Einhorn Katrina S, Rosenqvist Eva, Leverenz Jerry W
The Arboretum, The Royal Veterinary and Agricultural University, Kirkegaardsvej 3A, 2970, Hørsholm, Denmark.
Oecologia. 2004 Jul;140(2):241-51. doi: 10.1007/s00442-004-1591-6. Epub 2004 May 19.
Ash (Fraxinus excelsior L.) and beech (Fagus sylvatica L.) seedlings were grown in the field under three levels of natural light: (1) open, (2) gap and (3) shade. Light acclimation of photosynthesis was characterized by means of modulated chlorophyll a fluorescence of intact leaves and growth parameters were measured at the end of the growing season. Measurements of maximum photochemical efficiency (Fv/Fm) of dark-adapted leaves at intervals through the day showed that ash had a higher Fv/Fm than beech in open and gap plots but not in shade plots. This indicated a larger build-up of photoinhibition in beech under gap and open conditions. Steady-state light response curves of the operating efficiency of PSII (F'q/F'm), the electron transport rate (ETR) and the photochemical efficiency factor (F'q/F'v) showed greater variability across light treatments in ash than in beech. Both species exhibited similar responses of non-photochemical quenching (NPQ) to light. When the data were normalized to the mean maximum irradiance in the growth environment, all photochemical parameters showed a reduction in variation across treatments, indicating that light acclimation in the two species occurred primarily through adjustments in rates of photochemistry. Adjustments in thermal heat dissipation were small in both species. This pattern was stronger in ash, suggesting a greater degree of phenotypic plasticity in photosynthetic capacity in this earlier successional species. Contrary to our expectations, the build-up of photoinhibition in beech did not appear to have a negative effect on total biomass accumulation relative to ash.
欧洲白蜡树（Fraxinus excelsior L.）和山毛榉（Fagus sylvatica L.）幼苗在田间三种自然光水平下生长：（1）开阔地，（2）林窗，（3）荫蔽处。通过完整叶片的调制叶绿素a荧光对光合作用的光适应进行表征，并在生长季末测量生长参数。在一天中不同时间间隔对暗适应叶片的最大光化学效率（Fv/Fm）进行测量，结果表明，在开阔地和林窗地块中，欧洲白蜡树的Fv/Fm高于山毛榉，但在荫蔽地块中并非如此。这表明在林窗和开阔条件下，山毛榉的光抑制积累更大。PSII运转效率（F'q/F'm）、电子传递速率（ETR）和光化学效率因子（F'q/F'v）的稳态光响应曲线显示，欧洲白蜡树在不同光照处理下的变异性比山毛榉更大。两个物种对光的非光化学猝灭（NPQ）表现出相似的响应。当数据归一化为生长环境中的平均最大辐照度时，所有光化学参数在各处理间的变异性均降低，表明这两个物种的光适应主要通过光化学速率的调整来实现。两个物种通过热耗散进行的调整都很小。这种模式在欧洲白蜡树中更强，表明这个早期演替物种在光合能力上具有更大程度的表型可塑性。与我们的预期相反，相对于欧洲白蜡树，山毛榉中光抑制的积累似乎对总生物量积累没有负面影响。
