植物叶片水力与经济性状权衡关系的研究进展

叶片既是植物光合产物形成的主要场所, 又是整株植物的水力瓶颈、应对灾难性水力失调的安全阀门, 是植物碳水耦合权衡的重要器官。叶经济型谱反映了叶片经济性状“投资-收益”的权衡, 为验证植物进化过程中形成的物种对策提供了适用的理论框架。叶片水力性状变化会影响叶片经济性状及植物存活和生长。因此, 探索植物叶片水力与经济性状的权衡关系, 对建立植物碳-水耦合模型、揭示植物水-碳投资机理、扩展植物性状型谱等均有重要意义。该文首先综述了叶片水力性状、经济性状及两者之间的权衡关系, 分析了叶片导水率与水力脆弱性、失膨点水势、水容、安全阈值等水力性状以及与叶片的形态、结构和气体交换功能性状之间的关系。然后, 从叶片形态、解剖和叶脉网络结构以及气孔功能方面探讨了叶片水力性状与经济性状的调节机制。最后, 提出今后应加强三方面的研究: (1)探索建立植物根-茎-叶水力输导系统的碳-氮-水资源的整株经济型谱, 以揭示植物功能结构耦合、高效固碳用水的生理生态学机制; (2)探索叶片水力安全、水力效率和固碳效率之间的普适性权衡关系, 以深入理解抗旱植物叶片构建的生物物理结构与生理代谢的关系; (3)探索个体水平碳水代谢关系、水分运输与生长速率的耦合, 为代谢推演理论和植物群落尺度预测提供基础。     

Leaf hydraulic traits and their trade-offs for nine Chinese temperate tree species with different wood properties

Aims Trees with different wood properties display variations in xylem anatomy and leaf vein structure, which may influence tree water transport efficiency and water-use strategy, and consequently constrain tree survival, growth and distribution. However, the effects of wood properties on leaf hydraulic conductance and vulnerability and their potential trade-offs at leaf level are not well understood. Our aims were to examine variations in leaf hydraulic traits of trees with different wood properties and explore potential trade-offs between leaf hydraulic efficiency and safety.
Methods Nine tree species with different wood properties were selected for measuring the leaf hydraulic traits, including three diffuse-porous species (Populus davidiana, Tilia amurensis, Betula platyphylla), three ring-porous species (Quercus mongolica, Fraxinus mandshurica, Juglans mandshurica), and three non-porous species (Picea koraiensis, Pinus sylvestris var. mongolica, Pinus koraiensis). Four dominant and healthy trees per species were randomly selected. The hydraulic traits measured included leaf hydraulic conductance on leaf area (K_area) and dry mass (K_mass) basis, leaf hydraulic vulnerability (P₅₀), and leaf water potential at turgor loss point (TLP), while the leaf structural traits were leaf dry mass content (LDMC), leaf density (LD) and leaf mass per unit area (LMA).
Important findings The K_area, K_mass, and P₅₀ differed significantly among the tree species with different woody properties (p < 0.05). Both K_area and K_mass were the lowest for the non-porous trees, and did not differ significantly between the diffuse-porous and ring-porous trees. The ring-porous trees had the highest P₅₀ values, while the diffuse-porous and non-porous trees showed no significant differences in P₅₀. Both K_area and K_mass were negatively correlated with P₅₀ (p < 0.05) for all the trees, and the relationships for the diffuse-porous, ring-porous, and non-porous trees were fitted into linear, power, exponential functions, respectively. This indicates that significant trade-offs exist between leaf hydraulic efficiency and safety. The K_mass was correlated (p < 0.01) with TLP in a negative linear function for the diffuse- and ring-porous trees and in a negative exponential function for the non-porous trees. The P₅₀ increased with increasing TLP. These results suggest that apoplastic and symplastic drought resistance are strictly coordinated in order to protect living cells from approaching their critical water status under water stresses. The K_mass was negatively correlated (p < 0.01) with LDMC, LD, or LMA, while the P₅₀ was positively correlated with LDMC and LD; this suggests that variations in K_mass and P₅₀ are driven by similar changes in structural traits regardless of wood traits. We conclude that the tree tolerance to hydraulic dysfunction increases with increasing carbon investment in the leaf hydraulic system.     

九种不同材性的温带树种叶水力性状及其权衡关系

不同材性树种的解剖、叶脉分布等结构性状差异会影响树木的水分运输效率和水分利用策略, 进而限制树木的生存、生长和分布。然而, 材性对叶导水率、水力脆弱性及其潜在的权衡关系的影响尚不清楚。该研究选择东北温带森林中不同材性的9种树种(散孔材: 山杨(Populus davidiana)、紫椴(Tilia amurensis)、白桦(Betula platyphylla); 环孔材: 蒙古栎(Quercus mongolica)、水曲柳(Fraxinus mandshurica)、胡桃楸(Juglans mandshurica); 无孔材: 红皮云杉(Picea koraiensis)、樟子松(Pinus sylvestris var. mongolica)、红松(Pinus koraiensis), 测量其基于叶面积和叶质量的叶导水率(K_area和K_mass)、水力脆弱性(P₅₀)、膨压丧失点水势(TLP)及叶结构性状, 以比较不同材性树种叶水力性状的差异, 并探索叶水力效率与安全的权衡关系。结果表明: 3种材性树种的K_area、K_mass和P₅₀均差异显著(p < 0.05)。无孔材树种的K_area和K_mass最低, 而散孔材和环孔材树种差异不显著; 环孔材树种P₅₀最高, 而散孔材和无孔材树种差异不显著。K_area和K_mass均与P₅₀显著负相关(p < 0.05), 但散孔材、环孔材和无孔材树种的相关关系分别呈线性、幂函数和指数函数关系。这表明叶水力效率与安全之间存在一定的权衡关系, 但该关系受树木材性的影响。K_mass与TLP显著负相关(p < 0.01), 其中散孔材和环孔材树种呈线性负相关, 无孔材树种呈负指数函数关系; P₅₀随TLP的增加而增加, 这表明树木在面临水分胁迫时, 其质外体和共质体抗旱阻力共同协调保护叶片活细胞, 防止其水分状况到达临界阈值。K_mass与叶干物质含量、叶密度、比叶重均显著负相关, 而P₅₀与之显著正相关(p < 0.01, P₅₀与比叶重的关系除外), 表明树木叶水力特性的变化受相同叶结构特性驱动, 树木增加对水力失调的容忍需要在叶水力系统构建上增加碳投资。     

Plant water-regulation strategies: Isohydric versus anisohydric behavior

Water is a vital resource for plant survival, growth and distribution, and it is of significance to explore mechanisms of plant water-relations regulation and responses to drought in ecophysiology and global change ecology. Plants adapt to different climates and soil water regimes and develop divergent water-regulation strategies involving a suite of related traits, of which two typical types are isohydric and anisohydric behaviors. It is critical to distinguish water-regulation strategies of plants and reveal the underlying mechanisms for plant breeding and vegetation restoration especially in xeric regions; and it is also important for developing more accurate vegetation dynamic models and predicting vegetation distribution under climate change scenarios. In this review, we first recalled the definitions of isohydric and anisohydric regulations and three quantitative classification methods that were established based on the relationships (1) between stomatal conductance and leaf water potential, (2) between stomatal conductance and vapor pressure deficit, (3) between predawn and midday leaf water potentials. We then compared the two water-regulation strategies in terms of hydraulics and carbon-economics traits. We synthesized the mechanisms of plant water-regulation and found that the interaction between hydraulic and chemical signals was the dominant factor controlling plant water-regulation behavior. Last, we proposed three promising aspects in this field: (1) to explore reliable and universal methods for classifying plant water-regulation strategies based on extensive investigation of the traits related with plant water-relations in various regions; (2) to explore relationships between plant water-regulation strategies and traits of hydraulics, morphology, structure, and function in order to provide reliable parameters for improving vegetation dynamic models; and (3) to deeply understand the processes of plant water-regulation at different spatial and temporal scales, and reveal mechanisms of plants’ responses and adaption to environmental stresses (especially drought).     

木本植物木质部的冻融栓塞应对研究进展

冻融栓塞在中高纬度地区木本植物中普遍存在。抗冻融栓塞能力对在寒冷环境中木本植物的生长和安全越冬十分关键, 这直接决定植物分布范围。冻融栓塞是由于冰中气体溶解度低, 木质部水分在低温下冷冻, 使之前水中溶解的气体逸出到导管中, 随后木质部中的冰融化又使气泡扩张而引发的栓塞现象。木质部解剖结构的差异会影响植物的抗冻融栓塞能力, 植物还可以通过调节木质部正压、代谢耗能等方式主动修复冻融栓塞, 也可通过增加树液溶质含量等逃避冷冻, 以减少低温损伤。然而, 与干旱栓塞相比, 目前对木质部冻融栓塞的形成以及植物响应和调节机制的理解不足。为此, 该文首先综述了木质部冻融栓塞的形成机制和植物的逃避、忍耐、修复等3种冻融栓塞的应对策略, 然后总结了木质部抗低温胁迫能力的生理表现、影响因子和评价指标, 并在此基础上讨论了低温抗性、干旱抗性和水力效率之间的多元权衡关系, 最后提出今后该领域中的5个优先研究问题: (1)不同植物冰冻的最低温度阈值; (2)是否存在应对低温胁迫的水力脆弱性分割机制; (3)冻融栓塞修复与代谢消耗的关系; (4)低温抗性、干旱抗性和水力效率之间的权衡关系; (5)抗冻融栓塞性状是否能够纳入经济性状谱系。     

Variations and interrelationships of foliar hydraulic and photosynthetic traits for Larix gmelinii

Aims Variations and potential trade-offs of leaf hydraulic and photosynthetic traits are essential for assessing and predicting the effect of climate change on tree survival, growth and distribution. Our aims were to examine variations and interrelationships of leaf hydraulic and photosynthetic traits in response to changes in site conditions for Dahurian larch (Larix gmelinii)—a dominant tree species in Chinese boreal forests.Methods This study was conducted at the Maoershan Forest Ecosystem Research Station. A transect of 27 year-old Dahurian larch plantation was established that consisted of five plots extending from the valley to the ridge of a slope. The predawn leaf water potential (Ψ_pre), area- and mass-based leaf hydraulic conductance (K_area and K_mass, respectively), resistance to embolism capacity (P₅₀), leaf mass per area (LMA), net photosynthetic rate (A), and leaf nitrogen content (N) were measured in August 2016.Important findings The Ψ_pre, K_area, K_mass, P₅₀, A, LMA, and N all varied significantly among the plots (p < 0.05), indicating significant intra-specific variations in these traits in response to the changes in site conditions. The P₅₀ was significantly (p < 0.05) correlated with Ψ_pre, K_area or K_mass, suggesting that a trade-off between hydraulic efficiency and safety exist within the species to some degree. There were significant (p < 0.05) pairwise correlations between A, LMA, and N. Nevertheless, there was no significant (p < 0.05) correlation between the measured photosynthetic traits and hydraulic traits. We concluded that the intra-specific variations and multiple interrelationships of the leaf hydraulic and photosynthetic traits for the larch reflect the plasticity of its leaf traits and strategies of its survival and growth as a result of its acclimation to diverse site conditions.     

植物功能性状权衡关系的研究进展

植物功能性状权衡关系反映了植物在资源获取与分配中采取的不同策略, 是近年来生态学研究的一个热点问题。该综述从研究范围、叶性状、器官和植物类群4个方面入手, 简要介绍植物功能性状关系研究在近10余年是如何在叶经济谱(LES)的基础上逐渐扩展和深入的。1)相关研究拓展到全球更多极端环境与特殊气候地区, 发现在不同的气候环境条件下, 植物叶片功能性状关系相对稳定, 植物种内的功能性状关系已被证实与LES相似; 2)功能性状网络从最初的6个经济性状扩展到叶片的分解、燃烧和水力等性状, 发现叶片的分解速率和可燃性均与叶片形态性状、养分含量等显著相关, 但叶片水力性状与经济性状的关系则取决于所研究的物种及生存环境的水分条件; 3)研究对象从植物叶片拓展到了根、茎、花、种子及植株整体, 叶片的比叶质量与茎的木质密度、种子大小相耦合, 但叶片形态性状与根和花的相关性状却无显著相关关系, 证明这些器官可能是独立进化的; 4) LES可以很好地解释特殊维管植物的生存适应策略: 入侵植物具有较高的资源利用效率和更快的相对生长速率, 在LES中处于“低投入-快速回报”的一端; 食虫植物的叶片特化为捕食器官, 光合作用及生长速率相对较低, 居于LES “高投入-缓慢回报”的另一端, 此外, 无论是最古老的种子植物苏铁属(Cycas)植物, 或是蕨类和变水植物(苔藓和地衣), 其功能性状关系都与LES大致相同。该文梳理了功能性状关系研究的进展脉络, 提出了一些建议, 期望为未来植物功能性状关系研究的选题和发展提供一些参考。     

木本植物水力系统对干旱胁迫的响应机制

干旱导致树木死亡对生态系统功能和碳平衡有重大影响。植物水分运输系统失调是引发树木死亡的主要机制。然而, 树木对干旱胁迫响应的多维性和复杂性, 使人们对植物水分运输系统在极端干旱条件下的响应以及植物死亡机理的认识还不清楚。该文首先评述衡量植物抗旱性的指标, 着重介绍可以综合评价植物干旱抗性特征的新参数——气孔安全阈值(SSM)。SSM越高, 表明气孔和水力性状之间的协调性越强, 木质部栓塞的可能性越低, 水力策略越保守。然后, 阐述木本植物应对干旱胁迫的一般响应过程。之后, 分别综述植物不同器官(叶、茎和根)对干旱胁迫的响应机制。植物达到死亡临界阈值的概率和时间, 取决于相关生理和形态学特征的相互作用。最后, 介绍木本植物水力恢复机制, 并提出3个亟待开展的研究问题: (1)改进叶片水分运输(木质部和木质部外水力导度)的测量方法, 量化4种不同途径的叶肉水分运输的相对贡献; (2)量化叶片表皮通透性变化, 以便更好地理解植物水分利用策略; (3)深入研究树木水碳耦合机制, 将个体结构和生理特征与群落/景观格局和过程相关联, 以便更好地评估和监测干旱诱导树木死亡的风险。     

青藏高原东缘常见阔叶木本植物叶片性状对环境因子的响应

叶片性状-环境关系对于预测气候变化对植物的影响至关重要。该研究以青藏高原东缘常见阔叶木本植物为研究对象, 从47个样点采集了332个物种共666个种群的叶片, 测量了15个叶片性状, 调查了该区域木本植物叶片性状的变异程度, 并从种内和种间水平探讨了叶片性状对环境的响应及适应策略。结果表明, 反眏叶片大小的性状均具有较高的变异, 其中, 叶片面积是变异程度最大的性状。除气孔密度外, 大多数叶片性状与海拔显著相关。气候是叶片性状变异的重要驱动因素, 3.3%-29.5%的叶片性状变异由气候因子组合解释。其中, 气温对叶片性状变异解释度最高, 日照时间能解释大部分叶片性状的变异, 而降水量对叶片性状变异的解释度相对较小。与环境(海拔和气候因子)显著相关的叶片性状在种内明显少于种间水平, 可能是植物性状之间的协同变化与权衡使种内性状变异比较小, 从而减弱了种内叶片性状与环境因子的相关性。研究结果总体表明,叶片性状与木本植物对环境的适应策略密切相关, 植物通过选择小而厚的叶片和较短的叶柄以适应高海拔的 环境。     

Venation networks and the origin of the leaf economics spectrum

The leaf economics spectrum describes biome-invariant scaling functions for leaf functional traits that relate to global primary productivity and nutrient cycling. Here, we develop a comprehensive framework for the origin of this leaf economics spectrum based on venation-mediated economic strategies. We define a standardized set of traits - density, distance and loopiness - that provides a common language for the study of venation. We develop a novel quantitative model that uses these venation traits to model leaf-level physiology, and show that selection to optimize the venation network predicts the mean global trait-trait scaling relationships across 2548 species. Furthermore, using empirical venation data for 25 plant species, we test our model by predicting four key leaf functional traits related to leaf economics: net carbon assimilation rate, life span, leaf mass per area ratio and nitrogen content. Together, these results indicate that selection on venation geometry is a fundamental basis for understanding the diversity of leaf form and function, and the carbon balance of leaves. The model and associated predictions have broad implications for integrating venation network geometry with pattern and process in ecophysiology, ecology and palaeobotany.     

内蒙古荒漠草原植物叶片功能性状关系及其经济谱分析

气候变化和人为干扰导致草原荒漠化加剧, 引发了严重的环境问题。因此, 对荒漠草原植物与环境变化关系的研究愈加迫切, 分析比较荒漠草原不同功能型物种叶片经济谱具有重要意义。该研究通过测定内蒙古荒漠草原生态系统不同功能型植物叶片的光合及叶绿素荧光参数、比叶面积和叶片氮素含量, 验证了荒漠草原植物叶片经济谱的存在, 明确了各功能型植物叶片性状间的关系及其在叶片经济谱中的位置。荒漠草原不同功能型植物叶片性状差异明显, 草本植物的比叶面积(SLA)、单位质量叶氮含量(N_mass)分别是灌木的2.39倍和1.20倍; 一年生植物单位面积最大净光合速率(A_area)、SLA、光合氮利用效率(PNUE)分别是多年生植物的1.93倍、2.13倍和4.24倍; C₄植物的A_area、SLA、PNUE分别是C₃植物的2.25倍、1.73倍和3.61倍。除A_area与单位面积叶氮含量(N_area)、PSII的实际光化学效率(Φ_PSII)与SLA之间不存在显著相关关系外, 叶片性状间存在广泛的相关关系, 且均达到极显著水平。这验证了叶片经济谱在内蒙古荒漠草原植物中也同样存在。进一步分析表明, 一年生植物、草本植物、C₄植物叶片在叶片经济谱中位于靠近薄叶、光合能力强、寿命短的一端; 而多年生植物、灌木、C₃植物叶片靠近厚叶、光合能力弱、寿命长的一端。这说明荒漠草原中不同功能型植物可通过权衡其经济性状间的关系而采取不同的适应策略, 对于荒漠草原生态系统管理具有重要的理论指导意义。     

Climate and plant trait strategies determine tree carbon allocation to leaves and mediate future forest productivity

Forest leaf area has enormous leverage on the carbon cycle because it mediates both forest productivity and resilience to climate extremes. Despite widespread evidence that trees are capable of adjusting to changes in environment across both space and time through modifying carbon allocation to leaves, many vegetation models use fixed carbon allocation schemes independent of environment, which introduces large uncertainties into predictions of future forest responses to atmospheric CO₂ fertilization and anthropogenic climate change. Here, we develop an optimization‐based model, whereby tree carbon allocation to leaves is an emergent property of environment and plant hydraulic traits. Using a combination of meta‐analysis, observational datasets, and model predictions, we find strong evidence that optimal hydraulic–carbon coupling explains observed patterns in leaf allocation across large environmental and CO₂ concentration gradients. Furthermore, testing the sensitivity of leaf allocation strategy to a diversity in hydraulic and economic spectrum physiological traits, we show that plant hydraulic traits in particular have an enormous impact on the global change response of forest leaf area. Our results provide a rigorous theoretical underpinning for improving carbon cycle predictions through advancing model predictions of leaf area, and underscore that tree‐level carbon allocation to leaves should be derived from first principles using mechanistic plant hydraulic processes in the next generation of vegetation models.     

叶片结构的水力学特性对植物生理功能影响的研究进展

叶片是植物进行光合、呼吸、蒸腾作用的主要器官, 早期的研究主要集中于水分在叶片中的运输路径, 而对叶脉结构及其生态学意义研究甚少。近年来关于叶片叶脉结构、气孔结构的功能及叶片水力学特性的意义研究已经成为植物生理生态的研究热点。该文综述了叶脉的结构性状的指标(叶脉密度、直径、间距等), 叶片水力学结构特性对植物生长、水分运输、气体交换、光合作用等生理功能的影响, 及其与植物对干旱适应性之间的关系。叶脉结构是决定叶片生理功能的基础, 因此在未来的工作中应分析比较不同种类植物叶脉结构形态与导水、光合、呼吸、同化作用之间的关系, 建立植物茎干-枝-叶系统水力传导的机理性模型, 用以探索不同植物功能结构和高效用水生理生态学机制, 据此评估不同种类植物在未来气候情景下的地位。     

Vessel length as a key hydraulic structure in woody plants: A review

导管作为多数被子植物木质部水分运输的主要通道, 了解其结构及功能对研究被子植物水力学特性及植物对环境的适应性有着重要的作用。导管长度作为导管解剖特征之一, 对水分运输的安全性及有效性有着重要的影响。该文概述了导管长度测量及计算的方法, 导管长度在种内及种间的分布, 导管长度与导管直径的关系, 导管长度与导水率的关系及导管长度对建立栓塞脆弱曲线的影响, 并对未来导管长度的研究工作重点提出了建议: 1)改进灌注物质, 使灌注更加充分且更利于观察、提高计算精度、发展活体动态测量技术; 2)建立导管在植物不同器官及整体的分布网络以及不同生活型、不同地区的导管长度数据库; 3)对导管直径在导管方向的变化, 导管长度与其他导管特性之间的关系进行研究; 4)光学测量建立栓塞脆弱曲线技术的兴起, 可为解决离心机法建立栓塞脆弱曲线的真实与准确与否的争议提供新的方向。更深入地了解导管长度在植物水力功能中担负的角色, 可以为耐旱、抗旱品种选育提供理论基础。     

Leaf economics and hydraulic traits are decoupled in five species‐rich tropical‐subtropical forests

Leaf economics and hydraulic traits are critical to leaf photosynthesis, yet it is debated whether these two sets of traits vary in a fully coordinated manner or there is room for independent variation. Here, we tested the relationship between leaf economics traits, including leaf nitrogen concentration and leaf dry mass per area, and leaf hydraulic traits including stomatal density and vein density in five tropical‐subtropical forests. Surprisingly, these two suites of traits were statistically decoupled. This decoupling suggests that independent trait dimensions exist within a leaf, with leaf economics dimension corresponding to light capture and tissue longevity, and the hydraulic dimension to water‐use and leaf temperature maintenance. Clearly, leaf economics and hydraulic traits can vary independently, thus allowing for more possible plant trait combinations. Compared with a single trait dimension, multiple trait dimensions may better enable species adaptations to multifarious niche dimensions, promote diverse plant strategies and facilitate species coexistence.     

干旱胁迫植物个体生理响应及其生态模型预测研究进展

全球气候突变导致干旱事件频发,进而易引发严重的植物衰退甚至死亡,聚焦植物尤其是树木死亡的生理学机制并期望基于此评估及预测气候变化导致植物死亡风险已成为热点话题。植物通过调整内在生理代谢过程,例如通过调节渗透物质的含量,来平衡渗透势、维持细胞膨压、调节植物激素的信号水平,诱导植物气孔开放程度降低,有利于植物保存水分、调控植物水通道蛋白的表达,进而保持体内水分稳定并对干旱胁迫做出快速响应。这些生理过程中的每一环调节都为了确保水分运输的效率和安全性,增加植物抗旱性以及生态系统稳定性。植物的抗旱性不仅体现在生理代谢方面的调节,还表现在植物水力特性与解剖结构间相辅相成。当植物改变水力特性的同时,其茎叶会在解剖结构上做出调整以满足植物在干旱环境下水分供需平衡,从而降低植物蒸腾水分散失、增强细胞储水并提高生存能力。植物应对水分胁迫的策略通常与水分消耗和碳获取之间的平衡有关,明晰植物水分消耗与光合碳获取间存在平衡关系的性状特征便于更好地理解植物的水分利用策略。然而,植物表现出的任意单一性状特征的强弱都无法代表整个植物适应逆境的优劣,未来只有通过将植物更多性状特征进行相互关联,以具有代表植物水力功能、结...     

The leaf economics spectrum’s morning coffee: plant size-dependent changes in leaf traits and reproductive onset in a perennial tree crop

Background and AimsSize-dependent changes in plant traits are an important source of intraspecific trait variation. However, there are few studies that have tested if leaf trait co-variation and/or trade-offs follow a within-genotype leaf economics spectrum (LES) related to plant size and reproductive onset. To our knowledge, there are no studies on any plant species that have tested whether or not the shape of a within-genotype LES that describes how traits covary across whole plant sizes, is the same as the shape of a within-genotype LES that represents environmentally driven trait plasticity.MethodsWe quantified size-dependent variation in eight leaf traits in a single coffee genotype (Coffea arabica var. Caturra) in managed agroecosystems with different environmental conditions (light and fertilization treatments), and evaluated these patterns with respect to reproductive onset. We also evaluated if trait covariation along a within-genotype plant-size LES differed from a within-genotype environmental LES defined with trait data from coffee growing in different environmental conditions.Key ResultsLeaf economics traits related to resource acquisition – maximum photosynthetic rates (A) and mass-based leaf nitrogen (N) concentrations – declined linearly with plant size. Structural traits – leaf mass, leaf thickness, and leaf mass per unit area (LMA) – and leaf area increased with plant size beyond reproductive onset, then declined in larger plants. Three primary LES traits (mass-based A, leaf N and LMA) covaried across a within-genotype plant-size LES, with plants moving towards the ‘resource-conserving’ end of the LES as they grow larger; in coffee these patterns were nearly identical to a within-genotype environmental LES.ConclusionsOur results demonstrate that a plant-size LES exists within a single genotype. Our findings indicate that in managed agroecosystems where resource availability is high the role of reproductive onset in driving within-genotype trait variability, and the strength of covariation and trade-offs among LES traits, are less pronounced compared with plants in natural systems. The consistency in trait covariation in coffee along both plant-size and environmental LES axes indicates strong constraints on leaf form and function that exist within plant genotypes.     

Hydraulic architecture of evergreen broad-leaved woody plants at different successional stages in Tiantong National Forest Park,Zhejiang Province,China

Aims Hydraulic architecture is a morphological strategy in plants to transport water in coping with environmental conditions. Change of hydraulic architecture for plants occupying different canopy layers within community and for the same plant at different successional stages reflect existence and adaptation in plant's water transportation strategies. The objective of this study was to examine how hydraulic architecture varies with canopy layers within a community and with forest succession.Methods The study site is located in Tiantong National Forest Park, Zhejiang Province, China. Hydraulic architectural traits studied include sapwood-specific hydraulic conductivity, leaf-specific hydraulic conductivity, Huber value, sapwood channel area of twigs, total leaf area per terminal twig, and water potential of twigs. We measured those traits for species that occur in multiple successional stages (we called it "overlapping species") and for species that occur only in one successional stage (we called it "turnover species") along a successional series of evergreen broadleaved forests. For a given species, we sampled both overstory and understory trees. Hydraulic architectural traits between overstory and understory trees in the same community and at successional stages were compared. Pearson correlation was used to exam the relationship between hydraulic architectural traits and the twig/leaf traits.Important findings Sapwood-specific hydraulic conductivities and leaf-specific hydraulic conductivities were significantly higher in overstory trees than those in understory trees, but did not significantly differ from successional stages. Huber value decreased significantly for understory trees, but did not change for overstory trees through forest successional stages. For overstory trees, a trend of decreasing sapwood-specific hydraulic conductivity was observed for overlapping species but not for turnover species with successional stages. In contrast, for understory trees, a trend of decreasing Huber values was observed for turner species but not for overlapping species with successional stages. Across tree species, sapwood-specific hydraulic conductivity was positively correlated with sapwood channel area and total leaf area per terminal twig size. Huber value was negatively correlated to water potential of twigs and total leaf area per terminal twig size. These results suggest that water transportation capacity and efficiency are higher in overstory trees than in understory trees across successional stages in evergreen broadleaved forests in Tiantong region. The contrasting trends of sapwood-specific hydraulic conductivity between overlapping species and turnover species indicate that shift of microenvironment conditions might lead to changes of hydraulic architecture in overstory trees, whereas species replacement might result in changes of hydraulic architecture in understory trees.     

叶脉结构与功能及其对叶片经济谱的影响

叶脉由贯穿于叶肉内部的维管组织及其外围机械组织构成,多样化的脉序及网络结构使叶脉系统发生变异和功能分化。该文综述了叶脉系统结构与功能的最新研究进展。通过聚焦叶脉分级系统的结构与功能及其在叶片经济谱(LES)中的重要性,解释叶脉性状与其它叶片功能性状之间的关系及机制。不同等级叶脉在机械支撑与水分运输方面存在功能分化,其中1–3级粗脉在维持叶片形状和叶表面积以及物理支撑方面发挥重要作用,有利于维持叶片最大受光面积;4级及以上细脉具有水分调节功能,它们与气孔相互协调,影响叶片水分运输、蒸腾散热和光合作用速率。叶片生长过程与叶脉发育的动态变化模式决定叶脉密度,并影响叶脉密度与叶片大小之间的关系:叶面积与粗脉密度呈显著负相关,与粗脉直径呈显著正相关,而与细脉密度无关。与叶脉性状相关的叶片经济谱框架模型预测,叶脉密度较高的叶片寿命短、比叶重较小,叶片最大碳同化速率、代谢速率以及资源获取策略潜力较高。     

Leaf hydraulic safety margin and safety–efficiency trade-off across angiosperm woody species

Leaf hydraulic conductance and the vulnerability to water deficits have profound effects on plant distribution and mortality. In this study, we compiled a leaf hydraulic trait dataset with 311 species-at-site combinations from biomes worldwide. These traits included maximum leaf hydraulic conductance (K_leaf), water potential at 50% loss of K_leaf (P50_leaf), and minimum leaf water potential (Ψ_min). Leaf hydraulic safety margin (HSM_leaf) was calculated as the difference between Ψ_min and P50_leaf. Our results indicated that 70% of the studied species had a narrow HSM_leaf (less than 1 MPa), which was consistent with the global pattern of stem hydraulic safety margin. There was a positive relationship between HSM_leaf and aridity index (the ratio of mean annual precipitation to potential evapotranspiration), as species from humid sites tended to have larger HSM_leaf. We found a significant relationship between K_leaf and P50_leaf across global angiosperm woody species and within each of the different plant groups. This global analysis of leaf hydraulic traits improves our understanding of plant hydraulic response to environmental change.