O3 Uptake Research Articles

Ozone-induced change in the relationship between stomatal conductance and net photosynthetic rate is a factor determining cumulative stomatal ozone uptake by Fagus crenata seedlings

The change in the relationship between the net photosynthetic rate and stomatal conductance by exposure to ozone is a factor determining cumulative ozone uptake via stomata in Fagus crenata seedlings. Stomatal ozone (O3) uptake, one of the key factors determining the impact of O3 on trees, has been estimated using a coupled model of photosynthesis and stomatal conductance. Exposure to O3 increases or decreases stomatal conductance without changes in the net photosynthetic rate and maximum carboxylation velocity (Vcmax). Such changes in the coupling between photosynthesis and stomatal conductance may be important factors determining stomatal O3 uptake. We aimed to investigate impacts of O3-induced changes in stomatal conductance on the cumulative stomatal O3 uptake of Fagus crenata seedlings grown in three levels of gas treatments: charcoal-filtered air or O3 at 1.0- or 1.5-times the ambient concentration (CF, 1.0 × O3, and 1.5 × O3 treatments, respectively). In July, an O3-induced remarkable reduction in stomatal conductance compared to the net photosynthetic rate (a reduction in the intercept of the Ball–Berry–Leuning model) was observed. Moreover, the exposure to O3 significantly reduced Vcmax during the growing season. Model simulations showed that O3-induced reductions in the photosynthetic capacity, i.e., Vcmax, hardly affect stomatal conductance and cumulative O3 uptake during the growing season. Conversely, the O3-induced remarkable reduction in stomatal conductance compared to net photosynthetic rate in July limited the cumulative stomatal O3 uptake during the growing season by 6% and 10% in the 1.0 × O3 and 1.5 × O3 treatments, respectively. Therefore, we should consider O3-induced changes in the coupling between the net photosynthetic rate and stomatal conductance to calculate the cumulative O3 uptake via stomata of F. crenata using the coupled model.

Mitigation mechanism of ozone-induced reduction in net photosynthesis of Bangladeshi wheat under soil salinity stress

To clarify the combined effects of O3 and soil salinity on net photosynthetic rate, stomatal conductance, and radical scavenging system of Bangladeshi spring wheat cv. BAW1059, plants were grown in two soil salinity levels (irrigated with 0 and 150 mM NaCl solutions) and exposed to three O3 concentrations [charcoal-filtered air (CF), 1.0-fold the ambient O3 concentration (1.0×O3), and 1.5-fold the ambient O3 concentration (1.5×O3)]. The soil salinity mitigated adverse effects of O3 on net photosynthesis in the 7th and flag leaves. The soil salinity did not induce stomatal closure, indicating no limitation of stomatal O3 uptake. The activities of ascorbate peroxidase and catalase were stimulated by the soil salinity in the 7th and flag leaves, especially under 1.5×O3 concentration. In the flag leaf, the soil salinity induced a significant increase in dehydroascorbate reductase activity and ascorbate concentration. These results suggest that the soil salinity activated detoxification capacity related to mitigation of O3 damage on net photosynthesis in both 7th and flag leaves, while the activated enzymes and antioxidants were different between the leaves.

Relative importance of gas uptake on aerosol and ground surfaces characterized by equivalent uptake coefficients

Abstract. Quantifying the relative importance of gas uptake on the ground and aerosol surfaces helps to determine which processes should be included in atmospheric chemistry models. Gas uptake by aerosols is often characterized by an effective uptake coefficient (γeff), whereas gas uptake on the ground is usually described by a deposition velocity (Vd). For efficient comparison, we introduce an equivalent uptake coefficient (γeqv) at which the uptake flux of aerosols would equal that on the ground surface. If γeff is similar to or larger than γeqv, aerosol uptake is important and should be included in atmospheric models. In this study, we compare uptake fluxes in the planetary boundary layer (PBL) for different reactive trace gases (O3, NO2, SO2, N2O5, HNO3 and H2O2), aerosol types (mineral dust, soot, organic aerosol and sea salt aerosol), environments (urban areas, agricultural land, the Amazon forest and water bodies), seasons and mixing heights. For all investigated gases, γeqv ranges from magnitudes of 10−6–10−4 in polluted urban environments to 10−4–10−1 under pristine forest conditions. In urban areas, aerosol uptake is relevant for all species (γeff≥γeqv) and should be considered in models. On the contrary, contributions of aerosol uptakes in the Amazon forest are minor compared with the dry deposition. The phase state of aerosols could be one of the crucial factors influencing the uptake rates. Current models tend to underestimate the O3 uptake on liquid organic aerosols which can be important, especially over regions with γeff≥γeqv. H2O2 uptakes on a variety of aerosols are yet to be measured under laboratory conditions and evaluated. Given the fact that most models have considered the uptakes of these species on the ground surface, we suggest also considering the following processes in atmospheric models: N2O5 uptake by all types of aerosols, HNO3 and SO2 uptake by mineral dust and sea salt aerosols, H2O2 uptake by mineral dust, NO2 uptakes by sea salt aerosols and O3 uptake by liquid organic aerosols.

Leaf Traits That Contribute to Differential Ozone Response in Ozone-Tolerant and Sensitive Soybean Genotypes.

Ozone (O3) is a phytotoxic air pollutant that limits crop productivity. Breeding efforts to improve yield under elevated O3 conditions will benefit from understanding the mechanisms that contribute to O3 tolerance. In this study, leaf gas exchange and antioxidant metabolites were compared in soybean genotypes (Glycine max (L.) Merr) differing in ozone sensitivity. Mandarin (Ottawa) (O3-sensitive) and Fiskeby III (O3-tolerant) plants grown under charcoal-filtered (CF) air conditions for three weeks were exposed for five days to either CF conditions or 70 ppb O3 in continuously stirred tank reactors (CSTRs) in a greenhouse. In the CF controls, stomatal conductance was approximately 36% lower for Fiskeby III relative to Mandarin (Ottawa) while the two genotypes exhibited similar levels of photosynthesis. Ozone exposure induced significant foliar injury on leaves of Mandarin (Ottawa) associated with declines in both stomatal conductance (by 77%) and photosynthesis (by 38%). In contrast, O3 exposure resulted in minimal foliar injury on leaves of Fiskeby III with only a small decline in photosynthesis (by 5%), and a further decline in stomatal conductance (by 30%). There was a general trend towards higher ascorbic acid content in leaves of Fiskeby III than in Mandarin (Ottawa) regardless of treatment. The results confirm Fiskeby III to be an O3-tolerant genotype and suggest that reduced stomatal conductance contributes to the observed O3 tolerance through limiting O3 uptake by the plant. Reduced stomatal conductance was associated with enhanced water-use efficiency, providing a potential link between O3 tolerance and drought tolerance.

Evaluation of O3 Effects on Cumulative Photosynthetic CO2 Uptake in Seedlings of Four Japanese Deciduous Broad-Leaved Forest Tree Species Based on Stomatal O3 Uptake

The current level of tropospheric ozone (O3) is expected to reduce the net primary production of forest trees. Here, we evaluated the negative effects of O3 on the photosynthetic CO2 uptake of Japanese forest trees species based on their cumulative stomatal O3 uptake, defined as the phytotoxic O3 dose (POD). Seedlings of four representative Japanese deciduous broad-leaved forest tree species (Fagus crenata, Quercus serrata, Quercus mongolica var. crispula and Betula platyphylla var. japonica) were exposed to different O3 concentrations in open-top chambers for two growing seasons. The photosynthesis–light response curves (A-light curves) and stomatal conductance were measured to estimate the leaf-level cumulative photosynthetic CO2 uptake (ΣPn_est) and POD, respectively. The whole-plant-level ΣPn_est were highly correlated with the whole-plant dry mass increments over the two growing seasons. Because whole-plant growth is largely determined by the amount of leaf area per plant and net photosynthetic rate per leaf area, this result suggests that leaf-level ΣPn_est, which was estimated from the monthly A-light curves and hourly PPFD, could reflect the cumulative photosynthetic CO2 uptake of the seedlings per unit leaf area. Although the O3-induced reductions in the leaf-level ΣPn_est were well explained by POD in all four tree species, species-specific responses of leaf-level ΣPn_est to POD were observed. In addition, the flux threshold appropriate for the linear regression of the responses of relative leaf-level ΣPn_est to POD was also species-specific. Therefore, species-specific responses of cumulative photosynthetic CO2 uptake to POD could be used to accurately evaluate O3 impact on the net primary production of deciduous broad-leaved trees.

Observing Severe Drought Influences on Ozone Air Pollution in California.

Drought conditions affect ozone air quality, potentially altering multiple terms in the O3 mass balance equation. Here, we present a multiyear observational analysis using data collected before, during, and after the record-breaking California drought (2011-2015) at the O3-polluted locations of Fresno and Bakersfield near the Sierra Nevada foothills. We separately assess drought influences on O3 chemical production ( PO3) from O3 concentration. We show that isoprene concentrations, which are a source of O3-forming organic reactivity, were relatively insensitive to early drought conditions but decreased by more than 50% during the most severe drought years (2014-2015), with recovery a function of location. We find drought-isoprene effects are temperature-dependent, even after accounting for changes in leaf area, consistent with laboratory studies but not previously observed at landscape scales with atmospheric observations. Drought-driven decreases in organic reactivity are contemporaneous with a change in dominant oxidation mechanism, with PO3 becoming more NO x-suppressed, leading to a decrease in PO3 of ∼20%. We infer reductions in atmospheric O3 loss of ∼15% during the most severe drought period, consistent with past observations of decreases in O3 uptake by plants. We consider drought-related trends in O3 variability on synoptic time scales by analyzing statistics of multiday high-O3 events. We discuss implications for regulating O3 air pollution in California and other locations under more prevalent drought conditions.

Ozone effects on plants in natural ecosystems.

Tropospheric ozone (O3 ) is an important stressor in natural ecosystems, with well-documented impacts on soils, biota and ecological processes. The effects of O3 on individual plants and processes scale up through the ecosystem through effects on carbon, nutrient and hydrologic dynamics. Ozone effects on individual species and their associated microflora and fauna cascade through the ecosystem to the landscape level. Systematic injury surveys demonstrate that foliar injury occurs on sensitive species throughout the globe. However, deleterious impacts on plant carbon, water and nutrient balance can also occur without visible injury. Because sensitivity to O3 may follow coarse physiognomic plant classes (in general, herbaceous crops are more sensitive than deciduous woody plants, grasses and conifers), the task still remains to use stomatal O3 uptake to assess class and species' sensitivity. Investigations of the radial growth of mature trees, in combination with data from many controlled studies with seedlings, suggest that ambient O3 reduces growth of mature trees in some locations. Models based on tree physiology and forest stand dynamics suggest that modest effects of O3 on growth may accumulate over time, other stresses (prolonged drought, excess nitrogen deposition) may exacerbate the direct effects of O3 on tree growth, and competitive interactions among species may be altered. Ozone exposure over decades may be altering the species composition of forests currently, and as fossil fuel combustion products generate more O3 than deteriorates in the atmosphere, into the future as well.

Role of supplemental UV-B in changing the level of ozone toxicity in two cultivars of sunflower: growth, seed yield and oil quality.

Ultraviolet-B radiation (UV-B) is inherent part of solar spectrum and tropospheric ozone (O3) is a potent secondary air pollutant. Therefore the present study was conducted to evaluate the responses of Helianthus annuus L. cvs DRSF 108 and Sungold (sunflower) to supplemental UV-B (sUV-B; ambient + 7.2 kJ m-2 d-1) and elevated ozone (O3; ambient + 10 ppb), given singly and in combination under field conditions using open-top chambers. The individual and interactive effects of O3 and sUV-B induced varying changes in both the cultivars of sunflower ranging from ultrastructural variations to growth, biomass, yield and oil composition. Reduction in leaf area of Sungold acted as a protective feature which minimized the perception of sUV-B as well as uptake of O3 thus led to lesser carbon loss compared to DRSF 108. Number- and weight of heads plant-1 decreased although more in Sungold with decline of oil content. Both the stresses when given singly and combination induced rancidification of oil and thus made the oil less suitable for human consumption.

Investigation of ozone deposition to vegetation under warm and dry conditions near the Eastern Mediterranean coast

Dry deposition of ozone (O3) to vegetation is an important removal pathway for tropospheric O3, while O3 uptake through plant stomata negatively affects vegetation and leads to climate change. Both processes are controlled by vegetation characteristics and ambient conditions via complex mechanisms. Recent studies have revealed that these processes can be fundamentally impacted by coastal effects, and by dry and warm conditions in ways that have not been fully characterized, largely due to lack of measurements under such conditions. Hence, we hypothesized that measuring dry deposition of O3 to vegetation along a sharp spatial climate gradient, and at different distances from the coast, can offer new insights into the characterization of these effects on O3 deposition to vegetation and stomatal uptake, providing important information for afforestation management and for climate and air-quality model improvement. To address these hypotheses, several measurement campaigns were performed at different sites, including pine, oak, and mixed Mediterranean forests, at distances of 20–59 km from the Eastern Mediterranean coast, under semiarid, Mediterranean and humid Mediterranean climate conditions. The eddy covariance technique was used to quantify vertical O3 flux (Ftot) and its partitioning to stomatal flux (Fst) and non-stomatal flux (Fns). Whereas Fst tended to peak around noon under humid Mediterranean and Mediterranean conditions in summer, it was strongly limited by drought under semiarid conditions from spring to early winter, with minimum average Fst/Ftot of 8–11% during the summer. Fns in the area was predominantly controlled by relative humidity (RH), whereas increasing Fns with RH for RH < 70% indicated enhancement of Fns by aerosols, via surface wetness stimulation. At night, efficient turbulence due to sea and land breezes, together with increased RH, resulted in strong enhancement of Ftot. Extreme dry surface events, some induced by dry intrusion from the upper troposphere, resulted in positive Fns events.

On the effect of upwind emission controls on ozone in Sequoia National Park

Abstract. Ozone (O3) air pollution in Sequoia National Park (SNP) is among the worst of any national park in the US. SNP is located on the western slope of the Sierra Nevada Mountains downwind of the San Joaquin Valley (SJV), which is home to numerous cities ranked in the top 10 most O3-polluted in the US. Here, we investigate the influence of emission controls in the SJV on O3 concentrations in SNP over a 12-year time period (2001–2012). We show that the export of nitrogen oxides (NOx) from the SJV has played a larger role in driving high O3 in SNP than transport of O3. As a result, O3 in SNP has been more responsive to NOx emission reductions than in the upwind SJV city of Visalia, and O3 concentrations have declined faster at a higher-elevation monitoring station in SNP than at a low-elevation site nearer to the SJV. We report O3 trends by various concentration metrics but do so separately for when environmental conditions are conducive to plant O3 uptake and for when high O3 is most common, which are time periods that occur at different times of day and year. We find that precursor emission controls have been less effective at reducing O3 concentrations in SNP in springtime, which is when plant O3 uptake in Sierra Nevada forests has been previously measured to be greatest. We discuss the implications of regulatory focus on high O3 days in SJV cities for O3 concentration trends and ecosystem impacts in SNP.

Synthetic ozone deposition and stomatal uptake at flux tower sites

Abstract. We develop and evaluate a method to estimate O3 deposition and stomatal O3 uptake across networks of eddy covariance flux tower sites where O3 concentrations and O3 fluxes have not been measured. The method combines standard micrometeorological flux measurements, which constrain O3 deposition velocity and stomatal conductance, with a gridded dataset of observed surface O3 concentrations. Measurement errors are propagated through all calculations to quantify O3 flux uncertainties. We evaluate the method at three sites with O3 flux measurements: Harvard Forest, Blodgett Forest, and Hyytiälä Forest. The method reproduces 83 % or more of the variability in daily stomatal uptake at these sites with modest mean bias (21 % or less). At least 95 % of daily average values agree with measurements within a factor of 2 and, according to the error analysis, the residual differences from measured O3 fluxes are consistent with the uncertainty in the underlying measurements. The product, called synthetic O3 flux or SynFlux, includes 43 FLUXNET sites in the United States and 60 sites in Europe, totaling 926 site years of data. This dataset, which is now public, dramatically expands the number and types of sites where O3 fluxes can be used for ecosystem impact studies and evaluation of air quality and climate models. Across these sites, the mean stomatal conductance and O3 deposition velocity is 0.03–1.0 cm s−1. The stomatal O3 flux during the growing season (typically April–September) is 0.5–11.0 nmol O3 m−2 s−1 with a mean of 4.5 nmol O3 m−2 s−1 and the largest fluxes generally occur where stomatal conductance is high, rather than where O3 concentrations are high. The conductance differences across sites can be explained by atmospheric humidity, soil moisture, vegetation type, irrigation, and land management. These stomatal fluxes suggest that ambient O3 degrades biomass production and CO2 sequestration by 20 %–24 % at crop sites, 6 %–29 % at deciduous broadleaf forests, and 4 %–20 % at evergreen needleleaf forests in the United States and Europe.

The sap flow-based assessment of atmospheric trace gas uptake by three forest types in subtropical China on different timescales.

Assessing the uptake of trace gases by forests contributes to understanding the mechanisms of gas exchange between vegetation and the atmosphere and to evaluating the potential risk of these pollutant gases to forests. In this study, the multi-timescale characteristics of the stomatal uptake of NO, NO2, SO2 and O3 by Schima superba, Eucalyptus citriodora and Acacia auriculiformis were investigated by continuous sap flow measurements for a 3-year period. The peak canopy stomatal conductance (GC) for these three species appeared between 9:00 and 12:00, which was jointly regulated by the vapour pressure deficit (VPD) and photosynthetically active radiation (PAR). Additionally, annual and seasonal variations in the stomatal uptake of trace gases for these three tree species suggested that there was a combination effect between canopy stomatal conductance and ambient concentration on the uptake of trace gases. Furthermore, the result demonstrated that the trace gas absorption capacities among these three forest types followed the order of S. superba > E. citriodora > A. auriculiformis. The findings of this study have theoretical significance and application value in assessing air purification and the risk of harm to forests in Southern China.

Ozone Uptake by Clay Dusts under Environmental Conditions

Clay is the most emitted type of dust in the atmosphere and offers a large surface for heterogeneous interactions with atmospheric compounds. In this study, we focus on the uptake of ozone (O3) by montmorillonite and kaolinite dust samples at atmospheric pressure in a coated-wall flow tube reactor. The influence of relevant environmental parameters, such as O3 concentration, relative humidity, and temperature, is determined. A mechanism for O3 interaction with the surface sites of clays is described, and atmospheric implications are discussed. Although the impact of O3 uptake by fresh clay dust seems limited in the atmosphere, this work highlights the need to consider relevant and thoroughly defined uptake coefficients in models. Moreover, the presence of a pressure-dependence in the mechanism of O3 uptake by dust suggested in this work helps reconciling measurements made at atmospheric pressure with those performed at low pressure in Knudsen cells.

Geocatalytic Uptake of Ozone onto Natural Mineral Dust

Beyond tailored and synthetic catalysts sought out for ozone decomposition, mineral dusts provide naturally mixed metal oxide materials. The steady-state uptake of O3 evidenced across a wide concentration range signifies the catalytic decomposition of O3. The geocatalytic properties of such natural mineral dust open up new perspectives in atmospheric chemistry and catalytic processes.

Observational evidence for direct uptake of ozone in China by Asian dust in springtime

AbstractWhile there is ample observational evidence for ozone uptake by Sahara dust, whether Asian dust exerts a similar effect on ozone has not been well-established in the literature due in part to limited observations. In this study we investigate the impacts of Asian dust on surface ozone (O3) over northern China on a daily scale using observations from recently established air quality monitoring network during spring (March, April, May; MAM) 2015–2017, the peak season of Asian dust outbreaks. Dust days and non-dust days are selected based on the distribution of the coarse-mode particulate matter mass concentrations (PMcoarse) and then paired based on similar temperature (T) and relative humidity (RH) so as to minimize the effect of different local meteorological conditions on ozone. The majority of the dust days shows lower O3 compared to non-dust days both temporally and spatially. The regional average of seasonal-mean O3 differences between dust days and their reference non-day days are −10.1 ppbv (−24.6%), −2.4 ppbv (−4.8%) and −5.4 ppbv (−14.3%) over the Taklimakan Desert (TD), the Gobi Desert (GD) and North China (NC), respectively. The decrease of ozone tends to increase with increasing PMcoarse, although the use of PMcoarse to indicate dust is subject to uncertainty. Nitrogen dioxide (NO2), sulfate dioxide (SO2), and carbon monoxide (CO) appear to be higher during dust days outside dust source regions, possibly because of the compounding effects of large anthropogenic emissions over this region. In spite of higher or similar levels of primary pollutants, surface ozone concentrations are still lower during dust days over TD, GD and NC, supporting the mechanism of dust direct uptake of O3.

Ozone risk assessment is affected by nutrient availability: Evidence from a simulation experiment under free air controlled exposure (FACE)

Assessing ozone (O3) risk to vegetation is crucial for informing policy making. Soil nitrogen (N) and phosphorus (P) availability could change stomatal conductance which is the main driver of O3 uptake into a leaf. In addition, the availability of N and P could influence photosynthesis and growth. We thus postulated that the sensitivity of plants to O3 may be changed by the levels of N and P in the soil. In this study, a sensitive poplar clone (Oxford) was subject to two N levels (N0, 0 kg N ha−1; N80, 80 kg N ha−1), three P levels (P0, 0 kg P ha−1; P40, 40 kg P ha−1; P80, 80 kg P ha−1) and three levels of O3 exposure (ambient concentration, AA; 1.5 × AA; 2.0 × AA) for a whole growing season in an O3 free air controlled exposure (FACE) facility. Flux-based (POD0 to 6) and exposure-based (W126 and AOT40) dose-response relationships were fitted and critical levels (CLs) were estimated for a 5% decrease of total annual biomass. It was found that N and P availability modified the dose-response relationships of biomass responses to O3. Overall, the N supply decreased the O3 CLs i.e. increased the sensitivity of poplar to O3. Phosphorus alleviated the O3-caused biomass loss and increased the CL. However, such mitigation effects of P were found only in low N and not in high N conditions. In each nutritional treatment, similar performance was found between flux-based and exposure-based indices. However, the flux-based approach was superior, as compared to exposure indices, to explain the biomass reduction when all nutritional treatments were pooled together. The best O3 metric for risk assessments was POD4, with 4.6 mmol m−2 POD4 as a suitable CL for Oxford poplars grown under various soil N and P conditions.

鼎湖山南亚热带天然针阔叶混交林臭氧吸收特征

PDF HTML阅读 XML下载 导出引用 引用提醒 鼎湖山南亚热带天然针阔叶混交林臭氧吸收特征 DOI: 10.5846/stxb201709201687 作者: 作者单位: 华南植物园,华南植物园 作者简介: 通讯作者: 中图分类号: 基金项目: 广东省自然科学基金（2014A030313746）；国家自然科学基金项目（31670453） Ozone uptake by the dominant canopy tree species in a natural mixed conifer-broadleaf forest in Dinghushan, Guangdong Province, south China Author: Affiliation: South China Botanical Garden,South China Botanical Garden Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:针阔叶混交林是我国南亚热带针叶林向地带性常绿阔叶林演替的中间林分类型，为我国南亚地区主要森林类型，发挥着重要的生态系统服务功能。基于树干液流技术和对臭氧浓度的连续监测，评价该森林类型的臭氧吸收特征和能力有着重要的环境生态学意义。对鼎湖山天然针阔叶混交林优势种马尾松（Pinus manssoniana）、锥栗（Castanopsis chinensis）、木荷（Schima superba）和华润楠（Machilus chinensis）在自然环境条件下的臭氧吸收能力进行了分析研究。结果表明：在日尺度上，4个优势树种的冠层气孔对臭氧导度（GO3）和臭氧吸收通量（FO3）均呈单峰型曲线，其最大值的时间在干季（10月至竖年3月）比湿季（4月至9月）滞后；季节尺度上，臭氧浓度在湿季达到最大值48.94 nL/L，湿季GO3、FO3和年臭氧吸收累积量（accumulative stomatal O3 flux，AFst）均显著高于干季（P < 0.01），华润楠的臭氧吸收能力最强，在干季和湿季可分别达1.11 nmol m-2 s-1和1.71 nmol m-2 s-1。随着水汽压亏缺（VPD）增大，优势种GO3降低。光合有效辐射（PAR）超过1500 umol m-2 s-1时，优势树种GO3和FO3呈下降趋势。针阔叶混交林的年臭氧吸收累积量超过了保护森林树木所采用的临界阈值，可认为鼎湖山针阔叶混交林受臭氧危害的潜在风险较高。 Abstract:We determined ozone (O3) uptake rates of the dominant tree species (Pinus manssoniana, Castanopsis chinensis, Schima superba, and Machilus chinensis) in a natural mixed conifer-broadleaf forest based on sap flow measurements and environmental monitoring. On a diurnal scale, the ozone uptake flux (FO3) by the dominant tree species had a unimodal pattern, and that the maximum flux appeared earlier in the wet season (April-September) than in the dry season (October-March). Compared to the wet season, the time of the maximum flux in the dry season was delayed. Seasonally, the maximum O3 concentration occurred in the wet season (48.94 nL/L). Canopy stomatal conductance for O3 (GO3), FO3, and annual accumulative stomatal O3 uptake (AFst) in the wet season were significantly higher than in the dry season (P < 0.01). Machilus chinensis had the highest O3 uptake capacity among the four species considered. The maximum FO3 was 1.11 nmol m-2 s-1 in the dry season and 1.71 nmol m-2 s-1 in the wet season. GO3 decreased with increasing vapour pressure deficit (VPD) in all the studied species. At photosynthetically active radiation (PAR) > 1500 umol m-2 s-1, GO3 and FO3 for all species declined at higher PAR. Annual AFst exceeded the threshold that could be tolerated by forest trees, suggesting a potential O3 risk for mixed conifer-broadleaf forest in Dinghushan. 参考文献 相似文献 引证文献

Exposure- and flux-based assessment of ozone risk to sugarcane plants

Ozone (O3) is a toxic oxidative air pollutant, with significant detrimental effects on crops. Sugarcane (Saccharum spp.) is an important crop with no O3 risk assessment performed so far. This study aimed to assess O3 risk to sugarcane plants by using exposure-based indices (AOT40 and W126) based on O3 concentrations in the air, and the flux-based index (PODy, where y is a threshold of uptake) that considers leaf O3 uptake and the influence of environmental conditions on stomatal conductance (gsto). Two sugarcane genotypes (IACSP94-2094 and IACSP95-5000) were subjected to a 90-day Free-Air Controlled Experiment (FACE) exposure at three levels of O3 concentrations: ambient (Amb); Amb x1.2; and Amb x1.4. Total above-ground biomass (AGB), stalk biomass (SB) and leaf biomass (LB) were evaluated and the potential biomass production in a clean air was estimated by assuming a theoretical clean atmosphere at 10 ppb as 24 h O3 average. The Jarvis-type multiplicative algorithm was used to parametrize gsto including environmental factors i.e. air temperature, light intensity, air vapor pressure deficit, and minimum night-time temperature. Ozone exposure caused a negative impact on AGB, SB and LB. The O3 sensitivity of sugarcane may be related to its high gsto (∼535 mmol H2O m−2 s−1). As sugarcane is adapted to hot climate conditions, gsto was restricted when the current minimum air temperature (Tmin) was below ∼14 °C and the minimum night-time air temperature of the previous day (Tnmin) was below ∼7.5 °C. The flux-based index (PODy) performed better than the exposure-based indices in estimating O3 effect on biomass losses. We recommend a y threshold of 2 nmol m−2 s−1 to incorporate O3 effects on both AGB and SB and 1 nmol m−2 s−1 on LB. In order not to exceed 4% reduction in the growth of these two sugarcane genotypes, we recommend the following critical levels: 1.09 and 1.04 mmol m−2 POD2 for AGB, 0.91 and 0.96 mmol m−2 POD2 for SB, and 3.00 and 2.36 mmol m−2 POD1 for LB of IACSP95-5000 and IACSP94-2094, respectively.

Ozone Decomposition on Kaolinite as a Function of Monoterpene Exposure and Relative Humidity

Atmospheric processing of mineral aerosol by trace gases results in the formation of surface-adsorbed products that have the capacity to alter the chemical and physical properties of these airborne particulates. To investigate one potential impact of aerosol processing by biogenic volatile organic compounds (BVOCs), we investigated the heterogeneous decomposition of ozone on pure and monoterpene-processed kaolinite. We used a laminar flow reactor to measure O3 reactive uptake coefficients on kaolinite-coated tubes as a function of relative humidity, O3 concentration, and pre-exposure to gaseous limonene and α-pinene. At 26% RH, kaolinite has a near equivalent of a monolayer of adsorbed water, and the ozone steady-state uptake coefficient was γav = 2.9 × 10–9 assuming the BET surface area. Pre-exposing kaolinite to limonene and α-pinene increased O3 uptake coefficients by nearly 2 orders of magnitude to 2.1 × 10–7 and 2.5 × 10–7, respectively. At all humidities studied (10–50% RH), O3 uptake was at least 1...

Modeling ozone uptake by urban and peri-urban forest: a case study in the Metropolitan City of Rome.

Urban and peri-urban forests are green infrastructures (GI) that play a substantial role in delivering ecosystem services such as the amelioration of air quality by the removal of air pollutants, among which is ozone (O3), which is the most harmful pollutant in Mediterranean metropolitan areas. Models may provide a reliable estimate of gas exchanges between vegetation and atmosphere and are thus a powerful tool to quantify and compare O3 removal in different contexts. The present study modeled the O3 stomatal uptake at canopy level of an urban and a peri-urban forest in the Metropolitan City of Rome in two different years. Results show different rates of O3 fluxes between the two forests, due to different exposure to the pollutant, management practice effects on forest structure and functionality, and environmental conditions, namely, different stressors affecting the gas exchange rates of the two GIs. The periodic components of the time series calculated by means of the spectral analysis show that seasonal variation of modeled canopy transpiration is driven by precipitation in peri-urban forests, whereas in the urban forest seasonal variations are driven by vapor pressure deficit of ambient air. Moreover, in the urban forest high water availability during summer months, owing to irrigation practice, leads to an increase in O3 uptake, thus suggesting that irrigation may enhance air phytoremediation in urban areas.