Ozone (O₃) is a phytotoxic air pollutant, the adverse effects of which on growth and photosynthesis are modified by other environmental factors. In this study, we examined the combined effects of O₃, elevated CO₂, and soil nitrogen supply on Siebold's beech seedlings. Seedlings were grown under combinations of two levels of O₃ (low and two times ambient O₃ concentration), two levels of CO₂ (ambient and 700 ppm), and three levels of soil nitrogen supply (0, 50, and 100 kg N ha⁻¹ year⁻¹) during two growing seasons (2019 and 2020), with leaf photosynthetic traits being determined during the second season. We found that elevated CO₂ ameliorated O₃-induced reductions in photosynthetic activity, whereas the negative effects of O₃ on photosynthetic traits were enhanced by soil nitrogen supply. We observed three-factor interactions in photosynthetic traits, with the ameliorative effects of elevated CO₂ on O₃-induced reductions in the maximum rate of carboxylation being more pronounced under high than under low soil nitrogen conditions in July. In contrast, elevated CO₂-induced amelioration of the effects of O₃ on stomatal function-related traits was more pronounced under low soil nitrogen conditions. Although we observed several two- or three-factor interactions of gas and soil treatments with respect to leaf photosynthetic traits, the shoot to root dry mass (S/R) ratio was the only parameter for which a significant interaction was detected among seedling growth parameters. O₃ caused a significant increase in S/R under ambient CO₂ conditions, whereas no similar effects were observed under elevated CO₂ conditions. Collectively, our findings reveal the complex interactive effects of elevated CO₂ and soil nitrogen supply on the detrimental effects of O₃ on leaf photosynthetic traits, and highlight the importance of taking into consideration differences between the responses of CO₂ uptake and growth to these three environmental factors.

Arbuscular mycorrhizal fungi (AMF) are easily influenced by increasing atmospheric CO₂ concentration and heavy metals including cadmium (Cd), which can regulate antioxidant enzyme in host plants. Although the effect of AMF under individual conditions such as elevated CO₂ (ECO₂) and Cd on antioxidant enzyme in host plants has been reported widely, the effect of AMF under ECO₂ + Cd receives little attention. In this study, a pot experiment was conducted to study the effect of AMF community in roots on superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities in leaves of 135-d Robinia pseudoacacia L. seedlings under ECO₂ + Cd. The activities of SOD and CAT increased and POD activity and the richness and diversity of AMF community decreased under ECO₂ + Cd relative to Cd alone. The richness and diversity of AMF were negatively related to Cd content in roots and leaves. The richness and OTUs of AMF community positively and AMF gene abundance negatively affected POD activity under the combined treatments. Superoxide dismutase and POD activities were negatively and positively related to Archaeospora and Scutellospora, respectively, under ECO₂ + Cd. Cadmium in roots and leaves was negatively and significantly related to Glomus, Scutellospora, and Claroideoglomus abundance under ECO₂ + Cd. Overall, AMF diversity and Archaeospora and Scutellospora in roots significantly influenced SOD, POD, and CAT activities. The response of AM symbiosis to ECO₂ might regulate antioxidant capacity in host plants upon Cd exposure. Glomus, Scutellospora, and Claroideoglomus might be applied to phytoremediation of Cd-contaminated soils.

The present study evaluated the interactive effects of global change and heavy metals on the growth and development of three soybean [Glycine max (L.) Merrill] cultivars and the consequences on yield and food safety. Soybean cultivars (Alim 3.14 from Argentina, and ES Mentor and Sigalia, from Germany) were grown until maturity in heavy metals polluted soils from the Rhine Valley, Germany, at two CO₂ concentrations (400 and 550 ppm) and heat stress (HS) episodes (9 days with 10 °C higher than maximum regular temperature) during the critical growth period in controlled environmental chambers. Different morpho-physiological parameters, heavy metal concentration in aerial organs, seed quality parameters, and toxicological index were recorded. The results showed that no morphological differences were observed related to CO₂. Moreover, Alim 3.14 showed the highest yield under control conditions, but it was more sensitive to climatic conditions than the German cultivars, especially to heat stress which strongly reduces the biomass of the fruits. Heavy metals concentration in soil exceeds the legislation limits for agricultural soils for Cd and Pb, with 1.6 and 487 mg kg⁻¹ respectively. In all cultivars, soybeans accumulated Cd in its aerial organs, and it could be translocated to fruits. Cd concentration in seeds ranged between 0.6 and 2.4 mg kg⁻¹, which exceed legislation limits and with toxicological risk to potential Chinese consumers. Pb levels were lower than Cd in seeds (0.03–0.17 mg kg⁻¹), and the accumulation were concentrated in the vegetative organs, with 93% of the Pb incorporated. Moreover, pods accumulated 11 times more Pb than seeds, which suggests that they act as a barrier to the passage of Pb to their offspring. These results evidence that soybean can easily translocate Cd, but not Pb, to reproductive organs. No regular patterns were observed in relation to climatic influence on heavy metal uptake.

The interactive effects of elevated atmospheric CO₂ and nanoparticles (NPs) on the structure and function of soil bacterial community remain unknown. Here we compared the impacts of CeO₂ (nCeO₂) and Cr₂O₃ (nCr₂O₃) nanoparticles on the taxonomic compositions and functional attributes of bacterial communities under elevated CO₂ (eCO₂). The stimulated enzyme activities (dehydrogenase, acid phosphatase and urease), increased microbial biomass carbon (MBC), and higher bacterial alpha-diversity were observed under the combined effects of eCO₂ and NPs compared to the single NP treatment, indicating eCO₂ could mitigate the adverse effect of NPs on soil microorganisms. NPs and eCO₂ are important factors influencing the alpha- and beta-diversity (17% and 18% of variations were explained) as well as functional profile (20% and 26% of variations were explained) of bacterial communities. Rising CO₂ level promoted the resilience of NP-resistant bacterial populations, primarily the members of Alphaproteobacteria, Gammaproteobacteria and Bacteroidia, which are also characterized by the fast carbon use capability. Moreover, the significantly (P < 0.05) higher metabolic quotient (qCO₂), reduced available carbon and overrepresented carbon metabolism genes at eCO₂vs. ambient CO₂ (aCO₂) indicate the acceleration of available carbon turnover in NP-exposed soils. Correlation analysis revealed that mitigation of NPs toxicity by eCO₂ could be attributed to the remarkable decline of bioavailable metals disassociated from NPs and available carbon level, as well as promotion of the rapid carbon-metabolizing microbes. Our study pointed out the positive role of eCO₂ in alleviating the adverse effect of NPs on microbiological soil environment, and results can serve as important basis in establishing guidelines for lowering the ecotoxicity of NPs.

The potential leakage from marine CO2 storage sites is of increasing concern, but few studies have evaluated the probable adverse effects on marine organisms. Fish, one of the top predators in marine environments, should be an essential representative species used for water column toxicity testing in response to waterborne CO2 exposure. In the present study, we conducted fish life cycle toxicity tests to fully elucidate CO2 toxicity mechanism effects. We tested sub-lethal and lethal toxicities of elevated CO2 concentrations on marine medaka (Oryzias melastigma) at different developmental stages. At each developmental stage, the test species was exposed to varying concentrations of gaseous CO2 (control air, 5%, 10%, 20%, and 30%), with 96 h of exposure at 0–4 d (early stage), 4–8 d (middle stage), and 8–12 d (late stage). Sub-lethal and lethal effects, including early developmental delays, cardiac edema, tail abnormalities, abnormal pigmentation, and mortality were monitored daily during the 14 d exposure period. At the embryonic stage, significant sub-lethal and lethal effects were observed at pH < 6.30. Hypercapnia can cause long-term and/or delayed developmental embryonic problems, even after transfer back to clean seawater. At fish juvenile and adult stages, significant mortality was observed at pH < 5.70, indicating elevated CO2 exposure might cause various adverse effects, even during short-term exposure periods. It should be noted the early embryonic stage was found more sensitive to CO2 exposure than other developmental stages of the fish life cycle. Overall, the present study provided baseline information for potential adverse effects of high CO2 concentration exposure on fish developmental processes at different life cycle stages in marine ecosystems.

To explore the effect of elevated CO₂ concentrations ([CO₂]) on phosphine formation in paddy fields, the matrix-bound phosphine (MBP) content, different phosphorus fractions and various carbon forms in soil samples from rice cultivation under varying CO₂ concentrations of 400 ppm, 550 ppm and 700 ppm by indoor simulation experiment were determined. This study showed that MBP concentration did not increase significantly with elevated [CO₂] over four-week cultivation periods of rice seedlings, regardless of soil layers. MBP had a significant positive correlation with total phosphorus (TP) and inorganic phosphorus (IP), and multiple stepwise linear regression analysis further indicated that MBP preservation in neutral paddy soils with depths of 0–20 cm may have been due to conversion from FeP and CaP. Based on redundancy analysis and forward selection analysis, speculated that the formation of MBP in the neutral paddy soils as the response to atmospheric elevated [CO₂] was due to two processes: (i) FeP transformation affected by the changes of soil respiration (SCO₂) and TOC was the main precursor for the production of MBP; and (ii) CaP transformation resulting from variation in HCO₃⁻ was the secondary MBP source. The complex combination of these two processes is simultaneously controlled by SCO₂. In a word, the soil environment in the condition of elevated [CO₂] was in favor of MBP storage in neutral paddy soils. The results of our study imply that atmospheric CO₂ participates in and has a certain impact on the global biogeochemical cycle of phosphorus.

Environmental pollution by both ambient CO2 and heavy metals has been steadily increasing, but we do not know how fluctuating CO2 concentrations influence plant nutrients under high Cd pollution, especially in crops. Here, we studied the effects of elevated CO2 and Cd accumulation on proteins and amino acids in rice under Cd stress. In this pot experiment, we analyzed the amino-acid profile of 20 rice cultivars that accumulate Cd differently; the plants were grown in Cd-containing soils under ambient conditions and elevated CO2 levels. We found that although Cd concentrations appeared to be higher in most cultivars under elevated CO2 than under ambient CO2, the effect was significant only in seven cultivars. Combined exposure to Cd and elevated CO2 strongly decreased rice protein and amino acid profiles, including essential and non-essential amino acids. Under elevated CO2, the ratios of specific amino acids were either higher or lower than the optimal ratios provided by FAO/WHO, suggesting that CO2 may flatten the overall amino-acid profile, leading to an excess in some amino acids and deficiencies in others when the rice is consumed. Thus, Cd-tainted rice limits the concentration of essential amino acids in rice-based diets, and the combination with elevated CO2 further exacerbates the problem.

Seedlings of Psidium guajava cv. Pedro Sato were distributed into four open-top chambers: two with ambient CO2 (∼390 ppm) and two with elevated CO2 (∼780 ppm). Monthly, five individuals of each chamber were collected, separated into root, stem and leaves and immediately frozen in liquid nitrogen. Chemical parameters were analyzed to investigate how guava invests the surplus carbon. For all classes of phenolic compounds analyzed only tannins showed significant increase in plants at elevated CO2 after 90 days. There was no significant difference in dry biomass, but the leaves showed high accumulation of starch under elevated CO2. Results suggest that elevated CO2 seems to be favorable to seedlings of P. guajava, due to accumulation of starch and tannins, the latter being an important anti-herbivore substance.

We investigated the influence of elevated CO₂ and O₃ on soil N cycling within the soybean growing season and across soil environments (i.e., rhizosphere and bulk soil) at the Soybean Free Air Concentration Enrichment (SoyFACE) experiment in Illinois, USA. Elevated O₃ decreased soil mineral N likely through a reduction in plant material input and increased denitrification, which was evidenced by the greater abundance of the denitrifier gene nosZ. Elevated CO₂ did not alter the parameters evaluated and both elevated CO₂ and O₃ showed no interactive effects on nitrifier and denitrifier abundance, nor on total and mineral N concentrations. These results indicate that elevated CO₂ may have limited effects on N transformations in soybean agroecosystems. However, elevated O₃ can lead to a decrease in soil N availability in both bulk and rhizosphere soils, and this likely also affects ecosystem productivity by reducing the mineralization rates of plant-derived residues.

Elevated carbon dioxide (ECO₂) concentration has profound impacts on ecosystem carbon fluxes, with consequent changes in carbon sequestration and its feedback to climate change. Agroecosystem plays an essential role in global carbon sequestration. However, it is not well understood how the carbon fluxes of agroecosystem respond to increasing atmospheric CO₂ concentrations. In this study, an in-situ 2-year field experiment was conducted using open-top chamber with treatments including ambient CO₂ concentration (CK) and ambient plus 200 μmol mol⁻¹ (T) to investigate the characteristics and main factors influencing carbon fluxes during the 2017–2019 winter wheat growing seasons. Results showed that the dynamics of CO₂ fluxes under different treatments had similar seasonal trends, with the peak flux observed at the heading-filling stage. Compared to the CK, T treatment increased the cumulative amount of CO₂ (CAC) by 17.2% and 24.0% in 2017–2018 and 2018–2019 growing seasons, respectively. In addition, the seasonal CAC was highly dependent on treatment and varied with year, while there was no interactive effect of treatment and year (p > 0.05). ECO₂ concentration increased the biomass of wheat by an average of 8.28% over two growing seasons. There was a significant positive correlation between biomass and CAC, with biomass elucidating 52% and 76% of the variations in CAC under CK and T treatments, respectively. A good correlation was found between net ecosystem exchange (NEE) and environmental variables under different treatments. During the pre-milk ripening period, the NEE mainly depended on photosynthetically active radiation (PAR) and air temperature (Ta), while NEE was mainly controlled by PAR and soil water content (SWC) during the post-milk ripening period. Overall, the findings presented here demonstrate that the carbon exchange in wheat fields under different treatments serves as carbon sequestration, while ECO₂ concentration enhances the capacity of winter wheat fields to act as carbon sinks, which may have feedback to the climate system in the future.