Atmospheric CO2 Concentration Research Articles

Generalized stability landscape of the Atlantic meridional overturning circulation

Abstract. The Atlantic meridional overturning circulation (AMOC) plays a crucial role in shaping climate conditions over the North Atlantic region and beyond, and its future stability is a matter of concern. While the AMOC stability when faced with surface freshwater forcing (FWF) has been thoroughly investigated, its equilibrium response to changing CO2 remains largely unexplored, precluding a comprehensive understanding of its stability under global warming. Here we use an Earth system model to explore the stability of the AMOC when faced with combined changes in FWF in the North Atlantic and atmospheric CO2 concentrations between 180 and 560 ppm. We find four different AMOC states associated with qualitatively different convection patterns. Apart from an “Off” AMOC state with no North Atlantic deep-water formation and a “Modern”-like AMOC with deep water forming in the Labrador and Nordic seas as observed at present, we find a “Weak” AMOC state with convection occurring south of 55° N and a “Strong” AMOC state characterized by deep-water formation extending into the Arctic. The Off and Weak states are stable for the entire range of CO2 but only for positive FWF. The Modern state is stable under higher than pre-industrial CO2 for a range of positive FWF and for lower CO2 only for negative FWF. Finally, the Strong state is stable only for CO2 above 280 ppm and FWF < 0.1 Sv. Generally, the strength of the AMOC increases with increasing CO2 and decreases with increasing FWF. Our AMOC stability landscape helps to explain AMOC instability in colder climates, and although it is not directly applicable to the fundamentally transient AMOC response to global warming on a centennial timescale, it can provide useful information about the possible long-term fate of the AMOC. For instance, while under pre-industrial conditions the AMOC is monostable in the model, the Off state also becomes stable for CO2 concentrations above ∼ 400 ppm, suggesting that an AMOC shutdown in a warmer climate might be irreversible.

Climate Conundrum: A Wet or Dry European and Northern African Climate During the Middle Miocene

AbstractEnd of 21st‐century hydroclimate projections suggest an expansion of subtropical dry zones, with Mediterranean and Sahel regions becoming much drier. However, paleobotanical assemblage evidence from the middle Miocene (17‐12 Ma), suggests both regions were instead humid environments. Here we show that by modifying regional sea surface temperatures (SST) in an Earth System Model (CESM1.2) simulation of the middle Miocene, the increased ocean evaporation and integrated water vapor flux overrides any drying effects associated with warming‐induced land‐surface evaporation driven by atmospheric CO2 concentrations. These modifications markedly reduce the bias in the model‐data comparison for this period. A vegetation model (BIOME4) forced with simulated climatologies predicts both regions were dominated by mixed forest, which is largely consistent with the paleobotanical record. This study unveils the potential for wetter subtropical Mediterranean climates associated with warming, presenting an alternative scenario from future drying projections with localized SST warming governing regional climate change.

Distinct responses of climate-growth and iWUE in Fagus sylvatica L. at two low elevation sites in southern Italy

In this study, using a dendrological and isotopic approaches, we investigated the responses to climate of two pure Fagus sylvatica L. stands (Campobraca and Falode) in the southernmost part of the distribution range in southern Italy. The δ13C data were used for calculating the intrinsic water use efficiency (iWUE) as a proxy of the balance between the water and carbon cycles. The results showed that the iWUE of both stands was sensitive to the amount of precipitation during the summer months (negative, significant effect) and to atmospheric CO2 concentration. Growth was sensitive to climate only in the Campo Braca site; the most influential variables were the VPD (vapour pressure deficit) and precipitation of the summer months that had a negative and a positive effect, respectively. The iWUE showed a negative correlation with growth in Campo Braca and a non-significant one in Falode. Water availability was the most influential variable on F. sylvatica growth and physiology. The iWUE increase was mainly driven by atmospheric CO2 concentration, and by decreased precipitation, as a response of the trees to drought. Our results highlight the importance of understanding the hydrological changes due to climate change for forecasting/modelling forest responses. CO2 increase does not compensate for the effect of adverse climate on F. sylvatica in the forests of southern Italy, while local conditions play an important role in determining tree growth.

Laboratory experiments of carbon mineralization potential of the main terrestrial basalt reservoirs in China

Against the background of realizing the goal of “carbon peaking and carbon neutrality”, using basaltic rocks for carbon mineralization is one of the most promising approaches to reduce the rise in atmospheric CO2 concentrations. This study conducted a series of experiments to assess carbon mineralization in nine basalt samples from the main terrestrial basalt reservoirs in China within CO2-H2O/brine-rock systems at low temperatures (≤35 °C). The results indicate that the secondary carbonates formed in the CO2-H2O/brine-basalt system are predominantly calcite rather than Mg-carbonate minerals at low temperatures (≤35 °C). Hence, at low temperatures (≤35 °C), basalt rich in Ca-bearing minerals promotes the formation of stable carbonate minerals more effectively than basalt containing Mg-bearing minerals. Furthermore, under conditions of low temperatures (≤35 °C) and pressures of approximately 3 MPa, the results suggest that alkaline olivine basalt, with a higher content of Ca-minerals and typical alkaline minerals (nepheline and Na-sanidine), exhibits the highest pH value and the highest amount of calcite. Hence, the alkaline minerals, nepheline and Na-sanidine, serve as pH buffers to increase the pH and promote the precipitation of calcite within CO2-H2O– basalt systems at low temperatures (≤35 °C). Among the nine evaluated basalts, basalt from the Shandong Linqu-Changle volcanic basin exhibits the highest rate of carbon mineralization at low temperatures (≤35 °C). Hence, Cenozoic alkaline olivine basalt from Shandong Linqu-Changle volcanic basin is one of the most promising basalt reservoirs in China for future in- situ carbonation. As for ex- situ carbonation, compared with olivine, diopside or Ca-plagioclase may be more appropriate for increasing ocean negative emissions.

The effects of counter ion on CO2 capture performance of amino acid salt solutions for direct air capture applications

Direct CO2 capture from the atmosphere has received growing attention driven by the imperative of achieving global net-zero emission targets. Amino acid salt solutions are promising candidates for liquid-based direct air capture processes. Utilised as a neutralized salt by reacting initially with hydroxides, it has been speculated that their performance may vary with the type of counter ion present in the solution. This work investigates the influence of counter ions, potassium, sodium, and lithium, of amino acid salt solutions on the physical properties, the CO2 absorption capacities, and the CO2 absorption kinetics under atmospheric CO2 concentration levels. The potassium-containing amino acid solutions exhibited significantly lower viscosities and mildly elevated densities compared to sodium- and lithium-containing ones. At 25 °C, the potassium-prolinate solution demonstrated the highest viscosity (8.5 mPa⋅s), whereas K-glycinate exhibited the lowest viscosity (2.5 mPa⋅s). Additionally, potassium-based solutions consistently displayed the highest CO2 mass transfer coefficients, followed by sodium- and lithium-containing ones. The CO2 mass transfer coefficient was highest for potassium-prolinate (2.99 mmol m−2⋅s−1⋅kPa−1) with the lowest rate observed for potassium-β-alaninate (1.68 mmol m−2⋅s−1⋅kPa−1). Interestingly, the type of counter ion had minimal impact on the CO2 absorption capacity, with potassium-based solutions exhibiting only a slightly elevated capacity compared to sodium- and lithium-based solutions. Specifically, potassium-lysinate displayed the highest CO2 absorption capacity (0.7 mol CO2 /mol amine), while potassium-β-alaninate showed the lowest (0.65 mol CO2/mol amine). It should be noted that all lithium-based solutions of all amino acids formed precipitates during CO2 absorption. From a practical and operational perspective, these findings suggest that the potassium salt solution of amino acids would be the optimal choice for direct air capture applications due to their enhanced solubility and CO2 mass transfer rates compared to the corresponding sodium and lithium counter ion salt solutions.

Trace metal evolution of the Late Cretaceous Ocean

The Cenomanian-Turonian boundary (Late Cretaceous) witnessed the last spectacular manifestation of Mesozoic Anoxic Events (OAE 2, ~94 Ma), marked by a prominent carbon isotope excursion (CIE) and burial of organic-matter-rich sediments under high atmospheric CO2 concentrations. But the Late Cretaceous generally was a time of profound environmental change. OAE 2 was preceded by other CIEs, including the Mid-Cenomanian Event (MCE), and was punctuated by a short re‑oxygenation and cooling event (the Plenus Cold Event, PCE). Extensive previous studies, including many trace metal studies, have focused on OAE 2, but there is still debate concerning the degree of drawdown of oceanic trace metal reservoirs during OAE 2, whether this drawdown is global or local, its causes and consequences for ocean ecology. Here, we present records of eight trace metals, over about 5 Myr of the Late Cretaceous, from the Tarfaya Basin in the proto-North Atlantic. The long records from a core preserving a continuous sedimentary succession allow us to set changes occurring across OAE 2 in the broader context of Late Cretaceous, including the lead up to OAE 2. Moreover, the multiple trace metal dataset allows us to broadly investigate the oceanographic setting in the context of recent studies of multiple trace metals in modern organic-rich sediments aimed at refining the proxies.Trace metal enrichments in these organic-rich sediments are discussed on three different timescales. Firstly, comparison of these Late Cretaceous sediments with modern organic-rich sediments are consistent with deposition in an open ocean upwelling margin in the Late Cretaceous, very like the modern Peru or Namibian Margin, although the deep proto-North Atlantic was probably partially restricted. Secondly, in common with previous studies, metal/TOC ratios often show sharp drops in the early part of OAE 2. Thirdly, however, this sharp drop occurs within a framework of pseudo-cyclical variations in metal/TOC, with a period of about 143 ±19 kyr (1 SD), that is a feature of these long records well before OAE 2, including across the MCE. Different metals respond differently to the perturbation in the early part of OAE 2 itself. Simple mass balance considerations suggest that trace metal drawdown with organic carbon must be at least partially compensated by changes in the rate of chemical weathering on the continents, as previously inferred from Li and Ca isotopes. Moreover, changes in the patterns of variation between different metals, as well as covariation of metal/TOC ratios and Os isotopes, hint at changes in the pattern of chemical weathering, most prominently in the contribution of mafic rocks to the chemical weathering flux.

Alternative climatic steady states near the Permian-Triassic Boundary.

Due to spatial scarcity and uncertainties in sediment data, initial and boundary conditions in deep-time climate simulations are not well constrained. On the other hand, depending on these conditions, feedback mechanisms in the climate system compete and balance differently. This opens up the possibility to obtain multiple steady states in numerical experiments. Here, we use the MIT general circulation model to explore the existence of such alternative steady states around the Permian-Triassic Boundary (PTB). We construct the corresponding bifurcation diagram, taking into account processes on a timescale of thousands of years, in order to identify the stability range of the steady states and tipping points as the atmospheric CO2 content is varied. We find three alternative steady states with a difference in global mean surface air temperature of about 10°C. We also examine how these climatic steady states are modified when feedbacks operating on comparable or longer time scales are included, namely vegetation dynamics and air-sea carbon exchanges. Our findings on multistability provide a useful framework for explaining the climatic variations observed in the Early Triassic geological record, as well as some discrepancies between numerical simulations in the literature and geological data at PTB and its aftermath.

Carbon Sequestration in a Changing Climate: Management Techniques and Strategic Solutions

Carbon sequestration in agriculture plays a critical role in mitigating climate change by capturing and storing atmospheric carbon dioxide (CO2) in soil and biomass. This process involves various strategies and management practices aimed at enhancing soil organic carbon (SOC) levels while maintaining or improving agricultural productivity. Key strategies include no-tillage or reduced tillage, which minimizes soil disturbance and promotes residue retention, thus slowing down decomposition and enhancing carbon storage. Crop rotation and the use of cover crops further contribute to carbon sequestration by diversifying root structures and improving soil health. Organic farming practices, such as applying farmyard manure and compost, provide essential organic matter that enriches soil quality and increases carbon retention. Additionally, the incorporation of deep-rooted plants and biochar enhances carbon storage in deeper soil layers, making them more resilient to climate variability. The integration of these practices not only sequesters carbon but also improves soil fertility, water retention, and overall ecosystem health. Effective management of carbon sequestration in agricultural systems requires a holistic approach that considers local conditions, crop diversity, and sustainable land use practices. By adopting these strategies, agriculture can become a significant carbon sink, contributing to global efforts to reduce atmospheric CO2 concentrations while ensuring food security and environmental sustainability.

Shifting interactions between ectomycorrhizae, plants and insect herbivores in a CO2‐enriched world

Abstract Increasing atmospheric CO2 concentrations are changing how plants interact with their biotic mutualists and antagonists, but few syntheses consider how the three‐way interactions between mycorrhizae, plants and herbivores will shift under rising CO2. We summarise the mechanisms by which ectomycorrhizal (EcM)‐associated plants, their mycorrhizae and insect herbivores interact with each other under current conditions and evaluate a set of expectations for how these interactions might shift under higher CO2. We then outline priorities for future work on EcM–plant–herbivore interactions as atmospheric CO2 continues to rise. EcM colonisation has variable but often positive effects on herbivory, while herbivory has consistently negative impacts on EcM colonisation. Mechanistic evidence suggests that the positive EcM effect on herbivory will strengthen and the negative impact of herbivory on EcM will be ameliorated under higher CO2. Synthesis: While more empirical evidence on fungal–plant–herbivore interactions is needed in EcM systems, our synthesis suggests that EcM associations may play an under‐recognised role in dictating future terrestrial carbon capture by mediating herbivory and the ability of plants to compensate for herbivory as atmospheric CO2 continues to rise.

Metabolic engineering of the serine/glycine network as a means to improve the nitrogen content of crops.

In plants, L-serine (Ser) biosynthesis occurs through various pathways and is highly dependent on the atmospheric CO2 concentration, especially in C3 species, due to the association of the Glycolate Pathway of Ser Biosynthesis (GPSB) with photorespiration. Characterization of a second plant Ser pathway, the Phosphorylated Pathway of Ser Biosynthesis (PPSB), revealed that it is at the crossroads of carbon, nitrogen, and sulphur metabolism. The PPSB comprises three sequential reactions catalysed by 3-phosphoglycerate dehydrogenase (PGDH), 3-phosphoSer aminotransferase (PSAT) and 3-phosphoSer phosphatase (PSP). PPSB was overexpressed in plants exhibiting two different modes of photosynthesis: Arabidopsis (C3 metabolism), and maize (C4 metabolism), under ambient (aCO2) and elevated (eCO2) CO2 growth conditions. Overexpression in Arabidopsis of the PGDH1 gene alone or PGDH1, PSAT1 and PSP1 in combination increased the Ser levels but also the essential amino acids threonine (aCO2), isoleucine, leucine, lysine, phenylalanine, threonine and methionine (eCO2) compared to the wild-type. These increases translated into higher protein levels. Likewise, starch levels were also increased in the PPSB-overexpressing lines. In maize, PPSB-deficient lines were obtained by targeting PSP1 using Cas9 endonuclease. We concluded that the expression of PPSB in maize male gametophyte is required for viable pollen development. Maize lines overexpressing the AtPGDH1 gene only displayed higher protein levels but not starch at both aCO2 and eCO2 conditions, this translated into a significant rise in the nitrogen/carbon ratio. These results suggest that metabolic engineering of PPSB in crops could enhance nitrogen content, particularly under upcoming eCO2 conditions where the activity of GPSB is limited.

Anomalous wet summers and rising atmospheric CO2 concentrations increase the CO2 sink in a poorly drained forest on permafrost

At the northern high latitudes, rapid warming, associated changes in the hydrological cycle, and rising atmospheric CO2 concentrations, [CO2], are observed at present. Under rapid environmental changes, it is important to understand the current and future trajectories of the CO2 budget in high-latitude ecosystems. In this study, we present the importance of anomalous wet conditions and rising [CO2] on the long-term CO2 budget based on two decades (2003-2022) of quasicontinuous measurements of CO2 flux at a poorly drained black spruce forest on permafrost peat in interior Alaska. The long-term CO2 budget for the black spruce forest was a small sink of -53 ± 63 g C m-2 y-1. The CO2 sink increased from 49 g C m-2 y-1 for the first decade to 58 g C m-2 y-1 for the second decade. The increased CO2 sink was attributed to an 11.3% increase in gross primary productivity (GPP) among which 9% increase in GPP was explained by a recent increase in precipitation. Furthermore, a 3% increase in GPP in response to a 37-ppm increase in [CO2] was estimated from the data-model fusion. Our study shows that understanding the coupling between hydrological and carbon cycles and the CO2 fertilization effect is important for understanding the current and future carbon budgets of high-latitude ecosystems in permafrost regions.

Elevated CO2 Concentration Extends Reproductive Growth Period and Enhances Carbon Metabolism in Wheat Exposed to Increased Temperature.

Both elevated atmospheric CO2 concentration ([CO2]) and increased temperature exert notable influences on wheat (Triticum aestivum L.) growth and productivity when examined individually. Nevertheless, limited research comprehensively investigates the combined effects of both factors. Winter wheat was grown in environment-controlled chambers under two concentrations of CO2 (ambient CO2 concentration and ambient CO2 concentration plus 200 µmol mol-1) and two levels of temperature (ambient temperature and ambient temperature plus 2°C). The phenology, photosynthesis, carbohydrate and nitrogen metabolism, yield and quality responses of wheat were investigated. Elevated [CO2] did not counteract warming-induced shortening of wheat phenological period but prolonged grain filling. Even though photosynthetic adaptation occurred during the reproductive growth period, elevated [CO2] still significantly enhanced carbohydrate accumulation under warming, particularly at the grain filling stage, thereby increasing yield by 20.1% compared with the ambient control. However, elevated [CO2] inhibited nitrogen assimilation at the grain filling stage under increased temperature by downregulating the expression levels of TaNR, TaNIR, TaGS1 and TaGOGAT and reducing glutamine synthetase activity, which directly led to a significant decrease of 19.4% in grain protein content relative to the ambient control. These findings suggest that elevated [CO2] will likely increase yield but decrease grain nutritional quality for wheat under future global warming scenarios.

Persistently active El Niño–Southern Oscillation since the Mesozoic

The El Niño-Southern Oscillation (ENSO), originating in the central and eastern equatorial Pacific, is a defining mode of interannual climate variability with profound impact on global climate and ecosystems. However, an understanding of how the ENSO might have evolved over geological timescales is still lacking, despite a well-accepted recognition that such an understanding has direct implications for constraining human-induced future ENSO changes. Here, using climate simulations, we show that ENSO has been a leading mode of tropical sea surface temperature (SST) variability in the past 250 My but with substantial variations in amplitude across geological periods. We show this result by performing and analyzing a series of coupled time-slice climate simulations forced by paleogeography, atmospheric CO2 concentrations, and solar radiation for the past 250 My, in 10-My intervals. The variations in ENSO amplitude across geological periods are little related to mean equatorial zonal SST gradient or global mean surface temperature of the respective periods but are primarily determined by interperiod difference in the background thermocline depth, according to a linear stability analysis. In addition, variations in atmospheric noise serve as an independent contributing factor to ENSO variations across intergeological periods. The two factors together explain about 76% of the interperiod variations in ENSO amplitude over the past 250 My. Our findings support the importance of changing ocean vertical thermal structure and atmospheric noise in influencing projected future ENSO change and its uncertainty.

Variation of CO2 concentration and its provenance in alpine on the south slope of Tomur Peak, Tianshan Mountains.

This study analyzes the characteristics of near-surface atmospheric CO2 concentrations on the southern slope of Tomur Peak from 2013 to 2022. Utilizing the Boughton two-parameter algorithm, we determined the CO2 background and non-background concentrations. Additionally, the Hysplit model was employed to investigate the potential contributing areas of the CO2 non-background concentration. Our findings that the CO2 concentration in the study area was approximately 17% lower than the global average, with an annual growth rate that was only about 47% of the global rate. The CO2 non-background concentration accounted for only 6.25% of the observed concentration, but was largely unaffected by near-ground meteorological factors. The source of the CO2 non-background was mainly controlled by the westerly belt, with potential source area mainly located in Central Asia. However, the WPSCF values in the modern ice and snow distribution area south of Tomur Peak and west of the monitoring station were significantly elevated, suggesting a strong wind transport of CO2 after accumulation under the influence of the elevated terrain. The local supplying path accounted for only 12.87%, indicating that human activities in the oasis areas of the Tarim Basin had a limited influence on the study area. Due to the blocking effect of the Baikal high-pressure system and the towering topography of the Tianshan Mountains, the influence of human emissions from higher latitudes was likely negligible.

Influence of Orbital Forcing on the Snowball Earth Deglaciation

AbstractNeoproterozoic snowball Earth events lasted for multiple million years, experiencing many orbital cycles. Here we investigate whether the deglaciation of these events would be triggered more easily at certain orbital configurations than others, by using an atmosphere‐land model that considers meltpond formation on land ice. Results show that the threshold concentration of atmospheric CO2 (pCO2) required for deglaciation can vary from 6 to 10 × 104 ppmv under different orbital forcings. The threshold pCO2 decreases with the equatorial maximum monthly insolation (EMMI), which is affected most by the eccentricity and secondarily by obliquity. Therefore, we conclude that the snowball Earth deglaciation likely occurred when the eccentricity was high and obliquity was low. Compared to previous estimate that used present‐day orbital configuration which has a minimal eccentricity, the duration of snowball Earth events would likely be much shorter when the influence of orbital variations are considered.

Assessment of Meteorological Drought in a Changing Environment: An Example in the Upper Yangtze River

AbstractRecent studies have suggested that drought projections using Palmer drought severity index (PDSI) and standardized evapotranspiration precipitation index (SPEI) may overestimate drought severity. This overestimation occurs because the potential evapotranspiration (PET) calculations fail to consider the interactive effects of vegetation responses such as increased leaf area index (LAI) and constrained stomatal conductance, which are influenced by elevated atmospheric CO2 concentrations ([CO2]). To address this issue, our study replaced the traditional Penman‐Monteith (PM) equation with a recently proposed PET equation that includes the effects of changing [CO2] and LAI to assess droughts at monthly scale in the Upper Yangtze River basin, which experiences the vegetation greening. The findings indicated a consistent increasing trend in drought conditions with minimal discrepancy between the two equations over the historical period (1986–2017). This consistency arises because the water‐saving effects of increased [CO2] and the greening effects of rising LAI largely counterbalance each other. However, for the future period (2018–2100), projections using PM equation predicted an intensification of drought conditions. In contrast, the improved SPEI indicated no significant drought variations, and the improved PDSI suggested a wetting trend. This divergence can be attributed to the water‐saving effects increasingly outweighing the greening effects, as PET shows a decreasing sensitivity to LAI with LAI increasing, but maintains a near‐constant sensitivity to elevated [CO2]. Consequently, the indices based on PM equation tend to overestimate future drought severity. Overall, this study demonstrates that the new PET estimation method is more capable of responding to the changing environment.

Carbon dioxide fertilization enhanced carbon sink offset by climate change and land use in Amazonia on a centennial scale

The Amazon, the Earth's largest tropical forest, plays a critical role in the global carbon cycle, acting as a significant carbon sink. Recent studies, however, indicate a decline in its carbon sequestration capacity due to climate variability, intensive deforestation, and fires. This study aims to examine the impacts of these factors on the carbon dynamics of the Amazon over a centennial scale based on dynamic global vegetation models (DGVMs) of Trendy-v11. It was found that the Amazon region exhibited significant spatiotemporal variations in net land carbon (C) fluxes, and was a net C sink (40.02 ± 242.64 Tg C yr−1) during 1901–2021. The Amazonian net biome productivity (NBP) showed a 6-decades-scale shift from a decreasing trend (−3.78 Tg C yr−2) during 1901–1959 to an increasing trend (2.39 Tg C yr−2) during 1960–2021. The Amazonian NBP was negatively related to air temperature while positively related to dry-season precipitation during 1901–2021. Furthermore, the increase of atmospheric CO2 concentration during 1901–2020 enhanced Amazonian NBP by 36.40 ± 8.39 Pg C, which was largely offset by land use change (−18.84 ± 12.02 Pg C) and climate change (−10.03 ± 5.00 Pg C). Our findings underscore the critical need for sustainable management practices in the Amazon to enhance its C sink and preserve its function in the global climate system.

Integrated Analysis of Solar-Induced Chlorophyll Fluorescence, Normalized Difference Vegetation Index, and Column-Average CO2 Concentration in South-Central Brazilian Sugarcane Regions

Remote sensing has proven to be a vital tool for monitoring and forecasting the quality and yield of crops. The utilization of innovative technologies such as Solar-Induced Fluorescence (SIF) and satellite measurements of column-averaged CO2 (xCO2) can enhance these estimations. SIF is a signal emitted by crops during photosynthesis, thus indicating photosynthetic activities. The concentration of atmospheric CO2 is a critical factor in determining the efficiency of photosynthesis. The aim of this study was to investigate the correlation between satellite-derived Solar-Induced Chlorophyll Fluorescence (SIF), column-averaged CO2 (xCO2), and Normalized Difference Vegetation Index (NDVI) and their association with sugarcane yield and sugar content in the field. This study was carried out in south-central Brazil. We used four localities to represent the region: Pradópolis, Araraquara, Iracemápolis, and Quirinópolis. Data were collected from orbital systems during the period spanning from 2015 to 2016. Concurrently, monthly data regarding tons of sugarcane per hectare (TCH) and total recoverable sugars (TRS) were gathered from 24 harvest locations within the studied plots. It was observed that TRS decreased when SIF values ranged between 0.4 W m−2 sr−1 μm−1 and 0.8 W m−2 sr−1 μm−1, particularly in conjunction with NDVI values below 0.5. TRS values peaked at 15 kg t−1 with low NDVI and xCO2 values, alongside SIF values lower than 0.4 W m−2 sr−1 μm−1 and greater than 1 W m−2 sr−1 μm−1. These findings underscore the potential of integrating SIF, xCO2, and NDVI measurements in the monitoring and forecasting of yield and sugar content in sugarcane crops.

A Molecular Temporal Evolutionary Framework of Land Plants and the Age of Angiosperms

A series of Bayesian molecular clock analyses with varying model combinations, parameters, and tree topologies were conducted to establish a temporal evolutionary framework of land plants and to estimate the age of angiosperms. The data consisted of five organellar and nuclear genes, 633 taxa, and 23 fossil calibration points (FCPs). The analyses were evaluated using an internal search thoroughness measure, effective sample sizes, and two external criteria: the consensus land plant phylogeny and a newly developed method that used the Hennigian reciprocal illumination principle to compare molecular age estimates of 21 nodes representing major land plant clades and the root split in green plants with those of their fossils in an a posteriori fashion. The results show that an analysis using a general time reversible (GTR) DNA substitution model, log normal branch-rate distribution, and Yule tree prior represented the best model combination, with the Birth-Death tree prior being equally optimal. This analysis estimated the age of the land plant crown group as 496.95 million years (MY), with a 95% highest posterior density (HPD) of 465.66–531.43 MY, and the age of the angiosperm crown group as 219.93 MY, with a 95% HPD of 184.09–256.82 MY. The former agrees with the fossil evidence, but the latter is significantly older than the fossil ages. A thorough examination of fossil evidence of angiosperms, as well as their evolutionary history in light of recent knowledge of morphology, physiology, and atmospheric CO2 concentration in the Mesozoic era, suggests that angiosperm radiation might have been delayed after their origin and that the current fossil record probably reflects only the products of that radiation, not the origin of angiosperms. Overall, the study shows that both molecular clock analyses and fossil studies, while agreeing on some aspects but disagreeing on others, can help develop a complete understanding of the temporal evolutionary history of land plants.

Climate feedback from plant physiological responses to increasing atmospheric CO2 in Earth system models.

Plant physiological responses to increasing atmospheric CO2 concentration (iCO2), including enhanced photosynthesis and reduced stomatal conductance, impact regional and global climate. Here, I describe recent advances in understanding these effects through Earth system models (ESMs). Idealized simulations of a 1% annual iCO2 show that despite fertilization, CO2 physiological forcing contributes to 10% of warming and at least 30% of future precipitation decline in Amazonia. This reduces aboveground vegetation carbon storage and triggers positive carbon-climate feedback. ESM simulations indicate that reduced transpiration and increased heat stress from iCO2 could amplify meteorological drought and wildfire risks. Understanding these climate feedbacks is essential for improving carbon accounting in natural climate solutions, such as avoiding deforestation and reforestation, as iCO2 complicates assessing their climate benefits.