臭氧浓度升高对植物抗氧化系统的影响

臭氧是重要的温室气体之一,大气中臭氧浓度不断增加.高浓度臭氧对植物有高度毒性,能够给植物带来可见的叶片伤害,体内活性氧水平上升,同时也能刺激植物体内抗氧化系统的活性.目前高浓度臭氧对植物抗氧化系统的影响已经成为植物对全球变化响应研究的重要方向之一.本文综述了国内外关于高浓度臭氧对植物的毒害机理、植物对于高浓度臭氧伤害的抵御反应、以及在高浓度臭氧与CO2复合作用对植物影响的相关报道,以期改善人们对臭氧浓度升高对植物影响的理解.     

植物激素信号调控的“植物病毒-植物-媒介昆虫”三者互作对温室气体变化的响应

全球气候变化已成为农业生产的重要限制因子.它不仅直接影响植物的净初级生产力,同时还影响植物病虫害的发生.因此国内外非常重视病虫害对全球气候变化中的温室气体(二氧化碳和臭氧)增高的响应研究.二氧化碳或臭氧浓度增高影响植物的生理过程,进而通过寄主植物的"上行效应"影响植物病虫害的发生.已有的研究表明,二氧化碳或臭氧浓度升高可通过降低植物氮营养,影响媒介昆虫或植物病毒的发生;而且最近的研究发现,植物激素信号通路在调控媒介昆虫和植物病毒响应二氧化碳和臭氧浓度升高中发挥重要作用.本文根据国内外的研究和本研究组取得的进展,系统地阐述了二氧化碳和臭氧浓度升高如何通过改变激素信号介导的植物抗性代谢进而影响植物病毒-植物-媒介昆虫三者互作关系.     

臭氧和增温对醉蝶花(Cleome spinosa)氧化伤害及抗氧化酶活的影响

采用开顶箱气室(OTCs)研究不同臭氧浓度(80和160 nmol·mol-1)及增温(比对照的大气温度增加2℃)对园林观赏植物醉蝶花(Cleome spinosa)氧化及抗氧化特性的影响。结果表明:(1)经过160 nmol·mol-1高浓度臭氧急性熏蒸7 d后,醉蝶花叶片出现了明显的伤害症状,叶片表面呈现较大面积的漂白褪绿斑块,其他处理下无明显可见伤害症状;(2)与对照相比,高浓度臭氧(160 nmol·mol-1)处理下醉蝶花叶片丙二醛(MDA)含量、相对电导率、过氧化物酶(POD)活性、超氧化物歧化酶(SOD)活性均分别显著升高175.7%、259.9%、111.4%、54.3%(P0.05),而超氧自由基(O2-·)产生速率显著降低67%(P0.05);臭氧浓度80 nmol·mol-1处理下,MDA含量显著升高65.5%(P0.05),CAT活性显著下降65.9%(P0.05),说明醉蝶花在臭氧浓度80 nmol·mol-1左右时具有较高的臭氧耐受性,而臭氧浓度160 nmol·mol-1左右时植物叶片遭受臭氧胁迫,主要通过增强POD和SOD等抗氧化酶活性来抵御氧化伤害;(3)单独增温导致醉蝶花叶片的MDA含量和相对电导率显著升高62.1%和58.1%(P0.05),但O2-·产生速率和CAT活性显著低于对照(P0.05),分别降低了28.8%和71.1%,POD和SOD活性与对照相比差别不大,可能是增温使植物自身代谢增强产生这种现象;(4)与单独臭氧处理相比(80 nmol·mol-1),臭氧(80 nmol·mol-1)增温复合处理下植物叶片CAT、POD、SOD均分别显著升高141.7%、72.1%、107.9%(P0.05); O2-·产生速率显著下降51%(P0.05),说明臭氧和增温复合处理使醉蝶花遭受的臭氧胁迫加剧。该研究结果可为我国应对高浓度臭氧污染的突发急性事件下的园林及城市绿化植物选择和栽培提供科学依据。     

高浓度CO2对树木生理生态的影响研究进展

大气CO2浓度升高已成为世界范围内的重要环境问题。CO2浓度升高势必会对植物的生理生态变化产生重要影响。综述了国内外有关高浓度CO2对树木生理生态影响研究的最新进展,具体包括高浓度CO2对树木生长发育、光合和呼吸作用、抗氧化系统、树木代谢物质、挥发性有机化合物以及树木凋落物等方面的影响。高浓度CO2一般会促进树木地上植株的生长和发育,但也因树种差异而有所不同。最新研究表明,高浓度CO2促进了树木细根周转,树木根系生长在大气CO2浓度升高条件下表现为促进作用,这种作用加快了全球森林生态系统的C循环。高浓度CO2虽然在一定程度上促进树木光合速率的增加,但长期熏蒸也往往会发生光合驯化,这种现象产生的生理学机制目前仍无定论。高浓度CO2对树木呼吸作用尤其是根系呼吸的影响将是未来研究的重点和难点。高浓度CO2一般会提高树木抗氧化酶活性与抗氧化剂含量,但不同树种响应高浓度CO2的过程和机理也有所差异。研究表明,高浓度CO2一般对树木凋落物的分解产生不利影响,但也因树种而异。需要强调的是,目前关于树木地下部分、树木对高浓度CO2的适应机理和重要过程(碳氮水耦合及基因调控等)以及多个树种包括不同类型树种及不同品种之间比较研究较少;关于某一重要生理生态机制(如根系生理代谢)尤其是多个生态因子复合条件下缺乏长期深入的研究。在此基础上给出了大气CO2浓度升高下树木生理生态学研究的未来发展方向,包括高CO2浓度条件下树木根系生理代谢及机制、树木碳氮水耦合的生理过程及机制、不同生态因子复合作用对树木生理影响机制以及树木分子作用机理等方面的研究。这些研究不仅将丰富森林树木应对未来气候变化的有关科学理论,也为全球气候变化背景下实现森林树种生态功能的优化选择及森林生态系统的可持续发展与经营提供重要的生理生态学理论依据和参考。     

大气臭氧浓度升高对植物及其昆虫的影响

臭氧是最具危害性的空气污染物之一,从19世纪中叶开始,对流层中的臭氧水平增加了35％,在今后50—100年内还将继续升高。臭氧浓度升高对植物生理基本功能、植物体内信号分子以及挥发物都具有不同程度的影响,并严重影响作物的产量。臭氧也通过改变植物的原生代谢和次生代谢发生数量而影响植食性昆虫的取食偏嗜性、行为、生长和发育,进而影响天敌昆虫的适合度。臭氧还通过改变化学信息物质而影响昆虫的行为。根据国内外研究进展,介绍了大气臭氧浓度升高对植物、昆虫的影响,并讨论了目前存在的问题和研究前景。     

CO2和O3浓度升高及其复合作用对玉米（Zea mays L.）活性氧代谢及抗氧化酶活性的影响

为了揭示CO2和O3浓度升高及其复合作用对植物活性氧(ROS)代谢及抗氧化酶活性的影响机理,以玉米(Zea mays L.)为研究材料,利用开顶式气室(OTCs)研究了CO2和O3浓度升高及其复合作用下,玉米叶片活性氧产生速率、含量,膜脂过氧化程度,抗氧化酶活性,净光合速率及玉米籽粒产量的变化.结果表明,在整个生育期内,与对照相比,高浓度CO2((550±20)μmol · mol-1)处理下,玉米叶片净光合速率升高,O- ·2 产生速率、H2O2含量下降, MDA含量、相对电导率减小,SOD、CAT、POD活性增强,玉米百粒重和穗粒数增加;而在O3浓度为(80±10)nmol · mol-1的条件下,玉米叶片净光合速率下降,O- ·2 产生速率、H2O2含量升高,MDA含量、相对电导率增大,SOD、CAT、POD活性减弱,玉米百粒重和穗粒数降低;CO2和O3浓度升高复合((550±20)μmol · mol-1 (80±10)nmol · mol-1)处理下,玉米叶片的净光合速率、H2O2含量、SOD活性先升高后降低, MDA含量、相对电导率、CAT活性增加,POD活性减弱,而O- ·2 产生速率几乎不变化,且玉米的百粒重和穗粒数略低于对照.以上结果说明,CO2浓度升高抑制了玉米叶片活性氧的代谢速率,提高了抗氧化酶的活性,从而增强了光合作用,使玉米籽粒产量增加,对玉米表现为保护效应,而O3浓度升高促进了玉米叶片活性氧的代谢速率,降低了抗氧化酶的活性,抑制了光合作用,使玉米籽粒产量下降,对玉米表现为伤害效应.在CO2和O3浓度升高复合处理下,CO2浓度升高在一定程度上缓解了O3浓度升高对玉米的伤害效应,而O3浓度升高亦在一定程度上削弱了CO2浓度升高对玉米的保护效应.     

大气臭氧浓度升高对银杏叶片活性氧代谢及相关基因表达的影响

采用开顶式气室熏蒸法,设置自然条件下臭氧(O₃)浓度(对照,约40 nmol·mol^-1)、80、160及200 nmol·mol^-14个臭氧浓度,观测了不同浓度臭氧条件下银杏叶片可见伤害、活性氧生成量、抗氧化酶活性及相关基因表达变化情况,分析大气臭氧浓度升高对植物活性氧代谢的影响.结果表明: 160和200 nmol·mol^-1 O₃熏蒸明显伤害银杏叶片,80 nmol·mol^-1与对照无差异,无可见伤害.O₃处理20 d后,160和200 nmol·mol^-1条件下银杏叶片的超氧自由基(O₂^-·)产生速率显著高于80 nmol·mol^-1和对照,而80 nmol·mol^-1与对照无差异;O₃处理40 d后,160和200 nmol·mol^-1熏蒸下叶片过氧化氢(H₂O₂)含量显著高于80 nmol·mol^-1和对照,而过氧化氢酶(CAT)活性显著高于80 nmol·mol^-1和对照,各臭氧处理抗坏血酸过氧化物酶(APX)活性均低于对照.熏蒸40 d后,CAT、APX基因的转录表达持续加强;防御素(GbD)的表达强度则随着臭氧浓度的增加及熏蒸时间的延长而呈显著加强.高浓度臭氧胁迫可使银杏叶片活性氧生成量增加、抗氧化酶活性下降、相关基因表达水平上调,有明显可见叶片伤害.     

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。     

Effects of ozone and aerosol pollution on photosynthesis of poplar leaves

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。     

臭氧对生态系统地下过程的影响

对流层中高浓度的臭氧是一种严重危害植物的大气污染物,臭氧浓度的升高会对作物、林木等产生一系列的损害。本文综述了大气臭氧浓度升高对生态系统地下过程的影响,包括植物根系、根系分泌物、菌根、土壤-根呼吸、土壤酶以及土壤微生物的影响研究进展;阐述了目前研究中存在的争论以及今后需要研究的领域和方向。     

臭氧胁迫对植物主要生理功能的影响

近年来,由于光化学反应的臭氧前体增加,全球植物受对流层臭氧(O3)胁迫的程度越来越严重。臭氧污染被认为是造成东欧、西欧和整个美国的大片森林衰退和枯死的主要原因。臭氧胁迫严重影响植物叶片对光能的利用,通过气孔限制和非气孔限制,导致其光合速率的降低,影响光合产物的产量。臭氧对植物的影响与植物体内代谢物质的积聚量紧密联系。臭氧胁迫引发植物的各种防御保护机制,刺激抗氧化系统,影响膜系统,改变其体内碳和矿质养分的吸收并引起它们的重新分配,诱导其基因表达的深层变化。为了适应臭氧胁迫环境,植物通过生理生化机制的调节来保证其生命活动。如细胞通过调节渗透物质的含量来保持渗透势的平衡;细胞内各种抗氧化酶活性增加,以清除自由基,避免或者减轻细胞受到伤害;改变代谢途径以保持能量储备和降低代谢速率。可见,生态环境对生物进化具有重要影响。这个观点将在臭氧胁迫对植物生理的影响中得到证实,也是生物进化论的另一种证据。综述了臭氧对光合生理、呼吸代谢、抗氧化系统、膜系统、矿质养分的吸收和分配与分子生理等主要生理功能的影响,并提出臭氧胁迫对植物生理影响的今后研究方向与未来研究热点是:(1)加强在植物个体和群落水平上臭氧胁迫对植物生理影响的研究;(2)臭氧影响下植物的基因调控和相关信号传递网络系统的机理;(3)通过分子标记、基因图谱、基因组学和转基因技术等方法研究选育适应臭氧胁迫环境的植物;(4)尽可能在接近自然条件的环境中开展研究;(5)臭氧胁迫对亚热带和热带森林及其树种主要生理功能影响的研究;(6)建立模型评估臭氧对植物的影响。     

Effects of ozone and elevated atmospheric carbon dioxide on carbohydrate metabolism of spruce needles. Catabolic and detoxification pathways

We have studied the effects of ozone, carbon dioxide and ozone combined with carbon dioxide fumigations on catabolic and detoxification pathways in spruce ( Picea abies [L.] Karst.) needles. The results obtained showed an increase in the activities of three enzymes involved in the detoxification pathway, superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (AscPOD, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) when trees were exposed to ozone and to ozone‐carbon dioxide treatments. In these two treatments, the fraction of SOD activity due to the chloroplastic isoform was increased (1.5‐fold). In the needles of trees exposed to ozone and to ozone‐carbon dioxide fumigation, an increase in the activities of glucose‐6‐phosphate dehydrogenase (G‐6‐PDH, EC 1.1.1.49) showed that the cell had the capacity to produce more NADPH necessary for the detoxification. Stimulation of other enzymes of catabolic pathways (fumarase [EC 4.2.1.2], phosphofructokinase [PFK, EC 2.7.1.1] and phosphoenolpyruvate carboxylase [PEPC, EC 4.1.1.31]), was also observed making it possible for the cell to provide the reducing power necessary for detoxification as well as energy and carbon skeletons involved in the repair processes.
When carbon dioxide alone was applied, no effects could be detected on these enzyme activities. However, when carbon dioxide was combined with ozone, the effect of ozone on trees was less than that induced by ozone alone, suggesting that elevated atmospheric carbon dioxide concentrations may to some extent protect plants from ozone injury.     

Mechanism of oxidative damage to fish red blood cells by ozone

The present study was conducted to elucidate the adverse effects of ozone exposure on rainbow trout (Oncorhynchus mykiss) red blood cells (RBCs). We evaluated whether hemoglobin (Hb) or Hb-derived free iron could participate in the RBC damage using an in vitro ozone exposure system. Ozone exposure induced hemolysis, formation of methemoglobin, and RBC membrane lipid peroxidation. This RBC damage was not suppressed by the addition of a specific iron chelator (deferoxamine mesilate) to the medium but was suppressed by carbon monoxide (CO) treatment before ozone exposure. Generation of hydrogen peroxide (H2O2) in RBC was observed upon ozone exposure but was significantly suppressed by CO treatment before ozone exposure. Thus the Hb status (i.e., Hb redox condition) and H2O2 generation in RBC should play important roles in mediating RBC damage by ozone exposure. In other words, neither ozone nor its derivative directly attacked from the outside of the cell, but ozone that penetrated through the membrane derived the reactive oxygen species from Hb inside of the cell.     

Responses of trees to elevated carbon dioxide and climate change

The enhancement in photosynthesis at elevated concentration of carbon dioxide level than the ambient level existing in the atmosphere is widely known. However, many of the earlier studies were based on instantaneous responses of plants grown in pots. The availability of field chambers for growing trees, and long-term exposure studies of tree species to elevated carbon dioxide, has changed much of our views on carbon dioxide acting as a fertiliser. Several tree species showed acclimation or even down-regulation of photosynthetic responses while a few of them showed higher photosynthesis and better growth responses. Whether elevated levels of carbon dioxide can serve as a fertilizer in a changed climate scenario still remains an unresolved question. Forest-Air-Carbon dioxide-Enrichment (FACE) sites monitored at several locations have shown lately, that the acclimation or down regulation as reported in chamber studies is not as wide-spread as originally thought. FACE studies predict that there could be an increase of 23–28% productivity of trees at least till 2050. However, the increase in global temperature could also lead to increased respiration, and limitation of minerals in the soil could lead to reduced responses in growth. Elevated carbon dioxide induces partial closure of leaf stomata, which could lead to reduced transpiration and more economical use of water by the trees. Even if the carbon dioxide acts as a fertilizer, the responses are more pronounced only in young trees. And if there are variations in species responses to growth due to elevated carbon dioxide, only some species are going to dominate the natural vegetation. This will have serious implications on the biodiversity and the structure of the ecosystems. This paper reviews the research done on trees using elevated CO₂ and tries to draw conclusions based on different methods used for the study. It also discusses the possible functional variations in some tree species due to climate change.     

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。     

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。     

Decreased hydraulic conductance in plants at elevated carbon dioxide

Previous work indicated that long-term exposure to elevated carbon dioxide levels can reduce hydraulic conductance in some species, but the basis of the response was not determined. In this study, hydraulic conductance was measured at concentrations of both 350 and 700 cm³ m^–3 carbon dioxide for plants grown at both concentrations, to determine the reversibility of the response. In Zea mays and Amaranthus hypochondriacus , exposure to the higher carbon dioxide concentration for several hours reduced whole-plant transpiration rate by 22–40%, without any consistent change in leaf water potential, indicating reversible reductions in hydraulic conductance at elevated carbon dioxide levels. Hydraulic conductance in these species grown at both carbon dioxide concentrations responded similarly to measurement concentration of carbon dioxide, indicating that the response was reversible. In Glycine max , which in earlier work had shown a long-term decrease in hydraulic conductance at elevated carbon dioxide levels, and in Abutilon theophrasti , no short-term changes in hydraulic conductance with measurement concentration of carbon dioxide were found, despite lower transpiration rates at elevated carbon dioxide. In G. max and Medicago sativa , growth at high dew-point temperature reduced transpiration rate and decreased hydraulic conductance. The results indicate that both reversible and irreversible decreases in hydraulic conductance can occur at elevated carbon dioxide concentrations, and that both could be responses to reduced transpiration rate, rather than to carbon dioxide concentration itself.     

Impacts of elevated atmospheric ozone on peatland below-ground DOC characteristics

Rising concentrations of tropospheric ozone are having detrimental impacts on the growth of crop and forest species and some studies have reported inhibition of the allocation of carbon below ground. The effects of ozone on peatland ecosystems have received relatively little attention, despite their importance within the global carbon cycle. During this study, cores from a Welsh minerotrophic fen and ombrotrophic bog were exposed to four ambient/elevated ozone concentration regimes representing current and predicted 2050 profiles. A large and significant reduction in the concentration of porewater dissolved organic carbon (DOC) was recorded in the fen cores exposed to the elevated ozone concentrations (up to ?55%), with a concurrent shift to a higher molecular weight of the remaining soil carbon. No effects of ozone on DOC concentrations or characteristics were recorded for the bog cores. The data suggest higher ozone sensitivity of plants growing in the fen-type peatland, that the impacts on the vegetation may affect soil carbon characteristics through a reduction in root exudates and that there may have been a shift in the source of substrate DOC for microbial consumption from vegetation exudates to native soil carbon. There may also have been a direct effect of ozone molecules reacting with soil organic matter after being transported into the soil through the aerenchyma tissue of the overlying vegetation. These qualitative changes in the soil carbon in response to elevated ozone may have important implications for carbon cycling in peatland ecosystems, and therefore climate change.     

Repair and tolerance of oxidative DNA damage in plants

DNA damage caused by exposure to reactive oxygen species is one of the primary causes of DNA decay in most organisms. In plants, endogenous reactive oxygen species (ROS) are generated not only by respiration and photosynthesis, but also by active responses to certain environmental challenges, such as pathogen attack. Significant extracellular sources of activated oxygen include air pollutants such as ozone and oxidative effects of UV light and low-level ionizing radiation. Plants are well equipped to cope with oxidative damage to cellular macromolecules, including DNA. Oxidative attack on DNA generates both altered bases and damaged sugar residues that undergo fragmentation and lead to strand breaks. Recent advances in the study of DNA repair in higher plants show that they use mechanisms similar to those present in other eukaryotes to remove and/or tolerate oxidized bases and other oxidative DNA lesions. Therefore, plants represent a valuable model system for the study of DNA oxidative repair processes in eukaryotic cells.     

The mode of action of insecticidal controlled atmospheres

Arthropods cope with reduced oxygen and elevated carbon dioxide atmospheres with a reduction in metabolic rate, also called metabolic arrest. The reduction in metabolism lessens the pressure on the organism to initiate anaerobic metabolism, but also leads to a reduction in ATP production. The natural permeability of cellular membranes appears to be important for the survival of the arthropod under low oxygen or high carbon dioxide atmospheres. Despite the similarities in response, arthropod mortality is generally greater in response to high carbon dioxide as apposed to low oxygen atmospheres. There appears to be a greater decrease in ATP and energy charge in arthropods exposed to high carbon dioxide as compared with low oxygen atmospheres, and this may be due to greater membrane permeability under carbon dioxide leading to an inefficient production of ATP. Reduced oxygen and elevated carbon dioxide atmospheres can have an additive effect in some cases, depending on the concentrations used. The effect of these atmospheres on arthropods depends also on temperature, species and life stage. Additional work is needed to fully understand the mode of action of controlled atmospheres on arthropod pests.