Soil high Cd exacerbates the adverse impact of elevated O3 on Populus alba 'Berolinensis' L

A comparative study on cadmium tolerance and applicability of two Solanum lycopersicum L. cultivars

Solanum lycopersicum L. can be classified into low Cd-accumulating and high Cd-accumulating types based on their accumulation characteristics of cadmium (Cd). There are many common S. lycopersicum varieties available in the market, but their specific Cd tolerance and enrichment abilities are not well understood. This article uses two S. lycopersicum cultivars, Yellow Cherry and Yellow Pearl, as experimental materials. The experimental method of soil pot planting was adopted, and Cd concentrations in the soil were added at 0, 0.6, 1.5, 2.5, 5, and 10 mg/kg. The changes in Cd content, biomass, photosynthetic pigment content, and photosynthetic parameters of the two S. lycopersicum cultivars were analyzed to screen for low-accumulation S. lycopersicum cultivars. The results showed that S. lycopersicum are Cd-sensitive plants. The Cd accumulation, photosynthetic parameters, and other basic indicators of Yellow Cherry basically showed significant differences when the soil Cd concentration was 0.6 mg/kg, and the biomass showed significant differences when the soil Cd concentration was 1.5 mg/kg. Except for the Cd accumulation in the roots and leaves of Yellow Pearl, which showed significant differences at a soil Cd concentration of 0.6 mg/kg, the other indicators basically showed significant differences when the soil Cd concentration was 1.5 mg/kg. When the soil Cd concentration was 0.6 mg/kg, the Cd accumulation in the fruit of Yellow Pearl was 0.04 mg/kg, making it a low-accumulation S. lycopersicum variety suitable for promoting cultivation in Cd-contaminated soil at 0.6 mg/kg. In conclusion, the Cd accumulation in the fruit of Yellow Pearl is significantly lower than that of Yellow Cherry and even below the Cd limit value for fresh vegetables specified in GB2762-2017. Therefore, Yellow Pearl can be grown as edible crops in soils with Cd concentrations ≤0.6 mg/kg. Furthermore, Yellow Cherry demonstrate strong Cd tolerance and can be used for the remediation of Cd-contaminated soils.

Responses to Airborne Ozone and Soilborne Metal Pollution in Afforestation Plants with Different Life Forms

With the current increases in environmental stress, understanding species-specific responses to multiple stress agents is needed. This science is especially important for managing ecosystems that are already confronted with considerable pollution. In this study, responses to ozone (O3, ambient daily course values + 20 ppb) and mixed metal contamination in soils (MC, cadmium/copper/lead/zinc = 25/1100/2500/1600 mg kg-1), separately and in combination, were evaluated for three plant species (Picea abies, Acer pseudoplatanus, Tanacetum vulgare) with different life forms and ecological strategies. The two treatments elicited similar stress reactions, as shown by leaf functional traits, gas exchange, tannin, and nutrient markers, irrespective of the plant species and life form, whereas the reactions to the treatments differed in magnitude. Visible and microscopic injuries at the organ or cell level appeared along the penetration route of ozone and metal contamination. At the whole plant level, the MC treatment caused more severe injuries than the O3 treatment and few interactions were observed between the two stress factors. Picea trees, with a slow-return strategy, showed the highest stress tolerance in apparent relation to an enhancement of conservative traits and an exclusion of stress agents. The ruderal and more acquisitive Tanacetum forbs translocated large amounts of contaminants above ground, which may be of concern in a phytostabilisation context. The deciduous Acer trees-also with an acquisitive strategy-were most sensitive to both stress factors. Hence, species with slow-return strategies may be of particular interest for managing metal-polluted sites in the current context of multiple stressors and for safely confining soil contaminants below ground.

Influence of exposure history on the particle retention capacity and physiological responses of Euonymus japonicus Thunb. var. aurea-marginatus Hort

Green plants in urban environments experience cyclical particulate matter stress. And this history of exhaust exposure may generate stress memory in plants, which may alter their subsequent response. Studies combining urban pollution characteristics and stress memory are limited. Therefore, we selected E. japonicus var. aurea-marginatus, a common urban greening tree species in the Yangtze River Delta, and conducted an experiment in three periods: the initial pollution period (S1: 28 days), the recovery period (R: 14 days) and the secondary pollution period (S2: 28 days). The experimental design consisted of an elevated pollution treatment (173 μg•cm^-3) and an ambient control (34 μg•cm^-3) with three replicates. In S2, the net total particle retention and saturated particle retention decreased by 11.5% and 19.3%, respectively, while PM₁₀ and PM_2.5 did not change significantly. E. japonicus var. aurea-marginatus exhibited recovery of chlorophyll levels, slower degradation of carotenoid, faster accumulation of ASA, lower accumulation of MDA, reduced activity of SOD under the second pollution period, and the period had a significant effect on the physiological indicators. Collectively, the effect of autoexhaust exposure history on the particle retention capacity of selected plant varied across particle sizes, and stress memory may confer plant resistance to recurrent exhaust pollution via combined regulations of physiological responses. Fine particles which pose a great risk to human health arise predominantly from vehicular traffic and energy production. So, E. japonicus tends to play a stabilising role in particle retention in industrial, traffic and residential areas.

Reactive effects of pre-sowing magnetic field exposure on morphological characteristics and antioxidant ability of Brassica juncea in phytoextraction

As magnetic fields constantly act on living and biochemical processes, it is reasonable to hypothesize that magnetic field treatment of plant seeds would enhance the uptake capacity of non-essential elements. To verify this hypothesis, seeds of Brassica juncea were treated with 50, 100, 150, 200, and 400 mT fields, and the dry weight, Cd uptake capacity, ferritin content, antioxidant enzyme activity, and phytoremediation effects of the plant were compared at the end of the experiment. Relative to the control, low- and moderate-intensity fields (50-200 mT) enhanced the dry weight of plant leaves by 15.1%, 24.5%, 35.8%, and 49.1%, respectively, whereas the high-intensity field (400 mT) decreased the biomass yield by 18.9%. The content of Cd in the above-ground tissues of B. juncea enhanced with the increasing field intensity, accompanied by an increase in oxidative damage. The activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased with exposure to low (50 and 100 mT) and moderate (150 and 200 mT) intensities, followed by a reduction at a high intensity (400 mT). Catalase activity (CAT) and ferritin content exhibited an increasing trend with increasing intensity. The Cd decontamination index of B. juncea increased with the increasing magnetic field intensity until it reached a peak at 150 mT, after which the values remained constant. Considering the phytoremediation effect and energy consumption, 150 mT was the optimal scheme for magnetic-field-assisted phytoremediation using B. juncea. This study suggests that a suitable magnetic field can be regarded as an ecologically friendly physical trigger to improve the phytoextraction effect of B. juncea.

Responses of spring leaf phenological and functional traits of two urban tree species to air warming and/or elevated ozone

Climate warming and surface ozone (O₃) pollution are important global environmental issues today. However, the combined impacts of air warming and O₃ on phenology and its functional traits of urban trees are still poorly understood. Here, an experiment was performed to explore the variations of the spring phenological and functional traits in leaves of Populus alba 'Berolinensis' and Forsythia suspensa under ambient air (15.8 °C, 35.7 ppb), increased air temperature (IT, ambient air temperature + 2 °C, 17.9 °C), elevated O₃ (EO, ambient air O₃ concentrations + 40 ppb, 77.4 ppb), and their combined treatments (17.7 °C, 74.5 ppb). Our results showed that: IT advanced the beginning of leaf bud expansion phase of P. alba 'Berolinensis' and F. suspensa for 6 d and 5 d, respectively, increased leaf unfolding rate, leaf area and dry weight, and enhanced photosynthesis and antioxidative enzyme activities. EO delayed the beginning of leaf bud expansion phase of P. alba 'Berolinensis' for 5 d, decreased leaf area and biomass, and inhibited photosynthesis and caused oxidative damage of plant leaves. Compared to EO, the combined treatment advanced the spring phenophase, increased growth and induced the higher level of photosynthetic rate and antioxidative enzymes activities in plant leaves, which indicated that the positive effects of increased temperature (17.7 °C) alleviated the inhibition of growth and photosynthesis induced by ozone. Our findings can provide a theoretical reference for predicting the adaptation of functional traits of the two trees blossomed early under warming and O₃ pollution at spring phenological stage.

Responses of Growth, Oxidative Injury and Chloroplast Ultrastructure in Leaves of Lolium perenne and Festuca arundinacea to Elevated O3 Concentrations

The effects of increasing atmospheric ozone (O3) concentrations on cool-season plant species have been well studied, but little is known about the physiological responses of cool-season turfgrass species such as Lolium perenne and Festuca arundinacea exposed to short-term acute pollution with elevated O3 concentrations (80 ppb and 160 ppb, 9 h d−1) for 14 days, which are widely planted in urban areas of Northern China. The current study aimed to investigate and compare O3 sensitivity and differential changes in growth, oxidative injury, antioxidative enzyme activities, and chloroplast ultrastructure between the two turf-type plant species. The results showed that O3 decreased significantly biomass regardless of plant species. Under 160 ppb O3, total biomass of L. perenne and F. arundinacea significantly decreased by 55.3% and 47.8% (p < 0.05), respectively. No significant changes were found in visible injury and photosynthetic pigment contents in leaves of the two grass species exposed to 80 ppb O3, except for 160 ppb O3. However, both 80 ppb and 160 ppb O3 exposure induced heavily oxidative stress by high accumulation of malondialdehyde and reactive oxygen species in leaves and damage in chloroplast ultrastructure regardless of plant species. Elevated O3 concentration (80 ppb) increased significantly the activities of superoxide dismutase, catalase and peroxidaseby 77.8%, 1.14-foil and 34.3% in L. perenne leaves, and 19.2%, 78.4% and 1.72-fold in F. arundinacea leaves, respectively. These results showed that F. arundinacea showed higher O3 tolerance than L. perenne. The damage extent by elevated O3 concentrations could be underestimated only by evaluating foliar injury or chlorophyll content without considering the internal physiological changes, especially in chloroplast ultrastructure and ROS accumulation.

Influences of elevated O3 and CO2 on Cd distribution in different Festuca arundinacea tissues

It is necessary to reveal the responses of the biomass production and metal accumulation capacity of different plants to the variations of atmospheric conditions and soil metals, with the acceleration of urbanization and industrialization. In the present study, a series of experiments were designed to study the individual and interactive influences of O₃ and CO₂ fumigation on the biomass yield, variation in different leaf types, distribution of cadmium (Cd) in various tissues, and phytoremediation efficiency of Festuca arundinacea using open top chambers. The results found that an elevated O₃ content of 80 ppb, a potential O₃ content predicted for 2050, decreased the total dry mass of F. arundinacea and increased the proportion of falling leaf tissues of the species significantly. Under the same ambient CO₂ levels, O₃ fumigation increased the Cd concentrations in the roots and the fresh, mature, senescent, and dead leaf tissues by 27.8%, 133.3%, 94.4%, 125.3%, and 48.6%, respectively. An elevated CO₂ content (550 ppm) promoted the biomass yield of F. arundinacea, particularly in the falling leaf tissues. The results of the combined O₃ and CO₂ treatment showed that CO₂ fumigation alleviated the negative effects of O₃ on plant growth and increased the accumulation capacity in different plant tissues. Significantly more Cd was accumulated in senescent and dead leaves under the synergistic action of CO₂ and O₃, suggesting that the phytoremediation effect on F. arundinacea using the falling leaves harvesting method could be improved under the future atmospheric environment of high CO₂ and O₃ levels.

Long-term effects of phytoextraction by a poplar clone on the concentration, fractionation, and transportation of heavy metals in mine tailings

Mine tailings are one of main causes of diffused heavy metal pollution since the heavy metals in there may acquire mobility. The current knowledge of the processes at work in long-term phytoremediation by woody species remains insufficient. Through a 4-year field study, we evaluated the phytoextraction efficiency of Populus deltoides CL. 'Xianglin 90' grown on a mine tailing co-polluted by Cd, Cu, Cr, Ni, Pb, and Zn. The concentrations of Cd, Cu, Ni, Pb, and Zn in the rhizospheric soil were reduced by amounts ranging from 12.86 to 42.19% during the study period. Bioconcentration factors and translocation factors showed that the accumulation of Cd and Zn occurring in the shoots was the most effective. Combined with the considerable biomass produced by poplar, the extracted amounts of Cd and Zn could reach 0.61 g and 10.66 g plant^-1, respectively, in which the shoots account for 77.3% (Cd) and 89.0% (Zn) of the overall extraction amounts. Acid-soluble Cd and Zn increased by 5.49% and 4.29%, respectively, in the rhizosphere compared to the bulk soil, indicating that poplar enhanced the mobility of Cd and Zn in the rhizosphere, which explained its ability for bioaccumulation and root-shoot translocation. Moreover, calculated time required to address the issue of Cd and Zn pollution was theoretically shortened by more than half from 2015 to 2019. This study brings new insights into the long-term effects of phytoextraction on the concentration, fractionation, and transportation of heavy metals and confirms the potential of poplar as a Cd and Zn remediation species.

Responses of growth, photosynthesis and related physiological characteristics in leaves of Acer ginnala Maxim. to increasing air temperature and/or elevated O3

Regional warming and atmospheric ozone (O₃ ) pollution are two of the most important environmental issues, and commonly coexist in many areas. Both factors have an intense impact on plants. However, little information is available on the combined and interactive effects of air warming and elevated O₃ concentrations on physiological characteristics of plants. To explore this issue, we studied variations in growth, photosynthesis and physiological characteristics of leaves of Acer ginnala seedlings exposed to control (ambient temperature and O₃ ), increasing air temperature (ambient temperature + 2 °C), elevated O₃ (ambient O₃ concentration + 40 ppb) and a combination of the two abiotic factors at different phenological stages by using open-top chambers. The results showed that increasing air temperature had no significant effect on growth, but increased photosynthesis and antioxidant enzyme activity at the leaf unfolding and defoliation stages. In contrast, elevated O₃ decreased growth and photosynthesis and caused oxidative stress injury in A. ginnala leaves at each phenological stage. The combination of increasing air temperature and elevated O3 improved growth and net photosynthetic rates of tested plants and alleviated the oxidative stress compared to O₃ alone. Our findings demonstrated that moderate warming was beneficial to A. ginnala at leaf unfolding and defoliation stages, and alleviated the adverse effects of O₃ stress on growth, photosynthesis and the antioxidant system. These results will provide a theoretical reference and scientific basis for the adaptation and response of A. ginnala under regional air warming and atmospheric O₃ pollution.

Experimental warming alleviates the adverse effects from tropospheric ozone on two urban tree species

Atmospheric warming and increasing tropospheric ozone (O₃) concentrations often co-occur in many cities of the world including China, adversely affecting the health status of urban trees. However, little information is known about the combined and interactive effects from increased air temperature (IT) and elevated O₃ (EO) exposures on urban tree species. Here, Ginkgo biloba and Populus alba 'Berolinensis' seedlings were subjected to IT (+2 °C of ambient air temperature) and/or EO (+2-fold ambient air O₃ concentrations) for one growing season by using open-top chambers. IT alone had no significant effect on physiological metabolisms at the early growing stage, but significantly increased photosynthetic parameters, antioxidative enzyme activities (P < 0.05). EO alone decreased physiological parameters except for increased oxidative stress. Compared to EO exposure alone, plants grown under IT and EO combined showed higher antioxidative and photosynthetic activity. There was a significant interactive effect between IT and EO on net photosynthetic rate, stomatal conductance, water use efficiency, the maximum quantum efficiency of PSII photochemistry, the actual quantum efficiency of PSII, enzyme activities, aboveground biomass and root/shoot ratio (P < 0.05), respectively. These results suggested that during one growing season, IT mitigated the adverse effect of EO on the tested plants. In addition, we found that G. biloba was more sensitive than P. alba 'Berolinensis' to both IT and EO, suggesting that G. biloba may be a good indicator species for climate warming and air pollution, particularly under environmental conditions as they co-occur in urban areas.

Tropospheric ozone and cadmium do not have interactive effects on growth, photosynthesis and mineral nutrients of Catalpa ovata seedlings in the urban areas of Northeast China

Heavy metal contamination and tropospheric ozone (O₃) pollution often co-occur in heavy industrial urban areas, adversely affecting urban plant health. Little is known about the characteristics of growth, physiological metabolism, bioaccumulation of cadmium (Cd) and mineral nutrients in urban trees under the combination of soil Cd contamination and elevated O₃ exposure. In this study, one-year-old street tree Catalpa ovata G. Don seedlings were exposed to Cd contaminated soil (0, 100, 500 mg/kg soil) with 40 µg/m³ O₃ (ambient air) and 120 µg/m³ O₃ (elevated O₃ exposure) for 4 weeks. The results revealed that 500 mg/kg soil Cd addition alone decreased net photosynthetic rate, stomatal conductance, peroxidase activity and increased abscisic acid content and oxidative injury in the leaves of C. ovata. Furthermore, Cd soil contamination decreased leaf, stem, root and total biomass and affected Cd, Mg, Fe, and Zn contents in leaves (P < 0.01), but it did not affect Mg, Fe and Zn contents in roots. O₃ exposure did not affect growth, net photosynthetic rate, Cd accumulation and mineral nutrient contents of C. ovata. No interactive effect between Cd and O₃ was found on growth, oxidative injury, photosynthetic rate, and the contents of Cd, Mg, Fe and Zn in plant tissues (P > 0.05). Our findings suggest that C. ovata is an appropriate tree species for urban greening and afforestation in heavy industrial urban areas with high O₃ pollution in Northeast China. To ensure successful afforestation in heavy industrial areas, the long-term and large scale studies are needed to advance our understanding of the combined effects from extreme climate conditions and multi-pollutant exposure on the metabolism of mature urban trees.

Ethylenediurea (EDU) pretreatment alleviated the adverse effects of elevated O3 on Populus alba "Berolinensis" in an urban area

Ethylenediurea (EDU) has been used as a chemical protectant against ozone (O₃). However, its protective effect and physiological mechanisms are still uncertain. The present study aimed to investigate the changes of foliar visible injury, physiological characteristics and emission rates of volatile organic compounds (VOCs) in one-year-old Populus alba "Berolinensis" saplings pretreated with EDU and exposed to elevated O₃ (EO, 120 μg/m³). The results showed that foliar visible injury symptoms under EO were significantly alleviated in plants with EDU application (p < 0.05). Under EO, net photosynthetic rate, the maximum photochemical efficiency of PSII and the photochemical efficiency of PSII of plants pretreated with 300 and 600 mg/L EDU were similar to unexposed controls and significantly higher compared to EO-stressed plants without EDU pretreatment, respectively. Malondialdehyde content was highest in EO without EDU and decreased significantly by 14.9% and 21.3% with 300 and 600 mg/L EDU pretreatment, respectively. EDU pretreatment alone increased superoxide dismutase activity by 10-fold in unexposed plants with further increases of 88.4% and 37.5% in EO plants pretreated with 300 and 600 mg/L EDU pretreatment, respectively (p < 0.05). Abscisic acid content declined under EO relative to unexposed controls with the effect partially reversed by EDU pretreatments. Similarly, VOCs emission rate declined under EO relative to unexposed plants with a recovery of emission rate observed with 300 and 600 mg/L EDU pretreatment. These findings provided significant evidence that EDU exerted a beneficial effect and protection on the tested plants against O₃ stress.