Fetene M, Nauke P, Lüttge U, Beck E
Department of Biology, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia.
Lehrstuhl für Pflanzenphysiohgie, Universität Bayreuth, Universitätsstrasse 30, 95440 Bayreuth, Federal Republic of Germany.
New Phytol. 1997 Nov;137(3):453-461. doi: 10.1046/j.1469-8137.1997.00844.x.
Carbodioxide uptake, oxygen evolution and chlorophyll fluorescence of leaves of Lobelia Lobelia rhynchopetalum Hemsl., a giant rosette plant of the tropical alpine regions of Ethiopia, were studied under field conditions at 4000 m above sea level. Our objective was to investigate the photosynthetic adaptation to the combination of wide fluctuation in diurnal temperature, high photon flux densities (PFD) and low CO partial pressure encountered in these regions. At an ambient CO partial pressure of c. 17 Pa, maximal rates of CO uptake were low, ranging between 4 and 6 μmol m s . Such rates, however, required high PFDs and were observed only at levels of 1500 μmol photons m s . Carbon dioxide uptake was significantly inhibited when PFD was ≤ 2000 μmol photons m s . On the other hand, at saturating CO levels, maximal photosynthetic oxygen evolution was higher (30 μmol C m s ). saturating at the same PFD as CO uptake. Quantum efficiency of CO uptake (0.006 mol CO mol photons , at high altitude and a low CO, partial pressure of 17 Pa) and even of oxygen evolution under CO -saturating conditions in the leaf O electrode (0.05 mol O mo) photons ) indicated reduced photosynthetic efficiency. Electron transport rate (ETR) was strongly correlated with the leaf temperature. Non-photochemical quenching (NPQ) responded inversely to leaf temperature and stomatal conductance. The results indicated that in the morning, when the sun irradiates the partly frozen leaves with closed stomata, NPQ is the principal mechanism by which Lobelia leaves protect their photosynthetic apparatus. However, during the day, the predominant upright inclination of the leaves significantly contributes to protecting the leaves from excess light absorption. A comparison of the chlorophyll fluorescence of young and old leaves revealed that the former had high ETR and quantum efficiency of photosynthetic electron transport but a lower capacity for NPQ. Extremely high NPQ values but low ETR and low quantum efficiency were recorded for the old leaves. Thus, in the course of maturation the leaves apparently lose photosynthetic efficiency but increase their capability for protective non-photochemical quenching.
对埃塞俄比亚热带高山地区的一种巨型莲座状植物——长瓣半边莲（Lobelia rhynchopetalum Hemsl.）叶片的二氧化碳吸收、氧气释放和叶绿素荧光进行了实地研究，研究海拔为4000米。我们的目的是调查光合作用对这些地区昼夜温度大幅波动、高光子通量密度（PFD）和低二氧化碳分压组合的适应性。在约17帕的环境二氧化碳分压下，最大二氧化碳吸收速率较低，在4至6微摩尔·平方米·秒之间。然而，这样的速率需要高PFD，并且仅在1500微摩尔光子·平方米·秒的水平下观察到。当PFD≤2000微摩尔光子·平方米·秒时，二氧化碳吸收受到显著抑制。另一方面，在饱和二氧化碳水平下，最大光合氧气释放量较高（30微摩尔·碳·平方米·秒），在与二氧化碳吸收相同的PFD下达到饱和。在高海拔和17帕的低二氧化碳分压条件下，二氧化碳吸收的量子效率（0.006摩尔二氧化碳·摩尔光子），甚至在叶氧电极中二氧化碳饱和条件下的氧气释放量子效率（0.05摩尔氧气·摩尔光子）都表明光合效率降低。电子传递速率（ETR）与叶片温度密切相关。非光化学猝灭（NPQ）与叶片温度和气孔导度呈反向响应。结果表明，在早晨，当太阳照射部分冻结且气孔关闭的叶片时，NPQ是长瓣半边莲叶片保护其光合机构的主要机制。然而，在白天，叶片主要的直立倾斜显著有助于保护叶片免受过多光吸收。对幼叶和老叶叶绿素荧光的比较表明，前者具有较高的ETR和光合电子传递量子效率，但NPQ能力较低。老叶记录到极高的NPQ值，但ETR和量子效率较低。因此，在叶片成熟过程中，它们显然失去了光合效率，但增加了其保护性非光化学猝灭的能力。
