O3浓度升高对植物活性氧代谢系统影响的研究进展

为了揭示臭氧（O3）浓度升高对植物活性氧代谢系统的影响机理,从代谢生理角度,总结了近年来国内外关于臭氧浓度升高对植物活性氧自由基代谢速率、细胞膜脂过氧化程度、抗氧化系统及生物量和产量影响的研究进展,同时,就臭氧浓度升高与二氧化碳浓度升高的复合作用对植物活性氧代谢系统的影响,及阐明二者相互作用对植物抗氧化系统影响机理的研究进行了综述。在此基础上指出在未来研究中,要在分子水平上进一步深入研究植物活性氧代谢系统对高浓度臭氧、二氧化碳复合作用的响应机理,并应加强高浓度二氧化碳对臭氧胁迫下植物抗氧化系统影响的研究,为解决如何减轻臭氧浓度升高对植物造成的氧化伤害提供基础理论依据。     

地表臭氧浓度升高对陆地生态系统影响的研究进展

浓度不断升高的地表臭氧(O₃)已成为全球性环境问题, 中国也不例外。目前, 高浓度O₃对叶片光合气体交换、植物生长或生物量的影响已备受关注, 但有关O₃对生态系统层次的研究还相对稀缺且存在较大的不确定性。该文梳理了近40年来地表O₃浓度及其影响相关领域的发展趋势和研究热点, 回顾了地表O₃浓度升高对植物影响的研究手段和评估方法, 综述了地表O₃浓度升高对陆地生态系统影响方面取得的重要进展, 主要包括植物应对O₃胁迫的响应机制、地表O₃对粮食产量和作物品质、生态系统固碳能力、群落结构和地下过程的影响及地表O₃污染区域风险; 此外, 针对目前研究的不足, 对未来研究进行了展望。建议利用先进的完全开放式O₃熏蒸系统模拟O₃浓度升高对生态系统影响的同时加强对地下生态过程的研究, 开展O₃与其他环境因子的复合作用研究; 关注O₃污染对粮食安全的影响; 开展联网研究, 建立统一评价体系; 探索减缓地表O₃污染的生态防控措施; 以期为地表O₃污染生态效应领域的发展提供助力。     

Progress in the effects of elevated ground-level ozone on terrestrial ecosystems

浓度不断升高的地表臭氧(O₃)已成为全球性环境问题, 中国也不例外。目前, 高浓度O₃对叶片光合气体交换、植物生长或生物量的影响已备受关注, 但有关O₃对生态系统层次的研究还相对稀缺且存在较大的不确定性。该文梳理了近40年来地表O₃浓度及其影响相关领域的发展趋势和研究热点, 回顾了地表O₃浓度升高对植物影响的研究手段和评估方法, 综述了地表O₃浓度升高对陆地生态系统影响方面取得的重要进展, 主要包括植物应对O₃胁迫的响应机制、地表O₃对粮食产量和作物品质、生态系统固碳能力、群落结构和地下过程的影响及地表O₃污染区域风险; 此外, 针对目前研究的不足, 对未来研究进行了展望。建议利用先进的完全开放式O₃熏蒸系统模拟O₃浓度升高对生态系统影响的同时加强对地下生态过程的研究, 开展O₃与其他环境因子的复合作用研究; 关注O₃污染对粮食安全的影响; 开展联网研究, 建立统一评价体系; 探索减缓地表O₃污染的生态防控措施; 以期为地表O₃污染生态效应领域的发展提供助力。     

开放式空气中CO2浓度增高(FACE)对水稻生长和发育的影响

人类活动导致的大气和气候变化将极大地改变作物的生长环境,其中最大的一个变化就是大气二氧化碳(CO2)浓度的迅速上升:从工业革命前的平均270μmol/mol上升到目前的381μmol/mol,到2050年至少超过550μmol/mol。FACE(Free-air CO2 enrichment,开放式空气中CO2浓度增高)试验是目前评估未来高浓度CO2对作物生长和产量实际影响的最佳方法。水稻无疑是人类最重要的食物来源,迄今为止人类利用FACE技术开展水稻响应和适应的研究已有10a(19982008年)的历史。以生长发育为主线,首次系统综述了10a水稻FACE试验在该领域的研究成果,总结了FACE情形下高浓度CO2(模拟本世纪中叶大气CO2浓度)对主要供试水稻品种(小区面积大于4m2)光合作用、生育进程、地上部生长、地下部生长、物质分配、籽粒灌浆、产量构成以及倒伏性状等影响的研究进展,比较了FACE与非FACE研究之间以及中国和日本FACE研究(世界上唯一的两个大型水稻FACE研究)之间的异同点。根据研究进展以及当前的技术水平,文章最后提出了该领域的3个优先课题:(1)FACE情形下杂交稻生产力响应高于预期的生物学机制;(2)FACE情形下CO2与主要栽培措施的互作效应;(3)FACE情形下CO2与主要空气污染物臭氧的互作效应。这些响应的机理性解析将有助于从根本上减少人类预测未来粮食安全的不确定性,进而更加有效地制订出应对全球变化的适应策略。     

对流层臭氧浓度升高对植物光合特性影响的研究进展

作为重要的空气污染物之一,对流层臭氧浓度平均以每年2%的速率递增.高浓度臭氧可抑制植物的生长发育,影响生物量和产量的形成,且响应程度随O3设置浓度、试验平台和品种的不同而异.光合作用作为植物最基本的生理过程,同时也是对O3最敏感的生理过程之一.从植物损伤症状、光合作用的光反应、暗反应等方面概括了高浓度臭氧对植物光合特性影响的研究进展,为阐述O3损伤机理、耐性品种的选育提供理论依据.     

FACE实验技术和方法回顾及其在全球变化研究中的应用

化石燃料的燃烧和城市化进程的加快导致大气中二氧化碳(CO_2)和臭氧(O_3)浓度日益升高,大气气体浓度的变化会对植物个体和陆地生态系统结构与功能产生影响。CO_2浓度升高增加了陆地生态系统碳汇能力,而O_3导致作物减产和生态系统固碳损失。自由空气中气体浓度增加(FACE)系统是最接近自然的一种模拟大气气体浓度增加对生态系统影响的研究平台,已广泛应用于各种生态系统,为理解陆地生态系统生态过程对全球变化的响应及评估未来情景的生态风险提供了重要科学依据。该文从FACE技术特点出发,介绍了国内外建成的大型CO_2/O_3-FACE系统,分析了FACE系统的不同布气方式在不同生态系统研究过程中的优点与缺点,概述了全球FACE运行的现状和取得的主要成果,并指出了FACE系统存在的主要问题和前沿研究方向。     

FACE实验技术和方法回顾及其在全球变化研究中的应用

化石燃料的燃烧和城市化进程的加快导致大气中二氧化碳(CO₂)和臭氧(O₃)浓度日益升高, 大气气体浓度的变化会对植物个体和陆地生态系统结构与功能产生影响。CO₂浓度升高增加了陆地生态系统碳汇能力, 而O₃导致作物减产和生态系统固碳损失。自由空气中气体浓度增加(FACE)系统是最接近自然的一种模拟大气气体浓度增加对生态系统影响的研究平台, 已广泛应用于各种生态系统, 为理解陆地生态系统生态过程对全球变化的响应及评估未来情景的生态风险提供了重要科学依据。该文从FACE技术特点出发, 介绍了国内外建成的大型CO₂/O₃-FACE系统, 分析了FACE系统的不同布气方式在不同生态系统研究过程中的优点与缺点, 概述了全球FACE运行的现状和取得的主要成果, 并指出了FACE系统存在的主要问题和前沿研究方向。     

臭氧胁迫下硅对大豆抗氧化系统、生物量及产量的影响

在全球变化情景下,臭氧污染对作物产量将造成严重影响,臭氧将成为未来农业重要胁迫因素。研究缓解臭氧胁迫技术措施有利于保障粮食安全,其中硅元素添加可能是有效途径之一。利用开顶式同化箱(open top chambers,OTCs)装置,设置两个O3浓度(大气O3浓度<40μg/kg和高O3浓度约为80μg/kg)、两个硅浓度(0和100μg/g),研究不同O3浓度下硅对开花后大豆(Glycine max)株高、叶面积、叶绿素含量、抗氧化系统及产量的影响。结果表明:在无臭氧胁迫下,施硅可显著提高大豆根生物量、总生物量和单株籽粒重(14%、5%和20%)(P<0.05)。在O3胁迫下,施硅能使大豆维持较高的叶面积,显著提高大豆叶片叶绿素含量及SOD、POD、CAT活性,显著降低MDA含量,提高大豆根生物量、地上部生物量、总生物量、根冠比和单株籽粒重(29%,18%,19%,9%和17%)(P<0.05)。研究可为缓解O3对大豆危害提供合理可行的栽培管理措施与理论依据。     

臭氧和气溶胶复合污染对杨树叶片光合作用的影响

由于经济的快速发展, 中国大部分地区正面临着严峻的复合型大气污染, 其中臭氧和气溶胶是两种主要污染物。已有的研究表明臭氧对叶片的氧化性伤害能够抑制光合作用, 而气溶胶可通过增加散射辐射比例或缓解高温抑制促进光合作用。但复合污染下, 臭氧和气溶胶如何共同调控叶片光合作用, 仍缺乏研究。该研究利用北京及周边地区之间的污染梯度, 选择加杨(Populus × canadensis)作为实验对象, 于2012-2013年生长季期间对叶片光合速率进行连续观测, 并同时监测臭氧浓度(AOT40)、气溶胶光学厚度(AOD)、空气温度和冠层内外光合有效辐射(PAR)等环境因子, 以期探讨大气复合污染下臭氧和气溶胶变化对植物叶片光合作用的影响及相关机制。结果表明: (1)臭氧浓度与空气温度、气溶胶浓度之间均呈显著正相关关系, 但气溶胶浓度与空气温度没有显著相关关系; (2)臭氧浓度增加显著抑制了阳生叶片的光合作用, 但气溶胶浓度上升促进了阳生叶片的光合作用; 臭氧浓度升高对阴生叶片光合作用的影响较小, 但气溶胶浓度上升促进了阴生叶片的光合作用; (3)标准化后的结果显示, 臭氧对阳生叶片光合作用的影响最大, 此时气溶胶的促进作用一定程度上补偿了臭氧浓度上升所带来的抑制效应。对于阴生叶片光合作用而言, 气溶胶则是最重要的影响因素。该研究发现复合污染下阴生叶和阳生叶光合响应不同, 这表明冠层结构可能通过影响阴生叶和阳生叶的比例, 从而对植物生长产生不同影响。该研究对理解大气复合污染如何影响光合作用提供了的机理支持, 同时也表明, 为了维持生态系统生产力及功能, 需要同时控制气溶胶和臭氧污染。     

气温、CO2浓度和降水交互作用对作物生长和产量的影响

气温、大气CO₂浓度和降水等气候因子是影响作物生长发育的关键因子,而不同的气候因子对作物的影响并非独立的,多气候因子交互作用对作物的影响目前已成为研究的焦点问题.研究不同气候因子交互作用的影响,其结果更接近作物生长的实际情况,有助于了解作物甚至作物生态系统对气候变化的真实响应.国内外关于不同气候因子对作物影响的报道较多,要全面总结不同气候因子交互作用对作物的影响是非常困难的.因此,本文只对近年来有关气温升高、大气CO₂浓度增加和降水变化交互作用对作物生长发育、光合生理及产量影响的研究进展做一简要评述,并提出目前研究的不足和需要解决的关键问题,以期为气候变化对作物生长发育及产量影响的研究提供参考.     

Persistent rhinitis and epithelial remodeling induced by cyclic ozone exposure in the nasal airways of infant monkeys

Children chronically exposed to high levels of ozone (O(3)), the principal oxidant pollutant in photochemical smog, are more vulnerable to respiratory illness and infections. The specific factors underlying this differential susceptibility are unknown but may be related to air pollutant-induced nasal alterations during postnatal development that impair the normal physiological functions (e.g., filtration and mucociliary clearance) serving to protect the more distal airways from inhaled xenobiotics. In adult animal models, chronic ozone exposure is associated with adaptations leading to a decrease in airway injury. The purpose of our study was to determine whether cyclic ozone exposure induces persistent morphological and biochemical effects on the developing nasal airways of infant monkeys early in life. Infant (180-day-old) rhesus macaques were exposed to 5 consecutive days of O(3) [0.5 parts per million (ppm), 8 h/day; "1-cycle"] or filtered air (FA) or 11 biweekly cycles of O(3) (FA days 1-9; 0.5 ppm, 8 h/day on days 10-14; "11-cycle"). The left nasal passage was processed for light microscopy and morphometric analysis. Mucosal samples from the right nasal passage were processed for GSH, GSSG, ascorbate (AH(2)), and uric acid (UA) concentration. Eleven-cycle O(3) induced persistent rhinitis, squamous metaplasia, and epithelial hyperplasia in the anterior nasal airways of infant monkeys, resulting in a 39% increase in the numeric density of epithelial cells. Eleven-cycle O(3) also induced a 65% increase in GSH concentrations at this site. The persistence of epithelial hyperplasia was positively correlated with changes in GSH. These results indicate that early life ozone exposure causes persistent nasal epithelial alterations in infant monkeys and provide a potential mechanism for the increased susceptibility to respiratory illness exhibited by children in polluted environments.     

自由空气中臭氧浓度升高对大豆的影响

人类活动导致的大气和气候变化将极大地改变作物未来的生长环境,其中一个显著的变化就是近地层空气污染物臭氧浓度的迅速上升:从工业革命前低于10nL/L上升到现在的50nL/L(夏季每天8h平均),最新预测这一浓度将在2015-2050年增加20%-25%,本世纪末将增加40%-60%。目前大气背景臭氧浓度已经超过敏感植物的伤害阀值(即40nL/L),广泛地造成农作物减产,而未来臭氧浓度增加将使这种影响变得更为严重。与封闭式和开顶式试验相比,FACE(free-air gas concentration enrichment)研究使用标准的作物管理技术,在完全开放的农田条件下运行,代表了人类对未来大气环境的最好模拟。作为人类食物蛋白的重要来源,大豆是世界上种植面积最大的双子叶植物,也是1年生C3作物的模式作物,同时也被认为对臭氧污染最为敏感的作物之一。美国伊利诺伊大学的大豆FACE(SoyFACE)是世界上第1个利用FACE技术开展农作物对高浓度臭氧(模拟本世纪中叶近地层臭氧浓度)响应和适应的多学科合作研究。在阐述气室研究的局限性和介绍SoyFACE运行特点的基础上,首次综述了FACE情形下高浓度臭氧对大豆光合特性、冠层结构、物质生产与分配、产量及其构成因素以及虫害等方面的影响,并比较了FACE与气室研究结果的异同点。SoyFACE研究清楚地表明臭氧对未来粮食安全的影响必须作为一个重要的全球变化因子来加以考虑。利用FACE技术深入开展臭氧及其与其它全球变化因子的互作对世界主要粮食作物的影响、机制和调控的系统研究,是该领域未来优先考虑的方向。     

臭氧胁迫下冬小麦物质生产与分配的数值模拟

利用ML9810B型臭氧监测分析仪,测定了浙江嘉兴麦田空气O3浓度,并通过改进的开顶式气室实验确定O3浓度变化对冬小麦叶片光合速率的影响函数.在此基础上,加入O3对叶片生长和穗部光合影响的模拟函数,建立反映O3对冬小麦生长和产量形成影响的作物模型.模型的检验结果表明,该模型较好地反映了O3对冬小麦生长的影响,生物量平均相对误差为10.3%.对冬小麦春后生育期(3—5月)的研究表明,水肥适宜时,由O3影响造成的该地区冬小麦干物质累积总损失量为11.4%,产量损失为17.8%.     

The impact of ozone on juvenile maize (Zea mays L.) plant photosynthesis: effects on vegetative biomass, pigmentation, and carboxylases (PEPc and Rubisco)

The impact of ozone on crops was more studied in C (3) than in C (4) species. In C (3) plants, ozone is known to induce a photosynthesis impairment that can result in significant depressions in biomass and crop yields. To investigate the impact of O (3) on C (4) plant species, maize seedlings ( ZEA MAYS L. cv. Chambord) were exposed to 5 atmospheres in open-top chambers: non-filtered air (NF, 48 nL L (-1) O (3)) and NF supplied with 20 (+ 20), 40 (+ 40), 60 (+ 60), and 80 (+ 80) nL L (-1) ozone. An unchambered plot was also available. Leaf area, vegetative biomass, and leaf dry mass per unit leaf area (LMA) were evaluated 33 days after seedling emergence in OTCs. At the same time, photosynthetic pigments as well as carboxylase (PEPc and Rubisco) activities and amounts were also examined in the 5th leaf. Ozone enhanced visible symptoms characterizing foliar senescence. Across NF, + 20, + 40, and + 60 atmospheres, both chlorophylls and carotenoids were found to be linearly decreased against increasing AOT40 ( CA. - 50 % in + 60). No supplementary decrease was observed between + 60 and + 80. Total above-ground biomass was reduced by 26 % in + 80 atmosphere; leaf dry matter being more depressed by ozone than leaf area. In some cases, LMA index was consistent to reflect low negative effects caused by a moderate increase in ozone concentration. PEPc and Rubisco were less sensitive to ozone than pigments: only the two highest external ozone doses reduced their activities by about 20 - 30 %. These changes might be connected to losses in PEPc and Rubisco proteins that were decreased by about one-third. The underlying mechanisms for these results were discussed with special reference to C (3) species. To conclude, we showed that both light and dark reactions of C (4) photosynthesis can be impaired by realistic ozone doses.     

近地层高臭氧浓度对水稻生长发育影响研究进展

臭氧（O₃）被认为是最主要的空气污染物之一.目前地球对流层大气中平均O₃浓度已经从工业革命前的38 nl·L^-1（25～45 nl·L^-1,夏季每天8 h平均）上升到2000年的50 nl·L^-1,悲观估计到2100年近地层O₃浓度将上升到80 nl·L^-1.水稻是世界上最重要的粮食作物,准确评估近地层O₃浓度升高对水稻生长发育的影响具有重要意义.本文从叶片伤害特征、光合作用、水分关系、生育期、物质生产与分配、叶片膜保护系统、籽粒产量及产量构成因素等方面,系统收集和整理了气室条件下（包括封闭气室、开放式气室）高O₃浓度对水稻生长发育影响的研究进展,并对该领域有待深入研究的方向进行了展望.     

基于遥感信息的作物模型重新初始化/参数化方法研究初探

作物模型与遥感信息的结合有助于利用遥感监测的大范围植被信息解决作物模型区域应用时模型初始状态和参数值难以确定的问题。该文借助叶面积指数(LAI)将经过华北冬小麦(Triticum aestivium)适应性调整的WOFOST模型与经参数调整检验的SAIL-PROSPECT模型相嵌套,利用嵌套模型模拟作物冠层的土壤调整植被指数(SAVI),在代表点上借助FSEOPT优化程序使模拟SAVI_s与MODIS遥感数据合成SAVI_m的差异达到最小,从而对WOFOST模型重新初始化。结果表明,借助于遥感信息,出苗期的重新初始化使模拟成熟期与按实际出苗期模拟的结果相差在2天以内,模拟的LAI和总干重的误差比按实际出苗期模拟结果的误差降低3~8个百分点;返青期生物量的重新初始化使模拟LAI和地上总干重在关键发育时刻的误差降至16%以内,模拟LAI和贮存器官重在整个生育期内都更加接近实测值;对返青期生物量的动态调整显示返青到抽穗期间较少次数的遥感数据即能有效地提高作物模型的模拟效果。与国外同类研究相比,该文在作物模型本地化、重新初始化变量和优化比较对象的选择上都有所不同,而利用遥感数据动态调整作物模型初始状态或参数值更具有新意。该文对区域尺度上利用遥感信息优化作物模型的研究具有基础性、探讨性意义。     

鲁西北平原冬小麦田臭氧浓度变化特征及对产量的潜在影响和机理分析

近地层高浓度臭氧(O₃)对农作物生长和产量形成有明显的影响。利用在中国科学院禹城综合试验站(山东省)冬小麦(Triticum aestivum)农田生态系统上观测的O₃浓度及微气象资料, 分析了鲁西北平原冬小麦农田生态系统O₃浓度的日变化和季节变化规律, 在此基础上初步分析了O₃浓度与CO₂通量(F_c)的关系, 并用欧洲和美国科学家在实验室得到的O₃浓度-冬小麦产量关系模型估算了O₃对冬小麦产量的潜在影响。结果表明: O₃浓度存在明显的日变化规律, 日最小值和最大值分别出现在7:00和16:00左右。整个观测期间(2011年3-5月)平均O₃浓度为(30.4 ± 20.1) nL·L ^-1(平均值±标准误差); 30 min平均浓度的最大值为93.1 nL·L ^-1。在冬小麦春季生长季节, O₃浓度日平均值呈现逐步增加的趋势, O₃浓度日均增加约为0.17 nL·L ^-1·d ^-1; 白天7 h和12 h平均浓度(M7和M12)分别为45.7和43.1 nL·L ^-1; O₃浓度超过40 nL·L ^-1的3个月累积值(AOT40)为9.8 μL·L ^-1·h; 超过60 nL·L ^-1的O₃浓度累积值(SUM06)为12.6 μL·L ^-1·h; 经过权重修正的O₃污染指标W126为10.1 μL·L ^-1·h。在高浓度O₃ (>60 nL·L ^-1)情况下, CO₂通量与O₃浓度呈现负相关关系, 鲁西北平原O₃对冬小麦光合作用影响的阈值取60 nL·L ^-1比较合适, 该值高于欧洲国家普遍采用的40 nL·L ^-1。基于以上结果, 初步估算得出: 在目前的O₃浓度水平下, 鲁西北平原近地层O₃可能会使冬小麦产量减少5.2%-8.8%。     

An in vivo analysis of the effect of season-long open-air elevation of ozone to anticipated 2050 levels on photosynthesis in soybean

Rising atmospheric carbon dioxide concentration ([CO(2)]) is widely recognized, but less appreciated is a concomitant rise in tropospheric ozone concentration ([O(3)]). In industrialized countries, [O(3)] has risen by 0.5% to 2.5% per year. Tropospheric [O(3)] is predicted to reach a global mean of >60 nL L(-1) by 2050 with greater averages locally. Previous studies in enclosures suggest that this level of [O(3)] will decrease leaf photosynthesis, thereby limiting growth and yield of Glycine max L. Merr. SoyFACE (Soybean Free Air gas Concentration Enrichment) is the first facility to elevate atmospheric [O(3)] (approximately 1.2x current) in replicated plots under completely open-air conditions within an agricultural field. Measurements of gas exchange (assimilation versus light and assimilation versus intercellular [CO(2)]) were made on excised leaves from control and treatment plots (n = 4). In contrast to expectations from previous chamber studies, elevated [O(3)] did not alter light-saturated photosynthesis (A(sat), P = 0.09), carboxylation capacity (V(c,max), P = 0.82), or maximum electron transport (J(max), P = 0.66) for the topmost most recently fully expanded leaf at any stage of crop development. Leaves formed during the vegetative growth stage did not show a significant ozone-induced loss of photosynthetic capacity as they aged. Leaves formed during flowering did show a more rapid loss of photosynthetic capacity as they aged in elevated [O(3)]. A(sat), V(c,max), and J(max) (P = 0.04, 0.004, and 0.002, respectively) were decreased 20% to 30% by treatment with ozone. This is noteworthy since these leaves provide photosynthate to the developing grain. In conclusion, a small (approximately 20%) increase in tropospheric [O(3)] did not significantly alter photosynthetic capacity of newly expanded leaves, but as these leaves aged, losses in photosynthetic carbon assimilation occurred.     

Isoprene Produced by Leaves Protects the Photosynthetic Apparatus against Ozone Damage, Quenches Ozone Products, and Reduces Lipid Peroxidation of Cellular Membranes

Many plants invest carbon to form isoprene. The role of isoprene in plants is unclear, but many experiments showed that isoprene may have a role in protecting plants from thermal damage. A more general antioxidant action has been recently hypothesized on the basis of the protection offered by exogenous isoprene in nonemitting plants exposed to acute ozone doses. We inhibited the synthesis of endogenous isoprene by feeding fosmidomycin and observed that Phragmites australis leaves became more sensitive to ozone than those leaves forming isoprene. Photosynthesis, stomatal conductance, and fluorescence parameters were significantly affected by ozone only in leaves on which isoprene was not formed. The protective effect of isoprene was more evident when the leaves were exposed for a long time (8 h) to relatively low (100 nL L(-1)) ozone levels than when the exposure was short and acute (3 h at 300 nL L(-1)). Isoprene quenched the amount of H(2)O(2) formed in leaves and reduced lipid peroxidation of cellular membranes caused by ozone. These results indicate that isoprene may exert its protective action at the membrane level, although a similar effect could be obtained if isoprene reacted with ozone before forming active oxygen species. Irrespective of the mechanism, our results suggest that endogenous isoprene has an important antioxidant role in plants.     

Ozone effects on wheat in relation to CO2: modelling short‐term and long‐term responses of leaf photosynthesis and leaf duration

A combined stomatal–photosynthesis model was extended to simulate the effects of ozone exposure on leaf photosynthesis and leaf duration in relation to CO₂. We assume that ozone has a short‐term and a long‐term effect on the Rubisco‐limited rate of photosynthesis, A_c. Elevated CO₂ counteracts ozone damage via stomatal closure. Ozone is detoxified at uptake rates below a threshold value above which A_c decreases linearly with the rate of ozone uptake. Reduction in A_c is transient and depends on leaf age. Leaf duration decreases depending on accumulated ozone uptake. This approach is introduced into the mechanistic crop simulation model AFRCWHEAT2. The derived model, AFRCWHEAT2‐O3, is used to test the capability of these assumptions to explain responses at the plant and crop level. Simulations of short‐term and long‐term responses of leaf photosynthesis, leaf duration and plant and crop growth to ozone exposure in response to CO₂ are analysed and compared with experimental data derived from the literature. The model successfully reproduced published responses of leaf photosynthesis, leaf duration, radiation use efficiency and final biomass of wheat to elevated ozone and CO₂. However, simulations were unsatisfactory for cumulative radiation interception which had some impact on the accuracy of predictions of final biomass. There were responses of leaf‐area index to CO₂ and ozone as a result of effects on tillering which were not accounted for in the present model. We suggest that some model assumptions need to be tested, or analysed further to improve the mechanistic understanding of the combined effects of changes in ozone and CO₂ concentrations on leaf photosynthesis and senescence. We conclude that research is particularly needed to improve the understanding of leaf‐area dynamics in response to ozone exposure and elevated CO₂.