Evidence of widespread effects of ozone on crops and (semi‐)natural vegetation in Europe (1990–2006) in relation to AOT40‐ and flux‐based risk maps

Records of effects of ambient ozone pollution on vegetation have been compiled for Europe for the years 1990–2006. Sources include scientific papers, conference proceedings, reports to research funders, records of confirmed ozone injury symptoms and an international biomonitoring experiment coordinated by the ICP Vegetation. The latter involved ozone‐sensitive (NC‐S) and ozone‐resistant (NC‐R) biotypes of white clover (Trifolium repens L.) grown according to a common protocol and monitored for ozone injury and biomass differences in 17 European countries, from 1996 to 2006. Effects were separated into visible injury or growth/yield reduction. Of the 644 records of visible injury, 39% were for crops (27 species), 38.1% were for (semi‐) natural vegetation (95 species) and 22.9% were for shrubs (49 species). Owing to inconsistencies in reporting effort from year to year it was not possible to determine geographical or temporal trends in the data. Nevertheless, this study has shown effects in ambient air in 18 European countries from Sweden in the north to Greece in the south. These effects data were superimposed on AOT40 (accumulated ozone concentrations over 40 ppb) and POD3_gen (modelled accumulated stomatal flux over a threshold of 3 nmol m^?2 s^?1) maps generated by the EMEP Eulerian model (50 km × 50 km grid) that were parameterized for a generic crop based on wheat and NC‐S/NC‐R white clover. Many effects were found in areas where the AOT40 (crops) was below the critical level of 3 ppm h. In contrast, the majority of effects were detected in grid squares where POD3_gen (crops) were in the mid‐high range (>12 mmol m^?2). Overall, maps based on POD3_gen provided better fit to the effects data than those based on AOT40, with the POD3_gen model for clover fitting the clover effects data better than that for a generic crop.     

陆地生态系统臭氧通量观测和气孔吸收估算研究进展

近地面大气中臭氧(O3)对植物生长发育和产量会产生不良影响。工业和交通排放的增加使得全球地面O3浓度逐年增加,不断升高的O3浓度已开始影响到我国的粮食产量。O3对植物的影响是由于其进入植物体内发生生化反应所引起的,所以需要建立一种考虑到植物生理生态状况的评估指标来评估O3对植物的影响。其中基于O3通量(特别是植物气孔吸收)的评价指标和方法,被认为比传统的基于O3浓度的评价指标和方法更符合O3对植物的影响机理。介绍了O3对生态系统影响评估方法和评价指标,重点评述了生态系统尺度O3通量观测和气孔吸收估算的主要方法以及在不同生态系统上的研究进展分析了我国关于O3对植物和生态系统影响的研究现状,并对未来的研究工作进行了展望。     

Modelling rising groundwater and the impacts of salinization on terrestrial remnant vegetation in the Blackwood River Basin

Summary Southwest Western Australia has a particularly rich biodiversity. Clearing for agriculture has greatly reduced the extent of native vegetation in wheatbelt catchments; it also set into train hydrogeological and hydrological changes that are still evolving toward a new equilibrium. With those changes come widespread land salinization that presents a further risk to remnant vegetation, particularly in low portions of the landscape. The equilibrium position of shallow groundwater was modelled for the Blackwood Catchment, and used to assess the extent of risk to a set of remnant vegetation classes. A total of 37 368 ha of remnant vegetation was identified to be at risk of salinization when hydrological equilibrium is reached. Further hydrological modelling assessed the rate of development of these watertables (and hence the rate of impact on remnants), as well as the potential to protect remnants by controlling groundwater recharge with revegetation. The results demonstrate that only high levels of revegetation are effective at protecting high value remnants in the longer term. The timing of events is dependant on the accuracy of estimating recharge.     

气候年际变率对全球植被平均分布的影响

采用改进后的通用陆面模式的动态植被模式(CLM-DGVM)研究当前气候条件下气候年际变率对全球潜在植被平均分布的影响。设计两组区域数值实验,一组使用基于NCEP再分析资料衍生的1960-1999年多年气象数据循环驱动,对照实验使用这40a的气候平均态或单年气象资料驱动(即没有气候年际变率),分别考察有无气候年际变化对热带、温带和寒带的潜在植被分布平衡态的影响。在此基础上以1950-1999年上述数据及对应的气候平均态为驱动做两组全球实验。结果表明气候年际变率导致全球植被总覆盖度下降,其中树和灌木减少而草增加;全球平均覆盖度的变化按常绿树、草、灌木、落叶树顺序递减,而相对变化(即格点覆盖度差异的绝对值的全球平均值与气候平均态下植物覆盖度的比值)按灌木、草、落叶树、常绿树顺序递减。在温度、降水、风速、比湿、光照、气压等6种气候因子中降水年际变率对于植被平均分布影响最显著。受降水影响,当年降水小于1200mm时植被总覆盖度的差异随其变率增加而下降,其它时候影响不明显。年降水小于1500mm时树减少,幅度随其年际变率变大而增加。常绿树无论降水多寡均减少,而落叶树在年降水大于1500mm时随其变率变大而增加。草在年降水小于1500mm、变率为中等时差异最大,降水较大时其年际变化对草的影响不大。温度年际变率对落叶树分布影响不大而使常绿树减少,尤其是在寒带,其幅度大致随变率增加而变大。草主要在温度高于-10℃增加而灌木在温度低于0℃增加。植被总体覆盖度在温度高于0℃时受影响普遍降低,降低的区域对应于温度年际变率较大的区域。以上结果说明用气候模式或生物地理模式预测未来植物分布时要同时考虑气候平均态和气候变率两方面的变化。     

Quantifying the impact of current and future tropospheric ozone on tree biomass, growth, physiology and biochemistry: a quantitative meta-analysis

The northern hemisphere temperate and boreal forests currently provide an important carbon sink; however, current tropospheric ozone concentrations ([O₃]) and [O₃] projected for later this century are damaging to trees and have the potential to reduce the carbon sink strength of these forests. This meta‐analysis estimated the magnitude of the impacts of current [O₃] and future [O₃] on the biomass, growth, physiology and biochemistry of trees representative of northern hemisphere forests. Current ambient [O₃] (40 ppb on average) significantly reduced the total biomass of trees by 7% compared with trees grown in charcoal‐filtered (CF) controls, which approximate preindustrial [O₃]. Above‐ and belowground productivity were equally affected by ambient [O₃] in these studies. Elevated [O₃] of 64 ppb reduced total biomass by 11% compared with trees grown at ambient [O₃] while elevated [O₃] of 97 ppb reduced total biomass of trees by 17% compared with CF controls. The root‐to‐shoot ratio was significantly reduced by elevated [O₃] indicating greater sensitivity of root biomass to [O₃]. At elevated [O₃], trees had significant reductions in leaf area, Rubisco content and chlorophyll content which may underlie significant reductions in photosynthetic capacity. Trees also had lower transpiration rates, and were shorter in height and had reduced diameter when grown at elevated [O₃]. Further, at elevated [O₃], gymnosperms were significantly less sensitive than angiosperms. There were too few observations of the interaction of [O₃] with elevated [CO₂] and drought to conclusively project how these climate change factors will alter tree responses to [O₃]. Taken together, these results demonstrate that the carbon‐sink strength of northern hemisphere forests is likely reduced by current [O₃] and will be further reduced in future if [O₃] rises. This implies that a key carbon sink currently offsetting a significant portion of global fossil fuel CO₂ emissions could be diminished or lost in the future.     

Precipitation impacts on vegetation spring phenology on the Tibetan Plateau

The ongoing changes in vegetation spring phenology in temperate/cold regions are widely attributed to temperature. However, in arid/semiarid ecosystems, the correlation between spring temperature and phenology is much less clear. We test the hypothesis that precipitation plays an important role in the temperature dependency of phenology in arid/semiarid regions. We therefore investigated the influence of preseason precipitation on satellite‐derived estimates of starting date of vegetation growing season (SOS) across the Tibetan Plateau (TP). We observed two clear patterns linking precipitation to SOS. First, SOS is more sensitive to interannual variations in preseason precipitation in more arid than in wetter areas. Spatially, an increase in long‐term averaged preseason precipitation of 10 mm corresponds to a decrease in the precipitation sensitivity of SOS by about 0.01 day mm^?1. Second, SOS is more sensitive to variations in preseason temperature in wetter than in dryer areas of the plateau. A spatial increase in precipitation of 10 mm corresponds to an increase in temperature sensitivity of SOS of 0.25 day °C^?1 (0.25 day SOS advance per 1 °C temperature increase). Those two patterns indicate both direct and indirect impacts of precipitation on SOS on TP. This study suggests a balance between maximizing benefit from the limiting climatic resource and minimizing the risk imposed by other factors. In wetter areas, the lower risk of drought allows greater temperature sensitivity of SOS to maximize the thermal benefit, which is further supported by the weaker interannual partial correlation between growing degree days and preseason precipitation. In more arid areas, maximizing the benefit of water requires greater sensitivity of SOS to precipitation, with reduced sensitivity to temperature. This study highlights the impacts of precipitation on SOS in a large cold and arid/semiarid region and suggests that influences of water should be included in SOS module of terrestrial ecosystem models for drylands.     

Assessing the quality of native vegetation: The 'habitat hectares' approach

Summary Assessments of the 'quality', condition or status of stands of native vegetation or habitat are now commonplace and are often an essential component of ecological studies and planning processes. Even when soundly based upon ecological principles, these assessments are usually highly subjective and involve implicit value judgements. The present paper describes a novel approach to vegetation or habitat quality assessment (habitat hectares approach) that can be used in almost all types of terrestrial vegetation. It is based on explicit comparisons between existing vegetation features and those of 'benchmarks' representing the average characteristics of mature stands of native vegetation of the same community type in a 'natural' or 'undisturbed' condition. Components of the index incorporate vegetation physiognomy and critical aspects of viability (e.g. degree of regeneration, impact of weeds) and spatial considerations (e.g. area, distribution and connectivity of remnant vegetation in the broader landscape). The approach has been developed to assist in making more objective and explicit decisions about where scarce conservation resources are allocated. Although the approach does not require an intimate botanical knowledge, it is believed to be ecologically valid and useful in many contexts. Importantly, the index does not provide a definitive statement on conservation status nor habitat suitability for individual species. It purposefully takes a 'broad-brush' approach and is primarily intended for use by people involved with making environmentally sensitive planning and management decisions, but may be useful within environmental research programmes. The 'habitat hectares' approach is subject to further research and ongoing refinement and constructive feedback is sought from practitioners.     

A dynamic global vegetation model for use with climate models: concepts and description of simulated vegetation dynamics

Changes in vegetation structure and biogeography due to climate change feedback to alter climate by changing fluxes of energy, moisture, and momentum between land and atmosphere. While the current class of land process models used with climate models parameterizes these fluxes in detail, these models prescribe surface vegetation and leaf area from data sets. In this paper, we describe an approach in which ecological concepts from a global vegetation dynamics model are added to the land component of a climate model to grow plants interactively. The vegetation dynamics model is the Lund–Potsdam–Jena (LPJ) dynamic global vegetation model. The land model is the National Center for Atmospheric Research (NCAR) Land Surface Model (LSM). Vegetation is defined in terms of plant functional types. Each plant functional type is represented by an individual plant with the average biomass, crown area, height, and stem diameter (trees only) of its population, by the number of individuals in the population, and by the fractional cover in the grid cell. Three time‐scales (minutes, days, and years) govern the processes. Energy fluxes, the hydrologic cycle, and carbon assimilation, core processes in LSM, occur at a 20 min time step. Instantaneous net assimilated carbon is accumulated annually to update vegetation once a year. This is carried out with the addition of establishment, resource competition, growth, mortality, and fire parameterizations from LPJ. The leaf area index is updated daily based on prevailing environmental conditions, but the maximum value depends on the annual vegetation dynamics. The coupling approach is successful. The model simulates global biogeography, net primary production, and dynamics of tundra, boreal forest, northern hardwood forest, tropical rainforest, and savanna ecosystems, which are consistent with observations. This suggests that the model can be used with a climate model to study biogeophysical feedbacks in the climate system related to vegetation dynamics.     

Current and future ozone risks to global terrestrial biodiversity and ecosystem processes

Risks associated with exposure of individual plant species to ozone (O₃) are well documented, but implications for terrestrial biodiversity and ecosystem processes have received insufficient attention. This is an important gap because feedbacks to the atmosphere may change as future O₃ levels increase or decrease, depending on air quality and climate policies. Global simulation of O₃ using the Community Earth System Model (CESM) revealed that in 2000, about 40% of the Global 200 terrestrial ecoregions (ER) were exposed to O₃ above thresholds for ecological risks, with highest exposures in North America and Southern Europe, where there is field evidence of adverse effects of O₃, and in central Asia. Experimental studies show that O₃ can adversely affect the growth and flowering of plants and alter species composition and richness, although some communities can be resilient. Additional effects include changes in water flux regulation, pollination efficiency, and plant pathogen development. Recent research is unraveling a range of effects belowground, including changes in soil invertebrates, plant litter quantity and quality, decomposition, and nutrient cycling and carbon pools. Changes are likely slow and may take decades to become detectable. CESM simulations for 2050 show that O₃ exposure under emission scenario RCP8.5 increases in all major biomes and that policies represented in scenario RCP4.5 do not lead to a general reduction in O₃ risks; rather, 50% of ERs still show an increase in exposure. Although a conceptual model is lacking to extrapolate documented effects to ERs with limited or no local information, and there is uncertainty about interactions with nitrogen input and climate change, the analysis suggests that in many ERs, O₃ risks will persist for biodiversity at different trophic levels, and for a range of ecosystem processes and feedbacks, which deserves more attention when assessing ecological implications of future atmospheric pollution and climate change.     

Effects of elevated ozone on photosynthesis and stomatal conductance of two soybean varieties: a case study to assess impacts of one component of predicted global climate change

Global climatic change scenarios predict a significant increase in future tropospheric ozone (O₃) concentrations. The present investigation was done to assess the effects of elevated O₃ (70 and 100 ppb) on electron transport, carbon fixation, stomatal conductance and pigment concentrations in two tropical soybean ( Glycine max L.) varieties, PK 472 and Bragg. Plants were exposed to O₃ for 4 h·day⁻¹ from 10:00 to 14:00 from germination to maturity. Photosynthesis of both varieties were adversely affected, but the reduction was higher in PK 472 than Bragg. A comparison of chlorophyll a fluorescence kinetics with carbon fixation suggested greater sensitivity of dark reactions than light reactions of photosynthesis to O₃ stress. The O₃-induced uncoupling between photosynthesis and stomatal conductance in PK 472 suggests the reduction in photosynthesis may be attributed to a factor other than reduced stomatal conductance. An increase in internal CO₂ concentration in both O₃-treated soybean varieties compared suggests that the reduction in photosynthesis was due to damage to the photosynthetic apparatus, leading to accumulation of internal CO₂ and stomatal closure. The adverse impact of O₃ stress increased at higher O₃ concentrations in both soybean varieties leading to large reductions in photosynthesis. This study suggests that O₃-induced reductions in photosynthesis in tropical and temperate varieties are similar.     

Responses of vegetation structure and primary production of a forest transect in eastern China to global change

Aim A regional model of vegetation dynamics was enhanced to include biogeochemical cycling of nitrogen and was then applied to a forest transect in east China (FTEC) in order to investigate the responses of the transect to possible global change. Location Eastern China. Methods Biomass and nitrogen concentration of green and nongreen portions of vegetation, moisture contents of three soil layers, and total and available soil nitrogen are included as state variables in the enhanced model. The model was parameterized and validated against field observations of biomass, productivity, plant and soil nitrogen concentration, nitrogen uptake, a vegetation index derived from satellite remote sensing and digital maps of vegetation and soil distributions along a forest transect in eastern China (FTEC). The model was applied to FTEC in order to investigate the responsive characteristics of the ecosystems to global climatic change. Scenarios of climate change under doubled CO₂ produced by seven general circulation models (GCM) were used to drive the model. Results The simulations indicated that the model is capable of simulating accurately potential vegetation distribution and net primary productivity under contemporary climatic conditions. The simulations for GCM‐projected future climate scenarios with doubled atmospheric CO₂ concentration predicted that broadleaf forests would increase, but conifer forests, shrubs and grasses would decrease; and that deciduous forests would have the largest relative increase, but evergreen shrubs would have the largest decrease. Conclusions The overall effects of doubling CO₂ and climatic changes on FTEC were to produce an increased net primary productivity (NPP) at equilibrium for all seven GCM scenarios. The inclusion of nitrogen dynamics in the model imposes more constraint on the responses of FTEC to climatic change than the previous version of the model without nitrogen dynamics. Temperature exerts a stronger control on NPP than precipitation, as indicated by the negative correlations between NPP and temperature. The southern portion of FTEC, at latitudes less than 33 °N, show much larger increases in annual NPP than in the north. However, the predicted range of NPP increases is much larger in the north than in the south.     

Assessing vegetation condition in temperate montane grasslands

Rapid assessment techniques are commonly used for measuring vegetation condition at sites. Techniques for measuring site condition need to be quantitative, repeatable, rapid and simple. The key challenge is achieving a balance between simple techniques and adequate discrimination of condition between sites. This study compared a grassland condition index with the existing BioMetric condition index and showed that (i) the grassland index provided a strong measure of the relationship of temperate montane grassland sites with disturbance level, and differentiated condition of sites to a high degree and (ii) the simpler BioMetric index provided a strong measure of the relationship of the grassland sites with disturbance and differentiated their condition to a moderate degree. The choice of index to assess grassland condition should depend on purpose, cost and capacity.     

Assessing the assessors: Quantifying observer variation in vegetation and habitat assessment

Vegetation assessment protocols used in research, monitoring and statutory planning often rely on the consistent application of methods by multiple assessors. Consequently, a study was undertaken to evaluate the application of a vegetation condition assessment protocol by a range of assessors. The aim of the study was to quantify variation among assessors in their measurement of field‐based vegetation attributes using Queensland’s BioCondition protocol, and to determine the effect of variability on the final condition score. The study consisted of 77 assessors, ranging from nil to 25 years experience in vegetation assessment, who each undertook an assessment at one site following training. Six of the 20 attributes used to derive the final condition score were not assessed consistently, this being because of a small number of assessors who had misinterpreted the protocol and had inappropriately assessed some attributes. Despite inclusion of outliers, 82% of assessors were within 10 points of the median condition score for the site. Based on the results, the definition and measurement of problematic attributes have been either clarified or removed from the revised assessment procedure. The study demonstrated that with training prior to use, assessors were able to consistently assess condition at the study site.     

Evaluating the responses of forest ecosystems to climate change and CO2 using dynamic global vegetation models

The climate has important influences on the distribution and structure of forest ecosystems, which may lead to vital feedback to climate change. However, much of the existing work focuses on the changes in carbon fluxes or water cycles due to climate change and/or atmospheric CO₂, and few studies have considered how and to what extent climate change and CO₂ influence the ecosystem structure (e.g., fractional coverage change) and the changes in the responses of ecosystems with different characteristics. In this work, two dynamic global vegetation models (DGVMs): IAP‐DGVM coupled with CLM3 and CLM4‐CNDV, were used to investigate the response of the forest ecosystem structure to changes in climate (temperature and precipitation) and CO₂ concentration. In the temperature sensitivity tests, warming reduced the global area‐averaged ecosystem gross primary production in the two models, which decreased global forest area. Furthermore, the changes in tree fractional coverage (ΔF_tree; %) from the two models were sensitive to the regional temperature and ecosystem structure, i.e., the mean annual temperature (MAT; °C) largely determined whether ΔF_tree was positive or negative, while the tree fractional coverage (F_tree; %) played a decisive role in the amplitude of ΔF_tree around the globe, and the dependence was more remarkable in IAP‐DGVM. In cases with precipitation change, F_tree had a uniformly positive relationship with precipitation, especially in the transition zones of forests (30% < F_tree < 60%) for IAP‐DGVM and in semiarid and arid regions for CLM4‐CNDV. Moreover, ΔF_tree had a stronger dependence on F_tree than on the mean annual precipitation (MAP; mm/year). It was also demonstrated that both models captured the fertilization effects of the CO₂ concentration.     

全球环境变化对典型生态系统的影响研究:现状、挑战与发展趋势

随着全球环境变化和人类活动对生态系统影响的日益加深,生态系统结构和功能发生强烈变化,生态系统提供各类资源和服务的能力在显著下降。在这种背景下,全面认识生态系统的结构功能与全球环境变化的关系已成为当前生态学研究的热点之一。本文综述了全球环境变化对典型生态系统(包括森林生态系统、河口湿地生态系统、城市生态系统)影响以及全球环境变化适应的研究现状,分析研究面临的困难及挑战。在此基础上,提出对未来研究发展趋势的展望。在森林生态系统与全球环境变化研究上,未来应重视能更好模拟现实情景的、多因子、长期的全球环境变化控制试验,并注重不同生物地球化学循环之间的耦合作用。在湿地生态系统与全球环境变化研究上,未来应加强氮沉降、硫沉降及盐水入侵对湿地生态系统碳氮循环的影响,明晰滨海湿地的蓝碳功能,加强极端气候和人类干扰影响下湿地生态系统结构和功能变化及恢复力的研究。在城市生态系统与全球环境变化研究上,未来应深化城市生物地球化学循环机制研究,实现城市生态系统的人本需求侧重与转向,并开展典型地区长期、多要素综合响应研究。在全球环境变化适应研究上,未来应构架定量化、跨尺度的适应性评价体系,加强典型区域/部门的适应性研究以及适应策略实施的可行性研究,注重适应与减缓对策的关联研究及实施的风险评估。期望本综述为我国生态系统与全球环境变化研究提供一些参考。     

Carbon implications of converting cropland to bioenergy crops or forest for climate mitigation: a global assessment

The potential for climate change mitigation by bioenergy crops and terrestrial carbon sinks has been the object of intensive research in the past decade. There has been much debate about whether energy crops used to offset fossil fuel use, or carbon sequestration in forests, would provide the best climate mitigation benefit. Most current food cropland is unlikely to be used for bioenergy, but in many regions of the world, a proportion of cropland is being abandoned, particularly marginal croplands, and some of this land is now being used for bioenergy. In this study, we assess the consequences of land‐use change on cropland. We first identify areas where cropland is so productive that it may never be converted and assess the potential of the remaining cropland to mitigate climate change by identifying which alternative land use provides the best climate benefit: C₄ grass bioenergy crops, coppiced woody energy crops or allowing forest regrowth to create a carbon sink. We do not present this as a scenario of land‐use change – we simply assess the best option in any given global location should a land‐use change occur. To do this, we use global biomass potential studies based on food crop productivity, forest inventory data and dynamic global vegetation models to provide, for the first time, a global comparison of the climate change implications of either deploying bioenergy crops or allowing forest regeneration on current crop land, over a period of 20 years starting in the nominal year of 2000 ad . Globally, the extent of cropland on which conversion to energy crops or forest would result in a net carbon loss, and therefore likely always to remain as cropland, was estimated to be about 420.1 Mha, or 35.6% of the total cropland in Africa, 40.3% in Asia and Russia Federation, 30.8% in Europe‐25, 48.4% in North America, 13.7% in South America and 58.5% in Oceania. Fast growing C₄ grasses such as Miscanthus and switch‐grass cultivars are the bioenergy feedstock with the highest climate mitigation potential. Fast growing C₄ grasses such as Miscanthus and switch‐grass cultivars provide the best climate mitigation option on ≈485 Mha of cropland worldwide with ~42% of this land characterized by a terrain slope equal or above 20%. If that land‐use change did occur, it would displace ≈58.1 Pg fossil fuel C equivalent (C_eq oil). Woody energy crops such as poplar, willow and Eucalyptus species would be the best option on only 2.4% (≈26.3 Mha) of current cropland, and if this land‐use change occurred, it would displace ≈0.9 Pg C_eq oil. Allowing cropland to revert to forest would be the best climate mitigation option on ≈17% of current cropland (≈184.5 Mha), and if this land‐use change occurred, it would sequester ≈5.8 Pg C in biomass in the 20‐year‐old forest and ≈2.7 Pg C in soil. This study is spatially explicit, so also serves to identify the regional differences in the efficacy of different climate mitigation options, informing policymakers developing regionally or nationally appropriate mitigation actions.     

Comparing concentration‐based (AOT40) and stomatal uptake (PODY) metrics for ozone risk assessment to European forests

Tropospheric ozone (O₃) produces harmful effects to forests and crops, leading to a reduction of land carbon assimilation that, consequently, influences the land sink and the crop yield production. To assess the potential negative O₃ impacts to vegetation, the European Union uses the Accumulated Ozone over Threshold of 40 ppb (AOT40). This index has been chosen for its simplicity and flexibility in handling different ecosystems as well as for its linear relationships with yield or biomass loss. However, AOT40 does not give any information on the physiological O₃ uptake into the leaves since it does not include any environmental constraints to O₃ uptake through stomata. Therefore, an index based on stomatal O₃ uptake (i.e. PODY), which describes the amount of O₃ entering into the leaves, would be more appropriate. Specifically, the PODY metric considers the effects of multiple climatic factors, vegetation characteristics and local and phenological inputs rather than the only atmospheric O₃ concentration. For this reason, the use of PODY in the O₃ risk assessment for vegetation is becoming recommended. We compare different potential O₃ risk assessments based on two methodologies (i.e. AOT40 and stomatal O₃ uptake) using a framework of mesoscale models that produces hourly meteorological and O₃ data at high spatial resolution (12 km) over Europe for the time period 2000–2005. Results indicate a remarkable spatial and temporal inconsistency between the two indices, suggesting that a new definition of European legislative standard is needed in the near future. Besides, our risk assessment based on AOT40 shows a good consistency compared to both in‐situ data and other model‐based datasets. Conversely, risk assessment based on stomatal O₃ uptake shows different spatial patterns compared to other model‐based datasets. This strong inconsistency can be likely related to a different vegetation cover and its associated parameterizations.     

Quantifying the effects of ozone on plant reproductive growth and development

Tropospheric ozone (O₃) is a harmful air pollutant that can negatively impact plant growth and development. Current O₃ concentrations ([O₃]) decrease forest productivity and crop yields and future [O₃] will likely increase if current emission rates continue. However, the specific effects of elevated [O₃] on reproductive development, a critical stage in the plant's lifecycle, have not been quantitatively reviewed. Data from 128 peer‐reviewed articles published from 1968 to 2010 describing the effects of O₃ on reproductive growth and development were analysed using meta‐analytic techniques. Studies were categorized based on experimental conditions, photosynthetic type, lifecycle, growth habit and flowering class. Current ambient [O₃] significantly decreased seed number (?16%), fruit number (?9%) and fruit weight (?22%) compared to charcoal‐filtered air. In addition, pollen germination and tube growth were decreased by elevated [O₃] compared to charcoal‐filtered air. Relative to ambient air, fumigation with [O₃] between 70 and 100 ppb decreased yield by 27% and individual seed weight by 18%. Reproductive development of both C₃ and C₄ plants was sensitive to elevated [O₃], and lifecycle, flowering class and reproductive growth habit did not significantly affect a plant's response to elevated [O₃] for many components of reproductive development. However, elevated [O₃] decreased fruit weight and fruit number significantly in indeterminate plants, and had no effect on these parameters in determinate plants. While gaps in knowledge remain about the effects of O₃ on plants with different growth habits, reproductive strategies and photosynthetic types, the evidence strongly suggests that detrimental effects of O₃ on reproductive growth and development are compromising current crop yields and the fitness of native plant species.