Smith E C, Griffiths H, Wood L, Gillon J
Department of Agricultural and Environmental Science, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, UK.
To whom correspondence should be addressed. E-mail:
New Phytol. 1998 Feb;138(2):213-224. doi: 10.1046/j.1469-8137.1998.00106.x.
The photosynthetic properties of cyanobiont lichens from contrasting habitats were measured to identify whether the increased assimilation rates which characterized Peltigera membranacea (Ach.) Nyl. from an exposed habitat were correlated with increased carbon-concentrating mechanism (CCM) activity. The results were contrasted with data obtained from two populations of Peltigera praetextata (Flörke ex Sommerf.) Zopf collected from dry and damp microhabitats within a shaded woodland and Peltigera leucophlebia (Nyl.) Gyelnik, which has been shown to lack a carbon-concentrating mechanism. The differences in assimilation rates between the cyanobiont lichens were not accounted for by differences in chlorophyll content. Peltigera membranacea from the exposed habitat which had the highest assimilation rates had the lowest Gamma; and K values and accumulated the greatest C -pool indicating that increased C accumulation contributed towards the higher assimilation rates shown by these species. The convexity of the light response curve for the cyanobiont lichens decreased with increasing assimilation rates. This might have indicated a diversion of electron transport to energize the carbon-concentrating mechanism. The apparent quantum efficiency of CO assimilation (ΦCO ) was correlated with the genus of lichen photobiont. All cyanobiont lichens had comparable values for ΦCO which were greater than that of the tripartite Peltigera leucophlebia. Light compensation points reflected the exposure of the habitats with higher compensation points characterizing the cyanobiont population from the exposed crag and the tri-partite population from the open grassland. Carbon isotope discrimination values for organic matter and measured instantaneously were the same for all cyanobiont lichens and were comparable with values recorded for species with a carbon-concentrating mechanism. Carbon isotope measurements for P. leucophlebia were typical of those recorded for species without a carbon-concentrating mechanism. Variation in source isotope signature and refixation of respiratory CO were considered to be significant factors in determining organic matter and instantaneous carbon-isotope discrimination. These factors might have masked any subtle variation in carbon-isotope discrimination which resulted from variable CCM activity. The functional significance of increased carbon-concentrating mechanism activity in cyanobiont lichens occupying exposed habitats is discussed.
对来自不同生境的蓝藻地衣的光合特性进行了测量，以确定以暴露生境中的膜边皮果衣（Peltigera membranacea (Ach.) Nyl.）为特征的同化率增加是否与碳浓缩机制（CCM）活性增加相关。将结果与从阴暗林地内干燥和潮湿微生境中采集的两种前叶皮果衣（Peltigera praetextata (Flörke ex Sommerf.) Zopf）种群以及已被证明缺乏碳浓缩机制的白脉皮果衣（Peltigera leucophlebia (Nyl.) Gyelnik）的数据进行了对比。蓝藻地衣之间同化率的差异不能用叶绿素含量的差异来解释。来自暴露生境且同化率最高的膜边皮果衣具有最低的Gamma;值和K值，并积累了最大量的C库，这表明C积累的增加促成了这些物种所表现出的较高同化率。蓝藻地衣光响应曲线（light response curve）的凸度（convexity）随着同化率的增加而降低。这可能表明电子传递转向以驱动碳浓缩机制。CO同化的表观量子效率（ΦCO）与地衣共生藻的属相关。所有蓝藻地衣的ΦCO值相当，均大于三方型的白脉皮果衣。光补偿点反映了生境的暴露程度，较高的补偿点表征来自暴露峭壁的蓝藻种群和来自开阔草地的三方型种群。所有蓝藻地衣的有机物质碳同位素判别值（Carbon isotope discrimination values）以及瞬时测量值都相同，并且与具有碳浓缩机制的物种所记录的值相当。白脉皮果衣的碳同位素测量值是没有碳浓缩机制的物种所记录的典型值。源同位素特征的变化和呼吸CO的再固定被认为是决定有机物质和瞬时碳同位素判别的重要因素。这些因素可能掩盖了因CCM活性变化而导致的碳同位素判别中的任何细微变化。讨论了在占据暴露生境的蓝藻地衣中碳浓缩机制活性增加的功能意义。
