Effects Of High CO2 Levels Research Articles

Combined exposure to CO2 and H2S significantly reduces the performance of the Mediterranean seagrass Posidonia oceanica: Evidence from a volcanic vent

AbstractAlthough seagrasses are expected to thrive in future acidified oceans by overcoming low CO2 diffusion into plant tissues, the co‐occurrence of environmental stressors may affect their growth. Volcanic CO2 vents are often associated with toxic gases and metal‐rich fluids representing ideal sites to assess the effects of multiple stressors. We evaluated the response of Posidonia oceanica growing near shallow CO2 vents characterized by H2S spill‐out by comparing meadow structure and phenology to an area with no gas emissions. Seagrass descriptors at meadow, shoot and leaf level indicated that P. oceanica experienced stressful conditions at the vent area, in clear contrast to the flourishing features of P. oceanica previously described at CO2 vents with no evidence of toxic inputs. Furthermore, the reduction in both leaf δ34S and growth at the vent area indicates that sulfide intrusion occurs and affects seagrass growth performance, dampening the expected beneficial effects of high CO2 levels.

Ocean acidification alters foraging behaviour in Dungeness crab through impairment of the olfactory pathway.

Crustacean olfaction is fundamental to most aspects of living and communicating in aquatic environments and more broadly, for individual- and population-level success. Accelerated ocean acidification from elevated CO2 threatens the ability of crabs to detect and respond to important olfactory-related cues. Here, we demonstrate that the ecologically and economically important Dungeness crab (Metacarcinus magister) exhibits reduced olfactory-related antennular flicking responses to a food cue when exposed to near-future CO2 levels, adding to the growing body of evidence of impaired crab behaviour. Underlying this altered behaviour, we find that crabs have lower olfactory nerve sensitivities (twofold reduction in antennular nerve activity) in response to a food cue when exposed to elevated CO2 . This suggests that near-future CO2 levels will impact the threshold of detection of food by crabs. We also show that lower olfactory nerve sensitivity in elevated CO2 is accompanied by a decrease in the olfactory sensory neuron (OSN) expression of a principal chemosensory receptor protein, ionotropic receptor 25a (IR25a) which is fundamental for odorant coding and olfactory signalling cascades. The OSNs also exhibit morphological changes in the form of decreased surface areas of their somata. This study provides the first evidence of the effects of high CO2 levels at multiple levels of biological organization in marine crabs, linking physiological and cellular changes with whole animal behavioural responses.

The decline of plant mineral nutrition under rising CO2: physiological and molecular aspects of a bad deal.

The elevation of atmospheric CO2 concentration has a strong impact on the physiology of C3 plants, far beyond photosynthesis and C metabolism. In particular, it reduces the concentrations of most mineral nutrients in plant tissues, posing major threats on crop quality, nutrient cycles, and carbon sinks in terrestrial agro-ecosystems. The causes of the detrimental effect of high CO2 levels on plant mineral status are not understood. We provide an update on the main hypotheses and review the increasing evidence that, for nitrogen, this detrimental effect is associated with direct inhibition of key mechanisms of nitrogen uptake and assimilation. We also mention promising strategies for identifying genotypes that will maintain robust nutrient status in a future high-CO2 world.

GABA receptors in the olfactory epithelium of the gilthead seabream (Sparus aurata).

Exposure to high PCO2/low pH seawater induces behavioural alterations in fish; a possible explanation for this is a reversal of Cl-/HCO3- currents through GABAA receptors (the GABAA receptor theory). However, the main evidence for this is that gabazine, a GABAA receptor antagonist, reverses these effects when applied to the water, assuming that exposure to systems other than the CNS would be without effect. Here, we show the expression of both metabotropic and ionotropic GABA receptors, and the presence of GABAA receptor protein, in the olfactory epithelium of gilthead seabream. Furthermore, exposure of the olfactory epithelium to muscimol (a specific GABAA receptor agonist) increases or decreases the apparent olfactory sensitivity to some odorants. Thus, although the exact function of GABAA receptors in the olfactory epithelium is not yet clear, this may complicate the interpretation of studies wherein water-borne gabazine is used to reverse the effects of high CO2 levels on olfactory-driven behaviour in fish.

CO2 accelerates Candida albicans biofilm formation and reveals novel approaches to their inhibition on airway management devices

C. albicans is the predominant human fungal pathogen worldwide and frequently colonises medical devices, such as voice prosthesis, as a biofilm. It is a dimorphic yeast that can switch between yeast and hyphal forms in response to environmental cues, a property that is essential during biofilm establishment and maturation. One such cue is elevation of CO2 levels, as observed in exhaled breath for example. However, despite the clear medical relevance the effects of high CO2 levels on C. albicans biofilm growth has not been investigated to date. Here, we show that 5% CO2 significantly enhances each stage of the C. albicans biofilm forming process; from attachment through maturation to dispersion, via stimulation of the Ras/cAMP/PKA signalling pathway. Transcriptome analysis of biofilm formation under elevated CO2 conditions revealed the activation of key biofilm formation pathways governed by the central biofilm regulators Efg1, Brg1, Bcr1 and Ndt80. Biofilms grown in under elevated CO2 conditions also exhibit increases in azole resistance, tolerance to nutritional immunity and enhanced glucose uptake capabilities. We thus characterise the mechanisms by which elevated CO2 promote C. albicans biofilm formation. We also investigate the possibility of re-purposing drugs that can target the CO2 activated metabolic enhancements observed in C. albicans biofilms. Using this approach we can significantly reduce multi-species biofilm formation in a high CO2 environment and demonstrate a significant extension of the lifespan of voice prostheses in a patient trial. Our research demonstrates a bench to bedside approach to tackle Candida albicans biofilm formation.

Effect of high CO2 levels and low temperature on stilbene biosynthesis pathway gene expression and stilbenes production in white, red and black table grape cultivars during postharvest storage

Phenolic compounds, such as phytoalexin resveratrol, can be induced in grapes in response to biotic and abiotic stresses and have been related in many healthy effects. Stilbene synthases (STSs) are the key enzyme responsible for resveratrol biosynthesis. They have been already isolated and characterized from several plant species, however, VviSTS is a multigene family and little is known about their modulation in response to the application of gaseous treatments that maintain table grapes quality during postharvest. In this work, we have analyzed the effect of a 3-day CO2 treatment on the modulation of 4 STSs (VviSTS6, VviSTS7, VviSTS16 and VviSTS46) and on the accumulation of different stilbene compounds (resveratrol, resveratrol-glucoside, trans-piceatannol, z-miyabenol and pallidol) during the postharvest storage at 0 °C of white (Superior Seedless, Dominga), red (Red Globe) and black (Autumn Royal) table grapes. Results indicated that the accumulation of the stilbene compounds by the application of CO2 and low temperature storage were cultivar dependent. In white Dominga fruit, accumulation of stilbene compounds increased in CO2-treated samples what seems to be modulated by VviSTS6, VviSTS7 and VviSTS46. However, in Red Globe the accumulation of compounds was mainly due to the cold storage in air and seems to be also mediated by the induction of the same VviSTSs. By contrast, in Superior Seedless and Autumn Royal table grapes the modulation of VviSTSs genes and the stilbene accumulation was independent of the atmosphere storage. Further studies would be needed to elucidate the possible role of transcription factors involved on VviSTSs modulation.

Hypercapnic tumor microenvironment confers chemoresistance to lung cancer cells by reprogramming mitochondrial metabolism in vitro

The tumor microenvironment has previously been reported to be hypercapnic (as high as ~84 mmHg), although its effect on tumor cell behaviors is unknown. In this study, high CO2 levels, ranging from 5% to 15%, protected lung cancer cells from anticancer agents, such as cisplatin, carboplatin and etoposide, by suppressing apoptosis. The cytoprotective effect of a high CO2 level was independent of acidosis and was due to mitochondrial metabolic reprogramming that reduced mitochondrial respiration, as assessed by oxygen consumption, oxidative phosphorylation, mitochondrial membrane and oxidative potentials, eventually leading to reduced reactive oxidant species production. In contrast, high CO2 levels did not affect cisplatin-mediated DNA damage responses or the expression of Bcl-2 family proteins. Although high CO2 levels inhibited glycolysis, this inhibition was not mechanistically involved in high CO2-mediated reductions in mitochondrial respiration, because a high CO2 concentration inhibited isolated mitochondria. A cytoprotective effect of high CO2 levels on mitochondria DNA-depleted cells was not noted, lending support to our conclusion that high CO2 levels act on mitochondria to reduce the cytotoxicity of anticancer agents. High CO2-mediated cytoprotection was also noted in a 3D culture system. In conclusion, the hypercapnic tumor microenvironment reprograms mitochondrial respiratory metabolism causing chemoresistance in lung cancer cells. Thus, tumor hypercapnia may represent a novel target to improve chemosensitivity.

Effects of high CO2 levels on dynamic photosynthesis: carbon gain, mechanisms, and environmental interactions.

Understanding the photosynthetic responses of terrestrial plants to environments with high levels of CO2 is essential to address the ecological effects of elevated atmospheric CO2. Most photosynthetic models used for global carbon issues are based on steady-state photosynthesis, whereby photosynthesis is measured under constant environmental conditions; however, terrestrial plant photosynthesis under natural conditions is highly dynamic, and photosynthetic rates change in response to rapid changes in environmental factors. To predict future contributions of photosynthesis to the global carbon cycle, it is necessary to understand the dynamic nature of photosynthesis in relation to high CO2 levels. In this review, we summarize the current body of knowledge on the photosynthetic response to changes in light intensity under experimentally elevated CO2 conditions. We found that short-term exposure to high CO2 enhances photosynthetic rate, reduces photosynthetic induction time, and reduces post-illumination CO2 burst, resulting in increased leaf carbon gain during dynamic photosynthesis. However, long-term exposure to high CO2 during plant growth has varying effects on dynamic photosynthesis. High levels of CO2 increase the carbon gain in photosynthetic induction in some species, but have no significant effects in other species. Some studies have shown that high CO2 levels reduce the biochemical limitation on RuBP regeneration and Rubisco activation during photosynthetic induction, whereas the effects of high levels of CO2 on stomatal conductance differ among species. Few studies have examined the influence of environmental factors on effects of high levels of CO2 on dynamic photosynthesis. We identified several knowledge gaps that should be addressed to aid future predictions of photosynthesis in high-CO2 environments.

Unexpected decrease in yield and antioxidants in vegetable at very high CO2 levels

Global warming is partly due to the increase in atmospheric CO2 concentration. In the last two decades, many investigations have studied the effect of high CO2 levels on crops. However, nearly all studies have examined the effects of CO2 enrichment up to about 1200 μmol mol−1. In general, more CO2 is beneficial to plant growth because plants feed on CO2. Here we tested the effect of CO2 levels from 400 to 5000 μmol mol−1 on the yield and antioxidant capacity of Chinese cabbage, Brassica chinensis, and lettuce, Lactuca sativa. Total antioxidant capacity was measured using the ferric ion reducing antioxidant potential assay and the diphenyl-picryl-hydrazylhydrate free radical detection. Our results show that, as expected, CO2 concentrations of 1000–3000 μmol mol−1 enhance the yields and contents of polyphenols, flavonoids and vitamin C in both vegetables. However, surprisingly, further increase up to 5000 μmol mol−1 CO2 decreased yields and contents of polyphenols, flavonoids and vitamin C. Our findings thus show that very high atmospheric CO2 levels are impeding the growth of tested plants. They also suggest that agricultural food and production could be depleted at high atmospheric CO2 levels.

The response to high CO2 levels requires the neuropeptide secretion component HID-1 to promote pumping inhibition.

Carbon dioxide (CO2) is a key molecule in many biological processes; however, mechanisms by which organisms sense and respond to high CO2 levels remain largely unknown. Here we report that acute CO2 exposure leads to a rapid cessation in the contraction of the pharynx muscles in Caenorhabditis elegans. To uncover the molecular mechanisms underlying this response, we performed a forward genetic screen and found that hid-1, a key component in neuropeptide signaling, regulates this inhibition in muscle contraction. Surprisingly, we found that this hid-1-mediated pathway is independent of any previously known pathways controlling CO2 avoidance and oxygen sensing. In addition, animals with mutations in unc-31 and egl-21 (neuropeptide secretion and maturation components) show impaired inhibition of muscle contraction following acute exposure to high CO2 levels, in further support of our findings. Interestingly, the observed response in the pharynx muscle requires the BAG neurons, which also mediate CO2 avoidance. This novel hid-1-mediated pathway sheds new light on the physiological effects of high CO2 levels on animals at the organism-wide level.

Measuring the effects of high CO2 levels in Caenorhabditis elegans

Carbon dioxide (CO2) is an important molecule in cell metabolism. It is also a byproduct of many physiological processes. In humans, impaired lung function and lung diseases disrupt the body’s ability to dispose of CO2 and elevate its levels in the body (hypercapnia). Animal models allow further understanding of how CO2 is sensed in the body and what are the physiological responses to high CO2 levels. This information can provide new strategies in the battle against the detrimental effects of CO2 accumulation in lung diseases. The nematode Caenorhabditis elegans provides us with such a model animal due to its natural ability to sense and navigate through varying concentrations of CO2, as well as the fact that it can be genetically manipulated with ease. Here we describe the different methods used to measure the effects elevated levels of CO2 have on the molecular sensing mechanism and physiology of C. elegans.

Elevated Atmospheric CO2 Enhances Copper Uptake in Crops and Pasture Species Grown in Copper‐Contaminated Soils in a Micro‐Plot Study

The biomass of plants for the purpose of phytoremediation is often small. Carbon dioxide (CO2) can enhance plant biomass and so, it is reasonable to draw such an assumption that CO2 can be used to help plants to phytoremediate heavy metal contaminated soils through enhancing the biomass of remediating plants. To identify this assumption, a micro‐plot study in six separate growth chambers was conducted to investigate the effect of high CO2 levels (approximately 1000 ± 50 µL L−1) on Cu accumulation and the remediation potential of three rape varieties and another five crop and pasture species grown in soils contaminated with Cu (485 mg Cu kg−1, denoted as soil‐L, and 1200 mg Cu kg−1, denoted as soil‐H). The results showed that independently of the CO2 treatment, the shoot biomass and Cu concentration in the eight plants varied with the species and soil Cu levels. The plants grown in soil‐L produced a higher aboveground biomass than those grown in the more heavily contaminated soil‐H, but the Cu levels were high in all the plants grown in soil‐H. Regardless of the CO2 treatment, the shoot biomass and Cu concentration in the plant parts also varied with the species and soil Cu levels. Overall, the exposure of all the plants to elevated CO2 resulted in a biomass increase of 6–136% and a significantly higher remediation capacity. The results indicate that the ever‐increasing atmospheric CO2 may enhance the phytoremediation efficiency of Cu contaminated soils; however it also suggests a risk of food safety under the future scenario of elevated atmospheric CO2.

Molecular analysis of the improvement in rachis quality by high CO2 levels in table grapes stored at low temperature

Rachis browning is one of the main factors reducing the quality of table grapes during storage at low temperature. To better understand the effect of a 3-day CO2 pretreatment (20% CO2 plus 20% O2) on maintaining the rachis quality of table grapes (Vitis vinifera cv. Cardinal) at 0°C, we analyzed the expression of genes codifying enzymes related to the synthesis and oxidation of phenolic compounds (phenylalanine ammonia-lyase, VcPAL; and polyphenol oxidase, GPO) and the detoxification of reactive oxygen species (catalase, GCAT; and ascorbate peroxidase, VcAPX) in rachis of treated and non-treated bunches. Furthermore, due to their role in senescence, the implication of ethylene and abscisic acid (ABA) was also investigated by studying the expression pattern of key regulatory genes for these hormones such as ACC synthase (ACS1) and oxidase (ACO1), VvNCED1 and 2. To determine whether these changes in gene expression were specifically related to rachis deterioration, their expression pattern in pulp and skin of treated and non-treated grapes were evaluated. The appearance of browning in non-treated rachis was associated with an increase in GPO and VcPAL mRNA levels, whereas high CO2 levels arrested this accumulation. In pulp, even though browning was not evident, a slight increase in GPO1 mRNA accumulation in non-treated bunches was detected. Moreover, lipid peroxidation level revealed lower oxidative stress in rachis of CO2-treated bunches than in non-treated ones, which seemed to be regulated by VcAPX and GCAT gene expression induction. This regulation was specific to rachis, showing a different pattern in pulp and skin. Regarding phytohormones, the effect of high CO2 levels reducing rachis browning seems to be linked to the modulation of ethylene biosynthesis genes. On the other hand, neither VvNCED1 nor VvNCED2 expression levels were altered in rachis, but NCED1 was induced specifically by low temperature in pulp. Overall, our results suggest a specific response of rachis to high levels of CO2 that could be related to the mitigation of rachis browning.

The effect of climate change on plant diseases

The effects of climate change on plant diseases have been the subject of intense debate in the last decade; research in this sense has been carry out, however, more information is needed. Elevated temperatures and carbon dioxide concentrations associated with climate change will have a substantial impact on plant-disease interactions. Changes in temperature affect both the host and the pathogen; thus, risk analyses must be conducted for each pathosystem to determine the effects of climate change. Studies have been performed under controlled conditions, and the effects of high CO2 levels have been identified; however, field responses such as the adaptation of pathogens over time may be different. The climate influences the incidence as well as temporal and spatial distribution of plant diseases. The most likely effect of climate change in poleward modifies agroclimates zones, this causing a shift in the geographical distribution of host pathogens. Considering this climate change could profoundly affect the status of agricultural diseases, the focus of thisstudy was to review studies related to the effects of climate change on plant diseases. Taking into account the work done, this review addresses the impact of climate change on plant diseases, considering the effect on crop grown, development and the impact on crop production. Key words: CO2, global warming, temperature effect on diseases.

The effects of high CO2 levels on anthocyanin composition, antioxidant activity and soluble sugar content of strawberries stored at low non-freezing temperature

Anthocyanins and sugars are involved in the responses of fruit to environmental stress. The effect of low temperature (0 °C) in ‘Camarosa’ strawberries and also the influence of high CO2 levels (20% CO2 for 3 days) on the water-soluble sugars and on the levels of individual anthocyanins were assessed, as well as their association with antioxidant activity, total phenolics and colour. Anthocyanins were assessed by HPLC-DAD-MS, myo-inositol by IC-PAD and the antioxidant capacity using the ABTS scavenging assay. When compared with untreated strawberries, exposure to high CO2 prevented the increases in total phenolics and each of the five major anthocyanins quantified, while it triggered the consumption of soluble sugars, mainly sucrose and myo-inositol. The decrease of these soluble solutes could represent an adaptive strategy of CO2-treated strawberries to cope with storage at low temperature.

Ethanolic metabolism in cherimoya fruit during storage at ambient and under high CO2atmospheres

SummaryCherimoya fruits (Annona cherimola, Mill.) were kept in 20% O2 + 20% CO2 for up to 3 d at 20°C and then transferred to air to study the effect of high CO2 levels on fermentation enzymes, ethanol and acethaldehyde content and ripening evolution. Ethanol and acetaldehyde content increased during ripening in air mainly associated with the first respiration peak. At the end of the short-term high CO2 treatment, cherimoya fruit had a lower aerobic respiration rate while concentrations of acethaldehyde and ethanol were greatly increased compared with those of air-control fruit. The activation of fermentation pathway by high CO2 atmosphere is mainly due to an enhancement in pyruvate decarboxylase (PDC) activity. High CO2 treatment prevented the ripening process but, after transfer to air a decrease in fermentation metabolism was recorded and fruit was able to ripen, showing a typical decrease in tissue pH.

Effects of high CO2 levels on surface temperature and atmospheric oxidation state of the early Earth

One-dimensional radiative-convective and photochemical models are used to examine the effects of enhanced CO2 concentrations on the surface temperature of the early Earth and the composition of the prebiotic atmosphere. Carbon dioxide concentrations of the order of 100-1000 times the present level are required to compensate for an expected solar luminosity decrease of 25-30%, if CO2 and H2O were the only greenhouse gases present. The primitive stratosphere was cold and dry, with a maximum H2O volume mixing ratio of 10(-6). The atmospheric oxidation state was controlled by the balance between volcanic emission of reduced gases, photo-stimulated oxidation of dissolved Fe+2 in the oceans, escape of hydrogen to space, and rainout of H2O2 and H2CO. At high CO2 levels, production of hydrogen owing to rainout of H2O2 would have kept the H2 mixing ratio above 2x10(-4) and the ground-level O2 mixing ratio below 10(-11), even if no other sources of hydrogen were present. Increased solar UV fluxes could have led to small changes in the ground-level mixing ratios of both O2 and H2.