Elevated Carbon Dioxide Concentration Research Articles

Adapting fodder oats to climate change: Enhancing growth, yield, and microbial dynamics under elevated CO2 and temperature

The effects of elevated atmospheric carbon dioxide concentration (e[CO2]) and temperature (e°T) on various traits of oat (Avena sativa L.) varieties using open-top chambers (OTC) were investigated. A simulated environment was created for the experiment i.e., ambient temperature and CO2 (a°T + a[CO2]); elevated temperature (3 °C > ambient temperature) (e°T); elevated CO2 (550 ± 50 ppm) (e[CO2]); and a combination of ambient temperature with elevated CO2 (a°T + e[CO2]), for accessing the effect of e°T and e[CO2] on oats. a°T + e[CO2] increased plant height to 121 cm compared to 114 cm in a°T + a[CO2] and 111 cm in e°T + e[CO2]. Seed weight was highest in a°T + e[CO2] (3.09 g) compared to 2.53 g in a°T + a[CO2] and 2.60 g in e°T + e[CO2]. Leaf number and tillers were significantly higher in a°T + e[CO2] (61.4 leaves, 10 tillers) than in a°T + a[CO2] (27.6 leaves, 5.6 tillers) and e°T + e[CO2] (44.3 leaves, 6.93 tillers). Chlorophyll content was highest in a°T + e[CO2] (5.13 mg/g) compared to 3.61 mg/g in a°T + a[CO2] and 1.47 mg/g in e°T + e[CO2]. In contrast, germination rate was best in a°T + a[CO2] (81.6 %) compared to e°T + e[CO2] (60.3 %) and a°T + e[CO2] (63.1 %). Malondialdehyde (MDA), a stress marker, was significantly higher in e°T + e[CO2] (1.35 nmol/g) compared to a°T + a[CO2] (0.299 nmol/g). Membrane stability index (MSI) was lowest in e°T + e[CO2] (13.2) compared to 20.9 in a°T + a[CO2], indicating greater stress under e°T + e[CO2]. Starch content in a°T + e[CO2] (14.6 %) was more than double that of a°T + a[CO2] (7.09 %). Microbial activity also showed significant differences. Dehydrogenase was highest in e°T + e[CO2] (13.86 µg/g/day) compared to a°T + a[CO2] (8.80) and a°T + e[CO2] (12.62). Total bacterial count (TBC) increased in e°T + e[CO2] (72) compared to a°T + a[CO2] (61). Similarly, phosphate-solubilizing bacteria (PSB) and fungi (PSF) were highest in e°T + e[CO2] (PSB: 104.5, PSF: 8.5) compared to a°T + a[CO2] (PSB: 75.0, PSF: 4.0). Rhizobium and Azotobacter counts were elevated in a°T + e[CO2] (95 and 94) compared to a°T + a[CO2] (72.5 and 42.0), showing a strong positive impact of e[CO2] on microbial populations. Specific oat varieties such as JHO-2000–4 and JHO-99–2 performed best under these conditions, showing higher yields and better stress tolerance. While e[CO2] offers substantial benefits to oat plant growth and soil microbial activity, the additional stress from e°T complicates these benefits.

Elevated concentrations of soil carbon dioxide with partial root-zone drying enhance drought tolerance and agro-physiological characteristics by regulating the expression of genes related to aquaporin and stress response in cucumber plants

Water scarcity and soil carbon dioxide elevation in arid regions are considered the most serious factors affecting crop growth and productivity. This study aimed to investigate the impacts of elevated CO2 levels (eCO2 at rates of 700 and 1000 ppm) on agro-physiological attributes to induce drought tolerance in cucumbers by activating the expression of genes related to aquaporin and stress response, which improved the yield of cucumber under two levels of irrigation water conditions [75% and 100% crop evapotranspiration (ETc)]. Therefore, two field experiments were conducted in a greenhouse with controlled internal climate conditions, at the Mohamed Naguib sector of the national company for protected agriculture, during the winter seasons of 2021–2022 and 2022–2023. The treatments included eCO2 in soil under normal and partial root zoon drying (PRD, 100% ETc Full irrigations, and 75% ETc). All the applied treatments were organized as a randomized complete block design (RCBD) and each treatment was replicated six times. Untreated plants were designed as control treatment (CO2 concentration was 400 ppm). The results of this study showed that elevating CO2 at 700 and 1000 ppm in soil significantly increased plant growth parameters, photosynthesis measurements, and phytohormones [indole acetic acid (IAA) and gibberellic acid (GA3)], under partial root-zone drying (75% ETc) and full irrigation conditions (100% ETc). Under PRD condition, eCO2 at 700 ppm significantly improved plant height (13.68%), number of shoots (19.88%), Leaf greenness index (SPAD value, 16.60%), root length (24.88%), fresh weight (64.77%) and dry weight (61.25%) of cucumber plant, when compared to untreated plants. The pervious treatment also increased photosynthesis rate, stomatal conductance, and intercellular CO2 concentration by 50.65%, 15.30% and 12.18%; respectively, compared to the control treatment. Similar findings were observed in nutrient concentration, carbohydrate content, Proline, total antioxidants in the leaf, and nutrients. In contrast, eCO2 at 700 ppm in the soil reduced the values of transpiration rate (6.33%) and Abscisic acid (ABA, 34.03%) content in cucumber leaves compared to untreated plants under both water levels. Furthermore, the results revealed that the gene transcript levels of the aquaporin-related genes (CsPIP1-2 and CsTIP4) significantly increased compared with a well-watered condition. The transcript levels of CsPIP improved the contribution rate of cell water transportation (intermediated by aquaporin’s genes) and root or leaf hydraulic conductivity. The quantitative real-time PCR expression results revealed the upregulation of CsAGO1 stress-response genes in plants exposed to 700 ppm CO2. In conclusion, elevating CO2 at 700 ppm in the soil might be a promising technique to enhance the growth and productivity of cucumber plants in addition to alleviating the adverse effects of drought stresses.

Numerical analysis and evaluation of a tropical classroom for thermal comfort, indoor air quality, and energy consumption using ventilation with air-to-air total heat recovery system (MemHEX)

ABSTRACT Lecture rooms in the Philippines often experience unfavourable temperatures and elevated carbon dioxide (CO2) concentrations, impacting the well-being, health, and learning efficiency of both students and educators. This research seeks to evaluate the thermal comfort, indoor air quality, and energy usage in a standard Philippine lecture room by implementing a membrane-type total heat exchanger (MemHEX). The research used computational fluid dynamics (CFD) simulations, which were validated by field measurements and showed the effectiveness of the MemHEX. Energy consumption was modelled using EnergyPlus to compare potential impacts of various ventilation approaches. Room temperature and humidity fall short of thermal comfort standards, suggesting the need for a higher-capacity air conditioning unit (ACU). Average CO2 concentration exceeds 1000 ppm, signalling a demand for ventilation. Post-MemHEX installation, temperature and humidity slightly rise with increased air changes per hour (ACH), introducing warm outdoor air. Indoor air quality improves with rising ACH, reducing CO2 levels by exchanging fresh outdoor air. Comparing mechanical ventilation and MemHEX reveals MemHEX as more energy-efficient, maintaining better indoor conditions. These findings provide valuable insights for the field of research by demonstrating the feasibility and benefits of using MemHEX to improve the indoor environment and energy efficiency of a typical Philippine classroom.

Role of methanogenesis and methanotrophy in CH4 fluxes from rice paddies under elevated CO2 concentration and elevated temperature

The differential responses of methanogenesis and methanotrophy to elevated carbon dioxide concentrations ([CO2]) (e[CO2]) and elevated temperature ([T]) (e[T]) may lead to dramatic changes in the response of CH4 emissions from rice paddies to global warming. In this study, we systematically investigated the responses and mechanisms of CH4 flux from rice paddies to e[CO2] and e[T] based on the production and oxidation of CH4. The CH4 flux, soil properties, and soil methanogenesis and methanotrophy were observed under CK (ambient [CO2] + ambient [T]), EC (e[CO2] by 200 μmol mol−1 + ambient [T]), ET (ambient [CO2] + e[T] by 2 °C), and ECT (e[CO2] by 200 μmol mol−1 + e[T] by 2 °C) treatments. The results revealed that EC, ET, and ECT significantly increased the cumulative amount of CH4 (CAC) in the rice paddies by 10.63, 15.20, and 11.77 kg ha−1, respectively, compared with CK. ECT increased the CAC in the rice paddies by 1.14 kg ha−1 compared with EC. Moreover, EC, ET, and ECT significantly enhanced the methane production potential (MPP) and methane oxidation potential (MOP) and tended to increase the mcrA gene abundance of the methanogens. EC tended to prompt the pmoA gene abundance of the methanotrophs, but the effect of ET on the pmoA gene abundance was less consistent across the growth stages. ECT significantly decreased the relative abundances of Methanosarcina and Methylocystis (Type II) by 4.9 % and 14.2 %, respectively, while it increased the relative abundance of Methylosarcina (Type I) by 24.0 % compared with CK. Overall, the increased MPP/MOP, mcrA/pmoA, and microbial biomass carbon under climate change increased the CH4 flux from the rice paddies. The contribution of e[CO2] to the CH4 flux was significantly enhanced by e[T], which could further exacerbate the risk of global climate change induced by e[CO2].

Research progress on the effects of elevated atmospheric CO2 concentration on CH4 emission and related microbial processes in paddy fields.

Paddy fields are recognized as significant sources of methane (CH4) emissions, playing a pivotal role in global climate change. Elevated atmospheric carbon dioxide (CO2) concentrations (e[CO2]) exert a profound influence on the carbon cycling of paddy fields. Understanding the effects of e[CO2] on CH4 emissions, as well as the underlying microbial processes, is crucial for enhancing carbon sequestration and reducing emissions in paddy fields. We reviewed the impacts of e[CO2] on CH4 emission in paddy fields, focusing on the activity, abundance, community structure, and diversity of carbon-cycling-related microbes. We also delineated the roles of various microbial processes in mitigating CH4 emissions under e[CO2], as well as the primary environmental determinants. Overall, the type of e[CO2] experimental platforms, duration of fumigation, concentration gradients, and the methods of CO2 enrichment all influence CH4 emissions from paddy fields. e[CO2] initially stimulates CH4 emissions, which may decrease over time, indicating an adaptability of the methane-emitting microbial community to e[CO2]. This response exhibits a trend of initial attenuation followed by an intensification of the positive effects on CH4 emissions. Experiments with abrupt increase of CO2 concentration might overestimate CH4 emissions. The impact of e[CO2] on microbial processes is predominantly characterized by enhanced activities and abundance of methanogens, aerobic and anaerobic methanotrophs. It significantly alters the community composition and diversity of methanotrophs, with minimal effects on methanogens and anaerobic methanotrophic communities. Finally, we outlined future research directions: 1) Integrated investigations into the effects of e[CO2] on CH4 emissions, methanogenesis, and both aerobic and anaerobic methanotrophs in paddy fields could elucidate the mechanisms underlying the impacts of climate change on CH4 emissions; 2) Long-term studies are essential to understand the mechanisms of e[CO2] on CH4 emissions and associated microbial processes more accurately and realistically; 3) Multi-scale (temporal and spatial), multi-factorial (CO2 concentration, temperature, atmospheric nitrogen deposition, and water management practices), and multi-methodological (observational, data, and model integration) research is necessary to effectively reduce the uncertainties in assessing the response of CH4 emissions in paddy fields and related microbial processes to e[CO2] under future climate change scenarios.

Nitrogen form mediates sink strength and resource allocation of a C3 root crop under elevated CO2

Plant physiological processes alter with elevated carbon dioxide concentrations in the atmosphere (eCO2), which affects the growth and yield potential of crops. Among plants with C3 carbon fixation, root crops show highest yield response under eCO2 which is suggested to be linked to their large carbon (C) sink strength. The high C gain under eCO2 can be limited by processes that constrain sink capacity, such as nitrogen (N) supply. Different N sources may interact with eCO2 and thus have variable impacts on carboxylation activity, N uptake efficiency and plant development. This study aims at contributing to a better understanding of sink-driven assimilation, re-allocation and finally growth processes under eCO2 as a function of N-form. Radish (Raphanus sativus L. var. sativus), a C3 tuber plant with strong sink strength, was used. The plants were grown in pots in climate chambers at 400 ppm (aCO2) and 1000 ppm CO2 (eCO2) with either pure nitrate or ammonium-dominated nutrition. A split plot design was applied. Plants were harvested after four weeks and physiological, morphological and chemical parameters in leaves and tubers were assessed. The N-form had no effect on N acquisition, but affected C and N partitioning into plant organs differently under eCO2. N assimilation processes of nitrate-fed plants were focussed on leaves being both source and sink, and those of ammonium-fed plants on tubers, the strongly pronounced sink. Acclimation of CO2 fixation due to eCO2 did not occur for both N forms, probably due to altered sink strength and low N content in leaves. The N-form influences the sink-driven C and N balance and thus enables unrestricted carbon gain as well as the variation of organ development under future eCO2 conditions. These processes can be utilized in cultivation and breeding.

Selenium mitigates the loss of nutritional quality in rice grown at an elevated concentration of carbon dioxide

Atmospheric CO2 enrichment has the potential to improve rice (Oryza sativa L.) yield, but it may also reduce grain nutritional quality, by reducing mineral and protein concentrations. Selenium (Se) fertilization may improve rice grain nutritional composition, but it is not known if this response extends to plants grown in elevated carbon dioxide concentration (eCO2). We conducted experiments to identify the impacts of Se fertilization on yield and quality of rice grains in response to eCO2. The effect of the Se treatment was not significant for the grain yield within each CO2 condition. However, the reduction in macronutrients and micronutrients under eCO2 was mitigated in grains of plants fertilized with Se. Fertilization with Se increased the concentration of Se in roots, flag leaves, and grains independently of atmospheric CO2 concentrations. Elevation of the transcripts of ion transport-related genes could, at least partially, explain the positive relationship between mineral concentrations and grain mass resulting from Se fertilization under eCO2. Treatment with Se also increased the accumulation of total protein in grains under eCO2. Overall, our results revealed that Se fertilization represents a potential asset to maintain rice grain nutritional quality in a future with rising atmospheric CO2 concentration.

Land use modified impacts of global change factors on soil microbial structure and function: A global hierarchical meta-analysis

Nitrogen cycling in terrestrial ecosystems is critical for biodiversity, vegetation productivity and biogeochemical cycling. However, little is known about the response of functional nitrogen cycle genes to global change factors in soils under different land uses. Here, we conducted a multiple hierarchical mixed effects meta-analyses of global change factors (GCFs) including warming (W+), mean altered precipitation (MAP+/−), elevated carbon dioxide concentrations (eCO2), and nitrogen addition (N+), using 2706 observations extracted from 200 peer-reviewed publications. The results showed that GCFs had significant and different effects on soil microbial communities under different types of land use. Under different land use types, such as Wetland, Tundra, Grassland, Forest, Desert and Agriculture, the richness and diversity of soil microbial communities will change accordingly due to differences in vegetation cover, soil management practices and environmental conditions. Notably, soil bacterial diversity is positively correlated with richness, but soil fungal diversity is negatively correlated with richness, when differences are driven by GCFs. For functional genes involved in nitrification, eCO2 in agricultural soils and the interaction of N+ with other GCFs in grassland soils stimulate an increase in the abundance of the AOA-amoA gene. In agricultural soil, MAP+ increases the abundance of nifH. W+ in agricultural soils and N+ in grassland soils decreased the abundance of nifH. The abundance of the genes nirS and nirK, involved in denitrification, was mainly negatively affected by W+ and positively affected by eCO2 in agricultural soil, but negatively affected by N+ in grassland soil. This meta-analysis was important for subsequent research related to global climate change. Considering data limitations, it is recommended to conduct multiple long-term integrated observational experiments to establish a scientific basis for addressing global changes in this context.

The early Cretaceous was cold but punctuated by warm snaps resulting from episodic volcanism

The Cretaceous is characterized as a greenhouse climate from elevated atmospheric carbon dioxide concentrations, transgressive seas, and temperate ecosystems at polar paleolatitudes. Here we test the hypothesis that the early Cretaceous was a cold climate state with a new Aptian atmospheric carbon dioxide record from the C3 plant proxy and early Cretaceous sea level curve from stable oxygen isotopes of belemnites and benthic foraminifera. Results show that carbon dioxide concentrations were persistently below 840 ppm during the Aptian, validating recent General Circulation Model simulations of ice sheets on Antarctica at those concentrations. In addition, sea level was estimated to be within the ice sheet window for much of the early Cretaceous prior to the Albian. This background state appears to have been episodically interrupted by Large Igneous Province volcanism followed by long-term carbon burial from weathering. We hypothesize that the early Cretaceous was largely an icehouse punctuated by warm snaps.

Assessing watershed-scale impacts of best management practices and elevated atmospheric carbon dioxide concentrations on water yield

Changes in water yield are influenced by many intersecting biophysical elements, including climate, on-land best management practices, and landcover. Large-scale reductions in water yield may present a significant threat to water supplies globally. Many of these intersecting factors are intercorrelated and confounded, making it challenging to separate the factors' individual contributions to shaping local streamflow dynamics. Comprehensive hydrological models constructed based on a well-established understanding of biophysical processes are often employed to address these matters. However, these models rarely incorporate all relevant factors influencing local hydrological processes, due to the reliance of these models on the latest, albeit limited, state-of-the-art research. For instance, complexities inherent in watershed hydrology, which involve multilayered interactions among potentially many biophysical factors, leave the direct analysis of subtle impacts on water yields measured in-situ largely intractable. Therefore, we propose an innovative approach to assess impacts of elevated atmospheric CO2 concentrations and flow diversion terraces (FDTs) on stream discharge rates at the watershed scale. Initially, we use a comprehensive hydrological model to account for the impacts of major climatic and landuse/landcover factors on changes in field-acquired measurements of water yield. Next, we employ conventional and advanced statistical methods to decompose the residuals of model predictions to facilitate the identification of subtle influences promoted by increases in atmospheric CO2 concentrations and the application of FDTs in an agriculture-dominated watershed. Through this innovative approach, we find that FDTs contributed to a watershed-wide, net water-yield reduction of 188.0 mm (or 28.9 %) from 1992 to 2014. Ongoing increases in ambient CO2 concentrations, which are responsible for an overall reduction in a watershed-level assessment of stomatal conductance, have led to a minor increase in stream discharge rates during the same 23-year period, i.e., 0.45 mm of water yield per year, or 1.6 % overall. Streamflow reductions explicitly caused by regional warming in the area alone, on account of increased evapotranspiration, may be overestimated due to the opposing, synergistic effects on water yield associated with CO2-enrichment of the lower atmosphere and the annual application of FDTs.

Enhanced future vegetation growth with elevated carbon dioxide concentrations could increase fire activity

Many regions of the planet have experienced an increase in fire activity in recent decades. Although such increases are consistent with warming and drying under continued climate change, the driving mechanisms remain uncertain. Here, we investigate the effects of increasing atmospheric carbon dioxide concentrations on future fire activity using seven Earth system models. Centered on the time of carbon dioxide doubling, the multi-model mean percent change in fire carbon emissions is 66.4 ± 38.8% (versus 1850 carbon dioxide concentrations, under fixed 1850 land-use conditions). A substantial increase is associated with enhanced vegetation growth due to carbon dioxide biogeochemical impacts at 60.1 ± 46.9%. In contrast, carbon dioxide radiative impacts, including warming and drying, yield a negligible response of fire carbon emissions at 1.7 ± 9.4%. Although model representation of fire processes remains uncertain, our results show the importance of vegetation dynamics to future increases in fire activity under increasing carbon dioxide, with potentially important policy implications.

Low latitude mesospheric clouds in a warmer climate

AbstractObservations show that mesospheric clouds (MCs) have been increasing in recent decades, presumably due to increased mesospheric water vapor which is mainly caused by greater methane (CH4) oxidation in the middle atmosphere. Past warm climates such as those of the early Cretaceous and Paleogene periods are thought to have had higher CH4 concentrations than present day, and future CH4 concentrations will also likely continue to rise. Here, idealized atmosphere chemistry‐climate model experiments forced with strong polar‐amplified sea‐surface temperatures and elevated carbon dioxide (CO2) and CH4 concentrations predict a substantial spreading of MCs to middle and low latitudes, well beyond regions where they are currently found. Sensitivity tests show that increased water vapor from CH4 oxidation and cooling from increased CO2 and CH4 concentrations create favorable conditions for cloud formation, producing MC fractions of 0.02 in the low latitudes and 0.1 in the mid‐latitudes in the Northern Hemisphere when CH4 concentration is 16× higher than pre‐industrial. Further increases in CH4 result in a monotonic increase in low‐ and mid‐latitude MCs. A uniform surface ocean warming, changes in polar amplification, or the solar constant do not significantly affect our results. While the appearance of these clouds is interesting, their ice and liquid water content is not sufficient to cause a significant radiative effect. On the other hand, dehydration of the mesosphere due to these low‐ and mid‐latitude MCs could potentially lead to a reduction in atomic hydrogen, thereby affecting mesospheric ozone concentration, although further study is required to confirm this.

Elevated CO2 and nitrogen addition enhance the symbiosis and functions of rhizosphere microorganisms under cadmium exposure

Soil microbes are fundamental to ecosystem health and productivity. How soil microbial communities are influenced by elevated atmospheric carbon dioxide (eCO2) concentration and nitrogen (N) deposition under heavy metal pollution remains uncertain, despite global exposure of terrestrial ecosystems to eCO2, high N deposition and heavy metal stress. Here, we conducted a four year's open-top chamber experiment to assess the effects of soil cadmium (Cd) treatment (10 kg hm−2 year−1) alone and combined treatments of Cd with eCO2 concentration (700 ppm) and/or N addition (100 kg hm−2 year−1) on tree growth and rhizosphere microbial community. Relative to Cd treatment alone, eCO2 concentration in Cd contaminated soil increased the complexity of microbial networks, including the number links, average degree and positive/negative ratios. The combined effect of eCO2 and N addition in Cd contaminated soil not only increased the complexity of microbial networks, but also enhanced the abundance of microbial urealysis related UreC and nitrifying related amoA1 and amoA2, and the richness of arbuscular mycorrhiza fungi (AMF), thereby improving the symbiotic functions between microorganisms and plants. Results from correlation analysis and structural equation model (SEM) further demonstrated that eCO2 concentration and N addition acted on functions and networks differently. Elevated CO2 positively regulated microbial networks and functions through phosphorus (P) and Cd concentration in roots, while N addition affected microbial functions through soil available N and soil organic carbon (SOC) concentration and microbial network through soil Cd concentration. Overall, our findings highlight that eCO2 concentration and N addition make microbial communities towards ecosystem health that may mitigate Cd stress, and provide new insights into the microbiology supporting phytoremediation for Cd contaminated sites in current and future global change scenarios.

Elevated atmospheric CO2 promotes the contribution of autotrophic nitrification to N2O emissions in a typical summer maize field

Elevated atmospheric carbon dioxide (CO2) concentration generally stimulates nitrous oxide (N2O) emissions from upland soils, leading to a promoted feedback on climate change. However, the underlying mechanisms on how elevated CO2 (eCO2) stimulates N2O emissions from nitrogen (N)-fertilized upland soils remain poorly known. Here, we investigated the effects of eCO2 on soil N2O production pathways and associated gross N transformation rates, as well as on nitrifying and denitrifying microbes. Based on a 13 years of free-air CO2 enrichment (FACE) platform, we found that N2O emissions were significantly increased by 46.7% under eCO2 in a typical summer-maize field. The 15N tracing experiment showed that autotrophic nitrification rate was significantly increased by 11.6% under eCO2, coincided with the significantly higher abundance and shift composition of ammonia-oxidizing bacteria (AOB) under eCO2. Also, eCO2 enhanced gross ammonium (NH4+) immobilization rate but reduced gross nitrate (NO3−) immobilization rate. Autotrophic nitrification accounted for approximately 78% of N2O emissions, followed by heterotrophic nitrification (about 19%) and denitrification (about 3%). It was found that eCO2 increased carbon (C) deposition in soil, which could affect the availability of soil labile organic C and N and alter the composition and activity of nitrifiers. These changes promoted the N2O production derived from autotrophic nitrification, resulting in higher N2O emissions under eCO2. We could deduce that nitrifier denitrification contributed to the increased N2O emissions greatly under eCO2, derived by strongly stimulated ammonia oxidation and microbial respiration (i.e. higher soil CO2 emissions) caused suboxic conditions (i.e. lower soil oxygen (O2) concentration), along with higher abundance ratios of (nirK+nirS)/nosZ. Our results suggest that controlling autotrophic nitrification appropriately is crucial for mitigating N2O emissions from upland soils under rising atmospheric CO2 concentration.

Elevated carbon dioxide concentrations increase the risk of Cd exposure in rice.

Since the Industrial Revolution, crops have been exposed to various changes in the environment, including elevated atmospheric carbon dioxide (CO2) concentration and cadmium (Cd) pollution in soil. However, information about how combined changes affect crop is limited. Here, we have investigated the changes of japonica and indica rice subspecies seedlings under elevated CO2 level (1200 ppm) and Cd exposure (5 μM Cd) conditions compared with ambient CO2 level (400 ppm) and without Cd exposure in CO2 growth chambers with hydroponic experiment. The results showed that elevated CO2 levels significantly promoted seedling growth and rescued the growth inhibition under Cd stress. However, the elevated CO2 levels led to a significant increase in the shoot Cd accumulation of the two rice subspecies. Especially, the increase of shoot Cd accumulation in indica rice was more than 50% compared with control. Further investigation revealed that the decreases in the photosynthetic pigments and photosynthetic rates caused by Cd were attenuated by the elevated CO2 levels. In addition, elevated CO2 levels increased the non-enzymatic antioxidants and significantly enhanced the ascorbate peroxidase (APX) and glutathione reductase (GR) activities, alleviating the lipid peroxidation and reactive oxygen species (ROS) accumulation induced by Cd. Overall, the research revealed how rice responded to the elevated CO2 levels and Cd exposure, which can help modify agricultural practices to ensure food security and food safety in a future high-CO2 world.

Spatio-temporal variability of surface chlorophyll and pCO2 over the tropical Indian Ocean and its long-term trend using CMIP6 models

Under the global climate change scenario, ever-increasing ocean temperatures and elevated carbon dioxide (CO2) concentration levels in the ocean and atmosphere significantly affect ocean biogeochemistry. The spatiotemporal distribution of chlorophyll and partial pressure of CO2 (pCO2) over the Indian Ocean (IO) are investigated using satellite, in-situ, and simulations from eleven Coupled Model Inter-comparison Project phase 6 models. All the models show negative bias near the Somali region over the Arabian Sea (AS) during the southwest monsoon season. The CESMs and CanESM5 models show relatively less bias over the tropical IO except for the AS in all seasons compared to other models. The annual cycle of pCO2 shows a bimodal characteristic, with the first peak in May and the other in October over the northern IO, which the CanESM5, IPSL, and MPIs models reasonably well capture. All the models produce the phase of the annual cycle of pCO2 reasonably well for the southern IO. The pCO2 distribution and its trend decomposition are estimated using the multimodel mean from the CanESM5, IPSL-CM6A-LR, and MPIs models, suggesting that the increase in dissolved inorganic carbon is the dominant factor that contributes to about 70 % of the rise in the total pCO2 trend, and the total alkalinity and sea surface temperature have a secondary role. Region-wise analysis manifests that the southern IO and AS exhibit maximum susceptibility to the long-term variations in the pCO2 trend caused by the changes in dissolved inorganic carbon levels in the ocean. The study discusses substantive factors leading to the variability in the biogeochemical properties of the IO as simulated by these models and, thus, the possibilities for future improvements.

Simulation of the Modes of Medium Flow Movement through a Gas Pipeline during Corrosion Tests

Elevated concentrations of corrosive carbon dioxide or hydrogen sulfide in gas and gas condensate both produced and transported through pipelines lead to serious corrosion damage to the internal surfaces of steel infrastructure facilities. The paper presents the results of studying the corrosive effect of the medium flow along the lower component of the gas pipeline, which can exhibit a dynamic, intermittent or static character. During testing, the effect of both dynamic conditions of the medium flow on the U-shaped cell and static conditions of the permanent impact of the aqueous phase on the pipeline wall during the bubble test was evaluated. Modeling of variable wetting conditions inside the gas pipeline showed that such conditions are typical and occur upon production and transportation of raw gas to the places of gas processing and purification. We have simulated dangerous operational factors that occur inside the gas pipeline: the composition of the aquatic environment, temperature, and the content of corrosive gases. When determining the resistance of steels to local forms of corrosion (pitting, wide and shallow corrosion pits), we revealed that the rate of developing local and general corrosion of steel in aggressive carbon dioxide and hydrogen sulfide conditions can reach 2 – 3 mm/year. In addition, it has been shown that the use of corrosion inhibitors for protecting the equipment and pipelines of gas facilities can effectively prevent the occurrence of internal corrosion processes. The results obtained can be used in assessing the corrosion activity of operating media and selecting the most proven corrosion inhibitors for pilot testing at gas fields.

Manipulating atmospheric CO2 concentration induces shifts in wheat leaf and spike microbiomes and in Fusarium pathogen communities.

Changing atmospheric composition represents a source of uncertainty in our assessment of future disease risks, particularly in the context of mycotoxin producing fungal pathogens which are predicted to be more problematic with climate change. To address this uncertainty, we profiled microbiomes associated with wheat plants grown under ambient vs. elevated atmospheric carbon dioxide concentration [CO2] in a field setting over 2 years. We also compared the dynamics of naturally infecting versus artificially introduced Fusarium spp. We found that the well-known temporal dynamics of plant-associated microbiomes were affected by [CO2]. The abundances of many amplicon sequence variants significantly differed in response to [CO2], often in an interactive manner with date of sample collection or with tissue type. In addition, we found evidence that two strains within Fusarium - an important group of mycotoxin producing fungal pathogens of plants - responded to changes in [CO2]. The two sequence variants mapped to different phylogenetic subgroups within the genus Fusarium, and had differential [CO2] responses. This work informs our understanding of how plant-associated microbiomes and pathogens may respond to changing atmospheric compositions.

Soil geochemistry of hydrogen and other gases along the San Andreas fault

Natural hydrogen has generated great interest as a potential clean and renewable energy source. To understand the occurrence of natural hydrogen, 103 1-m deep soil gas samples were acquired near the San Andreas Fault at Jasper Ridge and Portola Valley, California, USA. The gas samples were analyzed for hydrogen, helium, carbon dioxide, light hydrocarbons, and fixed gas concentrations. Statistical data analysis was carried out to group samples, reveal their spatial distribution, and understand possible sources of the gases.High concentrations of hydrogen up to 20.3 ppmv and 17.3 ppmv occur in Jasper Ridge and Portola Valley, respectively, ∼30–35 times greater than the atmospheric concentration. Most samples with high hydrogen concentrations fall on or near faults, suggesting an origin by serpentinization or geomechanical activation of catalytic sites in minerals, although a deep-seated primordial origin cannot be excluded. Elevated concentrations of carbon dioxide resulted from aerobic microbial degradation of organic matter and elevated concentrations of light hydrocarbons likely resulted from thermal cracking of organic matter.

Responses of Two-Row and Six-Row Barley Genotypes to Elevated Carbon Dioxide Concentration and Water Stress

Barley (Hordeum vulgare L.) is a crucial cereal crop globally, and its productivity is influenced by environmental factors, including elevated carbon dioxide (CO2) levels and water stress. The aim of this study is to investigate the effects of water stress and increased CO2 concentration on the growth, physiological responses, and yield of two-row and six-row barley genotypes. Univariate data analysis revealed significant effects of CO2 concentration on most traits except chlorophyll a (Chla), crop antioxidant capacity as evaluated by the activity of plant extracts to scavenge the 2,2-diphenyl-1-picrylhydrazyl (DPPH), and on the maximum quantum yield of photosystem II (Fv/Fm). Mean comparisons showed that elevated CO2 increased certain traits such as shoot dry weight (ShDW) (34.1%), root dry weight (RDW) (50.8%), leaf area (LA) (12.5%), grain weight (GW) (64.1%), and yield-related traits and combination of significant indices (CSI) (72.5%). In comparison, Proline (−19.3%), Malondialdehyde (MDA) (−34.4%) levels, and antioxidant enzyme activities, including ascorbate peroxidase (APX) (−39.1%), peroxidase (POX) (−26.1%), and catalase (CAT), (−34.4%) decreased. Water stress negatively affected ShDW (−40.2%), GW (−43.7%), RDW (−28.5%), and LA (−28.8%), while it positively affected DPPH (36.0%), APX (54.8%), CAT (85.1%), and MDA (101%). Six-row barley genotypes (Goharan and Mehr) had the highest yield under normal humidity and elevated CO2 concentrations, while under water stress conditions, their yield decreased more than two-row genotypes (Behrokh and M9316). Principal component analysis and heatmapping revealed that two-row barley genotypes exhibited the highest stress resistance under elevated CO2 concentrations, with the highest levels of secondary metabolites.