Exogenous application of chemicals for protecting plants against ambient ozone pollution: What should come next?

Adapting crop production to climate change and air pollution at different scales

Air pollution and climate change are tightly interconnected and jointly affect field crop production and agroecosystem health. Although our understanding of the individual and combined impacts of air pollution and climate change factors is improving, the adaptation of crop production to concurrent air pollution and climate change remains challenging to resolve. Here we evaluate recent advances in the adaptation of crop production to climate change and air pollution at the plant, field and ecosystem scales. The main approaches at the plant level include the integration of genetic variation, molecular breeding and phenotyping. Field-level techniques include optimizing cultivation practices, promoting mixed cropping and diversification, and applying technologies such as antiozonants, nanotechnology and robot-assisted farming. Plant- and field-level techniques would be further facilitated by enhancing soil resilience, incorporating precision agriculture and modifying the hydrology and microclimate of agricultural landscapes at the ecosystem level. Strategies and opportunities for crop production under climate change and air pollution are discussed.

Spatiotemporal variations of ozone exposure and its risks to vegetation and human health in Cyprus: an analysis across a gradient of altitudes

Ground-level ozone (O₃) affects vegetation and threatens environmental health when levels exceed critical values, above which adverse effects are expected. Cyprus is expected to be a hotspot for O₃ concentrations due to its unique position in the eastern Mediterranean, receiving air masses from Europe, African, and Asian continents, and experiencing a warm Mediterranean climate. In Cyprus, the spatiotemporal features of O₃ are poorly understood and the potential risks for forest health have not been explored. We evaluated O₃ and nitrogen oxides (NO and NO₂) at four regional background stations at different altitudes over 2014-2016. O₃ risks to vegetation and human health were estimated by calculating accumulated O₃ exposure over a threshold of 40 nmol mol^-1 (AOT40) and cumulative exposure to mixing ratios above 35 nmol mol^-1 (SOMO35) indices. The data reveal that mean O₃ concentrations follow a seasonal pattern, with higher levels in spring (51.8 nmol mol^-1) and summer (53.2 nmol mol^-1) and lower levels in autumn (46.9 nmol mol^-1) and winter (43.3 nmol mol^-1). The highest mean O₃ exposure (59.5 nmol mol^-1) in summer occurred at the high elevation station Mt. Troodos (1819 m a.s.l.). Increasing (decreasing) altitudinal gradients were found for O₃ (NO_x), driven by summer-winter differences. The diurnal patterns of O₃ showed little variation. Only at the lowest altitude O₃ displayed a typical O₃ diurnal pattern, with hourly differences smaller than 15 nmol mol^-1. Accumulated O₃ exposures at all stations and in all years exceeded the European Union's limits for the protection of vegetation, with average values of 3-month (limit: 3000 nmol mol^-1 h) and 6-month (limit: 5000 nmol mol^-1 h) AOT40 for crops and forests of 16,564 and 31,836 nmol mol^-1 h, respectively. O₃ exposures were considerably high for human health, with an average SOMO35 value of 7270 nmol mol^-1 days across stations and years. The results indicate that O₃ is a major environmental and public health issue in Cyprus, and policies must be adopted to mitigate O₃ precursor emissions at local and regional scales.

Oxidative Stress Mitigation by Chitosan Nanoparticles in Durum Wheat Also Affects Phytochemicals and Technological Quality of Bran and Semolina

In our previous work, durum wheat cv. Fabulis was grown over two consecutive seasons (2016–2017 and 2017–2018) in an experimental field in the north of Italy. With the aim of mitigating oxidative stress, plants were subjected to four treatments (deionized water, CHT 0.05 mg/mL, CHT-NPs, and CHT-NPs-NAC) three times during the experiment. Chitosan nanoparticles (CHT-NPs) reduced symptom severity on wheat leaves and positively influenced the final grain yield. The present work aimed at investigating whether CHT treatments and particularly N-acetyl cysteine (NAC)-loaded or -unloaded CHT-NPs, while triggering plant defense mechanisms, might also vary the nutritional and technological quality of grains. For this purpose, the grains harvested from the previous experiment were analyzed for their content in phytochemicals and for their technological properties. The results showed that CHT increased the polyphenol and tocopherol content and the reducing capacity of bran and semolina, even if the positive effect of the nano-formulation remained still unclear and slightly varied between the two years of cultivation. The positive effect against oxidative stress induced by the chitosan treatments was more evident in the preservation of both the starch pasting properties and gluten aggregation capacity, indicating that the overall technological quality of semolina was maintained. Our data confirm the role of chitosan as an elicitor of the antioxidant defense system in wheat also at the grain level.

Characteristics, influence factors, and health risk assessment of volatile organic compounds through one year of high-resolution measurement at a refinery

From January 2020 to December 2020, high-resolution data of volatile organic compound (VOC) concentrations were monitored by online instruments at a petroleum refinery. The measurement results showed that the external contaminants, meteorological conditions and photochemical reactions had a great influence on the VOC data measured in the petroleum refineries. Some significant differences were observed in the emission composition of different refineries, while propene (34.2%), propane (10.2%), n-butane (5.6%), i-pentane (5.0%) were the dominant species emitted from the refinery in this study. The correlations between compounds with similar atmospheric lifetimes were strong (R² > 0.9), which indicated that the diagnostic ratios of these compounds could be used as indicators to identify the refinery emission source. Chronic health effects of non-carcinogenic risk results showed that acrolein had the highest non-carcinogenic risk and other compound-specific health risks may be of less concern in the refining area. Halogenates and aromatics accounted for 97.4% of the total carcinogenic risk values, while 1,2-dibromoethane, chloromethane, benzene, trichloromethane, 1,2-dichloroethane contributed approximately 80% of the total carcinogenic risk assessment values. This research has recorded valuable data about the VOC emission characteristics from the perspective of the high-resolution monitoring of the petroleum refinery. The results of this work will provide a reference to accurately quantify and identify the emission of petroleum refineries and further throw some light on effective VOC abatement strategies.

Foliar Application of Wood Distillate Alleviates Ozone-Induced Damage in Lettuce (Lactuca sativa L.)

This study examined whether foliar applications of wood distillate (WD) have a protective effect on photosynthesis and the antioxidant power of lettuce when exposed to an ecologically relevant O₃ concentration. Seedlings of lettuce (Lactuca sativa L.) were fumigated daily with 60 ppb of O₃ for 30 days, five hours per day. Once per week, 50% of the fumigated plants were treated with foliar applications of 0.2% WD, while control plants were treated with water. The results clearly showed the ability of WD to protect lettuce plants from ozone-induced damage. Specifically, WD-treated plants exhibited lower damage to the photosynthetic machinery, assessed through a series of chlorophyll fluorescence parameters, a higher chlorophyll content, higher antioxidant power, as well as antioxidant molecules, i.e., caffeic acid and quercetin, and higher biomass. Counteracting the overproduction of ozone-generated reactive oxygen species (ROS) is speculated to be the main mechanism by which WD protects the plant from ozone-induced damage.

Chitosan Nanoparticles Loaded with N-Acetyl Cysteine to Mitigate Ozone and Other Possible Oxidative Stresses in Durum Wheat

Modern durum wheat cultivars are more prone to ozone stress because of their high photosynthetic efficiency and leaf gas exchanges that cause a greater pollutant uptake. This, in turn, generates an increased reactive oxygen species (ROS) production that is a challenge to control by the antioxidant system of the plant, therefore affecting final yield, with a reduction up to 25%. With the aim of mitigating oxidative stress in wheat, we used chitosan nanoparticles (CHT-NPs) either unloaded or loaded with the antioxidant compound N-acetyl cysteine (NAC), on plants grown either in a greenhouse or in an open field. NAC-loaded NPs were prepared by adding 0.5 mg/mL NAC to the CHT solution before ionotropic gelation with tripolyphosphate (TTP). Greenhouse experiments evidenced that CHT-NPs and CHT-NPs-NAC were able to increase the level of the leaf antioxidant pool, particularly ascorbic acid (AsA) content. However, the results of field trials, while confirming the increase in the AsA level, at least in the first phenological stages, were less conclusive. The presence of NAC did not appear to significantly affect the leaf antioxidant pool, although the grain yield was slightly higher in NAC-treated parcels. Furthermore, both NAC-loaded and -unloaded CHT-NPs partially reduced the symptom severity and increased the weight of 1000 seeds, thus showing a moderate mitigation of ozone injury.