披针叶茴香对变化光环境的表型可塑性

植物对变化光环境的表型可塑性大小影响其在林下生境中分布、生长和更新。为探讨披针叶茴香在不同光环境下的整体表型可塑性及其适应机制,采用遮荫试验模拟5种光照条件(100%、52%、33%、15%和6%相对光照强度),研究了不同光环境下披针叶茴香叶片形态、生理、解剖结构、根系形态以及生物量分配等的变化。结果表明:叶生物量在5种光照处理之间差异不显著,但叶面积和比叶面积均随光照强度减弱显著增加。遮荫处理增加了叶绿素a、叶绿素b和类胡萝卜素的含量,但叶绿素a/b比值随光照强度减弱而降低。遮荫降低了非结构性碳水化合物(淀粉和可溶性糖)和可溶性蛋白的含量,增加了叶片氮和磷含量,对叶片氮/磷比影响较小。在52%和33%相对光照处理下,叶片中硝酸盐含量最低,而在100%和6%相对光照处理下硝酸盐积累较多。根生物量、细根和粗根的长度、表面积以及比根长和比根表面积在5种光照处理之间均没有显著差异,根系氮含量在低光环境(15%和6%相对光照处理)中显著降低。随光照强度减弱,披针叶茴香采取保守生存策略,并没有增加叶生物量的分配,而是分配较多的生物量给枝条和树干,储存能量。综合来看,披针叶茴香具有较宽的光生态幅,在6%—100%光照强度下均能正常生长,遮荫有利于披针叶茴香地上和总生物量的积累,52%的相对光照条件下生长最佳。变化光环境下根系性状和整体结构的可塑性相对较低,叶片生理性状的可塑性在披针叶茴香适应光环境变化过程中发挥了主要作用。     

南方灌草丛典型灌木不同叶片性状的相关性及其对不同光环境的响应

光照是影响植物生长和分布的重要环境因子,而叶片结构相对稳定,其性状对植物的碳收获非常重要,并且各性状间的相互关系格局相似,通过叶片性状有助于研究植物对不同光环境的响应及生态适应策略。本研究分析了南方灌草丛3种典型灌木——巴柳(Salix etosia)、川莓(Rubus setchuenensis)和马桑绣球(Hydrangea aspera)的叶片性状(单叶面积、叶干重、比叶面积、叶碳含量、叶氮含量、叶磷含量)之间的相关性以及在林内-林外2种不同光环境下叶片性状的差异,探讨不同植物叶片性状在不同光环境下的响应及适应策略。结果表明:1)3种灌木叶片性状之间的相关性差别较大,具有物种特异性。2)巴柳叶片性状在不同光环境下无显著差异,川莓和马桑绣球均提高了林内叶片的比叶面积和叶氮含量以适应弱光环境,且马桑绣球叶碳含量在林内显著增加,表现出较强的固碳能力。3)不同光环境中,影响川莓和马桑绣球叶片性状变化的主要环境因子均为土壤温度。研究结果进一步揭示了植物叶片性状具有表型可塑性,不同植物对环境变化的响应及适应策略具有物种特异性。     

夏蜡梅及其主要伴生种叶的灰分含量和热值

分别于2006年7月、10月和2007年4月,对全光照、林缘和林下3种光环境下夏蜡梅及群落中35种主要植物叶的灰分含量和去灰分热值进行测定,分析它们在光合作用中对太阳能的固定和积累能力。不同光环境下夏蜡梅叶灰分含量的大小顺序都是全光照＞林缘＞林下,10月3种光环境下夏蜡梅叶灰分含量均高于4月和7月,均差异显著。4月、7月和10月,林下和全光照环境下的叶去灰分热值呈先下降后上升的趋势,而林缘中叶去灰分热值却逐渐下降。群落各层植物的灰分含量大小顺序为草本层＞灌木层＞间层＞乔木层,夏蜡梅灰分含量略低于灌木层灰分含量的平均值;各层次植物平均去灰分热值大小顺序为乔木层＞灌木层＞草本层＞间层,夏蜡梅平均去灰分热值低于间层。多数植物不同季节叶的灰分含量、去灰分热值均以10月最高。     

广东南岭天然常绿阔叶林林下光环境对林下幼树功能性状的影响

光环境与幼树功能性状的关系对天然林的更新与演替具有重要的生态学意义。以广东南岭区域天然常绿阔叶林下不同林龄(幼龄林,中龄林,老龄林)的森林群落为研究对象,通过监测冠层结构、林下光照数据和林下幼树功能性状等指标,研究林龄梯度下其冠层结构与林下光环境之间的关系,以及林下幼树功能性状对光环境的响应。结果表明:(1)中龄林叶面积指数显著高于幼龄林和老龄林(P0.05),随着林龄的增长,林冠开度和透光率逐渐下降,林龄梯度下透光率、R/FR(红光/远红光比值)、Bw/Rw(宽带蓝光/宽带红光比值)差异极显著(P0.001);(2)天然常绿阔叶林中透光率与光质之间极显著相关(P0.001),R/FR随着透光率的增加而增加,Bw/Rw随着透光率的增加而减少。(3)林下幼树功能性状在光环境之间差异显著(P0.05),老龄林林下幼树叶片氮含量显著高于幼龄林,而叶片重叠率显著低于幼龄林;(4)在本试验地中,R/FR和Bw/Rw的变化对林下幼树的高径比和光合作用并无显著影响,光强对同种植物不同光环境下最大净光合速率的影响较大。总体而言,林龄梯度冠层结构和光环境的差异能在一定程度上解释幼树功能性状的差异,这将有助于我们理解光环境对林下幼树更新的影响机制,同时为天然植被恢复和森林经营提供指导。     

海岛植物不同演替阶段植物功能性状与环境因子的变化规律

植物功能性状与环境之间的关系是功能性状研究的重点,环境因子驱使植物功能性状发生变化,进而推动群落发生演替。以平潭岛4个不同演替阶段的森林植被(灌草丛、针叶林、针阔混交林、常绿阔叶林)为研究对象,结合不同群落演替阶段的物种特征和群落结构,分析海岛不同演替阶段茎、叶功能性状的变化规律,以及功能性状与环境因子的关系。结果表明:(1)随着演替的进行,土壤养分和水分逐渐增加,土壤pH逐渐下降。比叶面积(SLA)、叶片氮含量(LNC)、叶片磷含量(LPC)、茎氮含量(SNC)、茎磷含量(SPC)下降后上升,叶厚度(LT)、叶片碳含量(LCC)、茎碳含量(SCC)与之相反,叶干物质含量(LDMC)、茎组织密度(STD)逐渐上升。(2)冗余分析表明,演替早期植物主要分布在土壤pH、容重高的贫瘠环境,拥有较高SLA、SNC、SPC、LPC的性状组合;演替后期植物主要分布在土壤养分和水分高的肥沃环境,拥有较高的STD、LDMC、LCC、LNC的性状组合。其中,土壤有机质和全氮含量是影响海岛植物演替过程中功能性状变化的关键环境因子。研究海岛植物功能性状与环境之间的关系随演替的变化规律,探讨各演替阶段功能性状和环境特征,以及功能性状如何响应环境变化。旨在为今后选择合适的树种进行海岛植被修复和重建提供依据。     

极小种群野生植物黄梅秤锤树的光合生理特性

黄梅秤锤树(Sinojackia huangmeiensis)是我国特有种,被列为国家Ⅱ级重点保护植物和极小种群野生植物。为探讨黄梅秤锤树对不同光环境的响应与适应,选择3种生境中(林窗、林下、全光照)的植株为研究对象,比较不同生境中叶片表型性状、光合特征和叶绿素荧光特征。结果表明：林窗和林下生境黄梅秤锤树的比叶面积(SLA)显著高于全光照生境,叶厚度(LT)和叶干物质含量(LDMC)显著低于全光照生境;最大净光合速率(P_max)和光饱和点(LSP)在全光照生境中最高,光补偿点(LCP)和暗呼吸速率(R_d)在林下生境中最低;林窗和全光照生境黄梅秤锤树的表观电子传递速率(ETR)、PSⅡ实际光量子产量[Y(II)]、光化学猝灭系数(qP)和非光化学猝灭系数(NPQ)都高于林下生境。黄梅秤锤树通过增加SLA,降低LCP、R_d和NPQ来适应弱光环境,通过增加LT、LDMC、LSP和NPQ来适应强光环境,对不同的生境表现出较强的适应性,对其种群更新与维持具有重要意义,也为其人工引种的成功提供重要保障。     

不同光环境下胡桃楸幼苗的形态可塑性及其响应研究

为了探求不同光环境对胡桃楸幼苗生长的影响,对全光照（100%光照）、中光照（60%光照）、低光照（30%光照）3种光环境下胡桃楸幼苗的生长、形态特征、生物量分配和水分特征开展研究。结果表明：胡桃楸幼苗的形态在不同光环境下存在明显的可塑性变化,生物量分配和水分特征均表现出不同程度的差异。低光照条件下,胡桃楸幼苗生长快,株高、地径分别为全光照的1.14、1.18倍;冠幅大,是全光照的1.40倍;叶片宽大,叶长和叶宽分别是全光照的1.25和1.36倍;分枝数明显少于全光照。3种光环境下胡桃楸幼苗地上部分生物量存在显著差异,地下部分差异不显著。叶片相对含水量随着光照的降低呈现逐渐增加的趋势;全光照条件下叶片饱和持水量与叶片干鲜比明显大于遮阴条件;3种光照条件下叶绿素含量差异显著。胡桃楸幼苗为适应不同光环境,在形态和生理方面都做出适应性调整,适当的遮阴处理有利于胡桃楸幼苗生长。     

羊草草原群落6种植物叶片功能特性对氮素添加的响应

 该文比较了羊草草原群落中包括建群种和优势种在内的6种植物,羊草（Leymus chinensis）、西伯利亚羽茅（Achnatherum sibiricum）、大 针茅（Stipa grandis）、 冰草（Agropyron cristatum）、糙隐子草（Cleistogenes squarrosa）和黄囊苔草（Carex korshinskyi）的比叶 面积(Specific leaf area, SLA)、叶片含氮量和叶绿素含量等叶片功能特性( Leaf functional trait)对氮素添加的响应,旨在探讨草原生态 系统中,不同物种对氮素可利用性改变的响应和适应对策。结果表明：随着氮素添加量的增加,物种对光资源的竞争增强,不同物种在光资源 的竞争策略和竞争力间存在着显著的差异。羊草通过提高SLA、单位质量叶片的叶绿素含量和含氮量,使单位面积叶片含氮量和叶绿素含量均呈 线性提高,进而增强了其对光的竞争力。西伯利亚羽茅主要通过提高SLA增加光合总面积,来增强自身的光竞争力。冰草在SLA和单位质量叶片 的叶绿素和氮含量均有一定的可塑性,但对光的竞争力明显弱于羊草和西伯利亚羽茅。大针茅和黄囊苔草对SLA的调节能力较低,加之大针茅 SLA较低,而黄囊苔草处于群落的下层,这两种植物的光竞争力较弱。糙隐子草具有较高的SLA,对单位质量叶片叶绿素和氮含量的调节能力相 对较强,其光竞争力高于黄囊苔草。同时,糙隐子草叶片叶绿素a与叶绿素b的比值沿氮素添加梯度显著降低,进一步证实氮素添加改变了群落 的光环境。     

植株叶片的光合色素构成对遮阴的响应

叶绿素在植株体内负责光能的吸收、传递和转化, 类胡萝卜素则行使光能捕获和光破坏防御两大功能, 它们在光合作用中起着非常重要的作用。该文综述了几大主要光合色素的分布和功能, 以及不同物种的色素含量和构成差异。阳生植物的叶黄素库较大, 但脱环氧化水平不及阴生植物。黄体素与叶黄素库的比值与植物的耐阴性呈正相关关系。由不同的遮阴源造成的遮阴环境, 光强和光质有很大的差异, 总体来说对植物生长的影响, 建筑物遮阴<阔叶林遮阴<针叶林遮阴。光强的改变可诱导类胡萝卜素的两大循环——叶黄素循环和黄体素循环。由光强诱导的叶绿素含量和叶绿素a/b比值的改变与该物种的耐阴性无关。短时间的遮阴不会对植物的生长造成危害, 叶黄素库的大小不仅与每天接受的光量子有关, 更与光量子在一天的分布有关, 因为光照和温度是协同作用的。光合作用或色素构成是蓝光、红光和远红光共同作用的结果, 不是某一种单色光所能替代的。我们总结了影响植物色素构成的内因和外因, 指出植物主要通过调整光反应中心和捕光天线色素蛋白复合体的比例, 以及两个光系统的比值来调整色素含量和构成以适应不同的光照条件, 提出了现存研究中存在的一些问题, 旨在为今后的相关研究提供建议。     

延胡索光合与生长可塑性对光照的响应

林-药复合系统是经济收益显著的立体林农生态系统。以早春植物延胡索为研究对象, 分析其不同光环境下光合与生长的变化, 为其林下抚育、林木间伐和林药复合生态系统的构建提供依据。试验发现, 延胡索通过降低光饱和点、光补偿点和暗呼吸速率, 提高表观量子效率等方式以适应遮阴和弱光环境; 在高光照和中高光照条件下, 延胡索对两种光环境表现差异不显著, 在暗呼吸速率和最大净光合速率方面, 中高光照条件的均值甚至超过高光照条件; 弱光条件下的饱和光照强度、最大净光合速率和表观量子效率分别为高光照的 62.67%、43.25%和 58.42%。遮阴条件的净光合速率、气孔导度和蒸腾速率总体均低于高光照条件。遮阴后, 延胡索叶片的 Chl a、Chl b 及 Chl a+Chl b 皆随着有效光辐射的下降呈现先升后降的趋势, Chl a/Chl b 值在中高光照和中低光照条件下显著降低, 表现出耐阴性能, 而弱光条件下 Chl a/Chl b 值显著下降的原因是弱光导致延胡索的光合产物供应不足, 妨碍了叶绿素的合成。弱光下延胡索叶生物量、根生物量分别仅为高光照条件下的 34.78%和 22.03%; 随着有效光辐射的下降, 比叶面积先升后降, 在弱光条件下延胡索优先于叶片的形态构成, 而不再倾向于扩大叶面积捕获更多的光量子。延胡索耐阴能力介于阳性植物和阴性植物之间, 弱光下的延胡索光合机构可能已向耐阴植物转变。因此, 延胡索具有一定的耐阴能力, 但并不适合长期的弱光条件。野外疏林下进行仿野生延胡索栽培时, 当乔冠层的郁闭度过高时, 可适当采取间伐修枝或者开辟林窗等措施改善林下光环境, 提升林下延胡索的光合作用能力和光斑利用效率, 合理配置其光生态位和时间生态位以达到预期的经济效益。     

Phenotypic selection on leaf functional traits of two congeneric species in a temperate rainforest is consistent with their shade tolerance

Several studies across species have linked leaf functional traits with shade tolerance. Because evolution by natural selection occurs within populations, in order to explain those interspecific patterns it is crucial to examine variation of traits associated with shade tolerance and plant fitness at an intraspecific scale. In a southern temperate rainforest, two climbing plant species coexist but differ in shade tolerance. Whereas Luzuriaga radicans is most abundant in the shaded understory, L. polyphylla typically occurs in intermediate light environments. We carried out an intraspecific approach to test the hypothesis of differential selection patterns in relation to shade tolerance in these congeneric species. The probability of showing reproductive structures increased with specific leaf area (SLA) in L. polyphylla, and decreased with dark respiration in L. radicans. When reproductive output of fertile individuals was the fitness variable, we detected positive directional selection on SLA in L. polyphylla, and negative directional selection on dark respiration and positive directional selection on leaf size in L. radicans. Total light radiation differed between the microsites where the Luzuriaga species were sampled in the old-growth forest understory. Accordingly, L. radicans had a lower minimum light requirement and showed fertile individuals in darker microsites. L. radicans showed lower dark respiration, higher chlorophyll content, and greater leaf size and SLA than L. polyphylla. Results suggest that in more shade-tolerant species, established in the darker microsites, selection would favor functional traits minimizing carbon losses, while in less shade-tolerant species, plants displaying leaf traits enhancing light capture would be selected.     

Light- and seasonal-induced plasticity in leaf morphology, N partitioning and photosynthetic capacity of two temperate deciduous species

Processes involved in leaf photosynthetic acclimation to light and throughout the growing season were investigated in two hardwood species (Acer saccharum and Betula alleghaniensis), which differed in their level of shade-tolerance. For both species, variation in traits related to (i) leaf morphology (LMA, leaf mass:area ratio), (ii) leaf N content (N_A, leaf nitrogen content on an area basis and N_M, N concentration in leaf dry mass), (iii) leaf N partitioning among photosynthetic functions (P_r, N allocated to Rubisco, and P_b, N allocated to bioenergetics), and (iv) leaf photosynthetic capacity (V_cmax, maximal carboxylation rates, and J_max, maximal light-driven electron flow) were assessed at three different times during the growing season (early, mid- and late summer) and under four contrasting light regimes (40, 17, 6 and 2% of full sunlight). For both species, light-driven variation in most traits was greater than their seasonally driven variation. Furthermore, results showed for both species the pre-eminence of LMA changes in the light-driven acclimation of N_A. Importance of N_M to variation in N_A was restricted to seasonal acclimation, especially for the less shade-tolerant species, B. alleghaniensis. Similarly, for both species, light-driven acclimation of leaf photosynthetic capacities was tightly related to variation in N_A, which was related to LMA changes. However, variation in P_r and P_b better explained seasonally driven variation in V_cmax and J_max, specifically under lower light levels, where N_A was low. Thus, the great variability observed for leaf activity in response to contrasting light environments was related to efficient morphological adjustments, regardless of species level of shade-tolerance. Finally, physiological adjustments were mainly involved in fine-scale changes observed during seasonally driven acclimation of leaves, when LMA was constrained to a slight range of variation.     

云南文山石漠化区车桑子叶脉密度与叶氮含量关系对生境的响应

植物叶脉特征和叶氮含量的变化影响着叶片经济谱的形成,为验证叶片结构中叶脉网络构建提供了理论依据。该文以单位质量叶氮含量(N_(mass))和单位面积叶氮含量(N_(area))分别表示叶氮含量,采取主成分分析、线性回归分析的方法,研究了云南文山石漠化区旷地(Ⅰ)、林缘(Ⅱ)和林下(Ⅲ)3种自然生境下车桑子的叶脉密度(Vein density,VD)与N_(mass)和N_(area)的异速关系。结果表明:从乔灌群落的旷地到林下,车桑子的比叶面积、叶绿素总含量、光能利用率和N_(mass)逐渐增大,光饱和点、光补偿点、水分利用效率、VD、N_(area)逐渐减小,净光合速率、蒸腾速率、气孔导度呈先增大后减小的趋势。VD与叶氮含量呈不同程度的相关性,在生境I和III,VD与N_(mass)和N_(area)分别具有显著的负相关(P0.05)和正相关(P0.05);在生境Ⅱ,VD与N_(mass)和N_(area)分别呈不显著负相关(P0.05)和正相关(P0.05)。车桑子在旷地强光生境,高VD的叶片含有低N_(mass)高N_(area),而林下荫蔽生境偏向于相反的配置模式,反映了石漠化区植物较强的叶脉可塑性及其与氮利用性状的权衡机制。     

不同生境朝鲜淫羊藿生长与光合特征

选择朝鲜淫羊藿野外生存的林缘、林窗和林下3种生境,研究朝鲜淫羊藿形态特征、光合特征、叶绿素含量、生物量积累及分配对不同光环境的响应。结果表明,朝鲜淫羊藿株高、茎径、总叶面积等形态指标随光照强度减弱明显减小,各生境间差异显著。随光照强度降低,朝鲜淫羊藿的净光合速率、水分利用效率、气孔限制值、叶绿素a/b降低,而胞间CO2浓度、光能利用效率、叶绿素b和总叶绿素含量增加。各器官生物量积累随光照强度减弱而降低,各生境间差异极显著,其中,林缘地上生物量是林窗的1.6倍,林下的3.1倍。生物量分配方面,叶生物量比、叶面积比率、比叶面积随光照强度减弱而增加,根状茎生物量比和根冠比降低,林缘、林窗与林下差异极显著;林下、林缘、林窗朝鲜淫羊藿地上部分生物量比分别为0.733、0.659、0.664,林下朝鲜淫羊藿与林缘、林窗存在不同的光利用策略和生存策略。朝鲜淫羊藿作为极易遭受利用和生境破坏威胁的物种,宜在适度荫闭的林缘和疏林下开展野生抚育或仿生态栽培。     

黄土高原樟子松和落叶松与其他树种枯落叶混合分解对土壤的影响

通过采集树木枯落叶与土壤进行室内混合分解培养试验,研究了黄土高原常见的樟子松和落叶松与其他树种枯落叶混合分解对土壤性质的影响及存在的相互作用,从而为不同树木种间关系的探索和该地区人工纯林的混交改造提供科学指导。结果表明:12种枯落叶单一分解均明显提高了土壤脲酶(54%—110%)、脱氢酶(85%—288%)和磷酸酶(81%—301%)活性以及有机质(29%—55%)和碱解N(12%—49%)含量,但对土壤速效P含量和CEC的影响存在较大差异。综合而言,樟子松分别与白桦、刺槐、白榆、柠条和落叶松枯落叶混合分解在对土壤性质的影响中存在相互促进作用,而分别与小叶杨、沙棘、紫穗槐、侧柏和辽东栎枯落叶混合分解在对土壤性质的影响中存在相互抑制作用;落叶松分别与刺槐、白桦、小叶杨和紫穗槐枯落叶混合分解在对土壤性质的影响中存在相互促进作用,而分别与柠条、侧柏、辽东栎、沙棘、油松和白榆枯落叶混合分解在对土壤性质的影响中存在相互抑制作用。     

Within-canopy variation in photosynthetic capacity,SLA and foliar N in temperate broad-leaved trees with contrasting shade tolerance

Key message

The relative shade tolerance of T. cordata , F. sylvatica , and C. betulus in mature stands is based on different species-specific carbon and nitrogen allocation patterns.

Abstract

The leaf morphology and photosynthetic capacity of trees are remarkably plastic in response to intra-canopy light gradients. While most studies examined seedlings, it is not well understood how plasticity differs in mature trees among species with contrasting shade tolerance. We studied light-saturated net photosynthesis (A _max), maximum carboxylation rate (V _cmax), electron transport capacity (J _max) and leaf dark respiration (R _d) along natural light gradients in the canopies of 26 adult trees of five broad-leaved tree species in a mixed temperate old-growth forest (Fraxinus excelsior, Acer pseudoplatanus, Carpinus betulus, Tilia cordata and Fagus sylvatica), representing a sequence from moderately light-demanding to highly shade-tolerant species. We searched for species differences in the dependence of photosynthetic capacity on relative irradiance (RI), specific leaf area (SLA) and nitrogen per leaf area (N _a ). The three shade-tolerant species (C. betulus, T. cordata, F. sylvatica) differed from the two more light-demanding species by the formation of shade leaves with particularly high SLA but relatively low N _a and consequently lower area-based A _max, and a generally higher leaf morphological and functional plasticity across the canopy. Sun leaf morphology and physiology were more similar among the two groups. The three shade-tolerant species differed in their shade acclimation strategies which are primarily determined by the species’ plasticity in SLA. Under low light, T. cordata and F. sylvatica increased SLA, mass-based foliar N and leaf size, while C. betulus increased solely SLA exhibiting only low intra-crown plasticity in leaf morphology and N allocation patterns. This study with mature trees adds to our understanding of tree species differences in shade acclimation strategies under the natural conditions of a mixed old-growth forest.     

Plant biodiversity in a larch plantation from the view point of photosynthetic nitrogen use efficiency in northeast China

Forest floor of larch species often provides growth habitat for many kinds of understory species because of relatively sparse structure in a larch canopy. A rich flora of forest understory species may play an essential role in maintaining fertility of a larch stand. An attempt was made to evaluate photosynthetic nitrogen use efficiency (PNUE) of many understory and overstory species according to their Raunkiaer lifeform. By studying 72 perennial deciduous species in a larch plantation in northeast China, marked photosynthetic differences between phanerophytes (Ph) and other three lifeforms of chamaephytes (Ch), hemicryptophytes (He), and cryptophytes (Cr) were found, with marginal differences found among Ch, He, and Cr. Ph species had much lower PNUE, and much lower values of rate of nitrogen allocation to chlorophyll (Chl./N) and nitrogen allocation to carboxylation processes (V _cmax/N) were concurrently observed in Ph compared with the other three lifeforms. Ph had much lower leaf nitrogen per unit of projection area (N _area) and specific leaf area (SLA, cm² g^–1). At lower SLA, for Ph species the change of PNUE with SLA was small, but these changes became very large at higher SLA for Ch, He, and Cr species. Our findings indicate that leaf morphological change is important for clarifying photosynthesis differences among species with different lifeform.     

Comparison of the physiology, morphology, and leaf demography of tropical saplings with different crown shapes

Branch architecture, leaf photosynthetic traits, and leaf demography were investigated in saplings of two woody species, Homolanthus caloneurus and Macaranga rostulata, co-occurring in the understory of a tropical mountain forest. M. rostulata saplings have cylindrical crowns, whereas H. caloneurus saplings have flat crowns. Saplings of the two species were found not to differ in area-based photosynthetic traits and in average light conditions in the understory of the studied site, but they do differ in internode length, leaf emergence rate, leaf lifespan, and total leaf area. Displayed leaf area of H. caloneurus saplings, which have the more rapid leaf emergence, was smaller than that of M. rostulata saplings, which have a longer leaf lifespan and larger total leaf area, although M. rostulata saplings showed a higher degree of leaf overlap. Short leaf lifespan and consequent small total leaf area would be linked to leaf overlap avoidance in the densely packed flat H. caloneurus crown. In contrast, M. rostulata saplings maintained a large total leaf area by producing leaves with a long leaf lifespan. In these understory saplings with a different crown architecture, we observed two contrasting adaptation strategies to shade which are achieved by adjusting a suite of morphological and leaf demographic characters. Each understory species has a suite of morphological traits and leaf demography specific to its architecture, thus attaining leaf overlap avoidance or large total leaf area.     

Canopy structure,vertical radiation profile and photosynthetic function in a Quercus ilex evergreen forest

The studied evergreen forest dominated by Quercus ilex showed a leaf area index (LAI) of 4.5, of which 61 % was accumulated within the tree layer, 30 % within the shrub layer, and 9 % within the herb layer. The leaves of all the species were ± horizontally oriented (41°), absorbing a relevant percentage of incident irradiance. The high LAI drastically modified the quality and quantity of solar radiation on the forest underground. The spectral distribution of the radiation under the forest was markedly deficient in blue and red wavelengths. The maximum absorption in these spectral bands was found in spring, when net photosynthetic rate (P _N ) was at its maximum, and in summer, when new leaves reached 90 % of their definitive structure. The vertical radiation profile showed an evident reduction of the red-far red ratio (R/FR). Radiation quality and quantity influenced leaf physiology and morphology. Clear differences in leaf size, leaf water content per area (LWC) and specific leaf area (SLA) on the vertical profile of the forest were observed. All the shrub species showed similar SLA (12.02 m2 kg-1, mean value). The ability to increase SLA whilst simultaneously reducing leaf thickness maximized the carbon economy. The high chlorophyll (Chl) content of shrub layer leaves (1.41 g kg-1, mean value) was an expression of shade adaptation. Both leaf morphology and leaf physiology expressed the phenotypic plasticity. Q. ilex, Phillyrea latifolia and Pistacia lentiscus of the forest shrub layer showed wide differences in leaf structure and function with respect to the same species developing under strong irradiance (low maquis): a 57 % mean increase of SLA and a 86 % mean decrease of PN. They showed high leaf plasticity. Leaf plasticity implies that the considered sclerophyllous species has an optimum developmental pattern achieving adaptation to environments. This revised version was published online in September 2006 with corrections to the Cover Date.     

Responses of root length/leaf area ratio and specific root length of an understory herb, Pteridophyllum racemosum, to increases in irradiance

The understory evergreen perennial Pteridophyllum racemosum Sieb. et Zucc. (Papaveraceae) has the ability to increase root mass per unit transpiring leaf area (RMA) if irradiance increases gradually over several years. In this study, we examined how P. racemosum changes its root length/leaf area ratio and specific root length when the species encounters abrupt increases in irradiance, such as sudden and unexpected canopy openings. Plants were transplanted from a low light condition in a subalpine wave-regenerating forest (photon flux density on the forest floor relative to the full sun (RPFD) was 2.7%) to a high light condition in a glasshouse (30% RPFD) (LH treatment). Transplantation from the low light condition in the forest to a low light condition in the glasshouse (LL) and transplantation from a high light condition in the forest (33% RPFD) to a high light condition in the glasshouse (HH) were also conducted as controls. Compared to the LL plants, the LH plants exhibited significant increases in RMA and root length/leaf area ratio from 30 to 70 days after transplantation. On the other hand, the effect of increased irradiance on specific root length (SRL) was weak, and both the LL and LH plants showed increased SRL from 30 to 70 days after transplantation. Increased SRL results from longer root length per unit construction cost. We concluded that increased root length/leaf area ratio of P. racemosum in response to abrupt increases in irradiance was caused by a combination of enhanced carbon allocation to roots with increased SRL.