叶肉导度的组成、大小及其对环境因素的响应

植物光合作用过程中,大气中的CO2需要克服气孔和叶肉细胞等阻力传输到羧化位点。CO2从气孔下腔传输到羧化位点的阻力称为叶肉阻力,其倒数即为叶肉导度。近十年内,叶肉导度已经成为光合作用研究领域的一个重要方面。本文首先系统地阐述了叶肉导度的组成及各部分所占的比重;然后通过与气孔导度的比较,分析叶肉导度的大小及其对光合作用的影响;最后阐述了叶肉导度对环境变化的响应,并分析了其中可能的原因。     

海拔梯度对巴郎山奇花柳叶片δ13C的影响

2010年在四川卧龙自然保护区选择海拔为2350、2700、3150和3530 m的4个分布地点,研究了巴郎山海拔梯度对奇花柳叶片13C、光合、CO2扩散导度、氮含量、光合氮利用效率( PNUE)和比叶面积(SLA)的影响.结果表明:随着海拔的升高,目标树种叶片氮含量(尤其是单位面积氮含量)及PNUE增加,叶片δ13C值也随之显著增加,且海拔每升高1000 m,δ13C增加1.4‰;CO2扩散导度(气孔导度和叶肉细胞导度)的增加,在一定程度上阻碍了叶片δ13C值随海拔升高,但不足以改变δ13C值随海拔升高的趋势;羧化能力是羧化位点与外界CO2分压比( Pc/Pa),甚至δ13C的限制因子.在海拔2350～2700m,奇花柳光合系统内部氮素分配主要受温度的影响,而2700～3530 m的光照作用可能更大.奇花柳的SLA随海拔无显著变化.     

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。     

植物气孔导度的环境响应模拟及其尺度扩展

气孔导度是衡量植物和大气间水分、能量及CO2平衡和循环的重要指标,探讨气孔导度与环境因子的关系及其模拟,以及气孔导度在叶片、冠层及区域尺度间的尺度转换及累积效应,对更好地认识植被与大气间的水热运移过程,合理评价植被在陆面过程中的地位和作用都具有重要意义。从植物气孔导度与环境因子的关系、气孔导度模拟以及尺度扩展三个方面,对前人的研究成果进行了概括总结。从叶片和冠层两个尺度出发,归纳总结了前人对于不同植物气孔导度与环境因子关系的研究成果,发现由于不同植物的遗传特性、测定时的环境、时间尺度的不同,以及未考虑各个环境因子的相互作用对气孔导度的影响,由此得到的气孔导度与环境因子之间的关系也不尽一致。对各单一环境因子与气孔导度的关系,给出了生理学解释,从根本上说明了环境因子变化对气孔导度的影响,而研究环境因子对气孔导度的综合影响时,应对各环境因子进行系统控制与同步观测。模拟计算植物气孔导度的模型主要有Jarvis模型和BWB模型两类,这些模型的模拟能力随着研究对象、试验区域、环境条件的改变而存在一定的差异,在具体使用时应结合实际情况选择最优模型进行模拟。除上述常用模型外,还总结了其他学者分别从不同角度提出的新的模型,对现有气孔导度模型进行了全面的总结。从叶片-冠层、冠层-区域两个方面归纳总结了前人关于气孔导度尺度扩展的研究成果,发现叶片-冠层的尺度扩展研究较成熟而冠层-区域的尺度扩展在模拟精度的验证方面存在困难。针对以下几个方面提出了今后气孔导度的研究重点:(1)结合研究对象所在的区域及环境条件,选择最优模型进行模拟;(2)综合考虑环境因子之间的相互作用及其对气孔导度的累积影响;(3)BWB模型与光合模型的耦合;(4)提高大尺度范围内的气孔导度模拟精度。     

巴郎山异型柳叶片功能性状及性状间关系对海拔的响应

在卧龙自然保护区,按海拔梯度选择了4个异型柳分布地点(2350 m、2700 m、3150 m和3530 m),对各研究地点异型柳进行了叶片光合、CO2扩散导度(气孔导度(gs)和叶肉细胞导度(gm))、δ13C、氮素以及比叶面积(SLA)等参数的测量,以期揭示该植物叶片功能性状及功能性状间关系的海拔响应情况.结果表明:随着海拔的升高,大气温度和压强的降低,异型柳的叶片单位面积氮含量(Narea)、最大羧化速率(Vcmax)和最大净光合速率(Amax)均随之增加,这可能是该落叶灌木对于生长季节缩短的一种响应;同时,植物的光合氮利用效率(PNUE)和SLA却均随海拔降低,原因可能在于随着海拔的升高,植物将越来越多的氮素用于细胞壁等非光合组织的构建,这是高海拔植物对于外界恶劣环境的一种适应;最后,扩散导度和羧化能力是植物叶片δ13C的主要影响因子,而羧化能力较扩散导度对于异型柳叶片δ13C的作用更大些,进而导致该值呈现随海拔升高的趋势.氮素在光合与非光合系统间的分配是巴郎山异型柳适应不同海拔生境的关键.     

红树林植物叶片形态和解剖特征对叶肉导度、叶片导水率的影响

叶肉导度和叶片导水率是影响光合作用的两个重要过程,叶肉导度通过影响从气孔下腔到Rubisco酶位点的二氧化碳浓度梯度直接影响光合作用,而叶片导水率则通过影响水分供应或气孔行为来影响光合作用,然而对这两个生理过程之间的协同性研究较少。本研究选择9种红树林植物为研究对象,探讨盐生环境下植物叶肉导度和叶片导水率的协同性及其与叶片解剖结构特征之间的相关性。结果表明,9种红树林植物叶片导水率(0.78~5.83 mmol·m~(-2)·s~(-1)·MPa-1)、叶肉导度(0.06~0.36 mol·m~(-2)·s~(-1))、最大光合速率(7.23~23.71μmol·m~(-2)·s~(-1))等特征的差别较大;叶肉导度与最大光合速率呈显著正相关,而与比叶重无显著相关性,其原因是由于比叶重与叶片厚度、叶片密度不存在相关性;叶脉密度与气孔密度呈较强的相关性,说明红树林植物叶片水分运输与散失相关的叶片结构之间存在协同关系;叶片导水率不受叶脉密度影响,并且与叶肉导度、最大光合速率也不存在相关性,这很可能与红树林植物叶片的肉质化、有发达的储水组织有关,体现了红树林植物叶片结构和功能的特殊性。     

土壤干旱条件下不同施钾水平对烟草光合速率和蒸腾效率的影响

研究了土壤干旱条件下,不同的施钾水平对烟草光合速率,胞间CO2浓度,气孔导度,蒸腾速率,蒸腾效率及生物量的影响。结果表明：在土壤干旱条件下适量施钾可以减少叶肉细胞光合活性的下降,消弱非气孔因素对光合的限制,增强气孔调节能力,提高蒸腾效率,并获得较高的生物量。     

δ13C在植物生态学研究中的应用

稳定碳同位素技术已成为研究植物与环境之间关系最有效的方法之一。由于植物羧化效率的不同、12 C和13 C在植物体内迁移速率以及外界环境的不同,不同植物体内稳定性碳同位素比率(δ13 C值)有一定的差异。该文概述了稳定碳同位素的基本理论,并从气孔导度、叶肉细胞导度、叶片羧化效率分析了δ13 C变化的生物学机理;对近年来国内外有关不同环境因子对植物δ13 C值的影响、δ13 C值在群落及生态系统水平(以功能群、群落冠层及树轮为重点)、以及δ13 C值在碳循环中的应用研究进展进行综述,为以后稳定碳同位素研究提供参考。     

植被-大气相互作用中的气孔导度及其尺度转换

气孔导度是衡量植物和大气间水分、能量及CO2平衡和循环的重要指标,探讨气孔导度在叶片、冠层及区域尺度间的尺度转换及累积效应,对更好地认识植被与大气间的水热运移过程,合理评价植被在陆面过程中的地位和作用具有重要意义.本文着重从叶片尺度气孔导度模拟、气孔导度在冠层尺度的累积表现、冠层到区域尺度转换研究及气孔导度累积效应在陆面过程模型中的作用等4个层次总结了近期国内外研究状况,指出其中存在的异质性等问题,并就今后应加强多尺度间的同步观测提出了展望.     

气孔导度对CO_2浓度变化的模拟及其生理机制

基于气孔运动的生理生化机制重点进行了气孔导度(gs)对CO2浓度变化的响应机制分析,并推导得到气孔导度(gs)对CO2浓度变化响应模型,并以9种植物进行了模型验证。结果表明:随着CO2浓度的升高,气孔导度会逐渐降低,且下降的幅度会随着CO2浓度的升高而逐渐减弱。气孔导度对CO2浓度(Cs)变化的响应模型可以表达为gs=gmax/(1+Cs/Cs0),其中式中gmax是最大气孔导度和Cs0是实验常数。该模型较好地模拟了气孔导度随CO2浓度变化的规律,模型参数具有明确的生理意义,与Jarvis模型和Ball-Berry模型相比,该模型如何实现多种环境因子的耦合有待进一步突破。另外,模型是在短期改变叶片CO2浓度的条件下得出的,在CO2浓度长期胁迫下的适用性也有待进一步确认。     

On measuring the response of mesophyll conductance to carbon dioxide with the variable J method

The response of mesophyll conductance to CO(2) (g(m)) to environmental variation is a challenging parameter to measure with current methods. The 'variable J' technique, used in the majority of studies of g(m), assumes a one-to-one relationship between photosystem II (PSII) fluorescence and photosynthesis under non-photorespiratory conditions. When calibrating this relationship for Populus trichocarpa, it was found that calibration relationships produced using variation in light and CO(2) were not equivalent, and in all cases the relationships were non-linear-something not accounted for in previous studies. Detailed analyses were performed of whether different calibration procedures affect the observed g(m) response to CO(2). Past linear and assumed calibration methods resulted in systematic biases in the fluorescence estimates of electron transport. A sensitivity analysis on modelled data (where g(m) was held constant) demonstrated that biases in the estimation of electron transport as small as 2% (～0.5 μmol m(-2) s(-1)) resulted in apparent changes in the relationship of g(m) to CO(2) of similar shape and magnitude to those observed with past calibration techniques. This sensitivity to biases introduced during calibrations leads to results where g(m) artefactually decreases with CO(2), assuming that g(m) is constant; if g(m) responds to CO(2), then biases associated with past calibration methods would lead to overestimates of the slope of the relationship. Non-linear calibrations were evaluated; these removed the bias present in past calibrations, but the method remained sensitive to measurement errors. Thus measurement errors, calibration non-linearities leading to bias, and the sensitivity of variable J g(m) hinders its use under conditions of varying CO(2) or light.     

Relationships between leaf conductance to CO2 diffusion and photosynthesis in micropropagated grapevine plants, before and after ex vitro acclimatization

In vitro-cultured plants typically show a low photosynthetic activity, which is considered detrimental to subsequent ex vitro acclimatization. Studies conducted so far have approached this problem by analysing the biochemical and photochemical aspects of photosynthesis, while very little attention has been paid to the role of leaf conductance to CO(2) diffusion, which often represents an important constraint to CO(2) assimilation in naturally grown plants. Mesophyll conductance, in particular, has never been determined in in vitro plants, and no information exists as to whether it represents a limitation to carbon assimilation during in vitro growth and subsequent ex vitro acclimatization. In this study, by means of simultaneous gas exchange and chlorophyll fluorescence measurements, the stomatal and mesophyll conductance to CO(2) diffusion were assessed in in vitro-cultured plants of the grapevine rootstock '41B' (Vitis vinifera 'Chasselas'xVitis berlandieri), prior to and after ex vitro acclimatization. Their impact on electron transport rate partitioning and on limitation of potential net assimilation rate was analysed. In vitro plants had a high stomatal conductance, 155 versus 50 mmol m(-2) s(-1) in acclimatized plants, which ensured a higher CO(2) concentration in the chloroplasts, and a 7% higher electron flow to the carbon reduction pathway. The high stomatal conductance was counterbalanced by a low mesophyll conductance, 43 versus 285 mmol m(-2) s(-1), which accounted for a 14.5% estimated relative limitation to photosynthesis against 2.1% estimated in acclimatized plants. It was concluded that mesophyll conductance represents an important limitation for in vitro plant photosynthesis, and that in acclimatization studies the correct comparison of photosynthetic activity between in vitro and acclimatized plants must take into account the contribution of both stomatal and mesophyll conductance.     

Measurements of mesophyll conductance,photosynthetic electron transport and alternative electron sinks of field grown wheat leaves

Photosynthetic electron transport drives the carbon reduction cycle, the carbon oxidation cycle, and any alternative electron sinks such as nitrogen reduction. A chlorophyll fluorescence— based method allows estimation of the total electron transport rate while a gas-exchange-based method can provide estimates of the electron transport needed for the carbon reduction cycle and, if the CO₂ partial pressure inside the chloroplast is accurately known, for the carbon oxidation cycle. The gas-exchange method cannot provide estimates of alternative electron sinks. Photosynthetic electron transport in flag leaves of wheat was estimated by the fluorescence method and gasexchange method to determine the possible magnitude of alternative electron sinks. Under non-photorespiratory conditions the two measures of electron transport were the same, ruling out substantial alternative electron sinks. Under photorespiratory conditions the fluorescence-based electron transport rate could be accounted for by the carbon reduction and carbon oxidation cycle only if we assumed the CO₂ partial pressure inside the chloroplasts to be lower than that in the intercellular spaces of the leaves. To further test for the presence of alternative electron sinks, carbon metabolism was inhibited by feeding glyceraldehyde. As carbon metabolism was inhibited, the electron transport was inhibited to the same degree. A small residual rate of electron transport was measured when carbon metabolism was completely inhibited which we take to be the maximum capacity of alternative electron sinks. Since the alternative sinks were small enough to ignore, the comparison of fluorescence and gas-exchange based methods for measuring the rate of electron transport could be used to estimate the mesophyll conductance to CO₂ diffusion. The mesophyll conductance estimated this way fell as wheat flag leaves senesced. The age-related decline in photosynthesis may be attributed in part to the reduction of mesophyll conductance to CO₂ diffusion and in part to the estimated decline of ribulose 1,5-bisphosphate carboxylase amount.     

The contribution of photosynthesis to the red light response of stomatal conductance

To determine the contribution of photosynthesis on stomatal conductance, we contrasted the stomatal red light response of wild-type tobacco (Nicotiana tabacum 'W38') with that of plants impaired in photosynthesis by antisense reductions in the content of either cytochrome b(6)f complex (anti-b/f plants) or Rubisco (anti-SSU plants). Both transgenic genotypes showed a lowered content of the antisense target proteins in guard cells as well as in the mesophyll. In the anti-b/f plants, CO(2) assimilation rates were proportional to leaf cytochrome b(6)f content, but there was little effect on stomatal conductance and the rate of stomatal opening. To compare the relationship between photosynthesis and stomatal conductance, wild-type plants and anti-SSU plants were grown at 30 and 300 micromol photon m(-2) s(-1) irradiance (low light and medium light [ML], respectively). Growth in ML increased CO(2) assimilation rates and stomatal conductance in both genotypes. Despite the significantly lower CO(2) assimilation rate in the anti-SSU plants, the differences in stomatal conductance between the genotypes were nonsignificant at either growth irradiance. Irrespective of plant genotype, stomatal density in the two leaf surfaces was 2-fold higher in ML-grown plants than in low-light-grown plants and conductance normalized to stomatal density was unaffected by growth irradiance. We conclude that the red light response of stomatal conductance is independent of the concurrent photosynthetic rate of the guard cells or of that of the underlying mesophyll. Furthermore, we suggest that the correlation of photosynthetic capacity and stomatal conductance observed under different light environments is caused by signals largely independent of photosynthesis.     

Stomatal conductance does not correlate with photosynthetic capacity in transgenic tobacco with reduced amounts of Rubisco

High-resolution imaging of chlorophyll a fluorescence from intact tobacco leaves was used to compare the quantum yield of PSII electron transport in the chloroplasts of guard cells with that in the underlying mesophyll cells. Transgenic tobacco plants with reduced amounts of Rubisco (anti-Rubisco plants) were compared with wild-type tobacco plants. The quantum yield of PSII in both guard cells and underlying mesophyll cells was less in anti-Rubisco plants than in wild-type plants, but closely matched between the two cell types regardless of genotype. CO2 assimilation rates of anti-Rubisco plants were 4.4 micromol m(-2) s(-1) compared with 17.3 micromol m(-2) s(-1) for the wild type, when measured at a photon irradiance of 1000 micromol m(-2) s(-1) and ambient CO2 of 380 micromol mol(-1). Despite the large difference in photosynthetic capacity between the anti-Rubisco and wild-type plants, there was no discernible difference in the rate of stomatal opening, steady-state stomatal conductance or response of stomatal conductance to ambient CO2 concentration. These data demonstrate clearly that the commonly observed correlation between photosynthetic capacity and stomatal conductance can be disrupted in the long term by manipulation of photosynthetic capacity via antisense RNA technology. It was concluded that stomatal conductance is not directly determined by the photosynthetic capacity of guard cells or the leaf mesophyll.     

Mesophyll conductance to CO2: current knowledge and future prospects

During photosynthesis, CO2 moves from the atmosphere (C(a)) surrounding the leaf to the sub-stomatal internal cavities (C(i)) through stomata, and from there to the site of carboxylation inside the chloroplast stroma (C(c)) through the leaf mesophyll. The latter CO2 diffusion component is called mesophyll conductance (g(m)), and can be divided in at least three components, that is, conductance through intercellular air spaces (g(ias)), through cell wall (g(w)) and through the liquid phase inside cells (g(liq)). A large body of evidence has accumulated in the past two decades indicating that g(m) is sufficiently small as to significantly decrease C(c) relative to C(i), therefore limiting photosynthesis. Moreover, g(m) is not constant, and it changes among species and in response to environmental factors. In addition, there is now evidence that g(liq) and, in some cases, g(w), are the main determinants of g(m). Mesophyll conductance is very dynamic, changing in response to environmental variables as rapid or even faster than stomatal conductance (i.e. within seconds to minutes). A revision of current knowledge on g(m) is presented. Firstly, a historical perspective is given, highlighting the founding works and methods, followed by a re-examination of the range of variation of g(m) among plant species and functional groups, and a revision of the responses of g(m) to different external (biotic and abiotic) and internal (developmental, structural and metabolic) factors. The possible physiological bases for g(m), including aquaporins and carbonic anhydrases, are discussed. Possible ecological implications for variable g(m) are indicated, and the errors induced by neglecting g(m) when interpreting photosynthesis and carbon isotope discrimination models are highlighted. Finally, a series of research priorities for the near future are proposed.     

Ternary effects on the gas exchange of isotopologues of carbon dioxide

The ternary effects of transpiration rate on the rate of assimilation of carbon dioxide through stomata, and on the calculation of the intercellular concentration of carbon dioxide, are now included in standard gas exchange studies. However, the equations for carbon isotope discrimination and for the exchange of oxygen isotopologues of carbon dioxide ignore ternary effects. Here we introduce equations to take them into account. The ternary effect is greatest when the leaf-to-air vapour mole fraction difference is greatest, and its impact is greatest on parameters derived by difference, such as the mesophyll resistance to CO(2) assimilation, r(m) . We show that the mesophyll resistance to CO(2) assimilation has been underestimated in the past. The impact is also large when there is a large difference in isotopic composition between the CO(2) inside the leaf and that in the air. We show that this partially reconciles estimates of the oxygen isotopic composition of CO(2) in the chloroplast and mitochondria in the light and in the dark, with values close to equilibrium with the estimated oxygen isotopic composition of water at the sites of evaporation within the leaf.     

不同水肥条件对春玉米光合运转关系的影响及其产量效应的研究

以两种土壤水分和４种土壤肥力水平对春玉米光合运转关系的影响及其产量效应进行了较深入的探讨。在土壤水分适宜条件下,不同土壤肥力春玉米叶片光合速率随肥力水平的提高而增加的主要原因是气孔因素的限制,光合速率与籽粒产量呈现极显著正相关关系。     

CO_2 倍增对长白赤松幼苗根 土界面水分运输过程的影响(英文)

用具有非破坏性的电导率方法测定土壤水分的廓线 ,与挖掘法 (或打孔法 )获取的根系分布对比 ,研究CO2倍增条件下一年生的长白赤松 (PinussylvestrisLinn .var.sylvestriformis (Takenouchi)ChengetC .D .Chu)幼苗根 土界面的水分运输状态。结果表明 :(1)土壤水分廓线由植物的活性所调制 ,根系分布密集的土层其水分含量也高。(2 )CO2 倍增 ,根系 土壤水分运输的活跃层及根系分布都将向土壤深处位移。研究证明 ,电导率方法能够指示发生于根 土界面上的水分运输状态 ,方法简单 ,且对土壤无破坏