Elevated O3 Research Articles

Metabolic and physiological alterations indicate that the tropical broadleaf tree Eugenia uniflora L. is sensitive to ozone

Eugenia uniflora L. is an important fruit tree native to tropical South America that adapts to different habitats, thanks to its metabolic diversity and ability to adjust the leaf antioxidant metabolism. We hypothesized that this metabolic diversity would also enable E. uniflora to avoid oxidative damage and tolerate the enhanced ozone (O3) concentrations that have been registered in the (sub)tropics. We investigated whether carbohydrates, polyphenols and antioxidants are altered and markers of oxidative damage (ROS accumulation, alterations in leaf gas exchange, growth and biomass production) are detected in plants exposed to two levels of O3 (ambient air and twice elevated ozone level in a O3-FACE system for 75 days). Phytotoxic O3 dose above a threshold of 0 nmol m−2 s−1 (POD0) and accumulated exposure above 40 ppb (AOT40) were 3.6 mmol m−2 and 14.898 ppb h at ambient, and 4.7 mmol m−2 and 43.881 ppb h at elevated O3. Twenty-seven primary metabolites and 16 phenolic compounds were detected in the leaves. Contrary to the proposed hypothesis that tropical broadleaf trees are relatively O3 tolerant, we concluded that E. uniflora plants are sensitive to elevated O3 concentrations. Experimental POD0 values were lower than the critical levels for visible foliar O3, because of low stomatal conductance. In spite of this low stomatal O3 uptake, we found classic O3 injury, e.g. reduction in carbohydrates and fatty acids concentrations; non-significant changes in the polyphenol profile; inefficient antioxidant responses; increased contents of ROS and indicators of lipid peroxidation; reductions in stomatal conductance, net photosynthesis, root/shoot ratio and height growth. However, we also found some compensation mechanisms, e.g. increased leaf concentration of polyols for protecting the membranes, and increased leaf number for compensating the decline of photosynthetic rate. These results help filling the knowledge gap about tropical tree responses to O3.

Ozone disrupts the communication between plants and insects in urban and suburban areas: an updated insight on plant volatiles

Plant–insect interactions are basic components of biodiversity conservation. To attain the international Sustainable Development Goals (SDGs), the interactions in urban and in suburban systems should be better understood to maintain the health of green infrastructure. The role of ground-level ozone (O3) as an environmental stress disrupting interaction webs is presented. Ozone mixing ratios in suburbs are usually higher than in the center of cities and may reduce photosynthetic productivity at a relatively higher degree. Consequently, carbon-based defense capacities of plants may be suppressed by elevated O3 more in the suburbs. However, contrary to this expectation, grazing damages by leaf beetles have been severe in some urban centers in comparison with the suburbs. To explain differences in grazing damages between urban areas and suburbs, the disruption of atmospheric communication signals by elevated O3 via changes in plant-regulated biogenic volatile organic compounds and long-chain fatty acids are considered. The ecological roles of plant volatiles and the effects of O3 from both a chemical and a biological perspective are presented. Ozone-disrupted plant volatiles should be considered to explain herbivory phenomena in urban and suburban systems.

Enhanced atmospheric oxidation capacity and associated ozone increases during COVID-19 lockdown in the Yangtze River Delta

Aggressive air pollution control in China since 2013 has achieved sharp decreases in fine particulate matter (PM2.5), along with increased ozone (O3) concentrations. Due to the pandemic of coronavirus disease 2019 (COVID-19), China imposed nationwide restriction, leading to large reductions in economic activities and associated emissions. In particular, large decreases were found in nitrogen oxides (NOx) emissions (>50%) from transportation. However, O3 increased in the Yangtze River Delta (YRD), which cannot be fully explained by changes in NOx and volatile organic compound (VOCs) emissions. In this study, the Community Multi-scale Air Quality model was used to investigate O3 increase in the YRD. Our results show a significant increase of atmospheric oxidation capacity (AOC) indicated by enhanced oxidants levels (up to +25%) especially in southern Jiangsu, Shanghai and northern Zhejiang, inducing the elevated O3 during lockdown. Moreover, net P(HOx) of 0.4 to 1.6 ppb h−1 during lockdown (Case 2) was larger than the case without lockdown (Case 1), mainly resulting in the enhanced AOC and higher O3 production rate (+12%). This comprehensive analysis improves our understanding on AOC and associated O3 formation, which helps to design effective strategies to control O3.

Growth, Yield and Quality of Maize under Ozone and Carbon Dioxide Interaction in North West India

ABSTRACT Maize is an important C4 crop and how it will respond to elevated atmospheric carbon dioxide and ozone levels is not well documented. To understand how the growth and nutritional quality of maize will be affected under elevated carbon dioxide (CO2) and tropospheric ozone (O3) interaction, a field experiment was conducted under free air O3 and CO2 enrichment rings (FAOCE) growing HQPM-1 and PMH-1 maize cultivars at New Delhi, India. Each cultivar was exposed to ambient and elevated CO2 (559 ppm) alone and along with ambient and elevated O3 (71.8 ppb) throughout the growing period. Elevated CO2 (EC) significantly increased the leaf area index (10.8–22.5%), chlorophyll (11.2–17.3%) and photosynthetic rate (12.1–16.5%) in the two cultivars over the ambient. O3 exposure of 27 ppm hr (AOT4O) under elevated O3 (EO) treatment led to a significant decline in yield (p < 0.01) by 9.2% in HQPM-1 and 9.8% in PMH-1. Under elevated CO2 the increase in grain yield was higher under HQPM-1 (25.4%) as compared to PMH-1 (9.04%). The protein content increased under EO (8.1–12.5%) and decreased under EC (13.4–13.6%) in the two maize cultivars due to yield dilution effect. Lysine, phosphorus and potassium content of the grain significantly decreased in both the cultivars under elevated CO2. Carbohydrate and amylose concentrations in grains increased (9.9–15.5%) under EC and decreased (10.8–16.7%) under EO, however, no significant change in yield, protein, amylase, carbohydrate, lysine, potassium and phosphorus was observed under the interaction treatment ECO as compared to the ambient. After two years of study we could conclude that elevated CO2 (559 ppm) was able to offset the negative effect of elevated O3 (71 ppb) on grain yield by 11.2% in PMH-1 and by 18.8% in HQPM-1 without significantly affecting the grain quality in both the maize cultivars.

Effect of elevated ozone and carbon dioxide interaction on growth, yield, nutrient content and wilt disease severity in chickpea grown in Northern India

Wilt caused by Fusarium oxysporum, sp. Ciceris (FOC) is an important disease causing losses up to 10% in chickpea yield. Experiments were conducted growing chickpea in free air ozone and carbon dioxide enrichment rings under four treatments of elevated ozone (O3) (EO:60 ± 10 ppb), elevated carbon dioxide (CO2) (ECO2:550 ± 25 ppm), combination of elevated CO2 and O3 (EO + ECO2) and ambient control for quantifying the effect on growth, yield, biochemical and nutrient content of chickpea. For studying the impact on wilt disease, chickpea was grown additionally in pots with soil containing FOC in these rings. The incidence of Fusarium wilt reduced significantly (p < 0.01) under EO as compared to ambient and ECO2. The activities of pathogenesis-related proteins chitinase and β-1,3- glucanase, involved in plant defense mechanism were enhanced under EO. The aboveground biomass and pod weight declined by 18.7 and 15.8% respectively in uninnoculated soils under EO, whereas, in FOC inoculated soil (diseased plants), the decline under EO was much less at 8.6 and 9.9% as compared to the ambient. Under EO, the activity of super oxide dismutase increased significantly (p < 0.5, 40%) as compared to catalase (12.5%) and peroxidase (17.5%) without any significant increase under EO + ECO2. The proline accumulation was significantly (p < 0.01) higher in EO as compared to EO + ECO2, and ECO2. The seed yield declined under EO due to significant reduction (p < 0.01) in the number of unproductive pods and seed weight. No change in the protein, total soluble sugars, calcium and phosphorus content was observed in any of the treatments, however, a significant decrease in potassium (K) content was observed under EO + ECO2. Elevated CO2 (554ppm) countered the impacts of 21.1 and 14.4 ppm h (AOT 40) O3 exposure on the seed yield and nutrient content (except K) in the EO + CO2 treatment and reduced the severity of wilt disease in the two years' study.

Examining the effectiveness of biomass-derived biochar for the amelioration of tropospheric ozone-induced phytotoxicity in the Indian wheat cultivar HD 2967

A pot study was performed to evaluate the influence of O3 stress with different biochar treatments on a wheat cultivar (HD 2967). Plants were subjected to ambient and elevated (ambient+20 ppb) O3 along with three doses of biochar (0%, 2.5%, and 5%). Elevated ozone alone reduced most of the growth parameters, negatively affecting the test cultivar's physiology. Although enzymatic antioxidants were up-regulated by elevated O3, damage to the membrane integrity was evident by higher MDA content in the wheat leaves. Besides, the uptake of nutrients was observed to be reduced under elevated O3 due to the reduced phyto-availability of the soil's nutrients and cation exchange capacity. Such limitation of assimilates and nutrients marked a trade-off between growth and defence, translating to grain yield loss. However, applying biochar as a soil conditioner ameliorated the detrimental effects of O3 with respect to the economic yield of wheat. Biochar alone improved soil properties and nutrient phyto-availability, which translated to better plant growth, stronger physiological capacity, and higher crop productivity. Thus, the study inferred that altered nutrient phyto-availablity and its uptake, likely associated with biochar-induced improved soil properties, relayed stronger plant physiology and antioxidative defence system to combat O3 induced oxidative stress.

Tropospheric ozone rapidly decreases root growth by altering carbon metabolism and detoxification capability in growing soybean roots

High tropospheric ozone (O3) concentrations lead to significant global soybean (Glycine max) yield reductions. Research concerning O3 impacts on soybean has focused on the contributions of above-ground tissues. In this study, Mandarin (Ottawa) (O3-sensitive) and Fiskeby III (O3-tolerant) soybean genotypes provide contrasting materials to investigate O3 effects on root growth. We compared root morphological and proteomic changes when 16-day-old plants were treated with charcoal-filtered (CF) air or elevated O3 (80 ppb O3 for 7 h/day) in continuously stirred-tank reactors (CSTR) for 7 days. Our results showed that in Mandarin (Ottawa), decreased expression of enzymes involved in the tricarboxylic acid (TCA) cycle contributes to reduction of root biomass and diameter under elevated O3. In contrast, O3 tolerance in Fiskeby III roots was associated with O3-dependent induction of enzymes involved in glycolysis and O3-independent expression of enzymes involved in the ascorbate-glutathione cycle. We conclude that a decreased abundance of key redox enzymes in roots due to limited carbon availability rapidly alters root growth under O3 stress. However, maintaining a high abundance of enzymes associated with redox status and detoxification capability contributes to overall O3 tolerance in roots.

A measurement and model study on ozone characteristics in marine air at a remote island station and its interaction with urban ozone air quality in Shanghai, China

Abstract. To understand the characteristics and changes of baseline ozone (O3) in oceanic air in eastern China, a 6-year measurement of O3 concentration was conducted from 1 January 2012 to 15 September 2017 at a remote offshore station located on Sheshan Island (SSI) near the megacity of Shanghai. The observed monthly mean O3 concentrations at SSI ranged from 33.4 to 61.4 ppbv during the study period, which were about 80 % and 12 % higher, respectively, than those measured at downtown and rural sites in Shanghai. Compared to the remarkable O3 increases observed at urban and rural sites in Shanghai, observed O3 concentrations at SSI exhibited statistically insignificant increasing changes (1.12 ppbv yr−1, α&gt;0.10) during the observation period, suggesting less impacts of anthropogenic emissions on O3 levels in oceanic air. In addition, an insignificant decreasing change (−0.72 ppbv yr−1, α&gt;0.10) was detected in O3 concentrations at SSI in September and October when the influence of regional transport was minimum throughout the year, providing a good proxy to study the baseline oxidation capacity of the oceanic atmosphere. City plumes from Shanghai usually carried higher levels of NOx, resulting in decreased O3 concentrations at SSI during southwesterly and westerly winds. However, In MAM (March–May) and JJA (June–August), due to the enhanced production of oxygenated volatile organic compounds, O3 could be continuously produced during daytime in aged city plumes, resulting in elevated O3 concentrations transported to SSI. The impacts of the offshore O3 on O3 levels in Shanghai are quantified during an easterly wind dominant episode (1–30 September 2014) using the WRF-Chem model (Weather Research and Forecasting model coupled with Chemistry). Sensitivity results suggest that O3 in the oceanic air inflows can lead to 20 %–30 % increases in urban O3 concentrations, which should be crucially considered in dealing with urban O3 pollution in large coastal cities like Shanghai.

The effects of elevated CO2, elevated O3, elevated temperature, and drought on plant leaf gas exchanges: a global meta-analysis of experimental studies.

Global change significantly influences plant leaf gas exchange, which affects the carbon-water cycle of terrestrial ecosystems. However, the magnitudes of the effects of multiple global change factors on leaf gas exchanges are currently lacking. Therefore, a global meta-analysis of 337 published articles was conducted to determine the effects of elevated CO2 (eCO2), elevated O3 (eO3), elevated temperature (eT), and drought on plant leaf gas exchanges. The results indicated that (1) the overall responses of photosynthesis rate (Pn) and instantaneous water use efficiency (WUEi) to eCO2 increased by 28.6% and 58.6%. But transpiration rate (Tr) and stomatal conductance (gs) responded negatively to eCO2 (- 17.5% and - 17.2%, respectively). Furthermore, all Pn, gs, and WUEi responded negatively to eO3 (- 32.7%, - 24.6%, and - 27.1%), eT (- 23.2%, - 10.8%, and - 28.9%), and drought (- 53.6%, - 59.3%, and - 4.6%, respectively), regardless of functional groups and various complex experimental conditions. (2) Elevated CO2 increased WUEi combined with eO3, eT, and drought (26.6%, 36.0%, and 58.6%, respectively, for eCO2 + eO3, eCO2 + eT, and eCO2 + drought) and mitigated their negative impacts on Pn to some extent. (3) Plant form and foliage type play an important role in the responses of leaf gas exchanges. Trees responded mostly to eCO2, but responded least to eT in Pn, Tr, gs, and WUEi compared with shrubs and herbs. Evergreen broad-leaved species were more responsive to eCO2 and drought. (4) The stress level of each factor can also significantly influence the responses of leaf gas exchanges to environment change. Hopefully, the quantitative results are helpful for the further assessments of the terrestrial carbon-water cycle.

Spatio-Temporal Variation of Ozone Concentrations and Ozone Uptake Conditions in Forests in Western Germany

The study analyzes the long-term trends (1998–2019) of concentrations of the air pollutants ozone (O3) and nitrogen oxides (NOx) as well as meteorological conditions at forest sites in German midrange mountains to evaluate changes in O3 uptake conditions for trees over time at a plot scale. O3 concentrations did not show significant trends over the course of 22 years, unlike NO2 and NO, whose concentrations decreased significantly since the end of the 1990s. Temporal analyses of meteorological parameters found increasing global radiation at all sites and decreasing precipitation, vapor pressure deficit (VPD), and wind speed at most sites (temperature did not show any trend). A principal component analysis revealed strong correlations between O3 concentrations and global radiation, VPD, and temperature. Examination of the atmospheric water balance, a key parameter for O3 uptake, identified some unusually hot and dry years (2003, 2011, 2018, and 2019). With the help of a soil water model, periods of plant water stress were detected. These periods were often in synchrony with periods of elevated daytime O3 concentrations and usually occurred in mid and late summer, but occasionally also in spring and early summer. This suggests that drought protects forests against O3 uptake and that, in humid years with moderate O3 concentrations, the O3 flux was higher than in dry years with higher O3 concentrations.

Assessing the effects of elevated ozone on physiology, growth, yield and quality of soybean in the past 40 years: A meta-analysis

Soybean (Glycine max) production is seriously threatened by ground-level ozone (O3) pollution. The goal of our study is to summarize the impacts of O3 on physiology, growth, yield, and quality of soybean, as well as root parameters. We performed meta-analysis on the collated 48 peer-reviewed papers published between 1980 and 2019 to quantitatively summarize the response of soybean to elevated O3 concentrations ([O3]). Relative to charcoal-filtered air (CF), elevated [O3] significantly accelerated chlorophyll degradation, enhanced foliar injury, and inhibited growth of soybean, evidenced by great reductions in leaf area (−20.8%), biomass of leaves (−13.8%), shoot (−22.8%), and root (−16.9%). Shoot of soybean was more sensitive to O3 than root in case of biomass. Chronic ozone exposure of about 75.5 ppb posed pronounced decrease in seed yield of soybean (−28.3%). In addition, root environment in pot contributes to higher reduction in shoot biomass and yield of soybean. Negative linear relationships were observed between yield loss and intensity of O3 treatment, AOT40. The larger loss in seed yield was significantly associated with higher reduction in shoot biomass and other yield component. This meta-analysis demonstrates the effects of elevated O3 on soybean were pronounced, suggesting that O3 pollution is still a soaring threat to the productivity of soybean in regions with high ozone levels.

Impact of O3 on the phytoremediation effect of Celosia argentea in decontaminating Cd

Elevated atmospheric O3 can inhibit the growth rate of various plants and increase metal content in their tissues owing to the oxidative damage, thereby affecting their phytoremediation efficiency. In this study, a series of O3 fumigation treatments were designed to evaluate the dry weight, Cd content, and transpiration rate responses of Celosia argentea to different levels of O3 (40, 50, 55, 60, 65, and 80 ppb). The dry weight of C. argentea decreased as the atmospheric O3 level increased, and the Cd concentration of the plant leaves increased until the level of O3 reached 60 ppb before decreasing slightly. The variations in the transpiration rate followed a similar trend to the Cd content under different O3 levels. The phytoremediation efficiency of C. argentea increased with O3 fumigation at low (50 ppb) and moderate (55 and 60 ppb) levels, and significantly decreased at the highest level. The regression curves indicated that the plant species treated with 52 ppb of O3 exhibited the highest Cd accumulation capacity. Overall, the phytoremediation effect of C. argentea cultivated in Cd-polluted soil might be improved under the high-O3 conditions. This result might help to choose suitable plants for soil remediation in future atmospheric environment.

Effects of tropospheric ozone and elevated nitrogen input on the temperate grassland forbs Leontodon hispidus and Succisa pratensis

Atmospheric ozone (O3) and nitrogen (N) pollution have increased since pre-industrial times and pose a threat to natural vegetation. The implications of these pollutants for the perennial temperate grassland species Leontodon hispidus (Rough Hawkbit) and Succisa pratensis (Devil’s-bit Scabious) are largely unknown. Both species are important for pollinators and Succisa pratensis is the host plant for the threatened marsh fritillary butterfly (Euphydryas aurinia).We examine growth and physiological responses (leaf cover, leaf litter, flowering, chlorophyll index [Leontodon hispidus and Succisa pratensis]; photosynthesis and stomatal conductance [Succisa pratensis]) using an outdoor Free Air Ozone Enrichment system. Plants were exposed to Low, Medium and High ozone treatments over three growing seasons (treatment means: 24, 40 and 57 ppb, respectively), with and without the addition of nitrogen (40 kg ha−1 yr−1) during the first year.Decreases in leaf cover (p < 0.001) and chlorophyll index (p < 0.01) were observed with increased O3 for Leontodon hispidus. The addition of N resulted in a higher chlorophyll index only at the uppermost O3 level and also led to an overall increase in litter production of 6%. However, a stronger effect of both O3 and N treatments was observed with Succisa pratensis. Litter production increased with increasing O3 (p < 0.001) and an overall rise of 31% was recorded with added N (p < 0.05). However, O3 had the biggest impact on Succisa pratensis foliage leading to more damaged leaves (p < 0.05). During summer resources were prioritised to new leaves, maintaining stomatal conductance and photosynthesis rates. However, this was not sustained during autumn and accelerated senescence occurred with higher ozone, and rates declined faster with added nitrogen (p < 0.05). Elevated O3 also reduced Succisa pratensis flowering (p < 0.01).These effects have implications for inter- and intra-specific competition, seed establishment, nutrient cycling, as well as the provision of general pollinator resources with specific issues for butterfly larvae. Results highlight the need for concerted action to reduce pre-cursor ozone emissions to go alongside habitat management efforts to protect biodiversity.

High nitrogen addition decreases the ozone flux by reducing the maximum stomatal conductance in poplar saplings.

Ground-level ozone (O3) and nitrogen (N) deposition are major environmental pollutants, often occurring concurrently. Ozone exposure- and flux-response relationships for tree biomass are used for regional O3 risk assessment. In order to investigate whether soil N addition affects stomatal O3 uptake of poplar, poplar saplings were exposed to treatment combinations of five O3 levels and four N addition levels. High N addition treatment reduced the accumulated stomatal O3 uptake in the leaf due to reduced maximum stomatal conductance (gs). Nitrogen addition also significantly reduced the steady-state light-saturated gs in August and September. Elevated O3 significantly reduced and N addition increased total plant biomass; however, there were no significant O3×N interactions. The slopes of biomass-based O3 exposure- and flux-response relationships did not differ significantly among N treatments. The critical levels for a 5% biomass reduction were estimated at 15.4ppmh and 17.1mmol O3 m-2 projected leaf area (PLA) for Accumulated O3 exposure Over an hourly Threshold of 40ppb (AOT40) and Phytotoxic Ozone Dose above a threshold 1nmol O3 m-2 PLA s-1 (POD1). These results can facilitate the evaluations of O3 effect on the carbon-sink capacity and productivity of forest.

Host tree species mediate corticolous lichen responses to elevated CO2 and O3 after 10 years exposure in the Aspen-FACE system

Lichens contribute significantly to the biodiversity and functioning of many ecosystems. Although lichens are useful air pollution bioindicators and may respond in significant ways to global change, they are studied infrequently under field conditions in chamberless exposure systems. We surveyed corticolous lichens on paper birch (Betula papyrifera) and trembling aspen (Populus tremuloides) after 10 years exposure (1998–2007) to elevated CO2 (eCO2) and O3 (eO3) in the Aspen-FACE experiment in Rhinelander, WI, USA. This experiment utilized chamberless exposure rings, 30 m in diameter, with both host trees planted together in one quadrant. Four treatments were allocated among 12 rings: ambient, eCO2, eO3, and the combination of eCO2 + eO3, each replicated once in each of three blocks. Over the course of the experiment, ambient CO2 increased from 343 to 386 ppm while eCO2 averaged ~530 ppm CO2. Ambient ozone concentrations averaged ~37 ppb and ~49 ppb for eO3 although exposures decreased with time. Tree growth and leaf area index were negatively affected by eO3 and stimulated by eCO2, resulting in higher photosynthetically active radiation (PAR) in eO3 and lower in eCO2. We assessed lichen richness and cover on five host trees per ring on the north-facing side of the trunks, which were higher on birch than on aspen. Neither of the lichen measures on birch responded to the exposure treatments, while on aspen lichen cover was highest in eO3 and lowest in eCO2. On aspen, lichen cover was positively related to PAR and dominated by Caloplaca. No relationship was found for birch, although Lecanora exhibited a negative relationship with PAR. These lichens were insensitive to direct effects of eCO2 and eO3 at the levels applied. Instead, they responded to indirect effects, such as host tree species, and changes in understory PAR, resulting from direct effects of eO3 and eCO2 on the host trees.

Ethylenediurea (EDU) effects on Japanese larch: an one growing season experiment with simulated regenerating communities and a four growing season application to individual saplings

Japanese larch (Larix kaempferi (Lamb.) Carr.) and its hybrid are economically important coniferous trees widely grown in the Northern Hemisphere. Ground-level ozone (O3) concentrations have increased since the pre-industrial era, and research projects showed that Japanese larch is susceptible to elevated O3 exposures. Therefore, methodologies are needed to (1) protect Japanese larch against O3 damage and (2) conduct biomonitoring of O3 in Japanese larch forests and, thus, monitor O3 risks to Japanese larch. For the first time, this study evaluates whether the synthetic chemical ethylenediurea (EDU) can protect Japanese larch against O3 damage, in two independent experiments. In the first experiment, seedling communities, simulating natural regeneration, were treated with EDU (0, 100, 200, and 400 mg L−1) and exposed to either ambient or elevated O3 in a growing season. In the second experiment, individually-grown saplings were treated with EDU (0, 200 and 400 mg L−1) and exposed to ambient O3 in two growing seasons and to elevated O3 in the succeeding two growing seasons. The two experiments revealed that EDU concentrations of 200–400 mg L−1 could protect Japanese larch seedling communities and individual saplings against O3-induced inhibition of growth and productivity. However, EDU concentrations ≤ 200 mg L−1 did offer only partial protection when seedling communities were coping with higher level of O3-induced stress, and only 400 mg EDU L−1 fully protected communities under higher stress. Therefore, we conclude that among the concentrations tested the concentration offering maximum protection to Japanese larch plants under high competition and O3-induced stress is that of 400 mg EDU L−1. The results of this study can provide a valuable resource of information for applied forestry in an O3-polluted world.

Ozone impairs the response of isoprene emission to foliar nitrogen and phosphorus in poplar

Tropospheric ozone (O3) impairs physiological processes of plants while nitrogen (N) deposition may cause imbalances in soil N and other nutrients such as phosphorus (P) suggesting an increase of P demand for plants. However, the combined effect of O3, soil N and P on isoprene emission from leaves has never been tested. We therefore examined isoprene emission in leaves of Oxford poplar clone exposed to O3 (ambient, AA [35.0 nmol mol−1 as daily mean]; 1.5 × AA; 2.0 × AA), soil N (0 and 80 kg N ha−1) and soil P (0, 40 and 80 kg P ha−1) in July and September in a Free-Air Controlled Exposure (FACE) facility. We also investigated the response of isoprene emission to foliar N, P and abscisic acid (ABA) contents in September because the 2-C-methylerythritol-5-phosphate (MEP) pathway of isoprenoid biosynthesis produces ABA. We found that O3 increased isoprene emission in July, which was associated to increased dark respiration, suggesting an activation of metabolism against O3 stress as an initial response. However, O3 decreased isoprene emission in September which was associated to reduced net photosynthesis. In September, isoprene emission was positively correlated with leaf N content and negatively correlated with leaf P content in AA. However, no response of isoprene emission to foliar N and P was found in elevated O3, suggesting that the isoprene responses to foliar N and P depended on the O3 exposure levels. Isoprene emission rate in 1.5 × AA and 2.0 × AA increased with increasing leaf ABA content, indicating accelerated senescence of injured leaves to favor new leaf growth when high O3 and nutritional availability in the soil were combined. Even though foliar N and P usually act as a proxy for isoprene emission rate, the impact of recent abiotic factors such as O3 should be always considered for modeling isoprene emission under climate change.

Microbial-Mediated Plant Growth Promotion and Pest Suppression Varies Under Climate Change.

Climate change is altering the dynamics of crop pests and diseases resulting in reduced crop yields. Using beneficial soil bacterial to increase crop health is a quickly developing area in sustainable agriculture, but it is unknown if climate change or interactions with other species could alter their effect. The plant growth-promoting rhizobacterium Acidovorax radicis N35 is known to increase barley (Hordeum vulgare) plant growth under laboratory conditions, and we tested the stability of the plant-bacterial interactions when exposed to elevated carbon dioxide (CO2) and ozone (O3) levels while infesting the aboveground leaves with cereal aphids (Sitobion avenae) and the soil with beneficial earthworms. Acidovorax radicis N35 increased plant growth and reduced insect growth – with greatest effect in a high-stress elevated O3 environment, but reduced effects under elevated CO2. Earthworms promoted both plant and insect growth, but inoculation with A. radicis N35 alleviated some of the earthworm-mediated increase in pest abundance, particularly in the ambient environment. The consistency of these beneficial effects highlights the potential of exploiting local species interactions for predicting and mitigating climate change effects in managed systems. We conclude that microbial bioprotectants have high potential for benefiting agriculture via plant-growth promotion and pest suppression.

Interactive effects of ozone exposure and nitrogen addition on the rhizosphere bacterial community of poplar saplings

It is widely documented that elevated ground-level ozone (O3) has negative effects on tree physiological characteristics, and in return, affects forest ecosystem function. However, the effect may be modified by soil nitrogen (N) availability. Numerous studies have focused on the aboveground part of trees under elevated O3 alone or in combination with soil N; however, little is known about the response of soil bacterial communities. Here, we investigated the effects of O3 (charcoal-filtered air, CF, versus ambient air +40 ppb of O3, E-O3), N addition (0 kg ha−1 yr−1, N0, versus 200 kg ha−1 yr−1, N200), and their combination on rhizosphere soil bacterial communities of hybrid poplar, using an MiSeq targeted amplicon sequencing of the bacterial 16S rRNA gene. E-O3 significantly decreased bacterial abundance, and N200 significantly decreased the α-diversity. The negative impacts of N200 on α-diversity were alleviated by E-O3. Nitrogen and E-O3-N200 combination altered bacterial community composition, with a significant increase in the relative abundance of Proteobacteria and Bacteroidetes and a decrease in the abundance of Firmicutes. From an ecological network analysis, E-O3, alone and in combination with N200, complicated the co-occurrence network of bacterial communities by inducing a microbial survival strategy, shifting the hub species from RB41 to Bacillus and Blastococcus. Conversely, N200 led to simplification and decentralization of the co-occurrence network. These findings demonstrate that the rhizosphere bacterial communities exhibit divergent responses to E-O3 and N200, suggesting the need to consider the stability of the belowground ecosystem to optimize plantation management in response to environmental changes.

Substantial nitrogen oxides emission reduction from China due to COVID-19 and its impact on surface ozone and aerosol pollution

A top-down approach was employed to estimate the influence of lockdown measures implemented during the COVID-19 pandemic on NOx emissions and subsequent influence on surface PM2.5 and ozone in China. The nation-wide NOx emission reduction of 53.4% due to the lockdown in 2020 quarter one in China may represent the current upper limit of China's NOx emission control. During the Chinese New Year Holiday (P2), NOx emission intensity in China declined by 44.7% compared to the preceding 3 weeks (P1). NOx emission intensity increased by 20.3% during the 4 weeks after P2 (P3), despite the unchanged NO2 column. It recovered to 2019 level at the end of March (P4). The East China (22°N - 42°N, 102°E - 122°E) received greater influence from COVID-19. Overall NOx emission from East China for 2020 first quarter is 40.5% lower than 2019, and in P4 it is still 22.9% below the same period in 2019. The 40.5% decrease of NOx emission in 2020 first quarter in East China lead to 36.5% increase of surface O3 and 12.5% decrease of surface PM2.5. The elevated O3 promotes the secondary aerosol formation through heterogeneous pathways. We recommend that the complicated interaction between PM2.5 and O3 should be considered in the emission control strategy making process in the future.