Elevated CO2 Levels Research Articles

Wheat grown under elevated CO2 was more responsive to nitrogen fertilizer in Eastern India

Abstract Elevated CO2 might have differential impact on the growth, development, and yield of wheat under varying nutrient management, especially in a warmer climate when the global atmospheric temperature is already increasing. Field experiments were conducted in subtropical Eastern India during the rabi seasons of 2014–2016 to study the performance of wheat under the elevated CO2 environment with different nitrogen (N) management. Wheat was grown in open field and inside open top chambers (OTCs) with ambient (˜390 μmol mol−1) and elevated (˜585 μmol mol−1) level of CO2 without any fertilizer addition (N0), and with application of N through chemical fertilizer (CF) at normal (100%) recommendation [N100(CF)] and 50% higher dose [N150(CF)] and through integration of organic and chemical fertilizer [N150(OF + CF)]. Results showed that CO2 enrichment had a positive effect on various growth parameters and yield attributes of wheat. Elevated CO2 tended to increase the crop growth rate and the fraction of leaf biomass and leaf N, especially for the N management using chemical fertilizer [N100(CF) and N150(CF)]. Elevated CO2 [+˜200 μmol mol−1] caused 17% increase in wheat grain yield above ambient as averaged over the N fertilized treatments. Application of N at 50% higher dose than normal through CF did not increase the grain yield significantly under the open field and OTC with ambient [CO2] environment, whereas the yield increment was significant under the elevated [CO2] environment. Elevated CO2 also resulted in higher agronomic N use efficiency and nitrogen harvest index with the increased N fertilizer dose. Thus, wheat production under the elevated CO2 environment in Eastern India might be maintained or improved through the normal and increased dose of N fertilizer application.

Ambient conditions of elevated temperature and CO2 levels are detrimental to the probabilities of transmission by insects of a Potato virus Y isolate and to its simulated prevalence in the environment

Conditions of elevated temperature and CO2 levels [30 °C and 970 parts-per-million (ppm), respectively] reduced the systemic titers of a potato virus Y (PVY) isolate in Nicotiana benthamiana plants, relative to standard conditions (25 °C, ~405 ppm CO2). Under controlled conditions we studied how these growing environments affected the transmission of infection by aphids. Probabilities of transmission of infection by insects that fed on infected donor plants kept at either standard conditions, or at 30 °C and 970 ppm CO2 were both determined and found to positively correlate with titers in donor leaves, independently of the ambient conditions in which recipient plantlets would grow. With these data, viral prevalence was simulated under conditions of elevated temperature and CO2 levels and found that for it to remain comparable to that simulated under standard conditions, insect arrivals to recipient plants in the former scenario would have to increase several-fold in their frequency.

Nutrition from a climate change perspective.

Climate change is threatening future global food and nutrition security. Limiting the increase in global temperature to 1·5 °C set out in The Paris Agreement (2015) while achieving nutrient security means overhauling the current food system to create one that can deliver healthy and sustainable diets. To attain this, it is critical to understand the implications for nutrition of actions to mitigate climate change as well as the impacts of climate change on food production and the nutrient composition of foods. It is widely recognised that livestock production has a much greater environmental burden than crop production, and therefore advice is to reduce meat consumption. This has triggered concern in some sectors about a lack of protein in diets, which hence is driving efforts to find protein replacements. However, in most high- and middle-income countries, protein intakes far exceed dietary requirements and it would even if all meat were removed from diets. Reduction in micronutrients should be given more attention when reducing meat. Simply eating less meat does not guarantee healthier or more sustainable diets. Climate change will also affect the type, amount and nutrient quality of food that can be produced. Studies have shown that increased temperature and elevated CO2 levels can reduce the nutrient density of some staple crops, which is of particular concern in low-income countries. Nutrition from a climate change perspective means considering the potential consequences of any climate action on food and nutrition security. In this paper, we discuss these issues from an interdisciplinary perspective.

Comparing the effects of growing conditions on simulated Ethiopian tef and wheat yields

Tef and wheat are staple grains in Ethiopia and are an important part of Ethiopian food security. The DSSAT NWheat and DSSAT Tef models were used to examine the effects of nitrogen fertilizer, planting date, and atmospheric CO2 on tef and wheat grain yields across four locations in Ethiopia and a 30-year time period.Observed wheat yields were consistently higher than observed tef yields, but the models showed that tef could outproduce wheat in some low yielding scenarios. Wheat yields were more responsive to N fertilizer than tef, due to a higher harvest index causing more of the additional biomass to be allocated to grain yields. Frequently, high rainfall increased N leaching, exacerbated N stress, and reduced yields for both crops. Early planting was often detrimental to yields, except for regions and years with terminal drought and heat stress. With continuously increasing atmospheric CO2 concentrations, wheat, as a C3 crop, will further outperform tef, a C4 crop, in the future, as long as N is not limiting. Breeding for lodging resistance and a higher harvest index could significantly improve future tef yields, while higher N applications and the use of split fertilizer applications to avoid leaching would improve both tef and wheat yields. As wheat has a higher N response than tef, is more responsive to future elevated atmospheric CO2 levels, and is generally higher yielding, wheat could add more to food security in Ethiopia. However, under low input, low yielding conditions, growing tef will likely remain the preferred cereal in Ethiopia due to its higher cultural, nutritional and economic value.

Effect of elevated CO2 and temperature on spikelet sterility in rice

Increase in the concentration of greenhouse gases (GHGs) led to global climate change has both direct and indirect effects on crop production. An experiment was conducted in IARI farm, New Delhi during the kharif season of year 2017 to quantify the effect of elevated CO2 and temperature on yield attributes as well as spikelet sterility of rice crop. Rice seedlings were transplanted in crates placed inside open top chambers (OTC) subjected to two different CO2 concentrations i.e. ambient (400 ppm) and elevated (550 ± 25 ppm) and also two different temperature levels i.e. ambient and elevated (+2°C). Nitrogen (N) was applied in five doses i.e., 0%, 75%, 100% and 125% of recommended N dose. Elevated CO2 increased panicle number in rice which was further increased with increase in N doses. High temperature significantly decreased grain number per panicle but elevated CO2level was able to increase this yield attribute. Spikelet sterility increased in high temperature treatment (18.9%) due to poor grain filling than chamber control treatment (12.4%). But more biomass accumulation resulted in more grain filling and less spikelet sterility under elevated CO2 level. The study showed thatelevated CO2 level will be able to alleviate the negative effect of high temperature on certain yield attributes in rice.

Impact of climate change on disease scenario in crops

Climate change has posed a grim situation in front of us as global temperatures are rising unabated with imminent effect on production and productivity of crops. There is evidence that climate change has already negatively affected wheat and maize yields in many regions. Effect of climate change is also visible on plant-pathogens interactions generally in terms of their higher incidence, more severity and their wider geographical distribution. Pathogens still claim 10–16% of the global harvest. Climate models predict a gradual rise in CO2 concentration and temperature all over the world. Elevated levels of CO2 can directly affect the growth of pathogens. Changes in temperature and precipitation will alter the growth stage, development rate and pathogenicity of the plant pathogens and also physiology and resistance of the host plants. A change in temperature could directly affect the spread of infectious diseases and their survival between the seasons. Published observations on the distribution of 612 crop pests collected over the past 50 years indicate that crop pests have been spreading north and south a little less than 2 miles (3.2 km) a year since 1960. Specifically, losses from stripe rust of wheat were reported from just 11 of the 48 continental US states during the period 1960–1999, whereas during 2000–2014, the disease was reported in a total of 26 states in US and three Canadian provinces. Changing disease scenario with climate change emphasizes the need for developing regular monitoring, forecasting and early warning systems for important host-pathogens which have a direct bearing on the earnings of the farmers and food security at large. Further, adaptation through diversification will be required, which will produce changes in the crop profile that will have effects on disease incidence and severity.

Aerobic performance of two tropical cephalopod species unaltered by prolonged exposure to projected future carbon dioxide levels.

Squid and many other cephalopods live continuously on the threshold of their environmental oxygen limitations. If the abilities of squid to effectively take up oxygen are negatively affected by projected future carbon dioxide (CO2) levels in ways similar to those demonstrated in some fish and invertebrates, it could affect the success of squid in future oceans. While there is evidence that acute exposure to elevated CO2 has adverse effects on cephalopod respiratory performance, no studies have investigated this in an adult cephalopod after relatively prolonged exposure to elevated CO2 or determined any effects on aerobic scope. Here, we tested the effects of prolonged exposure (≥20% of lifespan) to elevated CO2 levels (~1000μatm) on the routine and maximal oxygen uptake rates, aerobic scope and recovery time of two tropical cephalopod species, the two-toned pygmy squid, Idiosepius pygmaeus and the bigfin reef squid, Sepioteuthis lessoniana. Neither species exhibited evidence of altered aerobic performance after exposure to elevated CO2 when compared to individuals held at control conditions. The recovery time of I. pygmaeus under both control and elevated CO2 conditions was less than 1hour, whereas S. lessoniana required approximately 8hours to recover fully following maximal aerobic performance. This difference in recovery time may be due to the more sedentary behaviours of I. pygmaeus. The ability of these two cephalopod species to cope with prolonged exposure to elevated CO2 without detriment to their aerobic performance suggests some resilience to an increasingly high CO2 world.

Palaeocene–Eocene Thermal Maximum prolonged by fossil carbon oxidation

A hallmark of the rapid and massive release of carbon during the Palaeocene–Eocene Thermal Maximum is the global negative carbon isotope excursion. The delayed recovery of the carbon isotope excursion, however, indicates that CO2 inputs continued well after the initial rapid onset, although there is no consensus about the source of this secondary carbon. Here we suggest this secondary input might have derived partly from the oxidation of remobilized sedimentary fossil carbon. We measured the biomarker indicators of thermal maturation in shelf records from the US Mid-Atlantic coast, constructed biomarker mixing models to constrain the amount of fossil carbon in US Mid-Atlantic and Tanzania coastal records, estimated the fossil carbon accumulation rate in coastal sediments and determined the range of global CO2 release from fossil carbon reservoirs. This work provides evidence for an order of magnitude increase in fossil carbon delivery to the oceans that began ~10–20 kyr after the event onset and demonstrates that the oxidation of remobilized fossil carbon released between 102 and 104 PgC as CO2 during the body of the Palaeocene–Eocene Thermal Maximum. The estimated mass is sufficient to have sustained the elevated atmospheric CO2 levels required by the prolonged global carbon isotope excursion. Even after considering uncertainties in the sedimentation rates, these results indicate that the enhanced erosion, mobilization and oxidation of ancient sedimentary carbon contributed to the delayed recovery of the climate system for many thousands of years. Delivery of fossil carbon to the oceans strongly increased about 15 kyr after the onset of the Palaeocene–Eocene Thermal Maximum as a result of oxidation of sedimentary carbon, suggests an analysis of geochemical measurements with a biomarker mixing model.

Elevated CO2 impairs olfactory-mediated neural and behavioral responses and gene expression in ocean-phase coho salmon (Oncorhynchus kisutch).

Elevated concentrations of CO2 in seawater can disrupt numerous sensory systems in marine fish. This is of particular concern for Pacific salmon because they rely on olfaction during all aspects of their life including during their homing migrations from the ocean back to their natal streams. We investigated the effects of elevated seawater CO2 on coho salmon (Oncorhynchus kisutch) olfactory-mediated behavior, neural signaling, and gene expression within the peripheral and central olfactory system. Ocean-phase coho salmon were exposed to three levels of CO2 , ranging from those currently found in ambient marine water to projected future levels. Juvenile coho salmon exposed to elevated CO2 levels for 2weeks no longer avoided a skin extract odor that elicited avoidance responses in coho salmon maintained in ambient CO2 seawater. Exposure to these elevated CO2 levels did not alter odor signaling in the olfactory epithelium, but did induce significant changes in signaling within the olfactory bulb. RNA-Seq analysis of olfactory tissues revealed extensive disruption in expression of genes involved in neuronal signaling within the olfactory bulb of salmon exposed to elevated CO2 , with lesser impacts on gene expression in the olfactory rosettes. The disruption in olfactory bulb gene pathways included genes associated with GABA signaling and maintenance of ion balance within bulbar neurons. Our results indicate that ocean-phase coho salmon exposed to elevated CO2 can experience significant behavioral impairments likely driven by alteration in higher-order neural signal processing within the olfactory bulb. Our study demonstrates that anadromous fish such as salmon may share a sensitivity to rising CO2 levels with obligate marine species suggesting a more wide-scale ecological impact of ocean acidification.

Changes of alternative splicing in Arabidopsis thaliana grown under different CO2 concentrations

Atmospheric CO2 level is one of the most important factors which affect plant growth and crop production. Although many crucial genes and pathways have been identified in response to atmospheric CO2 changes, the integrated and precise mechanisms of plant CO2 response are not well understood. Alternative splicing (AS) is an important gene regulation process that affects many biological processes in plants. However, the AS pattern changes in plants in response to elevated CO2 levels have not yet been investigated. Here, we used RNA-Seq data of Arabidopsis thaliana grown under different CO2 concentration to analyze the global changes in AS. We found that AS increased with the rise in CO2 concentration. Additionally, we identified 345 differentially expressed (DE) genes and 251 differentially alternative splicing (DAS) genes under the elevated CO2 condition. Moreover, the results showed that the expression of most of the DAS genes did not change significantly, indicating that AS can serve as an independent mechanism for gene regulation in response to elevated CO2. Furthermore, our analysis of function categories revealed that the DAS genes were associated mainly with the stimulus response. Overall, this the first study to explore the changes of AS in plants in response to elevated CO2.

Ocean acidification increases iodine accumulation in kelp-based coastal food webs.

Kelp are main iodine accumulators in the ocean, and their growth and photosynthesis are likely to benefit from elevated seawater CO2 levels due to ocean acidification. However, there are currently no data on the effects of ocean acidification on iodine metabolism in kelp. As key primary producers in coastal ecosystems worldwide, any change in their iodine metabolism caused by climate change will potentially have important consequences for global geochemical cycles of iodine, including iodine levels of coastal food webs that underpin the nutrition of billions of humans around the world. Here, we found that elevated pCO2 enhanced growth and increased iodine accumulation not only in the model kelp Saccharina japonica using both short-term laboratory experiment and long-term in situ mesocosms, but also in several other edible and ecologically significant seaweeds using long-term in situ mesocosms. Transcriptomic and proteomic analysis of S.japonica revealed that most vanadium-dependent haloperoxidase genes involved in iodine efflux during oxidative stress are down-regulated under increasing pCO2 , suggesting that ocean acidification alleviates oxidative stress in kelp, which might contribute to their enhanced growth. When consumed by abalone (Haliotis discus), elevated iodine concentrations in S.japonica caused increased iodine accumulation in abalone, accompanied by reduced synthesis of thyroid hormones. Thus, our results suggest that kelp will benefit from ocean acidification by a reduction in environmental stress however; iodine levels, in kelp-based coastal food webs will increase, with potential impacts on biogeochemical cycles of iodine in coastal ecosystems.

Effect of elevated atmospheric CO2 concentration on growth and physiology of wheat and sorghum under cadmium stress

ABSTRACT Elevated concentrations of carbon dioxide (e[CO2]) affect plant growth and physiological characteristics, including metal accumulation, and the activity of anti-oxidant enzymes. These effects were investigated in cadmium (Cd) tolerant wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor (L.) Moench.) cultivars. Plants were grown at the ambient and elevated CO2 levels, with four concentrations of Cd (0, 10, 20 and 40 mg kg−1) added to the soil. After 60 days, subsamples were tested for chlorophylls and carotenoids, protein, enzyme activities and morphological characteristics. Results showed that e[CO2] increased plant height, leaf area, and the dry weight of shoots and roots (P < 0.01). In addition, it decreased the Cd concentration in the shoots and roots of wheat, and increased the same concentrations for sorghum. With increasing Cd, the activities of the anti-oxidants, SOD and GSH-px increased in wheat. The differences in enzyme activity parallel the changes in Cd concentration in the plants of both species.

The effect of CO2 in enhancing photosynthetic cofactor recycling for alcohol dehydrogenase mediated chiral synthesis in cyanobacteria

The light harvesting photosystem in cyanobacteria offers a potential pathway for the regeneration of the nicotinamide cofactor NADPH, thereby facilitating the application of cyanobacteria as excellent whole cell biocatalysts in oxidoreductase-mediated biotransformation. The use of cyanobacterial metabolism for cofactor recycling improves the atom economy of the process compared to the commonly employed enzyme-coupled cofactor recycling using enzymes such as glucose dehydrogenase. Here we report the asymmetric conversion of acetophenone to chiral 1-phenylethanol by recombinant Synechococcus elongatus PCC 7942 whole cell biocatalyst that expresses the NADPH dependent L. kefir alcohol dehydrogenase. Besides light, it was observed that carbon dioxide levels play a critical role in improving the bioconversion efficiency possibly due to the enhanced growth rate and improved cofactor availability at elevated CO2 levels. Complete reduction of acetophenone to optically pure (R)-1-phenylethanol at 99% enantiomeric excess was achieved within 6 h with a relatively low cell density of 0.66 g/l by coupling optimum light and CO2 levels and without the need for a co-substrate.

Root growth responses of parthenium weed and different pasture plants under elevated atmospheric carbon dioxide

Parthenium weed (Parthenium hysterophorus L.) is an alien invasive species reducing pasture productivity and livestock production in Australia and other countries around the world. Three C-4 pasture grasses (Setaria incrassata, Astrebla squarrosa and Bothriochloa decipiens) and one C-3 pasture legume species (Clitoria ternatea), all previously known to be suppressive of the growth of parthenium weed under ambient CO2 (390 mu molmol(-1)), were re-tested under an elevated atmospheric CO2 (550 mu molmol(-1)) level in a controlled environment growth chamber. When grown alone and under elevated atmospheric CO2 level, the root dry biomass of S. incrassata and A. squarrosa did not get affected significantly, whereas that of B. decipiens, C. ternatea and P. hysterophorus significantly increased by 10,34 and 26 %, respectively. When S. incrassata and A. squarrosa were grown together with parthenium weed under the same conditions, their root dry biomass reduced by 20 and 16 %, while that of B. decipiens and C. ternatea was increased by 7 and 28 %, respectively. The root to shoot ratio of S. incrassata and A. squarrosa decreased significantly by 24 and 16 %, while that of B. decipiens, C. ternatea and parthenium weed increased by 6, 17 and 12 %, respectively, under the same conditions. These results have important implications for the management of parthenium weed in future climate scenarios involving elevated atmospheric CO2 levels. Our results suggest that some pasture species with the potential to suppress the growth of parthenium weed under the present climate will remain an important tool in managing pastures invaded by parthenium weed in the future.

Carbon dioxide is an absolute requirement for exsheathment of some, but not all, abomasal nematode species.

The first step in the infection process of grazing ruminants by gastrointestinal nematodes is the exsheathment of the third-stage larva (L3). Exsheathment of various species can be achieved in vitro using carbon dioxide (CO2) under the appropriate temperature and pH conditions. However, it remains unclear whether elevated CO2 levels are an absolute requirement for exsheathment. Exsheathment of four abomasal species was investigated in both the presence and absence of CO2, in either rumen fluid (cow or sheep) or buffer (standard or enriched). Exsheathment of Ostertagia ostertagi, Teladorsagia circumcincta and Ostertagia leptospicularis was observed in CO2-depleted rumen fluid and enriched buffer (respectively 46%, 22% and 15% in rumen fluid and 28% 18% and 26% in enriched buffer after 24h). The level of this response was dependent on the species as well as the medium, and exsheathment was significantly higher in the presence of CO2. For Haemonchus contortus, exsheathment could only be achieved under CO2-saturated conditions. In conclusion, even though these parasite species exsheath in the same environment, there were significant differences in the minimal requirements to trigger their exsheathment. Some abomasal species were capable of exsheathment in the absence of CO2, which is likely facilitated by cofactors present in the rumen fluid and/or enriched buffer.

Primary productivity and physiological responses of Vitis vinifera L. cvs. under Free Air Carbon dioxide Enrichment (FACE)

Abstract Two Vitis vinifera L. cultivars, Riesling and Cabernet Sauvignon, were grown in the Geisenheim VineyardFACE (Free Air Carbon dioxide Enrichment) system under rain-fed conditions to investigate the effects of elevated CO2 on the productivity of grapevines for three consecutive years (2014–2016) following planting in 2012. The FACE system consisted of six 12 m diameter rings, with three at ambient CO2 (aCO2, 400 ppm), and three rings at elevated CO2 (eCO2, + 20% of aCO2 level). Vegetative growth, single leaf gas exchange and yield parameters were monitored for the three growing seasons. Vegetative growth parameters responded differently to CO2 treatments depending on biomass components. Trunk cross section area, as an indicator of perennial growth, showed a significant increase for Riesling under eCO2 but not for Cabernet Sauvignon. Fresh biomass as lateral leaf area and fresh weight of summer pruning were stimulated by elevated CO2 for both cultivars. Leaf gas exchange measurements for both cultivars showed a significant increase in net assimilation rate and an improved intrinsic water use efficiency for all three years under eCO2 conditions. However, contrary to expected stomatal behaviour of grapevines, transpiration rate and stomatal conductance were higher under elevated CO2 for Riesling and Cabernet Sauvignon in all three seasons. Higher values of pre-dawn leaf water potential recorded under eCO2 point towards an interaction with soil water availability and root system development. Elevated CO2 resulted in higher yield in terms of higher bunch weight, but did not affect average number of bunches per vine or sugar content of must at harvest date. Accordingly, bunch architecture was altered under elevated CO2 levels. The increase in primary productivity of grapevines under eCO2 indicates yield gains that can be expected under even modest near-future CO2 scenarios. However, higher water use, particularly if maintained as grapevines transition to maturity, may have critical implications for the future adaptation of non-irrigated viticulture to increasing temperature and periods of rainfall deficit.

Annual ryegrass (Lolium rigidum Gaud) competition altered wheat grain quality: A study under elevated atmospheric CO2 levels and drought conditions

Annual ryegrass is one of the most serious, costly weeds of winter cropping systems in Australia. To determine whether its competition-mediated plant defence mechanisms effect on wheat grain quality, wheat (cv. Yitpi) and annual ryegrass were grown under two levels of CO2 (400 ppm; (a[CO2]) vs 700 ppm; (e[CO2]), two levels of water (well-watered vs drought) and two types of competition (wheat only; (W), and wheat × annual ryegrass; (W × R) with four replicates. The competition × [CO2] interaction had a significant effect on wheat grain protein content, where it was increased in W × R under both e[CO2] (+17%) and a[CO2] (+21%). Grain yield, total grain reducing power and phenolic content were significantly affected by [CO2] × drought × competition. In a summary, annual ryegrass competition significantly altered the wheat grain quality under both [CO2] levels (depending on the soil water level), while also decreasing the grain yield.

Elevated carbon dioxide and drought modulate physiology and storage-root development in sweet potato by regulating microRNAs.

Elevated CO2 along with drought is a serious global threat to crop productivity. Therefore, understanding the molecular mechanisms plants use to protect these stresses is the key for plant growth and development. In this study, we mimicked natural stress conditions under a controlled Soil-Plant-Atmosphere-Research (SPAR) system and provided the evidence for how miRNAs regulate target genes under elevated CO2 and drought conditions. Significant physiological and biomass data supported the effective utilization of source-sink (leaf to root) under elevated CO2. Additionally, elevated CO2 partially rescued the effect of drought on total biomass. We identified both known and novel miRNAs differentially expressed during drought, CO2, and combined stress, along with putative targets. A total of 32 conserved miRNAs belonged to 23 miRNA families, and 25 novel miRNAs were identified by deep sequencing. Using the existing sweet potato genome database and stringent analyses, a total of 42 and 22 potential target genes were predicted for the conserved and novel miRNAs, respectively. These target genes are involved in drought response, hormone signaling, photosynthesis, carbon fixation, sucrose and starch metabolism, etc. Gene ontology and KEGG ontology functional enrichment revealed that these miRNAs might target transcription factors (MYB, TCP, NAC), hormone signaling regulators (ARF, AP2/ERF), cold and drought factors (corA), carbon metabolism (ATP synthase, fructose-1,6-bisphosphate), and photosynthesis (photosystem I and II complex units). Our study is the first report identifying targets of miRNAs under elevated CO2 levels and could support the molecular mechanisms under elevated CO2 in sweet potato and other crops in the future.

Effect of CO2 exposure on the mobility of heavy metals in submerged soils

Increasing atmospheric carbon dioxide (CO2) concentration can affect CO2 level in soil, and this, in turn, may cause changes in soil chemical properties. This study investigated the effect of CO2 exposure on pH and heavy metal mobility in submerged soils. Laboratory-scale batch tests were carried out using two soil samples with different initial pH conditions (A: 5.3; B: 6.3). The changes in the pH values of the soil solutions (i.e., water layer above soil) of the CO2-affected soil samples and controls with time were not significant (p value > 0.05) with the both soil samples, and this may be attributed to the formation of bicarbonate, which may provide a buffering capacity. The effect on heavy metal mobility was different in the soil samples A and B. With the soil sample A, the soil heavy metal concentrations were generally lower in the CO2-affected soil than in the controls. Accordingly, the soil solution heavy metal concentrations were changed. With the soil sample B, the soil heavy metal concentrations of the CO2-affected soil and control did not show a significant difference (p value > 0.05). This can be partially attributed to the dissolution of carbonates that generate bicarbonates, and this is supported by the lower soil Ca concentration in the CO2-affected soil. Overall, the results suggest that the elevated CO2 level in submerged soils may have different effects on the soil chemical properties, and this necessitates continuous research efforts in order to manage and conserve soil environment under conditions of increasing atmospheric CO2 concentration.

Production of Pig Feed under Future Atmospheric CO2 Concentrations: Changes in Crop Content and Chemical Composition, Land Use, Environmental Impact, and Socio-Economic Consequences

With the rising atmospheric CO2, crops will assimilate more carbon. Yields will increase in terms of carbohydrates while diluting the content of protein and minerals in compound pig feed, calling for an altered formulation with more protein and less carbohydrate crops to maintain its nutritional value. Using crop response data from CO2 exposures in a linear modeling of feed formulation, we apply a consequential life cycle assessment (cLCA) to model all of the environmental impacts and socio-economic consequences that altered crop yields and chemical composition at elevated CO2 levels have on feed formulation, targeting altered amino acid contents rather than overall protein. An atmospheric CO2 of 550 µmole mole−1 gives rise to a 6% smaller demand for land use for pig feed production. However, feed produced at this CO2 must include 23% more soymeal and 5% less wheat than at present in order to keep its nutritional value. This counteracts the yield benefit. The monetized environmental cost of producing pig feed, where sunflower and soy contribute the most, equals the direct feed price in both scenarios. If external costs were internalized, honoring the Rio Declaration, feed prices would double. In contrast, the future composition of pig feed will increase the direct price by only 0.8%, while the external cost decreases by only 0.3%.