Effects of winter-stress on photosynthesis and antioxidants of exposed and shaded needles of Picea abies (L.) Karst. and Pinus cembra L. : 3rd EUROSILVA Workshop, Obergurgl, Austria, September, 10-14, 1998

1999

S. 205-212

4 Abb., 19 Lit.

Unselbständiges Werk

200086155

The aim of this study was to find out whether in conifers of regions with severe winters the photosynthetic depression during winter is the result of oxidative stress due to the concerted action of low temperatures and high light. Potential efficiency of PS II (FV/FM), light and CO2-saturated rates of photosynthetic O2-evolution (Pmax) and contents of ascorbate and glutathione in the reduced and oxidized state were measured in sun-exposed and shaded needles of Picea abies and Pinus cembra near the alpine timberline. In autumn, photosynthetic parameters decreased with decreasing temperatures: early in December FV/FM reached only 10% of summer values, whereas Pmax was almost completely extinguished. Recovery started in late February but was not complete until end of May. Winter depression was stronger and lasted longer in Pinus cembra than in Picea abies. In both species FV/FM was more reduced and reactivated later in sun-exposed than in shaded needles. The content of ascorbate followed a seasonal rhythm with a minimum level in summer and a 3 to 4 times higher level in late winter. Dehydroascorbic acid was always low and also analysis of glutathione did not indicate exhaustion of the reduced form during winter. Since needles with lowest photosynthetic activity contained high levels of antioxidants in the reduced state it is concluded that the reduction of FV/FM during winter was not the result of oxidative stress, but rather a preventive down regulation of PS II.