Stomatal O3 Flux Research Articles

Examining indicators and methods for quantifying ozone exposure to vegetation

The U.S. National Park Service uses W126 to assess critical levels of ozone (O3) exposure to sensitive plant species, whereas the scientific community considers the stomatal flux-based metric, phytotoxic O3 dose (POD), more relevant in foliar risk evaluation. This study found a decreasing trend of 0.15 ppm-hrs/yr (p = 0.049) in W126 at a Yellowstone National Park monitoring site during 1997–2021 and no trend at a Grand Teton National Park site over 2012–2021 but no trends at both sites in POD calculated following the United Nations Economic Commission for Europe Convention on Long-range Transboundary Air Pollution (CLRTAP) (2017). To evaluate the CLRTAP (2017) method, 2019 summer POD was calculated for comparison using the Big-leaf model and was found 20%–100% less than the CLRTAP (2017)-calculated leaf-level one already, let alone compared to the latter scaled up to canopy-level, owing to the much smaller stomatal O3 flux (SOF) estimates under most conditions. Further analysis revealed exceptions where larger SOF values (>0.02 mmol/m2/hr), obtained from using the Big-leaf model with measured sensible heat and water vapor flux included in input, were not captured by the CLRTAP (2017) method and the Big-leaf model with input of regular meteorological variables only. Those large SOF values resulted under cooler, less windy, more humid, and cloudier conditions, when the approximate water vapor concentration difference between the ambient and leaf saturation level was found <1 mol/m3. A multivariate function was developed, through machine learning, by regressing SOF on air temperature, wind speed, relative humidity, phytosynthetically active radiation, and O3 concentration. Its testing and evaluation demonstrated improved estimates of the large variability in SOF. This new parameterization showed promising capability of assessing critical levels of O3 exposure in park management, and it could be further improved with long-term flux measurement data becoming available and evapotranspiration better represented.

Influence of Ozone and Drought on Tree Growth under Field Conditions in a 22 Year Time Series

Studying the effect of surface ozone (O3) and water stress on tree growth is important for planning sustainable forest management and forest ecology. In the present study, a 22-year long time series (1998–2019) on basal area increment (BAI) and fructification severity of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H.Karst.) at five forest sites in Western Germany (Rhineland Palatinate) was investigated to evaluate how it correlates with drought and stomatal O3 fluxes (PODY) with an hourly threshold of uptake (Y) to represent the detoxification capacity of trees (POD1, with Y = 1 nmol O3 m−2 s−1). Between 1998 and 2019, POD1 declined over time by on average 0.31 mmol m−2 year−1. The BAI showed no significant trend at all sites, except in Leisel where a slight decline was observed over time (−0.37 cm2 per year, p &lt; 0.05). A random forest analysis showed that the soil water content and daytime O3 mean concentration were the best predictors of BAI at all sites. The highest mean score of fructification was observed during the dry years, while low level or no fructification was observed in most humid years. Combined effects of drought and O3 pollution mostly influence tree growth decline for European beech and Norway spruce.

The Influence of Ozone on Net Ecosystem Production of a Ryegrass–Clover Mixture under Field Conditions

In order to understand the effect of phytotoxic tropospheric ozone (O3) on terrestrial vegetation, we quantified the impact of current O3 concentration ([O3]) on net ecosystem production (NEP) when compared to the conditions of the pre-industrial era. We compared and tested linear mixed-effects models based on [O3] and stomatal O3 flux (Fsto). The managed ryegrass–clover (Lolium perenne and Trifolium pratense) mixture was grown on arable land in the Czech Republic, Central Europe. Values of [O3] and Fsto were measured and calculated based on resistance analogy, respectively, while NEP was calculated from eddy covariance CO2 fluxes. We found the Fsto-based model more precise when compared to measured NEP. High Fsto was found even at low [O3], while broad summer maximum of [O3] was not necessarily followed by significant NEP decline, due to low soil water content leading to a low stomatal conductivity and Fsto. Comparing to low pre-industrial O3 conditions, current levels of O3 resulted in the reduction of cumulative NEP over the entire growing season, up to 29.7 and 13.5% when the [O3]-based and Fsto-based model was applied, respectively. During the growing season, an O3-induced reduction of NEP ranged between 13.1% in May and 26.2% in July when compared to pre-industrial Fsto levels. Looking to the future, high [O3] and Fsto may lead to the reduction of current NEP by approximately 13.3% on average during the growing season, but may increase by up to 61–86.6% in autumn, indicating further O3-induced acceleration of the senescence. These findings indicate the importance of Fsto and its inclusion into the models estimating O3 effects on terrestrial vegetation. The interaction between environmental factors and stomatal conductance is therefore discussed in detail.

Assessment of ozone risk to Central European forests: Time series indicates perennial exceedance of ozone critical levels

In this study, the stomatal ozone (O3) fluxes were investigated at five low-elevation forest sites in Western Germany (Rhineland Palatinate) over the time period 1998–2019. The Phytotoxic Ozone Dose with an hourly threshold of uptake (Y), to represent the detoxification capacity of trees (POD1 in mmol m−2 per leaf area, with Y = 1 nmol O3 m−2 s−1), and the number of exceedances of the O3 critical level of 5.2 mmol O3 m−2 per leaf area for European beech and 9.2 mmol O3 m−2 per leaf area for Norway spruce were calculated by using the DO3SE model. A Principal Component Analysis revealed strong correlations between daily O3 concentrations, daytime O3 (for hours with global radiation exceeding 50 W m−2), POD1, global radiation, vapor pressure deficit and air temperature. Moreover, a significant correlation was obtained between POD1 and soil water content (SWC) at all sites (r = 0.51–0.74). The Random Forests Analysis confirmed that the SWC is the most important predictor of stomatal O3 fluxes. The soil water supply is very important for POD1 estimation, because drought decreases stomatal conductance, leading to a reduction of transpiration, as well as to lower O3 uptake through stomata. Between 1998 and 2019, the drier and warmer climate induced a soil drought (on average, SWC - 0.15 % per year) leading to lower stomatal O3 uptake by forests (- 0.36 mmol O3 m−2 per year). Hence, during growing seasons with sufficient water supply and often lower O3 levels compared to hot and dry periods, forests are at higher O3 risk than during hot and dry periods when the drought stress is more significant than O3 stress despite relatively higher O3 levels. Irrespective of these differences in O3 uptake between relatively cool and humid as compared to relatively hot and dry years in the study region, the Critical Level for O3 was exceeded in late spring/early summer (May/June) during all 22 years. Risk assessment for the protection of European forests, which is urgently needed due to the forests current critical state after several successive years of drought and exceedance of the O3 critical level in large areas of Europe, should therefore become flux-based to account for the inter-twined effects of drought and O3 on the physiology and health of forest trees in the region. For stomatal O3 fluxes estimation, a better soil water and leaf parameterization is needed e.g., by taking into account both O3- and drought-induced effects.

Testing visible ozone injury within a Light Exposed Sampling Site as a proxy for ozone risk assessment for European forests

Biologically meaningful and cost-effective indicators are needed for assessing and monitoring the impacts of tropospheric ozone (O3) on vegetation and are required in Europe by the National Emission Ceilings Directive (2016). However, a clear understanding on the best suited indicators is missing. The MOTTLES (MOnitoring ozone injury for seTTing new critical LEvelS) project set up a new generation network for O3 monitoring in forest plots in order to: 1) estimate the stomatal O3 fluxes (Phytotoxic Ozone Dose above a threshold Y of uptake, PODY); and 2) collect visible foliar O3 injury, both within the forest plot (ITP) and along the Light Exposed Sampling Site (LESS) along the forest edge. Nine forest sites at high O3 risk were selected across Italy over 2017 − 2019 and significant correlations (p < 0.05) were found between the percentage of symptomatic plant species within the LESS, and POD1 (PODY, with Y = 1 nmol O3 m−2 s−1) calculated for mixed forest species (r = 0.53) and with the occurrence and severity of visible foliar O3 injury on the dominant species in the plots (r = 0.65). A generic flux-based critical level for mixed forest species was derived within the LESS and it was recommended using 11 mmol m−2 POD1 as the critical level for forest protection against O3 injury, similar to the critical level obtained in the ITP (12 mmol m−2 POD1). It was concluded that the frequency of symptomatic plant species within a LESS is a suitable and effective plant-response indicator of phytotoxic O3 levels in forest monitoring. LESS is a non-destructive, less complex and less time-consuming approach compared to the ITP for monitoring foliar O3 injury in the long term. Assessing visible foliar O3 injury in the ITP might only underestimate the O3 risk assessment at individual sites. These results are biologically meaningful and useful to monitoring experts and environmental policy makers.

Impact of ground-level ozone on Mediterranean forest ecosystems health

Given the high ozone concentrations observed in the Mediterranean region during summer, it is crucial to extend our knowledge on the potential ozone impacts on forest health with in situ studies, especially to protect typical endemic forests of the Mediterranean basin.This study is focused on ozone measurements and exposures over the Eastern Adriatic coast and on the calculation of different O3 metrics, i.e., accumulated exposure AOT40 (AOT40dir, AOT40ICP, AOT40pheno) and stomatal O3 fluxes with an hourly threshold of uptake (Y) to represent the detoxification capacity of trees (PODY, with Y = 0, 1, 2 nmol O3 m−2 s−1) used for forest protection. Finally, we provide an assessment of the relationships between the forest response indicators and environmental variables.Passive ozone measurements and monitoring of forest health indicators, namely growth and crown defoliation, were performed for Quercus ilex, Quercus pubescens, Pinus halepensis, and Pinus nigra forests. Results showed that, for all the analysed species, ozone levels were close to reached the upper plausibility limits for passive monitoring of air quality at forest sites (100 ppb), with the highest values found on P. halepensis in the summer period. O3 metrics based on exposure were found to be higher in pine plots than in oak plots, while the highest values of uptake-based metrics were found on P. nigra.Regarding relationships between environmental variables and forest-health response indicators, the crown defoliation was significantly correlated with the soil water content at various depth while the tree growth was correlated with the different O3 metrics. The most important predictors affecting tree growth of Q. pubescens and Q. ilex were AOT40pheno and AOT40dir and POD0 for P. nigra.

Temporal Changes in Ozone Concentrations and Their Impact on Vegetation

Tropospheric concentrations of phytotoxic ozone (O3) have undergone a great increase from preindustrial 10–15 ppbv to a present-day concentration of 35–40 ppbv in large parts of the industrialised world due to increased emissions of O3 precursors including NOx, CO, CH4 and volatile organic compounds. The rate of increase in O3 concentration ranges between 1 ppbv per decade in remote locations of the Southern hemisphere and 5 ppbv per decade in the Northern hemisphere, where largest sources of O3 precursors are located. Molecules of O3 penetrating into the leaves through the stomatal apertures trigger the formation of reactive oxygen species, leading thus to the damage of the photosynthetic apparatus. Accordingly, it is assumed, that O3 increase reduces the terrestrial carbon uptake relative to the preindustrial era. Here we summarise the results of previous manipulative experiments in laboratory growth cabinets, field open-top chambers and free-air systems together with O3 flux measurements under natural growth conditions. In particular, we focus on leaf-level physiological responses in trees, variability in stomatal O3 flux and changes in carbon fluxes and biomass production in forest stands. As the results reported in the literature are highly variable, ranging from negligible to severe declines in photosynthetic carbon uptake, we also discuss the possible interactions of O3 with other environmental factors including solar radiation, drought, temperature and nitrogen deposition. Those factors were found to have great potential to modulate stomata openness and O3 fluxes.

Novel ozone flux metrics incorporating the detoxification process in the apoplast: An application to Chinese winter wheat

A modified Ball-Berry-Leuning model of stomatal conductance was applied to data from fully open-air ozone (O3)-enrichment experiments with winter wheat (Triticum aestivum L.). The O3 fluxes reaching both surface of cell wall (Fcw) and plasmalemma (Fpl) were estimated considering apoplastic ascorbate, a major scavenger of O3. The difference (D) between Fcw and Fpl was defined as detoxification capacity of O3 by reaction with ascorbate in the leaf apoplast (ASCapo). The accumulated stomatal O3 flux above D nmol O3 m−2 s−1 (AFstD) and the accumulated Fpl (AFpl) were calculated over the optimal integration period covering the whole reproductive development of wheat, and used to derive O3AFstD yield-response relationships in comparison with PODY (phytotoxic O3 dose above a threshold of Y nmol m−2 s−1) and AOT40 (accumulated O3 dose over a threshold of 40 ppb). There was a good agreement between the observed and modeled values of ASCapo and stomatal conductance. AFstD and AFpl performed better than PODY and AOT40 in terms of R2 and intercept. However, the AFstD metric was more suitable for assessing grain yield loss due to lower sensitivity of the regression slope to variations in the input parameters, compared with AFpl. The average critical level (CL) of four cultivars for 5% grain-yield reduction was 1.53 mmol m−2 using POD6 and 2.81 mmol m−2 using AFstD, with the latter being well above the POD6-derived value for European cultivars (1.3 mmol m−2). The minimum hourly averaged O3 concentration contributed to CLs was below 20 ppb according to AFstD, a value that is lower than that suggested by POD6 (≈27 ppb). O3 flux-response relationships and CLs on the basis of quantified detoxification capacity shall facilitate the understanding of the different degrees of susceptibility to O3 among species or cultivars, and improve the assessments of O3 impacts on plants.

Epidemiological derivation of flux-based critical levels for visible ozone injury in European forests

The European MOTTLES project set-up a new-generation network for ozone (O3) monitoring in 17 plots in France, Italy and Romania. These monitoring stations allowed: (1) estimating the accumulated exposure AOT40 and stomatal O3 fluxes (PODY) with an hourly threshold of uptake (Y) to represent the detoxification capacity of trees (POD1, with Y = 1 nmol O3 m−2 s−1 per leaf area); and (2) collecting data of forest-response indicators, i.e. crown defoliation and visible foliar O3-like injury over the time period 2017–2019. The soil water content was the most important parameter affecting crown defoliation and was a key factor affecting the severity of visible foliar O3-like injury on the dominant tree species in a plot. The soil water content is thus an essential parameter in the PODY estimation, particularly for water-limited environments. An assessment based on stomatal flux-based standard and on real plant symptoms is more appropriated than the exposure-based method for protecting vegetation. From flux-effect relationships, we derived flux-based critical levels (CLef) for forest protection against visible foliar O3-like injury. We recommend CLef of 5 and 12 mmol m−2 POD1 for broadleaved species and conifers, respectively. Before using PODY as legislative standard in Europe, we recommend using the CLec for ≥ 25% of crown defoliation in a plot: 17,000 and 19,000 nmol mol−1 h AOT40 for conifers and broadleaved species, respectively.

Evaluation of the Importance of Some East Asian Tree Species for Refinement of Air Quality by Estimating Air Pollution Tolerance Index, Anticipated Performance Index, and Air Pollutant Uptake

Potentials of tree species as biofilters depend on appropriate selection based on their tolerance to air pollution, which is usually evaluated by the air pollution tolerance index (APTI) and anticipated performance index (API). Thus, these index values need as a means of scientific understanding to assess the role of urban trees for better greenspace planning/management to mitigate impacts of gaseous air pollution such as ozone (O3) and sulfur dioxide (SO2). O3 exposure to Chionanthus retusus, Pinus densiflora, and Ginkgo biloba showed higher stomatal O3 flux than the others, finally resulting in both favoring stomatal movement and maintaining carbon fixation. In contrast, despite the whole tree enhanced SO2 uptake under excess SO2 exposure, the carbon assimilation capacity was only found in Taxus cuspidata and Zelkova serrata as a consequence of no stomatal sluggishness. On the basis of API, P. densiflora and Prunus × yedoensis were good performers for developing greenspace, while Z. serrata and G. biloba were moderate performers; however, C. retusus and T. cuspidata were estimated to be poor and very poor performers, respectively, for reducing the air quality injury caused by air pollutants. The present study suggests that an integration of both APTI and API based on stomatal absorption flux is needed for selecting sound tree-species in greenspace planning/construction to control gaseous air pollutions.

Effects of Elevated Temperature and Ozone in Brassica juncea L.: Growth, Physiology, and ROS Accumulation

Global warming and ozone (O3) pose serious threats to crop yield and ecosystem health. Although neither of these factors will act individually in reality, most studies have focused on the responses of plants to air pollution or climate change. Interactive effects of these remain poorly studied. Therefore, this study was conducted to assess the effects of optimal (22/20 °C day/night) and elevated temperature (27/25 °C) and/or ambient (10 ± 10 nL L−1) and elevated O3 concentrations (100 ± 10 nL L−1) on the growth, physiology, and reactive oxygen species (ROS) accumulation of leaf mustard (Brassica juncea L.). The aim was to examine whether elevated temperature increase the O3 damage due to increasing stomatal conductance, and thus, O3 flux into the leaf. Significant reductions in photosynthetic rates occurred under O (elevated O3 with optimal temperatures) and OT (elevated O3 and temperature) conditions compared to C (controls). Stomatal conductance was significantly higher under T than in the C at 7 DAE. Under OT conditions, O3 flux significantly increased compared to that in O conditions at 7 days after exposure (DAE). Significant reductions in total fresh and dry weight were observed under OT conditions compared to those under O. Furthermore, significant reductions in levels of carotenoids and ascorbic acid were observed under OT conditions compared to O. Lipid peroxidation and accumulation of ROS such as hydroxyl radical, hydrogen peroxide, and superoxide radical were higher under O and OT conditions than in C conditions at 7 and 14 DAE. As a result of O3 stress, the results of the present study indicated that the plant injury index significantly increased under OT compared to O conditions. This result suggested that elevated temperature (+5 °C) may enhance O3 damage to B. juncea by increasing stomatal conductance and O3 flux into leaves.

New Insights into Leaf Physiological Responses to Ozone for Use in Crop Modelling.

Estimating food production under future air pollution and climate conditions in scenario analysis depends on accurately modelling ozone (O3) effects on yield. This study tests several assumptions that form part of published approaches for modelling O3 effects on photosynthesis and leaf duration against experimental data. In 2015 and 2016, two wheat cultivars were exposed in eight hemispherical glasshouses to O3 ranging from 22 to 57 ppb (24 h mean), with profiles ranging from raised background to high peak treatments. The stomatal O3 flux (Phytotoxic Ozone Dose, POD) to leaves was simulated using a multiplicative stomatal conductance model. Leaf senescence occurred earlier as average POD increased according to a linear relationship, and the two cultivars showed very different senescence responses. Negative effects of O3 on photosynthesis were only observed alongside O3-induced leaf senescence, suggesting that O3 does not impair photosynthesis in un-senesced flag leaves at the realistic O3 concentrations applied here. Accelerated senescence is therefore likely to be the dominant O3 effect influencing yield in most agricultural environments. POD was better than 24 h mean concentration and AOT40 (accumulated O3 exceeding 40 ppb, daylight hours) at predicting physiological response to O3, and flux also accounted for the difference in exposure resulting from peak and high background treatments.

ROS production and its detoxification in early and late sown cultivars of wheat under future O3 concentration

The present field study was planned with an objective to unravel the mechanisms behind the differential responses of early and late sown wheat cultivars with respect to their defense capacity to scavenge ROS induced under elevated O3 (EO3). Experiments were performed under ambient and elevated levels of O3 (ambient + 20 ppb) to plants inside open-top chambers (OTCs). Ozone concentrations, stomatal flux of O3 and meteorological parameters were measured throughout the experiment. Contents of superoxide radicals (O2−) and hydrogen peroxide (H2O2) and their localization, lipid peroxidation, antioxidative enzyme activities, ascorbic acid and total phenolic contents were measured at vegetative and reproductive developmental stages. EO3 exposure induced higher stomatal flux of O3 in early sown cultivars. Higher contents of O2−, H2O2 and lipid peroxidation were noticed under EO3 in all the cultivars but the magnitude of increases was higher in late sown cultivars at the reproductive stage. Activities of glutathione reductase (GR) and ascorbate peroxidase (APX) were higher in late sown cultivars under EO3. Ascorbic acid and total phenolic contents were significantly higher in early sown than late sown cultivars under EO3 treatment. The present study concludes that early sown cultivars are more efficient in their defense response due to higher induction of enzymatic and non-enzymatic antioxidants, while the induction of enzymatic antioxidants was more distinct in late sown cultivars. Non-enzymatic linked defense mechanism requires additional metabolic cost than enzymatic defense, making early sown cultivars more susceptible to EO3. Differential response of early and late sown cultivars with respect to antioxidative defense against O3 stress suggests that yield responses are governed by the time of sowing and intrinsic defense responses of the cultivars. In future with rising trend of O3, early sown cultivars are expected to be more vulnerable to oxidative stress compared to late sown cultivars.

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.

Comparison of crop yield sensitivity to ozone between open-top chamber and free-air experiments.

Assessments of the impacts of ozone (O3 ) on regional and global food production are currently based on results from experiments using open-top chambers (OTCs). However, there are concerns that these impact estimates might be biased due to the environmental artifacts imposed by this enclosure system. In this study, we collated O3 exposure and yield data for three major crop species-wheat, rice, and soybean-for which O3 experiments have been conducted with OTCs as well as the ecologically more realistic free-air O3 elevation (O3 -FACE) exposure system; both within the same cultivation region and country. For all three crops, we found that the sensitivity of crop yield to the O3 metric AOT40 (accumulated hourly O3 exposure above a cut-off threshold concentration of 40 ppb) significantly differed between OTC and O3 -FACE experiments. In wheat and rice, O3 sensitivity was higher in O3 -FACE than OTC experiments, while the opposite was the case for soybean. In all three crops, these differences could be linked to factors influencing stomatal conductance (manipulation of water inputs, passive chamber warming, and cultivar differences in gas exchange). Our study thus highlights the importance of accounting for factors that control stomatal O3 flux when applying experimental data to assess O3 impacts on crops at large spatial scales.

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

Ozone risk assessment in three oak species as affected by soil water availability.

To derive ozone (O3) dose-response relationships for three European oak species (Quercus ilex, Quercus pubescens, and Quercus robur) under a range of soil water availability, an experiment was carried out with 2-year-old potted seedlings exposed to three levels of water availability in the soil and three levels of O3 pollution for one growing season in an ozone free-air controlled exposure (FACE) facility. Total biomass losses were estimated relative to a hypothetical clean air at the pre-industrial age, i.e., at 10ppb as daily average (M24). A stomatal conductance model was parameterized with inputs from the three species for calculating the stomatal O3 flux. Exposure-based (M24, W126, and AOT40) and flux-based (phytotoxic O3 dose (POD)0-3) dose-response relationships were estimated and critical levels (CL) were calculated for a 5% decline of total biomass. Results show that water availability can significantly affect O3 risk assessment. In fact, dose-response relationships calculated per individual species at each water availability level resulted in very different CLs and best metrics. In a simplified approach where species were aggregated on the basis of their O3 sensitivity, the best metric was POD0.5, with a CL of 6.8mmolm-2 for the less O3-sensitive species Q. ilex and Q. pubescens and of 3.5mmolm-2 for the more O3-sensitive species Q. robur. The performance of POD0, however, was very similar to that of POD0.5, and thus a CL of 6.9mmolm-2 POD0 and 3.6mmolm-2 POD0 for the less and more O3-sensitive oak species may be also recommended. These CLs can be applied to oak ecosystems at variable water availability in the soil. We conclude that PODy is able to reconcile the effects of O3 and soil water availability on species-specific oak productivity.

Quantification of ozone exposure- and stomatal uptake-yield response relationships for soybean in Northeast China

High ground-level O3 is a new threat to agricultural production in Northeast China with the increasing ambient O3 concentration. Little is known about its impacts on soybean production in this key agricultural region. Accumulated O3 exposure-response and stomatal O3 flux-response relationships were developed during two continuous growing seasons to evaluate O3-induced yield reduction of four typical soybean cultivars in Northeast China. Results showed that critical levels of AOT40 (accumulated hourly O3 concentrations over a threshold of 40nmol·mol−1), SUM06 (sum of all hourly average O3 concentrations over 0.06μmol·mol−1) and W126 (sum of O3 concentrations weighted by a sigmoidal function) in relation to 5% reduction in relative seed yield were 4.2, 7.6 and 6.8μmol·mol−1·h, respectively. The effect of O3 on plants was influenced by leaf position in canopy. An improved Jarvis stomatal conductance model including leaf (node) position fitted well with field measurements. The best linear relationship between stomatal O3 flux and relative soybean yield was obtained when phytotoxic ozone dose was integrated over a threshold of 9.6nmol·m−2·s−1 (POD9.6) to represent the detoxification capacity of soybean. POD9.6 and the commonly used POD6 in relation to 5% reduction in relative seed yield of soybean were 0.9mmol·m−2 and 1.8mmol·m−2, respectively. O3 concentrations above ~38nmol·mol−1 contributed to POD9.6 and caused seed yield loss in soybean. Current annual yield loss of soybean at ambient O3 was estimated to range between 23.4% and 30.2%. The O3 dose-response relationships and corresponding thresholds obtained here will benefit regional O3 risk assessment on soybean production in Northeast China.

No impact of tropospheric ozone on the gross primary productivity of a Belgian pine forest

Abstract. High stomatal ozone (O3) uptake has been shown to negatively affect crop yields and the growth of tree seedlings. However, little is known about the effect of O3 on the carbon uptake by mature forest trees. This study investigated the effect of high O3 events on gross primary productivity (GPP) for a Scots pine stand near Antwerp, Belgium over the period 1998–2013. Stomatal O3 fluxes were modelled using in situ O3 mixing ratio measurements and a multiplicative stomatal model, which was parameterised and validated for this Scots pine stand. Ozone-induced GPP reduction is most likely to occur during or shortly after days with high stomatal O3 uptake. Therefore, a GPP model within an artificial neural network was parameterised for days with low stomatal O3 uptake rates and used to simulate GPP during periods of high stomatal O3 uptake. Possible negative effects of high stomatal O3 uptake on GPP would then result in an overestimation of GPP by the model during or after high stomatal O3 uptake events. The O3 effects on GPP were linked to AOT40 and POD1. Although the critical levels for both indices were exceeded in every single year, no significant negative effects of O3 on GPP were found, and no correlations between GPP residuals and AOT40 and POD1 were found. Overall, we conclude that no O3 effects were detected on the carbon uptake by this Scots pine stand.

Testing approaches for calculating stomatal ozone fluxes from passive samplers

Current ozone (O3) levels are high enough to negatively affect vegetation and may become worse in the future. Ozone risk assessments have recently shifted from exposure-based to flux-based metrics. Modeling stomatal O3 fluxes requires hourly O3 and meteorological data, which are not always available. Large datasets of O3 concentrations measured with passive samplers exist worldwide, and usually provide weekly to monthly means. We tested the suitability of using aggregated data instead of hourly data for O3 flux calculations with 3-year time series of O3 data from 24 Spanish air quality stations. Five different approaches and three different parameterizations were tested. Ozone-averaged values in combination with hourly meteorological data provided the most robust estimates of accumulated O3 fluxes (Phytotoxic Ozone Dose with no threshold, POD0), and the median of the absolute percent error (MAPE) due to aggregation came close to 5%. Aggregations from 1week to 1month yielded similar errors, which is important in the cost-efficiency terms of the chosen passive sampler exposure periodicity. One major limitation of these approaches is that they are not suitable for high POD thresholds, and that accuracy of the measurements with passive samplers has to be strictly assured in order to finally obtain acceptable errors. A combination of meteorological data and O3 passive sampler measurements may be used to estimate O3 fluxes at remote forest sites as a valuable risk assessment tool.