栲树冠层光合生理特性的空间异质性

森林冠层在能量传输、光合有效辐射和微气象等方面的差异可导致冠层光合生产力空间分布的变化.叶片光合生理特性在空间上的差异对精确估算森林冠层的初级生产力十分重要.本文以亚热带常绿阔叶林优势种---栲树(Castanopsis fargesii)为对象,研究叶片光合生理特性在冠层空间上的变化.结果表明:1)在垂直方向上,冠层北向叶的饱和光合速率(Amax)、光饱和点(LSP)和CO2羧化效率(CCE)均表现为上部>中部>底部,且依次平均降低19.4%、18.1%和37.1%;光补偿点(LCP)、光下暗呼吸(Rd)以及冠层南向叶的饱和光合速率、光饱和点和CO2羧化效率均表现为上部>底部>中部,上部比中部和底部高出12.3%~71.4%;表观量子效率(AQY)表现为底部>上部>中部,底部分别是顶部和中部叶的1.2和1.3倍;2)在水平方向上,冠层上部和底部南向叶的饱和光合速率、光饱和点和CO2羧化效率比北向叶高0.9%~31.5%;冠层中部北向叶的饱和光合速率等6个参数比南向叶高9.6%~63.2%.因此,在冠层水平上模拟和估算植物生产力时,必须考虑冠层光合生理特性的空间差异.     

刺槐树冠光合作用的空间异质性

林木冠层是森林与外界环境相互作用最直接的部分,冠层光合作用是研究森林生产力的基础。为了深入了解冠层内部光合作用的差异性,以陕西省永寿县马莲滩流域阳坡和阴坡立地的刺槐林为研究对象,对比分析了光合速率(An)、蒸腾速率(E)、水分利用效率(WUE)、气孔导度(gs)、羧化效率(Vc)、水汽压亏缺(VPD)、气孔限制值(ls)、光合有效辐射(PAR)、空气温度(Ta)在树冠不同层次、不同方位,以及不同坡向之间的差异性。结果表明,刺槐树冠不同层次的光合作用差异性显著,大部分光合生理生态指标表现为:上中下。对于阳坡刺槐,VPD、Ta、gs、E是影响不同层次An的主要因子;对于阴坡刺槐,VPD、E、PAR是影响不同层次An的主要因子。光合作用在刺槐树冠的不同方位没有显著差异,大多数光合指标变化很小,E、ls、PAR、Ta是影响不同方位An的主要因子。对于刺槐冠层内部的任何层次或方位,阴坡刺槐具有更高的日均An、E、Vc、VPD、ls,而阳坡刺槐具有更高的日均WUE、gs、PAR、Ta。阳坡刺槐树冠中层西方和阴坡中层东方的日总光合速率值,可以分别代表阳坡和阴坡刺槐整个冠层的日总光合速率。研究认为,在冠层水平模拟和估计森林生产力时,必须考虑冠层光合作用的空间异质性,对于从单木到林分的尺度推演和模型拟合具有重要的意义。     

浙江天台山七子花群落主要植物种类的光合特性

对分布在浙江天台山的七子花群落主要植物种类的光合生理生态特性进行了研究。结果表明：夏季,位于群落冠层上层、林窗、林缘的七子花及主要伴生植物叶片的光合日进程均呈“双峰“曲线,有明显的光合“午休“现象。而位于冠层中、下层以及林下的七子花、草本植物,其光合日进程曲线平缓。从冠层上层到下层,七子花叶片的日均净光合速率（Pn）呈下降趋势。林窗、林缘的七子花小树叶片日均Pn比林下大,冠层上层的七子花中树叶片与林窗、林缘的小树叶片日均Pn差异不显著。七子花在不同生境中与伴生植物相比,日均Pn较低,光合能力较弱。同一植株七子花冠层上层叶片叶绿素含量最低,下层次之,中层最高。阴生草本植物在弱光下仍有很高的叶绿素含量。植物叶片的光合能力大小与叶绿素含量高低不呈正相关。相对常绿树种而言,七子花光补偿点较高、光饱和点较低,对光适应的生态幅度较窄。     

上海新江湾地区废弃地低干扰植物群落优势树种的光合生理生态特征

以上海市杨浦区原废弃地(新江湾地区)半自然群落的主要优势树种为对象,测定不同生活型植株在夏季不同生境下叶片的光合特性,从光合生理生态角度分析低干扰条件下上海城市废弃地的植物群落次生演替过程的特点,并结合环境因子分析并预测植物群落结构的动态变化。结果表明:(1)冠层树种光合作用日变化曲线呈双峰型,林窗树种呈单峰型,而林下树种呈不规则变化,体现出亚热带地区植物在夏季典型气候下的"光合午休"现象,而生境特点同时也影响植物光利用对策。(2)冠层成年树以落叶树种刺槐和朴树的日均净光合速率最高,且具有较高的光饱和点;在林下生境中,以强耐阴灌木植物胡颓子的日均净光合速率最高,其次为常绿树种香樟和女贞的幼树和幼苗,而林下落叶树种日均净光合速率均较低。(3)影响冠层树种的净光合速率因子中,生态因子是第一主成分,而对于林窗树种,第一主成分则是生理因子。(4)由于阳性落叶树种具有更高效的光合效率,能迅速占领上层空间,新江湾区域人为低干扰植物群落的演替早期均以扩散能力较强的先锋性树种为主;乔木群落形成后,林下更新苗则以光适应范围较宽的香樟、女贞为主,同时,上层落叶树种大规模自然衰退使得香樟和女贞逐步替代落叶树种。     

黑石顶常绿阔叶林群落冠层树木光合生理特性研究

本文用封闭式的光合作用测定仪测定了黑石顶南亚热带常绿阔叶林群落冠层的两种优势种群──相和光叶红豆的光合速率以及其它生理因子的日变化,同时测定了群落冠层的环境因子──光量子通量密度、气温和相对湿度等的日变化。冠层中ｃｏ＿２浓度的平均值为３０６．６ｍｇ／ｋｇ,日变幅为±６．０ｍｇ／ｋｇ。树种间光合速率差别很大,硬叶相叶片的日平均净光合速率为２．６３７４μｍｏｌ／ｍ￣２·ｓ．日最高净光合作用速率在１１时左右。分析了净光合速率与叶片气孔导度之间的显著相关性,并指出气孔导度的差异可能是引起不同种间净光合速率差异的主要原因之一。     

日光温室不同连作年限对黄瓜生理特性的影响

在日光温室条件下,研究了不同连作年限土壤对黄瓜生理特性的影响。结果表明,不同连作年限土壤对黄瓜光合速率、植株生长特性和产量均有极为显著的影响。在开始种植黄瓜的几年内,黄瓜的光合速率、株高、叶片数和生产力均维持在较高水平;随着连作年限延长,黄瓜的光合速率、株高、叶片数和产量明显降低;连作4a以后,黄瓜的生理障碍开始有明显表现。     

冠层高度对毛竹叶片光合生理特性的影响

借助LI-6400便携式光合作用系统,研究了冠层高度对不同林龄毛竹(Phyllostachys pubescens)叶片光合生理特性和水分利用效率(WUE)的季节性影响,为促进毛竹林碳汇能力和生产力提升的林分结构调整等可持续栽培技术提供理论依据。结果表明:(1)出笋期,不同竹龄毛竹叶片净光合速率(Pn)和蒸腾速率(Tr)的日均值呈现出冠层上部小于冠层下部的梯度变化趋势,且2a生毛竹不同冠层Pn日均值大于3a生毛竹;孕笋行鞭期,不同林龄毛竹各时间点Pn值和日均值、以及2年生毛竹各时间点的Tr值均为冠层上部大于冠层下部。各生长季节,不同林龄毛竹个体叶片的气孔导度(Gs)均与Tr的变化趋势一致。(2)2年生毛竹各季节仅冠层上部叶片会出现"光合午休",而3年生毛竹仅于出笋期时各冠层叶片出现"光合午休"现象。(3)出笋期毛竹叶片WUE日均值随着冠层高度增加而增加,这种变化趋势不受竹龄影响;而孕笋行鞭期,仅2年生毛竹叶片WUE日均值随着冠层高度增加而下降。不同冠层高度的孕笋行鞭期毛竹叶片WUE日均值都显著高于出笋期;冠层高度对毛竹叶片气体交换特性和WUE的影响受生长发育关键期的季节因素影响,且毛竹叶片WUE与Gs之间存在负相关关系,其不受毛竹个体年龄和叶片冠层高度影响。(4)不同生长季节各冠层叶绿素a/b值均随着冠层高度下降而降低,不同林龄毛竹叶片叶绿素含量基本随着冠层自上而下呈逐渐增加的趋势。各生长季节,不同林龄个体叶片氮素含量、比叶重随冠层高度垂直变化趋势与叶片Pn日均值的垂直变化趋势一致。研究认为,毛竹不同冠层部位叶片通过改变形态、氮素含量来适应不同生长季节生长环境的变化,以便充分利用光能提高光合能力。     

基于FvCB模型的叶片光合生理对环境因子的响应研究进展

为提高叶片光合速率并更好地理解叶片光合生理对环境因子变化的响应机制,FvCB模型(C_3植物光合生化模型)常用于分析不同环境条件下CO_2响应曲线并预测叶片活体内光合系统的内在变化状况。系统介绍了FvCB模型的建立、发展过程和拟合方法等基本理论,综述了该模型在叶片光合生理对光、CO_2、水、温度和N营养等环境因子变化的响应机制中的应用研究。为进一步完善FvCB模型并更好地理解叶片活体内光合系统对环境因子变化的响应机制,未来拟加强以下研究:1)羧化速率与光合电子传递速率之间的联系;2)叶肉导度的具体组分及其对FvCB模型参数估计的影响;3)叶片气孔导度和叶肉导度对环境因子变化的调控机制。     

不同水热梯度下冠层优势树种叶片热力性状及适应策略的变化趋势

叶片温度是植物能量交换和生理过程发生的重要微环境参数。叶片热力性状能够在一定程度上调控叶片温度,避免极端温度对叶片的伤害。但目前针对叶片热力性状的研究还很少。该研究选择云南省从热带到温带具有明显水热梯度的4种典型植被类型:干热河谷植被、热带雨林、亚热带常绿阔叶林、温带针阔混交林,对其冠层优势树种的叶片热力性状进行了系统地研究。这些性状包括了可能影响叶片温度的形态、光学、材料特性、解剖和生理的23个性状。研究结果表明:干热河谷植被的植物主要依靠蒸腾降温,叶片薄,叶寿命短,主要为“快速投资-收益”型植物;热带雨林植物叶片大,蒸腾速率不高,不利于降温,较厚的叶片、较高的含水量能在一定程度上缓解高温,采取“慢速投资-收益”策略;亚热带常绿阔叶林很少发生极端温度,叶片没有明显的热适应性状,叶片厚,叶寿命长,采取“慢速投资-收益”策略;温带针阔混交林植被的叶片小而厚,多成簇状生长,有一定保温作用。温带针阔混交林的冠层常绿植物光合速率较低,偏“慢速投资-收益”型;而落叶植物的光合速率较高,偏“快速投资-收益”型。该研究系统地研究了热力性状与植物适应策略沿水热梯度的变化,为深入认识植物对环境适应策略提...     

新疆超高产棉花冠层光分布特征及其与群体光合生产的关系

以新疆超高产棉田(皮棉产量在4000 kg·hm^-2以上)为研究对象,分析不同生育时期棉花冠层光分布、群体光合速率和干物质积累量的变化,研究不同产量水平棉田冠层的光环境变化特征及其与群体光合生产的关系.结果表明： 超高产田盛花期到盛铃后期冠层上、中、下层光吸收率的比例为2∶2∶1,呈均匀分布,群体散射辐射和直射辐射透过系数分别为0.20～0.55和0.22～0.56,处于较适宜范围,中、下层叶片受光良好,冠层各层次叶片群体光合速率差异较小.与高产(3500 kg·hm^-2)和一般高产(3000 kg·hm^-2)棉田相比,超高产田在盛铃前期具有较高的叶面积指数和群体光合速率峰值,在初絮期和盛絮期的叶面积指数下降缓慢,群体光合速率峰值仍保持较高值,非叶绿色器官对产量形成的光合贡献增大,群体干物质积累量较高.在栽培过程中,调节冠层结构,使垂直方向上光辐射和群体光合能力分布均匀是确保棉花高效利用光能、实现超高产的重要途径.     

天童国家森林公园常绿阔叶林不同演替阶段群落光环境特征比较

常绿阔叶林是我国中亚热带东部典型植被类型,根据野外踏查和固定样地调查发现,天童国家森林公园内发育着常绿阔叶林一个完整的演替系列,包含着6个不同演替阶段。应用W inScanopy For C anopy A na lys is软件对研究区内不同演替阶段群落冠层进行分析,得到不同群落冠层和林下的光环境特征指标:PPFD(光合光量子通量密度)和相关的冠层结构形态学指标G ap fraction(空隙度)、LA I(叶面积指数)、M LA(平均叶倾角),通过对这些指标的分析比较,得到的基本规律大致是林冠层的光合有效光量子通量密度随演替逐渐降低,林冠下面的光合有效光量子通量密度随着群落演替的进展变化更为明显。马尾松林的林冠空隙度明显高于其他阶段的群落,总的趋势是随群落演替的进展而降低。叶面积指数随演替的进展而呈增加趋势。平均叶倾角随演替的进展先增大而后减小。这些结果反映了常绿阔叶林不同演替阶段群落由于不同树种树冠形态学结构的差异和微环境的不同,形成了特定群落内的特定光环境。     

落叶阔叶林内的光合作用和气孔传导率特征(英文)

本文根据Wang和BMdocchi(1989)最近提出的冠层辐射模型,进一步给出了一个模拟冠层光合作用速率和气孔传导率的模式.模式将冠层中每一层的叶面积分为向光叶、半影叶、和全遮荫叶三种,并分别计算其光合作用速率和气孔传导率。计算得到的光合速率廓线表明,在落叶阔叶林内,冠层下部的叶片常处于光照不足状态;半影效应使得透过林冠达于底部的辐射量增大,这对于林下植物的光合作用是有利的。 模式计算值与实测值之间的微弱差别应归因于纯辐射模型无法考虑湍流输送机制造成的CO_2传输和冠层底部耐荫性叶对于低光照的适应能力。     

Diverse Optical and Photosynthetic Properties in a Neotropical Dry Forest during the Dry Season: Implications for Remote Estimation of Photosynthesis1

Using optical and photosynthetic assays from a canopy access crane, we examined the photosynthetic performance of tropical dry forest canopies during the dry season in Parque Metropolitano, Panama City, Panama. Photosynthetic gas exchange, chlorophyll fluorescence, and three indices derived from spectral reflectance (the normalized difference vegetation index, the simple ratio, and the photochemical reflectance index) were used as indicators of structural and physiological components of photosynthetic activity. Considerable interspecific variation was evident in structural and physiological behavior in this forest stand, which included varying degrees of foliage loss, altered leaf orientation, stomatal closure, and photosystem II downregulation. The normalized difference vegetation index and the simple ratio were closely related to canopy structure and absorbed radiation for most species, but failed to capture the widely divergent photosynthetic behavior among evergreen species exhibiting various degrees of downregulation. The photochemical reflectance index and chlorophyll fluorescence were related indicators of photosynthetic downregulation, which was not detectable with the normalized difference vegetation index or simple ratio. These results suggest that remote sensing methods that ignore downregulation cannot capture within‐stand variability in actual carbon flux for this diverse forest type. Instead, these findings support a sampling approach that derives photosynthetic fluxes from a consideration of both canopy light absorption (e.g., normalized difference vegetation index) and photosynthetic light‐use efficiency (e.g., photochemical reflectance index). Such sampling should improve our understanding of controls on photosynthetic carbon uptake in diverse tropical forest stands.     

Ecophysiological traits may explain the abundance of climbing plant species across the light gradient in a temperate rainforest

Climbing plants are a key component of rainforests, but mechanistic approaches to their distribution and abundance are scarce. In a southern temperate rainforest, we addressed whether the dominance of climbing plants across light environments is associated with the expression of ecophysiological traits. In mature forest and canopy gaps, we measured leaf size, specific leaf area, photosynthetic rate, and dark respiration in six of the most abundant woody vines. Mean values of traits and their phenotypic change (%) between mature forest and canopy gaps were predictor variables. Leaf size and specific leaf area were not significantly associated with climbing plant dominance. Variation in gas-exchange traits between mature forest and canopy gaps explained, at least partly, the dominance of climbers in this forest. A greater increase in photosynthetic rate and a lower increase in dark respiration rate when canopy openings occur were related to the success of climbing plant species. Dominant climbers showed a strategy of maximizing exploitation of resource availability but minimizing metabolic costs. Results may reflect phenotypic plasticity or genetic differentiation in ecophysiological traits between light environments. It is suggested that the dominant climbers in this temperate rainforest would be able to cope with forest clearings due to human activities.     

Some observations on the spectral distribution characteristics of short-wave radiation within Pinus radiata D. Don canopies

Abstract. Measurements of the photosynthetic photon flux density (400–700 nm) and of the spectral distribution of photon flux density across the 370–800 nm waveband, were made under both clear and overcast sky conditions above and at various positions within two Pinus radiata canopies of different stocking but similar leaf area indices. The spectra obtained for the daylight conditions (i.e. above forest canopy) were generally similar to those published previously. The spectra for shadelight within the forest canopy showed no blue peak which was characteristic of previously reported measurements which were restricted to the diffuse radiation component. There was almost neutral absorption within the 400–700 nm waveband, and typical lower attenuation in the 700–800 nm waveband. The blue: red ratio was largely unchanged by either canopy type or sky conditions and varied between 0.57 and 0.81. The red: far-red ratio in shadelight was between 0.22 and 0.41 under clear sky and between 0.68 and 0.95 under overcast sky conditions. Values for daylight were between 1.16–1.22. Calculated phytochrome photoequilibrium values in shadelight were approximately 0.35 under clear sky and 0.46 under overcast sky conditions. In each case there appeared to be no differences between the two canopies with respect to these minimum values.     

Spatial and temporal variations in the light environment in a primary and selectively logged forest long after logging in Peninsular Malaysia

Key message

We could show long-term effects of logging operation in a Malaysian forest. A forest selectively logged about 50 years ago had a longer sunfleck time and a less heterogeneous light spatially than primary forests.

Abstract

We compared forest light environments between a primary lowland tropical rainforest and a rainforest selectively logged 50 years ago in the Pasoh Forest Reserve, Peninsular Malaysia using two different approaches to assess forest light environments, hemispherical canopy photographs and continuous measurements of forest photosynthetic photon flux density (PPFD) and showed clear evidence of the long-term impact of selective logging on forest light environments. The selectively logged forest canopy consisted of shorter and smaller crowns with less variations of height and crown area than the primary forest. From the canopy structural characteristics of the selectively logged forest, we predicted that the selectively logged forest has brighter and more homogeneous forest light than the primary forest. Both hemispherical canopy photographs and measurements of PPFD showed that the selectively logged forest had more open canopies and longer sunfleck time than the primary forest. A significantly smaller variance of canopy openness and a shorter autocorrelation range in the selectively logged forest than in the primary forest were found, indicating that the selectively logged forest had a less heterogeneous light environment spatially than the primary forest. Therefore our predictions were confirmed. The results suggest that different light environments for the primary forest and forest after logging might promote different forest dynamics between them.     

不同生境刺五加生长发育及光合特性研究

以郁闭度分别为40%、60%和70%的蒙古栎林、针阔混交林和次生杂木林3种生境下野生刺五加种群为材料,考察了其生长发育、光合色素和光合特性的变化,探讨刺五加种群对光照条件的适应机制,寻找有利于刺五加种群生长和更新的适宜天然条件,为人工抚育生境的选择和促进天然次生林更新提供科学依据.结果表明:(1)不同生境下刺五加种群个体株高、基径和生物量均表现为蒙古栎林>针阔混交林>次生杂木林;随着郁闭度的增加,刺五加种群叶构件生物量比率呈现增加的趋势,而茎构件和根茎构件生物量比率则呈现下降的趋势.(2)刺五加种群叶绿素a、叶绿素b、类胡萝卜素含量随着生境郁闭度增加呈逐渐增加趋势,而叶绿素a/b却呈下降趋势.(3)随着郁闭度的增加,刺五加种群的净光合速率、气孔导度、蒸腾速率、水分利用效率、气孔限制值、光饱和点、光补偿点和暗呼吸速率等光合参数均显著降低,而胞间二氧化碳浓度却显著提高.(4)蒙古栎林下刺五加种群具有相对较高的净光合速率和水分利用效率,从而带动种群各构件旺盛生长,使其个体株高、基径、各功能构件生物量均显著高于针阔混交林和次生杂木林种群;光能不足是限制次生杂木林刺五加种群生长的主要因子之一.因此,在抚育刺五加人工林的过程中,应该充分考虑郁闭度对刺五加种群生长发育的影响,同时还要考虑其他植物对刺五加种群生态位的竞争,并以在郁闭度40%的蒙古栎林下抚育为佳.     

Canopy structure and vertical patterns of photosynthesis and related leaf traits in a deciduous forest

Canopy structure and light interception were measured in an 18-m tall, closed canopy deciduous forest of sugar maple (Acer saccharum) in southwestern Wisconsin, USA, and related to leaf structural characteristics, N content, and leaf photosynthetic capacity. Light attenuation in the forest occurred primarily in the upper and middle portions of the canopy. Forest stand leaf area index (LAI) and its distribution with respect to canopy height were estimated from canopy transmittance values independently verified with a combined leaf litterfall and point-intersect method. Leaf mass, N and A _max per unit area (LMA, N/area and A _max/area, respectively) all decreased continuously by over two-fold from the upper to lower canopy, and these traits were strongly correlated with cumulative leaf area above the leaf position in the canopy. In contrast, neither N concentration nor A _max per unit mass varied significantly in relation to the vertical canopy gradient. Since leaf N concentration showed no consistent pattern with respect to canopy position, the observed vertical pattern in N/area is a direct consequence of vertical variation of LMA. N/area and LMA were strongly correlated with A _max/area among different canopy positions (r²=0.81 and r²=0.66, respectively), indicating that vertical variation in area-based photosynthetic capacity can also be attributed to variation in LMA. A model of whole-canopy photosynthesis was used to show that observed or hypothetical canopy mass distributions toward higher LMA (and hence higher N/area) in the upper portions of the canopy tended to increase integrated daily canopy photosynthesis over other LMA distribution patterns. Empirical relationships between leaf and canopy-level characteristics may help resolve problems associated with scaling gas exchange measurements made at the leaf level to the individual tree crown and forest canopy-level.     

Assessing the use of camera-based indices for characterizing canopy phenology in relation to gross primary production in a deciduous broad-leaved and an evergreen coniferous forest in Japan

Recent studies have reported that seasonal variation in camera-based indices that are calculated from the digital numbers of the red, green, and blue bands (RGB_DN) recorded by digital cameras agrees well with the seasonal change in gross primary production (GPP) observed by tower flux measurements. These findings suggest that it may be possible to use camera-based indices to estimate the temporal and spatial distributions of photosynthetic productivity from the relationship between RGB_DN and GPP. To examine this possibility, we need to investigate the characteristics of seasonal variation in three camera-based indices (green excess index [GE], green chromatic coordinate [rG], and HUE) and the robustness of the relationship between these indices and tower flux-based GPP and how it differs among ecosystems. Here, at a daily time step over multiple years in a deciduous broad-leaved and an evergreen coniferous forest, we examined the relationships between canopy phenology assessed by using the three indices and GPP determined from tower CO₂ flux observations, and we compared the camera-based indices with the corresponding spectra-based indices estimated by a spectroradiometer system. We found that (1) the three camera-based indices and GPP showed clear seasonal patterns in both forests; (2) the amplitude of the seasonal variation in the three camera-based indices was smaller in the evergreen coniferous forest than in the deciduous broad-leaved forest; (3) the seasonal variation in the three camera-based indices corresponded well to seasonal changes in potential photosynthetic activity (GPP on sunny days); (4) the relationship between the three camera-based indices and GPP appeared to have different characteristics at different phenological stages; and (5) the camera-based and spectra-based HUE indices showed a clear relationship under sunny conditions in both forests. Our results suggest that it might be feasible for ecologists to establish comprehensive networks for long-term monitoring of potential photosynthetic capacity from regional to global scales by linking satellite-based, in situ spectra-based, and in situ camera-based indices.