Effects Of Elevated O3 Research Articles

Effects of O3 stress on photosynthesis of trees

The effects of elevated O3 (O3) on photosynthetic characteristics of urban trees were studied in an open-top air chamber. The results showed that net photosynthetic rate (Pn), transpiration rate (Et), stomatal conductance (Gs) and water use efficiency (WUE) of different tree species decreased significantly with the increase of O3 concentration, while intercellular CO2 (Ci) concentration of different tree species increased significantly with the increase of O3 concentration. Under different O3 concentrations, the net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2 concentration of Ginkgo biloba (G. biloba) and Koelreuteria paniculata (K. paniculata.) were higher than those of Pinus bungeana (P. bungeana) and Platycladus orientalis(P. orientalis), and the WUE of P. bungeana and P. orientalis was higher than that of G. biloba and K. paniculata. The effect of elevated O3 concentration on plant photosynthesis is more obvious in K. paniculata and G. biloba.

Performances of a system for free-air ozone concentration elevation with poplar plantation under increased nitrogen deposition.

The increasing emission of nitrogen oxides exerts large impacts on vegetation by raising surface ozone (O3) concentrations and enhancing atmospheric nitrogen (N) deposition. We established a free-air O3 concentration elevation and enhanced N deposition system (O3-N-FACE) in Beijing, China, to investigate long-term effects of elevated O3 and N deposition on poplar plantation. Eight square plots with a side length of 16 m were randomly allocated to elevated O3 (E-O3) and ambient air (AA) treatments. Ozone generated by electric discharge in pure oxygen is mixed with clean and dry air, and released from small holes on the tubes installed above the plant canopy at a rate controlled to keep O3 concentration in E-O3 plots by 50% higher than that in AA plots. Each O3 treatment plot consisted of four subplots with a factorial combination of 2 lines of poplar clones and 2 levels of N deposition rate. In enhanced N deposition subplots, we sprayed urea solution on the plantation floor at a rate of 60 kg ha-1 year-1. We hereby present the system performances during the growing seasons of 2018 and 2019: the first 2 years of experiment. The mean daytime O3 concentrations of E-O3 plots were 38% and 31% higher than AA plots in 2018 and 2019, respectively. And, in 2019, the accumulated O3 exposure over 40 ppb (AOT40) in E-O3 plots was 70% higher than that in AA plots. The hourly mean O3 concentrations in E-O3 plots were within 20% of the target for 83% of time on average across the four E-O3 plots. Within the E-O3 plots, spatial distribution of the hourly O3 concentration exhibited the maximum deviation at 24% in 2019. We concluded that performance of this system is better than other similar facilities for trees and suitable for a long-term experiment of enhanced O3 and N.

Experimental warming alleviates the adverse effects from tropospheric ozone on two urban tree species

Atmospheric warming and increasing tropospheric ozone (O3) concentrations often co-occur in many cities of the world including China, adversely affecting the health status of urban trees. However, little information is known about the combined and interactive effects from increased air temperature (IT) and elevated O3 (EO) exposures on urban tree species. Here, Ginkgo biloba and Populus alba ‘Berolinensis’ seedlings were subjected to IT (+2 °C of ambient air temperature) and/or EO (+2-fold ambient air O3 concentrations) for one growing season by using open-top chambers. IT alone had no significant effect on physiological metabolisms at the early growing stage, but significantly increased photosynthetic parameters, antioxidative enzyme activities (P < 0.05). EO alone decreased physiological parameters except for increased oxidative stress. Compared to EO exposure alone, plants grown under IT and EO combined showed higher antioxidative and photosynthetic activity. There was a significant interactive effect between IT and EO on net photosynthetic rate, stomatal conductance, water use efficiency, the maximum quantum efficiency of PSII photochemistry, the actual quantum efficiency of PSII, enzyme activities, aboveground biomass and root/shoot ratio (P < 0.05), respectively. These results suggested that during one growing season, IT mitigated the adverse effect of EO on the tested plants. In addition, we found that G. biloba was more sensitive than P. alba ‘Berolinensis’ to both IT and EO, suggesting that G. biloba may be a good indicator species for climate warming and air pollution, particularly under environmental conditions as they co-occur in urban areas.

Isotopic and Water Relation Responses to Ozone and Water Stress in Seedlings of Three Oak Species with Different Adaptation Strategies

The impact of global changes on forest ecosystem processes is based on the species-specific responses of trees to the combined effect of multiple stressors and the capacity of each species to acclimate and cope with the environment modification. Combined environmental constraints can severely affect plant and ecological processes involved in plant functionality. This study provides novel insights into the impact of a simultaneous pairing of abiotic stresses (i.e., water and ozone (O3) stress) on the responses of oak species. Water stress (using 40 and 100% of soil water content at field capacity—WS and WW treatments, respectively) and O3 exposure (1.0, 1.2, and 1.4 times the ambient concentration—AA, 1.2AA, and 1.4AA, respectively) were carried out on Quercus robur L., Quercus ilex L., and Quercus pubescens Willd. seedlings, to study physiological traits (1. isotope signature [δ13C, δ18O and δ15N], 2. water relation [leaf water potential, leaf water content], 3. leaf gas exchange [light-saturated net photosynthesis, Asat, and stomatal conductance, gs]) for adaptation strategies in a Free-Air Controlled Exposure (FACE) experiment. Ozone decreased Asat in Q. robur and Q. pubescens while water stress decreased it in all three oak species. Ozone did not affect δ13C, whereas δ18O was influenced by O3 especially in Q. robur. This may reflect a reduction of gs with the concomitant reduction in photosynthetic capacity. However, the effect of elevated O3 on leaf gas exchange as indicated by the combined analysis of stable isotopes was much lower than that of water stress. Water stress was detectable by δ13C and by δ18O in all three oak species, while δ15N did not define plant response to stress conditions in any species. The δ13C signal was correlated to leaf water content (LWC) in Q. robur and Q. ilex, showing isohydric and anisohydric strategy, respectively, at increasing stress intensity (low value of LWC). No interactive effect of water stress and O3 exposure on the isotopic responses was found, suggesting no cross-protection on seasonal carbon assimilation independently on the species adaptation strategy.

Elevated CO2 offsets the alteration of foliar chemicals (n-icosane, geranyl acetate, and elixene) induced by elevated O3 in three taxa of O3-tolerant eucalypts

Eucalypts are important forest resources in southwestern China, and may be tolerant to elevated ground-level ozone (O3) concentrations that can negatively affect plant growth. High CO2 may offset O3-induced effects by providing excess carbon to produce secondary metabolites or by inducing stomatal closure. Here, the effects of elevated CO2 and O3 on leaf secondary metabolites and other defense chemicals were studied by exposing seedlings of Eucalyptus globulus, E. grandis, and E. camaldulensis × E. deglupta to a factorial combination of two levels of O3 (< 10 nmol mol−1 and 60 nmol mol−1) and CO2 (ambient: 370 μmol mol−1 and 600 μmol mol−1) in open-top field chambers. GC-profiles of leaf extracts illustrated the effect of elevated O3 and the countering effect of high CO2 on compounds in leaf epicuticular wax and essential oils, i.e., n-icosane, geranyl acetate and elixene, compounds known as a first-line defense against insect herbivores. n-Icosane may be involved in tolerance mechanisms of E. grandis and the hybrid, while geranyl acetate and elixene in the tolerance of E. globulus. Elevated O3 and CO2, singly or in combination, affected only leaf physiology but not biomass of various organs. Elevated CO2 impacted several leaf traits, including stomatal conductance, leaf mass per area, carbon, lignin, n-icosane, geranyl acetate and elixene. Limited effects of elevated O3 on leaf physiology (nitrogen, n-icosane, geranyl acetate, elixene) were commonly offset by elevated CO2. We conclude that E. globulus, E. grandis and the hybrid were tolerant to these O3 and CO2 treatments, and n-icosane, geranyl acetate and elixene may be major players in tolerance mechanisms of the tested species.

Tolerance to ozone might impose restrictions to plant disease management in tomato

Tropospheric ozone (O3 ) is considered a major air pollutant having negative effects on plant growth and productivity. Background concentrations are expected to rise in several regions of the world in the next 50years, affecting plant responses to diseases, thus requiring new management strategies for food production. The effects of elevated O3 on the severity of a bacterial disease, and the effectiveness of a chemical defence inducer, were examined in two cultivars of tomato, Roma and Moneymaker, which present different tolerance to this pollutant. The two cultivars differ in their ability to produce and accumulate reactive oxygen species (ROS) in leaf tissues. Tomato plants were challenged with a strain of Xanthomonas vesicatoria, Xv9, which is pathogenic on tomato. Ozone consistently increased severity of the disease by over 40% in both cultivars. In the more tolerant cultivar, O3 pollution increased disease intensity, even after applying a commercially available product to enhance resistance (acibenzolar-S-methyl, BTH). In the more susceptible cultivar, level of disease attained depended on the oxidative balance that resulted from other stress factors. The antioxidant capacity of the plant at the time of infection was relevant for controlling development of the disease. Our results suggest that development of O3 tolerance in commercial crops might impose a penalty cost in terms of disease management under projected higher O3 concentrations.

Cascading effects of elevated ozone on wheat rhizosphere microbial communities depend on temperature and cultivar sensitivity

Tropospheric ozone (O3) concentrations have now reached levels that can potentially affect crop production in several regions of the world. The interacting effects of the elevated O3 and temperature on plants are still unclear and their consequences on the rhizosphere microbial communities never studied yet. Here, we conducted a 3-week fumigation experiment on two cultivars of wheat with different tolerance to O3 (Premio and Soissons) at two temperatures (20 °C and 30 °C). The impacts of O3 were measured on plants physiology, rhizosphere chemical environment and microbial communities. Globally, most of the results showed that elevated O3 effects were more pronounced at 20 °C than 30 °C, especially on the most O3-sensitive cultivar (Soissons). Elevated O3 reduced significantly plant root biomass (up to −37% for Soissons) compared to non-fumigated plants. A decrease in the dissolved organic matter with a relative increase of aromatic compounds concentration was also observed under elevated O3, suggesting quantitative and qualitative impacts on roots exudation. While bacterial abundance was negatively affected by O3 plant stress, fungal abundance was found to be stimulated (up to 12 fold compared to non-fumigated plants for Soissons at 20 °C). These changes were accompanied by modifications of the genetic structures and metabolic profiles, with a relative increase of amino acids catabolism. This fully controlled laboratory experiment showed that the effects of elevated O3 on soil microbial communities i) are plant-mediated and depend on the cultivar sensitivity, ii) decrease in warming condition, iii) increase the fungi to bacteria ratio and iv) alter both the genetic structure and the metabolic activities. This study highlights the importance of considering interactive effects between pollutants and climate changes on plant-microbe relationship to better inform models and improve predictions of future states of agroecosystems.

Effects of Ambient Ozone on Soybean Biophysical Variables and Mineral Nutrient Accumulation

The effects of increasing ambient ozone (O3) concentrations on food security has become a major concern as the demand for agricultural productivity is projected to increase significantly over the next several decades. In this contribution, the responses of common soybean genotypes (AK-HARROW, PI88788, DWIGHT, PANA, and WILLIAMS82) to ambient O3 are characterized using hyperspectral data and foliar biophysical, mineral nutrient concentrations and soybean yield. Specifically, leaf reflectance spectra measured at different growth stages and canopy layers were used to examine the spectral indices that were most strongly correlated with leaf physiological status. The effects of elevated O3 on six important nutrients (K, Ca, Mg, Fe, Mn and Cu) were evaluated by analyzing the variations in nutrient concentrations at two critical growth stages with increasing ambient O3 concentration using Partial Least Square Regression (PLSR). Lastly, the identified best spectral indices and the robust nutrient prediction models were extrapolated to the entire growth period to explore their ability to track the effects of ambient O3 concentrations on soybean physiology and nutrient uptake. The results showed that fluorescence yield (ΔF/Fm’) and photochemical quenching (qP) appear to be good indicators of soybean physiological responses to O3 stress that are echoed by the harvest index (HI). Newly identified normalized difference spectral index (NDSI) [R416, R2371] always had the highest correlation (R2 &gt; 0.6) with ΔF/Fm’, qP and electron transport rate (ETR, μmol m−2 s−1) compared to the published indices. Additionally, there were significant and broad spectral regions in visible and near infrared region that were well-correlated with ΔF/Fm’ and selected NDSIs that were applicable to satellite observations. The results of nutrient modeling using PLSR explained 54–87% of the variance in nutrient concentrations, and the predicted mineral nutrient accumulation throughout the growing season reflected the responses of ozone tolerant and sensitive genotypes well. NDSI [R416, R2371] demonstrated great potential in regard to its sensitivity in tracking plant physiological responses to changing ambient O3 concentrations. The outcome of this research has potential implications for development of space-based observation of large-scale crop responses to O3 damage, as well as for biotechnological breeding efforts to improve ozone tolerance under future climate scenarios.

Effect of elevated O3 on rhizospheric enzymatic activities of ozone sensitive and tolerant wheat cultivars

ABSTRACTTropospheric ozone (O3) is considered harmful to agriculture production and soil community. Wheat cultivars HD 2987 (O3 sensitive) and Kharchiya 65 (O3 tolerant) were grown under ambient and elevated (ambient + 30 ppb) levels of O3 (EO) using open top chambers, and microbial biomass and enzymatic activities were investigated in soil rhizosphere. Elevated O3 declined soil enzymatic activities related to carbon cycling viz. β-glucosidase, cellobiohydrolase, cellulase and amylase more in sensitive cultivar compared to tolerant. Enzymatic activities linked to nitrogen cycling like N-acetyl-glucosaminidase and urease decreased while protease and glycine aminopeptidase increased. Microbial biomass carbon and nitrogen declined more in sensitive cultivar by 11.1 and 21.2%, respectively. Root biomass reduced in wheat cultivars with an increase of their phenolics contents by 34.3 and 10.2% in HD 2987 and Kharchiya 65, respectively at 60 days after germination. Non-significant changes were observed in soil organic carbon and total nitrogen in both the cultivars. Redundancy analysis suggested that soil enzymatic activities were predominantly affected by O3 induced changes in microbial biomass carbon and root biomass. Study also showed that rhizosphere of sensitive cultivar HD 2987 was affected more under EO as compared to tolerant Kharchiya 65.

Ozone Pollution Increases CO2 and N2O Emissions in Ozone‐sensitive Wheat System

Core Ideas Elevated O3 (EO3) effects on GHG flux and GWP from O3‐sensitivity wheat systems were studied.EO3 reduced belowground biomass of O3‐sensitive (SW) and O3‐tolerant (TW) wheat cultivars.O3‐sensitivty of wheat cultivar affected responses of gaseous C and N emission and GWP to EO3.SW wheat would release more freshly assimilated C, adding GHG emission and GWP under EO3. The effects of elevated O3 (EO3) on greenhouse gas (GHG) emissions and global warming potential (GWP) from wheat systems with differential O3 sensitivity are not well understood. The nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) emissions from cropping (CP) and bare soil or root‐free (BS) plots, GWP, GWP per unit yield, and biomass and its allocation to belowground between O3‐sensitive (cultivar YN19) and tolerant (cultivar Y15) wheat (Triticum aestivum L.) systems were investigated at EO3 and ambient O3 (AO3) with an open‐air O3 fumigation system. Results indicated that a 50% elevation above AO3 significantly reduced belowground biomass of the two cultivars. The EO3 significantly increased the cumulative emissions of CO2 and N2O but did not change that of CH4 in YN19 CP. For BS, it significantly increased the emission of CO2 but decreased that of CH4 and N2O. The EO3 significantly increased the GWP and GWP per unit yield in YN19 CP but reduced the GWP in BS. The O3 sensitivity of wheat cultivar affected the responses of gaseous C and N emission, GWP and GWP per unit yield to EO3. The O3‐sensitive wheat cultivar would release more freshly assimilated C, increasing cumulative GHG emissions, GWP and GWP per unit yield in response to O3 stress, when compared to the O3 O3‐tolerant wheat cultivar. Our results suggest that EO3 may impair soil C and N sequestration in an O3 O3‐sensitive wheat–soil system in view of lower root biomass but higher CO2 and N2O emissions under EO3.

Effects of elevated O3 on physiological and biochemical responses in three kinds of trees native to subtropical forest in China during non-growing period.

Numerous studies have documented the negative effects of ozone (O3) on tree species in growing season, however, little is done in non-growing season. Three evergreen tree species, Phoebe bournei (Hemsl.) Yang (P.bournei), Machilus pauhoi Kanehira (M.pauhoi) and Taxus chinensis (Pilger) Rehd (T.chinensis), were exposed to non-filtered air, 100nmolmol-1 O3 air (E1) and 150nmolmol-1 O3 air (E2) in open-top chambers in subtropical China. In the entire period of experiment, O3 fumigation decreased net photosynthesis rate (Pn) through stomatal limitation during the transition period from growing to non-growing season (TGN), and through non-stomatal limitation during the period of non-growing season (NGS) in all species tested. Meanwhile, O3 fumigation reduced and delayed the resilience of Pn in all species tested during the transition period from non-growing to growing season (TNG). O3 fumigation significantly decreased chlorophyll contents during NGS, whereas no obvious injury symptoms were observed till the end of experiment. O3 fumigation induced increases in levels of malondialdehyde, superoxide dismutase, total phenolics and reduced ascorbic acid, and changes in four plant endogenous hormones as well in all species tested during NGS. During NGS, E1 and E2 reduced Pn by an average of 80.11% in P.bournei, 94.56% in M.pauhoi and 12.57% in T.chinensis, indicating that the O3 sensitivity was in an order of M.pauhoi>P.bournei>T.chinensis. Overall, O3 fumigation inhibited carbon fixation in all species tested during NGS. Furthermore, O3-induced physiological activities also consumed the dry matter. All these suggested that elevated O3, which is likely to come true during NGS in the future, will adversely affect the accumulation of dry matter and the resilience of Pn during TNG in evergreen tree species, and further inhibit their growth and development in the upcoming growing season.

Differential root responses in two cultivars of winter wheat (Triticum aestivum L.) to elevated ozone concentration under fully open‐air field conditions

AbstractThe effect of elevated tropospheric ozone concentration [O3] on root processes in wheat systems of different O3 sensitivity is not well understood. Two wheat cultivars (cv. Y15 and YN19) with contrasting O3 tolerance were grown in a fully open‐air O3 enrichment platform for one season. We found that elevated O3 (EO3) (50% above the ambient O3) significantly decreased the total biomass at all key growth stages and the yield of the O3‐sensitive cultivar YN19 but did not affect those of the O3‐tolerant cultivar Y15. EO3 significantly decreased the root biomass of two wheat cultivars at the jointing and grain‐filling stages. EO3 significantly decreased the root length, length density, surface area and volume of the two cultivars at the jointing stage but increased those of YN19 at the grain‐filling stage. EO3 significantly increased the root activities (specific root respiration rates) of Y15 and YN19 at the jointing, heading and grain‐filling stages. EO3 significantly decreased the contribution of fresh root respiration to soil respiration (CRS) of YN19 at the jointing stage but increased it at the heading stage; however, it did not change the CRS of Y15 at any growth stages. This study indicates that the effects of EO3 on root morphology and activity varied among wheat cultivars, and suggest that we can breed O3‐tolerant cultivars to maintain crop yield under higher [O3] scenarios.

Sensitivity of global greenhouse gas budgets to tropospheric ozone pollution mediated by the biosphere

Tropospheric ozone (O3), a harmful secondary air pollutant, can affect the climate via direct radiative forcing and by modifying the radiative forcing of aerosols through its role as an atmospheric oxidant. Moreover, O3 exerts a strong oxidative pressure on the biosphere and indirectly influences the climate by altering the materials and energy exchange between terrestrial ecosystems and the atmosphere. However, the magnitude by which O3 affects the global budgets of greenhouse gases (GHGs: CO2, CH4, and N2O) through altering the land–atmosphere exchange is largely unknown. Here we assess the sensitivity of these budgets to tropospheric O3 pollution based on a meta-analysis of experimental studies on the effects of elevated O3 on GHG exchange between terrestrial ecosystems and the atmosphere. We show that across ecosystems, elevated O3 suppresses N2O emissions and both CH4 emissions and uptake, and has little impact on stimulation of soil CO2 emissions except at relatively high concentrations. Therefore, the soil system would be transformed from a sink into a source of GHGs with O3 levels increasing. The global atmospheric budget of GHGs is sensitive to O3 pollution largely because of the carbon dioxide accumulation resulting from suppressed vegetation carbon uptake; the negative contributions from suppressed CH4 and N2O emissions can offset only ∼10% of CO2 emissions from the soil–vegetation system. Based on empirical data, this work, though with uncertainties, provides the first assessment of sensitivity of global budgets of GHGs to O3 pollution, representing a necessary step towards fully understanding and evaluating O3–climate feedbacks mediated by the biosphere.

Leaf stoichiometry of deciduous tree species in different soils exposed to free-air O3 enrichment over two growing seasons

The effects of elevated O3 in different soil conditions on foliar elements stoichiometry were investigated in 3 native tree species with a free-air enrichment system in northern Japan over two growing seasons. Essential elements (Mg, K, Ca, Mn, Fe, Ni, P, N) and two non-essential elements (Cr, Al) were analyzed in leaf samples obtained from 6 different treatments of O3 and soils at 5 collection times from 2014 to 2015. In this study, relationships among the foliar elements within each species were investigated and negative correlations between foliar N and the metal elements were observed in birch (Betula platyphylla var. japonica). From the differences of foliar contents as well as their retranslocation rate, beech (Fagus crenata) with determinate shoot growth pattern were rather more sensitive to O3 stress on foliar contents, meanwhile oak (Quercus mongolica var. crispula) was possibly susceptible to O3 on dynamics of immobile elements. Soil nutrients have distinct impacts on retranslocation rate of K, Fe, and P. Principal component analysis revealed that Mn and K can become indices in assessing the O3 and soil effects in both short and long term monitoring of the growth of these tree species. Our findings are essential in further comprehension to nutrient conservation mechanism in the nutrient dynamics of cool-temperate forests.

Effects of elevated O3 and CO2 on the relative contribution of carbohydrates to soil organic matter in an agricultural soil

As labile fraction of soil organic matter, soil carbohydrates are sensitive to environmental changes due to their high turnover rates. The effects of elevated O3 and CO2 on the concentration and composition of soil carbohydrates in agroecosystems have been rarely studied. The present experiment was conducted to investigate the dynamics of the concentration and composition of neutral sugars in soil under the influence of elevated O3 and CO2 with different N application rates (150kgNha−1 and 225kgNha−1). Our results showed that elevated O3 decreased soil carbohydrate accumulation, with the effect being more pronounced with high than with low N application rate. Elevated O3 significantly increased the ratio of (mannose+galactose)/(arabinose+xylose), indicating that elevated O3 promoted the relative contribution of microbe-derived carbohydrates to soil organic matter (SOM). The high N application rate further increased the contribution of microbe-derived carbohydrates to SOM under elevated O3 conditions. However, elevated CO2 had no effect on soil carbohydrate accumulation and little effects on carbohydrate composition in the study soil, regardless of N application rates. The elevated O3-induced effects were not altered by elevated CO2 at the low N application rate, and the change in composition mediated by elevated CO2 was observed only at the high N application rate. Our results suggest that elevated O3 affected soil carbohydrate accumulation and their composition and that the effects on composition were mediated by elevated CO2 and N application rates.

The influence of ozone pollution on CO2, CH4, and N2O emissions from a Chinese subtropical rice–wheat rotation system under free-air O3 exposure

A better understanding of the effects of ozone (O3) on greenhouse gas (GHG) emissions in rotational rice (Oryza sativa L.)–wheat (Triticum aestivum L.) systems is essential for reducing potential GHG emissions in agroecosystems due to the projected increase in O3 concentrations. Rice and wheat were rotationally grown in a free-air O3 enrichment platform, and crop production and N2O, CH4, and CO2 emissions from the soils were investigated as well as the global warming potential (GWP) of the GHGs. Exposure to elevated O3 (50% greater than ambient O3) slightly reduced the total biomass of wheat and significantly decreased that of rice, significantly decreased the root to total biomass ratio of wheat and slightly increased that of rice. Elevated O3 significantly increased the CO2 emission but did not influence the CH4 and N2O emissions in the rice–soil system; however, elevated O3 did not influence the CO2 emission, significantly increased the CH4 emission, and significantly reduced N2O emissions in the root-free soil during the rice season. Elevated O3 increased the CO2 emission and decreased the CH4 and N2O emissions in the wheat–soil system and root-free soil during the wheat season, although the decrease in N2O emission in the wheat–soil system was not significant. The effects of elevated O3 on GHGs emissions and biomass accumulation were related to crop species, plant coverage, and GHG type. Elevated O3 significantly increased the GWP in the rice–soil system and the GWP per unit of rice yield; however, it did not change the GWP in the wheat–soil system or in the root-free soil during the wheat–rice growing period, nor did it change the GWP per unit of wheat yield. Considering the decreases in wheat and rice dry matter, reducing CO2 emissions and planting O3-tolerant crop cultivars during future elevated O3 scenarios, especially during the rice-growing season, should be a primary focus of the research aimed at reducing the GWP and increasing the soil C and N sequestration of rotational rice–wheat cropping systems.

Fungi in the future: interannual variation and effects of atmospheric change on arbuscular mycorrhizal fungal communities.

Understanding the natural dynamics of arbuscular mycorrhizal (AM) fungi and their response to global environmental change is essential for the prediction of future plant growth and ecosystem functions. We investigated the long-term temporal dynamics and effect of elevated atmospheric carbon dioxide (CO2) and ozone (O3) concentrations on AM fungal communities.Molecular methods were used to characterize the AM fungal communities of soybean (Glycine max) grown under elevated and ambient atmospheric concentrations of both CO2 and O3 within a free air concentration enrichment experiment in three growing seasons over 5 yr.Elevated CO2 altered the community composition of AM fungi, increasing the ratio of Glomeraceae to Gigasporaceae. By contrast, no effect of elevated O3 on AM fungal communities was detected. However, the greatest compositional differences detected were between years, suggesting that, at least in the short term, large-scale interannual temporal dynamics are stronger mediators than atmospheric CO2 concentrations of AM fungal communities.We conclude that, although atmospheric change may significantly alter AM fungal communities, this effect may be masked by the influences of natural changes and successional patterns through time. We suggest that changes in carbon availability are important determinants of the community dynamics of AM fungi.

Photosynthetic Responses of Four Urban Tree Species Exposed to Elevated CO&lt;sub&gt;2&lt;/sub&gt; and/or Elevated O&lt;sub&gt;3&lt;/sub&gt;

We compared the differences in photosynthesis of four urban tree species (Ginkgo biloba, Pinus tabulaeformis, Quercus mongolica and Pinus armandii) exposed to long-term elevated CO2(700 ppm) and/or O3(80 ppb) fumigation in (open top chamber) OTC. Our results suggest that elevated CO2alleviated the damaging influence of elevated O3on photosynthesis in the four urban tree species. Both Q. mongolica and P. armandii showed photosynthetic acclimation after long-term treatment under elevated CO2. The combined effect of elevated CO2and O3caused the changes including net photosynthetic rates (Pn), stomatal conductance (gs) and chlorophyll content that were more similar to ambient air (CK) or slightly lower than elevated CO2, indicating that elevated CO2is able to totally or partly alleviate the harmful effects of elevated O3on urban tree species.

Effects of ambient and elevated level of ozone on Brassica campestris L. with special reference to yield and oil quality parameters

Tropospheric ozone (O3) has become a serious threat to growth and yield of important agricultural crops over Asian regions including India. Effect of elevated O3 (ambient+10ppb) was studied on Brassica campestris L. (cv. Sanjukta and Vardan) in open top chambers under natural field conditions. Eight hourly mean ambient O3 concentration varied from 26.3ppb to 69.5ppb during the growth period. Plants under O3 exposure showed reductions in photosynthetic rate, reproductive parameters, yield as well as seed and oil quality. Cultivar Sanjukta showed more reduction in photosynthetic characteristics, reproductive structures and seed and oil quality. However, total yield was more affected in Vardan. Exposure of O3 increased the degree of unsaturation and level of PUFA, ω-6fatty acid, linolenic acid and erucic acid in oil indicating the deterioration of its quality. The study further confirmed that there is a correspondence between O3 induced change in photosynthetic processes, reproductive development and yield and did not find any compensatory response in the final yield.

Elevated O3 reduces the fitness of Bemisia tabaci via enhancement of the SA-dependent defense of the tomato plant

The effect of elevated O3 on tomato plants of three different genotypes (wild-type, a jasmonic acid (JA) defense-enhanced genotype (35S) and a JA-deficient genotype (spr2)) grown in association with the whitefly Bemisia tabaci Gennadius biotype B was examined in the field in open-top chambers. We experimentally tested the hypothesis that elevated O3 tends to reduce the nutrition of tomato plants, and to increase the SA-dependent pathway defenses and the secondary metabolites, and therefore decrease the population fitness of the whitefly. The results show that for all three tomato genotypes, elevated O3 reduced the soluble sugars and free amino acids, increased the phenylalanine ammonia-lyase enzyme activity and the accumulated salicylic acid (SA), and up-regulated the pathogenesis-related protein (PR1), which is commonly considered to be the whitefly-resistance gene product involved in SA-dependent defense. Elevated O3 did not affect the JA level in any of the three plant genotypes, but it increased the levels of some secondary metabolites, including total phenolics and condensed tannins. Elevated O3 prolonged the developmental time of whiteflies fed on the three plant genotypes, and it also reduced the fecundity and the intrinsic rate of increase of whiteflies fed on either the 35S or the wild-type plants. These results suggest that elevated O3 reduces the nutrition of tomato plants and enhances their SA content, relative PR mRNA expression and secondary metabolism, resulting in decreased fitness of whiteflies on these tomato plants.