叶脉网络功能性状及其生态学意义

叶脉网络结构是叶脉系统在叶片里的分布和排列样式。早期叶脉网络结构研究主要集中在其分类学意义上; 近年来叶脉网络功能性状及其在植物水分利用上的意义已成为植物生态学研究的热点。该文介绍了叶脉网络功能性状的指标体系(包括叶脉密度、叶脉直径、叶脉之间的距离、叶脉闭合度等), 综述了叶脉网络功能性状与叶脉系统功能(包括水分、养分和光合产物等物质运输、机械支撑和虫害防御等)的关系, 叶脉网络功能性状与叶片其他功能性状(包括比叶重、叶寿命、光合速率、叶片大小、气孔密度等)的协同变异和权衡关系, 以及叶脉网络功能性状随环境因子(包括水分、温度、光照等)的变化规律等方面的最新研究进展。此外, 叶脉网络功能性状的研究成果也被应用于古环境重建、城市交通规划、流域规划及全球变化研究中。由于叶脉网络功能性状是环境因子与系统发育共同作用的结果, 未来开展分子—叶片—植物—生态系统等多尺度的叶脉网络功能性状研究, 理清叶脉网络功能性状与气孔失水—茎干导水—根系吸水等植物水分利用的关系, 将为预测植物及生态系统对全球变化的响应提供新的启示。     

喀斯特石漠化地区土壤养分对泡核桃功能性状的影响

为了探究喀斯特石漠化地区植物叶片功能性状及影响因素,以及揭示其对石漠化环境的适应机理,该文以中国南方喀斯特高原峡谷地区的泡核桃(Juglans sigillata)为对象,揭示土壤养分对叶片结构和光合性状的影响效应。结果表明：(1)泡核桃叶功能性状随石漠化等级增加,叶面积减小,比叶面积增大,叶干物质含量和叶组织密度先降后升,蒸腾速率、胞间CO₂浓度、气孔导度和光能利用率先下降后升高,其他性状变化趋势不显著。(2)冗余分析表明土壤养分能够解释37.4%的光合性状变异与53.4%的结构性状变异,其中全磷和溶解性有机碳对光合性状影响最大,而对结构性状影响最显著的是碱解氮和速效磷。(3)比叶面积分别与叶干物质含量极显著负相关,与净光合速率极显著正相关,叶厚度与叶组织密度极显著负相关,蒸腾速率与胞间CO₂浓度、气孔导度极显著正相关,水分利用速率与蒸腾速率、胞间CO₂浓度、气孔导度极显著负相关,光能利用率与净光合速率显著正相关。研究结果表明,泡核桃为适应喀斯特石漠化的特殊生境采取增强生长功能性状,同时提高资源获取能力的开拓型生长策略...     

九种维管植物水力性状的演化趋势

维管植物从蕨类植物、裸子植物到被子植物的演化过程中, 生理结构和功能都被认为更趋向于适应干旱的环境。但是关于3类植物是否提升了水分传导和水分利用效率的研究目前多基于叶脉和气孔的形态结构推断, 而对水分传导速率的直接测量则集中于被子植物内部。因此, 同时测定3类植物叶片和枝条尺度的水力性状, 可以研究维管植物水力性状的演化趋势和协同演化关系。该研究测定了中国科学院华南植物园内的蕨类植物(芒萁(Dicranopteris pedata)、华南毛蕨(Cyclosorus parasiticus)、乌毛蕨(Blechnum orientale)), 裸子植物(罗汉松(Podocarpus macrophyllus)、竹柏(Podocarpus nagi)、落羽杉(Taxodium distichum))和被子植物(海南木莲(Manglietia fordiana var. hainanensis)、东京油楠(Sindora tonkinensis)、羊蹄甲(Bauhinia purpurea))共9种植物的水力结构与功能的相关性状。发现9种植物从原始到更演化物种的枝条比导水率(K_S)、叶片比导水率(K_L)和叶片水力导度(K_leaf)依次升高; 叶片蒸腾速率(E)和潜在水分利用效率(WUE_i)升高趋势不显著; 气孔面积指数(SPI)和木材密度(WD)在3个类群间无明显变化趋势。水力功能性状在枝条(K_S)和叶片(K_L、K_leaf和E)尺度显著相关, 但和两个结构性状并无显著相关性。对显著相关的性状进行系统发育独立差分析发现相关性依然存在, 表明枝条导水和叶片导水、叶片失水的协同性独立于系统发育而存在。该文以9种维管植物为例, 发现演化过程中水分传导相关的功能性状有显著提升, 且导水和失水的性状存在着协同演化关系。上述维管植物水力性状演化趋势的结论需要对更多物种、更精细的水力结构性状的进行测定验证。     

气孔特征与叶片功能性状之间关联性沿海拔梯度的变化规律——以长白山为例

气孔是陆生植物与外界环境进行水分和气体交换的主要通道,控制着植物的光合作用和蒸腾过程。植物往往通过多种性状的组合来适应变化的环境,叶片功能性状之间的紧密关系已经在不同尺度得到证实。然而,植物气孔特征与叶片其它功能性状是否存在关联性以及这种关联性是否会受到环境变化梯度的影响仍鲜少报道。沿长白山北坡6个海拔梯度,测定了150种植物的气孔特征和叶片功能性状。结果发现,气孔密度(SD)与比叶面积(SLA)负相关,与单位面积的叶氮含量(N_(area))正相关;除了SLA和N_(area)外,气孔长度(SL)与SLA、叶片厚度(LT)和单位质量的叶氮含量(N_(mass))均存在显著的相关性(P0.05)。然而,气孔特征与叶片功能性状的相关性只在部分海拔梯度存在。此外,发现SD与SL之间存在稳定一致的负相关关系。这些结果表明,植物气孔特征与叶片形态和化学特征对环境变化的适应存在一定的协同变异性,但这种关系不具有普适性,主要与气孔特征和叶片功能性状的选择压力存在差异以及物种分布范围相关。未来仍需要在更多物种和不同区域内来验证气孔特征与植物功能性状之间的关联关系。     

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。     

基部被子植物气孔性状与叶脉密度的关联进化

植物叶片通过气孔的水分蒸腾散失和叶脉的水分供应达到水分平衡,而基部被子植物在进化过程中叶片水分供应和蒸腾散失是否达到平衡或关联进化还缺乏了解。本研究以11种基部被子植物为材料,测定了气孔密度、气孔长度、叶脉密度和叶片厚度4个叶片性状,并结合系统发育树,利用系统发育独立对比的方法分析这些性状之间的关联进化。结果显示：沿进化方向,气孔密度和叶脉密度逐渐增加,而气孔长度和叶片厚度有减小的趋势;无论是否考虑系统发育的影响,气孔密度都与叶脉密度呈显著正相关关系,说明二者之间存在关联进化,并证实了基部被子植物叶片水分平衡假说;气孔密度和长度、叶脉密度均与叶片厚度呈显著线性相关,但在去除系统发育的影响后这种线性相关关系不再显著,说明叶片厚度与其它三个叶片性状不存在关联进化。本研究结果还表明,叶片的水分供应和散失乃至CO2通透性的平衡主导着基部被子植物叶片结构和功能的进化。     

玛曲高寒沼泽化草甸51种植物光合生理和叶片形态特征的比较

基于功能性状的研究方法广泛地应用于生态学研究, 用于解释不同层次的复杂的生态学过程, 而绿色植物叶片的功能性状长期被认为对植物的生存、生长和繁殖具有重要的影响。该研究对玛曲高寒沼泽化草甸51个植物种(分属于14科)的叶片形态和光合性状进行测量, 比较不同物种和不同功能群(莎草科、禾本科和双子叶类杂草)的差异, 分析叶片形态特征和叶片光合性状之间的相关性。结果表明: 1)不同物种、不同功能群之间在比叶面积、净光合速率和水分利用效率等叶片形态和光合特征方面有着显著的差异, 例如禾本科植物具有较高的比叶面积和水分利用效率, 双子叶类杂草具有较大的叶面积, 而莎草科植物具有较高的净光合速率。2)相关性分析结果显示, 无论在物种水平还是功能群水平, 叶片形态和叶片光合性状之间都具有显著的相关关系。该研究揭示了高寒沼泽化草甸植物物种在叶片功能性状上的显著分化, 进而使得这些物种能在同一个草地群落中共存, 而群落中不同功能群物种的组成差异将会对群落的结构、功能和资源利用产生显著的影响。该研究将为进一步研究高寒沼泽化草甸提供基础研究数据并为其保护和恢复提供生理生态学依据。     

Changes in hydraulic traits of nine vascular plants from different evolutionary lineages

维管植物从蕨类植物、裸子植物到被子植物的演化过程中, 生理结构和功能都被认为更趋向于适应干旱的环境。但是关于3类植物是否提升了水分传导和水分利用效率的研究目前多基于叶脉和气孔的形态结构推断, 而对水分传导速率的直接测量则集中于被子植物内部。因此, 同时测定3类植物叶片和枝条尺度的水力性状, 可以研究维管植物水力性状的演化趋势和协同演化关系。该研究测定了中国科学院华南植物园内的蕨类植物(芒萁(Dicranopteris pedata)、华南毛蕨(Cyclosorus parasiticus)、乌毛蕨(Blechnum orientale)), 裸子植物(罗汉松(Podocarpus macrophyllus)、竹柏(Podocarpus nagi)、落羽杉(Taxodium distichum))和被子植物(海南木莲(Manglietia fordiana var. hainanensis)、东京油楠(Sindora tonkinensis)、羊蹄甲(Bauhinia purpurea))共9种植物的水力结构与功能的相关性状。发现9种植物从原始到更演化物种的枝条比导水率(K_S)、叶片比导水率(K_L)和叶片水力导度(K_leaf)依次升高; 叶片蒸腾速率(E)和潜在水分利用效率(WUE_i)升高趋势不显著; 气孔面积指数(SPI)和木材密度(WD)在3个类群间无明显变化趋势。水力功能性状在枝条(K_S)和叶片(K_L、K_leaf和E)尺度显著相关, 但和两个结构性状并无显著相关性。对显著相关的性状进行系统发育独立差分析发现相关性依然存在, 表明枝条导水和叶片导水、叶片失水的协同性独立于系统发育而存在。该文以9种维管植物为例, 发现演化过程中水分传导相关的功能性状有显著提升, 且导水和失水的性状存在着协同演化关系。上述维管植物水力性状演化趋势的结论需要对更多物种、更精细的水力结构性状的进行测定验证。     

天山森林植物功能性状与碳库沿海拔梯度的变化

植物功能性状是能够将植物个体特征、群落结构和生态系统功能结合起来的良好载体,但关于在环境梯度上如何通过植物功能性状的连续变化来构建群落、以及植物功能性状如何反映生态系统功能等问题尚有较多疑问。为探讨天山森林植物功能性状与其碳库在海拔梯度上的联系,分析了14个群落尺度上的植物功能性状指标和各组分碳密度沿海拔的变化规律及二者之间的关系。结果表明:(1)受海拔梯度上环境因子的影响,群落尺度上植物功能性状和碳密度的垂直分布并不一致:随海拔升高,叶片碳氮比(C/N)逐渐上升,叶片碳含量(C_(leaf))、比根长(SRL)和植株高度(H)升高后降低,叶绿素含量(Chl)、细根磷含量(P_(root))、叶片氮磷比(N/P)逐渐下降,细根碳含量(C_(root))先升高后趋于平缓,细根氮含量(N_(root))先下降后又有所回升,叶片氮含量(N_(leaf))、木质素含量(LLC)、叶干物质含量(LDMC)、细根干物质含量(RDMC)在各海拔段间无显著差异;(2)比根长(SRL)和植株高度(H)通过影响资源的获取和利用,C与P通过对养分的限制和在器官中的分配,从而影响植被光合作用,与天山森林碳密度显著相关;高木质素含量(LLC)导致植物残体分解速率变慢而与土壤碳密度(SCD)和群落总碳密度(TCD)呈显著负相关关系。随海拔升高,植被碳密度(VCD)先升后降,土壤碳密度(SCD)和总碳密度(TCD)逐渐升高。植物功能性状与环境因子和森林的结构功能相互作用、相互影响,三者之间的关系还需在大尺度上进一步验证。     

小兴安岭不同生长型阔叶植物叶性状变异及权衡

植物叶功能性状的变异模式以及相关关系一直是解析植物对气候变化响应机制的关键,然而不同生长型阔叶植物间叶片结构性状和光合生理性状变异及相关性的异同性尚不清晰。该研究以典型阔叶红松(Pinuskoraiensis)林中的优势或常见的18种阔叶植物为研究对象,通过测量4个结构性状(叶面积(LA)、叶片厚度(LT)、叶干物质含量(LDMC)和比叶质量(LMA))和4个光合生理性状(叶绿素值(SPAD)、胞间CO₂浓度(Ci)、气孔导度(G_s)和净光合速率(P_n)),分析了在不同生长型阔叶植物叶片结构性状和光合生理性状的变异及相关性。结果表明:不同生长型植物叶功能性状的变异范围为7.73%–74.54%,其中种间变异是LA和LT的主要变异来源, C_i、SPAD、LDMC以及LMA的变异主要由生长型驱动, G_s和P_n变异的主要来源是种内;不同生长型叶功能性状间存在显著差异,其中草本的LA、LT和Ci显著高于灌木和乔木,乔木的LMA、LDMC、SPAD、P_n<...     

Correlations among leaf structure,drought tolerance and photosynthetic capacity in saplings of Euphorbiaceae from different micro-habitats in a seasonal tropical rainforest

Aims Leaf structural and functional traits have been extensively studied to explain community assembly mechanisms, species distributions, niche differentiations, and even ecosystem services functions. However, these traits are influenced by both environment and phylogeny, showing correlations or trade-offs among them. In this study, we assessed the impacts of leaf structure on drought tolerance and photosynthetic potential, and the trade-off between drought tolerance and photosynthetic capacity, to provide an explanation for species coexistence and the maintenance of high biodiversity in tropical rainforests.
Methods We chose 18 species in the Euphobiaceae family differing in distribution patterns along topographic gradients in a 20 hm² forest dynamics monitoring plot (FDP) in Xishuangbanna. We measured leaf anatomy, leaf water relations characteristics, maximum photosynthetic rate, and dark respiration, and used two different methods—the traditional Pearson correlation and phylogenetic independent contrasts—to analyze the relationships among those traits.
Important findings We found that: 1) species showed convergence in structures and functions within specific habitat; species on ridge or slope had a stronger water loss-tolerance abilities than species in the valley. 2) Correlations among some key traits (specifically, leaf density, water potential at turgor loss point, and water potential at full turgor, etc.) were found among habitats; plants adjusted leaf structure to influence simultaneously plant water loss-tolerance abilities and photosynthetic capability, which may result in a trade-off between drought tolerance (high leaf density, leaf mass per area) and photosynthetic capability (low leaf density, leaf mass per area). 3) The phylogenetic independent contrasts must be used when analyzing correlations among the traits of geneticallyrelated species due to the weakness of traditional Pearson analysis. The ecological niche differentiation to water and light gradients as revealed by the present study provides a potential explanation for the high diversity of the seasonal tropical rainforest.     

Morphological and physiological differentiation of seedlings between dry and wet habitats in a tropical dry forest

A common observation in tropical dry forests is the habitat preference of tree species along spatial soil water gradients. This pattern of habitat partitioning might be a result of species differentiation in their strategy for using water, along with competing functions such as maximizing water exploitation and tolerating soil water stress. We tested whether species from drier soil conditions exhibited a tolerance strategy compared with that of wet-habitat species. In a comparison of 12 morphophysiological traits in seedlings of 10 closely related dry and wet-habitat species pairs, we explored what trade-offs guide differentiation between habitats and species. Contrary to our expectations, dry-habitat species showed mostly traits associated with an exploitation strategy (higher carbon assimilation capacity, specific leaf area and leaf-specific conductivity and lower water-use efficiency). Strikingly, dry-habitat species tended to retain their leaves longer during drought. Additionally, we detected multiple strategies to live within each habitat, in part due to variation of strategies among lineages, as well as functional differentiation along the water storage capacity-stem density (xylem safety) trade-off. Our results suggest that fundamental trade-offs guide functional niche differentiation among tree species expressed both within and between soil water habitats in a tropical dry forest.     

Key characteristics for facilitating Leucaena leucocephala to successfully invade pioneer communities of tropical rain forests

Aims Due to fast-growing and high drought stress tolerance, Leucaena leucocephala has been widely used for afforestation in degraded tropical forests worldwide, but it is also a global invasive exotic species. Studies have shown that fast-growing can help L. leucocephala successfully invade subtropical forests. In this study, we aimed to investigate whether fast-growing and high drought stress tolerance can help L. leucocephala invade tropical rain forests.Methods The pioneer community of tropical rain forest which had been invaded by L. leucocephala in the Baopoling Mountain, Sanya, China was the research object. Through the t-test, we compared the differences in key functional traits that were related to growth rate (photosynthesis rate, stomatal conductance and transpiration rate) and drought stress tolerance (leaf turgor loss point) in both wet and dry seasons between L. leucocephala and eight dominant native species of pioneer community of tropical rain forest. And the principal component analysis (PCA) was used to investigate whether these functional traits can best discriminate between Leucaena leucocephala and the eight dominant native species.Important findings Leucaena leucocephala could be invariably growing fast (photosynthesis rate, stomatal conductance and transpiration rate much higher than native species) from wet to dry seasons and had higher drought stress tolerance (leaf turgor loss point much lower than native species) in the dry season. The results of PCA showed that these functional traits could significantly discriminate between L. leucocephala and the eight dominant native species. Therefore, invariable fast-growing from wet to dry season and high drought stress tolerance in the dry season make L. leucocephala successfully invade pioneer communities of tropical rain forests. In the future, these functional traits can be used to select many native species to perform biological control of L. leucocephala in other tropical forests.     

银合欢成功入侵热带雨林先锋群落的关键因素

由于生长速率高, 耐旱性强, 银合欢(Leucaena leucocephala)被广泛应用于世界各地退化热带亚热带森林的修复, 但它也是一种全球性的外来入侵植物。已经有研究发现高生长速率可以帮助银合欢成功入侵亚热带森林, 但是目前还不清楚高生长速率和强耐旱性是否能帮助银合欢成功入侵热带森林。该研究以位于中国三亚抱坡岭被银合欢入侵的热带雨林先锋群落为研究对象, 通过t检验比较干季和湿季银合欢和8个热带雨林先锋群落的本地优势种与快速生长(光合速率、气孔导度和蒸腾速率)和耐旱性(叶片膨压丧失点)紧密相关的功能性状的差异, 并利用主成分分析(PCA)研究这些功能性状是否能很好地区分银合欢和其他8个本地优势种。结果表明: 银合欢在干湿季均能快速地生长(比本地物种显著更高的光合速率、气孔导度和蒸腾速率), 且在干季拥有更强的耐旱性(比本地物种显著更低的叶片膨压丧失点)。PCA结果表明这些功能性状能够显著区分银合欢和其他8个本地优势种。因此干湿季的稳定的快速生长和干季的强耐旱性使银合欢成功入侵热带雨林先锋群落。未来可利用这些功能性状筛选合适的本地物种对入侵其他热带森林的银合欢进行有效的生物防治。     

Diverging drought-tolerance strategies explain tree species distribution along a fog-dependent moisture gradient in a temperate rain forest

The study of functional traits and physiological mechanisms determining species’ drought tolerance is important for the prediction of their responses to climatic change. Fog-dependent forest patches in semiarid regions are a good study system with which to gain an understanding of species’ responses to increasing aridity and patch fragmentation. Here we measured leaf and hydraulic traits for three dominant species with contrasting distributions within patches in relict, fog-dependent forests in semiarid Chile. In addition, we assessed pressure–volume curve parameters in trees growing at a dry leeward edge and wet patch core. We predicted species would display contrasting suites of traits according to local water availability: from one end favoring water conservation and reducing cavitation risk, and from the opposite end favoring photosynthetic and hydraulic efficiency. Consistent with our hypothesis, we identified a continuum of water use strategies explaining species distribution along a small-scale moisture gradient. Drimys winteri, a tree restricted to the humid core, showed traits allowing efficient water transport and high carbon gain; in contrast, Myrceugenia correifolia, a tree that occurs in the drier patch edges, exhibited traits promoting water conservation and lower gas exchange rates, as well low water potential at turgor loss point. The most widespread species, Aextoxicon punctatum, showed intermediate trait values. Osmotic compensatory mechanism was detected in M. correifolia, but not in A. punctatum. We show that partitioning of the pronounced soil moisture gradients from patch cores to leeward edges among tree species is driven by differential drought tolerance. Such differences indicate that trees have contrasting abilities to cope with future reductions in soil moisture.     

Seasonal variation in native hydraulic conductivity between two deciduous oak species

植物抗旱性机制包括耐旱性和避旱性。耐旱性的特征主要是木质部易栓塞性和膨压损失点,而避旱性的特征则是叶片脱落和落叶性。虽然这些机制可以权衡物种连续性,但对于干旱引发的叶片脱落和持续时间的变化如何影响木质部和叶片耐受性之间的关系却知之甚少。在本研究中,我们研究两种具有不同叶片脱落叶行为的橡树(栎属)的耐旱性程度差异。我们预测了Quercus deserticola 在旱季结束时落叶(晚落叶)而面临更大的空化风险,导致其比Q. laeta更耐旱,对水分的利用也更加保守。Q. laeta 只在旱季中期很短的时间内落叶(短落叶)。本研究在墨西哥中部进行,两种橡树各具有单个种群,它们之间相距1.58公里,海拔差为191米。Q. deserticola (晚落叶)多出现在下坡,而Q. laeta (短落叶)多出现在沿坡度海拔较高的地方。我们评估了样地内茎干的水分传导率的季节差异(雨季和旱季),并检测了两个物种间木质部对空化的脆弱性、叶片水分利用和叶片膨松损失点的差异。两种橡树在耐旱性状方面没有显著差异,主要包括木质部易栓塞性、叶片膨松损失点和气孔导度。然而,两种植物在旱季都有不同的表现：短落叶植物对木质部功能的负面影响要比晚落叶植物低。综上所述,两种橡树在植物生理性能方面的季节变化取决于冠层叶面积的减少。     

Hydraulics and life history of tropical dry forest tree species: coordination of species' drought and shade tolerance

Plant hydraulic architecture has been studied extensively, yet we know little about how hydraulic properties relate to species' life history strategies, such as drought and shade tolerance. The prevailing theories seem contradictory. We measured the sapwood (K(s) ) and leaf (K(l) ) hydraulic conductivities of 40 coexisting tree species in a Bolivian dry forest, and examined associations with functional stem and leaf traits and indices of species' drought (dry-season leaf water potential) and shade (juvenile crown exposure) tolerance. Hydraulic properties varied across species and between life-history groups (pioneers vs shade-tolerant, and deciduous vs evergreen species). In addition to the expected negative correlation of K(l) with drought tolerance, we found a strong, negative correlation between K(l) and species' shade tolerance. Across species, K(s) and K(l) were negatively correlated with wood density and positively with maximum vessel length. Consequently, drought and shade tolerance scaled similarly with hydraulic properties, wood density and leaf dry matter content. We found that deciduous species also had traits conferring efficient water transport relative to evergreen species. Hydraulic properties varied across species, corresponding to the classical trade-off between hydraulic efficiency and safety, which for these dry forest trees resulted in coordinated drought and shade tolerance across species rather than the frequently hypothesized trade-off.     

Stem hydraulic traits and leaf water-stress tolerance are co-ordinated with the leaf phenology of angiosperm trees in an Asian tropical dry karst forest

Background and Aims

The co-occurring of evergreen and deciduous angiosperm trees in Asian tropical dry forests on karst substrates suggests the existence of different water-use strategies among species. In this study it is hypothesized that the co-occurring evergreen and deciduous trees differ in stem hydraulic traits and leaf water relationships, and there will be correlated evolution in drought tolerance between leaves and stems.

Methods

A comparison was made of stem hydraulic conductivity, vulnerability curves, wood anatomy, leaf life span, leaf pressure–volume characteristics and photosynthetic capacity of six evergreen and six deciduous tree species co-occurring in a tropical dry karst forest in south-west China. The correlated evolution of leaf and stem traits was examined using both traditional and phylogenetic independent contrasts correlations.

Key Results

It was found that the deciduous trees had higher stem hydraulic efficiency, greater hydraulically weighted vessel diameter (D_h) and higher mass-based photosynthetic rate (A_m); while the evergreen species had greater xylem-cavitation resistance, lower leaf turgor-loss point water potential (π₀) and higher bulk modulus of elasticity. There were evolutionary correlations between leaf life span and stem hydraulic efficiency, A_m, and dry season π₀. Xylem-cavitation resistance was evolutionarily correlated with stem hydraulic efficiency, D_h, as well as dry season π₀. Both wood density and leaf density were closely correlated with leaf water-stress tolerance and A_m.

Conclusions

The results reveal the clear distinctions in stem hydraulic traits and leaf water-stress tolerance between the co-occurring evergreen and deciduous angiosperm trees in an Asian dry karst forest. A novel pattern was demonstrated linking leaf longevity with stem hydraulic efficiency and leaf water-stress tolerance. The results show the correlated evolution in drought tolerance between stems and leaves.Key words: Tropical dry forest, karst, leaf habit, hydraulic conductivity, cavitation resistance, leaf water-stress tolerance, wood density, leaf density, phylogenetic independent contrasts     

Hydraulic and photosynthetic characteristics differ between co-generic tree and liana species: a case study of Millettia and Gnetum in tropical forest

木质藤本是热带森林的重要组成部分, 显著影响森林的结构和功能。已有研究发现木质藤本与乔木的水力结构存在显著差异: 木质藤本的缠绕或攀缘茎细小, 但其木质部具有粗大的长导管, 输水效率高, 抗栓塞能力低。为降低基因型差异对比较结果的影响, 该研究选取热带崖豆藤属(Millettia)和买麻藤属(Gnetum)的乔木和木质藤本, 比较同属内不同生长型植物的水力和光合性状的差异, 分析水分传导效率与抗栓塞能力之间以及水力与光合性状之间的相关关系。结果发现: (1)崖豆藤属植物水力性状的种间差异大, 与生活型和需光性有关。耐阴的木质藤本反而具有较低的水分传导效率和较高的抗栓塞能力。(2)买麻藤属植物是裸子植物较为进化的类群(具有导管和阔叶), 其乔木的水分传导效率很低, 但是其木质藤本的水分传导效率高于其他阳生性的被子植物。(3)不论乔木还是木质藤本, 水分传导的有效性与安全性在枝条和叶片水平上均没有显著的权衡关系。(4)与同属乔木相比, 木质藤本的叶片较枝条的抗栓塞能力更强, 在旱季具有更高的最大净光合速率和气孔导度, 支持了木质藤本的“旱季生长优势假说”。该研究揭示了热带木质藤本水力性状的多样性和重要性, 为阐明环境变化对这一重要植物类群的影响, 需要对它们的水力特征进行更广泛的研究。