Diurnal dynamics of photosynthetic parameters of Norway spruce trees cultivated under ambient and elevated CO2: the reasons of midday depression in CO2 assimilation

摘要: Diurnal courses of net CO2 assimilation, non-assimilatory processes, electron transport rate, photosystem (PS) II photochemical efficiency, and pigment composition were investigated during summer days for sun exposed needles Norway spruce trees grown under ambient (AC) and/or elevated (EC; 700 mu mol (CO2) mol(-1)) atmospheric carbon dioxide concentration ([CO2]). Daily assimilation (AN c,) documented significantly higher values cultivated EC conditions at irradiances above 250 m(-2) s(-1). In comparison with the AC variant, treatment led to diminution midday photosynthesis depression that was predominantly caused by stomatal closure subsequent decrease intercellular [CO2] (Ci). A partial recovery ability shoots correlated restoration conductivity afternoon hours. On contrary, maximum light-saturated rate (A(Nmax)), permanent capacity (A(Nsat)) over day an atypical daily course gross (P-act) suggested increased contribution non-stomatal processes in a down-regulation carboxylation efficiency noon The relatively high potential quantum yield PS photochemistry (F-V/F-M >= 0.8), estimated on both dark adapted throughout day, confirmed photoinhibition not primary reason photosynthesis. However, feedback effects enhanced induced: (a) slight inactivation reduction rates, (b) demand xanthophyll dependent non-radiative dissipation excess light energy (accumulation deepoxidized antheraxanthin zeaxanthin), (c) adjustment harvesting complexes (increase chlorophyll a/b ratio). 2005 Elsevier Ireland Ltd. All rights reserved.