Elevated Ozone Research Articles

Long‐term ozone effects on vegetation, microbial community and methane dynamics of boreal peatland microcosms in open‐field conditions

AbstractTo study the effects of elevated ozone concentration on methane dynamics and a sedge species, Eriophorum vaginatum, we exposed peatland microcosms, isolated by coring from an oligotrophic pine fen, to double ambient ozone concentration in an open‐air ozone exposure field for four growing seasons. The field consists of eight circular plots of which four were fumigated with elevated ozone concentration and four were ambient controls. At the latter part of the first growing season (week 33, 2003), the methane emission was 159±14 mg CH4 m−2 day−1 (mean±SE) in the ozone treatment and 214±8 mg CH4 m−2 day−1 under the ambient control. However, towards the end of the experiment the ozone treatment slightly, but consistently, enhanced the methane emission. At the end of the third growing season (2005), microbial biomass (estimated by phospholipid fatty acid biomarkers) was higher in peat exposed to ozone (1975±108 nmol g−1 dw) than in peat of the control microcosms (1589±115 nmol g−1 dw). The concentrations of organic acids in peat pore water showed a similar trend. Elevated ozone did not affect the shoot length or the structure of the sedge E. vaginatum leaves but it slightly increased the total number of sedge leaves towards the end of the experiment. Our results indicate that elevated ozone concentration enhances the general growth conditions of microbes in peat by increasing their substrate availability. However, the methane production did not reflect the increase in the concentration of organic acids, probably because hydrogenotrophic methane production dominated in the peat studied. Although, we used isolated peatland microcosms with limited size as study material, we did not find experimental factors that could have hampered the basic conclusions on the effects of ozone.

Sweet Potato [Ipomoea batatas (L.) Lam.] Cultivated as Tuber or Leafy Vegetable Supplier As Affected by Elevated Tropospheric Ozone

Sweet potato cultivars respond differently to elevated tropospheric ozone concentrations of ca. 130 mug m (-3), 8 h a day for 4 weeks, which affects their selection for cultivation. In the first cultivar presented here, an adequate leafy vegetable supplier, the ozone load resulted in a shift of biomass to maintain the canopy at the expense of tuber development. Starch content of leaves was reduced, indicating an impairment of quality, but carotenoid content remained stable. The second cultivar may be grown for tuber production. Although the ratio tuber/plant remained stable under ozone, tuber yield and its starch content were significantly reduced. The lower starch content indicated a worse quality for certain industrial processing, but it is desirable for chip production. Elevated tropospheric ozone concentrations also influenced free amino acids and macronutrient contents of tubers, but these modifications were of minor significance for tuber quality in the second cultivar.

Nutrient contents and efficiencies of beech and spruce saplings as influenced by competition and O3/CO2 regime

Saplings of Fagus sylvatica and Picea abies were grown under conditions of intra and interspecific competition in a 2-year phytotron study under combinations of ambient and elevated ozone (+O3 which is 2 × O3, but <150 nl l−1) as well as carbon dioxide concentrations (+CO2 which is amb. CO2 + 300 μl CO2 l−1) in a full factorial design. Saplings were analysed for various mineral nutrients in different plant organs as well as biomass production and crown development. The study was based on the assumption that nutritional parameters important for growth and competitiveness are affected by stress defence under limiting nutrient supply. The hypotheses tested were (1) that nutrient uptake-related parameters (a) as well as efficiencies in nutrient use for above-ground competition (b) of beech rather than spruce are impaired by the exposure to elevated O3 concentrations, (2) that the efficiency in nutrient uptake of spruce is enhanced by elevated CO2 concentrations in mixed culture, and (3) that the ability to occupy above-ground space at low nutrient cost is co-determinant for the competitive success in mixed culture. Clear nitrogen deficiencies were indicated for both species during the 2-year phytotron study, although foliar nitrogen-biomass relationships were not so close for spruce than for beech. O3 stress did not impair nutrient uptake-related parameters of beech; thus hypothesis (1a). was not supported. A negative effect of elevated O3 (under amb. CO2) on the N and P based efficiencies in above-ground space occupation (i.e. lower crown volume per unit of N or P invested in stems, limbs and foliage) of beech supported hypothesis (1b). It appeared that ozone stress triggered a nutrient demand for stress defence and tolerance at the expense of above-ground competition (trade-off). Crown volume of beech under O3 stress was stabilized in monoculture by increased nutrient uptake. In general, the +CO2-treatment was able to counteract the impacts of 2 × O3. Elevated CO2 caused lower N and S concentrations in current-year foliage of both tree species, slightly higher macronutrient amounts in the root biomass of spruce, but did not increase the efficiencies in nutrient uptake of spruce in mixed culture. Therefore hypothesis (2) was not supported. At the end of the experiment spruce turned out to be the stronger competitor in mixed culture as displayed by its higher total shoot biomass and crown volume. The amounts of macronutrients in the above-ground biomass of spruce individuals in mixed culture distinctly exceeded those of beech, which had been strongly reduced by interspecific competition. The superior competitiveness of spruce was related to higher N and P-based efficiencies in above-ground space occupation as suggested in hypothesis (3).

Sampling Soybean Roots: A Comparison of Excavation and Coring Methods

Accurate estimates of soybean root productivity are needed to estimate carbon (C) inputs to soil. Soil excavation and coring methods were compared where soybean was subject to ambient, elevated carbon dioxide (CO2) and ozone (O3) treatments. We evaluated within‐season changes in biomass and shoot–root production, labor requirements, and damage to plots. Estimates of root biomass were similar, but excavation‐based estimates required less total time. Core‐based estimates provided similar levels of precision, allowed sampling of deeper depths, and reduced both plot disturbance and the amount of effort devoted to tasks performed in the field. Correlations between root and shoot biomass were weak and varied with time of sampling. Collectively, results suggest caution should be exercised when making predictions about C allocation to roots or soils based on shoot–root ratios or when scaling up field‐based findings to predict larger or longer‐scale trends.

European surface ozone in the extreme summer 2003

Measurements of ozone and other trace species in the European EMEP network in 2003 are presented. The European summer of 2003 was exceptionally warm, and the surface ozone data for central Europe show the highest values since the end of the 1980s. The 95th percentiles of daily maximum hourly ozone concentrations in 2003 were higher than the corresponding parameter measured in any previous year at many sites in France, Germany, Switzerland and Austria. In this paper we argue that a number of positive feedbacks between the weather conditions and ozone contributed to the elevated surface ozone. First, we calculated an extended residence time of air parcels in the atmospheric boundary layer for several sites in central Europe. Second, we show that it is likely that extensive forest fires on the Iberian Peninsula, resulting from the drought and heat, contributed to the peak ozone values in north Europe in August. Third, regional‐scale model calculations indicate that enhanced levels of biogenic isoprene could have contributed up to 20% of the peak ozone concentrations. Measurements indicate elevated concentrations of isoprene compared to previous years. Sensitivity runs with a global chemical transport model showed that a reduction in the surface dry deposition due to drought and the elevated air temperature both could have contributed significantly to the enhanced ozone concentrations. Because of climate change, such heat waves may occur more frequently in the future and may gradually overshadow the effect of reduced emissions from anthropogenic sources of VOC and NOx in controlling surface ozone.

Longevity and Fecundity of Japanese Beetle (&lt;I&gt;Popillia japonica&lt;/I&gt;) on Foliage Grown Under Elevated Carbon Dioxide

Atmospheric levels of carbon dioxide (CO(2)) have been increasing steadily over the last century. Plants grown under elevated CO(2) experience physiological changes that influence their suitability as food. Previous studies have found increased insect herbivory on plants grown under elevated CO(2). To determine effects of consuming foliage of soybean (Glycine max) grown under elevated CO(2) on adult survivorship and fecundity, Japanese beetles (Popillia japonica Newman) were fed for the duration of their adult lives leaves grown under elevated CO(2) (550 mumol/mol), under ambient atmosphere (370 mumol/mol), or grown under ambient atmosphere but supplemented with a solution of sugars. To determine effects of a diet of foliage grown under elevated ozone (O(3)), another anthropogenic gaseous pollutant, beetles in the laboratory were fed soybean leaves grown under elevated CO(2), elevated O(3), or a combination of both elevated gases. Leaf tissue was also analyzed for longevity-enhancing antioxidants, because increases in dietary antioxidants can increase lifespan. Lifespan of Japanese beetles was prolonged by 8-25% when fed foliage developed under elevated CO(2), but consuming foliage that had taken up sugars to approximately the same level as foliage grown under elevated CO(2) had no effect on fecundity or longevity. Females consuming elevated CO(2) foliage laid approximately twice as many eggs as females fed foliage grown under ambient conditions. Consuming foliage grown under elevated O(3) had no effect on fecundity. No significant differences in total antioxidant content of foliage from ambient and elevated CO(2) conditions were detected. Although the precise mechanism is unclear, by altering components of leaf chemistry other than sugar content, elevated CO(2) may increase populations of Japanese beetles and their impact on crop productivity.

Aerosol distribution over Europe: a model evaluation study with detailed aerosol microphysics

Abstract. This paper summarizes an evaluation of model simulations with a regional scale atmospheric climate-chemistry/aerosol model called REMOTE, which has been extended by a microphysical aerosol module. Model results over Europe are presented and compared with available measurements in surface air focusing on the European distribution and variability of primary and secondary aerosols. Additionally, model results obtained with detailed aerosol microphysics are compared to those based on an aerosol bulk mass approach revealing the impact of dry deposition fluxes on atmospheric burden concentration. An improved determination of elevated ozone and sulfate concentrations could be achieved by considering a diurnal cycle in the anthropogenic emission fluxes. Deviation between modelled and measured organic carbon concentrations can be mainly explained by missing formation of secondary organic aerosols and deficiencies in emission data. Changing residential heating practices in Europe, where the use of wood is no longer restricted to rural areas, need to be considered in emission inventories as well as vegetation fire emissions which present a dominant source of organic carbon.

Elevated ozone modifies the feeding behaviour of the common leaf weevil on hybrid aspen through shifts in developmental, chemical, and structural properties of leaves

AbstractIn this study, we tested the impact of moderately elevated ozone (O3) – 1.5 × ambient, equivalent to predicted near‐future ozone concentrations – on the feeding behaviour of the common leaf weevil Phyllobius pyri L. (Coleoptera: Curculionidae), on two hybrid aspen [Populus tremula ×Populus tremuloides (Salicaceae)] clones (clones 55 and 110) differing in ozone sensitivity using the open‐air ozone exposure site in Kuopio, Finland. Three host‐selection tests (test between treatments, test between clones, and test between treatments* clones) with common leaf weevil females were carried out in the laboratory in the 2nd year of ozone exposure. The beetles were offered two (four for the tests between treatments and clones) freshly cut leaf discs from first flush leaves. After 24 h, the beetles were removed and the leaf disc area consumed was measured. In the field, the unfolding of the buds was followed and samples were taken for anatomical and chemical (salicylates, condensed tannins, nitrogen, and water content) leaf analyses. Phyllobius pyri significantly preferred leaves from clone 55 to those from clone 110 in the ambient air treatment, whereas this preference was less evident under elevated ozone. Leaves from ozone‐exposed trees were significantly preferred to leaves grown in ambient air. Our results suggest that the preference of clone 55 and of ozone‐exposed leaves can be explained by phenotypic properties of the plant and prevailing ozone concentration through shifts in leaf development process, phenolic composition, and leaf thickness.

Rice production in a changing climate: a meta‐analysis of responses to elevated carbon dioxide and elevated ozone concentration

AbstractRice is arguably the most important food source on the planet and is consumed by over half of the world's population. Considerable increases in yield are required over this century to continue feeding the world's growing population. This meta‐analysis synthesizes the research to date on rice responses to two elements of global change, rising atmospheric carbon dioxide concentration ([CO2]) and rising tropospheric ozone concentration ([O3]). On an average, elevated [CO2] (627 ppm) increased rice yields by 23%. Modest increases in grain mass and larger increases in panicle and grain number contributed to this response. The response of rice to elevated [CO2] varied with fumigation technique. The more closely the fumigation conditions mimicked field conditions, the smaller was the stimulation of yield by elevated [CO2]. Free air concentration enrichment (FACE) experiments showed only a 12% increase in rice yield. The rise in atmospheric [CO2] will be accompanied by increases in tropospheric O3 and temperature. When compared with rice grown in charcoal‐filtered air, rice exposed to 62 ppb O3 showed a 14% decrease in yield. Many determinants of yield, including photosynthesis, biomass, leaf area index, grain number and grain mass, were reduced by elevated [O3]. While there have been too few studies of the interaction of CO2 and O3 for meta‐analysis, the interaction of temperature and CO2 has been studied more widely. Elevated temperature treatments negated any enhancement in rice yield at elevated [CO2], which suggests that identifying high temperature tolerant germplasm will be key to realizing yield benefits in the future.

Comparison of a diurnal vs steady-state ozone exposure profile on growth and yield of oilseed rape (Brassica napus L.) in open-top chambers in the Yangtze Delta, China

Most available exposure-response relationships for assessing crop loss due to elevated ozone (O(3)) have been established using data from chamber and open-top chamber experiments, using a simulated constant O(3) concentration exposure (square wave), which is not consistent with the diurnal variation of O(3) concentration that occurs in nature. We investigated the response of oilseed rape (Brassica napus L.) to O(3) as affected by two exposure regimes: one with a diurnal variation (CF100D) and another with a constant concentration (CF100). Although the two exposure regimes have the same mean O(3) concentration and accumulated O(3) concentration above 40 ppb (AOT40), our results show that O(3) at CF100D reduced biomass and number of pods/plant more than O(3) at CF100. Both O(3) exposures resulted in larger seed weights/100 pods compared to CF. Numbers of seeds/100 pods were reduced by CF100, while numbers of seeds/100 pods in the CF100D chambers were comparable to those in CF. Our results suggest that chamber experiments that use a constant O(3) exposure may underestimate O(3) effects on biomass and yields.

Proteome analysis of proteins responsive to ambient and elevated ozone in rice seedlings

Ozone is a major gaseous pollutant that induces crop loss. Although the physiological and morphological responses of crops to ambient ozone have been well characterized, little is known about the protein responses. We firstly investigated the protein responses in rice seedlings under ambient and elevated ozone stress by a proteome approach. Twenty proteins were differentially expressed. Expression of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) large subunit (LSU) and their 17–18 kDa fragments and RuBisCO activase were reduced by both ambient and elevated ozone. RuBisCO small subunit (SSU), large subunit fragment (37 kDa), and oxygen-evolving enhancer proteins 1 and 2 increase in expression with ambient ozone, and decreased with elevated ozone. Ambient ozone induced a slight reduction, and elevated ozone induced a significant reduction in the expression of energy metabolism proteins. Expression of the antioxidant proteins glutathione S-transferase and Mn superoxide dismutase increased upon ozone exposure, but thioredoxin peroxidase expression decreased. Three defense/stress-related proteins, pathogenesis-related (PR) class 5 protein (PR5) and two PR10 proteins OsPR10/PBZ1 and RSOsPR10, were significantly induced after 2 days exposure to elevated ozone and gradually increased during exposure period. The results not only indicate the difference in protein responses between leaves exposed to ambient and elevated ozone, but also demonstrated the highly damaging effect of elevated ozone on rice seedlings at the proteome level.

Phenogenetic response of silver birch populations and half-sib families to elevated ozone and ultraviolet-B radiation at juvenile age

Phenogenetic response of silver birch populations and half-sib families to separate and combined elevated ozone (O(3)) concentrations and ultraviolet-B (UV-B) radiation dozes was studied at juvenile age in the climatic chambers. Significant population and family effects were found for seedling height, lamina width, and leaf damage. The exposure to UV-B radiation decreased genetic variation at the stage of seed germination. Complex exposure to UV-B and O(3) caused an increase of genetic variation at the stage of intensive seedling growth: seedling height genetic variation in separate treatments increased from 23.7-38.6 to 33.7-65.7%, the increase for lamina width was from 10.2-13.9 to 13.6-31.8%. Different populations and families demonstrated differing response to elevated complex UV-B and O(3) exposure. Changes of genetic intra-population variation were population-specific. Such changes in genetic variation under the impact of stressors can alter adaptation, stability, and competitive ability of regenerating populations in a hardly predictive way.

A study of VOC reactivity in the Houston-Galveston air mixture utilizing an extended version of SAPRC-99 chemical mechanism

The Houston-Galveston area is the region where National Ambient Air Quality Standard (NAAQS) for ozone is often violated. Emissions from industrial sources contribute significantly to elevated ozone concentrations and make air composition quite unique in comparison to typical urban composition. In this study, source-oriented reactivity of individual organic compounds, released in urban and industrial areas inside Houston-Galveston region, with regard to ozone formation is determined. The CMAQ model and an extended version of SAPRC-99 mechanism, representing 26 additional individual compounds explicitly, is employed for the model simulations. The incremental volatile organic compound (VOC) reactivities calculated for the Houston-Galveston conditions show variations with respect to the differences in the air compositions between urban and industrial areas as well as meteorological conditions. The compounds with the highest reactivities, such as 2-methyl-2-butene, trans-2-butene and cis-2-butene, were found to be most sensitive to the environment in which they were released. According to the reactivities weighted by VOC mixing ratios, ethene, propene and formaldehyde show the highest impact on ozone formation. Reactivities of most investigated compounds estimated for the Houston-Galveston air conditions are in good agreement with the ‘reference’ maximum incremental reactivity (MIR) scale.

Host location behavior of Cotesia plutellae Kurdjumov (Hymenoptera: Braconidae) in ambient and moderately elevated ozone in field conditions

In field O(3)-enrichment experiments increased herbivore densities have been reported, which could be due to negatively affected host location behavior of natural enemies. We addressed the impact of doubling background O(3) on the host location of the parasitoid Cotesia plutellae by conducting 24-h trials in an open-air O(3)-fumigation system during two consecutive years. Two circles (radii 1.40 and 4.00 m) of Plutella xylostella-infested potted cabbage plants were placed in the O(3) and ambient plots. Female wasps were released into each plot from the center, and observed 5 times over a 24-h period to assess their host location capability. Thereafter, plants were kept in laboratory conditions until larvae pupation to determine parasitism rates. No significant differences were detected between ambient and O(3)-enriched environments either in the number of wasps found in the field, or in the percentages of parasitized larvae. This suggests that moderately elevated O(3) will not affect the behavior of this parasitoid.

Effects of elevated ozone on growth and yield of field-grown rice in Yangtze River Delta, China

With rapid industrialization and urbanization in the Yangtze Delta, China, the tropospheric ozone concentration has increased to levels that induce crop yield loss. Rice, a widely grown crop in China, was investigated in field-established, open-top chambers. Four treatments were used: charcoal-filtered air (CF), non-charcoal-filtered air (NF), and charcoal-filtered air with two levels of additional ozone (O3-1 and O3-2). The AOT40s (accumulated hourly mean ozone concentration above 40 ppbv) were 0, 0.91, 23.24, and 39.28 ppmv x h for treatment of CF, NF, O3-1, and O3-2, respectively. The rice height and biomass were reduced in the elevated ozone concentration. Less organic matter partitioning to roots under the elevated ozone significantly decreased rice root activity. The yield loss was 14.3% and 20.2% under O3-1 and O3-2 exposure, respectively. This was largely caused by a reduction in grain weight per panicle.

Modelling the impact of possible snowpack emissions of O(3P) and NO2 on photochemistry in the South Pole boundary layer

Environmental context. The study of surface photochemical ozone production on the Antarctic continent has direct relevance to climate change and general air quality and is scientifically noteworthy given the otherwise pristine nature of this environmental region. The identification of possible direct ozone emissions from snow surfaces and their contribution to the already active photochemical pollution present there represents a unique physical phenomenon. This process could have wider global significance for other snow-covered regions and therefore for global climate change. Abstract. O(3P) emissions due to photolysis of nitrate were recently identified from ice surfaces doped with nitric acid. O(3P) atoms react directly with molecular oxygen to yield ozone. Therefore, these results may have direct bearing on photochemical activity monitored at the South Pole, a site already noted for elevated summertime surface ozone concentrations. NO2 is also produced via the photolysis of nitrate and the firn air contains elevated levels of NO2, which will lead to direct emission of NO2. A photochemical box model was used to probe what effect O(3P) and NO2 emissions have on ozone concentrations within the South Pole boundary layer. The results suggest that these emissions could account for a portion of the observed ozone production at the South Pole and may explain the observed upward fluxes of ozone identified there.

Numerical study on the ozone formation inside street canyons using a chemistry box model

Tropospheric ozone is a secondary air pollutant produced in the presence of nitrogen oxides (NOx), volatile organic compounds (VOCs), and solar radiation. In an urban environment, ground-level vehicular exhaust is the major anthropogenic source of ozone precursors. In the cases of street canyons, pollutant dilution is weakened by the surrounding buildings that creates localized high concentration of NOx and VOCs, and thus leads to high potential of ozone formation. By considering the major physical and chemical processes, a chemistry box model is employed to investigate the characteristics of ozone formation due to vehicular exhaust inside street canyons under the worst case scenario, i.e. the calm wind condition. It is found that a high level of ozone concentration, of the order of 100 ppbv and higher, would occur inside the street canyons, in particular, when the emission rate (concentration) ratio of VOCs to NOx is greater than 10. This elevated ozone concentration appears at the transition from VOCs to NOx sensitivity and may extend to a few hundreds.

Plant and Soil System Responses to Ozone After 3 Years in a Lysimeter Study with Juvenile Beech (Fagus sylvatica L.)

A lysimeter study was performed to monitor effects of elevated ozone on juvenile trees of Fagus sylvatica L. as well as on the plant–soil system. During a fumigation period over almost three growing seasons, parameters related to plant growth, phenological development and physiology as well as soil functions were studied. The data analyses identified elevated ozone to delay leaf phenology at early and to accelerate it at late developmental stages, to reduce growth, some leaf nutrients (Ca, K) as well as some soluble phenolics (hydroxycinnamic acid derivatives, total flavonol glycosides). No or very weak ozone effects were found in mobile carbon pools of leaves (starch, sucrose), and other phenolic compounds (flavans). Altered gene expression related to stress and carbon cycling corresponded well with findings from leaf phenology and chemical composition analyses indicating earlier senescence and oxidative stress in leaves under elevated ozone. Conversely in the soil system, no effects of ozone were detected on soil enzyme activities, rates of litter degradation and lysimeter water balances. Despite the fact that the three reported years 2003–2005 were climatically very contrasting including a hot and dry as well as an extremely wet summer, and also mild as well as cold winters, the influence of ozone on a number of plant parameters is remarkably consistent, further underlining the phytotoxic potential of elevated tropospheric ozone levels.

Seasonal differences and within-canopy variations of antioxidants in mature spruce ( Picea abies) trees under elevated ozone in a free-air exposure system

The effect of free-air ozone fumigation and crown position on antioxidants were determined in old-growth spruce ( Picea abies) trees in the seasonal course of two consecutive years (2003 and 2004). Levels of total ascorbate and its redox state in the apoplastic washing fluid (AWF) were increased under double ambient ozone concentrations (2 × O 3), whilst ascorbate concentrations in needle extracts were unchanged. Concentrations of apoplastic and symplastic ascorbate were significantly higher in 2003 compared to 2004 indicating a combined effect of the drought conditions in 2003 with enhanced ozone exposure. Elevated ozone had only weak effects on total glutathione levels in needle extracts, phloem exudates and xylem saps. Total and oxidised glutathione concentrations were higher in 2004 compared to 2003 and seemed to be more affected by enhanced ozone influx in the more humid year 2004 compared to the combined effect of elevated ozone and drought in 2003 as observed for ascorbate.

Effects of tropospheric ozone pollution on net primary productivity and carbon storage in terrestrial ecosystems of China

We investigated the potential effects of elevated ozone (O3) along with climate variability, increasing CO2, and land use change on net primary productivity (NPP) and carbon storage in China's terrestrial ecosystems for the period 1961–2000 with a process‐based Dynamic Land Ecosystem Model (DLEM) forced by the gridded data of historical tropospheric O3 and other environmental factors. The simulated results showed that elevated O3 could result in a mean 4.5% reduction in NPP and 0.9% reduction in total carbon storage nationwide from 1961 to 2000. The reduction of carbon storage varied from 0.1 Tg C to 312 Tg C (a decreased rate ranging from 0.2% to 6.9%) among plant functional types. The effects of tropospheric O3 on NPP were strongest in east‐central China. Significant reductions in NPP occurred in northeastern and central China where a large proportion of cropland is distributed. The O3 effects on carbon fluxes and storage are dependent upon other environmental factors. Therefore direct and indirect effects of O3, as well as interactive effects with other environmental factors, should be taken into account in order to accurately assess the regional carbon budget in China. The results showed that the adverse influences of increasing O3 concentration across China on NPP could be an important disturbance factor on carbon storage in the near future, and the improvement of air quality in China could enhance the capability of China's terrestrial ecosystems to sequester more atmospheric CO2. Our estimation of O3 impacts on NPP and carbon storage in China, however, must be used with caution because of the limitation of historical tropospheric O3 data and other uncertainties associated with model parameters and field experiments.