贡嘎山常绿落叶阔叶混交林主要树种叶功能性状

以贡嘎山常绿落叶阔叶混交林5种主要树种为研究对象,分析其叶片比叶面积(SLA)、叶干重(LDW)、碳(C)、氮(N)、磷(P)含量、同位素丰度(δ13C、δ15N)等叶属性特征,阐明常绿落叶阔叶混交林主要物种叶片性状的差异以及各种性状之间的相关关系,揭示主要树种叶片的水分和养分利用效率之间的关系以及这种关系对该群落中主要树种共存的影响机制。结果表明:贡嘎山常绿落叶阔叶混交林常绿树种与落叶树种比叶面积存在显著差异,叶片C含量与N、P含量呈显著负相关,N含量和P含量呈显著正相关;SLA与N含量、N∶P呈显著正相关关系,与δ13C、C含量、C∶N呈显著负相关关系,而与P相关性不显著;叶片δ13C与C∶N相关性不显著;SLA较高的叶片具有较高的叶片N含量,较低的叶C含量、氮素利用效率(NUE)和水分利用效率(WUE);叶片的WUE和NUE之间不存在权衡关系,未采用水氮耦合的权衡机制以适应潮湿多雨的环境;孑遗植物康定木兰(Indigofera souliei)和连香树(Cercidiphyllum japonicum)均采用异于非孑遗物种的养分利用策略,形成生态位的分化而共存于群落。     

丛林式橡胶林内植物水分利用效率与叶片养分含量

选取西双版纳地区丛林式橡胶林为研究对象,以纯橡胶林为对照,分别在2016年干季(3月)和雨季(5、6、7月)进行取样,测定两个样地内植物叶片δ13C值,比较植物水分利用效率,测定叶片C、N、P含量,计算叶片N/P值,分析植物对养分的利用与竞争关系,并综合分析植物水分利用效率与养分之间的相关性。结果表明,干季橡胶树受到干旱胁迫,其水分利用效率显著高于雨季,此时叶片N、P含量也显著高于雨季;丛林式橡胶林内橡胶树水分利用效率低于纯橡胶林内橡胶树,叶片N、P含量和N/P值均高于纯橡胶林中橡胶树;两个样地内不同植物与不同时间的水分利用效率,叶片C、N、P含量和N/P值均存在显著差异;相关性分析表明,水分利用效率与叶片N、P含量呈正相关,与叶片C含量、N/P值呈负相关。因此,丛林式橡胶林内橡胶树能更好地应对干旱,具有较强的养分获取能力。该研究揭示了丛林式橡胶林内植物水分利用效率以及养分利用特征,表明丛林式橡胶林是一种值得推广的农林复合生态系统。     

桂西北喀斯特坡地典型生境不同植物叶片的碳同位素差异

通过测定7种典型植物的叶片δ13C值,比较了桂西北喀斯特坡地连片裸露石丛及其临近浅薄土层处植物叶片δ13C值及其季节性差异。结果表明:旱季(2008年11月、2009年3月)植物叶片δ13C值显著高于雨季(2009年7月)(P0.05);旱季和雨季菜豆树、铁线莲、黄荆的δ13C值无显著差异(P0.05),而盐肤木、红背山麻杆、蕨、肾蕨旱季显著高于雨季(P0.05);季节性降雨差异对乔木类菜豆树、藤本类的铁线莲以及根系较深灌木叶片δ13C值的影响较小,而对浅根系草本植物、浅根灌木影响较大;旱季和雨季2种生境下菜豆树叶片δ13C值差异均不大,旱季和雨季连片裸岩生境的红背山麻杆和黄荆叶片δ13C值与临近浅薄土层生境值的差异虽不显著(P0.05),但差异大于菜豆树,说明生境条件的差异对这2种灌木叶片δ13C值的影响较大。     

浙江天童常绿阔叶林、常绿针叶林与落叶阔叶林的C:N:P化学计量特征

以浙江天童常绿阔叶林、常绿针叶林和落叶阔叶林为对象, 通过对叶片和凋落物C:N:P比率与N、P重吸收的研究, 揭示3种植被类型N、P养分限制和N、P重吸收的内在联系。结果显示: 1)叶片C:N:P在常绿阔叶林为758:18:1, 在常绿针叶林为678:14:1, 在落叶阔叶林为338:11:1; 凋落物C:N:P在常绿阔叶林为777:13:1, 常绿针叶林为691:14:1, 落叶阔叶林为567:14:1; 2)常绿阔叶林和常绿针叶林叶片与凋落物C:N均显著高于落叶阔叶林; 叶片C:P在常绿阔叶林最高, 常绿针叶林中等, 落叶阔叶林最低, 常绿阔叶林和常绿针叶林凋落物C:P显著高于落叶阔叶林; 叶片N:P比也是常绿阔叶林最高、常绿针叶林次之, 落叶阔叶林最低, 但常绿阔叶林凋落物N:P最低; 3)植被叶片N、P含量间(N为x, P为y)的II类线性回归斜率显著大于1 (p < 0.05), 表明叶片P含量的增加可显著提高叶片N含量; 凋落物N、P含量的回归斜率约等于1, 反映了凋落物中单位P含量与单位N含量间的等速损耗关系; 4)常绿阔叶林N重吸收率显著高于常绿针叶林与落叶阔叶林, 落叶阔叶林P重吸收率显著高于常绿阔叶林和常绿针叶林。虽然植被的N:P指示常绿阔叶林受P限制, 落叶阔叶林受N限制, 常绿针叶林受N、P的共同限制, 但是N、P重吸收研究结果表明: 受N素限制的常绿阔叶林具有高的N重吸收率, 受P限制的落叶阔叶林并不具有高的P重吸收率。可见, 较高的N、P养分转移率可能不是植物对N、P养分胁迫的一种重要适应机制, 是物种固有的特征。     

大兴安岭泥炭地植物叶片碳氮磷含量及其化学计量学特征

叶片碳(C)、氮(N)、磷(P)含量及其化学计量特征为植物养分状况和元素限制性提供依据。为了解不同生活型植物叶片C、N、P化学计量特征的变化,该研究测定、分析了大兴安岭地区18个泥炭地常见的3种草本植物——白毛羊胡子草(Eriophorum vaginatum)、玉簪薹草(Carex globularis)、小叶章(Deyeuxia angustifolia), 5种落叶灌木——柴桦(Betula fruticosa)、越桔柳(Salix myrtilloides)、细叶沼柳(Salix rosmarinifolia)、笃斯越桔(Vaccinium uliginosum)、越桔(Vaccinium vitis-idaea)和3种常绿灌木——杜香(Ledum palustre)、地桂(Chamaedaphne calyculata)、头花杜鹃(Rhododendron capitatum)的叶片C、N、P含量。结果表明: (1)落叶和常绿灌木叶片C、N、P含量总体高于草本植物而C:N、C:P、N:P低于草本植物, 说明不同生活型植物具有不同的养分利用策略,灌木叶片C、N、P储存高于草本植物而N、P利用效率低于草本植物; (2)小叶章和头花杜鹃叶片N:P小于10, 同时其N含量小于全球植物叶片平均N含量, 相比其他植物来说更易受N限制; (3)采样地点解释了叶片C、N、P指标变异的12.8%-40.8%, 植物种类对叶片C、N、P指标变异的解释量占9.3%-25.5%; (4)草本植物C、N、P指标的地点间变异系数高于落叶和常绿灌木, 草本植物C、N、P指标对地点因素变化的响应较灌木敏感; (5)草本植物N含量种间变异系数高于落叶和常绿灌木, 落叶灌木P含量种间变异系数高于草本植物和常绿灌木, 草本植物和落叶灌木N、P吸收的种间生理分化较常绿灌木高。     

Leaf C,N, and P concentrations and their stoichiometry in peatland plants of Da Hinggan Ling,China

叶片碳(C)、氮(N)、磷(P)含量及其化学计量特征为植物养分状况和元素限制性提供依据。为了解不同生活型植物叶片C、N、P化学计量特征的变化,该研究测定、分析了大兴安岭地区18个泥炭地常见的3种草本植物——白毛羊胡子草(Eriophorum vaginatum)、玉簪薹草(Carex globularis)、小叶章(Deyeuxia angustifolia), 5种落叶灌木——柴桦(Betula fruticosa)、越桔柳(Salix myrtilloides)、细叶沼柳(Salix rosmarinifolia)、笃斯越桔(Vaccinium uliginosum)、越桔(Vaccinium vitis-idaea)和3种常绿灌木——杜香(Ledum palustre)、地桂(Chamaedaphne calyculata)、头花杜鹃(Rhododendron capitatum)的叶片C、N、P含量。结果表明: (1)落叶和常绿灌木叶片C、N、P含量总体高于草本植物而C:N、C:P、N:P低于草本植物, 说明不同生活型植物具有不同的养分利用策略,灌木叶片C、N、P储存高于草本植物而N、P利用效率低于草本植物; (2)小叶章和头花杜鹃叶片N:P小于10, 同时其N含量小于全球植物叶片平均N含量, 相比其他植物来说更易受N限制; (3)采样地点解释了叶片C、N、P指标变异的12.8%-40.8%, 植物种类对叶片C、N、P指标变异的解释量占9.3%-25.5%; (4)草本植物C、N、P指标的地点间变异系数高于落叶和常绿灌木, 草本植物C、N、P指标对地点因素变化的响应较灌木敏感; (5)草本植物N含量种间变异系数高于落叶和常绿灌木, 落叶灌木P含量种间变异系数高于草本植物和常绿灌木, 草本植物和落叶灌木N、P吸收的种间生理分化较常绿灌木高。     

海南霸王岭不同森林类型附生兰科植物的多样性和分布

附生兰科植物是热带林附生植物的主要类群之一,对于维持热带林生态系统的物种多样性及生态功能具有重要的作用。以海南岛霸王岭国家级自然保护区内的6种热带原始林类型(热带季雨林、低地雨林、热带针叶林、山地雨林、山地常绿林及山顶矮林)中的附生兰科植物为研究对象,通过样带调查(每个森林类型设置12个10m×50m的样带,记录每个样带内胸径(DBH)≥5cm的树木及藤本上附生兰科植物的物种名称、株数及附生位置)分析了附生兰科植物的物种多样性、附生位置及其在不同森林类型中的分布规律。结果表明:1)3.6hm2森林调查样带内共记录到附生兰科植物9634株,分属于26属60种;2)除趋势对应分析(DCA)结果表明,6种森林类型中的附生兰科植物可分成5组(其中,山地常绿林与山顶矮林内的附生兰科植物归为一组);3)分布海拔范围相临近的森林类型的附生兰科植物具有较高的相似性,山地常绿林和山顶矮林附生兰科植物的相似性最高(88.9%);4)6种森林类型中,较高海拔的3种森林类型(山地雨林、山地常绿林和山顶矮林)中,附生兰科植物的丰富度和多度均显著高于其在较低海拔的3种森林类型(热带季雨林、低地雨林和热带针叶林),其中,附生兰科植物在山地常绿林内的丰富度和多度均最高;5)热带季雨林、低地雨林、热带针叶林及山地雨林内,宿主冠区附生兰科植物的多度均高于干区;山地常绿林内两者之间无显著差异;而山顶矮林干区的附生兰科植物的多度高于冠区;6)调查木上附生兰科植物的发生率在高海拔森林类型均高于其在低海拔森林类型,各森林类型内附生兰科植物的多度及物种丰富度与宿主胸径均存在显著正相关关系。     

北京城市绿化树种叶片碳同位素组成的季节变化及与土壤温湿度和气象因子的关系

城市绿化树种是城市生态系统的重要组成部分,为了探讨城市绿化树种水分利用效率的季节变化及其影响因素,本文对北京24个城市绿化树种(包括6个常绿针叶和18个落叶阔叶树种)叶片碳同位素组成(δ13C)的季节变化以及与土壤温湿度和气象因子的相关性进行了研究.结果表明:常绿树种叶片δ13C季节间差异不显著,春、夏和秋季的平均值都接近-25.9‰,在-27.0‰～-24.5‰间变化;落叶树种叶片δ13C季节间差异极显著(p=1.97×10-7秋季>夏季,表明绿化树种水分利用效率(WUE)也为春季>秋季>夏季.研究发现:叶片δ13C与比叶面积(SLA)呈显著的负相关(落叶p=6.195×10-8相似文献   

中国四种森林类型主要优势植物的C∶N∶P化学计量学特征

为了评价不同森林类型的生态化学计量特征的差异,以吉林长白山温带针阔混交林、广东鼎湖山亚热带常绿阔叶林、云南西双版纳热带季雨林和江西千烟洲亚热带人工针叶林为研究对象,通过对2007年4月-2008年5月4种典型区域森林植物叶片和凋落物的碳(C)氮(N)磷(P)元素质量比与N、P再吸收率的分析,探讨了4种森林类型N、P养分限制和N、P养分再吸收的内在联系.结果表明:1)从森林类型上看,温带针阔混交林叶片的C∶N∶P为321∶13∶1,亚热带常绿阔叶林叶片的C∶N∶P为561∶22∶1,热带季雨林叶片的C∶N∶P为442∶19∶1,亚热带人工针叶林叶片的C∶N∶P为728∶18∶1;凋落物的C∶N∶P也是亚热带人工林最高,达1950∶27∶1,温带针阔混交林的最低,为552∶14∶1,热带季雨林的为723∶24∶1,亚热带常绿阔叶林的为1305∶35∶1,不同森林类型凋落物的C∶N∶P的计量大小关系与叶片的结果一致;2)从植物生活型上看,常绿针叶林叶片的C∶N均显著高于常绿阔叶林及落叶阔叶林;叶片C∶P与森林类型的关系并不十分密切;常绿阔叶林叶片的N∶P最高,常绿针叶林次之,落叶阔叶林最低;3)植物叶片的N∶P与月平均气温有显著的负相关关系,但叶片的C∶P基本不受月平均气温影响,叶片的C、N、P计量比与降水的线性关系不显著;4)高纬度地区的植物更易受N元素限制,而低纬度地区植物更易受P元素的限制;但受N或P限制的植物并不一定具有高的N或P再吸收率.研究结果表明,不同类型森林的叶片与凋落物的化学计量特征具有一致性,但是环境因子对不同类型植物化学计量比的影响并不相同.     

木兰科常绿与落叶物种叶片构建策略的差异

为探究木兰科(Magnoliaceae)常绿与落叶物种叶片构建的生理生态策略,选取黄山木兰(Yulaniacylindrica)、玉兰(Y.denudata)和鸡公山玉兰(Y. jigongshanensis) 3种落叶物种,以及荷花玉兰(Magnolia grandiflora)、含笑花(Michelia figo)、石碌含笑(M. shiluensis) 3种常绿物种,对其叶片构建成本和叶片寿命相关的性状进行比较。结果表明,木兰科3落叶种的单位叶片面积成本(CCarea)显著低于3常绿种,但落叶和常绿物种的叶片质量成本(CCmass)差异不显著。落叶物种的叶氮、磷含量(Nmass,Pmass)和比叶面积(SLA)均显著高于常绿物种,而叶片寿命(LLS)显著低于常绿物种。CCarea与LLS呈显著正相关,Nmass、Pmass和SLA均与LLS呈显著负相关。这说明木兰科玉兰属落叶物种单位面积叶片构建成本小于常绿物种;落叶物种叶片寿命短,但采取低成本构建策略,提高比叶面积获得更多光资源,增加营养积累,也揭示了玉兰属落叶物种适应北亚热带较短的生长季和较低水热条件的生理生态策略。     

Reproduction in an Orchid Can Be Resource‐Limited over its Lifetime1

Most orchids studied thus far show long‐term resource adjustments to increases in fruit production within a flowering season, but none of these offers rewards to their potential pollinators. If nectar production is energetically expensive, then resources utilized to produce fruits and seeds may be even more limited in pollinator‐rewarding orchids than in non‐rewarding ones. Thus, resource adjustments may be more dramatic or entirely different in nectar producing plants. In this study, we performed artificial hand‐pollinations for two consecutive flowering seasons in die nectar producing orchid Comparettia falcata, and tested whether or not fruit set, seed set, and seed viability were limited by the quantity of pollinations or by resources. In addition, we compared mechanisms of short‐term (fruit abortion within seasons) and long‐term consequences (percent change in leaf length and change in flower number per plant between seasons, probability of shoot and inflorescence production, and mortality) between hand‐ pollinated and unmanipulated plants. The relationships among plant traits related to vegetative size and reproduction also were examined. Hand‐pollinations showed some negative effects. Fruit set was higher in hand‐pollinated plants in the first season but was similar to the controls in the second. Seed set was significantly lower and abortions were higher than in unmanipulated plants. On the other hand, some of our measurements were unaffected by die hand‐pollination treatment. Unexpectedly, there were no significant differences between groups in percent change in leaf length, change in flower number per plant between seasons, or die probability of shoot and inflorescence production. Although there was a strong correlation between leaf size and die number of flowers produced within a season, associations between leaf size and traits related to current or future reproduction were not consistent. Like other epiphytic orchids, pollination limitation occurred within a single season in C. falcata., but increases in fruit production also resulted in reduced lifetime fitness as estimated by a compounded fitness index. Contrary to all other epiphytic orchids studied, long‐term adjustments to increased fruit production in C. falcata through reduction in future growth or flower and inflorescence production were either minor or lacking. Our results suggest that the nature of plant strategies associated with resource constraints during sexual reproduction may be dependent on whether or not plants have evolved traits that are costly.     

The effect of nitrogen on plant water relations in tea (Camellia sinensis)

An experiment was carried out to study the effect of nitrogen deficiency on the water relations of tea (Camellia sinensis). The plants were grown in sand and nitrogen deficiency induced by witholding the supply of nitrogen. Nitrogen deficiency increased stomatal resistance and reduced transpiration. The capacity of the stomata to open fully in the morning was not impaired by nitrogen deficiency. Leaf water potential and probably root resistance were not affected by nitrogen deficiency. The sensitivity of transpiration and stomatal resistance to sand water stress was increased by nitrogen deficiency.     

Response of stomatal resistance and photosynthesis to night temperature in Populus deltoides

Summary Ramets from stem cuttings of three populations of Populus deltoides Bartr. from Wisconsin, Illinois, and Louisiana representing a latitudinal gradient were grown in pots outdoors at Urbana, Illinois and brought indoors for growth chamber studies. Leaf resistance and photosynthetic response to low night temperatures of 4° and 10° C were determined relative to 20° C controls for plants measured over one growing season. Plants from Louisiana, where nights are warm, reacted to cool nights of 4° and 10° C by opening their stomata slower upon illumination the following day than those from farther north where nights are cooler. The optimum night temperature for rate of opening was lower in the Wisconsin population than in populations from farther south. The Wisconsin population showed more ideal homeostasis of photosynthesis at different temperatures than the southern population which exhibited greater plasticity. No seasonal differences in these relationships were apparent other than at the time of leaf senescence.As plants approached senescence, which occurred earliest in the Wisconsin population, leaf resistance increased and photosynthesis declined, but stomata still retained their functional ability to respond to changes in night temperature. The change in leaf resistance, noted in the Wisconsin population, was related more to closure of lower-leaf surface stomata than upper. Only the Louisiana population had significantly more stomata on the lower than upper leaf surface.     

北京山区油松和元宝槭冠层气孔导度特征及其环境响应

叶片气孔是植物进行水汽交换的通道, 影响着植物的蒸腾和光合作用。然而叶片气孔行为受环境条件和树种类型的影响, 不同树种冠层气孔导度对环境因子响应的差异性, 以及在生长季不同时期叶片气孔对冠层蒸腾的调节作用是否会发生改变, 仍不清楚。该研究目的是通过探究各环境因子对不同树种冠层气孔导度的相对贡献率以及叶片气孔对冠层蒸腾的调节作用, 为深入了解植物水分利用状况和山区森林经营提供参考依据。于2018年生长季以北京八达岭国家森林公园内的58年生油松(Pinus tabuliformis)和39年生元宝槭(Acer truncatum)为研究对象, 利用热扩散技术对其树干液流进行连续监测, 并同步监测环境因子。利用彭曼公式计算冠层气孔导度(G_s)。主要结果: (1)油松和元宝槭日间G_s在日、月时间尺度上存在明显差异。5-7月油松和元宝槭日动态G_s均随饱和水汽压差(VPD)和太阳辐射(GR)的增加呈上升趋势, 上升持续时间比8月和9月长; 在月尺度上, 随着VPD、GR的降低和土壤湿度(VWC)的升高, G_s从5月到9月整体上升。(2)利用增强回归树法分析得到VWC和VPD对G_s的贡献率最大, 其次是GR、气温和风速。VWC和VPD对油松G_s的贡献率分别为66.4%和17.4%, 对元宝槭G_s的贡献率分别为54.8%和21.0%。(3)油松和元宝槭的dG_s/dlnVPD值与参考冠层气孔导度之间的斜率均显著高于0.6, 气孔调节作用相对较强。综上所述, 气孔对环境因子的响应在树种以及生长季不同时期之间存在差异, 为防止水分过度散失, 两树种在不同土壤水分条件下均通过严格的气孔调节控制蒸腾量。     

Large-scale patterns of stomatal traits in Tibetan and Mongolian grassland species

We aimed to disentangle the influence of environmental variables on the spatial patterns in stomatal occurrence and stomatal traits. We surveyed the stomatal occurrence and the stomatal length (SL), density (SD) and index (SI) of 99 species in 150 grassland sites on the Tibetan and Inner Mongolian Plateau to explore their spatial patterns and evaluate the influence of climate. Of all species studied, two thirds were amphistomatous. The species from the Tibetan Plateau had larger but fewer stomata than those from Inner Mongolia. Among the climate factors examined, temperature and insolation affected SD, SI and SL, whereas the CO₂ partial pressure and the relative humidity affected SD. The climatic variables showed similar effects on the spatial variation of the adaxial and abaxial stomatal traits. We conclude that the low temperature and high insolation at high altitudes may be responsible for the larger and fewer stomata in plants on the Tibetan Plateau. The stomatal parameters that are presented here can be used to model the gas exchanges at the ecosystem scale.     

Effects of fire regimen on two species of epiphytic orchids in tropical savannas of the Northern Territory

The effect of four fire regimens (early dry season annual, late dry season annual, early dry season biennial, unburnt) on the numbers of epiphytic orchids in a savanna community in Kakadu National Park was investigated. These fire regimens had been maintained on I ha plots for 16 years. Two species of epiphytic orchid were present — Cymbidium canaliculatum and Dendrobium affine. The numbers of Cymbidium plants were insufficient to enable statistical analysis, but plants were present in the unburnt, early annual and early biennial fire treatments. Dendrobium occurred in substantial numbers irrespective of fire treatment, but the extent of colonization of all available host trees was greater in the unburnt than the burnt treatments. The lower numbers of Dendrobium plants in burnt treatments was due to a lower proportion of potential host trees being colonized and a lower number of orchids on each colonized tree. The proportion of small trees colonized was markedly lower in burnt treatments. Frequent fires late in the dry season may prevent recruitment of the main host species. Eucalyptus tectifica. The survival of orchids despite frequent fires depended on the availability of relatively protected sites for colonization and the ability of the orchids to withstand some fire damage.     

南京地区落叶栎林主要木本植物的展叶动态研究

 植物的展叶过程是由自身遗传因子决定的,同时又受到多种生态因子的调节,反映了植物的生活史对策和群落物种多样性的维持机制。在2001和2002年的3～6月间,不定期记录了南京地区三个落叶栎(Quercus spp.)林中主要木本植物的展叶情况,包括被标记标准枝的叶数、叶的长度、宽度、叶面积、叶干重等参数。结果表明在所调查的落叶栎林中,林冠层物种的成熟叶面积和单位叶面积干重都显著大于林下层物种;最早展叶的物种为林下层物种,但林冠层展叶顺序与林下层无显著差异。叶面积越大、单位叶面积干重越小的物种展叶越晚;林冠层物种展叶较林下层快,物种成熟叶面积越大,展叶速率越大。最后对展叶顺序和展叶速度的生态学意义作了讨论。     

Leaf nitrogen distribution in relation to leaf age and photon flux density in dominant and subordinate plants in dense stands of a dicotyledonous herb

We studied the effects of photon flux density (PFD) and leaf position, a measure of developmental age, on the distribution of nitrogen content per unit leaf area (N _area) in plants of different heights, in dense stands grown at two nitrogen availabilities and in solitary plants of the erect dicotyledonous herb Xanthium canadense. Taller more dominant plants received higher PFD levels and experienced a larger difference in relative PFD between their youngest and oldest leaves than shorter subordinate plants in the stands. Differences in PFD between leaves of solitary plants were assumed to be minimal and differences in leaf traits, found for these plants, could thus be mainly attributed to an effect of leaf position. In the solitary plants, N _area decreased with leaf position while in the plants from the stands it decreased with decreasing relative PFD, indicating both factors to be important in determining the distribution of N _area. Due to the effect of leaf position on N _area, leaves of subordinate plants had a higher N _area than older leaves of dominant plants which were at the same height or slightly higher in the canopy. Consequently, the N _area distribution patterns of individual plants plotted as a function of relative PFD were steeper, and probably closer to the optimal distribution which maximizes photosynthesis, than the average distribution in the stand. Leaves of subordinate plants had a lower mass per unit area (LMA) than those of dominant plants. In the dominant plants, LMA decreased with decreasing relative PFD (and with leaf position) while in the subordinate plants it increased. This surprising result for the subordinate plants can be explained by the fact that, during the course of a growing season, these plants became increasingly shaded and newer leaves were thus formed at progressively lower light availability. This indicates that LMA was strongly determined by the relative PFD at leaf formation and to a lesser extent by the current PFD. Leaf N content per unit mass (N _mass) was strongly determined by leaf position independent of relative PFD. This indicates that N _mass is strongly ontogenetically related to the leaf-aging process while changes in N _area, in response to PFD, were regulated through changes in LMA. Received: 11 May 1997 / Accepted: 9 September 1997     

14种木犀榄族植物叶表皮微形态的研究

利用光学显微镜和扫描电子显微镜对木犀榄族（Oleeae）5属14种植物的叶表皮微形态特征进行了观察,结果表明：（1）叶表皮细胞形状有无规则形和多边形两种;下表皮腺点的数目远远大于上表皮,流苏树上表皮细胞没有腺点;叶下表皮有气孔器,形状为圆形、椭圆形;气孔器均为不规则型;气孔器外围角质层有放射状、条状、环状、颗粒状等多种类型;（2）气孔器和叶表皮细胞许多特征具有明显的种间差异,可以作为种间鉴定的重要依据;（3）叶表皮微形态结构上的许多共同特征,表明木犀榄族植物是单独一自然类群。上述特征可为木犀榄族植物属及物种的划分与鉴定、系统演化关系的探讨等提供参考。     

Leaf anatomical structures of <Emphasis Type="Italic">Paphiopedilum</Emphasis> and <Emphasis Type="Italic">Cypripedium</Emphasis> and their adaptive significance

Paphiopedilum and Cypripedium are closely related in phylogeny, but have contrasting leaf traits and habitats. To understand the divergence in leaf traits of Paphiopedilum and Cypripedium and their adaptive significance, we analyzed the leaf anatomical structures, leaf dry mass per area (LMA), leaf lifespan (LL), leaf nitrogen concentration (N _mass), leaf phosphorus concentration (P _mass), mass-based light-saturated photosynthetic rate (A _mass), water use efficiency (WUE), photosynthetic nitrogen use efficiency (PNUE) and leaf construction cost (CC) for six species. Compared with Cypripedium, Paphiopedilum was characterized by drought tolerance derived from its leaf anatomical structures, including fleshy leaves, thick surface cuticles, huge adaxial epidermis cells, lower total stoma area, and sunken stomata. The special leaf structures of Paphiopedilum were accompanied by longer LL; higher LMA, WUE, and CC; and lower N _mass, P _mass, A _mass, and PNUE compared with Cypripedium. Leaf traits in Paphiopedilum helped it adapt to arid and nutrient-poor karst habitats. However, the leaf traits of Cypripedium reflect adaptations to an environment characterized by rich soil, abundant soil water, and significant seasonal fluctuations in temperature and precipitation. The present results contribute to our understanding of the divergent adaptation of leaf traits in slipper orchids, which is beneficial for the conservation of endangered orchids.