Assessing the costs of ozone pollution in India for wheat producers, consumers, and government food welfare policies.

We assess wheat yield losses occurring due to ozone pollution in India and its economic burden on producers, consumers, and the government. Applying an ozone flux-based risk assessment, we show that ambient ozone levels caused a mean 14.18% reduction in wheat yields during 2008 to 2012. Furthermore, irrigated wheat was particularly sensitive to ozone-induced yield losses, indicating that ozone pollution could undermine climate-change adaptation efforts through irrigation expansion. Applying an economic model, we examine the effects of a counterfactual, "pollution-free" scenario on yield losses, wheat prices, consumer and producer welfare, and government costs. We explore three policy scenarios in which the government support farmers at observed levels of either procurement prices (fixed-price), procurement quantities (fixed-procurement), or procurement expenditure (fixed-expenditure). In pollution-free conditions, the fixed-price scenario absorbs the fall in prices, thus increasing producer welfare by USD 2.7 billion, but total welfare decreases by USD 0.24 billion as government costs increase (USD 2.9 billion). In the fixed-procurement and fixed-expenditure scenarios, ozone mitigation allows wheat prices to fall by 38.19 to 42.96%. The producers lose by USD 5.10 to 6.01 billion, but the gains to consumers and governments (USD 8.7 to 10.2 billion) outweigh these losses. These findings show that the government and consumers primarily bear the costs of ozone pollution. For pollution mitigation to optimally benefit wheat production and maximize social welfare, new approaches to support producers other than fixed-price grain procurement may be required. We also emphasize the need to consider air pollution in programs to improve agricultural resilience to climate change.

Date palm responses to a chronic, realistic ozone exposure in a FACE experiment.

Date palms are highly economically important species in hot arid regions, which may suffer ozone (O3) pollution equivalently to heat and water stress. However, little is known about date palm sensitivity to O3. Therefore, to identify their resistance mechanisms against elevated O3, physiological parameters (leaf gas exchange, chlorophyll fluorescence and leaf pigments) and biomass growth responses to realistic O3 exposure were tested in an isoprene-emitting date palm (Phoenix dactylifera L. cv. Nabut Saif) by a Free-Air Controlled Exposure (FACE) facility with three levels of O3 (ambient [AA, 45 ppb as 24-h average], 1.5 x AA and 2 x AA). We found a reduction of photosynthesis only at 2 x AA although some foliar traits known as early indicators of O3 stress responded already at 1.5 x AA, such as increased dark respiration, reduced leaf pigment content, reduced maximum quantum yield of PSII, inactivation of the oxygen evolving complex of PSII and reduced performance index PITOT. As a result, O3 did not affect most of the growth parameters although significant declines of root biomass occurred only at 2 x AA. The major mechanism in date palm for reducing the severity of O3 impacts was a restriction of stomatal O3 uptake due to low stomatal conductance and O3-induced stomatal closure. In addition, an increased respiration in elevated O3 may indicate an enhanced capacity of catabolizing metabolites for detoxification and repair. Interestingly, date palm produced low amounts of monoterpenes, whose emission was stimulated in 2 x AA, although isoprene emission declined at both 1.5 and 2 x AA. Our results warrant more research on a biological significance of terpenoids in plant resistance against O3 stress.

Quantifying determinants of ozone detoxification by apoplastic ascorbate in peach (Prunus persica) leaves using a model of ozone transport and reaction.

Ascorbate in leaf apoplast (ASCapo ) reacts with ozone (O3 ) and thereby reduces O3 flux reaching plasmalemma (Fpl ). Some studies have shown significant protection of cells from O3 by ASCapo , while others have questioned its efficacy. Hypothesizing that the protection by ASCapo depends on other variables, we quantified determinants of O3 detoxification with a model of O3 transport and reaction in apoplast. The model determines ascorbic acid concentration in apoplast (AAapo ) using measured values of O3 concentration (co ), leaf tissue ascorbic acid concentration (AAleaf ), cell wall thickness (L3 ), apoplastic pH (pHapo ), and stomatal conductance (Gsw ). We compared the measured and model-estimated AAapo in leaves of peach (Prunus persica) grown in open-top chambers under non-filtered air (NF) and elevated (EO3 : NF + 80 ppb) O3 concentrations. The estimated AAapo in individual leaves agreed well with the measured values (R2  = .91). Analyses of the simulation results yielded the following findings: (a) The efficacy of O3 reduction with ASCapo as quantified by fractional reduction (ϕ3 ) of O3 flux at the surface of plasmalemma (Fpl ) was lowered from 70% in NF to 40% in EO3 due to the reduction of L3 . The EO3 reduced AAapo , but the lower Gsw and L3 in EO3 increased AAapo resulting in no significant change in AAapo due to EO3 . ϕ3 can be calculated with measured values of AAapo and L3 , and Fpl can be estimated with the measurement-based ϕ3 . (b) When c0 is increased, Fpl increased curvilinearly with the increase of Fst : nominal O3 flux via stomatal diffusion, exhibiting apparent threshold on Fst . The deviation of Fpl from Fst became greater when L3 , pHapo , and AAleaf were increased. The quantification of ϕ3 and Fpl using leaf traits shall facilitate the understanding of the mechanisms of differential plant sensitivity to O3 and improve quantification of the O3 impacts on plants.

A unifying explanation for variation in ozone sensitivity among woody plants.

Tropospheric ozone is considered the most detrimental air pollutant for vegetation at the global scale, with negative consequences for both provisioning and climate regulating ecosystem services. In spite of recent developments in ozone exposure metrics, from a concentration-based to a more physiologically relevant stomatal flux-based index, large-scale ozone risk assessment is still complicated by a large and unexplained variation in ozone sensitivity among tree species. Here, we explored whether the variation in ozone sensitivity among woody species can be linked to interspecific variation in leaf morphology. We found that ozone tolerance at the leaf level was closely linked to leaf dry mass per unit leaf area (LMA) and that whole-tree biomass reductions were more strongly related to stomatal flux per unit leaf mass (r2  = 0.56) than to stomatal flux per unit leaf area (r2  = 0.42). Furthermore, the interspecific variation in slopes of ozone flux-response relationships was considerably lower when expressed on a leaf mass basis (coefficient of variation, CV = 36%) than when expressed on a leaf area basis (CV = 66%), and relationships for broadleaf and needle-leaf species converged when using the mass-based index. These results show that much of the variation in ozone sensitivity among woody plants can be explained by interspecific variation in LMA and that large-scale ozone impact assessment could be greatly improved by considering this well-known and easily measured leaf trait.

Ozone concentrations, flux and potential effect on yield during wheat growth in the Northwest-Shandong Plain of China.

Ozone (O3) concentration and flux (Fo) were measured using the eddy covariance technique over a wheat field in the Northwest-Shandong Plain of China. The O3-induced wheat yield loss was estimated by utilizing O3 exposure-response models. The results showed that: (1) During the growing season (7 March to 7 June, 2012), the minimum (16.1 ppbV) and maximum (53.3 ppbV) mean O3 concentrations occurred at approximately 6:30 and 16:00, respectively. The mean and maximum of all measured O3 concentrations were 31.3 and 128.4 ppbV, respectively. The variation of O3 concentration was mainly affected by solar radiation and temperature. (2) The mean diurnal variation of deposition velocity (Vd) can be divided into four phases, and the maximum occurred at noon (12:00). Averaged Vd during daytime (6:00-18:00) and nighttime (18:00-6:00) were 0.42 and 0.14 cm/sec, respectively. The maximum of measured Vd was about 1.5 cm/sec. The magnitude of Vd was influenced by the wheat growing stage, and its variation was significantly correlated with both global radiation and friction velocity. (3) The maximum mean Fo appeared at 14:00, and the maximum measured Fo was -33.5 nmol/(m(2)·sec). Averaged Fo during daytime and nighttime were -6.9 and -1.5 nmol/(m(2)·sec), respectively. (4) Using O3 exposure-response functions obtained from the USA, Europe, and China, the O3-induced wheat yield reduction in the district was estimated as 12.9% on average (5.5%-23.3%). Large uncertainties were related to the statistical methods and environmental conditions involved in deriving the exposure-response functions.

Epidemiological Estimate of Growth Reduction by Ozone in Fagus sylvatica L. and Picea abies Karst.: Sensitivity Analysis and Comparison with Experimental Results.

The critical level of ozone flux for forest trees is based entirely on biomass data from fumigation experiments with saplings, mostly in open-top chambers. Extrapolation to mature forests asks, therefore, for validation, which may be performed by epidemiological data analysis. This requires a multivariable regression analysis with a number of covariates to account for potential confounding factors. The present paper analyses the ozone sensitivity of volume increments of mature European beech (Fagus sylvatica) and Norway spruce (Picea abies), with the addition, or removal, of covariates. The comparison of the epidemiological dose-response relationship with experimental data shows very good agreement in beech and a more sensitive relationship in the epidemiological analysis of Norway spruce compared to the experiments. In Norway spruce, there was also a strong interaction between the effects of ozone and temperature; at high July temperatures, the ozone effect was stronger. This interaction may explain the disagreement between the epidemiological study and the experiments, of which the majority were performed in Sweden.

Foliage visible injury in the tropical tree species, Astronium graveolens is strictly related to phytotoxic ozone dose (PODy).

The present study evaluates the development of visible injury related to phytotoxic ozone dose (PODy) in native tropical species Astronium graveolens Jacq. (Anacardiaceae) and validates the symptoms using structural markers attributed to oxidative burst and hypersensitive responses. Increasing POD0 was associated with increasing O3 visible injury using different metrics as the incidence (INC = number of injured plants/total number of plants × 100), severity (SF = number of injured leaves/total number of leaves on injured plant × 100), and severity leaflet (SFL = number of injured leaflets/total number leaflets injured plant × 100). The effective dose (ED), which represents the POD0 dose responsible for inducing 20 (ED20), 50 (ED50), or 80% (ED80) of visible injury, were used to demonstrate that for this species, the response is similar even when the plants are exposed to diverse climate environments. Further investigation of the INC and SF index may help in long-term forest monitoring sites dedicated to O3 assessment in forests, while the SFL index seems to be an excellent indicator to be used in the short term to investigate the effects of O3.

Interactive effects and competitive shift between Triticum aestivum L. (wheat) and Chenopodium album L. (fat-hen) under ambient and elevated ozone.

The aim of this study was to evaluate the impact of ambient and elevated O3 (ambient+20 ppb) under the competition between a crop plant Triticum aestivum L.cv. HD 2967 and a weed, Chenopodium album L. (fat-hen) grown singly and in mix-culture (1:1) using open-top chambers. The competition posed a relatively lesser effect on the growth of fat-hen as compared to the wheat under ambient O3 at both the sampling time, however, the effects of stress factors (competition and O3) were more pronounced at the reproductive stage on both the plants. Fat-hen possess a stronger antioxidative potential against elevated O3 (eO3), irrespective of competition, making it more resistant against the existing stress factors. Significant stimulation in the activities of CAT, POX, GR and SOD in fat-hen and non-enzyme antioxidants (AsA, thiols, and total phenolics) might have helped the plants to pose a superior ROS scavenging potential under competition + O3. Strong stimulation of flavonols (kaempferol and quercetin) and phenolic acid (p-coumaric acid and ferulic acid) in fat-hen not only helped the plants to withstand the oxidative damage under eO3 but also might have influenced the allelopathic interaction (competition + O3). Yield loss in wheat was observed to be larger under competition + O3 (33.1%) followed by O3 (20.5%) than only under competition (16.3%). The study suggests stringent weed management strategies to be established recognizing the existing threat from O3 to the productivity of a staple crop-wheat.

Ozone flux in plant ecosystems: new opportunities for long-term monitoring networks to deliver ozone-risk assessments.

Ozone (O3) is a photochemically formed reactive gas responsible for a decreasing carbon assimilation in plant ecosystems. Present in the atmosphere in trace concentrations (less than 100 ppbv), this molecule is capable of inhibiting carbon assimilation in agricultural and forest ecosystems. Ozone-risk assessments are typically based on manipulative experiments. Present regulations regarding critical ozone levels are mostly based on an estimated accumulated exposure over a given threshold concentration. There is however a scientific consensus over flux estimates being more accurate, because they include plant physiology analyses and different environmental parameters that control the uptake-that is, not just the exposure-of O3. While O3 is a lot more difficult to measure than other non-reactive greenhouse gases, UV-based and chemiluminescence sensors enable precise and fast measurements and are therefore highly desirable for eddy covariance studies. Using micrometeorological techniques in association with latent heat flux measurements in the field allows for the partition of ozone fluxes into the stomatal and non-stomatal sinks along the soil-plant continuum. Long-term eddy covariance measurements represent a key opportunity in estimating carbon assimilation at high-temporal resolutions, in an effort to study the effect of climate change on photosynthetic mechanisms. Our aim in this work is to describe potential of O3 flux measurement at the canopy level for ozone-risk assessment in established long-term monitoring networks.

Five-year volume growth of European beech does not respond to ozone pollution in Italy.

A unique database of stand volume growth, estimated as periodic annual volume increment (in m3 ha-1 per year over the period 2001-2005) from 728 European beech (Fagus sylvatica L.) sites distributed across Italy, was used to assess the effects of ambient ozone (O3), expressed as annual average (M24), accumulated exposure above a 40 ppb hourly threshold (AOT40), and total stomatal ozone flux (POD0). Growth data were from the National forest inventory of Italy, while climate data and ozone concentrations were computed by the WRF and CHIMERE models, respectively. Results show that the growth increased with increasing solar radiation and air temperature and decreased with increasing number of cold days, while effects of soil water content and O3 were not significant. In contrast, the literature results suggest that European beech is sensitive to both drought and O3. Ozone levels resulted to be very high (48 ppb M24, 51,200 ppb h AOT40, 21.08 mmol m-2 POD0, on average) and thus able to potentially affect European beech growth. We hypothesize that the high-frequency signals of soil water and O3 got lost when averaged over 5 years and recommended finer time-resolution investigations and inclusion of other factors of variability, e.g., thinning, tree age, and size.

Ozone-induced stomatal sluggishness changes stomatal parameters of Jarvis-type model in white birch and deciduous oak.

Stomatal ozone flux is closely related to ozone injury to plants. Jarvis-type multiplicative model has been recommended for estimating stomatal ozone flux in forest trees. Ozone can change stomatal conductance by both stomatal closure and less efficient stomatal control (stomatal sluggishness). However, current Jarvis-type models do not account for these ozone effects on stomatal conductance in forest trees. We examined seasonal course of stomatal conductance in two common deciduous tree species native to northern Japan (white birch: Betula platyphylla var. japonica; deciduous oak: Quercus mongolica var. crispula) grown under free-air ozone exposure. We innovatively considered stomatal sluggishness in the Jarvis-type model using a simple parameter, s, relating to cumulative ozone uptake (defined as POD: phytotoxic ozone dose). We found that ozone decreased stomatal conductance of white birch leaves after full expansion (-28%). However, such a reduction of stomatal conductance by ozone fell in late summer (-10%). At the same time, ozone reduced stomatal sensitivity of white birch to VPD and increased stomatal conductance under low light conditions. In contrast, in deciduous oak, ozone did not clearly change the model parameters. The consideration of both ozone-induced stomatal closure and stomatal sluggishness improved the model performance to estimate stomatal conductance and to explain the dose-response relationship on ozone-induced decline of photosynthesis of white birch. Our results indicate that ozone effects on stomatal conductance (i.e. stomatal closure and stomatal sluggishness) are crucial for modelling studies to determine stomatal response in deciduous trees, especially in species sensitive to ozone.

[Influencing Mechanism and Spatio-temporal Pattern of Stomatal Ozone Flux of Winter Wheat Under Ozone Pollution].

As one of the main atmospheric pollutants over surface layer,researches on the increasing surface ozone concentration and its impact on main crops have become the focus of every government and the public.In this paper,based on the observations in Nanjing using the main local cultivars in China's major winter wheat producing areas,it was expected to obtain the data including ozone concentration,meteorological data and stomatal conductance by continuous observation.Stomatal conductance model was used and parameterized,combined with flux model,we analyzed the characteristics of stomatal flux in winter wheat under ozone pollution.At the same time,the stomatal conductance and stomatal ozone absorption flux of winter wheat were simulated in Jiangsu Province.The main results were as follows:Elevated ozone concentration could reduce stomatal conductance of winter wheat leaf and stomatal conductance decreased with the increase of ozone concentration.According to the observational data through the experiment,based on the boundary line technology,stomatal conductance model was parameterized to simulate stomatal conductance of wheat leaves from environmental factors.Approximately 90%,77% and 83% variation of measured stomatal conductance could be explained by the stomatal conductance model.In the experiment,the total ozone absorption flux in ozone concentration of CK (53.67 nL·L-1),100nL·L-1,150nL·L-1 was 6.42 mmol·m-2,12.27 mmol·m-2,13.90 mmol·m-2 respectively.The ozone concentration gradually increased from early period to late period during the period of winter wheat growth in Jiangsu area.The average stomatal conductance followed the order of the middle stage >the later stage >the early stage.Winter wheat ozone cumulative absorption flux was the highest during the middle stage.

Ozone risk assessment for an Alpine larch forest in two vegetative seasons with different approaches: comparison of POD1 and AOT40.

The upper vegetation belts like larch forests are supposed to be under great pressure because of climate change in the next decades. For this reason, the evaluation of the risks due to abiotic stressors like ozone is a key step. Two different approaches were used here: mapping AOT40 index by means of passive samplers and direct measurements of ozone deposition.Measurements of ozone fluxes using the eddy-correlation technique were carried out for the first time over a larch forest in Paspardo (I) at 1750 m a.s.l. Two field campaigns were run: the first one in 2010 from July to October and the second one in the following year from June to September. Vertical exchange of ozone, energy, and momentum were measured on a tower platform at 26 m above ground level to study fluxes dynamics over this ecosystem. Since the tower was located on a gentle slope, an "ad hoc" methodology was developed to minimize the effects of the terrain inclination. The larch forest uptake was estimated by means of a two-layer model to separate the understorey uptake from the larch one. Even if the total ozone fluxes were generally high, up to 30-40 nmol O3 m-2 s-1 in both years, the stomatal uptake by the larch forest was relatively low (around 15% of the total deposition).Ozone risk was assessed considering the POD1 received by the larch forest and the exposure index AOT40 estimated with both local data and data from the map obtained by the passive samplers monitoring.

Ozone stomatal flux and O3 concentration-based metrics for Astronium graveolens Jacq., a Brazilian native forest tree species.

The current levels of surface ozone (O3) are high enough to negatively affect trees in large regions of São Paulo State, southeastern Brazil, where standards for the protection of vegetation against the adverse effects of O3 do not exist. We evaluated three O3 metrics - phytotoxic ozone dose (POD), accumulated ozone exposure over the threshold of 40 ppb h (AOT40), and the sum of all hourly average concentrations (SUM00) - for the Brazilian native tropical tree species Astronium graveolens Jacq. We used the DO3SE (Deposition of Ozone for Stomatal Exchange) model and calculated PODY for different thresholds (from 0 to 6 mmol O3 m(-2) PLA s(-1)), evaluating the model's performance through the relationship between measured and modelled conductance. The response parameters were: visible foliar injury, considered as incidence (% injured plants), severity (% injured leaves in relation to the number of leaves on injured plants), and leaf abscission. The model performance was suitable and significant (R(2) = 0.58; p < 0.001). POD0 was better correlated to incidence and leaf abscission, and SUM00 was better correlated to severity. The highest values of O3 concentration-based metrics (AOT40 and SUM00) did not coincide with those of POD0. Further investigation may improve the model and contribute to the proposition of a national standard for the protection of native species.

New flux based dose-response relationships for ozone for European forest tree species.

To derive O3 dose-response relationships (DRR) for five European forest trees species and broadleaf deciduous and needleleaf tree plant functional types (PFTs), phytotoxic O3 doses (PODy) were related to biomass reductions. PODy was calculated using a stomatal flux model with a range of cut-off thresholds (y) indicative of varying detoxification capacities. Linear regression analysis showed that DRR for PFT and individual tree species differed in their robustness. A simplified parameterisation of the flux model was tested and showed that for most non-Mediterranean tree species, this simplified model led to similarly robust DRR as compared to a species- and climate region-specific parameterisation. Experimentally induced soil water stress was not found to substantially reduce PODy, mainly due to the short duration of soil water stress periods. This study validates the stomatal O3 flux concept and represents a step forward in predicting O3 damage to forests in a spatially and temporally varying climate.

Concentration- and flux-based ozone dose-response relationships for five poplar clones grown in North China.

Concentration- and flux-based O3 dose-response relationships were developed for poplars in China. Stomatal conductance (gs) of five poplar clones was measured to parameterize a Jarvis-type multiplicative gs model. The maximum gs and other model parameters varied between clones. The strongest relationship between stomatal O3 flux and total biomass was obtained when phytotoxic ozone dose (POD) was integrated using an uptake rate threshold of 7 nmol m(-2) s(-1). The R(2) value was similar between flux-based and concentration-based dose-response relationships. Ozone concentrations above 28-36 nmol mol(-1) contributed to reducing the biomass production of poplar. Critical levels of AOT40 (accumulated O3 exposure over 40 nmol mol(-1)) and POD7 in relation to 5% reduction in total biomass for poplar were 12 µmol mol(-1) h and 3.8 mmol m(-2), respectively.

Comparing i-Tree modeled ozone deposition with field measurements in a periurban Mediterranean forest.

Ozone flux estimates from the i-Tree model were compared with ozone flux measurements using the Eddy Covariance technique in a periurban Mediterranean forest near Rome (Castelporziano). For the first time i-Tree model outputs were compared with field measurements in relation to dry deposition estimates. Results showed generally a good agreement between predicted and measured ozone fluxes (least sum square=5.6 e(-4)) especially when cumulative values over the whole measurement campaign are considered. However at daily and hourly time-step some overestimations were observed in estimated values especially in hot dry periods. The use of different m values in the Ball-Berry formula in the different periods, produced the best fit between predicted and measured ozone fluxes. This suggests that a variable value for the coefficient m accounting for water availability may be appropriate to improve model estimates for Mediterranean and drought prone regions.

Growth losses in Swiss forests caused by ozone: epidemiological data analysis of stem increment of Fagus sylvatica L. and Picea abies Karst.

The estimate of growth losses by ozone exposure of forest trees is a significant part in current C sequestration calculations and will also be important in future modeling. It is therefore important to know if the relationship between ozone flux and growth reduction of young trees, used to derive a Critical Level for ozone, is also valid for mature trees. Epidemiological analysis of stem increment data from Fagus sylvatica L. and Picea abies Karst. observed in Swiss forest plots was used to test this hypothesis. The results confirm the validity of the flux-response relationship at least for beech and therefore enable estimating forest growth losses by ozone on a country-wide scale. For Switzerland, these estimates amount to 19.5% growth reduction for deciduous forests, 6.6% for coniferous forests and 11.0% for all forested areas based on annual ozone stomatal uptake during the time period 1991-2011.