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.

Use of ChatGPT: What does it mean for biology and environmental science?

Artificial intelligence (AI) large language models (LLMs) have emerged as important technologies. Recently, ChatGPT (Generative Pre-trained Transformer) has been released and attracted massive interest from the public, owing to its unique capabilities to simplify many daily tasks of people from diverse backgrounds and social statuses. Here, we discuss how ChatGPT (and similar AI technologies) can impact biology and environmental science, providing examples obtained through interactive sessions with ChatGPT. The benefits that ChatGPT offers are ample and can impact many aspects of biology and environmental science, including education, research, scientific publishing, outreach, and societal translation. Among others, ChatGPT can simplify and expedite highly complex and challenging tasks. As an example to illustrate this, we provide 100 important questions for biology and 100 important questions for environmental science. Although ChatGPT offers a plethora of benefits, there are several risks and potential harms associated with its use, which we analyze herein. Awareness of risks and potential harms should be raised. However, understanding and overcoming the current limitations could lead these recent technological advances to push biology and environmental science to their limits.

Model-based estimation of the leaf area of ozone-indicator tobacco (Nicotiana tabacum L.) plants under ambient ozone conditions.

Bel-W3 is an ozone-sensitive tobacco (Nicotiana tabacum L.) cultivar widely used worldwide for ozone biomonitoring. Despite its extensive use, there is no comprehensive predictive model to non-destructively estimate the leaf area using only a common ruler, yet leaf area is a major evaluative trait in plants under ozone stress and of economic value in tobacco plants. In this method, we aimed at developing a predictive model to estimate leaf area using the product between leaf length and leaf width. To this end, we conducted a field experiment with ground-grown Bel-W3 plants treated with different solutions under ambient ozone conditions. The solutions were water, the antiozonant ethylenediurea (EDU; 500 ppm), and the antitranspirant pinolene (Vapor Gard; 1%, 5%, 10%). The chemical treatments were introduced to enhance leaves pool and capture different conditions that can occur in ozone biomonitoring projects.•A simple linear predictive model was developed and validated using data from a previous chamber experiment with small seedlings.•Overestimation of the model led to the integration of data from both experiments and development of another simple linear predictive model.•This integrated model provides improved estimation of leaf area and can be used for representative estimation of the area of Bel-W3 leaves of any sizes.

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 (NOx), 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.

Mechanisms of cerium-induced stress in plants: A meta-analysis.

A comprehensive evaluation of the effects of cerium on plants is lacking even though cerium is extensively applied to the environment. Here, the effects of cerium on plants were meta-analyzed using a newly developed database consisting of approximately 8500 entries of published data. Cerium affects plants by acting as oxidative stressor causing hormesis, with positive effects at low concentrations and adverse effects at high doses. Production of reactive oxygen species and its linked induction of antioxidant enzymes (e.g. catalase and superoxide dismutase) and non-enzymatic antioxidants (e.g. glutathione) are major mechanisms driving plant response mechanisms. Cerium also affects redox signaling, as indicated by altered GSH/GSSG redox pair, and electrolyte leakage, Ca2+, K+, and K+/Na+, indicating an important role of K+ and Na+ homeostasis in cerium-induced stress and altered mineral (ion) balance. The responses of the plants to cerium are further extended to photosynthesis rate (A), stomatal conductance (gs), photosynthetic efficiency of PSII, electron transport rate, and quantum yield of PSII. However, photosynthesis response is regulated not only by physiological controls (e.g. gs), but also by biochemical controls, such as via changed Hill reaction and RuBisCO carboxylation. Cerium concentrations <0.1-25 mg L-1 commonly enhance chlorophyll a and b, gs, A, and plant biomass, whereas concentrations >50 mg L-1 suppress such fitness-critical traits at trait-specific concentrations. There was no evidence that cerium enhances yields. Observations were lacking for yield response to low concentrations of cerium, whereas concentrations >50 mg Kg-1 suppress yields, in line with the response of chlorophyll a and b. Cerium affects the uptake and tissue concentrations of several micro- and macro-nutrients, including heavy metals. This study enlightens the understanding of some mechanisms underlying plant responses to cerium and provides critical information that can pave the way to reducing the cerium load in the environment and its associated ecological and human health risks.

Strategic roadmap to assess forest vulnerability under air pollution and climate change.

Although it is an integral part of global change, most of the research addressing the effects of climate change on forests have overlooked the role of environmental pollution. Similarly, most studies investigating the effects of air pollutants on forests have generally neglected the impacts of climate change. We review the current knowledge on combined air pollution and climate change effects on global forest ecosystems and identify several key research priorities as a roadmap for the future. Specifically, we recommend (1) the establishment of much denser array of monitoring sites, particularly in the South Hemisphere; (2) further integration of ground and satellite monitoring; (3) generation of flux-based standards and critical levels taking into account the sensitivity of dominant forest tree species; (4) long-term monitoring of N, S, P cycles and base cations deposition together at global scale; (5) intensification of experimental studies, addressing the combined effects of different abiotic factors on forests by assuring a better representation of taxonomic and functional diversity across the ~73,000 tree species on Earth; (6) more experimental focus on phenomics and genomics; (7) improved knowledge on key processes regulating the dynamics of radionuclides in forest systems; and (8) development of models integrating air pollution and climate change data from long-term monitoring programs.

Exogenous application of melatonin to plants, algae, and harvested products to sustain agricultural productivity and enhance nutritional and nutraceutical value: A meta-analysis.

Melatonin is produced by plants, algae, and animals. Worldwide studies show diverse positive effects of exogenous melatonin on plants, edible plant products, and algae, but the potential of melatonin to enhance food and feed systems through these positive effects remains largely unexplored. Through a meta-analysis of about 25,000 observations, we show for the first time that exogenous application of melatonin significantly increases crop productivity and yields, and enhances the nutritional and nutraceutical value of edible plant products and algae by regulating diverse biological functions. We demonstrate that melatonin can improve plants, edible plant products, and algae under various current climate change scenarios, environmental pollution factors, and other stresses by about 7% to nearly 30%, on average, depending on the stressor. We also analyze various technical/methodological factors influencing the desired outcomes and identify conditions that offer optimal enhancement. We show that the positive effect of melatonin on plants and edible plant products varies among species, genera, and families, and strongly depends on the concentration of melatonin and treatment duration. The effect of melatonin is slightly lower on the monocot clade Commelinids than on the eudicot clades Asterids and Rosids. We also show that its stimulatory effect on plants depends on cultivation system, with a larger effect obtained in hydroponic systems. However, it does not depend on application stage (seed or vegetative), application route (foliage, roots, or seed), and whether the cultivation system is ex vivo or in vivo. This is the first meta-analysis examining the effects of melatonin on plants, edible plant products, and algae, and offers a scientific and technical roadmap facilitating sustainable food and feed production through the application of exogenous melatonin.

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

Elevated ground-level ozone (O3) pollution can adversely affect plants and inhibit plant growth and productivity, threatening food security and ecological health. It is therefore essential to develop measures to protect plants against O3-induced adverse effects. Here we summarize the current status of phytoprotection against O3-induced adverse effects and consider recent scientific and engineering advances, to provide a novel perspective for maximizing plant health while reducing environmental/ecological risks in an O3-polluted world. We suggest that nanoscience and nanotechnology can provide a new dimension in the protection of plants against O3-induced adverse effects, and recommend that new studies are based upon a green chemistry perspective.

Ozone affects plant, insect, and soil microbial communities: A threat to terrestrial ecosystems and biodiversity.

Elevated tropospheric ozone concentrations induce adverse effects in plants. We reviewed how ozone affects (i) the composition and diversity of plant communities by affecting key physiological traits; (ii) foliar chemistry and the emission of volatiles, thereby affecting plant-plant competition, plant-insect interactions, and the composition of insect communities; and (iii) plant-soil-microbe interactions and the composition of soil communities by disrupting plant litterfall and altering root exudation, soil enzymatic activities, decomposition, and nutrient cycling. The community composition of soil microbes is consequently changed, and alpha diversity is often reduced. The effects depend on the environment and vary across space and time. We suggest that Atlantic islands in the Northern Hemisphere, the Mediterranean Basin, equatorial Africa, Ethiopia, the Indian coastline, the Himalayan region, southern Asia, and Japan have high endemic richness at high ozone risk by 2100.

Plant susceptibility to ozone: A tower of Babel?

In a world with climate change and environmental pollution, modern Biology is concerned with organismic susceptibility. At the same time, policy and decision makers seek information about organismic susceptibility. Therefore, information about organismic susceptibility may have far-reaching implications to the entire biosphere that can extend to several forthcoming generations. Here, we review a sample of approximately 200 published peer-reviewed articles dealing with plant response to ground-level ozone to understand how the information about susceptibility is communicated. A fuzzy and often incorrect terminology was used to describe the responsiveness of plants to ozone. Susceptibility was classified too arbitrarily and this was reflected to the approximately 50 descriptive words that were used to characterize susceptibility. The classification of susceptibility was commonly based on calculated probability (p) value. This practice is inappropriate as p values do not provide any basis for effect or susceptibility magnitude. To bridge the gap between science and policy decision making, classification of susceptibility should be done using alternative approaches, such as effect size estimates in conjunction with multivariate ordination statistics.

A quantitative assessment of hormetic responses of plants to ozone.

Evaluations of ozone effects on vegetation across the globe over the last seven decades have mostly incorporated exposure levels that were multi-fold the preindustrial concentrations. As such, global risk assessments and derivation of critical levels for protecting plants and food supplies were based on extrapolation from high to low exposure levels. These were developed in an era when it was thought that stress biology is framed around a linear dose-response. However, it has recently emerged that stress biology commonly displays non-linear, hormetic processes. The current biological understanding highlights that the strategy of extrapolating from high to low exposure levels may lead to biased estimates. Here, we analyzed a diverse sample of published empirical data of approximately 500 stimulatory, hormetic-like dose-responses induced by ozone in plants. The median value of the maximum stimulatory responses induced by elevated ozone was 124%, and commonly <150%, of the background response (control), independently of species and response variable. The maximum stimulatory response to ozone was similar among types of response variables and major plant species. It was also similar among clades, between herbaceous and woody plants, between deciduous and evergreen trees, and between annual and perennial herbaceous plants. There were modest differences in the stimulatory response between genera and between families which may reflect different experimental designs and conditions among studies. The responses varied significantly upon type of exposure system, with open-top chambers (OTCs) underestimating the maximum stimulatory response compared to free-air ozone-concentration enrichment (FACE) systems. These findings suggest that plants show a generalized hormetic stimulation by ozone which is constrained within certain limits of biological plasticity, being highly generalizable, evolutionarily based, and maintained over ecological scales. They further highlight that non-linear responses should be taken into account when assessing the ozone effects on plants.

Stress response and population dynamics: Is Allee effect hormesis?

Hormesis is a fundamental notion in ecotoxicology while competition between organisms is an essential notion in population ecology and species adaptation and evolution. Both sub-disciplines of ecology deal with the response of organisms to abiotic and biotic stresses. In ecotoxicology, the Linear-non-Threshold (LNT), Threshold and Hormetic models are used to describe the dominant responses of a plethora of endpoints to abiotic stress. In population ecology, the logistic, theta-logistic and the Allee effect models are used to describe the growth of populations under different responses to (biotic) stress induced by population density. The per capita rate of population increase (r) measures species fitness. When it is used as endpoint, the responses to population density seem to perfectly correspond to LNT, Threshold and Hormetic responses to abiotic stress, respectively. Our analysis suggests the Allee effect is a hormetic-like response of r to population density, an ultimate biotic stress. This biphasic dose-response model appears across different systems and situations (from molecules to tumor growth to population dynamics), is highly supported by ecological and evolutionary theory, and has important implications in most sub-disciplines of biology as well as in environmental and earth sciences. Joined multi-disciplinary efforts would facilitate the development and application of advanced research approaches for better understanding potential planetary-scale implications.

Effects of ozone and ammonium sulfate on cauliflower: Emphasis on the interaction between plants and insect herbivores.

Ammonium sulfate [(NH4)2SO4] deposition and elevated ozone (O3) concentrations may negatively affect plants and trophic interactions. This study aimed to evaluate for the first time the interactive effects of high (NH4)2SO4 load and elevated O3 levels on cauliflower (Brassica oleracea L.) under field conditions. Cauliflower seedlings were treated with 0 (AS0) or 50 (AS50) kg ha-1 (NH4)2SO4 and exposed to ambient (AOZ, ≈20 ppb) or elevated (EOZ, ≈55 ppb) O3 for about one month, in a Free Air O3 Concentration Enrichment (FACE) system. The oligophagous diamondback moth (Plutella xylostella Linnaeus, 1758) showed a clear preference towards the seedlings treated with AS50, which intensively grazed. Plant-herbivore interactions were driven by (NH4)2SO4 availability, rather than O3, via increased nitrogen content in the leaves. Further laboratory bioassays were followed to confirm the validity of these observations using polyphagous Eri silkmoth larvae (Samia ricini) as a biological model in a standardized experimental setup. Choice assays, where larvae could select leaves among leaf samples from the different experimental conditions, and no-choice assays, where larvae could graze leaves from just one experimental condition, were conducted. In the choice assay, the larvae preferred AS50-treated leaves, in agreement with the field observations with diamondback moth. In the no-choice assay, larval body mass growth was inhibited when fed with leaves treated with EOZ and/or AS50. Larvae fed with AS50-treated leaves displayed increased mortality. These observations coincide with higher NO3 and Zn content in AS50-treated leaves. This study shows that plant-herbivore interactions can be driven by (NH4)2SO4 availability, independently of O3, and suggests that high N deposition may have severe health implications in animals consuming such plant tissues. Key message: Plant-herbivore interactions are driven by high (NH4)2SO4 availability, independently of O3.

Predicting the effect of ozone on vegetation via linear non-threshold (LNT), threshold and hormetic dose-response models.

The nature of the dose-response relationship in the low dose zone and how this concept may be used by regulatory agencies for science-based policy guidance and risk assessment practices are addressed here by using the effects of surface ozone (O3) on plants as a key example for dynamic ecosystems sustainability. This paper evaluates the current use of the linear non-threshold (LNT) dose-response model for O3. The LNT model has been typically applied in limited field studies which measured damage from high exposures, and used to estimate responses to lower concentrations. This risk assessment strategy ignores the possibility of biological acclimation to low doses of stressor agents. The upregulation of adaptive responses by low O3 concentrations typically yields pleiotropic responses, with some induced endpoints displaying hormetic-like biphasic dose-response relationships. Such observations recognize the need for risk assessment flexibility depending upon the endpoints measured, background responses, as well as possible dose-time compensatory responses. Regulatory modeling strategies would be significantly improved by the adoption of the hormetic dose response as a formal/routine risk assessment option based on its substantial support within the literature, capacity to describe the entire dose-response continuum, documented explanatory dose-dependent mechanisms, and flexibility to default to a threshold feature when background responses preclude application of biphasic dose responses. CAPSULE: The processes of ozone hazard and risk assessment can be enhanced by incorporating hormesis into their principles and practices.

Commentary: EPA's proposed expansion of dose-response analysis is a positive step towards improving its ecological risk assessment.

The United States Environmental Protection Agency (US EPA) has recently proposed changes to strengthen the transparency of its pivotal regulatory science policy and procedures. In this context, the US EPA aims to enhance the transparency of dose-response data and models, proposing to consider for the first time non-linear biphasic dose-response models. While the proposed changes have the potential to lead to markedly improved ecological risk assessment compared to past and current approaches, we believe there remain open issues for improving the quality of ecological risk assessment, such as the consideration of adaptive, dynamic and interactive effects. Improved risk assessment including adaptive and dynamic non-linear models (beyond classic threshold models) can enhance the quality of regulatory decisions and the protection of ecological health. We suggest that other countries consider adopting a similar scientific-regulatory posture with respect to dose-response modeling via the inclusion of non-linear biphasic models, that incorporate the dynamic potential of biological systems to adapt (i.e., enhancing positive biological endpoints) or maladapt to low levels of stressor agents.

Parasitoids and Predators of Physokermes hellenicus (Hemiptera: Coccomorpha: Coccidae) in Greece.

The genus Physokermes Targioni Tozzetti includes species that are distributed in the Holarctic region and feed on conifers. The recently described scale Physokermes hellenicus (Kozár and Gounari) (Hemiptera: Coccidae) is an endemic species of Greece whose host plants are fir trees of the genus Abies (Pinales: Pinaceae). It is considered as beneficial scale insect species since its honeydew secretions are exploited by honeybees leading to the production of a special honey with important physicochemical characteristics. Since there are no previous data on the natural enemies of P. hellenicus, an investigation was carried out during 2013 in forested areas of eight mountains in south and central Greece aiming to correlate the presence of P. hellenicus with certain parasitoids and predators. Seven species of Encyrtidae, Eulophidae, Pteromalidae, and Eurytomidae (Hymenoptera); five species of Anthribidae and Coccinellidae (Coleoptera); and four species of Dictinidae, Linyphiidae, and Theridiidae (Araneae) were identified. Twelve of them were identified at the species level while four at the genus level. Among them Microterys lunatus (Dalman) (Hymenoptera: Encyrtidae), Pseudorhopus testaceus (Ratzeburg) (Hymenoptera: Encyrtidae), and Anthribus fasciatus Forster (Coleoptera: Anthribidae) were the most abundant natural enemies of P. hellenicus adult female while Metaphycus unicolor Hoffer (Hymenoptera: Encyrtidae) and Trichomasthus sp. (Hymenoptera: Encyrtidae) were found to parasitize P. hellenicus male nymph. Cinetata gradata (Simon) (Araneae: Linyphiidae) is reported for first time in the Greek arachnofauna. Our results suggest that the abundance of the fir scale P. hellenicus could be affected by a complex of parasitoid and predator species of different taxa. Future long-term research on these species in relation with abiotic factors would help to understand possible fluctuation of the scale's population.

Effects of ozone (O3) and ethylenediurea (EDU) on the ecological stoichiometry of a willow grown in a free-air exposure system.

Ground-level ozone (O3) concentrations have been elevating in the last century. While there has been a notable progress in understanding O3 effects on vegetation, O3 effects on ecological stoichiometry remain unclear, especially early in the oxidative stress. Ethyelenediurea (EDU) is a chemical compound widely applied in research projects as protectant of plants against O3 injury, however its mode of action remains unclear. To investigate O3 and EDU effects early in the stress, we sprayed willow (Salix sachalinensis) plants with 0, 200 or 400 mg EDU L-1, and exposed them to either low ambient O3 (AOZ) or elevated O3 (EOZ) levels during the daytime, for about one month, in a free air O3 controlled exposure (FACE); EDU treatment was repeated every nine days. We collected samples for analyses from basal, top, and shed leaves, before leaves develop visible O3 symptoms. We found that O3 altered the ecological stoichiometry, including impacts in nutrient resorption efficiency, early in the stress. The relation between P content and Fe content seemed to have a critical role in maintaining homeostasis in an effort to prevent O3-induced damage. Photosynthetic pigments and P content appeared to play an important role in EDU mode of action. This study provides novel insights on the stress biology which are of ecological and toxicological importance.

High doses of ethylenediurea (EDU) as soil drenches did not increase leaf N content or cause phytotoxicity in willow grown in fertile soil.

Ground-level ozone (O3) levels are nowadays elevated in wide regions of the Earth, causing significant effects on plants that finally lead to suppressed productivity and yield losses. Ethylenediurea (EDU) is a chemical compound which is widely used in research projects as phytoprotectant against O3 injury. The EDU mode of action remains still unclear, while there are indications that EDU may contribute to plants with nitrogen (N) when the soil is poor in N and the plants have relatively small leaf area. To reveal whether the N content of EDU acts as a fertilizer to plants when the soil is not poor in N and the plants have relatively large total plant leaf area, willow plants (Salix sachalinensis Fr. Schm) were exposed to low ambient O3 levels and treated ten times (9-day interval) with 200mL soil drench containing 0, 800 or 1600mg EDU L-1. Fertilizer was added to a nutrient-poor soil, and the plants had an average plant leaf area of 9.1m2 at the beginning of EDU treatments. Indications for EDU-induced hormesis in maximum electron transport rate (Jmax) and ratio of intercellular to ambient CO2 concentration (Ci:Ca) were observed at the end of the experiment. No other EDU-induced effects on leaf greenness and N content, maximum quantum yield of photosystem II (Fv/Fm), gas exchange, growth and matter production suggest that EDU did not act as N fertilizer and did not cause toxicity under these experimental conditions.

Application and further characterization of the snap bean S156/R123 ozone biomonitoring system in relation to ambient air temperature.

Increased mixing ratios of ground-level ozone (O3) threaten individual plants, plant communities and ecosystems. In this sense, O3 biomonitoring is of great interest. The O3-sensitive S156 and the O3-tolerant R123 genotypes of snap bean (Phaseolus vulgaris L.) have been proposed as a potential tool for active biomonitoring of ambient O3. In the present study, an O3 biomonitoring was conducted, with the S156/R123 tool, along with a monitoring of O3 and other environmental conditions in an urban area in Athens, Greece, during the growing seasons of 2012 and 2013. Plant yield was evaluated to assess the effectiveness of AOT40 in interpreting O3-induced phytotoxicity. Across the two genotypes, an approximately two times lower total number of pods - and consequently lower bulk mass of seeds - was found in 2012 than in 2013, although there was no significant difference in the final AOT40 between the two years. No significant differences were observed in the stomatal density or conductance between the two genotypes, whereas it was estimated that, in both genotypes, the abaxial leaf surface contributes 2.7 fold to O3 intake in comparison to the adaxial one. By testing the role of ambient air temperature in outdoor plant environment chambers (OPECs), it was found that increased temperature limits mature pod formation and complicates interpretation of O3 impacts in terms of S156/R123 yields ratios. This is the first study providing evidence for a hormetic response of plants to ambient air temperature. This study also points out the complexity of using yield as a measure of O3 impact across different environments with the snap bean system, whereas visible foliar injury is more consistently related to O3 effects.

Impacts of ethylenediurea (EDU) soil drench and foliar spray in Salix sachalinensis protection against O3-induced injury.

It is widely accepted that elevated levels of surface ozone (O3) negatively affect plants. Ethylenediurea (EDU) is a synthetic substance which effectively protects plants against O3-caused phytotoxicity. Among other questions, the one still open is: which EDU application method is more appropriate for treating fast-growing tree species. The main aims of this study were: (i) to test if chronic exposure of Salix sachalinensis plants to 200-400mgEDUL-1, the usually applied range for protection against O3 phytotoxicity, is beneficial to plants; (ii) to evaluate the effects of chronic exposure to elevated O3 on S. sachalinensis; (iii) to assess the efficacy of two methods (i.e. soil drench and foliar spray) of EDU application to plants; (iv) to investigate the appropriate concentration of EDU to protect against elevated O3-induced damage in S. sachalinensis; and (v) to compare the two methods of EDU application in terms of effectiveness and EDU consumption. Current-year cuttings grown in infertile soil free from organic matter were exposed either to low ambient O3 (AOZ, 10-h≈28.3nmolmol-1) or to elevated O3 (EOZ, 10-h≈65.8nmolmol-1) levels during daylight hours. Over the growing season, plants were treated every nine days with 200mL soil drench of 0, 200 or 400mgEDUL-1 or with foliar spray of 0, 200 or 400mgEDUL-1 (in two separate experiments). We found that EDU per se had no effects on plants exposed to AOZ. EOZ practically significantly injured S. sachalinensis plants, and the impact was indifferent between the experiments. EDU did not protect plants against EOZ impact when applied as soil drench but it did protect them when applied as 200-400mgL-1 foliar spray. We conclude that EDU may be more effective against O3 phytotoxicity to fast-growing species when applied as a spray than when applied as a drench. Keymessage: Soil-drenched EDU was ineffective in protecting willow plants against O3-induced injury, whereas foliar-sprayed EDU was effective even at the concentration of 200mgL-1.