【作者】 何春霞；

【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】 树木是地球上生长最高的生命体。但即使资源丰富、各类胁迫因子很小,树木也不能无限长高、且不同树种最大高度不同、同一树种在不同生境下最大高度亦不同。而树高生长的停滞是造成群落生产力降低的主要因素之一。目前树高极限的限制因子引起很多学者的关注。而研究树高极限的限制因子对群落的生理生态学有重要意义,并对提高林分生产力的具有指导意义。为了更好地了解树高极限的限制因素,本文对全国典型水分分布区域西双版纳、广州、郑州、北京、贺兰山和毛乌素沙地等地区生长的望天树、浆果乌桕、小叶藤黄、柠檬桉、巨尾桉、南洋楹、毛白杨、悬铃木、银杏、油松、榆树、沙枣、小黄柳等32种较高的木本植物进行了研究。采用石蜡切片法观察叶片的解剖结构、用指甲油印模法观察叶片的气孔特性,丙酮浸提法测定叶片的光合色素含量、用Licor-6400光合仪测定叶片的气体交换特性、压力势法测定小枝的水势和用P-V法估计组织细胞的水分参数等指标随树高的变化关系以及17种广布种上述指标沿环境梯度的差异进行了研究,以初步探讨树木长高和外界环境对叶片结构、生理特性和水分参数的影响,找出影响树高极限的主要因素。本文主要得出以下结论:（1）叶片结构随树高的变化:研究的25种树种表现为越往树顶处:1)角质层越厚;2)栅栏组织越发达,全栅特征越明显;3)叶组织细胞排列越紧密;4)叶肉细胞越小;5)表皮层越厚,气孔越小而密、单叶的气孔总面积越小;6)叶片越小而厚,LMA越大。上部叶片趋于旱生型的形态解剖结构特征反映出了其在结构上具有较强的适应水分胁迫的能力,证实其遭受了水分胁迫。（2）叶片的气体交换特性随树高的变化:32树种中的大多数种的叶绿素含量随树高增加而变少、δ¹³C与树高呈正相关而△则与树高呈负相关。而研究的4树种的叶片光合、蒸腾速率、气孔导度和胞间CO₂浓度等均与树高呈负相关。与气孔大小及开口面积随树高变小的结论一致,表明随树高水力阻力的增大限制了叶片的气体交换特性、水分利用效率和光合能力。（3）水分参数随树高的变化:28树种的水势与树高呈线性负相关、通过水势预测的国内树木极限高度为86～100m。随树高的增加,细胞的弹性减小、渗透调节和抗旱能力增强,而维持最大膨压的能力降低,使得细胞伸展受限。与叶片结构和生理特性的变化趋势一致。应该是水力限制影响了叶片的水势和膨压、同时造成叶片的结构发生改变,而结构的改变加剧了水力对气体交换的限制、影响了光合碳同化以及对CO₂的分馏效应、使叶片的水分利用效率和抗旱性增强。（4）广布种叶片结构、水分参数等对环境梯度的响应:17种广布种由南向北、随着水热条件的递减,叶片、栅栏组织、角质层、上下表皮的厚度、LMA递增或先减后增、气孔的大小和总开口面积递减、而气孔密度递增,大多树种抗旱性增强、所有树种的δ¹³C增大,表明随着水热状况变差、叶片的气体交换受到限制、水分利用效率增加。植物叶片δ¹³C值受到多个气候要素的影响、而水分是最重要的影响因子。降雨量、年均温与δ¹³C呈负相关,而降雨量1100mm和年均温19℃是叶片碳同位素分辨率的分界点,在此基础上,水分变好对δ¹³C的影响减小、而温度过高反而对碳稳定同位素分馏产生负影响。（5）综上,叶片的结构、生理特性和水分参数等指标随树高的变化与随水分梯度递减的变化趋势一致,证实随树高长高水力限制显著增大。水分对树高生长的限制首先是外在的水分状况,群落的总体高度随外界水分状况的变差而变矮;再就是水力限制对单株树木的结构和功能的影响,水势降低、膨压减小使细胞的分裂和扩展受限,旱生型结构加剧水力对气体交换能力的限制、使光合碳同化能力受到限制、而呼吸消耗却随着树木个体的增大而增大,制造营养物质不足、使得营养亏缺、造成投入新枝叶的营养受限,最终限制了树高继续增长。即水力限制引发了营养限制,最终限制了树高极限。更多还原

【Abstract】 The tallest living organisms are trees.While tree height growth slows down as trees grow taller even where resources are abundant,stresses are minor.The maximum tree height is different within different tree species and the same tree species differs in height in different environments.The stop of tree height growth is one of the main factors that would reduce community production.Many researchers focus on tree height limitation factors now.Researches on tree height limitation mechanisms are significant on community ecophysiology,and are also meaningful in improving stand productivity.In order to better understand the determinants of tree height limit,32 tall tree species such as Parashorea chinensis,Sapium baccatum,Garcinia cowa,Eucalyptus citriodora,E.grandis×E.urophylla,Albizia falcataria,Populus tomentosa,Platanus hispanica,Ginkgo biloba,Pinus tabulaeformis,Ulmus pumia,Salix gordeivii,and Elaeagnus angustifolia from typical environments such as Xishuangbanna rainforest,Guangzhou subtropical area,Zhengzhou,Beijing,Helanshan mountain and Maowusu sandland in China were studied.Respectively with the method of porraffin and nail varnish method,acetone extraction,Lior-6400 portable photosynthesis system and pressure bomb and P-V method,morphological,photosynthetic pigments content,gas exchange characteristics and leaf water potential and water parameters with tree height of the 32 tree species were studied and The above indices of 17 tree species that widely spread in different environment gradients were also measured in order to find the environmental limitation factors on tree height.Main conclusions are as follows:（1） changes of leaf morphological and anatomical structures with tree height:25 researched tree species exhibited xeromorphic structures at tree top,that is,toward tree top,leaves were with 1) increased cuticle thickness;2) developed palisade tissue and even double-palisade structure;3) densely arranged tissue cells;4) smaller cells;5) thicker epidermis,smaller and denser stomata;6) smaller and thicker leaf,great LMA value.Xeromorphic structure reflected tree top leaves with stronger adaptability to water stress,and suggested that they were under water stress condition.（2） changes of gas exchange capabilities with tree height:leaf photosynthetic pigments and△value of 32 researched tree species decreased,while leafδ¹³C value increased with tree height. Photosynthetic rate,transpiration rate,stomata conductance and internal CO₂ concentration of 4 researched tree species were negative with tree height.The results were consistent with the result of the changes of stomata structure with tree height and suggested that increased hydraulic limitation with tree height influenced gas exchange characteristics,water use efficiency and photosynthetic capability. （3） changes of water parameters with tree height:water potential of 28 tree species were negatively and linearly related to tree height.Maximum tree height of 86～100m was estimated with water potential in China.Water relations of 22 tree species estimated with P-V method showed that cell wall elasticity,osmotic adjustment,and drought resistant capability of most tree species were positive with tree height,while turgor maintenance capability reduced with tree height,which limit cell division and tree height growth.The trends were consistent with the changes of leaf structure and biophysical characteristics.It’s possibly that increase of hydraulic limitation with tree height influenced leaf water potential and turgor as well as leaf structure,which strengthened hydraulic limitation on leaf gas exchange characteristics including photosynthesis and transpiration rate, resultantly influenced carbon assimilation and CO₂ fractionation and increased water use efficiency and drought resistance capability.（4） response of leaf structure and water parameters of widely spread trees species to environmental gradients:from south to north,with the reduction of water and heat condition, thickness of leaf,palisade tissue,cuticle,epidermis and LMA increased or decreased firstly then increased;stomata size and aperture reduced,while stomata density,drought resistance capability andδ¹³C increased.It suggested that worse water and heat condition limited gas exchange capability and increased water use efficiency.Leafδ¹³C value of tree species from different climate condition was influenced by many climate elements and water condition was the most important one.Precipitation and average temperature were negative withδ¹³C value,rainfall and average temperature respectively at 1100mm and 19℃were dividing point for carbon isotope discrimination.Higher temperature increasedδ¹³C,while better water condition influencedδ¹³C less.（5） To sum up,the trend of leaf structure,biophysical characteristics and water parameters with tree height was similar with the change trend of these indices with water gradients.It proves that tree top leaves suffer from water stress and hydraulic limitation becomes greater with tree height.Water stress influence tree height growth in several aspects:firstly is the influence of exterior water condition,and community average tree height is positive with exterior water condition.Secondly, hydraulic limitation influences individual tree structure and function.Xeromorphic structure,Lower water potential and turgor pressure limit cell division and expansion,which restrict gas exchange and carbon assimilation capability.However,respiration consumption increases with the spread of tree crown.Shortage of nutrient limits carbon investigation on new leave growth and may ultimately limit tree growth.Thus,the main limitation of tree height is water.And hydraulic limitation may firstly cause nutrient limitation and ultimately limit tree height.更多还原