO2 to freshwaters, yet this remains largely unquantified. Flood pulse lakes and rivers in the tropics are hypothesized to receive large inputs of dissolved CO2 and CH4 from floodplains characterized by hypoxia and reducing conditions. We measured stable C isotopes of CO2 and CH4, aerobic respiration, and CH4 production and oxidation during two flood stages in Tonle Sap Lake (Cambodia) to determine whether dissolved CO2 in this tropical flood pulse ecosystem has a methanogenic origin. Mean CO2 supersaturation of 11,000 ± 9,000 µatm could not be explained by aerobic respiration alone. 13C depletion of dissolved CO2 relative to other sources of organic and inorganic C, together with corresponding 13C enrichment of CH4, suggested extensive CH4 oxidation. A stable isotope-mixing model shows that the oxidation of 13C depleted CH4 to CO2 contributes between 47 and 67% of dissolved CO2 in Tonle Sap Lake. 13C depletion of dissolved CO2 was correlated to independently measured rates of CH4 production and oxidation within the water column and underlying lake sediments. However, mass balance indicates that most of this CH4 production and oxidation occurs elsewhere, within inundated soils and other floodplain habitats. Seasonal inundation of floodplains is a common feature of tropical freshwaters, where high reported CO2 supersaturation and atmospheric emissions may be explained in part by coupled CH4 production and oxidation.

Steering the Selectivity of Carbon Dioxide Electroreduction from Single-Carbon to Multicarbon Products on Metal-Organic Frameworks via Facet Engineering.

Although metal-organic frameworks (MOFs) have attracted more attention for the electrocatalytic CO2 reduction reaction (CO2RR), obtaining multicarbon products with a high Faradaic efficiency (FE) remains challenging, especially under neutral conditions. Here, we report the controlled synthesis of stable Cu(I) 5-mercapto-1-methyltetrazole framework (Cu-MMT) nanostructures with different facets by rationally modulating the reaction solvents. Significantly, Cu-MMT nanostructures with (001) facets are acquired using isopropanol as a solvent, which favor multicarbon production with an FE of 73.75% and a multicarbon:single-carbon ratio of 3.93 for CO2RR in a neutral electrolyte. In sharp contrast, Cu-MMT nanostructures with (100) facets are obtained utilizing water, promoting single-carbon generation with an FE of 63.98% and a multicarbon: single-carbon ratio of only 0.18. Furthermore, this method can be extended to other Cu-MMT nanostructures with different facets in tuning the CO2 reduction selectivity. This work opens up new opportunities for the highly selective and efficient CO2 electroreduction to multicarbon products on MOFs via facet engineering.

Atomic Defects Engineering Boosts Urea Synthesis toward Carbon Dioxide and Nitrate Coelectroreduction.

The atomic defect engineering could feasibly decorate the chemical behaviors of reaction intermediates to regulate catalytic performance. Herein, we created oxygen vacancies on the surface of In(OH)3 nanobelts for efficient urea electrosynthesis. When the oxygen vacancies were constructed on the surface of the In(OH)3 nanobelts, the faradaic efficiency for urea reached 80.1%, which is 2.9 times higher than that (20.7%) of the pristine In(OH)3 nanobelts. At -0.8 V versus reversible hydrogen electrode, In(OH)3 nanobelts with abundant oxygen vacancies exhibited partial current density for urea of -18.8 mA cm-2. Such a value represents the highest activity for urea electrosynthesis among recent reports. Density functional theory calculations suggested that the unsaturated In sites adjacent to oxygen defects helped to optimize the adsorbed configurations of key intermediates, promoting both the C-N coupling and the activation of the adsorbed CO2NH2 intermediate. In-situ spectroscopy measurements further validated the promotional effect of the oxygen vacancies on urea electrosynthesis.

Effects of periodic breathing on sleep at high altitude: a randomized, placebo-controlled, crossover study using inspiratory CO2.

Hypoxia at high altitude facilitates changes in ventilatory control that can lead to nocturnal periodic breathing (nPB). Here, we introduce a placebo-controlled approach to prevent nPB by increasing inspiratory CO2 and used it to assess whether nPB contributes to the adverse effects of hypoxia on sleep architecture. In a randomized, single-blinded, crossover design, 12 men underwent two sojourns (three days/nights each, separated by 4 weeks) in hypobaric hypoxia corresponding to 4000 m altitude, with polysomnography during the first and third night of each sojourn. During all nights, subjects' heads were encompassed by a canopy retaining exhaled CO2 , and CO2 concentration in the canopy (i.e. inspiratory CO2 concentration) was controlled by adjustment of fresh air inflow. Throughout the placebo sojourn inspiratory CO2 was ≤0.2%, whereas throughout the other sojourn it was increased to 1.76% (IQR, 1.07%-2.44%). During the placebo sojourn, total sleep time (TST) with nPB was 54.3% (37.4%-80.8%) and 45.0% (24.5%-56.5%) during the first and the third night, respectively (P = 0.042). Increased inspiratory CO2 reduced TST with nPB by an absolute 38.1% (28.1%-48.1%), the apnoea-hypopnoea index by 58.1/h (40.1-76.1/h), and oxygen desaturation index ≥3% by 56.0/h (38.9.1-73.2/h) (all P < 0.001), whereas it increased the mean arterial oxygen saturation in TST by 2.0% (0.4%-3.5%, P = 0.035). Increased inspiratory CO2 slightly increased the percentage of N3 sleep during the third night (P = 0.045), without other effects on sleep architecture. Increasing inspiratory CO2 effectively prevented hypoxia-induced nPB without affecting sleep macro-architecture, indicating that nPB does not explain the sleep deterioration commonly observed at high altitudes. KEY POINTS: Periodic breathing is common during sleep at high altitude, and it is unclear how this affects sleep architecture. We developed a placebo-controlled approach to prevent nocturnal periodic breathing (nPB) with inspiratory CO2 administration and used it to assess the effects of nPB on sleep in hypobaric hypoxia. Nocturnal periodic breathing was effectively mitigated by an increased inspiratory CO2 fraction in a blinded manner. Prevention of nPB did not lead to relevant changes in sleep architecture in hypobaric hypoxia. We conclude that nPB does not explain the deterioration in sleep architecture commonly observed at high altitude.

Severe hypoxaemic hypercapnia compounds cerebral oxidative-nitrosative stress during extreme apnoea: Implications for cerebral bioenergetic function.

We examined the extent to which apnoea-induced extremes of oxygen demand/carbon dioxide production impact redox regulation of cerebral bioenergetic function. Ten ultra-elite apnoeists (six men and four women) performed two maximal dry apnoeas preceded by normoxic normoventilation, resulting in severe end-apnoea hypoxaemic hypercapnia, and hyperoxic hyperventilation designed to ablate hypoxaemia, resulting in hyperoxaemic hypercapnia. Transcerebral exchange of ascorbate radicals (by electron paramagnetic resonance spectroscopy) and nitric oxide metabolites (by tri-iodide chemiluminescence) were calculated as the product of global cerebral blood flow (by duplex ultrasound) and radial arterial (a) to internal jugular venous (v) concentration gradients. Apnoea duration increased from 306 ± 62 s during hypoxaemic hypercapnia to 959 ± 201 s in hyperoxaemic hypercapnia (P ≤ 0.001). Apnoea generally increased global cerebral blood flow (all P ≤ 0.001) but was insufficient to prevent a reduction in the cerebral metabolic rates of oxygen and glucose (P = 0.015-0.044). This was associated with a general net cerebral output (v > a) of ascorbate radicals that was greater in hypoxaemic hypercapnia (P = 0.046 vs. hyperoxaemic hypercapnia) and coincided with a selective suppression in plasma nitrite uptake (a > v) and global cerebral blood flow (P = 0.034 to <0.001 vs. hyperoxaemic hypercapnia), implying reduced consumption and delivery of nitric oxide consistent with elevated cerebral oxidative-nitrosative stress. In contrast, we failed to observe equidirectional gradients consistent with S-nitrosohaemoglobin consumption and plasma S-nitrosothiol delivery during apnoea (all P ≥ 0.05). Collectively, these findings highlight a key catalytic role for hypoxaemic hypercapnia in cerebral oxidative-nitrosative stress. KEY POINTS: Local sampling of blood across the cerebral circulation in ultra-elite apnoeists determined the extent to which severe end-apnoea hypoxaemic hypercapnia (prior normoxic normoventilation) and hyperoxaemic hypercapnia (prior hyperoxic hyperventilation) impact free radical-mediated nitric oxide bioavailability and global cerebral bioenergetic function. Apnoea generally increased the net cerebral output of free radicals and suppressed plasma nitrite consumption, thereby reducing delivery of nitric oxide consistent with elevated oxidative-nitrosative stress. The apnoea-induced elevation in global cerebral blood flow was insufficient to prevent a reduction in the cerebral metabolic rates of oxygen and glucose. Cerebral oxidative-nitrosative stress was greater during hypoxaemic hypercapnia compared with hyperoxaemic hypercapnia and coincided with a lower apnoea-induced elevation in global cerebral blood flow, highlighting a key catalytic role for hypoxaemia. This applied model of voluntary human asphyxia might have broader implications for the management and treatment of neurological diseases characterized by extremes of oxygen demand and carbon dioxide production.

Transcriptomic responses in the nervous system and correlated behavioural changes of a cephalopod exposed to ocean acidification.

BACKGROUND: The nervous system is central to coordinating behavioural responses to environmental change, likely including ocean acidification (OA). However, a clear understanding of neurobiological responses to OA is lacking, especially for marine invertebrates. RESULTS: We evaluated the transcriptomic response of the central nervous system (CNS) and eyes of the two-toned pygmy squid (Idiosepius pygmaeus) to OA conditions, using a de novo transcriptome assembly created with long read PacBio ISO-sequencing data. We then correlated patterns of gene expression with CO2 treatment levels and OA-affected behaviours in the same individuals. OA induced transcriptomic responses within the nervous system related to various different types of neurotransmission, neuroplasticity, immune function and oxidative stress. These molecular changes may contribute to OA-induced behavioural changes, as suggested by correlations among gene expression profiles, CO2 treatment and OA-affected behaviours. CONCLUSIONS: This study provides the first molecular insights into the neurobiological effects of OA on a cephalopod and correlates molecular changes with whole animal behavioural responses, helping to bridge the gaps in our knowledge between environmental change and animal responses.

Plant diversity decreases greenhouse gas emissions by increasing soil and plant carbon storage in terrestrial ecosystems.

The decline in global plant diversity has raised concerns about its implications for carbon fixation and global greenhouse gas emissions (GGE), including carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). Therefore, we conducted a comprehensive meta-analysis of 2103 paired observations, examining GGE, soil organic carbon (SOC) and plant carbon in plant mixtures and monocultures. Our findings indicate that plant mixtures decrease soil N2O emissions by 21.4% compared to monocultures. No significant differences occurred between mixtures and monocultures for soil CO2 emissions, CH4 emissions or CH4 uptake. Plant mixtures exhibit higher SOC and plant carbon storage than monocultures. After 10 years of vegetation development, a 40% reduction in species richness decreases SOC content and plant carbon storage by 12.3% and 58.7% respectively. These findings offer insights into the intricate connections between plant diversity, soil and plant carbon storage and GGE-a critical but previously unexamined aspect of biodiversity-ecosystem functioning.

Recent Advances and Challenges in Efficient Selective Photocatalytic CO2 Methanation.

Solar-driven carbon dioxide (CO2) methanation holds significant research value in the context of carbon emission reduction and energy crisis. However, this eight-electron catalytic reaction presents substantial challenges in catalytic activity and selectivity. In this regard, researchers have conducted extensive exploration and achieved significant developments. This review provides an overview of the recent advances and challenges in efficient selective photocatalytic CO2 methanation. It begins by discussing the fundamental principles and challenges in detail, analyzing strategies for improving the efficiency of photocatalytic CO2 conversion to CH4 comprehensively. Subsequently, it outlines the recent applications and advanced characterization methods for photocatalytic CO2 methanation. Finally, this review highlights the prospects and opportunities in this area, aiming to inspire CO2 conversion into high-value CH4 and shed light on the research of catalytic mechanisms.