鼎湖山森林群落不同演替阶段优势种叶生态解剖特征研究

对南亚热带鼎湖山森林群落不同演替阶段8种优势树种进行了叶生态解剖学研究。观察的叶片解剖特征有：叶腹角质膜厚度、栅栏组织厚度、海绵组织厚度、叶背角质膜厚度及叶总厚度等。马尾松（Pinus massoniana)在针叶林群落和针阔叶混交林群落生境中,针阔叶混交林中叶片厚度变小,主脉管胞、树脂道平均直径变小。从针阔叶混交林演替阶段到季风常绿阔叶林演替阶段,锥栗（Castanopsis chinensis)叶片厚度、海绵组织厚度增加,栅栏组织厚度、P／S值（栅栏组织与海绵组织厚度比）减少;荷木（Schima superba)和黄果厚桂（Cryptocarya concinna)叶片厚度、栅栏组织厚度、叶腹及叶背角质膜厚度差异显著;从针阔叶混交林演替阶段到季风常绿阔叶林演替阶段,锥栗、荷木、黄果厚寺叶片厚度和栅栏组织厚度等差异均显著。不同生境下林内气温、相对湿度、光合有效辐射等小气候特征是叶片结构特征差异的主要影响因子,叶片结构差异反映了叶片结构在一定程度上对生境的适应。     

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。     

苦瓜叶片结构与白粉病抗性的关系

以不同抗白粉病的苦瓜品系幼苗为材料,对它们的叶片及上下表皮厚度、栅栏组织及海绵组织厚度、叶片结构紧密度及疏松度、蜡质含量、比叶重、气孔及茸毛密度等叶片结构进行观察比较,探讨苦瓜白粉病抗性与其主要叶片结构指标的关系。结果显示:（1）抗病苦瓜品系叶片的蜡质含量显著高于感病品系,与病情指数呈显著负相关关系,蜡质层是其抵抗和延迟病原菌侵入的一个有力结构屏障。（2）感病品系叶片的气孔和叶背面茸毛数量显著多于抗病品系,且叶背面的气孔及茸毛密度与病情指数呈显著正相关关系,即气孔和茸毛越少越抗病。（3）抗病苦瓜品系的叶片栅栏组织以及海绵组织排列整齐、紧密,而高感品系的叶片组织出现大量孔隙,较难观察到完整细胞。（4）抗病品系叶片厚度、下表皮厚度、栅栏组织厚度、叶片结构紧密度明显高于感病品系,而感病品系的海绵组织厚度、叶片结构疏松度明显高于抗病品系;且苦瓜比叶重与其白粉病抗性关系不大。研究认为,苦瓜叶片蜡质含量、叶背面气孔及茸毛密度可以作为苦瓜白粉病抗性鉴定的参考指标。     

茂兰喀斯特森林不同演替阶段植物叶片功能性状与土壤因子的关系

植物如何改变功能性状来适应环境一直是生态学的研究征点。为探究茂兰喀斯特森林不同演替阶段植物叶片的适应策略，该文以茂兰自然保护区5个不同演替阶段(草本、灌木、灌乔、乔木和顶极群落阶段)优势种为研究对象，测定不同演替阶段的优势植物叶片功能性状与土壤理化性质。结果表明：(1)随着植被正向演替的进行，土壤全氮(STN)含量、土壤有机质(SOM)含量、土壤含水量(SWC)逐渐增加，土壤全磷(STP)含量和土壤全钾(STK)含量先增加后减少，土壤pH值整体呈减小的趋势。(2)随着植被演替的进行，叶面积(LA)、叶干物质含量(LDMC)、叶厚度(LT)和叶片碳含量(LCC)逐渐上升，比叶面积(SLA)与叶片钾含量(LKC)则与之相反，叶片氮含量(LNC)呈先升后降的趋势，叶片磷含量(LPC)呈先降后升的趋势。(3)冗余分析表明，演替初期植物主要分布在土壤pH值高而STK、STP、SWC、SOM、STN相对低的环境中，群落内植物叶片采取高SLA、LNC、LPC,低LA、LDMC、LT、LWC的性状组合，演替晚期植物主要分布在土壤水分和养分含量较高的环境，LDMC、LT、LA、LWC与演替初期相比呈上升...     

润楠属广布种和狭域种幼苗生理生态特征

润楠属植物属于基部被子植物类群,大部分物种局限分布于热带亚热带森林的潮湿生境,但也有些物种分布范围较广。本研究以润楠属11个物种的幼苗为材料,测定了一系列植物叶片水力学性状和解剖结构,包括:比叶重、叶片密度、气孔密度、叶脉密度、膨压丧失点水势、栅栏组织和海绵组织厚度等。结果表明:与其它分布在热带亚热带地区的被子植物相比,润楠属植物的叶脉密度较低,推测叶脉密度受强烈的进化限制;该属植物叶脉密度与气孔密度、栅栏和海绵组织的比值呈显著的正相关,表明该属植物能够维持叶片水平的水分供需平衡;广布种比狭域种具有更低的叶片膨压丧失点和更高的叶片密度,耐旱能力更强,但是比叶重差异不显著;叶片的膨压丧失点与物种的最大树高呈反比,即更高的物种叶片耐失水能力更强,说明植物叶片耐旱性与植物本身的遗传特性有关。本研究结果显示,叶片水力学性状可以较好地用于解释润楠属植物的地理分布。     

不同放牧率对内蒙古典型草原植物叶片解剖结构的影响

以内蒙古草原生态系统定位研究站15a长期放牧样地的7种主要植物(扁蓿豆、冰草、糙隐子草、冷蒿、小叶锦鸡儿、星毛委陵菜、羊草)为材料,通过对不同放牧率(无牧、轻牧、中牧、重牧)下植物叶片解剖结构(角质层厚度、表皮细胞面积、叶肉细胞面积、栅栏/海绵组织厚度、叶片厚度、中脉厚度)特征以及化学成分变化的研究,探讨不同植物对长期放牧的适应策略,从而为典型草原放牧演替规律提供理论依据.结果表明:总体上,植物角质层厚度随放牧率的增加而增加;而表皮细胞面积、叶肉细胞面积、叶片厚度等指标不同植物的反应不同.植物叶片化学成分(全N、全C、纤维素含量、叶绿素a+b及a/b)随放牧率的变化较小.放牧率对冰草、冷蒿、羊草的全C、全N、叶绿素和纤维素含量均没有显著影响(P＞0.05),但却显著降低了糙隐子草的比叶面积及星毛委陵菜和小叶锦鸡儿的叶绿素含量,提高了糙隐子草的纤维素含量及扁蓿豆叶片的全N含量(P<0.05).因此,不同植物对放牧的反应存在着明显的种间差异,其中植物角质层厚度、表皮细胞面积、叶片厚度和中脉厚度是植物对放牧响应最为敏感的指标.     

淮北相山恢复演替群落优势树种叶片的生态解剖

对淮北相山混交林5个优势种叶片的生态解剖学观察表明,其叶片结构具有一定的旱生特征:表皮具发达的表皮毛或角质层,全栅等面叶或具发达的栅栏组织,维管组织发达。牡荆(Vitex negundo var. cannabifolia)和酸枣(Ziziphus jujuba var. spinosa)作为两个广布优势树种,叶片结构表现出很大的可塑性:1)同一群落环境(混交林)中,叶片结构随着季节的变化表现出发育可塑性(5月初的叶片比9月中旬更具有阳生叶的特点);2)不同恢复演替阶段的群落中,叶片结构随着群落环境的变化表现出环境可塑性,其变化趋势为:灌草丛(旱生/阳生)-灌丛(旱生/阳生)-落叶疏林(中生/阳生)-人工侧柏(Platycladus orientalis)林(中生/阴生)。这种可塑性既是植物适应其异质生境的一种重要机制,同时又是不同群落环境的反映。非参数相关分析表明,牡荆和酸枣的叶片结构受多个生态因子综合影响,其中水分和风速是影响叶片结构的主导因子。叶片的上表皮角质层厚度、气孔器密度、栅栏组织厚度、叶片厚度、木质部厚度、韧皮部厚度、维管束厚度等性状均与土壤含水量和空气相对湿度呈显著负相关,与风速呈显著正相关。     

南亚热带森林不同演替阶段植物与土壤中N、P的化学计量特征

选择南亚热带森林演替过程3个阶段(初期、中期和后期)的典型森林生态系统为研究对象, 在测定植物与土壤中全N、全P含量的基础上, 阐明了森林演替过程中植物与土壤的N、P化学计量特征。结果显示: 1)土壤中全N含量随演替进行而增加, 马尾松(Pinus massoniana)林(初期)、混交林(中期)和季风林(后期) 0-10 cm土层中全N含量分别为0.440、0.843和1.023 g·kg^-1; 混交林0-10 cm土层中全P的含量最为丰富, 为0.337 g·kg^-1, 马尾松林和季风林土壤全P含量分别为0.190和0.283 g·kg^-1。2)植物叶片中全N、全P的含量随演替呈减少的趋势, 但根系中全N、全P的含量都以马尾松林为最多, 混交林和季风林含量彼此相当。3)各土层中N:P随演替的进行呈现明显增加趋势, 马尾松林、混交林和季风林0-10 cm土层中N:P分别为2.3、2.5和3.6; 植物各器官中N:P随演替的进行也呈增加趋势, 且叶片和根系中的N:P相近, 马尾松林、混交林和季风林叶片中N:P分别为22.7、25.3和29.6。基于上述结果, 探讨了南亚热带森林生态系统植物与土壤中N:P特征、森林演替过程中植物与土壤中N:P变化规律以及P对南亚热带森林生态系统的限制作用。结果表明, P已经成为南亚热带森林生态系统生物生长和重要生态过程的限制因子。     

延河流域植物叶性状间关系及其在不同植被带的表达

以延河流域不同植被带的地带性植物群落为研究对象,对群落优势种和主要伴生种的6种叶片性状进行测定,分析这些性状及其关系随环境梯度的变化,以了解该区域植物对环境变化的适应策略.结果表明: 植物比叶面积(SLA)与叶组织密度(LTD)、叶片单位面积氮和磷含量均呈显著负相关,与单位质量叶片磷含量呈显著正相关;各性状间的尺度关系和生存对策在不同植被带不同,典型草原带和森林草原带植物LTD SLA的尺度依赖关系比森林带植物的强,而森林带植物叶片单位〖JP2〗面积N、P含量与SLA、LTD间的尺度关系较草原带更明显,植物对环境的适应策略发生了位移.在干旱贫瘠的草原带和森林草原带,植物以防御和抗胁迫策略为主,而在环境条件相对湿润、富养的森林带,植物以快速生长和资源优化配置策略为主.     

长期不同放牧强度下荒漠草原建群种短花针茅(Stipa breviflora)叶片解剖结构变化

植物叶片解剖结构随放牧强度的变化而发生变化。以短花针茅荒漠草原长期(19年)固定监测放牧样地为研究区,以建群种短花针茅叶片作为实验材料,测量不同放牧强度(对照(CK)、轻度放牧(LG)、中度放牧(MG)、重度放牧(HG))下短花针茅叶片保护组织、输导组织、机械组织、同化组织有关的14个解剖结构指标,分析短花针茅叶片解剖结构随长期不同放牧强度的变化,从生理角度探讨荒漠草原植物对长期放牧的适应及响应。研究结果表明：(1)叶片层次上,短花针茅通过增加其叶片横切面面积和叶厚度去适应放牧干扰;(2)保护组织方面,与对照区相比,重度放牧区角质层厚度增加,但未达到差异显著性(P>0.05),角质层厚度占叶厚度比例随放牧强度的增加整体呈增加趋势;(3)输导组织方面,木质部面积随放牧强度的增加呈下降趋势,而韧皮部面积、主导管面积、维管束面积等指标均随放牧强度的增加呈增加趋势,但没有达到显著性(P>0.05);(4)机械组织方面,厚壁组织面积和厚壁组织占叶面积比例均随放牧强度的增加呈增加趋势;(5)同化组织方面,随着放牧强度的增加,短花针茅叶片叶肉组织面积显著增加(P<0.05)。可见,...     

Leaf trait co‐variation,response and effect in a chronosequence

Question: Is there any generality in terms of leaf trait correlations and the multiple role of leaf traits (response to and/or effect on) during secondary succession? Location: A secondary successional sere was sampled at four different ages since abandonment from several years to nearly 150 years on the Loess Plateau of northwestern China. Method: Specific leaf area (SLA), leaf mass per area (LMA), leaf nitrogen (N_mass, N_area), leaf phosphorus (P_mass, P_area) and leaf dry matter content (LDMC) were measured for all species recorded in the successional sere. Above‐ground net primary productivity (ANPP) and specific rate of litter mass loss (SRLML) were measured as surrogates for ecosystem properties. Soil total carbon (C) and nitrogen (N) were measured in each stage. Leaf traits were related to ecosystem properties and soil nutrient gradients, respectively. Results: LMA is correlated with N_area and P_area' and negatively with N_mass. Correlation between N_area and P_area was higher than between N_mass and P_mass. At the community level, field age, community hierarchy and their interaction explain 64.4 ‐ 93.5% of the variation in leaf traits. At the species level, field age explains 22.4 ‐ 45.5% of the variation in leaf traits (excl. P_area) while plant functional group has a significant effect only for N_mass. LDMC is correlated with ANPP and negatively with SRLML; P_mass is correlated with SRLML. Conclusions: Mean values of LMA, N_mass and N_area are close to the worldwide means, suggesting that large‐scale climate has a profound effect on leaf mass and leaf nitrogen allocation, while environmental gradients represented by succession have little influence on leaf‐trait values. Correlations between leaf traits, such as LMA‐N_area, LMA‐P_area and LMA‐N_mass shown in previous studies, are confirmed here. Although none of the leaf traits is proved to be both a response trait and an effect trait independent of time scale and community hierarchy, mass‐based leaf N is likely a sensitive response trait to soil C and N gradients. In addition, LDMC can be a marker for ANPP and SRLML, while mass‐based leaf P can be a marker for SRLML.     

Linking vein properties to leaf biomechanics across 58 woody species from a subtropical forest

• Leaf venations have elements with relatively lower elasticity than other leaf tissue components, which are thought to contribute to leaf biomechanics. A better mechanistic understanding of relationships between vein traits and leaf mechanical properties is essential for ecologically relevant interpretation of leaf structural variations.
• We investigated 13 major (first to third order) and minor (>third order) vein traits, six leaf mechanical properties and other structural traits across 58 woody species from a subtropical forest to elucidate how vein traits contribute to leaf biomechanics.
• Across species, vein dry mass density (ρ_v), total vein dry mass per leaf area (VMA) and minor vein diameter (VD_min), but not the lower‐order vein density (VLA_1?2), were positively correlated with leaf force to punch (F_p) and force to tear (F_t). Structural equation models showed that ρ_v and VD_min not only contribute to leaf mechanical properties directly (direct pathway), but also had impacts on leaf biomechanics by influencing leaf thickness and leaf dry mass per area (indirect pathway).
• Our study demonstrated that vein dry mass density and minor vein diameter are the key vein properties for leaf biomechanics. We also suggest that the mechanical characteristics of venations are potential factors influencing leaf mechanical resistance, structure and leaf economics spectrum.

     

唐古特白刺叶功能性状沿气候梯度的变异特征

叶功能性状与植物的生长对策及资源利用效率密切相关,研究叶功能性状沿气候梯度的变异特征能为理解植物对气候变化的响应机制提供一种简便可行的测定指标。以我国西北荒漠地区广泛分布的唐古特白刺（Nitraria tangutorum）为研究对象,对其比叶面积（SLA）、单位质量和单位面积叶氮含量（N_mass、N_area）、单位质量和单位面积叶建成成本（CC_mass、CC_area）进行测定,分析这些叶功能性状及性状相关关系沿气候梯度的变异特征。结果表明,唐古特白刺叶功能性状（CC_area除外）在气候梯度下存在显著差异,其中,温度是决定唐古特白刺SLA变化的主要因子,SLA随着温度的增加而增加;降水和温度对唐古特白刺N_mass、N_area和CC_mass均有显著影响,N_mass和N_area随着降水和温度的增加而降低,而CC_mass呈增加趋势。沿气候梯度,唐古特白刺SLA-N_mass、CC_mass-N_mass和CC_area-N_area的线性正相关关系发生平移,导致在相同SLA、CC_mass和CC_area下,降水和温度较低的地区具有更高的N_mass和N_area。这一结果表明唐古特白刺能通过调节叶功能性状之间的关系来适应气候的变化,并形成性状间的最佳功能组合。     

Nutritional differences and leaf acclimation of climbing plants and the associated vegetation in different types of an Andean montane rainforest

Climbing plants are known to play an important role in tropical forest systems, but key features for their distribution are only partly understood. Investigation was carried out to find if climbers differ from self-supporting vegetation in their adjustment of leaf parameters over a wide variety of light regimes in different forest types along an altitudinal gradient. Relative photon flux density (PFD_rel) was assessed above 75 pairs of strictly linked climbers and supporting vegetation on seven plots between 2,020 and 2,700 m a.s.l. along a mountain range in South-Ecuador up to the Páramo vegetation. Leaf samples from both growth forms were analyzed for leaf area (LA), specific leaf mass (LMA), mass and area-based carbon and nitrogen concentration (C, C_area, N, and N_area) and concentrations of P, K, Ca, Mg, Mn and Al. Leaf size of climbers was independent of general light condition, whereas the leaf size of the self-supporting vegetation increased in shade. LMA increased as expected with altitude and irradiance for both growth forms, but climbers generally built smaller leaves with lower LMA. N, P, and K concentrations were higher in the leaves of climbers than in their supporters. Relationships of LMA and N_area to the light conditions were more pronounced within the climbers than within their supporters. Slope for the regression between climber’s N_area and LMA was twice as steep as for the supporter leaves. Al accumulators were only found within the self-supporting vegetation. The investigated traits indicate improved adjustment towards light supply within climbers compared to self-supporting vegetation. Thus climbing plants seem to have a higher potential trade off in resource-use efficiency regarding irradiance and nutrients.     

Spatial patterns of photosynthetic characteristics and leaf physical traits of plants in the Loess Plateau of China

The spatial patterns of photosynthetic characteristics and leaf physical traits of 171 plants belonging to nine life-forms or functional groups (trees, shrubs, herbs, evergreen trees, deciduous trees, C₃ and C₄ herbaceous plants, leguminous and non-leguminous species) and their relationships with environmental factors in seven sites, Yangling, Yongshou, Tongchuan, Fuxian, Ansai, Mizhi and Shenmu, ranging from south to north in the Loess Plateau of China were studied. The results showed that the leaf light-saturated photosynthetic rate (P_max), photosynthetic nitrogen use efficiency (PNUE), chlorophyll content (Chl), and leaf mass per area (LMA) of all the plants in the Loess Plateau varied significantly among three life-form groups, i.e., trees, shrubs and herbs, and two groups, i.e., evergreen trees and deciduous trees, but leaf nitrogen content differed little among different life-form groups. For the 171 plants in the Loess Plateau, leaf P_max was positively correlated with PNUE. The leaf nitrogen content per unit area (N_area) was positively correlated but Chl was negatively correlated with the LMA. When controlling the LMA, the N_area was positively correlated with the Chl (partial r = 0.20, P < 0.05). With regard to relationships between photosynthetic characteristics and leaf physical traits, the P_max was positively correlated with N _area, while the PNUE was positively correlated with the Chl and negatively correlated with the N_area and LMA. For all the species in the Loess Plateau, the PNUE was negatively correlated with the latitude and annual solar radiation (ASR), but positively correlated with the mean annual rainfall (MAR) and mean annual temperature (MAT). With regard to the leaf physical traits, the leaf Chl was negatively correlated with the latitude and ASR, but positively correlated with the MAR and MAT. However, the N_area and LMA were positively correlated with the latitude and ASR, but negatively correlated with the MAR and MAT. In general, leaf N_area and LMA increased, while PNUE and Chl decreased with increases in the latitude and ASR and decreases in MAR and MAT. Electronic supplementary material The online version of this article () contains supplementary material, which is available to authorized users.     

Do higher resource capture ability and utilization efficiency facilitate the successful invasion of native plants?

The great damage caused by native invasive species on natural ecosystems is prompting increasing concern worldwide. Many studies have focused on exotic invasive species. In general, exotic invasive plants have higher resource capture ability and utilization capacity, and lower leaf construction cost (CC) compared to noninvasive plants. However, the physiological mechanisms that determine the invasiveness of native plants are poorly understood. We hypothesized that native invaders, like exotic invaders, may have higher resource capture ability and utilization efficiency compared to native noninvaders. To test this hypothesis, ecophysiological traits including light-saturated photosynthetic rate (A_max), specific leaf area (SLA), photosynthetic nitrogen use-efficiency (PNUE), photosynthetic energy-use efficiency (PEUE), and mass-based and area-based leaf construction cost (CC_mass and CC_area) were measured. We compared the above traits between three pairs of native invasive and noninvasive native species, and between three pairs of exotic invasive and noninvasive species in Guangzhou, southern China. Our results showed that the native invaders had higher A_max, SLA, PNUE, PEUE and lower CC_mass, CC_area, compared to native noninvaders and that these traits were also found in the exotic invaders. PNUE and PEUE in the native invaders were 150.3 and 129.0% higher, respectively, than in noninvasive native species, while these same measures in exotic invaders were 43.0 and 94.2% higher, respectively, than in exotic noninvasive species. The results indicated that native invaders have higher resource capture ability and resource utilization efficiency, suggesting that these traits may be a common biological foundation underlying successful invasion by both native and exotic invasives.     

Plastic changes of leaf mass per area and leaf nitrogen content in response to canopy openings in saplings of eight deciduous broad-leaved tree species

Leaf nitrogen content per area (N_area) is a good indicator of assimilative capacity of leaves of deciduous broad-leaved trees. This study examined the degrees of increase in N_area in response to canopy openings as leaf mass per area (LMA) and leaf nitrogen content per mass (N_mass) in saplings of eight deciduous broad-leaved tree species in Hokkaido, northern Japan. Five of the species were well-branched species with a large number of small leaves (lateral-growth type), and the other three species were less-branched species with a small number of large leaves (vertical-growth type). The degrees of increase in N_area were compared between the two crown types. In closed-canopy conditions, leaves of the vertical-growth species tended to have a lower LMA and higher N_mass than those of the lateral-growth species, which resulted in similar N_area for both. LMA increased in canopy openings in the eight species, and the degrees of increase were not largely different between the lateral- and vertical-growth species. On the contrary, N_mass was unchanged in canopy openings in the eight species. As a result, N_area of each species increased in canopy openings in proportion to the increase in LMA, and the degrees of increase in N_area were similar in the lateral- and vertical-growth species. Therefore, this study showed that the degrees of increase in N_area were not correlated with the crown architecture (i.e., the lateral- and vertical-growth types).     

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     

Leaf traits of natural populations of <Emphasis Type="Italic">Adiantum reniforme</Emphasis> var. <Emphasis Type="Italic">sinensis</Emphasis>, endemic to the Three Gorges region in China

Leaf mass per unit area (LMA), carbon and nitrogen contents, leaf construction cost, and photosynthetic capacity (P _max) of Adiantum reniforme var. sinensis, an endangered fern endemic to the Three Gorges region in southwest China, were compared in five populations differing in habitat such as soil moisture and irradiance. The low soil moisture and high irradiance habitat population exhibited significantly higher LMA, area-based leaf construction (CC_A), and carbon content (C_A), but lower leaf nitrogen content per unit dry mass (N_M) than the other habitat populations. The high soil moisture and low irradiance habitat populations had the lowest CC_A, but their cost/benefic ratios of CCA/P _max were similar to the medium soil moisture and irradiance habitat population due to their lower leaf P _max. Hence A. reniforme var. sinensis prefers partially shaded, moist but well-drained, slope habitats. Due to human activities, however, its main habitats now are cliffs or steeply sloped bare rocks with poor and thin soil. The relatively high energy requirements and low photosynthetic capacity in these habitats could limit the capability of the species in extending population or interspecific competition and hence increase its endangerment.