【作者】 刘娟娟；

【导师】 李吉跃；

【作者基本信息】 北京林业大学 ， 森林培育， 2009， 博士

【摘要】 CO₂浓度上升影响植物的生长、竞争及水分关系,可以引起植物快速生长而可能使植物在干旱胁迫下更易遭受空穴和栓塞,导致输水系统破坏而不能存活,从而严重影响陆地植物的输水安全与生存。本文以在北京林业大学苗圃内的密闭式生长箱内经过不同时间的高CO₂浓度处理的7个主要造林和绿化树种（油松、侧柏、刺槐、元宝枫、丁香、大叶黄杨和白蜡）为试验对象,研究CO₂浓度增加与干旱胁迫对植物水分运输的影响。通过系统测定其生长指标（苗高、地径、叶生长、叶解剖结构和生物量）、生理指标（气体交换特性、荧光参数、光合特性和碳同位素比值）、水分利用效率、耗水特性、水力结构参数（导水率、比导率、叶比导率和胡伯尔值）、水分参数等分别在720μmol·mol^-1CO₂和380μmol·mol^-1CO₂（大气现有CO₂浓度）浓度下随着干旱胁迫的变化,得出以下主要结论:（1）高CO₂浓度下,7树种的苗高、地径、叶面积、生物量、根茎比、光合速率、胞间CO₂浓度、Fv/Fm、Fv/Fo、WUE_i和WUE_L均增加,阔叶树的海绵组织厚度、栅栏组织厚度、叶片厚度、叶片紧密度、气孔长径、短径、气孔长径和短径比、单个气孔面积均增加。其中,叶面积增长大小为刺槐＞白蜡＞丁香＞元宝枫＞大叶黄杨＞侧柏＞油松,栅栏组织厚度增加的幅度最大。同时,气孔密度、蒸腾速率、暗呼吸速率、比叶重、δ¹³C值和耗水量下降,气孔导度是先减小后增大。针叶树的叶δ¹³C值高于阔叶树,叶δ¹³C值明显小于枝条和根系的,刺槐和白蜡的δ¹³C值超出了全球C₃植物的δ¹³C值的极限范围,720μmol·mol^-1CO₂所有树种的平均值远高于C₃植物的平均值27.0‰。（2）随着干旱胁迫的增加,海绵组织厚度、栅栏组织厚度、叶片厚度、叶片紧密度、疏松度、气孔长径和短径比、耗水量、叶片、枝条和根生物量均减小,油松和侧柏的角质层厚度、上下表皮厚度、根茎比和WUE_L增加。4树种的耗水量日变化呈单峰型曲线,耗水速率在叶面积变化较大时与耗水量的变化不同。CO₂增加和干旱胁迫减弱了干旱或者CO₂浓度增加中的某一单因子对气孔变化的敏感性,使得气孔变化缓慢。（3）不同CO₂浓度培养时间的侧柏,总生物量不是随着培育的时间越长其生物量增加的越大。培养1年时间的枝条和根系的δ¹³C值均大于2年培养时间的。元宝枫叶片δ¹³C多重复干旱循环的变化曲线呈波浪形,在重度干旱时达到每个波段的顶点,随着循环次数的增加波动幅度越小。高CO₂浓度下树种发生干旱胁迫的时间比正常CO₂浓度的时间慢,延长了植物的干旱周期,720μmol·mol^-1CO₂处理可以减缓水势的降低,减少干旱胁迫对植物造成空穴和栓塞的危险性,CO₂浓度增加延迟了水分胁迫的发生,改善了植物体内的水分状况。（4）不同CO₂浓度元宝枫在多重复干旱循环中,第2次重复干旱是一个比较复杂的过程,是多重复干旱调节的重要时期。随着CO₂浓度的增加,RWC⁰/RWC_s下降,Ψ⁰π和Ψ¹⁰⁰π在循环1时先增加后下降,一直持续到循环3,高CO₂浓度下元宝枫维持膨压的能力增强,渗透调节和自身保护能力,以及忍耐脱水能力虽然增加,但是抗脱水能力却减弱了,不能同时兼得。720μmol·mol^-1CO₂元宝枫ε^max在水分条件较好时增加,细胞壁较坚硬,弹性小,但是到循环3时,ε^max在轻度干旱和中度干旱时下降,到后期水分严重胁迫时却升高。（5）随着CO₂浓度增加,7树种的0级、1级和2级分枝的导水率增加,比导率增加而大叶黄杨和丁香的1级和2级分枝下降,叶比导率在各分枝级的变化不一致,胡伯尔值变化不明显。2级分枝的导水率增幅大于0级和1级。分枝级导水率、比导率和胡伯尔值随着干旱胁迫的增加而逐渐下降,叶比导率在720μmolmol^-1CO₂浓度下随着干旱胁迫的增加非线性变化。不同茎段所在区域的导水率、比导率和叶比导率CO₂浓度的增加均增加,随着干旱胁迫的增加而减小。（6） PLC为50%的水势Ψ₅₀作为脆弱曲线的拐点,随着相对分枝级的增加Ψ₅₀值增大;拐点将曲线分为两部分,靠右段和靠上段。靠右段越靠右,水势阈值越大,PLC=0时的水势值甲Ψ₀值为发生栓塞的水势阈值。综合考虑甲Ψ₀、Ψ₅₀和Ψ_max,植物相对分枝级的栓塞脆弱性大小为2级＞1级＞0级,2年侧柏大于1年侧柏,不同茎段所在区域的栓塞脆弱性大小为限速区＞非限速区,1年侧柏大于2年侧柏。首先受害的是2级分枝,也就是说在干旱胁迫到一定严重程度后,植物采取抵御干旱胁迫的生态策略是尽可能的保存主干和低分枝级的部分。（7）不同树种在不同干旱胁迫,不同相对分枝级,不同茎段所在区域采取不同的方式来适应由水势降低而引起的栓塞变化,在不同的水势阶段,而采取有效性和安全性折衷的策略,这些策略有:保持较高的水分安全性;减轻安全性而对有效性的折衷;同时降低有效性和安全性但不是终止任何生产力或树高的组织生长的所需水的限制。更多还原

【Abstract】 The water,growth and competition of trees were influenced by elevated CO₂ concentration,which caused quickly growth of trees might easier to suffer cavitation and embolism and can not surive because of water transport system destroyed.It can seriously influenced the water transport efficiency and security.The water transport of trees under 720μmol·mol^-1CO₂ and drought stress were measured after 7 trees have been exposed to 720μmol·mol^-1CO₂ for different times.The growth index（the growth quantity,leaf area, leaf tissue characteristics and biomass）,physiological index(gas exchange parameters, chlorophyll fluorescence parameters,photosynthesis characteristics andδ¹³C),water use efficiency,water consumption characteristic,hydraulic architecture parameters（hydraulic conductivity,specific conductivity,leaf specific conductivity,Huber values）,water parameters were measured under 720μmol·mol^-1CO₂ and 380μmol·mol^-1CO-2 with drought stress.The results show that:（1） The 7 trees growth quantity,leaf area,biomass,root/shoot ratio,photosynthesis rate,Ci,Fv/Fm,Fv/Fo,WUE_i and WUE_L increased with elevated CO₂ concentration.Also, the thickness of spongy tissue,thickness of palisade tissue,thickness of leaves,stomatal long diameter,stomatal wide diameter,stomatal area and stomatal long diameter/stomatal wide diameter increased.The sequence of leaf area was Robinia pseudoacacia,Fraxinus chinesis,Syringa oblate,Acer truncatum,Euonymus japonicus,Platycladus orientali and Pinus tabulaeformis.The stomatal density,transpiration rate,dark respiration rate,specific leaf weight,δ¹³C and water consumption was decreased,while stomatal conductance was firstly decreased and then increased along elevated CO₂ concentration.Theδ¹³C of conifer trees were higher than broad-leaves trees and root and branch ofδ¹³C were obviously bigger than leaf.Theδ¹³C of Robinia pseudoacacia and Fraxinus chinesis were gone beyond the range of C₃ plants,and the averageδ¹³C of 7 trees under 720μmol·mol^-1CO₂ were higher than the average of C₃ plants,which is 27.0‰.（2） Thickness of spongy tissue,thickness of palisade tissue,thickness of leaves, stomatal long diameter/stomatal wide diameter,water consumption and biomass decreased along water stress,while cuticle thickness of epidermis of Pinus tabulaeformis and Platycladus orientalis,thickness of epidermis,root/shoot ratio and long-term water use efficiency increased.The water consumption curve of trees was unimodal curve,which different from water consumption rate when the leaf area great changed.The stoma changed slowly because of the interaction between elevated CO₂ concentration and water stress which changed the sensitivity of stoma under only CO₂ concentration or water stress.（3） The total biomass of Platycladus orientalis was not increased with long times under elevated CO₂ concentration.Theδ¹³C of root and branch under elevated CO₂ concentration with 1 year were also bigger than that of 2 years.The leafδ¹³C of Acer truncatum was undulate under controlled cycles of dehydration and rehydration and CO₂ concentrations.The peak of the curve were appeared at serious water station,and the fluctuate range decreased with the circles of the water stress.The water potential were decreased under 720μmolmol^-1CO₂,which reduced the occurrence of cavitation and embolism,delayed the happen of water stress and changed the water stress in plants.（4） The circle 2 was a more complicated and important phase of Acer truncatum under controlled cycles of dehydration and rehydration and CO₂ concentrations.RWC⁰/ RWC_s decreased whileΨ⁰πandΨ¹⁰⁰πincreased firstly in circle 1,and then decreased from circle 1 to 3 along elevated CO₂ concentrations.The ability of maintaining turgor pressure, osmotic adjustment,capable of preserving and endurance of water separation capability were increased under elevated CO₂ concentrations,whereas the resistance of water separation capability decreased.Theε^max) increased in normal water condition of Acer truncatum under 720μmol·mol^-1CO₂,and cytoderm more hardness and less elasticity.But in circle 3,ε^max decreased in light and middle drought conditions and increased in serious drought condition.（5） The branch 0,branch 1 and branch 2 of hydraulic conductivity of 7 trees increased along elevated CO₂ concentration.Specific conductivity increased,while Euonymus japonicus and branch 1 and branch 2 of Syringa oblata were decreased.The leaf specific conductivity and Huber values changed ruleless.Branch 0 and branch 1 of hydraulic conductivity increased amplitude were smaller than branch 2.Hydraulic conductivity, specific conductivity and Huber values with relative ramification rate were gradually decreased along water stress,while leaf specific conductivity was not linearity changed under 720μmol·mol^-1CO₂ along water stress.Hydraulic conductivity,specific conductivity and leaf specific conductivity in different area stem segment increased under elevated CO₂ concentration and decreased under water stress.（6） The water potentialΨ₅₀ of 50%of PLC was the inflexion of the vulnerability curve,which increased with relative ramification rate;the inflexion divided the curve,the right part and upside part.The more right the right part keep,the bigger the water potential threshold value.The water potential ofΨ₅₀.which is PLC equal to 0,is the threshold value of occurrence embolism.General considerd theΨ₀,Ψ₅₀ andΨ_max,the embolism vulnerability with relative ramification rate was branch 2,branch 1 and branch 0,1 year of Platycladus orientalis smaller than that of 2 years.The embolism vulnerability in different area stem segment was restricted stem segment bigger than non-restricted stem segment, while 1 year of Platycladus orientalis bigger than that of 2 years.Branch 2 was the first damaged part of trees.It means that the ecological strategy of trees adopting the water stress was trying their best to keep the trunk and low branch part.（7） Use different manners to accommodate to the embolism which caused by decreased water potential,7 trees with relative ramification rate and in different area stem segment,were taking ecological strategy of tradeoff of efficiency and security in different water stress.This strategy include keeping high water transport security,alleviating water transport security to tradeoff the efficiency,and at the same time,reducing the water transport security and efficiency but not end the needing of water to growth and any productivity.更多还原