净光合速率与气孔导度相互关系的电学类比分析和模拟研究

对Ｂａｌｌ等的气孔模型所依据的实验事实之一（净光合速率与气孔导度呈线性关系）作了只考虑各阻力与总通量之间关系的电学类比分析和模拟检验。从电学类比分析得到的关系式可以看出,净光合速率与气孔导度的关系是非线性的,只有当叶片的边界层导度比较大时,两者的关系才接近线性。模拟得到的结论也是一样的。另外还模拟了气孔内外ＣＯ２ 浓度之比随光强的变化以及边界层导度的影响,模拟结果可以解释已有的实验结果     

对一个气孔经验模型的电学类比分析和模拟检验

对Ｂａｌｌ等人提出的气孔经验模型进行了分析和模拟检验,分析是通过电学类比实现的,在引进叶片边界层导度很大等假设后可以从气孔内外ＣＯ２浓度之比保持恒定的实验事实推导出这个经验模型的表达式;在其它类似的实验事实的基础上已可作同样的推导。模拟检验中采用的是由我们建立的人为完整的气孔对环境响应的机理性定态数学模型。两种方法得出的结论是一致的：Ｂａｌｌ等人的经验模型有一定的局限性,因为它不能模拟边界层阻力和叶温对气孔导度的影响。由此我们指出叶片表面的风速是影响气孔导度的重要环境因子之一。一个完整的气孔模型必须包括它的影响。     

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。     

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。     

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。     

对一个气孔经验模型的电学类化分析和模拟检验

对Ｂａｌｌ等人提出的气孔经验模型进行了分析和模拟检验,分析是通过电学类比实现的,在引进叶片边界层导度很大等假设后可以从气孔内外ＣＯ２浓度之比保持恒定的实验事实推导出这个经验模型的表达式,在其它类似的实验事实的基础上已可作同样的推导。模拟检验中采用的是由我们建立的,较为完整的气孔对环境响应的机理性定性数学模型。两种方法得出结论是一致的：Ｂａｌｌ等人的经验模型有一定的局限性,因为它不能模拟边界层阻力叶     

水稻叶片气孔导度与冠层反射光谱的定量关系分析

研究了不同土壤水氮条件下水稻(Oryza sativa)叶片气孔导度与冠层光谱反射特征的量化关系。结果表明,不同水分处理下,水稻不同叶位气孔导度变化趋势为:GsL1>GsL2>GsL3>GsL4。高于W3水分条件下,高氮处理的叶片气孔导度高于低氮处理,而低于W3水分条件下,高低氮处理条件下叶片气孔导度差异不显著。发现比值指数R(1 650,760)与不同叶位叶片及不同层次叶片气孔导度的相关性大小为:GsL1>GsL12>GsL123>GsL1234>GsL2>GsL3>GsL4(水稻顶部自上而下第一、二、三、四叶以及自上而下顶部2张、3张、4张叶片的气孔导度值分别表示为:GsL1、GsL2、GsL3、GsL4、GsL12、GsL123和GsL1234),而顶1叶气孔导度与叶面积指数的乘积(冠层叶片气孔导度)同比值指数R(1 650,760)相关程度更高。R(1 650,760)与顶1叶和冠层叶片气孔导度之间皆呈极显著的幂函数负相关。利用不同年份的不同水稻试验对两者的监测模型进行了检验,模型的检验误差RMSE分别为0.05和0.24,表明比值指数R(1 650,760)可以较好地监测不同水氮条件下水稻叶片的气孔开闭特征。     

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。     

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。     

麦田冠层气孔导度的分层研究

小麦灌浆期和乳熟期冠层各层叶片上、下表面的气孔导度之间呈正相关关系;冠层不同层的叶片气孔导度从早到傍晚有平行变化的趋势,数值上存在较大的差异,一般从冠层上到下递减。经分析,这主要与冠层叶片接受的光强自上而下递减有关,且这时所对应的叶片水势自冠层上到下递增的幅度大。测算结果表明,冠层气孔导度白天亦呈明显的日变化,灌浆期的值大于乳熟期的值。     

Effects of Boundary Layer Conductance on Leaf Gas Exchange

Using an improved gas-exchange technique for leaf chamber the authors' conclusions derived from electrical analogy analysis and simulation have been tested. In most devices for gas-exchange measurements, a fixed ventilation speed is used, which results in a fixed boundary layer conductance of leaf, but the results of experiments are often used to predict canopy transpiration or photosynthesis where the boundary layer conductance changes with the position of the leaf in the canopy and the wind speed above the canopy. To change the boundary layer conductance of a leaf, a barrier of variable size was inserted into the leaf chamber to decrease the wind speed over the leaf. The responses of stomatal conductance, net photosynthetic rate, and transpiration rate to light were then measured. The relationships amongst them have been tested. The experimental results matched well with the results predicted by electrical analogy analysis and simulation in most cases.     

Gas exchange in leaves of the root hemiparasitemelampyrum arvense L. before and after attachment to the host plant

Gas exchange characteristics of a hemiparasiteMelampyrum arvense L. before and after attachment to the hostCapsella bursa pastoris (L.) Med. were compared. The net photosynthetic rates (P_N) on a leaf area basis were extremely low and in comparison to the value obtained for the host were about 15 % and 23 % for the unattached and attached hemiparasite, respectively. Also the concentration of photosynthetic pigments was low (as compared with the host the content of chlorophylls was about 33 % and 49 % and of carotenoids about 38 % and 36 % in the unattached and attached hemiparasite, respectively). On the other hand the rates of respiration were high (about 1.8 and 2.6 times higher in the unattached and attached hemiparasite, respectively, than in the host). In darkness stomatal conductance (g_S) of the host and the unattached hemiparasite was rapidly reduced to 10 % of the value obtained in light, g_S of the attached hemiparasite was decreased only by about 30%. A total reduction of g_S occurred at relative water content (RWC) of 85 %, 75% and 45 % for the unattached hemiparasite, the host, and the attached hemiparasite, respectively. The transpiration (E) rate in the preparasitic stage was very low, being 2.6 and 4.5 times smaller than in the host and the attached hemiparasite, respectively. In the attached hemiparasite WUE was 7.5 and 3 times poorer than in the host and in the preparasitic stage, respectively.     

Gas exchange inHardwickia binata after water stress and rewatering

The net photosynthetic rate (P_N), stomatal conductance (g_s) and transpiration (E) ofHardwickia binata Roxb. leaves were reduced due to decrease in the leaf water potential (ψ_w) from -2.0 to - 5.7 MPa. P_N partially recovered in the treated plants upon rewatering. Decrease in g_s due to water stress may be the main factor for reduction of P_N. This work was supported by a financial grant from the MNES, India to KP.     

In vivo temperature limitations of photosynthesis in Phaseolus vulgaris L

The purpose of this study was to evaluate the temperature response of photosynthesis in two common bean genotypes differing in crop yield when grown under warm conditions. The cultivar Nobre is sensitive to high temperatures, whereas Diplomata shows better crop yield under high temperatures. Plants were grown in a greenhouse prior to transferring to a controlled environment cabinet for the temperature treatments. In a first experiment, 30 days-old plants were subjected to a short exposure (1 day) at temperatures that varied from 9 °C to 39 °C. Diplomata had lower net CO₂ assimilation rate (A) at 15 °C and 21 °C, but higher from 27 °C to 39 °C. Photosynthetic parameters calculated from modeling the response of A to the intercellular CO₂ concentration suggested that the different temperature responses of the two genotypes are caused by different rates of diffusion of CO₂ to the assimilation site, not by differences in biochemical limitations of photosynthesis. While stomatal conductance (g_s) did not differ between the genotypes, mesophyll conductance (g_m) was slightly greater for Nobre at 15 °C, but much higher in Diplomata from 21 °C to 39 °C. In a second experiment, no difference was observed in biomass accumulation between the two genotypes after growth for 24 days under a 35/20 °C (day/night) regime. Hence, the differences in photosynthesis did not cause variation in plant growth at the vegetative stage. The differential genotypic response of g_m to temperature suggests that g_m might be an important limitation to photosynthesis in Nobre, the common bean genotype sensitive to elevated temperature. However, more studies are needed employing other methods for g_m evaluation to validate these results.     

The Electrical Analogy Analysis and Simulation Testing of the Relationship Between Net Photosynthetic Rate and Stomatal Conductance

The hypothesis about the linear relationship between net photosynthetic rate and stomatal conductance, which had formed the basis of the empirical model proposed by Ball et al, was analyzed by analogy with electrical resistance and simulation testing. The results showed that the relationship between stomatal conductance and net photosynthetic rate was non-linear, but approaches a linear one when there was a large the boundary layer conductance of leaf. In addition, the way in which the ratio of CO2 concentrations in and out of the stomata changes with light and the influence of boundary layer conductance on the ratio had also been simulated.     

Photosynthetic Response to Soil Water Contents of an Annual Pioneer C4 Grass (Agriophyllum squarrosum) in Hunshandak Sandland,China

Net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and leaf water potential (Ψ_l) of an annual pioneer C₄ grass (Agriophyllum squarrosum) were compared under different simulated precipitation events in a field of Hunshandak Sandland, China. The increase of soil water content (SWC) had significant effect on these physiological traits (p<0.001). In the vegetative stage, the values of P _N, E, and g _s went up sharply when SWC increased at the beginning, while they went down with continuous increase of SWC. P _N, E, and g _s increased 1.4, 1.7, and 1.7 fold, respectively, with SWC range from 6.7 to 11.6 %. In the reproductive stage, similar trends were found, except for the climate with a higher SWC. This indicated that A. squarrosum was very sensitive to the small increment of SWC which might have a large photosynthetic potential. Ψ_l increased by about 8 % as the SWC changed from 6.7 to 8.8 %, and then maintained a steady level when the SWC was higher than 8.8 %, while the values of P _N, E, and g _s kept increasing even after this SWC. This might indicate that the adjustment of Ψ_l response to the changes of SWC lagged that of the photosynthetic parameters. This revised version was published online in August 2006 with corrections to the Cover Date.     

羊草种群对遮荫的适应性生长对策

自20世纪50年代以来,太阳到达整个地球的短波光能辐射量每10年减少2.7％,即“全球变暗”,这会对植物及其所在的生态系统的功能产生影响,然而,目前关于这种影响的研究尚未得出一致的结论.本文利用不同程度的遮荫(0、30％、50％和70％)模拟全球变暗的效应,研究了我国北方草原优势植物羊草的种群密度、形态指标和光合生理等对遮荫的响应.结果表明:遮荫使羊草枝条密度有所降低,枝条高度明显增加,叶面积显著扩大,抽穗枝条比例即抽穗率升高;遮荫使羊草接受到的光合有效辐射显著下降,在0、30％、50％遮荫强度下羊草的气孔导度、光合速率和蒸腾速率仍表现出“午休”现象,而遮荫70％的处理下气孔导度、光合和蒸腾速率在11:00-16:00时间段均高于其他处理,而且光合和蒸腾速率未出现“午休”现象.这种“午休”现象的消失可能是一定程度遮荫或全球变暗导致某些植被系统生产力增加的重要原因之一.为更加准确预测各类生态系统对全球变暗的响应,必须针对更多地域、更多生境、更多类群和更多生育期植物对遮荫的响应开展实验研究,并加以整合和模拟.     

沙埋对两种一年生藜科植物存活及光合生理的影响

为了解沙埋对沙生植物存活的影响及其光合生理响应特征,比较不同藜科沙生植物耐沙埋能力及其光合响应,在内蒙古科尔沁沙地研究了沙米(Agriophyllum squarrosum)和大果虫实(Corispermum marocarpum)在不同沙埋深度下第5、10、15天的净光合速率、气孔导度、蒸腾速率、水分利用效率的变化,并于植物生长末期对存活率进行了测定。结果表明:沙米较大果虫实具有较强的耐沙埋能力,其中沙米幼苗最大耐沙埋深度超过苗高10 cm,大果虫实在埋深等于其苗高时全部死亡;随沙埋深度增加,沙米和大果虫实的存活率均显著下降,但沙米的下降幅度明显小于大果虫实;沙埋后,2种植物的气孔关闭或开放程度减小,通过降低蒸腾速率和提高水分利用效率来适应沙埋胁迫;随着沙埋胁迫的加剧,2种植物的净光合速率下降,表明沙埋胁迫对植物的光合作用破坏较大;相比于大果虫实,沙米对于沙埋胁迫有着更好的光合适应,随着胁迫的时间增加,其净光合速率有所恢复。