Effects of leaf shape plasticity on leaf surface temperature

干旱区植物叶片形态可塑性是植物适应高温干旱环境的重要生存策略, 但目前仍缺乏直观的数据予以证明。该研究应用热成像技术和图像分析技术, 同步测定真实叶片与模拟叶片的叶温、形态及风速、辐射和温度等环境参数。研究结果显示: 在干旱、高温环境下, 除了蒸腾, 叶片形态变化也是调控叶温的重要因子。干旱区植物叶片变小, 有利于加速叶片与环境的物质及热量交换, 从而达到降低叶温的目的。样地数据显示, 在高温、低风速环境下, 叶片宽度每减少1 cm, 叶片表面温度降低约2.1 ℃, 而模拟叶片叶宽度每减少1 cm, 叶片表面温度降低0.60-0.86 ℃。该研究对深入理解植物生存策略与环境适能力具有重要意义。     

干旱区叶片形态特征与植物响应和适应的关系

叶片形态是指示植物适应特定环境的重要指标。由于植物叶片形态不仅对时空环境变化具有极强的敏感性和可塑性, 而且能够通过叶片形态的调整调节自身的生存适应能力, 所以叶片形态学研究一直是植物生理及植物生态学研究中的热点。该文在总结前人叶片形态学研究成果的基础上, 探索建立了简单的叶片形态指标分类体系; 结合物质能量交换的物理学原理, 回顾总结了叶片表观形态变化与叶片物质能量交换之间的相关关系; 应用叶片形态影响物质能量交换的物理学原理, 重点分析了干旱区植物叶片表观形态对低水分环境、高辐射(或高温)的响应与适应特征; 最后, 在回顾分析的基础上, 对叶片形态研究中存在的几个问题进行了讨论。     

干旱区植物叶片大小对叶表面蒸腾及叶温的影响

利用热及物质交换原理, 并结合前人研究成果, 在单叶尺度上建立了简单的叶温和水气蒸腾模型。模型通过预设值驱动, 预设值参照干旱区环境及植物叶片特征设置。模拟结果显示: 随气孔阻力的增加, 叶片蒸腾速率降低, 叶温升高; 同一环境下, 具有低辐射吸收率的叶片蒸腾速率和叶温更低, 并且气孔阻力越大, 这种差异越明显。另外, 叶片宽度及风速是影响叶片蒸腾及叶温的重要因子。干旱地区植物生长季节, 风速小于0.1 m·s ^-1、气孔阻力接近1000 s·m ^-1时, 降低叶片宽度不仅有利于降低叶片温度, 而且能够降低叶片蒸腾速率, 从而实现保持水分, 增强植物适应高温、干旱的能力。     

玉米叶片三维形态的数学模拟研究

根据玉米叶片三维形态特征,应用悬臂梁模型来描述玉米叶曲线,对描述玉米叶片边缘扭曲的数学模型进行改进后,提出了基于特征参数的玉米叶片三维形态数学模型及其实现方法,本模型大大减少了描述全米叶片三维形态的信息量,并具有较高的逼真性,同时适用于描述其它禾谷类作物叶片的三维形态。     

木兰科植物叶片光合系统耐热性与叶片形态及温度生态位的关系

全球气候变化背景下,极端高温事件日益频繁,对植物的生长、存活造成严重威胁,准确评估植物的耐热性,对物种保育和适应性预测具有重要作用。木兰科是中国亚热带常绿阔叶林的标志类群,也是被子植物基部类群,具有重要的生态价值和演化生物学地位,然而目前对其耐热性尚缺乏了解。该研究以种植于同质园的23种木兰科植物为研究对象,利用叶绿素荧光技术研究了叶片光合系统的耐热性,同时测定了叶片形态性状,并基于这些物种在全球的分布地气候数据,分析了叶片光合系统耐热性与叶片形态及温度生态位的关系。发现木兰科植物光系统II最大光化学效率降低50%时的温度(T50)范围在46.1–56.7℃之间,且常绿物种的T50显著高于落叶物种。叶片形态方面, T50与叶面积显著正相关,与叶片厚度无显著相关关系。温度生态位方面, T50与年平均气温、最冷月最低气温呈显著正相关关系,但与最暖月最高气温无显著相关关系。T50具有较弱的系统发育信号,暗示T50受系统发育影响较小,受叶片形态与环境气候的影响较大。研究结果说明木兰科植物的叶片光合系统耐热性较强,但耐热性的气候适应可能并不受高温环境驱动,未来的高温事件对生活于更炎热地区的木兰科...     

植物叶片形态解剖结构对环境变化的响应与适应

叶片是植物进化过程中对环境变化比较敏感且可塑性较大的器官,环境变化常导致叶的长、宽及厚度,叶表面气孔、表皮细胞及附属物,叶肉栅栏组织、海绵组织、胞间隙、厚角组织和叶脉等形态解剖结构的响应与适应。本文综述了陆生植物叶片上述形态解剖结构对水分、温度、光照、CO2浓度和UV-B辐射等环境因子变化以及多因子复合作用的响应与适应,分析了该领域的研究特点及其存在的问题,指出了未来研究的重点和方向。     

CO2浓度倍增对10种禾本科植物叶片形态结构的影响

在CO_2正常浓度(350μL/L)和倍增(700μL/L)条件下,对小麦(Triticum aestivum L.)、半野生小麦(T.aestivum ssp.tibeticum)、大麦(Hordeum vulgare L.)、野大麦(H.brevisubulatum(Trin.)Link)、水稻(Oryza sativa L.)、野生稻(O.meyeriana subsp.granulata)、谷子(Setaria italica(L.)Beauv)、狗尾草(S.viridis (L.)Beauv)、高粱(Sorghum vulgare Pers.)和玉米(Zea mays L.)等10种禾本科植物幼苗期叶的形态结构进行比较研究。结果表明,在CO_2浓度倍增条件下,除野大麦和玉米外,其它几种禾本科植物的叶片厚度普遍增加;表皮细胞密度下降(野大麦和谷子的远轴面除外)。其中C_3种类的平均气孔密度和气孔指数下降,C_4种类则呈相反趋势。在CO_2浓度倍增条件下,栽培种类表皮细胞密度和维管束鞘细胞中的叶绿体数明显增加,野生种类则呈相反趋势。气孔密度与气孔指数基本呈正相关。     

不同供硼水平对绿豆植株形态及其叶片生长特征的影响

利用水培以绿豆为材料,研究不同供硼水平对绿豆植株形态和叶片生长特征的影响。结果表明缺硼抑制绿豆生长,但对根的影响较对冠的影响更大,表现在缺硼导致冠根比增大;缺硼明显抑制叶面积;降低特定叶面积（SLA）,这可能是由于缺硼影响细胞伸展的缘故,造成叶片密度增加,缺硼也提高叶片重量比（LWR)并导致叶脉间失绿,说明缺硼叶片可能过量碳水化合物积累,引起叶绿素降解,与适量供硼比较,过量供硼也影响绿豆的生长,但对冠根比没有影响,表明过量供硼对根和冠具有相同的抑制作用,硼中毒导致成熟叶片脱落,从而影响叶面积,但对特定叶面积（SLA）和叶片重量比（LWR）没有影响。     

龙须草叶片形态结构与生理功能的研究

利用定样平行配套观测方法 ,研究了龙须草叶片形态结构和光合、蒸腾等生理功能 ,结果表明 :龙须草叶片呈长剑形 ,叶长为 35～ 1 50 cm,最长可达 2 0 0 cm以上 ,叶宽为 0 .1 9～0 .48cm;功能叶结构具有典型的 C4 “花环结构”;上表皮中具有十分发达的保护水分过度蒸腾的“泡状细胞”;上表皮气孔分布密度大于下表皮。功能叶叶绿素 a/ b值为 3.2 8± 0 .2 6。背面叶平均光合强度为 62 .4( CO2 mg/ dm2 · h)、呼吸强度为 3.57( CO2 mg/ dm2 · h)、蒸腾强度为 372 6( H2 O mg/ dm2 · h)、气孔阻力为 0 .2 1 ( sec./ cm)、水分利用效率为 1 6.747。背面叶的光合强度和蒸腾强度明显高于腹面叶。     

甘蔗品种(系)叶片形态特征数学分析

本文对48份甘蔗品种(系)的叶片形态特征进行主成分、聚类和判别分析.结果表明,品种(系)间的叶片形态特征差异达到极显著水平(P＞0.01);主成分分析选出了3个主成分,方差累积贡献率达到97.52%,叶长、叶宽及形态因子分别是第一、二、三主成分的主导因子;在聚类分析基础上用判别分析选出对甘蔗品种(系)叶片形态分类有极显著影响的面积、长度、宽度、周长、长宽比及形态因子参数,同时建立了4个判别能力较高的判别模型.     

Effects of leaf shape plasticity on leaf surface temperature北大核心CSCD

Aims The shape plasticity of plant leaves is an important survival strategy to high temperature and drought in arid region, yet reliable evidences are insufficient to validate the fundamental concepts. Our objective was to demonstrate the specific effects of leaf morphology on leaf surface temperature. Methods Infrared thermal images were processed to determine the leaf temperature and shape parameters of simulated and actual leaf shape. Microclimatic conditions were recorded using a automatic weather station near the sampling plot, including wind speed, radiation and air temperature. Important findings Under the drought and high temperature, the plasticity of leaf shape appeared an important measure to regulate leaf temperature, except leaf transpiration. The exchange rates of matter and energy between leaves and the environment were enhanced by smaller leaves that effectively decreased leaf temperature. With low wind speed and high temperature, leaf surface temperature decreased 2.1 °C per 1 cm reduction in leaf width. However, leaf surface temperature of a simulated leaf decreased 0.60–0.86 °C per 1 cm reduction in leaf width. Results from this study will help us to understand plant adaptability and survival strategy in arid region. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

The influence of leaf size and shape on leaf thermal dynamics: does theory hold up under natural conditions?

Laboratory studies on artificial leaves suggest that leaf thermal dynamics are strongly influenced by the two‐dimensional size and shape of leaves and associated boundary layer thickness. Hot environments are therefore said to favour selection for small, narrow or dissected leaves. Empirical evidence from real leaves under field conditions is scant and traditionally based on point measurements that do not capture spatial variation in heat load. We used thermal imagery under field conditions to measure the leaf thermal time constant (τ) in summer and the leaf‐to‐air temperature difference (?T) and temperature range across laminae (T_range) during winter, autumn and summer for 68 Proteaceae species. We investigated the influence of leaf area and margin complexity relative to effective leaf width (w_e), the latter being a more direct indicator of boundary layer thickness. Normalized difference of margin complexity had no or weak effects on thermal dynamics, but w_e strongly predicted τ and ?T, whereas leaf area influenced T_range. Unlike artificial leaves, however, spatial temperature distribution in large leaves appeared to be governed largely by structural variation. Therefore, we agree that small size, specifically w_e, has adaptive value in hot environments but not with the idea that thermal regulation is the primary evolutionary driver of leaf dissection.     

The influence of temperature on leaf development and growth in potatoes in controlled environments

Three controlled environment experiments were conducted at different temperatures to determine the relation between temperature and leaf development and growth in the potato (cv. Maris Piper). Developmental stages are defined for the appearance and duration of leaf extension in the potato and comparisons made with other temperate zone crops. The rate of leaf appearance was linear over the temperature range (9–25°C) and above 25°C there was no further increase in the rate. The temperature coefficient for the rate of appearance of leaves was 0.032 leaves (degree days)^-1 using a base temperature of 0°C. The duration of extension of an individual leaf decreased with increase in temperature up to 25°C such that the thermal duration was constant at 170 degree days using a base temperature of 0°C for leaf positions 4–10 on the main stem. At higher leaf positions the thermal duration was similar or greater. The advantages and limitations of controlled environment work as a parallel to field experimentation are discussed.     

Use of thermography for quantitative studies of spatial and temporal variation of stomatal conductance over leaf surfaces

This paper describes a new approach to the calibration of thermal infrared measurements of leaf temperature for the estimation of stomatal conductance and illustrates its application to thermal imaging of plant leaves. The approach is based on a simple reformulation of the leaf energy balance equation that makes use of temperature measurements on reference surfaces of known conductance to water vapour. The use of reference surfaces is an alternative to the accurate measurement of all components of the leaf energy balance and is of potentially wide application in studies of stomatal behaviour. The resolution of the technique when applied to thermal images is evaluated and some results of using the approach in the laboratory for the study of stomatal behaviour in leaves of Phaseolus vulgaris L. are presented. Conductances calculated from infrared measurements were well correlated with estimates obtained using a diffusion porometer.     

Temperature heterogeneity over leaf surfaces: the contribution of the lamina microtopography

Temperature is spatially heterogeneous over leaf surfaces, yet the underlying mechanisms are not fully resolved. We hypothesized that the 3D leaf microtopography determines locally the amount of incoming irradiation flux at leaf surface, thereby driving the temperature gradient over the leaf surface. This hypothesis was tested by developing a model of leaf temperature heterogeneity that includes the development of the leaf boundary layer, the microtopography of the leaf surface and the physiological response of the leaf. Temperature distributions under various irradiation loads (1) over apple leaves based on their 3D microtopography, (2) over simulated flat (2D) apple leaves and (3) over 3D leaves with a transpiration rate distributed as in 2D leaves were simulated. Accuracy of the predictions was quantified by comparing model outputs and thermographic measurements of leaf surface temperature under controlled conditions. Only the model with 3D leaves predicted accurately the spatial heterogeneity of surface temperature over single leaves, whereas the mean temperature was well predicted by both 2D and 3D leaves. We suggest that in these conditions, the 3D leaf microtopography is the primary driver of leaf surface heterogeneity in temperature when the leaf is exposed to a light/heat source.     

Effect of water deficits on transpiration, photosynthesis and leaf conductance in cassava

Transpiration, net photosynthesis and leaf conductance decreased when leaf water potential dropped below -0.30 MPa. Both transpiration and net photosynthesis rates were considerably reduced before the leaves were visibly wilted at -0.95 MPa. Consequently, visual symptoms are unlikely to provide a useful index for characterizing water deficits in cassava ( Manihot esculenta Crantz cv. Llanera). Decreases in net photosynthesis closely followed decreases in transpiration and this suggests that stomatal closure controls both processes.