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Ozone (O3) air pollution is well known to adversely affect both the grain and protein yield of wheat, an important staple crop. This study aims to identify and model the key plant processes influencing the effect of O3 on wheat protein. We modified the DO3SE-Crop model to incorporate nitrogen (N) processes, and parameterised the O3 effect on stem, leaf and grain N using O3 fumigation datasets spanning 3 years and 4 O3 treatments. Our results show the new model captures the O3 effect on grain N concentrations, and anthesis leaf and stem concentration, well. However, the O3 effect on harvest leaf and stem N is exaggerated. Further, a sensitivity analysis revealed that, irrespective of O3 treatment, accelerated senescence onset was the primary plant process affecting grain N. This modelling study therefore demonstrates the capability of the DO3SE-CropN model to simulate processes by which O3 affects N content, and thereby determines that senescence onset is the main driver of O3 reductions in grain protein yield. The implication of the sensitivity analysis is that breeders should focus their efforts on stay-green cultivars that do not experience a protein penalty when developing O3 tolerant lines, to maintain both wheat yield and nutritional quality under O3 exposure.

Tropospheric ozone (O3) is a global air pollutant that adversely affects plant growth. Whereas the impacts of O3 have previously been examined for some tropical commodity crops, no information is available for the pantropical crop, banana (Musa spp.). To address this, we exposed Australia’s major banana cultivar, Williams, to a range of [O3] in open top chambers. In addition, we examined 46 diverse Musa lines growing in a common garden for variation in three traits that are hypothesised to shape responses to O3: (1) leaf mass per area; (2) intrinsic water use efficiency; and (3) total antioxidant capacity. We show that O3 exposure had a significant effect on the biomass of cv. Williams, with significant reductions in both pseudostem and sucker biomass with increasing [O3]. This was accompanied by a significant increase in total antioxidant capacity and phenolic concentrations in older, but not younger, leaves, indicating the importance of cumulative O3 exposure. Using the observed trait diversity, we projected O3 tolerance among the 46 Musa lines growing in the common garden. Of these, cv. Williams ranked as one of the most O3-tolerant cultivars. This suggests that other genetic lines could be even more susceptible, with implications for banana production and food security throughout the tropics.

Extreme weather events are increasing in frequency and magnitude with profound effects on ecosystem functioning. Further, there is now a greater likelihood that multiple extreme events are occurring within a single year. Here we investigated the effect of a single drought, flood or compound (flood + drought) extreme event on temperate grassland ecosystem processes in a field experiment. To assess system resistance and resilience, we studied changes in a wide range of above- and below-ground indicators (plant diversity and productivity, greenhouse gas emissions, soil chemical, physical and biological metrics) during the 8 week stress events and then for 2 years post-stress. We hypothesized that agricultural grasslands would have different degrees of resistance and resilience to flood and drought stress. We also investigated two alternative hypotheses that the combined flood + drought treatment would either, (A) promote ecosystem resilience through more rapid recovery of soil moisture conditions or (B) exacerbate the impact of the single flood or drought event. Our results showed that flooding had a much greater effect than drought on ecosystem processes and that the grassland was more resistant and resilient to drought than to flood. The immediate impact of flooding on all indicators was negative, especially for those related to production, and climate and water regulation. Flooding stress caused pronounced and persistent shifts in soil microbial and plant communities with large implications for nutrient cycling and long-term ecosystem function. The compound flood + drought treatment failed to show a more severe impact than the single extreme events. Rather, there was an indication of quicker recovery of soil and microbial parameters suggesting greater resilience in line with hypothesis (A). This study clearly reveals that contrasting extreme weather events differentially affect grassland ecosystem function but that concurrent events of a contrasting nature may promo

Impacts of tropospheric ozone on sweet potato (Ipomoea batatas) are poorly understood despite being a staple food grown in locations deemed at risk from ozone pollution. Three varieties of sweet potato were exposed to ozone treatments (peaks of: 30 (Low), 80 (Medium), and 110 (High) ppb) using heated solardomes. Weekly measurements of stomatal conductance (gs) and chlorophyll content (CI) were used to determine physiological responses, along with final yield. gs and CI were reduced with increasing ozone exposure, but effects were partially masked due to elevated leaf senescence and turnover. Yield for the Erato orange and Murasaki varieties was reduced by ∼40% and ∼50% (Medium and High ozone treatments, respectively, vs Low) whereas Beauregard yield was reduced by 58% in both. The DO3SE (Deposition of Ozone for Stomatal Exchange) model was parameterized for gs in response to light, temperature, vapour pressure deficit and soil water potential. Clear responses of gs to the environmental parameters were found. Yield reductions were correlated with both concentration based AOT40 (accumulated ozone above a threshold of 40 ppb) and flux based POD6 (accumulated stomatal flux of ozone above a threshold of 6 nmol m− 2 s− 1) metrics (R2 0.66 p = 0.01; and R2 0.44 p = 0.05, respectively). A critical level estimate of a POD6 of 3 (mmol m−2 Projected Leaf Area−1) was obtained using the relationship. This study showed that sweet potato yield was reduced by ozone pollution, and that stomatal conductance and chlorophyll content were also affected. Results from this study can improve model predictions of ozone impacts on sweet potato together with associated ozone risk assessments for tropical countries.

Oilseed rape (Brassica napus L.) is cultivated worldwide, producing 11.5% of global oilseeds at an economic value of 38 billion USD in 2020. It is sensitive to phytotoxic damage from exposure to tropospheric ozone (O3), a major air pollutant, which disrupts plant physiological processes and thus decreases biomass accumulation. As background ozone concentrations continue to increase globally, we investigated the impact of ozone exposure on seed and oil yield of a shorter-lived spring (cv. Click) and a longer-lived winter (cv. Phoenix) oilseed rape cultivar to ozone levels (treatments with peaks of 30, 55, 80, 110 ppbv) representative of typical European conditions where these cultivars are common. Thousand Seed Weight (TSW), an important measure of final yield, decreased more in Phoenix (40%) than Click (20%) with increasing ozone exposure. Click produced more racemes and many small seeds while Phoenix produced fewer racemes and larger seeds. However, seed quality declined more substantially in Click than Phoenix. The oil content in Click’s seed significantly decreased with increased ozone exposure, while less desirable components (moisture, chlorophyll, ash) increased. Scaled to field-level, our findings imply substantial economic penalties for growers, with potential losses of 175 to 325 USD ha-1 in Click and 500 to 665 USD ha-1 in Phoenix under ozone concentrations typical of spring and summer periods in Europe. Decreased total yield would likely outweigh the benefits of any improvement in animal oilseed cake quality (increased protein and key micronutrients for livestock feed). Neither cultivar sustained visible injury at earlier growth stages, and Phoenix sustained photosynthesis even under high exposure, thereby making ozone an invisible threat. Our findings of reduced oilseed quantity and quality threaten oilseed rape production, but differences between the cultivars may also offer an opportunity for breeders and agronomists to identify and exploit variation i

Increasing tropospheric ozone poses a potential threat to both above- and belowground components of the terrestrial biosphere. Microorganisms are the main drivers of soil ecological processes, however, the link between soil microbial communities and ecological functions under elevated ozone remains poorly understood. In this study, we assessed the responses of three crop seedlings (i.e., soybean, maize, and wheat) growth and soil microbial communities to elevated ozone (40 ppb O3 above ambient air) in a pot experiment in the solardomes. Results showed that elevated ozone adversely affected ecosystem multifunctionality by reducing crop biomass, inhibiting soil extracellular enzyme activities, and altering nutrient availability. Elevated ozone increased bacterial and fungal co-occurrence network complexity, negatively correlated with ecosystem multifunctionality. Changes in the relative abundance of some specific bacteria and fungi were associated with multiple ecosystem functioning. In addition, elevated ozone significantly affected fungal community composition but not bacterial community composition and microbial alpha-diversity. Crop type played a key role in determining bacterial alpha-diversity and microbial community composition. In conclusion, our findings suggest that short-term elevated ozone could lead to a decrease in ecosystem multifunctionality associated with changes in the complexity of microbial networks in soils.

Restoration ecologists have local- to global-scale ambitions in a policy framework of sustainable development goals and reversing biodiversity loss. Emphasis is given to environmental alteration, typically considering land degradation and climate change. Other environmental drivers, such as pollution, receive less attention. Here we emphasize that terrestrial restoration discourse needs to consider tropospheric ozone (O3) pollution. O3’s pervasive influence on plants and other ecosystem components provides for the possibility of consequences at community and ecosystem levels. The precursor chemicals which lead to O3 formation are increasing, precipitously so in rapidly-industrialising regions of the world. Yet, a review of critical restoration guidance and journals suggests that because O3 is out of sight, it remains out of mind. Based on a narrative cross-discipline literature review, we examine: (i) how O3 could affect the achievement of restoration goals; and, (ii) how restoration interventions could feedback on tropospheric O3. Evidence, currently limited, suggests that O3 could impair the achievement of restoration goals to as great an extent as other drivers, but, in general, we lack direct quantification. Restoration interventions (e.g. tree planting) that may be considered successful can actually exacerbate O3 pollution with negative consequences for food security and human health. These wide-ranging effects, across multiple goals, mean that O3 is not out of scope for restoration science, policy and practice. In detailing a strategic ozone-aware restoration agenda, we suggest how restoration science and policy can quantify O3’s influence, while outlining steps practitioners can take to adapt to/mitigate the impacts of O3 pollution.

Restoration ecologists have local- to global-scale ambitions in a policy framework of sustainable development goals and reversing biodiversity loss. Emphasis is given to environmental alteration, typically considering land degradation and climate change. Other environmental drivers, such as pollution, receive less attention. Here we emphasize that terrestrial restoration discourse needs to consider tropospheric ozone (O3) pollution. O3’s pervasive influence on plants and other ecosystem components provides for the possibility of consequences at community and ecosystem levels. The precursor chemicals which lead to O3 formation are increasing, precipitously so in rapidly-industrialising regions of the world. Yet, a review of critical restoration guidance and journals suggests that because O3 is out of sight, it remains out of mind. Based on a narrative cross-discipline literature review, we examine: (i) how O3 could affect the achievement of restoration goals; and, (ii) how restoration interventions could feedback on tropospheric O3. Evidence, currently limited, suggests that O3 could impair the achievement of restoration goals to as great an extent as other drivers, but, in general, we lack direct quantification. Restoration interventions (e.g. tree planting) that may be considered successful can actually exacerbate O3 pollution with negative consequences for food security and human health. These wide-ranging effects, across multiple goals, mean that O3 is not out of scope for restoration science, policy and practice. In detailing a strategic ozone-aware restoration agenda, we suggest how restoration science and policy can quantify O3’s influence, while outlining steps practitioners can take to adapt to/mitigate the impacts of O3 pollution.

The sensitivity of photosynthesis to temperature has been identified as a key uncertainty for projecting the magnitude of the terrestrial carbon cycle response to future climate change. Although thermal acclimation of photosynthesis under rising temperature has been reported in many tree species, whether tropospheric ozone (O3) affects the acclimation capacity remains unknown. In this study, temperature responses of photosynthesis (light‐saturated rate of photosynthesis (Asat), maximum rates of RuBP carboxylation (Vcmax), and electron transport (Jmax) and dark respiration (Rdark) of Populus tremula exposed to ambient O3 (AO3, maximum of 30 ppb) or elevated O3 (EO3, maximum of 110 ppb) and ambient or elevated temperature (ambient +5°C) were investigated in solardomes. We found that the optimum temperature of Asat (ToptA) significantly increased in response to warming. However, the thermal acclimation capacity was reduced by O3 exposure, as indicated by decreased ToptA, and temperature optima of Vcmax (ToptV) and Jmax (ToptJ) under EO3. Changes in both stomatal conductance (gs) and photosynthetic capacity (Vcmax and Jmax) contributed to the shift of ToptA by warming and EO3. Neither Rdark measured at 25°C (urn:x-wiley:13541013:media:gcb15564:gcb15564-math-0001) nor the temperature response of Rdark was affected by warming, EO3, or their combination. The responses of Asat, Vcmax, and Jmax to warming and EO3 were closely correlated with changes in leaf nitrogen (N) content and N use efficiency. Overall, warming stimulated growth (leaf biomass and tree height), whereas EO3 reduced growth (leaf and woody biomass). The findings indicate that thermal acclimation of Asat may be overestimated if the impact of O3 pollution is not taken into account.

Tropospheric (ground-level) ozone is a harmful phytotoxic pollutant, and can have a negative impact on crop yield and quality in sensitive species. Ozone can also induce visible symptoms on leaves, appearing as tiny spots (stipples) between the veins on the upper leaf surface. There is little measured data on ozone concentrations in Africa and it can be labour-intensive and expensive to determine the direct impact of ozone on crop yield in the field. The identification of visible ozone symptoms is an easier, low cost method of determining if a crop species is being negatively affected by ozone pollution, potentially resulting in yield loss. In this study, thirteen staple African food crops (including wheat (Triticum aestivum), common bean (Phaseolus vulgaris), sorghum (Sorghum bicolor), pearl millet (Pennisetum glaucum) and finger millet (Eleusine coracana)) were exposed to an episodic ozone regime in a solardome system to monitor visible ozone symptoms. A more detailed examination of the progression of ozone symptoms with time was carried out for cultivars of P. vulgaris and T. aestivum, which showed early leaf loss (P. vulgaris) and an increased rate of senescence (T. aestivum) in response to ozone exposure. All of the crops tested showed visible ozone symptoms on their leaves in at least one cultivar, and ozone sensitivity varied between cultivars of the same crop. A guide to assist with identification of visible ozone symptoms (including photographs and a description of symptoms for each species) is presented.

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

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.

Northern, Southern and Equatorial Africa have been identified as among the regions most at risk from very high ozone concentrations. Whereas we know that many crop cultivars from Europe, north America and Asia are sensitive to ozone, almost nothing is known about the sensitivity of staple food crops in Africa to the pollutant. In this study cultivars of the African staple food crops, Triticum aestivum (wheat), Eleusine coracana (finger millet), Pennisetum glaucum (pearl millet) and Phaseolus vulgaris (bean) were exposed to an episodic ozone regime in solardomes in order to assess whether African crops are sensitive to ozone pollution. Extensive visible leaf injury due to ozone was shown for many cultivars, indicating high sensitivity to ozone. Reductions in total yield and 1,000‐grain weight were found for T. aestivum and P. vulgaris, whereas there was no effect on yield for E. coracana and P. glaucum. There were differences in sensitivity to ozone for different cultivars of an individual crop, indicating that there could be possibilities for either cultivar selection or selective crop breeding to reduce sensitivity of these crops to ozone.