三种经验模型模拟荒漠河岸柽柳叶片气孔导度

植物叶片气孔是控制水分和CO_2出入的通道,是植物水分蒸腾和气体交换的门户。植物叶片气孔导度地准确模拟,对于植物蒸腾作用地有效模拟以及植物与大气间能量和质量平衡的研究至关重要。基于黑河下游阿拉善群落水热平衡综合观测场实际观测数据,采用LI-COR 6400光合作用测定系统,对荒漠河岸柽柳叶片气孔导度进行观测,分析晴朗天气条件下气孔导度日变化特征,同时,结合微气象及植物生理相关数据,运用学术界3种最常用的(半)经验模型对柽柳叶片气孔导度进行模拟,结果表明:(1)柽柳叶片气孔导度日变化大致呈先升高后降低的趋势。上午随着太阳辐射逐渐增强,气温逐渐升高,气孔导度值逐渐升高,蒸腾速率也逐渐增大,在10:00—12:00时间段内达到最大值。绝大部分观测日内12:00前后气孔导度呈现出一定的波动,原因在于温度过高致使叶片气孔关闭。随后,太阳辐射减弱,气温逐渐降低,空气中相对湿度增加,柽柳叶片内外水汽压差减小,气孔导度减小导致蒸腾速率下降。(2)通过3种最常用的(半)经验模型(Jarvis、Ball-Woodrow-Berry(BWB)和Ball-Berry-Leuning(BBL))模拟气孔导度的结果可以看出,Jarvis模型的修正效率系数(0.775、0.891)、修正一致系数(0.887、0.945)和决定系数(0.590、0.645)在3个模型中均是最高或次最高的,说明其模拟精度最高。(3)BWB模型与BBL模型的模拟精度相近,说明水汽压差、大气湿度与气孔导度的密切程度相近,没有明显的区别。     

冬小麦叶片气孔导度模型水分响应函数的参数化

植物气孔导度模型的水分响应函数用来模拟水分胁迫对气孔导度的影响过程, 是模拟缺水环境下植物与大气间水、碳交换过程的关键算法。水分响应函数包括空气湿度响应函数和土壤湿度(或植物水势)响应函数, 该研究基于田间实验观测, 分析了冬小麦(Triticum aestivum)叶片气孔导度对不同空气饱和差和不同土壤体积含水量或叶水势的响应规律。一个土壤水分梯度的田间处理在中国科学院禹城综合试验站实施, 不同水分胁迫下的冬小麦叶片气体交换过程和气孔导度以及其他的温湿度数据被观测, 同时观测了土壤含水量和叶水势。实验数据表明, 冬小麦叶片气孔导度对空气饱和差的响应呈现双曲线规律, 变化趋势显示大约1 kPa空气饱和差是一个有用的阈值, 在小于1 kPa时, 冬小麦气孔导度对空气饱和差变化反应敏感, 而大于1 kPa后则反应缓慢; 分析土壤体积含水量与中午叶片气孔导度的关系发现, 中午叶片气孔导度随土壤含水量增加大致呈现线性增加趋势, 但在平均土壤体积含水量大于大约25%以后, 气孔导度不再明显增加, 而是维持在较高导度值上下波动; 冬小麦中午叶片水势与相应的气孔导度之间, 随着叶水势的增加, 气孔导度呈现增加趋势。根据冬小麦气孔导度对空气湿度、土壤湿度和叶水势的响应规律, 研究分别采用双曲线和幂指数形式拟合了水汽响应函数, 用三段线性方程拟合了土壤湿度响应函数和植物水势响应函数, 得到的参数可以为模型模拟冬小麦的各类水、热、碳交换过程采用。     

气孔导度模型在北方农牧交错带的适用性评价——以马铃薯和油葵为例

基于北方农牧交错带主要作物马铃薯和油葵的叶片气孔导度、净光合速率和气象因子的平行观测数据,对常用气孔导度模型(Jarvis模型、Ball-Berry模型、Leuning模型和Medlyn模型)进行了适用性评价.结果表明:马铃薯的气孔导度与净光合速率呈现较强的线性关系,而油葵气孔导度与净光合速率的线性关系较弱.对于马铃薯气孔导度,Ball-Berry模型模拟效果最佳,Leuning模型和Medlyn模型次之,Jarvis模型模拟效果最差;各模型的模拟值与观测值的均方根误差(RMSE)分别为0.0331、0.0371、0.0456和0.0794 mol·m^-2·s^-1,归一化均方根误差(NRMSE)分别为26.8%、30.0%、36.9%和64.3%,拟合度(R²)分别为0.96、0.61、0.91和0.88.对于油葵的气孔导度,Jarvis模型模拟效果略好于Ball-Berry模型、Medlyn模型和Leuning模型,其RMSE分别为0.2221、0.2534、0.2547和0.2758 mol·m^-2·s^-1,NRMSE分别为40.3%、46.0%、46.2%和50.1%,R²分别为0.38、0.22、0.23和0.20.气象因子对气孔导度作用的通径分析表明,北方农牧交错带马铃薯和油葵气孔导度日变化主要受饱和水汽压差影响.模型评价结果表明用于油葵的气孔导度模型需要进一步改进.     

春玉米持续干旱过程中常用气孔导度模型的比较研究

气候变化背景下,干旱频发导致的土壤水分变化将影响气孔导度模型的适用性,进而影响生态系统碳-氮-水循环模拟的准确性。基于春玉米持续干旱田间模拟试验资料,比较了常用气孔导度模型在干旱条件下的模拟效果,评价了土壤水分响应函数对气孔导度模型效果的影响,并探讨了气孔导度模型的适用土壤水分范围。结果表明,在持续干旱过程中,模型模拟效果表现为BBL模型最优,其次是USO模型和BWB模型,Jarvis模型最差;引入土壤水分响应函数,提高了BWB模型和USO模型的模拟效果,而降低了Jarvis模型和BBL模型模拟效果,模型模拟效果表现为USO修正模型最优,其次是BBL修正模型和BWB修正模型,Jarvis修正模型最差。在持续干旱过程中,Jarvis模型和BWB模型的剩余气孔导度较大,而BBL模型和USO模型的剩余气孔导度相对较小,表明BBL模型和USO模型在干旱条件下具有一定的稳定性。基于95%置信区间判断表明:Jarvis模型、BBL模型和USO模型在土壤相对湿度范围为33%—83%条件下适用,而BWB模型的适用土壤相对湿度范围为33%—76%,引入水分响应函数后可在试验条件下适用。研究结果可为干旱条件下选取合适的气孔导度模型以准确模拟陆地生态系统碳循环和水循环提供依据,并为改善农业水资源的有效使用和评估提供支撑。     

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。     

植物气孔导度的机理模型

Ball-Berry气孔导度模型及其修正模型是评价植物叶片气孔调节的重要工具。该文从CO₂分子在叶片气孔中扩散这个最基本的物理过程出发, 应用物理学中的分子扩散和碰撞理论、流体力学与植物生理学等知识, 严格推导出叶片气孔导度的机理模型。利用美国Li-Cor公司生产的Li-6400光合作用测定仪控制CO₂浓度、湿度和温度, 测量了华北平原冬小麦(Triticum aestivum)的光响应数据和气孔导度数据。拟合结果表明: 推导的气孔导度机理模型较之Ball-Berry气孔导度模型和Tuzet等气孔导度模型, 能更好地描述冬小麦的气孔导度与净光合速率之间的关系。如果用气孔导度的机理模型耦合光合作用对光响应的修正模型, 则耦合模型可以很好地描述华北平原冬小麦叶片气孔导度对光强的响应曲线, 并可直接估算冬小麦的最大气孔导度和对应的饱和光强, 同时可以研究最大气孔导度是否与最大净光合速率同步的问题。拟合结果还表明: 冬小麦在30 ℃、560 μmol·mol^-1CO₂, 或在32 ℃、370 μmol·mol^-1CO₂条件下, 最大气孔导度与最大净光合速率并不同步。     

额济纳荒漠河岸胡杨林叶片气孔导度与微环境因子关系的模拟研究

以额济纳荒漠河岸胡杨(Populus euphratica)为研究对象,利用LI-6400光合测定仪于2005年5~9月份观测了胡杨叶片气体交换数据,研究了胡杨叶片气孔导度与光合速率、光合有效辐射与光合速率之间的关系.结果表明:(1)胡杨叶片净光合速率随气孔导度的增大而升高,但当气孔导度增加到一定值后,光合速率的增加变缓慢直至平稳,并主要是非气孔限制因素造成的;Ball-Berry模型(B-B模型)能够很好地描述气孔导度与光合速率之间的关系(R2=0.92).(2)叶片净光合速率随着有效辐射的变化符合非直角双曲线规律(R2=0.99).(3)B-B模型和非直角双曲线光合模型耦合后模拟值与观测值之间存在很好的正相关性(r=0.93),但耦合模型的模拟值还是较实测值偏大.因此,在干旱区还必须考虑水分限制因素对气孔开闭的控制作用,进一步构建适合干旱区生态系统特点的水-碳耦合循环机理模型.     

光合作用—蒸腾作用—气孔导度的耦合模型及C3植物叶片对环境因子的生理 …

以叶片的气体传输过程为基础,将蒸腾作用包括在以往光合作用－气孔导度的耦合模型中,建立了光合作用－蒸腾作用－气孔导度的耦合模型。该模型可以模拟边界层导度对生理过程的影响。模拟了Ｃ３植物叶片对环境因子,如光照、温度、湿度、边界层导度和ＣＯ２浓度等的生理响应（光合作用、蒸腾作用、气孔导度）以及Ｃｉ和水分利用效率的变化。在环境因子变化于较大范围的情况下,模拟结果符合许多实验结论。     

光合作用-蒸腾作用-气孔导度的耦合模型及C_3植物叶片对环境因子的生理响应(英文)

以叶片的气体传输过程为基础,将蒸腾作用包括在以往光合作用气孔导度的耦合模型中,建立了光合作用蒸腾作用气孔导度的耦合模型。该模型可以模拟边界层导度对生理过程的影响。模拟了Ｃ３植物叶片对环境因子,如光照、温度、湿度、边界层导度和ＣＯ２浓度等的生理响应（光合作用、蒸腾作用、气孔导度）以及Ｃｉ和水分利用效率的变化。在环境因子变化于较大范围的情况下,模拟结果符合许多实验结论。     

红树林生境中互花米草气孔导度的动态变化

以生长在山口红树林保护区内壤质海滩上的互花米草(Spartina alterniflora)为对象,对午间退潮到天黑这一特定时间段其叶片气孔导度及相应环境因子的变化进行了测定和分析.结果表明:互花米草不同叶位的叶片气孔导度不同,在垂直方向上,其排序大致呈现中上部>顶部>中下部>下部的趋势;叶片气孔导度与光强、叶温呈幂函数关系,与时间、相对湿度呈负指数函数关系;在相对湿度为50%～60%时,气孔导度最大,随着湿度的增加,气孔有关闭的趋势,气孔导度变小;互花米草植株中部的叶片对整个植株光合产物积累的贡献较大.各种环境因子对互花米草气孔的开闭存在交互作用,因此,互花米草叶片的气孔导度是对环境因子的综合反应.     

Stomatal Responses of Tradescantia albiflora to Changing Air Humidity in Light and in Darkness

Tradescantia albiflora has green variegated and white leaves.Its stomatal apparatus consists of the guard cells and two pairsof subsidiary cells. Investigations were carried out by observingthe stomata microscopically by means of a video system in situin a CO₂ exchange chamber and by simultaneously measuring thegas exchange of the leaves. In response to air humidity changes,stomatal movements in T. albiflora begin, owing to turgor changes,in the polar and lateral subsidiary cells. The stomatal responseof green leaves to changes of air humidity showed typical transientand oscillatory phases prior to steady-state reactions. In darkness,stomata closed when air humidity decreased; however, they didnot reopen when air humidity was raised again. Stomata of illuminatedwhite leaves responded like those of green leaves in darkness.With increasing soil water stress stomata responded to changingair humidity with reductions of the transient phases and a decreasingtendency to reopen when air humidity became high again. CO₂deficiency of the air caused the stomata to open in the dark,and interacted with the air humidity effect in such a way thatstomata of green leaves responded to air humidity changes indarkness in a similar way as they did in light. Key words: Stomata, humidity response, green and white leaf areas, CO₂ deficient air     

Is stomatal conductance in a tomato crop controlled by soil or atmosphere?

Summary The effects of soil water deficits and air vapour pressure deficits on stomatal conductance of tomato leaves were analysed separately under field conditions in central Portugal. Three conditions were created: low soil and air humidity (A), high soil and air humidity (B) and low soil but high air humidity (C). The results show that the effect of air vapour pressure deficit on stomatal behaviour is more important than the effect of soil water deficit when the predawn leaf water potential is above –0.4 MPa.     

Rapid stomatal responses to humidity

The response of leaf conductance in apple to rapid changes in atmospheric humidity was studied using a continuous flow porometer. Leaf-air vapour pressure difference was changed by adjusting the humidity of the inlet air or by altering the flow rate of the air through the chamber. The time course of the response of leaf conductance to leaf-air vapour pressure difference was monitored for periods up to 10 min using a chart-recorder. There were significant changes in leaf conductance within seconds of changing humidity. These were attributed to alterations in stomatal aperture.Abbreviations E evaporation rate - g leaf conductance - PAR photosynthetically active radiation     

Studies in Stomatal Behaviour: The Effects of Moving, Normal and Carbon Dioxide-Free Air on the Stomata of Some Plants

A series of experiments were conducted to investigate the effects of moving, normal and carbon dioxide-free air on the stomata within porometer cups attached to the illuminated leaves of Datura stramonium, Pelargonium zonale, Duranta plumieri and Clerodendron inerme. A marked opening stomatal response was obtained in Datura and Pelargonium on changing to carbon dioxide-free air. In general no such response was established in Duranta and Clerodendron. Indications of even an opposite closing effect were shown in the case of Duranta. The present results seem to disprove the reduction of carbon dioxide by photosynthesis as the major factor controlling the wide stomatal opening within a porometer cup. The possibility of a humidity effect is also suggested.     

Stomatal response of engelmann spruce to humidity, light, and water stress

Stomatal response of Engelmann spruce (Picea engelmannii Engelm.) to environmental conditions was studied in the natural subalpine environment and under controlled laboratory conditions. Stomata of naturally occurring trees responded to the difference in absolute humidity from leaf to air. When foliage was exposed to full sunlight, stomatal conductance decreased as the absolute humidity difference increased. In the shade, where photosynthetically active radiation was 10% of that in full sunlight, stomatal closure at large absolute humidity differences was much more complete. No effect of soil or air temperatures on stomatal aperture was observed in the field, nor were differences among three contrasting sites detected. Under growth chamber conditions, stomata responded to photosynthetically active radiation, but conductances were influenced by leaf-to-air differences in absolute humidity. Leaf water potentials below - 15 bars resulted in lower conductances over a range of humidity and light conditions. Because net photosynthesis under shaded conditions in the natural environment must be very low, stomatal closure could result in considerable savings in water while having a minimum effect on net photosynthesis.     

Measurements of electrical leaf surface conductance reveal re-condensation of transpired water vapour on leaf surfaces

Electrical conductance ( λ ) was measured continuously and in vivo on leaf surfaces of Vicia faba and Aegopodium podagraria . λ increased with rise and decreased with fall in humidity, exhibiting a hysteresis during an applied humidity cycle [90–20–-90% relative humidity (r.h.)]. After treatment with NaNO₃ aerosols, a sudden increase in λ was observed at 73% r.h., which is close to the deliquescence point of the salt. Transpiration and electrical conductance of untreated leaves were measured simultaneously under conditions of constant r.h., while the photosynthetic photon flux density and CO₂ concentration of the air were varied to induce changes of stomatal aperture. At 35% r.h., changes of light and CO₂ level revealed a strong correlation between stomatal conductance ( g _S) and λ for Vicia faba leaves. This was also found at 90, 75, 60, 45 and 25% r.h. on the lower but not on the astomatous, upper surface of Aegopodium podagraria . The correlation between g _S and λ for stomata-bearing leaf surfaces indicates that an equilibrium exists between the ambient water vapour phase and the liquid water phase on and within the cuticle. This is modified by transpired water vapour influencing the air humidity inside the boundary layer. Our results imply re-condensation of transpired water vapour to salts on the leaf surface and its sorption to the cuticle.     

几个气孔模型在自然条件下的适用性

在自然条件下,用气孔下腔与叶面间的水汽压差（ＶＰＤｓ）取代原有气孔模型中的大气湿度因子,可以明显提高气孔模型在自然条件下的适用性。理论分析指出,在气孔模型中,用ＶＰＤｓ表达气孔导度对湿度的响应与用蒸腾速率表达气孔导度对蒸腾失水的响应是等价的。     

氮肥对旱作小麦光合作用与环境关系的调节

土壤水分胁迫下,测定不同供氮小麦生理指标与环境因子的结果表明,25％的空气湿度是氮对作物调控的下限。在此值以上,增施氮肥可以提高光合速率适应高温和高湿的能力,扩大气孔导度受空气温度和湿度抑制的范围,提高叶片保水能力,从而增强小麦抗旱能力。     

Control of stomatal conductance by leaf water potential in Hymenoclea salsola (T. & G.), a desert subshrub

The role of leaf water potential in controlling stomatal conductance ( g _s) was examined in the desert subshrub Hymenoclea salsola . For plants operating at high irradiance, stomatal closure in response to high leaf-air humidity gradient ( D ) was largely reversed by soil pressurization. Stomatal re-opening eliminated, on average, 89% of the closure normally induced by high D . Transpiration rates ( E ) reached under these conditions were far higher than maximal rates normally observed at any point of the D response. In situ stem psychrometry indicated that water flux at all times conformed to a simple Ohm's-law analogy. Under conditions of high D, E increased substantially in response to soil pressurization. Stomatal regulation did not constrain E during this treatment, but did result in nearly constant minimum leaf water potentials.     

Responses of stomata to changes in humidity

Summary Large areas of the lower epidermis of full-grown leaves of Polypodium vulgare (and Valerianella locusta) are normally separated from the mesophyll by an extensive subepidermal airspace. Epidermal stripes were prepared for experiments to simulate these conditions in order to investigate stomatal reactions. They were placed with their inner surface in contact with an airspace of uniformly high humidity. The outer surface was treated with air of varying degrees of humidity. The stomatal reactions were observed by microscope and the opening of the guard cells determined photographically.Treatment of the outer side of the epidermis with dry air led to a rapid closing of the stomata, whilst moist air caused opening. This induction of opening and closing movements could be repeated up to 15 times with the same stoma by changing the degree of humidity. Neighbouring groups of stomata showed different apertures according to their individual humidity conditions. The degree of aperture of the stomata depended on the water potential of the ambient air and also on the humidity conditions in the subepidermal airspace.The cause of this stomatal behaviour could lie in the peristomatal transpiration. In this way, the guard cells are able to function as humidity sensors which measure the difference in water potential inside and outside the leaf. Their aperture thus is controlled by their individual transpiration conditions. This controlling mechanism could be very important for the water economy of plants. They would appear to be able to reduce their transpiration through an increase in diffusion resistance of the stomata during decreasing humidity in the ambient air, without changing the water status of the whole leaf.