O3 Stress Research Articles

Ozone Pollution, Nitrogen Addition, and Drought Stress Interact to Affect Non-structural Carbohydrates in the Leaves and Fine Roots of Poplar

Ground-level ozone (O3) pollution frequently co-occurs with drought and nitrogen (N) deposition during the growing season. It is important to understand how the carbon dynamics of plants respond to O3 pollution in drier and N-enriched environments. Here we present the patterns of non-structural carbohydrates and its components (soluble sugar and starch) in the leaves and fine roots in poplar clone 546 (Populus deltoides cv. '55/56'×P. deltoides cv. 'Imperial') for one growing season at two O3 concentrations (control, charcoal-filtered air, and elevated O3, non-filtered air+40 nmol·mol-1 of O3), two watering regimes (well-watered and reduced watering at 40% of well-watered irrigation), and two soil nitrogen addition treatments[no addition and the addition of 50 kg·(hm2·a)-1]. The results showed that O3 stress significantly increased the content of soluble sugar in leaves and starch in fine roots but decreased the content of starch and total non-structural carbohydrate (NSC) in leaves. Drought stress significantly reduced the content of starch and total NSC in leaves but increased the contents of soluble sugar and total NSC in fine roots. Nitrogen addition had no significant effect on NSC and its components in leaves and fine roots. NSC and its components in leaves and fine roots were positively correlated with photosynthetic rate and biomass. With an increase in the number of environmental stress factors, NSC in leaves showed a significant downward trend while NSC in fine roots showed a significant upward trend. The study demonstrates that environmental stress can promote the transformation of starch into soluble sugars in plant leaves and the transfer of NSC from leaves to roots for storage, which may be a coping strategy for plants exposed to environmental stress.

Ethylenediurea regulates growth and physiochemical responses of Pisum sativum to ambient O3

Tropospheric ozone (O3) is a widespread secondary photochemical air pollutant, which occurs naturally at ground level in low concentration and is regarded the most damaging air toxicant. Current study was conducted to evaluate the potential of ethylenediurea (EDU) on the growth and physiochemical attributes of pea cultivar exposed to ambient O3 stress. Ozone stress reduced growth and biomass production of Pisum sativum. Application of EDU concentration of 450 ppm via soil drenching significantly enhanced growth and biomass of P. sativum. Application of EDU escalated relative water content and ascorbic acid content in P. sativum seedlings ultimately showing a significant increment in air pollution tolerance index up to 38.6% with EDU-450 treatment making the seedling more tolerant to the air pollution. The increasing concentrations of EDU showed significant increase in total soluble sugar, protein and proline contents, while phenolic contents were significantly decreased up to 36.6% with 450 ppm treatment of EDU. Furthermore, EDU treatment enhanced the activity of superoxide dismutase and ascorbate peroxidase. Current research reveals that EDU ameliorates the deleterious O3 effects on P. sativum and it can be used as an effective tool to enhance crop productivity at elevated levels of O3 concentration.

Visible symptoms and changes in physiological parameters of <i>Cinnamomum camphora</i> and <i>Michelia chapensis</i> under ozone stress

The responses of Cinnamomum camphora and Michelia chapensis to ozone (O3) exposure in terms of the O3 injury and changes in the physiological parameters of their leaves were examined in charcoal-filtered (CF) air and O3 at 1×, 2×, and 4×O3 ambient concentrations in open-top chambers in an eight-month experimental period. High levels of O3 exposure led to visible injuries in both species. The increased chlorophyll content in the second month and increased carotenoid content of the 1×O3 treatment group at the end of experiment were identified as hormetic-compensatory strategies that enhance tolerance and acclimation to O3 stress. Significant interaction effect between O3and tree species with respect to the superoxide dismutase (SOD) activity and proline content suggests that the effects induced by O3 were highly dependent on the tree species. C. camphora showed more foliar injury symptoms and greater O3-induced decreases in the chlorophyll, carotenoid, and protein contents than M. chapensis, which suggests that C. camphora is more sensitive to O3 than M. chapensis.

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.

Role of antioxidant pool in management of ozone stress through soil nitrogen amendments in two cultivars of a tropical legume.

The present experiment was done on two different cultivars of a tropical legume, Cymopsis tetragonoloba L. Taub. (cluster bean) cvv. Pusa-Naubahar (PUSA-N) and Selection-151 (S-151). The experiment was conducted under ambient ozone (O3) conditions with inputs of three different doses of inorganic nitrogen (N1, recommended; N2, 1.5-times recommended and N3, 2-times recommended) as well as control plants. The objective of this study was to evaluate the effectiveness of soil nitrogen amendments in management of ambient ozone stress in the two cultivars of C. tetragonoloba. Our experiment showed that nitrogen amendments can be an efficient measure to manage O3 injury in plants. Stimulation of antioxidant enzyme activities under nitrogen amendments is an important feature of plants that help plants cope with ambient O3 stress. Nitrogen amendments strengthened the antioxidant machinery in a more effective way in the tolerant cultivar PUSA-N, while in the sensitive cultivar S-151, avoidance strategy marked by more reduction in stomatal conductance was more prominent. Enzymes of the Halliwell-Asada pathway, especially ascorbate peroxidase and glutathione reductase, were more responsive and synchronised in PUSA-N than S-151, under similar nitrogen amendment regimes and were responsible for the differential sensitivities of the two cultivars of C. tetragonoloba. The present study shows that 1.5-times recommended dose of soil nitrogen amendments was sufficient in partial mitigation of O3 injury and the higher nitrogen dose (2-times recommended, in our case), did not provide any extra advantage to the plant's metabolism compared with plants treated with the lower nitrogen dose (1.5-times recommended).

Differential Ozone Responses Identified among Key Rust-Susceptible Wheat Genotypes

Increasing ambient ozone (O3) concentrations and resurgent rust diseases are two concomitant limiting factors to wheat production worldwide. Breeding resilient wheat cultivars bearing rust resistance and O3 tolerance while maintaining high yield is critical for global food security. This study aims at identifying ozone tolerance among key rust-susceptible wheat genotypes [Rust near-universal susceptible genotypes (RnUS)], as a first step towards achieving this goal. Tested RnUS included seven bread wheat genotypes (Chinese Spring, Line E, Little Club, LMPG 6, McNair 701, Morocco and Thatcher), and one durum wheat line (Rusty). Plants were treated with five O3 concentrations (CF, 50, 70, 90, and 110 ppb), in two O3 exposure systems [continuous stirred tank reactors (CSTR) and outdoor-plant environment chambers (OPEC)], at 21–23 Zadoks decimal growth stage. Visible injury and biomass accumulation rate were used to assess O3 responses. Visible injury data showed consistent order of genotype sensitivity (Thatcher, LMPG 6 > McNair 701, Rusty > Line E, Morocco, Little Club > Chinese Spring). Additionally, leaves at different orders showed differential O3 responses. Biomass accumulation under O3 stress showed similar results for the bread wheat genotypes. However, the durum wheat line “Rusty” had the most O3-sensitive biomass production, providing a contrasting O3 response to the tolerance reported in durum wheat. Chinese Spring was the most tolerant genotype based on both parameters and could be used as a source for O3 tolerance, while sensitive genotypes could be used as sensitive parents in mapping O3 tolerance in bread wheat. The suitability of visible symptoms and biomass responses in high-throughput screening of wheat for O3 tolerance was discussed. The results presented in this research could assist in developing future approaches to accelerate breeding wheat for O3 tolerance using existing breeding materials.

Current and future impacts of drought and ozone stress on Northern Hemisphere forests.

Rising ozone (O3 ) concentrations, coupled with an increase in drought frequency due to climate change, pose a threat to plant growth and productivity which could negatively affect carbon sequestration capacity of Northern Hemisphere (NH) forests. Using long-term observations of O3 mixing ratios and soil water content (SWC), we implemented empirical drought and O3 stress parameterizations in a coupled stomatal conductance-photosynthesis model to assess their impacts on plant gas exchange at three FLUXNET sites: Castelporziano, Blodgett and Hyytiälä. Model performance was evaluated by comparing model estimates of gross primary productivity (GPP) and latent heat fluxes (LE) against present-day observations. CMIP5 GCM model output data were then used to investigate the potential impact of the two stressors on forests by the middle (2041-2050) and end (2091-2100) of the 21st century. We found drought stress was the more significant as it reduced model overestimation of GPP and LE by ~11%-25% compared to 1%-11% from O3 stress. However, the best model fit to observations at all the study sites was obtained with O3 and drought stress combined, such that the two stressors counteract the impact of each other. With the inclusion of drought and O3 stress, GPP at CPZ, BLO and HYY is projected to increase by 7%, 5% and 8%, respectively, by mid-century and by 14%, 11% and 14% by 2091-2100 as atmospheric CO2 increases. Estimates were up to 21% and 4% higher when drought and O3 stress were neglected respectively. Drought stress will have a substantial impact on plant gas exchange and productivity, off-setting and possibly negating CO2 fertilization gains in future, suggesting projected increases in the frequency and severity of droughts in the NH will play a significant role in forest productivity and carbon budgets in future.

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.

An assessment of growth, floral morphology, and metabolites of a medicinal plant Sida cordifolia L. under the influence of elevated ozone.

Tropospheric ozone (O3) is a major secondary air pollutant and greenhouse gas, and its impact on growth, yield, and its quality is well established in the case of crop plants. However, the effects of tropospheric O3 have not been comprehensively studied on medicinal plants. Therefore, a field study was planned on a medicinally important Sida cordifolia L. plant (commonly known as country mallow or Bala) to assess the expected changes on the morphology, growth, and leaf injury under elevated O3 (ambient + 20ppb) by using open-top chambers (OTCs) at 30, 60, and 90days after treatment (DAT), while leaf and root metabolites were observed at 60 DAT. At all the growth stages, significant leaf damage was recorded as foliar injury symptoms. Most of the growth parameters also showed significant reductions at all the growth stages. Plants under elevated O3 showed a significant negative impact on most of the reproductive parts of the plant. Leaf weight ratio (LWR) showed significant increment at early stages while reduced at 90 DAT; however, root shoot ratio (RSR) showed a significant reduction at 60 DAT. The majority of the steroid metabolites showed an increase in root and leaves under elevated O3, while terpenes showed variable response. Due to O3 stress, most of the major metabolites showed an increase possibly due to their role in defense and other metabolic activities. Based on the outcomes, it is concluded that the future increase in the levels of tropospheric O3 will impact a significant effect on important metabolites of medicinal plants growing in tropical countries like India.

Metabolite profiling for model cultivars of wheat and rice under ozone pollution

As essential source for human consumption, plants of wheat and rice are highly sensitive to ozone (O3), resulting in significant agricultural losses under O3 pollution. According to our results, photosynthesis and shoot biomass of wheat and rice were significantly reduced under elevated O3. The activities of SOD, POD and CAT were responsive to O3 pollution in two crops. However, little is known about the effects of elevated O3 concentration on their metabolite profiling. The response of metabolites to elevated ozone was investigated in model cultivars of wheat and rice. A total of 172 compounds significantly changed in seedlings of wheat (103) and rice (89) under O3 pollution. The strong up-regulation of phospholipids and markedly declined of fatty acids were detected in wheat and rice under elevated O3. Methylerythritol 4-phosphate pathway was altered in both crops with reduced accumulation of carbon compound terpene under O3 stress. Meanwhile, O3 treatment led to the high levels of aspartate-derived asparagine or aspartate, which regulated carbon and nitrogen metabolism. Additionally, O3 suppressed the generation of environmental stress-related flavonoids and cinnamic acids via shikimate pathway in the two crops. Moreover, the biosynthesis of sterols was suppressed and isocitrate was not changed under ozone fumigation in wheat, while both of them were increased in rice. The metabolic results reveal the involvement of O3-related metabolites in photosynthesis, oxidative stress and carbon/nitrogen balance. Our findings provide valuable information for understanding of ozone's effects on the physiology and metabolite profiling of crop plants, boosting efforts to screen genetic resources for valuable traits to adapt to O3 pollution.

How does Malus crabapple resist ozone? Transcriptomics and metabolomics analyses.

Ozone (O3), an oxidizing toxic air pollutant, is ubiquitous in industrialized and developing countries. To understand the effects of O3 exposure on apple (Malus) and to explore its defense mechanisms, we exposed 'Hongjiu' crabapple to O3 and monitored its responses using physiological, transcriptomics, and metabolomics analyses. Exposure to 300nLL-1 O3 for 3h caused obvious damage to the leaves of Malus crabapple, affected chlorophyll and anthocyanin contents, and activated antioxidant enzymes. The gene encoding phospholipase A was highly responsive to O3 in Malus crabapple. McWRKY75 is a key transcription factor in the response to O3 stress, and its transcript levels were positively correlated with those of flavonoid-related structural genes (McC4H, McDFR, and McANR). The ethylene response factors McERF019 and McERF109-like were also up-regulated by O3. Exogenous methyl jasmonate (MeJA) decreased the damaging effects of O3 on crabapple and was most effective at 200μmolL -1. Treatments with MeJA altered the metabolic pathways of crabapple under O3 stress. In particular, MeJA activated the flavonoid metabolic pathway in Malus, which improved its resistance to O3 stress.

Application of Bacillus sp. N7 to enhance ozone tolerance of various Oryza sativa in vegetative phase: Possible mechanism and rice productivity

Abstract Ozone (O3), a phytotoxic compound, can reduce crop productivity. Improving the O3 tolerance capacity of Oryza sativa L. var. indica cv. Pathum Thani 1 (PTT1) and Oryza sativa L. var. indica cv. RD41 (RD41) by adding a soil bacterium, Bacillus sp. N7, was investigated. After cultivation in an O3 open-top chamber fumigation system (70–150 ppb) for 10 days, the results showed that Bacillus sp. N7 had the ability to protect PTT1 and RD41 plants against O3 stress while maintaining rice quality. Bacillus sp. N7 addition resulted in a significant decrease in malondialdehyde (MDA) levels by enhancing ascorbic acid (AsA) contents. This contributed to the maintenance of a higher photosynthetic performance, including higher stomatal conductance, Fv/Fm ratio, chlorophyll a and chlorophyll b contents and increased O3 tolerance. In addition, plant inoculation with Bacillus sp. N7 led to increased relative water content (RWC) and indole-3-acetic acid (IAA) levels. We therefore suggest that Bacillus sp. N7 is a high-performance plant growth-promoting bacteria (PGPB) and can enhance the O3 tolerance capacity of plants while maintaining rice quality.

Ozone-induced changes in physiological and biochemical traits in Elaeocarpus sylvestris and Michelia chapensis in South China

The influences of elevated ozone (O3) concentrations on biomass, leaf gas exchange, fluorescence parameters, and leaf physiological and biochemical traits were examined in Elaeocarpus sylvestris and Michelia chapensis seedlings under four O3 conditions for a growing season in open-top chambers (OTCs). The four O3 concentrations were charcoal-filtered air (CF) (20 ppb), 1 × O3 air (40 ppb), 2 × O3 air (80 ppb), and 4 × O3 air (160 ppb), respectively. The significant decrease in the root/shoot (R/S) ratios of both species indicated that under O3 stress root biomass was more negatively affected than shoot biomass for both tree seedlings. Along with the loss of chlorophyll and carotenoid contents, decrease in the superoxide dismutase (SOD), and enhanced level of lipid peroxidant, the light-saturated net photosynthesis rate (Pnmax) of E. sylvestris, the effective quantum yield of PSII photochemistry (Y(II)) and the electron transport rate (ETR) of both species decreased, suggesting that impaired photosynthesis occurred. The negative effect of O3 on physiological and biochemical parameters was greater for M. chapensis than for E. sylvestris. As the O3 concentration increased, the leaf mass per area (LMA) of E. sylvestris decreased, while that of M. chapensis increased. Therefore, the increased SOD activity as a hormetic-compensatory response, the increases in LMA and longer vegetative period contributed to the good adaptability and high tolerance of M. chapensis.

Transcriptome profiles of Quercus rubra responding to increased O3 stress

BackgroundClimate plays an essential role in forest health, and climate change may increase forest productivity losses due to abiotic and biotic stress. Increased temperature leads to the increased formation of ozone (O3). Ozone is formed by the interaction of sunlight, molecular oxygen and by the reactions of chemicals commonly found in industrial and automobile emissions such as nitrogen oxides and volatile organic compounds.Although it is well known that productivity of Northern red oak (Quercus rubra) (NRO), an ecologically and economically important species in the forests of eastern North America, is reduced by exposure to O3, limited information is available on its responses to exogenous stimuli at the level of gene expression.ResultsRNA sequencing yielded more than 323 million high-quality raw sequence reads. De novo assembly generated 52,662 unigenes, of which more than 42,000 sequences could be annotated through homology-based searches. A total of 4140 differential expressed genes (DEGs) were detected in response to O3 stress, as compared to their respective controls. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses of the O3-response DEGs revealed perturbation of several biological pathways including energy, lipid, amino acid, carbohydrate and terpenoid metabolism as well as plant-pathogen interaction.ConclusionThis study provides the first reference transcriptome for NRO and initial insights into the genomic responses of NRO to O3. Gene expression profiling reveals altered primary and secondary metabolism of NRO seedlings, including known defense responses such as terpenoid biosynthesis.

Water use strategy affects avoidance of ozone stress by stomatal closure in Mediterranean trees-A modelling analysis.

Both ozone (O3 ) and drought can limit carbon fixation by forest trees. To cope with drought stress, plants have isohydric or anisohydric water use strategies. Ozone enters plant tissues through stomata. Therefore, stomatal closure can be interpreted as avoidance to O3 stress. Here, we applied an optimization model of stomata involving water, CO2 , and O3 flux to test whether isohydric and anisohydric strategies may affect avoidance of O3 stress by stomatal closure in four Mediterranean tree species during drought. The data suggest that stomatal closure represents a response to avoid damage to the photosynthetic mechanisms under elevated O3 depending on plant water use strategy. Under high-O3 and well-watered conditions, isohydric species limited O3 fluxes by stomatal closure, whereas anisohydric species activated a tolerance response and did not actively close stomata. Under both O3 and drought stress, however, anisohydric species enhanced the capacity of avoidance by closing stomata to cope with the severe oxidative stress. In the late growing season, regardless of the water use strategy, the efficiency of O3 stress avoidance decreased with leaf ageing. As a result, carbon assimilation rate was decreased by O3 while stomata did not close enough to limit transpirational water losses.

Effects of Elevated Temperature and Ozone in Brassica juncea L.: Growth, Physiology, and ROS Accumulation

Global warming and ozone (O3) pose serious threats to crop yield and ecosystem health. Although neither of these factors will act individually in reality, most studies have focused on the responses of plants to air pollution or climate change. Interactive effects of these remain poorly studied. Therefore, this study was conducted to assess the effects of optimal (22/20 °C day/night) and elevated temperature (27/25 °C) and/or ambient (10 ± 10 nL L−1) and elevated O3 concentrations (100 ± 10 nL L−1) on the growth, physiology, and reactive oxygen species (ROS) accumulation of leaf mustard (Brassica juncea L.). The aim was to examine whether elevated temperature increase the O3 damage due to increasing stomatal conductance, and thus, O3 flux into the leaf. Significant reductions in photosynthetic rates occurred under O (elevated O3 with optimal temperatures) and OT (elevated O3 and temperature) conditions compared to C (controls). Stomatal conductance was significantly higher under T than in the C at 7 DAE. Under OT conditions, O3 flux significantly increased compared to that in O conditions at 7 days after exposure (DAE). Significant reductions in total fresh and dry weight were observed under OT conditions compared to those under O. Furthermore, significant reductions in levels of carotenoids and ascorbic acid were observed under OT conditions compared to O. Lipid peroxidation and accumulation of ROS such as hydroxyl radical, hydrogen peroxide, and superoxide radical were higher under O and OT conditions than in C conditions at 7 and 14 DAE. As a result of O3 stress, the results of the present study indicated that the plant injury index significantly increased under OT compared to O conditions. This result suggested that elevated temperature (+5 °C) may enhance O3 damage to B. juncea by increasing stomatal conductance and O3 flux into leaves.

Ozone risk assessment of grapevine ‘Cabernet Sauvignon’ using open-top chambers

ObjectiveGround-level ozone (O3) is an important photochemical pollutant that can damage plant tissue structures, seriously affect plant physiological metabolism and biochemical reactions, inhibit plant growth and accelerate leaf senescence. Some ozone-sensitive grape varieties show ozone injury symptoms in the field. The purpose of this study was to study the effects of long-term O3 stress on the plant growth, fruit quality, carbon and nitrogen absorption and distribution of the main cultivar ‘Cabernet Sauvignon’. MethodsO3 was administered for 2 h daily for three months to three-year-old Vitis vinifera L.cv. ‘Cabernet Sauvignon’ grapes at 75 nL/L, and the effects of O3 stress on the grape plants, the fruit growth and development, the leaves of photosystem II (PSII) and Psi activity and the carbon and nitrogen absorption and distribution were analyzed. ResultsThe results suggest that ozone pollution substantially affected the growth and physiology of ‘Cabernet Sauvignon’. Plant biomass and fruit quality were also negatively influenced by ozone pollution. Chlorophyll fluorescence analysis showed that O3 stress caused noticeable decreases in the maximum fluorescence Fm and the maximum photooxidizable P700 (Pm); the actual photochemical efficiency of PSII Y(II) decreased significantly, but the quantum yield of regulated energy dissipation Y(NPQ) increased significantly; the Psi donor side limitation Y(ND) increased, but there was no significant change in the Psi acceptor side limitation Y(NA); and the actual photochemical efficiency of Psi decreased. The carbon and nitrogen labeling of plants revealed that after O3 stress, compared with the control, the amounts of 15N and 13C absorbed by the leaves were significantly reduced, the amounts of 15N and 13C absorbed by the roots were significantly increased, and the proportions of 15N and 13C transported to the fruits were significantly reduced.

Salt Stress Reduced the Seedling Growth of Two Larch Species Under Elevated Ozone

The effect of elevated ozone (O3) and soil salinization with alkaline salts in northeastern (NE) China is a serious concern in the success of the national replanting project. As the areas planted exceed 4 million hectares in China, we must consider the future afforestation after thinning and harvest at some parts of them. Here, we investigated the effects of O3 and salt stress on seedlings of Dahurian larch (Larix gmelinii var. japonica; DL) and Japanese larch (L. kaempferi; JL). The two species of seedlings were exposed to elevated O3 [approximately 70 nmol mol-1] and ambient control [approximately 40 nmol mol-1] for one growing season in an open top chamber (OTC) system that simulated the salinity in NE China [alkaline salt, NaHCO3 : NaCl = 9:1, 20mM Na+]. The seedlings under salt free treatment received tap water. Effects of O3 on the growth of both larches were not significant, although the LMA of JL was reduced more than that of DL seedlings. Further, the combined effects of O3 and salt stress were not significant. This may be attributable to the stronger effects of salt stresses on both larch seedlings. Salt stress decreased the total dry mass in both larch species by more than 10%. DL seedlings showed specific salt tolerance in absorption of some mineral nutrients. Although salt stress reduced Ca and Mg content in needles, we found the degree of reduction was lower in DL than JL, with specific salt tolerance of mineral homeostasis in DL seedlings. Our results indicated that DL seedlings may be future candidate afforestation species even in saline soil and O3 levels less than 70 nmol mol-1.

Investigating the effect of methyl jasmonate and melatonin on resistance of Malus crabapple 'Hong Jiu' to ozone stress.

Ozone (O3) is an adverse environmental factor posing damage to ornamental plants. Thus, it is important to seek an effective way of enhancing plant tolerance to O3-induced damage. Methyl jasmonate (MJ) and melatonin (MT) are plant growth regulators (PGRs) involved in plant abiotic stress responses. In this study, compared with the control group of plants without ozone, the influence of exogenous MJ (0, 10, 50, 100, and 150μM) and MT (0, 0.1, 0.5, 2.5, and 12.5μM) on the resistance of Malus crabapple 'Hong Jiu' was evaluated under O3 stress (100 ± 10nL/L for 3h). Our data revealed that levels of MDA were significantly enhanced following O3 treatment compared with plants without O3. O3 induced the activities of antioxidant enzymes and the accumulation of non-enzymatic antioxidants. While lower malondialdehyde (MDA) content, greater activities of antioxidant enzymes, and higher levels of soluble protein and non-enzymatic antioxidants were observed in PGRs-pretreated plants than in non-PGRs-pretreated plants under O3 stress. Based on the above results and air pollution tolerance index (APTI), an exogenous supply of MJ and MT to Malus crabapple 'Hong Jiu' seedlings was protective for O3-induced toxicity. The present study provides new insights into the mechanisms of MJ and MT amelioration of O3-induced oxidative stress damages in Malus crabapple 'Hong Jiu.'